.l-“""~ r: '9 ‘-’I F m ‘ Michigan Se P] I. _ .. In . r, ‘h' 6 .3. ' ‘i_ H V ..'. ‘.-1 J This is to certify that the thesis entitled A TECHNICAL AND ECONOMIC STUDY OF THE SLIP-BELT AND LUBRICATION SYSTEM USED ON COMMERCIAL TRUNK SHAKERS presented by EDWARD JAMES TIMM has been accepted towards fulfillment of the requirements for MS degree in MT W Major professor Datew 2/11?3§ 0-7639 MS U is an Afiirmau'vc Action/Equal Opportunity Institution 4. rhl a. 4 MSU LIBRARIES an 5' RETURNING MATERIALS: Place in book drop to remove this checkout from your record. FINES wil] be charged if book is returned after the date stamped beiow. A TECHNICAL AND ECONOMIC STUDY OF THE SLIP-BELT.AND LUBRICATION SYSTEM USED ON COMMERCIAL TRUNK SHAKERS BY Edward James Timm A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Agricultural Engineering 1986 ABSTRACT A TECHNICAL AND ECONOMIC STUDY OF THE SLIP-BELT AND LUBRICATION SYSTEM USED ON COMMERCIAL TRUNK SHAKERS BY Edward James Timm The decline in the productive life of commercial cherry orchards in Michigan has indicated that mechanical harvesting may be the potential cause. Despite continued improvement in the design of commercial tree shakers, bark damage is still reported. A systems study of the slip-belt and lubrication system was needed in order to reduce bark damage, thereby increasing orchard life and ~improving harvesting economics. Static and dynamic friction tests were conducted in the laboratory to identify possible changes in the belting and lubrication choices. Evaluations of the slip-belts and lubrication systems were then conducted under actual harvesting conditions. An economic analysis was, performed to determine the cost/benefit implications of reduced bark damage. Friction forces were higher for the conventional neoprene belting and all lubricants compared to either nitrile or polyurethane belting in both the static and dynamic friction tests. Field evaluations confirmed that bark damage was reduced by using nitrile or polyurethane Edward James Timm belting. An improved clamp system that reduces damage and tree death will result in substantial economical gains. Approved: a” /{ W Major Professor Approved: Department Chairman To my mother and father ii ACKNOWLEDGEMENTS The author would like to express his sincere appreciation to the following people who provided encouragement and assistance throughout my graduate program. I wish to give credit and extend a special thanks to the following individuals: To Dr. Galen K. Brown, my major professor, for his professional advice, guidance and support provided throughout the duration of my academic program and for his many hours of editing this manuscript. . To Dr. Larry J. Segerlind and Dr. Gary Van Ee for serving on my guidance committee and for their advise in the development of my academic program. I To USDA Technician, Mr.. Richard Wolthuis, Specialist, Mr. Mike Rauch, and undergraduate, Mr. Phil Richey, for their assistance in designing and building the testing machines. To the Michigan cherry growers who participated in the research project for their interest and cooperation. A very special thanks to my parents, Edward and Helen, and my family, for providing continuing love, encouragement and support throughout my academic endeavor. Last of all, to Jay, for bringing' love and happiness into my life. iii TABLE OF CONTENTS ACKNOWLEMEMENTS O O 0 O O O C O O O 0 LI ST OF TABLES O O O O O O O O O C O L I ST OF F I GURES O O O O O O O O O O 0 CHAPTER 1. I NTRODUCT I ON. C O O O O O O O O 1.1 1.2 1.3 1.4 The Problem . . . . . . . Cherry Production and Harvesting Pract1ces . . Need for an Improved Slip-Belt and Lubrication System . . . . . . Objectives of the Study . . . . LITERATURE REVIEW . . . . . . . . 2.1 NNNNN O I O O O 0‘01!th History of Mechanically Harvesting Cherries . . . . . . . Causes of Bark Damage . . Bark Structure and Strength Trunk Shaker Clamp Pads . Reducing Bark Damage . . Summary. . . . . . . MATER I ALS AND WTHODS C O O O O I O wwwww U'IIFUJNH Laboratory and Field Analysis Belting and Lubricants. . . Static Friction Machine Dynamic Friction Machine Field Evaluations . . RESULTS AND DISCUSSION . . . . . . 4.1 4.2 4.3 4.4 Static Friction Tests . Dynamic Friction Tests. Field Evaluations . . Summary. . . . . . iv PAGE iii vi vii NmNi-‘H CHAPTER PAGE 5. ECONOMIC IMPLICATIONS OF AN IMPROVED CLAMP SYSTEM. 0 O O C O O O O 0 O O O O 79 5.1 IntrOduction ; O O O O O O O I O 79 5.2 Assumptions and Analysis . . . . . . 81 5.3 Results and Discussion. . . . . . . 86 5.4 Summary. . . . . . . . . . . . 94 6. SUMRY O O O O O O O O O O O O O 97 7. CONCLUSIONS . . . . . . . . . . . . 100 8. RECOMMENDATIONS FOR FUTURE RESEARCH . . . . 102 BIBLIWRAPHY O O I O O O O O O O O O O O 103 TABLE 1.1 3.1 4.2 4.3 5.2 5.3 5.4 LIST OF TABLES Survey of varieties of cherries produced in MiChigan' 1985 O O O O O O O O O O O O O O Compatability with selected lubricants for nitrile, polyurethane, and neoprene rubber compounds. . . . . . . . . . . . . . . . . Maximum force required to slide belting on the tenth replication, static friction maChine' 1985. O O O O I O O I O O O O O 0 Torque required to slide belting on the fifth replication after 10 s of turning at a constant r/min, with the dynamic friction maChine' 1985. O O O O O O O O O O O O O 0 Field evaluations of the nitrile and poly- urethane covered belting, 1985 . . . . . . (Cont'd) . . . . . . . . . . . . . . . . . (Cont'd) . . . . . . . . . . . . . . . . . (Cont'd) . . . . . . . . . . . . . . . . . Average potential yield of a tart cherry tree versus age (Bradford and Kesner, 1986). Estimated damage and tree death that occurs each harvest year based upon tree age and clamp system . . . . . . . . . . . . . . . Estimated total accumulated bark damage and tree death for each harvest season . . . . Annual pad and belting replacement cost for each clamp system. . . . . . . . . . . . . vi PAGE 40 57 66 68 69 70 71 83 84 87 91 LIST OF FIGURES FIGURE 1.1 1.2 1.3 3.2 4.1 4.2 4.3 Michigan cherry production between 1979 and 1984. (Michigan Department of Agriculture, 1985). O O O O O O O O O O O O O O O O O O O 0 Survey of cherry tree age in 1982. (Michigan Department of Agriculture, 1983) . . . . . . . Survey of cherry tree age in 1982. (Michigan Department of Agriculture, 1983) . . . . . . . Pad system used to clamp to the trunk. . . . . Possible stresses that may cause bark damage . Shaking and clamping forces that may be major causes of bark damage (Cargill et a1. 1982). . Shaking and clamping forces that may be major causes of bark damage (Cargill et a1. 1982 . . Schematic diagram of the static friction maChine. I O O O I O O O O 0' O O O O C O O O 0 Schematic diagram of the dynamic friction maChine. O O O O O O O O O O O O O O O O O O 0 Static friction vs seconds of travel at 3.3 mm/s and 1400 kPa load for various belting- 1ubricant combinations tested in the stat1c friction machine, 1985 . . . . . . . . . . . . Static friction vs seconds of travel at 3.3 mm/s and 1400 kPa load for various beltin - lubricant combinations tested in the stat1c friction machine, 1985 . . . . ... . . . . . . Static friction vs seconds of travel at 3.3 mm/s and 1400 kPa load for various beltin - lubricant combinations tested in the stat1c friction machine, 1985 . . . . . . . . . . . . vii PAGE 10 21 24 25 42 45 51 52 53 F I GURE PAGE 4.4 Static friction vs seconds of travel at 3.3 mm/s and 1400 kPa load for various belting- lubricant combinations tested in the static friction machine, 1985 . . . . . . . . . . . . . 54 4.5 Static friction vs seconds of travel at 3.3 mm/s and 1400 kPa load for various belting- lubricant combinations tested in the stat1c friction machine, 1985 . . . . . . . . . . . . . 55 4.6 Dynamic friction vs seconds of travel at 380 mm/s and 1350 kPa load for various belting-lubricant combinations tested in the dynamic friction machine, 1985 . . . . . . . 60 4.7 Dynamic friction vs seconds of travel at 380 mm/s and 1350 kPa load for various belting-lubricant combinations tested in the dynamic friction machine, 1985 . . . . . . . 61 4.8 Dynamic friction vs seconds of travel at 380 mm/s and 1350 kPa load for various belting-lubricant combinations tested in the dynamic friction machine, 1985 . . . . . . . 62 4.9 Dynamic friction vs seconds of travel at 380 mm/s and 1350 kPa load for various belting-lubricant combinations tested in the dynamic friction machine, 1985 . . . . . . . 63 4.10 Dynamic friction vs seconds of travel at 380 mm/s and 1350 kPa load for various belting-lubricant combinations tested in the dynamic friction machine, 1985 . . . . . . . 64 5.1 Annual yield harvested with standard clamp system at 5, 10, 20, and 40% yield loss on damaged trees and 100% yield loss on dead trees. . . . . . . . . . . . . . . . . . . . . . 88 5.2 Annual yield harvested with improved clamp system at 5, 10, 20, and 40% yield loss on damaged trees and 100% yield loss on dead trees. . . . . . . . . . . . . . . . . . . . . . 89 5.3 Annual yield loss with each system at 5, 10, 20, and 40% yield loss on damaged trees and 100% y1eld loss on dead trees. . . . . 90 viii F I GURE PAGE 5.4 5.5 Net loss for each clamp system at 5, 10, 20, and 40% yield loss on damaged trees and 100% yield loss on dead trees. . . . . . . . 92 Annual net gain for using the improved versus standard clamp system at 5, 10, 20, and 40% yield loss on damaged trees and 100% yield loss on dead trees. . . . . . . . . . 93 ix CHAPTER 1 INTRODUCTION 1.1 The Problem Since the early 1960's, bark damage from mechanical harvesters used to shake harvest several kinds of fruit and nut trees has been recognized as a major problem. In 1958, a tractor-mounted hydraulically-activated boom-shaker was used to harvest tart cherries in Michigan. The mechanical harvester resulted in less labor requirements and increased productivity, however, damage occurred from excessive forces being applied by the shaker (Levin, et a1. 1960). Bark damage caused from mechanical harvesting has caused a decline in the productive life of many commercial .cherry orchards in Michigan. Grower and researchers' observations during the harvesting of cherry trees have suggested that the current slip-belt and lubrication system used on trunk shaker clamp pads may be a major factor in bark damage. An evaluation of the slip-belt and lubrication system as a potential cause of bark damage was needed. This study involves the use of two machines in the laboratory for estimating friction forces existing between various lubricated belting surfaces, followed by actual field testing of two different beltings and several lubricants for potential use in improved slip-belt and lubrication systems. Based upon information obtained from these laboratory and field tests, a cost/benefit analysis of an improved slip-belt and lubrication system that reduces the incidence of bark damage is completed. Previous knowledge on ways to reduce bark damage, combined with a better understanding of the slip-belt and lubrication system, may help reduce the decline in the productivity of commercial cherry orchards. 1.2 Cherry Production and HarvestingPractices In 1984, Michigan ranked first as the Nation's leading producer of tart cherries with almost 80 percent of the total 0.5. output. Sweet cherry production ranked third, with Washington and Oregon ranked first and second, respectively. Total production of the State's tart cherry crop was 95,256 tonnes with a value of 49.55 million dollars. The sweet cherry crop had a total production of 29,938 tonnes with a value of 13.12 million dollars. Tart cherry production for Michigan in 1984 was 2 1/2 times greater than the small 1983 crop, but 19 percent less than the near record 1982 crop, Figure 1.1. Tart and sweet cherries are either processed or sold in the fresh market. Ninety-seven percent of the tart cherries were processed to be made into juice, jam, wine and pie, while 84 percent of the sweet cherries were processed for juice, jelly, ice cream and other frozen goods. In 1984, there was a 12 percent increase in the TOTAL CHERRY PRODUCTION IN MICHIGAN EEBTARTCHBHQ’ EZEISWEETCHERRY fiflfififififififilflflfififlfifii ”19202929101031.{01029102020191 J )3333333333333333333333)!!!3331 150 125— I I In 0 IN 10 IOO~ SBNNOJ. CINVSOOHJ. 25~ O 1984 1983 1982 1981 1980 1979 YEAR Figure 1.1 Michigan Cherry Production Between . 1979 and 1984. (Michigan Department of Agriculture. 1985) number of bearing red tart cherry trees compared to 1983, and a 23 percent increase compared to 1982. This increase was due to the heavy plantings in the late 1970's, (Michigan Department of Agriculture, 1985). Tart cherry tree numbers increased more than planted acreage due to closer tree spacing in the new plantings. In 1982, 63 percent of all tart cherry trees were in the range of l to 11 years old, Figure 1.2. Closer tree spacing and the increase in the number of younger trees being mechanically harvested will be significant factors in the future design of the mechanical harvester. The production of tart and sweet cherries is predominately in the Northwest, West Central and Southwest regions of lower Michigan along the Lake Michigan shoreline. Over 99 percent of the tart cherries produced in Michigan are of the Montmorency variety, Table 1.1. The sweet cherry trees consist of six main varieties with 31 percent of the total being Napoleon. Tree age ranges from 1 to 22 years or more, Figure 1.3. Trunk diameter of the commercially harvested trees ranges from 50 mm to 400 mm and up. Mechanical harvesting of cherry trees in Michigan takes place during the months of July and August, depending on region and cultural practices. Removal of the cherries is accomplished by securely clamping the shaking mechanism of the harvester to the trunk and shaking the trees for a period of 3 to 5 seconds, or until nearly all of the fruit is removed. Unripe cherries require longer shaking times AGE OF CHERRY TREES IN MICHIGAN Q TART CHERRY T T T T W- [xxxxxxxxxxxxm- flMMMWW”HMMHWMHWM”WMNWNHMNMMMHMHHMHHKMHHN- II.IOIOIOIOIQIOIOIOIOIOIOIOIOIO10202910101 920291020102020191010191910103202.1910)2.191010101010201 P '.0292919101020192910291.1010I”20201031920202.3292”II 22-25 26—29 30+ 12-21 7—11 6 TREE AGE IN YEARS 1000 8004 6004 400— 2004 83381 CINVSI'IOHJ. Figure 1.2 Survey of Cherry Tree Age in 1982, (Michigan Department of Agriculture, 1983) Table 1.1. Survey of varieties of cherries produced in Michigan, 1982. Variety Number of Trees Percent of Total Tart: Montmorency 4,484,500 99.7 Others 15,500 0.3 Total 4,500,000 100.0 Sweet: Emperor Fransis 94,300. 10.6 Golds 153,500 17.3 Hedelfingen 71,700 8.1 Napoleon 275,000 31.0 Schmidt 107,600 12.1 Windsor 67,800 7.7 Other 116,900 13.2 Total 887,000. 100.0 Michigan Department of Agriculture, 1983. +NN Anmme .0..3_:o_._m< Lo EcoEtoamo coming—2v Nmmr E 0?. 00.; buoco *0 >025 m; 330E mmfi» z_ mo< mmE films :in mi. "1’ N 0 l . V A 9191019191919 9' I 0191 .7 A V I. it»?! '7 I. >KMmIULMM3m_Nmu noo— noow loom 00¢ 24.0.19: 2. mmmmp >mmmIo mo mo< 83381 CINVSI'IOHI and increase the potential for tree damage. The trees are sometimes sprayed with ethephon several days before harvest to "loosen" the cherries and reduce the shaking needed for fruit removal. Currently there are several different types of mechanical harvesting systems used in commercial cherry production. Depending on the type of harvesting system, between 60 and 120 trees/h can be harvested. The catching frame on the harvester directs the fruit to a conveyer that transports the cherries to a tank partially filled with water at about 10°C. When trees are severly damaged and die, or as older trees become unproductive, they are usaully replaced with young trees. This common practice, however, results in a non-uniform orchard with many different sizes of trees. If the operator fails to reset the shaker for different tree sizes, the possibility of damage to the small trees is greatly increased. 1.3 Need for a Improved Slip-Belt and Lubrication System. With the rapid adoption of the mechanical shake- and-catch system in the early 1960's, hand harvesting became obsolete due to the high cost and shortage of labor. Currently over’ 95 percent of the sweet and tart crops in Michigan are mechanically harvested. Despite continued, improvement in the design of the shaking mechanism and shaker pads, serious bark damage is still reported every year by cherry growers. With the replacement of most old orchards in Michigan in the late 1970's and early 1980's, bark damage occuring on young trees has been a great concern. ‘ Bark strength in relation to tree age, date within growing season, and irrigation have been studied (Fridley, et al. 1970, Brown, et al. 1984a). Cherries are harvested early in the growing season when bark strength is low due to high cambium activity, thus the bark is easily damaged. The use of trickle irrigation also promotes high cambial activity, which increases the possibility of bark damage. Bark strength has been found to increase as tree age increases.‘ The function of the mechanical shaker is to cause relative accelerations between the attached cherries and tree, resulting in removal of the fruit. The pad system used to clamp to the trunk consists of two molded rubber pads covered by two layers of belting, Figure 1.4. Each pad is wrapped with one layer of belting to form a sling that holds the pad in place. The second belting layer, or flap, is placed over the sling and contacts the tree. The sling and flap system currently used on most trunk shakers consists of lO-mm thick neoprene-covered conveyor belting. Lubricants are applied between the two layers of belting to promote slip and reduce shear force transmission to the bark. Research has shown that shear force transmitted to the trunk is reduced when the pad system is lubricated (Brown, et al. 1984b). Relubrication frequency for the belting 10 Figure 4.1 Pad system used to clamp to the trunk. ll depends on tree size, shaking time, pad design, clamping force and lubricant type.. The function of the pad is to effectively, but safely, transmit shaking forces to the tree that are generated by the shaker. To minimize stress in the bark, the pad must be soft enough to conform to the tree and provide a large contact area. The pad must also be firm enough to effectively transmit shaking forces. Insufficient contact area can result in excessive compressive stress being applied to the bark (Frahm et a1. 1983). In Michigan, research on compressive and shear strength of intact cherry bark showed that compressive stress above 1000 kPa on both sweet and tart cherry (14 years old) initiated failure of the cambium (Brown, et a1. 1982, Brown, et al. 1984a). Cambium shear strength of tart cherry bark increased as clamping pressures (compressive stress) increased, but the cambium was significantly damaged at compressive stresses above 2070 kPa. After reviewing the general causes of bark damage, I decided to perform a systems study of the slip-belt and lubrication system used on commercial trunk shakers. A study of the static and dynamic friction forces existing between two belting surfaces treated with various lubricants was initiated to identify possible changes in belting and lubrication choices. By minimizing the shear force transmitted in the trunk shaker clamp pads, bark damage 12 during the shake-harvesting of cherry trees should be reduced. The annualized cost of a new slip-belt system was compared to the standard system, and the reduction in bark damage was used to estimate the concurrent reduction in annual economic losses caused by tree death and yield losses. 1.4 Objectives of the Study The goal of this systems study was to reduce bark damage and thereby increase orchard life and harvesting economics when trunk shakers are used in the mechanical harvesting of cherry trees. An improved slip-belt and lubrication system could possibly reduce the amount of shear force transmitted during shaking and reduce the incidence of bark damage. The following specific objectives were selected to meet the goal of this investigation: 1. Evaluate the static and dynamic friction properties of several beltings and lubricants for potential use in the slip-belt and lubrication system for commercial trunk shakers. 2. Determine which combination of belting and lubricant will minimize shear force transmission, require the least frequent lubrication, and have good durability. 3. Conduct field evaluations of selected belting and lubricants under actual harvesting conditions to estimate the incidence of bark damage and the useful life of the belting. 13 4. Estimate the cost/benefit relationship of an improved slip-belt and lubrication system for several harvesting situations. 5. Recommend, if possible, an improved slip-belt and lubrication system that will improve orchard life and harvesting economics when adopted by growers. CHAPTER 2 L I TERATURE REV I EW 2.1 Historyof Mechanically Harvesting Cherries. Cherries, compared to other fruits, are relatively small in size. Levin et al. (1960) reported that hand picking cherries is slow tedious work and takes approximately ten times as many man- hours to pick a tonne of cherries compared to the same amount of apples, peaches or pears. Because the cherry harvest season is short, large numbers of hand pickers are required. In 1960 the Michigan Employment Security Commission reported that 45,000 workers were needed to harvest the Michigan cherry crop. Because sufficient local help was not available, many workers were recruited from other parts of Michigan, other States, and foreign countries. Brown (1980) states that Public Law 78 (the Bracero Program), which allowed the importation of migrant workers, was used to meet the seasonal needs during the years 1951 through 1964. Harvesting costs were sometimes half of the total production costs of cherries. Due to the low availability of skilled labor and high costs of harvesting, a less expensive and more effective means of harvesting was needed. During the 1956 season, Levin et a1. initiated studies to develop practical mechanical harvesting equipment 14 15 for use in cherries. The purpose of the work was to develop equipment and methods that would reduce the number of human pickers required, lower harvesting costs and help maintain on-the-tree quality. A variety of hand and pole shaking methods were tried in 1956. This involved hand shaking limbs using poles with various types of hooks or short lengths of rubber hose, however, these proved to be exhausting and unsatisfactory. The following year several hand-held mechanical shakers that were hooked or held against individual limbs were tried. Because the weight and much of the shock was transferred to the workers' arms, these mechanisms were also exhaustive and production rates were low. In 1958 a tractor-mounted hydraulically-activated boom-shaker used in California to harvest nuts, was used to mechanically harvest cherries in Michigan. The harvesting unit consisted of a tractor mounted boom with a claw at the end which was attached to the primary branches. The claw was clamped to the limb so the angle between it and the boom was 90°. When the angle deviated from 90°, the forces created on the tree resulted in slippage between the point of attachment and bark. Bark damage due to slippage and excessive clamp pressure varied from none to quite serious. Under favorable conditions the boom-shaker was able to remove approximately 95 percent of the cherries from the tree. In 1963 and 1965 Adrian et a1. looked at the l6 feasibility of ,using permanent installed fastners for shaking attachments. Various sizes of lag screws and threaded rod were installed into the main scaffold limbs or trunks for shaker attachment. The advantage of this method was transmitting shaking forces through fastners to structural wood rather than clamping against vulnerable bark. Because of problems with fastners pulling out, bending, breaking and misalignment of the shaker, Adrian et a1. concluded that direct clamping of the shaker to the limb or trunk was the most efficient and economical method of operation. With the adoption of the mechanical harvester in Michigan during the 1960's, (bearing tart cherry trees trained for hand harvesting required drastic pruning. The number of main scaffold branches was reduced and the lower portion of the tree thinned out to allow for movement of the shaking and catching equipment. Opening the tree resulted in better colored fruit, less bruising of cherries during shaking, and more effective removal of cherries (Mitchell and Levin, 1969). As mechanical harvesting proved to be an effective method to harvest cherries, harvester design changed during the 1960's. The small limb shakers were replaced by more powerful trunk shakers that resulted in a higher magnitude of clamping and shaking forces applied to the tree. Currently there are several designs of commercial shakers 17 used to mechanically harvest cherries. These commercial machines use trunk shakers for fruit removal and inclined catching surfaces for crop collection. The operator of the shake-catch harvester must stop at each tree, securely clamp the shaking mechanism to the tree, and shake until nearly all the fruit has been removed. A recent trend in the fruit industry has been to plant trees at a higher density to obtain higher yield/ha, improved cultural pratices, and shortening the time to get the orchard into economical production (Peterson, 1982). Orchards that once had 75 to 300 trees/ha now are planted at densities of 350 to 700 trees/ha. Because harvesting rates of only 60 to 120 trees/h are obtainable with the stop and go harvesting systems, Peterson and Monroe (1977) and Peterson (1982) developed continuous moving harvesters. Harvesting rates of over 300 trees/h were achieved in tart cherries with Peterson's harvesting system. Problems of obtaining and managing labor to harvest several fruit crops have led researchers to develop mechanical harvesters for citrus, apples, and peaches. Gentry (1980) originally developed a shaker for harvesting lemons, however, because of bark damage occuring too frequently at the attachment point between the clamp and the tree, grapefruit were harvested instead. Citrus harvested with Trunk shakers also caused bark damage when harvesting citrus in Florida which led Coppock and Donhaiser (1980) to look at an alternative method of harvesting. They developed 18 a conical air shaker for harvesting citrus. By using an abscission chemical and the air shaker they were able to remove 97 percent of the fruit with harvesting rates of up to 170 trees/h. Commercial cherry orchards have a high initial investment before trees become productive enough to economically harvest. If trees are severely damaged during the first mechanical harvest, tree death may occur and the total investment in that tree is lost. Researchers continue to improve the design >and efficiency of mechanical harvesters. The negative impact of tree decline in commercial cherry orchards has resulted in increased efforts to determine and eliminate the causal factors. 2.2 Causes of Bark Damage One major problem in the cherry industry has been damage to the bark of cherry trees at the point of shaker clamp attachment during mechanical harvesting. Cargill et al. (1982) states that tree damage in general takes on three different forms: 1. Damage to the bark at the point of attachment of the shaker clamp. 2. Breakage of large stiff limbs. 3. Breakage of small branches, fruiting spurs, new growth, and removal of leaves. When bark is stripped or broken loose from the trunk it becomes an excellent host for air- and soil-borne 19 insects and diseases. If visible damage goes unnoticed by the harvester operator and he fails to correct the problem, a large percentage of the orchard may be damaged. Brown et a1. (1982) notes that in many cases damaged bark stays in place although it is cracked or separated from the wood at the cambium. This damage may be hidden for several weeks or months and is later recognized as areas with exuding gum, open cracks, abnormal bark growth. or the bark tissue has died. Because detection of hidden bark damage is possible only through subjective tests that are destuctive to the tree, Brown et al.. (1984c) examined several methods for detecting this damage. Bark damage combined with adverse weather conditions, disease and insect attacks, improper nutritional levels, improper use of growth regulators, and insufficient or excess moisture may result in tree decline. Brown et al. (1984a) defines tree decline as the loss of vigor and yield with early replacement of the orchard. Levin et a1. (1960) reported that the first mechanical cherry harvester used in Michigan caused bark damage to some of the trees. Some bark damage had been accepted in the earlier years of mechanical harvesting, until a serious gummosis disease known as mallet wound canker caused by the fungus Ceratocystis fimbriata, common to bark injury on almonds, infected some of the mechanically harvested prune orchards in California. Evidence showed 20 that insects were involved as vectors by transporting the fungus to fresh bark wounds (Devay et a1. 1960, 1962, 1965). Devay et a1. (1965) also suggested that C. fimbriata was carried from tree to tree by the shaker clamp attachment, infecting the trees that were damaged. Because the fungus is favored by fresh bark wounds, it tends to grow well on exposed wood where the bark has been stripped off, or in cracks and underneath the bark. The use of mechanical shakers for harvesting almonds and prunes increased the frequency of bark injury for subsequent years. Devay et a1. (1965) reported that an estimated one million or approximately 59 percent of the prune and almond trees in the Sacramento Valley were infected with C. fimbriata. Because the fungus is perennial and continues activity on trees year after year, girdling the limbs, it eventually kills the infected tree. g; fimbriata has not been a threat in Michigan cherries, but other canker can develop at damage sites and eventual death of limbs and trees has been observed. By examining bark damage, researchers have identified many conditions thought to be potential causes of bark damage. Adrian and Fridley (1963) stated that injury to the bark may be caused by tangential (shear) stresses resulting from poor design or operation of the clamp, radial (compression) stresses caused by clamping to firmly, and longitudinal stresses which occur when shaking force is not directed perpendicular to the limbs or trunk, Figure 2.1. 21 I . ' —-> ‘- -<— RADIAL I .,\ (COMPRESSIVE) TANGENTIAL H Q. ,. I (LONGITUDINAL ‘- Figure 2.1 Possible stresses that may cause bark damage. 22 In 1965 Adrian et a1. approached the problem of shaker clamp injury and the general causes. They found that some of the variables affecting bark injury were soil and bark moisture, varietal differences _and tree age. Diener et a1. (1968) observed that the amount of bark damage caused to a trunk or limb was determined by the bark properties, radius of the limb or trunk, and the resistence of the tree to be shaken. In 1982 Brown et a1. and Cargill et a1. classified the general causes of bark damage into ten broad areas: 1. Operator error and inadequate operator training. . Improper shaker adjustment. Improper clamp adjustment and maintenance. Improper shaker clamp attachment. 0" IF an N o . Poor judgement in selection of a machine for young trees and/or failure to make adjustments for the size of the tree on existing machine. 6. High (cambial activity at harvest due to excessive irrigation, rainfall or physiological activity. 7. Immature fruit which requires an excessive force for removal. 8. Improper machine design. 9. Settling or moving of the shaker due to soft soil conditions or excessive side hill slope. 10. Improperly pruned trees requiring excessively long shaking cycles. Because many different conditions exist during the shake- 23 harvesting of cherry trees, finding the most common causes of bark damage is difficult. Brown et al. (1982) found after direct observations of cherry harvesting operations, that a major cause of bark damage was poor operation of the shaker and clamp. A list of specific examples included: 1. Failing to center the clamp on the trunk. 2. Clamping to firmly causing excessive clamping pressure and crushing (splitting) of the bark, Figure 2.2a. 3. Clamping to loosely, allowing the pads to scuff (slide) across the bark during shaking causing tearing of the bark (tangential shear), Figure 2.2b. 4. Clamp pads not slipping internally due~ to improperly lubricated slip surfaces causing high shear forces (pads become over heated, sticky, and worn), Figure 2.2c. . 5. Clamp pads too small or firm causing high stress in the bark due to small contact area, Figure 2.2a. 6. Excessive eccentric weight setting causing excessive tree displacement and bark strain, Figures 2.2d, 2.2e, and 2.2f. 7. Excessive power applied to small trees, causing excessive displacement, Figures 2.2d, 2.2e, and 2.2f. 8. Shaker gallop during starting and stopping causing excessive torque (shear) on the bark, Figure 2.2e. 9. Settling of the shaker carrier into the earth during shaking causing longitudinal shear, Figure 2.3a. 10. Shaking forces not perpendicular to the trunk causing 24 I I ‘1 n 1 L; r A i ‘l D 5,: ’1 I _\X\\\\X‘ I}? MIA A'A FIXED PAD MOVABLE FAD FIXED PAD MOVABLE PAD TREETRUNK TBEETRUNK a. Compressive stress caused by b. A loose clamp during shaking excessive clamping force. can batter the bark until it fails. ______ _____1 ‘1 a I r > I ,4 ‘ I é‘d .5: A A FIXED PAD MOVABLE PAD FIXED PAD MOVABLE PAD TREE TRUNK TREE TRUNK c. Tangential shear caused by d. Tangential shear caused by flow of clamp pad during shaker displacement. clamping. . _____19 4 J .12 ._4 FIXED PAD MOVABLE PAD FIXED PAD MOVABLE PAD TREETRUNK TREETRUNK e. Tangential shear caused by f. Compressive stress caused shaker rotation. by shaker displacement. Figure 2.2 Shaking and clamping forces that may be major causes of bark damage (Cargill et a1. 1982). 25 LONGITUDINAL SHEAR CAUSED BY SHAKER WEIGHT OR LIFTING FORCE ' AREAS oF STRESS CONCENTRATION NAP <-— a7 uFLA' ' AREAS oF NON - oR PObR_ coNtAcr LONGITUDINAL SHEAR COMPONENTS 8. Longitudinal shear will be caused b. Longitudinal shear will be caused if the shaker rises or falls dur- if a leaning trunk is clamped and ing shaking. shaken. RIGHT - JUST BELOW LIME SCAFFOLDS AREAS oP StRESS coNCENrRAnoN \1 \/ “HON“ - TOO HIGH 0" TRUNK do FLAP ;'--..- 3 CI: .0 --.. , AREAS OF NON - OR POOR . .' CONTACT ' ' ‘, wRoRa :- TOO LOW on mm“ 5 . 0 k;1;; LONGITUDINAL SHEAR COMPONENTS fig v __ c. Longitudinal shear will be caused d. Longitudinal shear will be caused if the shaker is tilted when if the shaker is clamped on a tap- clamped to the trunk. ered part of the trunk near roots or limbs. Figure 2.3 Shaking and clamping forces that may be major causes of bark damage (Cargill et a1..1982). 26 longitudinal shear, Figures 2.3b and 2.3c. ll. Clamping too low to the ground where the trunk is most rigid or too high near the lower scaffolds causing excessive forces applied to the trunk, Figure 2.3d. Many of the examples listed can be corrected if the operator is well-trained and experienced with harvesting. Shaker pads, bark strength and structure have been studied in an effort to reduce bark damage. Operating limits must be known for a wide range of harvesting conditions so that damage is unlikely to occur, even in the most extreme cases. 2.3 Bark Structure and Strength Since the 1960's the structural and strength. characteristics of tree bark on several fruit and nut trees have been studied in an effort to define the magnitude and variation of bark-strength properties. With this information, researchers developed design and operating parameters for mechanical harvesting systems used in commercial fruit and nut operations. A tree trunk is composed of concentric layers of cells known as the heartwood, sapwood, cambium, phloem, and the cork or periderm, (Curtis 1979). The heartwood is composed entirely of dead cells and is the central supporting column of the tree. Sapwood is made up of xylem tissue which contains the tracheids and vessels through which water and minerals move from the soil to the leaves and other living parts of the tree. The cambium layer 27 produces secondary xylem and phloem. Sugars produced by photosynthesis are conducted to the roots and other living nonphotosynthetic parts of the tree through the phloem. Periderm is a dead tissue which protects the inner tissues from drying out, mechanical injury, insects, and herbivores. The phloem and periderm together make up the bark of a tree. The stress which bark can stand is directly related to the physiological condition of the cambium. Fridley et a1. (1970) reported that seasonal factors such as moisture content and cambial activity have an appreciable affect on bark strength. Each year trees go through a cycle where the tree becomes active in the spring and later goes into a dormant stage in the fall. During reactivation in the spring, cells in the cambial layer swell and enlarge in the radial direction, the radial walls become thinner, and the cell contents seem to change from a solid to a liquid consistency, (Priestly 1930). The intercellular spaces in the cambial zone become saturated with water and the cambial walls break readily causing the bark to "slip" over the wood. "Slip" as described by Fridley et a1. (1970) is the ability to peel bark from the limb or trunk with a smooth separation in the cambial zone. Cessation of cambial activity occurs in the fall or before a normal rest period. During this period the bark and cambium are low in moisture, fibers toughen, and "slip" does not occur as easily. 28 In 1968 Diener et a1. studied the directional strength properties of tart cherry bark. They found that the periderm had the highest strength in the tangential direction compared to the longitudinal direction. The periderm also had five to six times the tangential elongation before rupturing compared to the phloem. Phloem strength was opposite compared to the periderm with the highest strength being in the longitudinal direction. Diener et al. reported that cherry bark with the periderm attached would typically! have a tangential strength of approximately 420 N per 25 mm of width compared to 110 N without the periderm. This can be explained due to the nature of the periderm and phloem cell alignment. The phloem cells have their long axis in the longitudinal (vertical to the trunk) direction, while the periderm cells have their long axis in the tangential (horizontal to the trunk) direction. It is then posSible for the phloem to be ruptured underneath the periderm but not be visible since the outer periderm may still be intact. Bark acts as a viscoelastic material in its longitudinal direction. Bark fails in this direction by incremental failure of the fibers and tissues, accompanied by sliding and continued failure. Failure of the periderm occurred along a smooth plane indicating the long direction of it's cells. When bark is damaged to the point where cells are ruptured or the bark separates from the wood, the flow of 29 fluids which transport the essential nutrients both up and down the tree is disrupted. Hairline cracks may form in the bark tissue allowing air to enter and oxidize the cambial tissue causing it to turn brown. Fridley et a1. (1970) used browning of the cambium as a test for defining the magnitude of radial (compressive) stress that could be applied to the bark of apricots, peaches, almonds, olives, and prune trees. They found as stress increased, discoloration extended in the cambium and increased with an increase in force. Tests were also conducted to determine the relationship between visible injury Iand the fungus C. fimbriata. Radial stresses exceeding 6900 kPa resulted in bark being visibly cracked to the cambium in 20-year-old prune trees and the occurence of the canker infection. On 6-year-old trees cracking and infection occurred atv 75 percent of this radial stress value. Brown et al. (1984a) states that bark damage is more likely to occur on sweet than tart cherry trees and is more likely on 4- to 8-year-old trees than on 10- to 20- year-old trees. In 1982 Brown et al. made preliminary studies on the response of compressive and shear stresses applied to the bark of sweet and tart cherry. They found that compressive failure of the cambium occured at lower clamping pressures on sweet cherry compared to tart cherry. Clamping pressures of about 1000 kPa initiated 'failure on sweet cherry compared to 2300 kPa on tart cherry. The 30 following year, compressive failure was initiated by clamping pressures of about 1000 kPa on tart cherry trees that were irrigated through the harvest season. This demonstrates the importance of avoiding irrigation near harvest to reduce bark moisture content and cambial activity. Shear strength for sweet cherry was lower than for tart cherry. Cambial shear strength decreased as moisture content increased. Clamping pressures above 2070 kPa increased shear strength apparently due to friction, but damage to the cambium occurred. Average cambium shear strength may range from 350 to 700 kPa depending on the clamping pressure used and bark moisture content, (Brown et al. 1984). The affects of moisture, tree age, variety, species and growth cycle all cause a variation in bark strength. Because most of Michigan's cherry crop is harvested during the months of June and July, cambial activity is high and slip occurs much easier. Excessive clamping and shear stresses on the bark can increase the likelihood of damage. Brown et al. (1984a) suggests that peak clamping pressures not exceed 2070 kPa and shear stresses not exceed 300 kPa on tart cherry trees. 2.4 Trunk Shaker Clamp Pads The function of trunk shaker clamp pads is to transmit and distribute both shaking and clamping forces 31 from the shaker to the tree. Because modern shakers use multidirectional' shaking force patterns, the pads must conform to the tree, yet be firm enough to effectively transmit longitudinal and tangential forces to the tree. To minimize stresses in the bark, clamping forces 'must be distributed over as large an area as possible. If contact area is insufficient, due to small or very firm pads, excessive force applied to the tree may cause the bark to split or be crushed. Insufficient clamping force may cause scouring of the bark due to slippage between the pad and tree, or compressive stress from a beating action. Pads that are to soft can result in excessive deflection of the tree into the pad and poor transmission of shaking forces. The use of improperly designed pads can increase the potential for bark damage even though all other factors are carefully controlled. Adrian and Fridley (1963) looked at several materials and designs for limb shaker pads. Results from their previous work indicated that tangential forces and radial loads could be minimized by increasing the contact area of the pad-tree interface and having a surface within the clamp that was free to slip under shear loads so that shear loads on the bark were low. A number of possible designs were considered, however, only two were developed and field tested. Both designs resulted in no detectable injury during the field testing. The materials and design of trunk shaker clamp pads 32 used in commercial cherry harvesting has changed as researchers have become more aware of damage caused to cherry trees by improperly designed pads. Currently there are several designs of pads used in shakEr clamp-pad systems. The types include round and flattened hollow neoprene tubes, round inflatable neoprene tubes filled with ground nutshells, and rectangular neoprene pads with small circular holes running parallel to the tree trunk axis. Frahm et a1. (1983) evaluated the mechanical properties of four commercial trunk shaker clamp pads to determine their relationship to bark damage during harvesting. Pads were tested for contact pressures, contact areas and stiffness. Pad contact areas and pressures were determined for clamping forces ranging from 50 to 150 percent of the manufacturers recommendations. Results show that each pad appeared to have sufficient contact area to distribute shaking forces on a 50 mm diameter trunk, however, all pads exceeded the contact pressure limit of 2070 kPa. On a 115 mm diameter trunk all pads had sufficient contact area but two of the pads had excessive pressure eareas. All pads had sufficient contaCt area on a 165 mm diameter trunk, however, three of the pads tested had excessive pressure areas. These peak pressures suggest that clamping pressure on the bark may be excessive in some cases. Excessive pressure can cause compressive failure of the cambium or splitting of the inner bark during high 33 moisture conditions for sweet and tart cherries. Compressive failure of the cambium was initiated at about 1000 kPa on tart cherries (Brown et a1. 1984). Because peak pressure observations were taken during stationary tests, much higher pressure will likely occur during shaking. Contact areas were measured for clamping force corresponding to a peak contact pressure of 2070 kPa for each pad and tree combination (instrumented steel pipe). Three of the pads tested required reduced clamping force to limit peak contact pressure. However, Frahm et a1. states that on the fourth pad this would result in insufficient contact area to hold the tree securely when shear loads are developed. (If pads are too soft shaking forces will be poorly transmitted to the tree. Greatly reducing the clamping pressure on two of the pads was possible but bark scuffing and inefficient shaking transmission could occur on the other two. 2.5 Reducing Bark Damage When mallet wound canker became a serious threat to California's stone fruit ochards, Devay et al. (1965) found that C. fimbriata could be prevented or controlled by wise use of mechanical harvesting equipment capable of reducing bark damage, and by removing all canker infected areas and limbs. Frahm et a1. (1983) developed recommendations for reducing bark damage based upon the properties of the four clamp pads and the tart cherry bark strength data. In 1983 34 Brown et a1. suggested lower hydraulic circuit clamping pressures for Several brands of shakers so peak clamping pressure was below 2070 kPa on young tart cherry trees. Growers since then have reported that obvious damage was reduced as a result of this suggestion. As researchers and growers continue to look for better and improved methods of harvesting our nations cherry crop, a reduction in the amount of bark damage inflicted on trees is needed. Brown et al. (1982) and Cargill et a1. (1982) provide a summary on ways to minimize bark damage. They suggest to: 1. Develop trees with a straight trunk, with at least 750 mm to 900 mm before the first scaffold limbs. 2. Instruct shaker operators on proper use of the shaker and to recognize and correct operational problems that may cause bark damage. 3. Adjust hydraulic pressure on the clamp to minimum levels for the tree condition and size. 4. Keep the area between the flap and sling properly lubricated where the flap directly contacts the tree (shear movement between the lubricated flap and sling will minimize shear in the bark). 5. Maintain the shaker pad system in good condition. Check and test operation before the harvesting season. Replace pads if they do not properly cushion the bark, or flaps if they stick and induce shear in the bark. 6. Test the hydraulic control valves in the shaker clamping 10. 11. 35 circuit before the harvesting season to confirm that the set pressure is maintained. In young trees or trees in a "bark slipping" condition, reduce clamping pressure, shaking force and frequency to the minimum effective level. Don't shake young trees that are too small for the clamp. Avoid multiple shaking cycles. Operators sometimes use several short duration shaking cycles to remove the last few fruit, but this will cause excessive torque on the bark compared to one continuous shake cycle. On high scaffold mature trees (scaffolds 750 mm or higher) locate the clamp at the center, or just above the center of the trunk, to reduce the power required to shake the tree (the lower the attachment the greater the force and power required to obtain equivalent tree vibration). Attach the clamp perpendicular to the trunk (tendency for a very high clamp attachment is to have the shaker arm angled up to the tree creating a high longitudinal shear). Use sod culture between rows to provide a firm orchard floor for harvester operation (sod culture helps prevent carrier settlement during the shaking operation). If these recommendations are carefully followed bark damage should be minimal. Operators of harvesters should be familiar with clamping pressure limits for various 36 harvest conditions. Minimizing bark damage will help eliminate one of the factors involved in tree decline. 2.6 Summary Mechanical harvesting of fruit and nut trees was developed in the 1950's to insure that the crop could be harvested when sufficient hand labor wasn't available and to provide a more economical method of harvesting. Researchers studied' a variety of methods of mechanically harvesting cherries ranging from hand- held mechanical shakers to tractor-mounted. boom shakers. As mechanical harvesting proved to be both effective and economical in commercial cherry orchards, small limb shakers yielded to more powerful trunk shakers. New orchards were planted at higher densities to obtain higher yield/ha and shorten the time to get the orchard into economical production. However, the negative impact of tree decline has resulted in extensive research to eliminate the causal factors. One of the major causes of tree decline has been bark damage at the point of attachment between the tree and shaker. If this occurs, trees become susceptible to attack by air- and soil-borne insects and diseases. In the early 1960's an estimated one million prune and almond trees in the Sacramento Valley were infected with a killing canker due to bark injury caused by mechanical harvesting. By wise use of mechanical harvesting and removing all canker infected areas and limbs, the disease could be prevented and 37 controlled. Because of the serious problems associated with bark damage, researchers have attempted to define the magnitude of bark strength properties in an effort to develop design and operating parameters for mechanical harvesting systems that would minimize bark damage. Recommendations based upon bark strength, harvester design, and mechanical properties of shaker clamp pads were developed in an effort to minimize bark damage. Despite continued improvement in shaker and pad design, serious bark damage is still reported each year. A wide array of research has focussed on reducing and possibly eliminating bark damage, however, a study of the slip-belt and lubrication system used on trunk shaker, pads as a potential cause of bark damage has not been made. High shear forces can develop between the pads and trunk during the shaking process causing considerable damage to the bark. By reducing the amount of shear force transmitted to the trunk with an improved slip-belt and lubrication system, bark damage will be reduced. Eliminating the causal factors involved in bark damage will be a step toward preventing tree decline. CHAPTER 3 MATERIALS AND METHODS 3.1 Laboratory and Field Analysis A series of laboratory analyses were conducted to analyze the systems of slip-belts and lubrication currently used on trunk shaker clamp pads. Two different machines were developed in 1984 for estimating the relative static and dynamic friction forces that exist between the two lubricated belting surfaces. Static friction, the characteristic of the belting surface to resist the start of sliding, and dynamic friction, the resistence of the belting surfaces to sliding at high velocity were estimated for the smooth surfaces of three different beltings (Polymate 135 Polyurethane COS, Polymate 135 Nitrile COS, and conventional neoprene)' and five lubricants (Modoc oil, light bearing grease, food grade grease, Crisco shortening and silicone spray). A field analysis of the slip-belts and lubrication systems was conducted to analyze the polyurethane and nitrile belting under actual harvesting conditions. Harvesters equipped with either a nitrile or polyurethane slip-belt system were operated by cooperating growers throughout Michigan to provide field data not obtainable, in the laboratory. 38 39 3.2 Belting and Lubricants Most conventional neoprene belts used in the slip— belt systems covering the shaker pads are about 10 mm thick, stiff and hard. On small diameter trunks these belts may prevent full pocketing and adequate cushioning for the trunk. Neoprene belts also may become sticky as petroleum- based products used as lubricants in the slip-belt system are used ups For these reasons, thinner belts that are flexible, softer, covered with smooth surfaces and do not become sticky were needed for this study. Three different types of belting were obtained from Industrial Belting Supply, Grand Rapids, MI; Polymatel/ 135 Nitrile COS, Polymatel/ 135 Polyurethane COS and a conventional neoprene. Both of the Polymate belts have the same mechanically locked carcass whose tensile members are totally >encapsulated with fibers and saturants to form a homogeneous mass. These belts were selected because of their flexibility, thickness, strength, heat tolerance and expected low friction properties. The nitrile belting has a smooth nitrile cover on one side, a nominal thickness of 3.7 mm, is white in color, and has a maximum intermittent operating temperature of 120° C. The polyurethane belting has a smooth ,polyurethane cover on one side, a nominal thickness of 3.8 mm, is dark green in color, and has a maximum intermittent operating temperature of 93° C. The l/ Polymate is manufactured by Globe International, 1400 Clinton Street, Buffalo, NY 14240. 40 conventional neoprene selected has smooth neoprene on both sides, a nominal thickness of 10 mm, is black in color and has a maximum intermittent operating temperature of 120° C. Another important factor in selecting the Polymate belts was compatability with lubricants, which is superior for the nitrile and polyurethane belting compared to neoprene, Table 3.1. Table 3.1. Compatability with selected lubricants for nitrile, pglyurethane and neoprene rubber compounds._ Nitrile Polyurethane 'Neoprene Lubricant Vegetable Oil A A C Gulfcrown Grease A A B Light Grease A A U An1ma1 Fats A A- C Lubricating Oil A B B SAE 10,20,30,40,50 Shell Alvania A A B Grease #2 Silicone Oils A A A Silicone Grease A A A Sunoco All Purpose A A B Grease Texaco 3450 A A U Gear Oil ll An Engineering Guide to Elastomer Selection and Manufacturers Standards, Minor Rubber Co., Bloomfield, N.J. Recommended Minor to Moderate Effect Moderate to Severe Effect Unsatisfactory C0111? 41 3.3 Static Friction Machine The static friction machine was designed as a flat- surface test stand with a second class lever above it to apply a constant compressive load to the belts,’ and to measure the friction forces between the belting surfaces as they were pulled from rest to a low linear velocity, Figure 3.1. The lever assembly had to be constructed to allow for linear movement but still apply a constant compressive load during a linear pull test. Two SKF 6306 ball bearings were spaced 200 mm apart on a shaft that was welded to the hinge-end of the lever. A square frame with two flat horizontal surfaces was welded to the hinge-end of the test stand allowing the two ball-bearings and lever assembly to travel freely during a linear pull test. On the test stand surface two strips of belting 25 mm wide by 722 mm long were fastened parallel to the lever. Two strips 76 mm wide and 400 mm long were then fastened to a separate roller-guided slide-plate and placed directly on top of the belting on the test stand surface. Total contact area between the belting surfaces was 15,500 mmz. This area was loaded to a uniform pressure of 1,400 kPa by placing a hydraulic jack between the slide-plate and the lever and hanging 22.7 kg weights on the load carrying end of the lever. The loaded plate was pulled from rest to a constant velocity using a 48 r/min Master XL Gear Motor operating .0559: aowuofium uwumum on: no wnymuv uwumamaom H6. anamwm nu. / «hi—- MOHOZ U Hafiumam _h.' 0 42 mmuaamm ammmm A150 939 1? _AI ”$0:ng ~4ng 155m .HgHmmDAJUZHHAmm mgmmmMm . _ H m oszdmm . @ mmagom ET Aggy fimzHA 43 through a Eberhardt Denver Co. right angle speed reducer. A 12 tooth chain sprocket was mounted on the output shaft of the speed reducer. An endless chain was connected to both ends of the slide plate, ran over the speed-reducer sprocket and an idler sprocket on the opposite end of the test stand. This resulted in very high torque output ability, and a steady state linear velocity of 3.3 mm/s between the surfaees of the belting. Pull forces were measured by placing an oil-filled Clippard Minimatic Model UDR-17 stainless steel cylinder equipped with a 13,760 kPa Celesco Model PLC pressure transducer in the pull chain. Transducer voltage readings were recorded on graph paper using a Mosley Autograph Model 135 X-Y recorder, after calibrating the recorder to directly show pressure. Calibration of the pressure transducer was performed with a hydraulic dead-weight tester. A Heathkit Model IP62718 regulated power supply provided an input voltage of +7.95 Vdc to the transducer. The testing procedure for each combination of belting and lubricant involved applying a thick film of lubricant to the belting surfaces _then measuring the resistance to sliding between the smooth sides of the belt while the belts were under uniform pressure. The static friction tests were replicated 10 times without relubrication. Sliding lasted a total time of 10 s for each replication. 44 3.4 Dynamic Friction Machine The dynamic friction machine was designed as two bearing-mounted circular plates arranged like a disc-clutch with a second class lever above it to apply a constant compressive load, and to measure the friction forces between belting surfaces as they were rotated from rest to a high linear velocity, Figure 3.2. The disc-clutch arrangement consisted of two separate 200 mm OD by 6_mm thick circular plates. One circular plate was mounted on the end of a shaft supported by two four-bolt flange bearings atttached to the test frame. On the top end of this shaft a 38 mm OD by 50 mm deep hole was drilled into the shaft center and a Torrington B-2020 needle bearing inserted. This permitted the second circular plate, with a 32 mm OD by 50 mm long shaft mounted in the center, to be placed in the same rotational axis during a rotary test. Testing was done by fastening two circular rings of belting to the interfaces of the circular plates. One belting ring was 100 mm ID and 127 mm OD whereas the other was 50 mm ID and 200 mm OD. Total contact area between belting surfaces was 4,560 mmz. This area was loaded to a uniform pressure of 1,350 kPa by placing a support between the lever and a thrust bearing mounted in the center of the upper circular plate and hanging 22.7 kg weights on the loading end of the lever. The hinge end of the lever did 45 .mawnoma aowuowum awn—mama on» mo wnwamup owumaonom .N.m ounwfim .I-I-ub ‘-H-I all mmamzomoaa UHHmzu u‘-o 10 .loil'l. 4 TIME. s POLYURETHANE CRISCO SHORTENINO 10 -n I. -.' I. W D'l'll -Ii, 1" -|' F1 . . . M "| I“ ll . u I-I D .l b 0 I+ [I . I' i r- “a . a . p . u‘ FICA . — I dl i II] o It ‘ TI- Yl I Ir . III W b H III. a l ' O ‘l | I’- ‘ III IP' I... ...|.l..-” III I- Id III. ‘ ll-ll- ll! 2 Home... TIME. s W TIME. 8 FIGURE 4.4 Static friction vs seconds of travel at s and 1400 kPa load for various —{Jbricant combinations tested in the static friction machine. 1985. 3.3 mm belting 56 Several things can be concluded from Figures 4.1 to 4.5. The results show that all combinations of the nitrile or polyurethane belting with the five lubricants resulted in lower frictional forces between the smooth surfaces than did the neoprene belting with the five lubricants. There was no practical difference between the breakaway and static friction behavior for any of the nitrile or polyurethane- lubricant combinations tested. The neoprene belting exhibited an increase in static friction behavior after each initial breakaway for all tests. All of the neoprene tests show a steady and large increase in friction force between the first and tenth replication. I interpret this to mean that these lubricants caused a breakdown of the neoprene surface, which resulted in higher frictional forces. In the neoprene-lubricant tests shown in Figure 4.1 and Figure 4.3, fluctuations in the static friction measured occurred in the seventh through tenth replication. After observing these fluctuations for the neoprene-Modoc oil and food grade grease tests, I inspected the interfaces of the belting and found the surfaces felt quite sticky. This stickiness may result in high shear forces being transmitted to the bark and an increase in the incidence of bark damage. The nitrile and polyurethane tests all show very slight increases between the first and tenth replication, Figures 4.1 to 4.5. Inspection of the polyurethane and nitrile surfaces revealed no stickiness. Table 4.1 lists 57 Table 4.1. Maximum force required to slide belting on the tenthl/replication, static friction machine, 1985.- . ' Lubricant Static Friction Force Nitrilez/ Polyurethaneé/ Neoprenei/ Belt Belt Belt N N N Modoc 011' 145 120 ' 1115 Light Bearing Grease 160 135 1010 Food Grade Grease 155 , . 125 1080 Crisco Shortening 125 125 ' 775 Silicone Spray 190 235 790 Average contact pressure between surfaces of belting was 1400 kPa and velocity was 3.3 mm/s. Polymate 135 Nitrile COS is a nitrile covered belting with a nominal thickness of 3.7 mm and has a maximum intermittent operating temperature of 120° C., Industrial Belting Supply, Grand Rapids, MI. Polymate 135 Polyurethane COS is a polyurethane covered belting with a nominal thickness of 3.8 mm and has a maximum intermittent operating temperature of 93° C., Industrial Belting Supply, Grand Rapids, MI. Conventional Neoprene is a three layer neoprene belting with a nominal thickness of 10 mm and has a maximum intermittent operating temperature of 120° C., Industrial Belting Supply, Grand Rapids, MI. 58 the maximum frictional force measured on the tenth replication for' each belting-lubricant combination. The highest magnitude of force measured for the nitrile and polyurethane tests occurred with the silicone spray. This may be accounted for due to the minimal amount of lubricant that I could apply to the surfaces of the belting compared to the other lubricants. Silicone was applied to the surfaces through aeresol spray versus spreading a much thicker layer of the other lubricants on by hand. Friday commercial trunk shakers (Friday Tractor Company Inc., Hartford, MI 49057) use a lubrication system that automatically relubricates the slip-belts with Modoc oil after every tree harvested. The benefit of this type of lubrication system would include preventing the large increases in frictional forces between the slip—belts internal surfaces as observed in the neoprene-Modoc oil test, Figure 4.1. I After my initial observations and results of the static tests it appeared that if nitrile and polyurethane belting were installed as the slip-belts on trunk shaker clamp pads, they should transmit far less shear force to the bark and require less frequent lubrication when compared to the neoprene. 4.2 Dynamic Friction Tests When cherry trees are mechanically harvested with trunk shakers, two masses rotate at a high r/min causing the 59 shaker and tree to vibrate at a high frequency (eg. 9 to 15 Hz). If movement between the pad and tree is occurring during the shaking process, the internal surfaces between the sling and flap may be sliding across one another at high velocities. If this sliding action occurs, the lubricant between the belting surfaces may deteriorate quickly and possibly cause excessive heating and wear of the slip-belts. As a second test for selecting a slip-belt and lubrication system that would minimize shear force transmission, require the least frequent relubrication, and also have good durability, tests were conducted to measure the dynamic friction forces between two belting surfaces with various lubricants applied. The dynamic friction force was measured for each combination of belting and lubricant using the dynamic friction machine as previously described in Section 3.4. Results of the dynamic friction tests are presented in Figures 4.6 to 4.10. The vertical axis represents the magnitude of torque measured at 305 mm from the center of the upper circular plate due to the friction between the two surfaces of belting. The results show that nitrile or polyurethane covered belting with any of the five .lubricants had the lowest friction between the smooth surfaces compared to the neoprene belting with the five lubricants. The breakaway friction behavior in most of the belting-lubricant combinations tested was higher than the dynamic friction 60 .—f.. aw m Hm: v . .....mflwl U - ! -. ---..- '0'! I Illrllll'b. III '5 m . -..- - ”...”..-s. - u m m... .HHUHMJ m n .....- . .mmwmummw- I m p - m w m m 5.: Mnomg E.z Macao... E . z Macy—E. Inafions t comb fnctlon machine ncan ynamlc -lub ‘ d s and 1350 kPa load for 9 tion vs seconds of travel beltéi tested in the 1985. TIME. s fric 380 mm nanuc VOHOUS 0 FIGURE 4.6 D UGH‘I'BEARINOGREASE ummemss 10 a. .l- '0’. Ila . o O I 0 00 C - --.. -..... ' -l t ‘ -d ‘ | I. I C- C " - I - I! - I |- I O . -l'... O n -.. O O I- '- " ‘ ' g. - L—'- . -‘ ' . Cl. .' o u O to ... .-. . a . III; 0 0| I Iv II- .9 VI IIIO| I.--cl «I . "uo O'-.Ivllo'i..' ...I' 'u o a. .00 o. 1' cl ' 'II I I I 0--.-.. r000nu..‘.0 o l . II... a - II 'I'ICi-o- -.. . 't'lll- I'll- . ' ...! I... r ."-I. . -.. I'. H'. l”|"l- , I o O Lil-1|... I II 1' Is- -.. O- "0 ill-r-" llrolll+lii ..Ili _ l.d-..'o 1"...'.. I -ll... ....L '0- ...- |In.r.'- I-'.-|¢ . Fifi 'l I'l Illl; l‘: .,' I; . I 0..., . .00..--3 I TIME. 3 TIME. s I i l l l DYNAMIC FRICTION MEASUREMENT 40.5- ..I'I...'0.I.WIllll.u.|a.. ll "2. -... ...,ILIIIIII.-. not '. .--.-- ... .I - .I-|!'. I O --.I I I l 'I' . I ,rl‘ O .I ...I I‘ll."' -... -lo'-, III.O-.I . . ""W. ...ITIn'!I I- ' uIIHHli..l..Hu.u:hnH-. .HH n. ...- u IlIIi . o ...Illlvi- .-...l- -..... ..-.T. . .. Till... 00'...,o.l a: u. .I.... .I I 0 ...I0. llllm'l ’II I III- I ..l ill-IDe: - III-l I.-. Ir. 0 '0 II o l.l .qu I... III. nl.-. In- oi - . o . ...... ..li IL--. .... I F2 luHiwflmU ..x -... ..lu.......n..... r. I ...... .J H . - a? ..w W n. m n .. .. m .2 game. 5.2 Usage. 5.2 99.2 27.0-I E ine fions ma non vs seconds of travel 3 and 1350 kPa load for -Iubricant comb' TIME. s t / ting the dynamic friction mach fric 380 mm bel tested in 1985. ”OMIC various 0 FIGURE 4.7 D 62 I I. .I. '0' DYNAMIC FRICTION MEASUREMENT I--. -0.-. It In. 0 '00... -- -‘¢,‘|I..-I ' . IIIII'I. I- II- Ann.-nl -..-I I- II"!:III-u -... ..- - ".- -‘Uu-. I . " ..- 0". I -II. ... ' ." r'.'--.h.'l .--- '. '0’..- 'I'IOOan. I'll! O.l-‘¢'... --. I..- ‘- '- 'e.-0'l ---II. ' I I- . - II "IO'!II .- I-. II II' . llt'.'."L.I I #I TIME. s HHI+I- I .-54' an'..L'I-'I.I- - I I-r'-. r“. TIME. s a.".‘l'||'-.ll| 0'. II lrll.I IIIIIIII . .Io If- . ...-I "I. -.. -I 27,0uu I 0 0'4 E.z Macao... E.z M3018 5.2 Macao... ds of travel and 1350 kPa load for -lubricant combinations TIME. a non vs secon ynamic friction machine 9 tested in the d 1985. / fric 380 mm namlc various beltin oi FIGURE 4.8 D 63 DYNAMIC FRICTION MEASUREMENT I II IIIIIIIII .Ia III I.I.II II I.Il .IIIIIPI II I II... . F. 27.0.. ... 13.54 . z Macao... E. z Macao... I I-I| III. ' ' ' ~i‘ I ' . II II I‘I.I.I .I IIIII I III.IIIII.II III- . - III-.. I .- IV-I.vI I PII I III III I I I I "IIIIIIII I . a II II.I II I I I 'III I II I. II - ' |.- I ~ - I' II III Ifi I. uII IIIII- ’ 1' -- ..-! II -I .. . I II III II I I H I. I III I III I I I- III . III .IIIIIIIIn II _III I , III-I I. III . III r. I I I I I III ill- I IIII II II I ,II II... I " .I ' .I.II II IIIIIIII. .1... .I. o .I. ... o l . . I I o .I. I I. II III.I. cIIII. III. I v1.I.I III a u .w ..-..u ...IIHH .-. “Ir. mun...“ H I V I .- . I-‘ . I I n h ... H ..Ih. . ..- . II 40.51 27.04 3.5 . 0.0 E . z Macao... ‘IIME. s s and 1350 kPa load for -lubricant combinations / namic friction vs seconds of travel various belting 380 mm tested in the static friction machine. a 1985. FIGURE 4.9 D 64 DYNAMIC FRICTION MEASUREMENT E .z .macao... TIME. I mm mm .I.. III. ....I.. .-.... .31.] II- I I II IIII II III. I O In I III .I‘ I II I I I I III-III I. I I. IIITIII I I I II In I III-I II I I I'II 0.I -.Ir'lI'... II . II II II I III II I I H1" III- II I II:- IIIII ... II II. I IIIIIIIIII r . III. III IWI III II III III IIlLiIIII I n”... “Minx ..I..T . II. Lr II II .z Macao... W m m II 1'.IIIIIIIUI uh” ...h...h--.... I I . II I I I IIII I I I II I I. III..II I I I IIOIIO III I I II I . I I I I. III tut-I II .I II I I.IIIII.I,OIIIIIII 0:. I . IIIIqI II I I I TIIII, I Io II. IIIII II. III I TIME; s vel s and 1350 kPa load for namic friction vs seconds of tra ynamic friction -lubricant combina— 9 tions tested in the d / machine. 1985. 380 mm various beltin 0? FIGURE 4.10 D 65 behavior. This is especially evident in the neoprene-Modoc oil test, Figure 4.6, where the initial breakaway friction is high in magnitude and the dynamic friction steadily drops during the replication as time proceeds. Table 4.2 lists the torque measured on the fifth replication after turning at a constant r/min for each of the belting-lubricant combinations. The highest torque measurements occurred with the silicone spray and the Modoc oil when tested with all three beltings. Again it was difficult to apply equal amounts of silicone lubricant to the belting surfaces compared to the other lubricants due to the nature of the application method. In the polyurethane-lubricant tests, scouring (due to the frictional load and heat) of the belting surfaces occurred and may have increased the dynamic friction force measured in some of the tests. The results shown in Figures 4.6 to 4.10 are for the belting surfaces sliding across each other, and cover a period of 10 5. If a replication was run longer than 10 s, the surfaces of the polyurethane belting would become hot causing the lubricant to deteriorate at a rapid rate and the belting in some cases welded together. The surfaces of the neoprene belting also were slightly scoured, however, the surfaces of the nitrile belting showed no evidence of scouring. This observation suggests that during the shaking of trees, long shaking times may require an increase in the frequency of lubrication of the slip- 66 Table 4.2. Torque required to slide belting on the fifth replication after 10 s of turning at a constant r/min1 with the dynamic friction machine, 1985._/. Lubricant Dynamic Friction Torque Nitrile Polyurethane Neoprene Belt Belt Belt N'm N'm N‘m Modoc Oil 17.5 19.5 29.0 Light Bearing Grease 9.0 13.5 20.5 Food Grade Grease 8.0 12.5 17.0 Crisco 9.5 13.0 16.0 Silicone Spray 23.0 25.5 47.0 l/ Average contact pressure between surfaces of belting was 1350 kPa and average linear velocity was 380 mm/s. belts to prevent scouring and welding of the slip-belts. The results from the friction tests show the nitrile and polyurethane belting compared to the neoprene are lower in both static and dynamic friction characteristics when tested with any of the five lubricants. Based upon this information, it appears that a nitrile or polyurethane covered slip-belt system will reduce shear force transmission and should reduce the incidence of bark damage. 67 4.3 Field Evaluations The results from both the static and dynamic friction tests suggest that installing nitrile or polyurethane covered belting in the pad system on trunk shakers will reduce the amount of shear force transmitted to the bark and reduce the incidence of bark damage. Based upon the friction tests, field evaluations of the nitrile and polyurethane belting were conducted by cooperating cherry growers during the l985'harvest season in Michigan. Growers were assigned either the nitrile or polyurethane belting, and were advised on maximum clamping pressures, based upon clamp and pad design they used, and the size of trees to be harvested. Interviews were conducted after each grower had completed their harvesting operations. The interviews did not provide precise data, due to each grower's own estimation of certain aspects relating to the slip-belt system. Bark damage resulting from operator error, compared to damage caused by the pad system without operator error, could not be discriminated in many cases. The ointerviews, however, provided consistent trends allowing reasonable assumptions to be made. The results obtained from each grower's harvesting operation and evaluation of the nitrile or polyurethane are presented in Table 4.3. Each harvester is listed by a number along with clamp and pad design used, slip-belting, 68 Table 4.3. Field evaluations of the nitrile and polyurethane covered belting, 1985. Clamp , Pad Slip- Circuit Clamping Harvester Design Design Belting Pressure, kPa 1 Friday C-Clamp Kilby Nitrile 2750 2 Friday C-Clamp Kilby Polyurethane 5500 3 OMC-scissor OMC Polyurethane 4135-4825 4 Friday C-Clamp Kilby Nitrile 6200-10340 5 Friday C-Clamp Kilby Nitrile 6200-10340 6 Halsey-scissor Martin Nitrile 1725-2070 7 OMC-scissor OMC Polyurethane 4650-4825 8 OMC-scissor OMC Polyurethane 3450-6200 9 Friday C-Clamp Kilby Nitrile 3790 10 FMC-scissor OMC Polyurethane 4135 11 Friday Tri-Clamp Friday Nitrile 12410-13790 12 OMC-scissor OMC Nitrile 3450-8270 13 OMC-scissor OMC Polyurethane 3450-8270 14 OMC-scissor OMC Polyurethane 3450-8270 15 Friday Tri-Clamp Friday Polyurethane 3965 16 Friday Tri-Clamp Friday Polyurethane 7580 17 Friday Tri-Clamp Friday Nitrile 7580 18 Friday C-Clamp. Exp._ Polyurethane 4825-11030 19 Kilby-scissor Kilby Nitrile 4480-5000 20 OMC-scissor OMC Nitrile 5515 21 Friday C- Clamp%/ Bxp.%/ Nitrile 5860-11030 22 Friday c- -c1amp_/ Exp._ / Polyurethane 5860-11030 l/ A new experimental clamp and pad design was developed in cooperation with Friday Tractor Co. and U. S. D. A. 69 Table 4.3. (cont'd) No. Trees Tree Trunk Tree Tree Harvester Harvested Dia. (mm) Age (yrs) Variety l 600 75-130 4-6 Tart 2 1300 50-90 3-5 Tart, Sweet 3 2200 65-130 6-10 Tart 4 6000 90-190 7-up Tart 5 1000 90-190 7-up Tart 6 2500 65-180 5-8 Tart, Sweet 7 800 75-100 6 Tart 8 2645 75-250 6-12 Tart, Sweet 9 4000 75-115 6 Tart 10 1000 ' 100-150 7 Tart 11 7000 75-200 7-9 Tart 12 8480 130-300 7-12 Tart 13 7000 130-150 7-12 Tart _ 14 5700 130-150 7-12 Tart 15 2500 50-130 7-8 Tart 16 1000 50-165 5-7 Tart 17 500 100-165 5-7 Tart 18 600 -100-165 5-7 Tart 19 4640 75-130 6-7 Tart 20 12000 65-150 6-9 Tart 21 18000 75-150 6-9 Tart 22 12000 75-150 6-9 Tart 70 Table 4.3. (cont'd) Relubricationz/ Shakeé/ Harvester Lubricant Frequency Time (s) 1 Food Grade Grease 200 trees 5-20 2 Light Bearing Grease 30 min. 5-10 3 Food Grade Grease 25-50 trees 3-5 4 Silicone Spray, Crisco 18 trees 5 5 Silicone Spray, Crisco 18 trees 5 6 Light Bearing Grease 35 trees 5-10 7 Light Bearing Grease 70 trees 10 8 Food Grade Grease 50 trees 5 9 Silicone Spray ' 100 trees 5-10 10 Food Grade Grease 100 trees . 5-10 11 Gear Oil 1 tree, auto. 5-10 12 Light Bearing Grease 1 hour 5-10 13 Light Bearing Grease 1 hour 5-10 14 Light Bearing Grease 1 hour 5-10 15 Silicone Spray 50-75 trees 5-10 16 Hydraulic Oil 1 tree, auto. 4-5 17 Silicone Spray 20-40 trees 4-5 18 Light Bearing Grease 20-40 trees 4-5 19 Light Bearing Grease 40-50 trees 5-10 20 Silicone Spray 60-70 trees 2-3 21 Silicone Spray 100 trees 5-10 22 Silicone Spray 100 trees 5-10 3/ Number of trees harvested or period of time before slip-belts were relubricated. 3/ Estimated average shaking time for each tree. 71 Table 4.3. (cont'd) Trickle Release Visible Slip-Belt Harvester Irrigation_ Agent Used Damage (%) Condition 1 No Yes NAi/ Good 2 No Yes 2.50 Good 3 Yes No .20 Good 4 No Yes 1.60 Fair 5 No Yes NA Fair 6 Yes Yes NA Good 7 No No NA Poor 8 No No .50 Good 9 Yes Yes 1.50 Good 10 No No NA Fair 11 No Yes .60 Good 12 No No .40 Poor 13 No No NA Fair 14 - No No NA Fair 15 No Yes 3.90 Good 16 Yes Yes NA Poor 17 Yes Yes NA Good 18 Yes Yes 2.40 Good 19 Yes Yes .90 Good 20 Yes Yes .90 Good 21 No Yes NA Good 22 No Yes 2.20 Good 4/ NA, not available 72 circuit clamping pressure, number of trees harvested, trunk diameter, age and variety, lubricant and lubrication frequency, shake time, if the orchard was trickle irrigated, if a release agent was used, percent visible damage and condition of the slip-belting after harvesting. Pad and clamp design, shaking time and relubrication frequency were considered to be critical in the reduction of shear force transmission. There were five designs of pads and seven different types of shaker clamps, Table 4.3. Growers used various clamping pressures depending on the size of trees they harvested and the type of pad and clamp design used on their harvester. Some of the 'clamping pressures used by the growers were excessive, for the size of trees they were harvesting and compressive damage may be visible in later years. Growers estimated that shaking time ranged from 3 to 20 s, and duration was related to tree size and fruit maturity. To increase fruit ripening and possibly reduce the shake time, a majority of the growers applied a release agent (Etherel) to their trees prior to harvest. In some instances growers stated that the cherries were not shaking off the tree easily, which resulted in longer shaking times than desired. The size of trees in the study ranged from 50 to 300 mm in trunk diameter, were between 3 and 12 years old, and consisted mainly of the tart variety, Table 4.3. The frequency at which growers relubricated the 73 slip-belts depended on tree size, shaking time, pad type, clamping pressure, and lubricant type. Relubrication frequency ranged between 18 and 200 trees. Many of the growers establish regular schedules in which I they relubricate the slip-belt system, however, a few growers only relubricate during breakdowns, tank changes, or when visible damage was occurring. Relubrication should take place periodically so that flaps can be checked for dirt buildup, excessive wear, and cleaned if necessary. Harvesting larger trees, using higher circuit clamping pressures, and using longer shaking times, requires more frequent relubrication and causes greater wear of the nitrile and polyurethane belts. There were several different types of lubricants used in the evaluation with silicone spray and light bearing grease being the most frequently used. Each lubricant worked equally as well, however silicone spray has several advantages. The advantages of using silicone spray include, easy application and cleanup, less heat buildup, and less dirt buildup. Because silicone spray applied to the slip- belts results in a very thin film of lubricant compared to the greases, the inner surfaces of the slip-belts did not stick together allowing air to flow between the surfaces and and cool the pad system. Slip-belts lubricated with grease causes the inner surfaces of the slip-belts to stick together notu allowing heat in the pad to dissipate. In somes cases growers that used Crisco shortening, bearing and 74 food grade greases had problems with heat buildup and dirt buildup between belting layers. One of the main concerns with the nitrile or polyurethane belting during the field evaluation was durability under actual harvesting conditions. The durability of the belting was found to be related to size of trees harvested, lubrication practices, shaking time, pad type, and operator skill. The number of trees shaken with each slip-belt system ranged from 600 to 15,000 with nitrile and from 800 to 18,000 with polyurethane, Table 4.3. or the 22 sets of belting used, only 3 were in poor condition and could not be used for another harvest season. The poor condition of 2 of the 3 sets was due to operator carelessness in lubrication practices and harvesting practices. The 5 sets that were in fair condition had worn through the nitrile or polyurethane cover in a few places. This was due to poor lubrication practices, shaking trees that were too large (greater than 125 mm diameter trunks) with high clamping pressures, and mechanically worn shaker clamps. All the sets of belting that were in good condition showed a small amount of wear on the outer flap which contacts the tree. Based upon the condition of the slip-belting used in the evaluation, it can be concluded that a nitrile or polyurethane belt set could last several seasons for the average grower. However, the nitrile belting appears to be 75 the best belting for the slip-belt and lubrication system. The lower maximum intermittent operating temperature limit of the polyurethane belting compared to the nitrile belting could create a fusing, melting, or sticking failure of the polyurethane slip-belts if used on large trees that require a longer shaking time. In some cases the smooth cover of the polyurethane belting had delaminated when high clamping pressures and long shaking times were use when harvesting trees. For these reasons, nitrile belting was recommended to growers for the 1986 harvest season. To keep the flaps in good condition they must be cleaned periodically. to prevent dirt buildup, lubricated frequently, and used only on trees having 40 to 125 mm diameter trunks. Orchards were observed after harvest for visible damage caused by the trunk shakers. Visible damage was any trunk that had been barked, cracked or sheared as previously defined in Section 3.5. The amount of visible bark damage ranged from 0.2 percent to 3.9 percent of the trees observed, Table 4.3. Damage caused by operator error could not be distinquished from damage resulting from the pad system. Most of the damage observed on the trees was classified in the barked catagory. Trickle irrrigation of some of the orchards did not appear to be a factor in the amount of damage caused to the trees. Growers felt that the rainfall during the 1985 growing season was quite high and there was no difference in the amount of damage caused to 76 the irrigated versus nonirrigated orchards. After observing the orchards, most of the damage occurred in sequential order down a row of harvested trees. Some of the grower's comments suggest that the slip-belts were relubricated only after some visible damage to the trees had occurred. Thus, some of the damage observed could have been eliminated if relubrication of the slip-belts was more frequent. Growers attributed most of the damage to dirt buildup between the sling and flap, operator carelessness, and inadequate relubrication. Excessive clamp wear and loss of clamping pressure during the shaking procedure were also observed on some of the trunk shakers which, may result in increased bark damage. The results from the static friction tests compared to the dynamic friction tests appear to be more consistent with the results from the field evaluations. In the dynamic friction 'tests, problems with scouring and welding of the 'belting surfaces occurred. However, this was not evident in any of the sets of slip-belts used in the field evaluations. Because the neoprene belting was not involved in the field evaluations, direct comparisons of bark damage with the nitrile or polyurethane belting could not be made. All growers had used neoprene belting previous years, and reported that their use of nitrile or polyurethane .belting in 1985 resulted in a reduction in the amount of bark damage. Based upon the interviews with the growers and my 77 observations of the harvesters used in the study and the orchards, results indicate that the incidence of bark damage was reduced by using the nitrile and polyurthane belting. 4.4 Summary A study of the slip-belt and lubrication system used on trunk shaker clamp pads was initiated in an effort to reduce the amount of bark damage occuring each year on young trees. Static and dynamic friction tests were conducted in the laboratory on several beltings and lubricants. Results show that friction forces for the neoprene-lubricant combinations were higher compared to the nitrile- and polyurethane-lubricant combinations in both the static and dynamic tests. Based upon the friction tests, field evaluations of the nitrile and polyurethane belting were conducted using harvesters operated by cooperating growers. The number of trees shaken with a nitrile or polyurethane slip-belt system ranged from 600 to 18,000 trees with visible damage ranging from 0.2 percent to 3.9 percent. Growers attributed most of the damage to operator carelessness, dirt buildup between the sling and flap and inadequate lubrication. Silicone spray appears to be the best lubricant for nitrile or polyurethane slip-belts because of it's good lubrication, easy application and less heat and dirt buildup during use. Only 3 out of the 22 sets of belting used in the evaluation were in poor condition due to operator 78 carelessness in lubrication and harvesting practices. To keep the flaps. in good condition they must be cleaned, lubricated properly, and used on trees less than 125 mm. The results obtained from the field evaluations did not provide precise data. However, consisent trends allowed reasonable assumptions to be made. The static friction tests appear to be more consistent with the results from the field evaluations compared to the dynamic friction tests. Both the grower's and my observations indicate that bark damage was reduced by using nitrile or polyurethane belting. This improved slip-belt and lubrication system has significant economic implications, which are discussed in Chapter 5. CHAPTER 5 ECONOMIC IMPLICATIONS OF AN IMPROVED CLAMP SYSTEM 5.1 Introduction The potential yield of commercial cherry orchards can be affected each year by weather, insects, disease, mechanical damage, birds, etc., resulting in substantial economic losses to the grower. If the bark on the tree is damaged, it becomes susceptible to disease and insect attack. A reduction in yield, or in some cases tree death, may occur. Estimating the amount of reduction in yield and annual economic loss due to tree death and bark damage that may occur each year from mechanical harvesting is‘a complex problem. Results from the field evaluations indicate that bark damage was reduced by using the nitrile or polyurethane belting, Chapter 4. The focus of this Chapter is to estimate the annual economic losses resulting from bark damage and tree death when using an improved clamp system compared to a standard clamp system. Based on the annual losses, a cost/benefit comparison between the improved clamp system versus the standard system will be estimated. The two systems will be compared on a basis of S/ha loss per year, based upon the average size of a bearing tart cherry orchard in Michigan. To estimate the economic losses for 79 80 each system the following information was needed: 1. Initial cost of the improved clamp system. 2. Replacement cost of pads for the improved system. 3. Number of harvest seasons before the pads for the improved clamp system are replaced. 4. Replacement cost of the nitrile belting. 5. Number of harvest seasons before the nitrile belting is replaced. 6. Replacement cost of the standard neoprene belting. 7. Number of harvest seasons before the neoprene belting is replaced. . 8. Average size of a bearing tart cherry orchard in Michigan. 9. Average number of trees per hectare. 10. Potential yield of tart cherry trees versus age. 11. Expected life of a tart cherry orchard. 12. Age of orchard at which mechanical harvesting starts. 13. Percent of trees with bark damage and killed each year due to mechanical harvesting. 14. Percent reduction in yield due to bark damage 15. Average price the grower receives for his cherries. In some cases information for the items listed above was not available, so estimations were based upon information obtained from County Cooperative Extension offices, shaker manufacturers, and Michigan Department of Agriculture surveys. The percent bark damage, tree death, and reduction in yield that occurs each year due to mechanical harvesting 81 have not been reported. However, estimations based on a harvesting experiment, conducted by researchers at Michigan State University, on a tart cherry orchard from 1982 through 1986 will be used. 5.2 Assumptions and Analysis The cost/benefit analysis will examine a specific situation, calculating only the economic losses due to yield reduction resulting from bark damage and tree death and the cost of switching from a standard to an improved clamp system. The analysis will not include initial investments in the harvester or trees, replacement of dead trees, cultural care of the orchard, labor costs, processing and harvesting costs of the cherries, and loss of yield due to bruising and scald of the fruit. Losses due to yield reduction will be based on the present value of cherries. Inflation will not be calculated in the analysis. The standard clamp system selected for this analysis consists of a Friday Tri-clamp installed with standard Friday pads and conventional neoprene slip-belts. The improved system consists of a C-clamp kit that bolts to the Friday Tri-clamp shaker and is equipped with improved pads and nitrile slip-belts. These clamp systems represent the most damaging and least damaging pad systems presently available for the Tri-clamp shaker. In comparing the cost of the standard Tri-clamp versus an improved clamp, the assumption that the grower 82 already owns a Tri-clamp shaker results in an estimated initial cost of $650 for the new clamp, pads and nitrile slip-belts for the first year of change (Friday 1986). Replacement cost for the pads on the improved clamp is estimated to be $200.00 with a replacement life of 4 years. The nitrile belting used on the improved system has a replacement cost of $90.00 plus labor (Industrial Belting Supply, 1986) and will be replaced every 2 years. The replacement cost of the neoprene belting on the standard system will be $106.00 (Industrial Belting Supply, 1986) plus labor and will be replaced every 5 harvest seasons. The pads on the Tri-clamp will be considered to last the life of the orchard they harvest. The average size' of a tart cherry orchard of bearing age was 8.0 ha in 1982, and the the average number of bearing trees/ha was 237 (Michigan Department of Agriculture, 1983). The yield of a tart cherry tree depends on many factors such as weather, nutrients, age, vigor, etc. The average potential yield is presented in Table 5.1. These yields represent the average of both low and high productive years. Yields of 60 kg/tree are not uncommon on mature trees. The average life of a mechanically harvested tart orchard with reduced bark damage is estimated to be 25 years, whereas orchards with standard levels of bark damage have a life of 20 years. Most growers start mechanically harvesting when the trees are 6 years old (Bradford and 83 Table 5.1. Average potential yield of a tart cherry tree versus age (Bradford and Kesner, 1986). A e of Tree Yield A e of Tree Yield ?Years) (Kg/tree) (Years) (Kg/tree) 4 4.5 18 38.5 5 6.8 19 36.3 6 9.0 20 36.3 7 18.1 21 34.0 8 22.7 22 31.8 9 29.5 23 27.2 10 34.0 24 22.7 11 36.3 25 22.7 12 38.5 26 22.7 13 38.5 27‘ 22.7 14 38.5 28 22.7 15 38.5 29 22.7 16 38.5 30+ 18.1 17 38.5 Kesner, 1986). The estimated percent bark damage and tree death that occurs each year from using the improved and standard clamp systems are presented in Table 5.2. The percent of trees damaged were trees classified as having damage to the cambium or greater. A minimum of 1 percent of the trees were assumed to incur bark damage annually for each clamp system. However, in the 1985 field evaluations (Chapter 4) and the harvesting experiment conducted by researchers, damage to the cambium or greater using the improved system ranged from 0.2 to 1.0 percent. . Estimating the percent yield reduction due to bark damage, and when the reduction occurs during the life of a tree, presents a 84 Table 5.2. Estimated damage and tree death that occurs each harvest year based upon tree age and clamp system.l/ Standard Clamp Improved Clamp Tree Harvest Damage Tree Death Damage Tree Death Age Year (%) (%) (%) (%) 6 l 25 0 l 0 7 2 20 0 1 0 8 3 10 0 1 0 9 4 5 O 1 0 10 5 3 0 l 0 ll 6 l 1 l 0 12 7 1 1 1 0 l3 '8 l 2 l 0 l4 9 l 2 l 0 15 10 l 3 1 0 16 ll 1 3 l l 17 12 1 4 1 1 18 13 1 4 l 1 19 14 l 5 1 1 20 15 l 5 l l ll Estimates are based upon a harvesting experiment conducted by Michigan State University researchers. 85 problem. To simplify this analysis, yield reduction was analyzed at 5, 10, 20 and 40 percent. The time at which the reduction occurs during thelife of the tree was estimated to occur 2 years after being damaged. Therefore, a tree that is damaged will yield only 95, 90, 80, or 60 percent of its potential yield at 2 to n years after being damaged. Damaged trees were assumed to result in a 100 percent yield loss only when they died. The annual economic losses for each clamp system due to yield reduction and tree death, was analyzed for a new orchard and a period of 15 years starting when the trees were 6 years old. Economic losses for each year (i) of this period were calculated as follows:' S/ha (lost) a Yield Loss (kg/ha) x Price of Fruit ($/kg)) + Clamp System Costs ($/ha) Where, Yield Loss = (% Accumulated Damage - % Accumulated (bark damage) Dead) x Trees/ha x Potential Yield/Tree x % Yield Loss Yield Loss = % Accumulated Dead x Trees/ha x (dead trees) Potential Yield/Tree x 100%.Yield Loss Clamp System (Annualized Pad Cost + Annualized Cost Belting Cost)/ ha Harvested Price of Fruit = Avera e price of processed tart cherrles from 1979-1984 was $.75/kg The average economic gain ($/ha) each year for using the improved clamp system was calculated by subtracting the differences in the annual losses for each clamp system. 86 5.3 Results and Discussion Table 5.3 lists the total accumulated bark damage and tree death for each year of harvesting with each clamp system. The estimated total accumulated bark damage and dead trees at the end of a lS-year harvesting period was 15 and 5 percent for the improved clamp and 73 and 30 percent for the standard clamp. The estimates for the improved clamp may be high, however, the differences between the two clamp systems is large enough to show the benefits of reduced damage. Figures 5.1 and 5.2 represent the annual yield harvested with each clamp system. The potential yield represents the annual yield assuming a 0 percent bark damage and tree death during the life of the orchard. Potential yield for the 15 years of harvesting ranged from 2133 to 9125 kg/ha. Annual yield losses when harvesting with the improved clamp were calculated to be from 0 kg/ha to 692 kg/ha, Figure 5.3. The standard clamp would have annual yield losses of 0 kg/ha to 3568 kg/ha, Figure 5.3. The annual clamp system costs for each harvest year are presented in Table 5.4. The annual costs represent the initial cost for both clamp systems the first harvest year, followed by periodic pad and slip-belt replacement costs. The estimated replacement time for the slip-belts on the improved system may have been too frequent based upon the number of trees that would be harvested. However, these 87 Table 5.3. Estimated total accumulated bark damage and tree death for each harvest year. Standard Clamp Improved Clamp Tree Harvest Damage Tree Death Damage Tree Death Age Year (%) (%) (%) (%) 6 l 25 O 1 0 7 2 45 0 2 0 8 3 55 0 3 0 9 '4 60 o 4 o 10 5 63 0 5 0 ll 6 64 l 6 0 12 7 65 2 7 0 l3 8 66 4 8 0 l4 9 67 6 9 0 15 10 68 9 10 0 16 11 69 12 ll 1 17 12 70 16 12 2 18 13 71 20 13 3 l9 14 72 25 14 4 20 15 73 30 15 5 88 on do poop co go. 203 N09 uco nook on 256 ca 82 203 N365 .ON .9 .n no 832? 9:20 93:3» 53 33020... 203 .0352. 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