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MATERIAL

 

LIBRARY
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University

 

 

 

 

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A STUDY OF THE KILN DRYING OF LUMBER
FROM COTTONWOOD
(POPULUS DELTOIDES MARSHALL)

by
FRED EUGENE DICKINSON

A THESIS

Submitted to the Graduate School of Michigan
State College of Agriculture and Applied
Science in partial fulfilment of the
requirements for the degree of

MASTER OF SCIENCE

Department of Forestry

191d

 

 

 

THESIS

 

ACKNOWLEDGMENT

The writer wishes to acknowledge the

valuable assistance and cooperation of mr. W} J. Baker,

,associate professor of Forestry, in the performance of

this Work. Appreciation is also extended to Dr. A. J.

Panshin, assistant professor of Forestry, for his help-

ful suggestions.

 

 

an 2: it: it - 1‘3" gt: Er TI -' ?
TABLE OF CONTENTS
Page no.
INTRODUCTION . . . . . . . . . . 1
EQUIPMENT . . . . . . . . . . . 5
CHECKING THE INSTRUMENT . . . . . . . h
DETERMINATION OF THE RATE OF CIRCULATION . . . h
' MATERIAL . . . . . . . . . . . 5
LOADING THE KILN . . . . . . . . . 5
OPERATION OF THE KILN . . . . . . . . 6
* RECORDING THE DATA . . . . . . . . . 7
MOISTURE CONTENT DETERMINATION . . . . . . 8
} KILN RUNS . . . . . . . . . . . 10
THE DRYING OF WOOD . . . . . . . . . 35
’ PLOTTING 0F DRYING CURVES . . . . . . . 3;
EFFECT OF CIRCULATION ON THE DRYING CURVES . . . 39
' EFFECT OF CIRCULATION ON DRYING TIME . . . . ho
A SEASONING DEFECTS . . . . . . . . . Al
F LIMITATIONS OF RESULTS . . . . . . . . Ah
} SUMMARY . . . . . . . . . . . Ah
_ LITERATURE CITED . . . . . . . . . L7
it
i.

 

 

CHARTS AND TABLES

 

CHART I

Drying Curves for Run 1 . . . . . In Folder
CHART II

Drying Curves for Run 2 . . . . . In Folder
CHART III

Drying Curves for Run 3 . . . . . In Folder
CHART IV

Drying Curves for Run h . . . . . In Folder

i

CHART V

Drying Curves for Run 5 . . . . . In Folder

CHART VI
Drying Curves for Run 6 . . . . . In Folder

, CHART VII
Drying Curves for Run 7 . . . . . In Folder

TABLE I
slopes of the Linear Portions of the Drying
Curves for each Schedule Change of Runs
i to 7, inclusive . . . . . . . . 36

TABLE II
Effect of Increased Rate of Circulation on
the Slopes of the Linear Portions of the Dry-
ing Curves for Runs 2 to 7, inclusive . . . 39

TABLE III
Effect of Increased Rate of Circulation on
Rate of Drying from a Moisture Content of
95% 1:0 148% o e e o e o e o o ’40

 

TABLE IV
Occurrence of Collapse in CottonWOcd as
Related to Temperature, Equilibrium Mois-
ture Content, and Rate of Circulation . . . h2

 

 

 

 

 

 

INTRODUCTION

At the present time the kiln drying of lumber has reached a
point of high efficiency due to the rapid advancement in dry kiln equip-
ment and drying methods during the last several decades. Even so, the
kiln operator often finds that the available information and equipment
are inadequate to solve his many problems.

Little is known about the drying of some of the lower quality
woods such as cottonwood. more information is needed about suitable
schedules and some of the more harmful defects that are liable to
appear during the seasoning process. The true drying conditions in the
kiln are another problem that arises. Does the operator have the con-
diticns in the kiln that he desires, and if not, what can he do to ar-
rive at these conditions?

While little information is available concerning the kiln dry-
ing of cottonwood, several drying schedules have been developed, the
latest of which is contributed by the Forest Products Laboratory (13).

Tiemann OI» has given considerable attention to seasoning de-
facts in both hardw00ds and conifers. He has been particularly in-
terested in collapse, a defect very likely to occur when drying green
cottonwood.

Circulation in the kiln has received attention, both in re-
spect to rate of circulation and uniformity of circulation. Hermann
and Rasmussen (h) in their work with Western pine in 1938 discovered
that the rate of drying was increased by increasing the rate of circu-

lation. Greenhill (2) Working with Australian timbers had previously

arrived at the same general conclusions in 1936.

 

 

 

2
The mathematical part of the Work herein described is based

on drying experiments with sitka spruce carried on by Tuttle (12) in
1925 and with poplar slabs by Sherwood (8) several years later. In
both instances the Fourier heat conduction equations were used in the
analysis of the drying. Additional work using the same principle was
carried on by Nelson (7) in l93h using Douglas fir lumber.

The objects of the problem were: (a) to find a suitable sched-
ule for drying green cottonWood, (b) to study any defects liable to oc-
cur while drying green cottonwood, and (c) to obtain the best possible
drying conditions in the dry kiln with the available equipment.

The experiment was performed at the Department of Forestry,
Michigan State College, East Lansing, Michigan during the years 19h0
and l9hl.

 

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EQUIPMENT

 

The experimental dry kiln used is of the recirculating come
partment type, located in the basement of the forestry building.

The compartment, constructed with double walls and ceiling to
prevent escape of heat and moisture, is 10 feet wide, 17 feet long,
and 8 feet high. Back of this is located a housing which incloses the
blower, heating coils, and spray jets.

The kiln is equipped with a Toledo scale capable of weighing
loads up to 10,500 pounds. Four corner posts resting on cement piers
support the scale platform on which the lumber is piled in loading the
kiln. By means of a series of lovers, the platform is connected with
the scale dial located outside the compartment. weights can be estim-
ated to a quarter of a pound, as the dial is graduated in two-pound
divisions.

Provision is made for circulation of air in the kiln by the
external blower system which consists of one large non-reversible fan
powered by a 1 H.P. electric motor. Entering the compartment through a
central duct running lengthwise along the floor of the kiln, the air
passes through the load, and is returned to the blower by two exhaust
ducts, one located on each side of the kiln.

Temperature and humidity in the kiln are automatically con-
trolled and recorded by a Foxboro controller-recorder. Two bulbs, one
dry and one kept wet by an enveloping wick, are connected by vapor
filled tubes to the instrument located on the outside of the kiln. The
two bulbs are placed in the center of the kiln directly above the enter-

ing air duct so that the condition of the air is measured immediately

 

_

5

before entering the load of lumber.

 

Any desired wet and dry bulb temperatures up to 200 degrees
Fahr. are obtained in the kiln by setting the instrument for those
temperatures. Using compressed air, valves on the steam and spray
lines are operated by the instrument to maintain the desired temper—
ature and relative humidity conditions. Steam furnished by the College
power plant is used in operating the kiln.

Additional equipment consisted of a small band saw, triple beam
balance, and an electric oven which were used in moisture content deter-

minati on.

CHECKING THE INSTRUMENT
To make sure the instrument was in perfect adjustment, it was

calibrated on a rising temperature before the first and fourth runs.

DETERMINATION OF THE RATE OF CIRCULATION

During Runs 1, 2, and 3 the velocity of the air in the kiln
was measured by an manometer on the leaving side of the load. As the
movement of air was Just sufficient to move the anemometer, a velocity
of 15 feet per minute was assumed.

During Run LI after a new method of piling the lumber was adopted,
the rate of circulation was measured on the leaving side of the load
using a velometer. Readings were taken in the air space between every
board at both ends and in the middle of the load. The average velocity
after adjusting for temperature, humidity, and atmospheric pressure
was found to be 1148 feet per minute at a temperature of 117.5 degrees

Fahr. and 21; percent relative humidity.

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MATERIAL

 

The lumber, cottonwood (Populus deltoides Mrshall), used
was sawed at the Forestry Department's sawmill from logs out on
College property during 191m. It was flat grained stock of random
widths, 12 feet long, 1 1/8 inches thick and contained both heart-
wood and sapwood. After sawing, the lumber was piled without stickers

to prevent as little drying as poasible before placing it in the kiln.

LOADING THE KILN

Three methods of piling were used in the experiment to deter-
mine the effect cn air flow through the load and the slope of the
drying curves. For each piling method, 1 by lisinch basswood stickers
placed at 3-foot intervals were used.

The lumber in Runs 1 and 2 was flat piled, leaving a central
chimney 20 inches wide for the incoming air. Each load was 20 courses
high and 12 inches wide on each side of the central chimney.

For Run 3, a modification of the first method was used. The
lumber was flat piled with a chimney tapering from a width of 20 inches
at the base to 114 inches at the top. The load was 16 courses high and
12 inches wide on each side of the central chimney. In all three loads,
the chimney was roofed over so that the air had to pass through the load.

To combat recirculation of air through the bottom of the load
during Run 3, a wooden grille was constructed and placed in the central
chimney at the same level as the bottom boards of the pile. By breaking
up the air stream, recirculation was stopped and even distribution of
air throughout the load was produced.

To obtain faster circulation of air through the load during

5.

 

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Rx r

6

the remaining four runs, baffles, 20 inches apart, were constructed
on each side of the incoming air duct to a height of 11; inches above
the wet and dry bulbs. Standards upon which the lumber was piled
were built up from the scale platform to a height of 2 inches above
the wet and dry bulbs. Each of the remaining four loads was edge-
piled on the standards and was 10 boards wide. The height of the
loads varied from 10 to 12 inches as determined by the width of the
boards. Bindings which could be tightened with turnbuckles were
placed at 3-foot intervals to hold the loads together. These bindings
kept the stickers from falling out and prevented the lumber from cup-
ping and warping badly.

Before loading the kiln, the stickers, and for Runs )4 to 7,
inclusive, the standards and bindings, were weighed and their weight
set off on the tare beam of the scale. Hence, the reading on the scale

dial was tl’nt of the weight of the lumber and its moisture.

OPERATION OF THE KILN

Before each run was started, a new wick was placed on the wet
bulb and a new chart on the instrument. The fan and motors were in-
spected, greased and oiled.

The drying operation was begun by starting the blower and open-
ing the valves on the steam and spray lines. The instrument was set
for the desired wet and dry bulb temperatures which were recorded con-
tinuously on the chart by two pens. [eight of the lumber was read at
the time of starting and then at fifteen minute intervals until conden-

sation within the kiln caused by the steam striking the cold lumber had

stopped and the load had nearly regained its original weight through
drying.

 

   
      

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During the rest of the run, readings of the weight of the lump
her were taken at 2- to 8-hour intervals excepting at schedule changes
when readings were taken at fifteen minute intervals for several hours.

During Runs 6 and 7, the wet and dry bulb temperatures on the
leaving air side of the load were checked twice daily by a hygrometer
to determine the drop in temperature across the load. These readings
were taken directly above the location of the wet and dry bulbs of the
instrument.

The schedules used for the runs were based on the equilibrium
moisture content principle. Badger and McCabe (l) explain this as
follows:

"In general, a given material, if brought into contact With
air of definite temperature and humidity, will reach a definite
moisture content that will be unchanged by further exposure to this
same air. This is known as the equilibrium moisture content of the
material under the specified conditions. If the material contains more
moisture than the equilibirum value, it will dry until its moisture
content reached the equilibrium value. 0n the other hand, if the mater-
ial is drier than the equilibrium.value and is brought into contact with
air of the stated temperature and humidity, it will absorb water until
it reaches this same equilibirum point."

Four different schedules were used and their effects on the
rate of drying and seasoning defects observed. A constant dry bulb was

used with all runs except the first.

RECORDING THE BAIL

Complete information for each run was recorded on a prepared

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form. This included such items as load Weights, corresponding
moisture contents, kiln schedule followed, drying time, kind of mater-

ial,and condition of the lumber before and after drying.

MOISTURE CONTENT DETERMINATION

The moisture content of the lumber can most accurately be
determined by taking small samples of the wood which are weighed,
dried, and then weighed again and the two weights used in determining
the moisture content in percent based on the oven-dry weight of the
wood.

The method used was to cross-cut a board about 2 feet from one
end to get away from the effect of and drying. Then a section firinch
wide was cut from the board using the band saw. Loose splinters were
removed from the section and the section weighed immediately on the
balance. It was then placed in the electric oven at a temperature of
212 degrees Fahr. until the sample reached a constant weight when it
was removed from the oven, weighed, and the weight recorded as the
oven-dry weight of the wood. The moisture content of the sample was
calculated by the following formula:

Moisture Content in Percent = (gigginAI :zight __1)100

When loading the kiln, the moisture contents of samples from
four or five boards were determined. The average moisture content of
these samples was taken as the average moisture content of the load
and was used in determining when the schedule should be changed during
the run.

On completion of the run, one sample was cut from each board

in Runs h to 7, inclusive, and from every other board in the first

 

 

 

three runs. Alternate samples were taken from alternate ends

of the load. The average moisture content of these samples was
calculated and used as the true moisture content of the load at

the time the samples were out. Using this moisture content, the aver-

age original moisture content of the load and the intermediate mois-

ture contents during the run were calculated.

 

 

 

 

 

 

 

 

 

 

 

10
Run 1
Equilibrium Moisture
Moisture Content
Dry Bulb wet Bulb Content of
Temperature Temperature in Percent Stock
Degrees Fahr. Degrees Fahr. e Percent
135 127 l3.h 105.3
lbO 130 12.1 h3.8
1h5 126 8.3 35-h
155 129 6.h 25.2
165 127 h.6 18.0
Ayerage Original moisture Content (o) . . . . 105.3%
Awerage Final moisture Content . . . . . . 9.1%
CO llapse e e s e a e e e e e 25% Of mad
Cupping e e s e e e e e e e e e Slight
} warping . . . . . . . . . . . . None
Current '
Age Weight Moisture ' (c-e)100 = E
of of Content ' Io-e,
Run Load in Percent '
Hours Pounds c c-e o-e E
0.00 2&53 105.3 91.9 91.9 100.0
.25 2&88 108.2 9h.8 105.2
.50 2517 110.5 97.1 105.7
.75 2526 111.5 98.1 106.7
1.00 2522 111.0 97.6 106.2
1.25 2518 110.8 97.h 106.0
1.50 2515 110.5 96.9 105.h
2.75 2h98 109.0 95.6 10h.o
3.00 2b96 108.9 95.5 103.9
5.50 21.75 107.0 95.6 101.8
6.00 2h7o 106.6 95.2 101.h
6.50 2h65 106.2 92.8 101.0
17.00 237k 98.? 85.3 92.8
19.25 2356 97.0 83.6 91.0
25.00 2528 95.0 81.6 88.8
26.00 2508 95.h 80.0 87.1

29.25 2283 91.2 77.8 8h.7

 

 

 

 

 

 

 

 

11
Run 1 $0ont'd)
Current '
Age Weight Moisture ' (c-e)100 _ E
of of Content ' o-e
Run Load in Percent '

Hours Pounds c c-e o-e E
50.50 2276 90.5 77.1 85.9
hl.OO 2200 8h.h 71.0 77.5
hh.oo 2182 82.5 69.1 75.2
h9-75 21th 79-h 66.0 71.8
5h.oo 2118 77.1 65.7 69.5
65.00 2052 72.8 59.h 6h.6
69.00 2051 70.5 56.9 61.9
72.50 2012 69.h 56.0 60.9
7h-50 2002 67.7 5h-3 59-1
76.75 1992 66.9 55.5 58.2
90.50 1925 61.1 h7.7 51.9
9h.oo 1908 59.5 A6.1 50.2

‘ 97-75 1891 58.5 h5.1 h9-1

101.25 1876 57.0 h5.6 h7.h

115.75 1821 52.5 59.1 h2.5

116.50 1811 51.8 58.h h1.8

122.25 1792 50.0 56.6 59.8

126.50 1771. L185 55.1 58.2

157.75 175h L5.1 51.7 3h.5

lh0.oo 1728 hh.5 51.1 55.8

1h3-00 1718 h5-8 30-h 91 9 33.1

.1h5.oo 1718 h5.8 51.7 95 2 5h.0
5.25 1716 b5.6 51.5 55.8

1h5o50 171h hb-h 31.3 35-6

1h5.75 1712 h5.2 51.1 33.h

1hh.00 1711 h5.l 51.0 55.5

1th.25 1709 h2.9 30 8 33-0

1hh.50 1708 h2.8 50.7 52.9

1hh.75 1706 h2.7 50.6 52.8

115.00 1706 has 50.1. 52.6

1h6.00 1698 h2.1 50.0 52.2

150.25 1672 no.0 27.9 29.0

161.00 161R 55.1 25.0 2h.7

16h.oo 1598 55.7 21.6 25.2

165.00 1595 55.h 21.5 95.2 22.9

*165.00 1595 53-h 25.1 97.0 25-9

165-25 1592 33-2 2h.9 25.7

165-50 1589 53.0 2h.7 25.5

165-75 1587 32-7 2h-h 25.2

166.00 158 52.5 2h.2 2h.9

166.25 1582 52.5 2h.o 2h.7

166.50 1579 52.1 25.8 2h.5

167.00 1575 51.8 25.5 2h.2

167.25 1572 51.5 25.2 25.9

 

 

 

 

 

 

 

 

12
Run 1 (Cont'd)
Current '
Age weight Moisture ' (c-e)lOO _ E
of of Content ' o-e
Run Load in Percent *
Hours Pounds c c-e o-e E
170.00 1555 50.0 21.7 22.5
17h.25 152h 27.5 19.2 19.8
181.75 1h82 2h.o 15.7 16.2
185.50 1h72 25.2 1h.9 97.0 15.h
*183.50 1&72 25.2 16.8 98.9 17.0
185.75 1h7o 25.1 16.7 16.9
18h.00 1h69 22.9 16.5 16.7
18h.25 22.7 16.5 16.5
18h.50 22.5 16.1 16.5
18h.75 1h62 22.5 15.9 16.1
185.00 1h61 22.2 15.8 16.0
185.25 22.2 15.8 16.0
185.75 1&57 22.0 15.6 15.8
187-75 1bh5 20.9 lho5 1A.?
190-25 1h32 19.9 13-5 13-7
192.00 1h22 19.0 12.6 12.7
19h.25 lhlo 18.0 11.6 98.9 11.7
*19h.25 1h10 18.0 15.h 100.7 15.5
19h.50 1h08 17.8 15.2 15.1
19h.75 1h06 17.5 12.9 12.8
195.00 lush 17.5 12.7 12.6
195.25 1&05 17.2 12.6 12.5
198.00 1586 15.9 11.5 11.2
210.25 1555 11.6 7.0 7.0
211.75 1550 11.2 6.6 6.6
215.00 1521 10.6 6.0 6.0
218.00 1512 9.8 5.2 5.2
221.75 15oh 9.1 h.5 100.7 h.5
*Schedule change.

 

 

 

15

 

 

 

Run 2
Equilibrium 'Mcisture
Moisture Content
Dry Bulb wet Bulb Content of

Temperature Temperature in Percent Stock
Degrees Fahr. Degrees Fahr. e Percent

135 127 lick 97.1

135 125 12.1 h5.2

135 116 8.3 35.5

135 109 6.6 18.9

 

Average Original Moisture Content (o) . . . . . . 97.1%
Average Final Moisture Content . . . . . . . . 11.0%
Collapse . . . . . . . . . . . . . . . None
Cupping . . . . . . . . . . . . . . . Slight

Warping e n a e e e e e e e e e e e e e None

 

 

 

Current '
Age Height moisture ' (c-e)100 8 E
of of Content ' o-e .
Run Load in Percent '
Hours Pounds c c-e o-e E
0.00 2538 97.1 83.7 83.7 100.0
.25 2558 98.7 85.3 101.9
.50 2580 100.h 87.0 103.9
.75 2590 101.2 87.8 10h.9
1.00 2592 101.3 87.9 105.0
1.25 2590 101.2 87.8 10h.9
2.25 2579 100.3 86.9 103.8
5.75 2560 98.9 85.5 102.2
5.75 2537 97.1 83.7 100.0
7-25 2520 95.7 82-3 98-5
11.00 21182 92.8 79.1. 911.9
22.25 2580 811.9 71.5 85.1.
25-25 2355 82-9 69-5 83.0
26.25 23h6 82.2 68.8 82.2
29.25 2321 80.3 66.9 79.9
31.25 2306 79.1 65.7 78.5
36.00 2269 76.2 62.8 75.0
1.6.50 2191 70.2 56.8 67.9
h9-25 217h 68.9 55-5 66.5

 

 

 

 

 

 

 

 

18
Run 2 (Cont'd)
urren '
Age weight Moisture ' (c-e)100 - E
of of Content ' o-e
Run Load in Percent '
Hours Pounds c c-e o-e E
r 58.00 2158 66.1 52.7 65.0
55.00 2152 65.6 52.2 62.8
59.75 2105 63-8 50.0 59.7
70-50 2039 58.8 85.0 53-8
78.50 2016 56.6 85.2 51.6
77.75 1996 55.0 81.6 89.7
85.75 1968 52.9 59.5 87.2
96.00 1910 88.8 55.0 81.8
100.75 1888 86.7 55.5 39.8
105.25 1869 85.2 51.8 85.7 58.0
*105.25 1869 85.2 55.1 85.0 58.9
105.50 1867 85.0 52.9 58.7
105.75 1865 88.9 52.8 58.6
106.00 1865 88.7 52.6 58.8
106.25 1861 88.6 _ 52.5 58.2
109.75 1888 85.2 52.1 57.8
118.50 1800 39.8 27.7 52.6
122.00 1782 58.8 26.5 50.9
125.50 1775 57.9 25.8 50.8
125-50 1769 57.8 25.3 29.8
127.50 1765 56.9 28.8 29.2
152.00 1785 55.5 25.8 85.0 27.5
*152.oo 1785 55.5 27.2 88.8 50.6
152.25 1782 55.5 27.0 50.8
152.50 1780 55.2 26.9 50.5
152.75 1758 55.0 26.7 50.1
155.00 1755 58.8 26.5 29.8
188.00 1668 29.5 21.0 25.6
186.25 1652 28.5 20.0 22.5
189.00 1656 27.1 18.8 21.2
152.25 1622 26.0 17.7 19.9
155.25 1610 25.1 16.8 18.9
156.00 1608 28.6 16.5 18.8
168.25 1589 20.5 12.0 15.5
175.25 1551 18.9 10.6 88.8 11.9
*175.25 1551 18.9 12.5 90.5 15.6
175.50 1528 18.7 12 1 15 8
175.75 1527 18.6 12 o 15.5
178.00 1528 18.8 11.8 12.0
178.25 1525 18.5 11.7 12.9
178.50 1520 18.1 11.5 12.7
177.00 1510 17.5 10.7 11.8
181.25 1895 16.0 9.8 10.8
192.75 1859 13-3 6-7 7-8
198-75 1553 12-9 6.3 7.0
199-50 1880 11.9 5.3 5-9
205.00 11.0 8.8 90.5 8.9
*Sohedule Change

 

 

 

Run 3

 

 

 

 

 

 

 

 

Equilibrium moisture
Moisture Content
Dry Bulb wet Bulb Content of
Temperature Temperature in Percent Stock
Degrees Fahr. Degrees FEEr. e Percent
135 127 13.8 115.8
135 125 12.1 33.3
135 120 9.7 23.3
135 115 8.0 15.5
135 110 6.7 10.7
155 105 5-7 8.9
Awerage Original Moisture Content (0) . . . . 115.8%
Ayerege Final Moisture Content . . . . . . 6.6%
COIIaPBe o o e o o e o o 0 None
Cupping o e o o o e o e o Slight
lhrping . . . . . . . . . None
Current '
Age weight Moisture ' (c-e)100 _ E
or of Content ' o-e
Run Load in Percent '

Hours Pounds o o-e o-e E
0.00 2117 115.8 102.8 102.8 100.0
0.25 2151 119.3 105.9 103.8
0.50 2169 121.1 107.7 105.2
0.75 2168 121.0 107.6 105.1
1.00 2168 120.6 107.2 108.7
1.25 2158 120.0 106.6 108.1
1.50 2153 \ 119.5 106.1 103.6
1.75 2150 119.2 105.8 103.3
2.00 2186 118.8 105.8 102.9
2.50 2137 117.8 108.8 102.0
8.00 2118 115.5 102.1 99.7
5.00 2100 118.1 100.7 98.5
5-75 2090 115.0 99.6 97.3
7.00 2073 111.3 97.9 95.6
8.75 2055 109.5 96.1 93.8

18.75 1985 102.3 88.9 86.8

 

 

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16

Run 3 (Cont'd)

‘Current '

Age Weight Moisture '

of of Content '

Run Load in Percent '

Hours Pounds o E

25.75 1905 98.2 80.8 78.9
26.00 1888 92.9 78.6 76.8
26.50 1880 91.6 78.2 76.8
29.00 1859 89.5 76.1 78.5
51.50 1857 87.2 75.8 72.1
36.75 1798 82.9 69.5 67-9
89.25 1705 75.6 60.2 58.8
58-00 1672 70.8 57.0 55-7
56-25 1657 68.9 55.5 58.2
70.75 1572 60.2 86.8 85.7
78.00 1558 58.8 85.0 85.9
76.00 1588 57.8 88.0 85.0
79.00 1528 55.8 82.8 81.8
83-75 1508 55.3 39-9 39-0
96.00 1850 87.8 38-8 33.6
98.50 1880 86.8 33.2 32.8
100.00 1858 86.2 52.8 52.0
105.25 1820 88.8 51.8 50.7
107.75 1807 85.8 - 29-3
119.50 1571 59.8 25.8
122.00 1568 59.0 25.0
128.00 1558 58.8 28.8
127.00 1550 57.6 25.6
152.00 1557 56.5 22.8
182.50 1518 33.9 20.0
185.00 1508 55.5 19.8
t185.00 1508 55.5 20.8
185.25 1506 55.1 20.5
185.50 1506 55.1 21.0 20.5
185.75 1505 55.0 20.9 20.2
186.00 1508 52.9 20.8 20.1
186.25 1508 52.9 20.8 20.1
186.50 1502 52.7 20.6 19.9
188.00 1298 52.5 20.2 19.5
151.00 1288 51.5 19.2 18.5
155.75 1276 50.1 18.0 17.8
168.00 1250 27.8 15.5 18.8
171.00 1288 26.8 18.7 18.2
175.00 1257 26.1 18.0 15.5
180.25 1228 25.2 15.1 12.6
192.00 1211 25.8 11.5 10.9
192.50 1210 25.5 11.2 10.8
t192.50 1210 25.5 15.6 12.8
192.75 1209 25.2 15.5 12.7
195.00 1208 25.1 15.8 12.6
195.25 1207 25.0 15.5 12.5

 

 

 

Run 3 (Cont'd)

17

 

 

Current '

 

 

Age Weight Moisture ' (c-e)100 . E
of of Content ' o-e
Run Load in Percent '

Hours Pounds o .o-e o-e E
195.50 1206 22.9 15.2 12.8
195.75 1205 22.8 15.1 12.5
198.00 1208 22.7 15.0 12.5
198.25 1205 22.6 12.9 12.2
195.00 1201 22.8 12.7 12.0
197.00 1196 21.9 12.2 11.5
198.75 1191 21.8 11.7 11.0
205.75 1180 20.5 10.6 10.0
216.50 1159 18.1 8.8 7.9
225.00 1150 17.2 7.5 7.1
225.25 1188 17.0 7.5 6.9
229.75 1182 16.8 6.7 6.5
259.00 1155 15.5 5.8 106.1 5.5

*259.00 1155 15.5 7.5 107.8 7.0
259.25 1152 15.8 7.8 6.9
259.50 1151 15.5 7.5 6.8
259.75 1150 15.2 7.2 6.7
280.00 1150 15.2 7.2 6.7
280.25 1129 15.1 7.1 6.6
280.50 1129 15.1 7.1 6.6
281.75 1126 18.8 6.8 6.8
282.50 1125 18.7 6.7 6.2
288.50 1122 18.8 6.8 6.0
286.25 1119 18.1 6.1 5.7
287.25 1118 18.0 6.0 5.6
252.00 1112 15.8 5.8 5.0
265.25 1100 12.2 8.2 5.9
266.50 1098 11.9 5.9 5.6
268.25 1097 11.8 5.8 5.5
270.75 1095 11.6 5.6 5.5
278.75 1092 11.8 5.8 5.2
286.75 1086 1 10.7 2.7 107.8 2.5

t286.75 1086 10.7 8.0 109.1 5.7
287.00 1086 10.7 8.0 5.7
287.25 1085 10.6 5.9 5.6
287.50 1088 10.5 5.8 5.5
287.75 1088 10.5 5.8 5.5
288.00 1088 10.5 5.8 5.5
288.25 1085 10.8 5.7 5.8
288.50 1085 10.8 5.7 5.8
289.50 1082 10.5 5.6 5.5
291.75 1080 10.1 5.8 5.1
295.50 1077 9.8 5.1 2.8
502.75 1075 9.8 2.7 2.5
511.50 1069 9.0 2.5 2.1

 

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W

 

Run 3 (Cont'd)
‘ Current '
Age Weight Moisture '

     

 

 

(c-e)100 . E
of of Content ' o-e

Run Load in Percent '

Hours Pounai c c-e o-e E
312.75 1068 8.9 2.2 109.1 2.0
*312.75 1068 8.9 3.2 110.1 2.9
313.00 1068 8.9 3.2 2.9
515.25 1067 8.8 5.1 2.8
313.50 1067 8.8 3.1 2.8
313.75 1066 8.7 3.0 2.7
518.00 1066 8.7 5.0 2.7
515.50 1065 8.6 2.9 2.6
516.75 1068 8.5 2.8 2.5
317.75 1063 8.8 2.7 2.5
320.75 1061 8.2 2.5 2.3
558.00 1056 7.6 1.9 1.7
335.75 1055 7.5 1.8 1.6
338-25 1058 7-h 1-7 1-5
380-75 1053 7.5 1.6 1-5
385.50 1052 7.2 1.5 1.8
357.75 1089 6.9 1.2 1.1
360.25 1088 6.8 1.1 1.0
365.75 1087 6.7 1.0 .9
370.50 1086 6.6 0.9 110.1 .8

 

s Schedfile Change

 

19

 

 

 

 

 

 

 

 

 

Run 8
Equilibrium Moi sture
‘ Moi sture Content
Dry Bulb Wet Bulb Content of
Tegpg'ature Temperature in Per cent stock
Degrees Fahr. Degrees Tab: . 9 Percent
135 127 15.8 155.1
135 125 12.1 86.8
135 120 9.7 58.0
135 115 8 .0 23 .O
135 105 5.7 17.0
Average Original Moi sture Content (0) . . . . 133 . 1%
Average Final Moi sture Content . . . . . . 11 . 2%
Collapse . . . . . . . . . . 10% of Load
Cupping - a e e e e e o e a e Slight
lax-ping . . . . . «. . . . . . . None
. Current '
Age Weight Moi sture ' c-e 100 _
of of Content ' LTF-Ler E
Run Load in Percent '

Hours Pounds o c-e o-e B
0.00 586.00 133.1 119.7 119.7 100.0
0.25 560.00 139 .0 125.6 108.9
0 .50 562.00 139 .9 126.5 105 .7
0.75 559.50 138.8 125.8 108.8
1.00 557.00 137.8 128.3 103.8
1.25 558.50 136.7 123.3 103.0
1.50 552.50 135.8 122.8 102.3
1.75 550 .00 138.8 121.8 101.8
2.00 589.00 138.8 121.0 101.1
2.25 587.00 133.5 120.1 100.3

13.00 500.00 113.8 100 .0 83.5
16.00 890.50 109.8 96.0 80.2
18.50 883.00 106.2 92.8 77.5
19.00 882.00 105.8 92.8 77.2
20.50 878.00 108.0 90.6 75.7
21.50 878.00 102.3 88 .9 78.3
26.00 862.00 97.2 83.8 70.0

Weight

um

Run_8.(Cont'd)

'
I
I

(o-e)100 . E
ca

 

 

Pounds

 

860.00
855-00
826.00
818.00
807.50
587.00
582.00

365.00
550.00
585-00
383.00
382.50
382.00
381-50
381~25
581.00
80

358.50
333.00
518.00
515.50
518.00
318-00
515.00
512.50
512.00
511.50
511.00
510.50
510.25
508.00
508.25
501.00
292.00
288.25
288.25
288.00
287.50
287.00
287.00
286.50
286.00
288.50
282.00

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119.7
121.0

121.0
123.8

123.8
125.1

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19.2

10.7
9-9

 

 

 

Run 8 (Cont'd)

 

21

 

 

 

rent '
,Age weight Mbisture ' (o-e)100 .
of of Content ' lo-e’ E

Run load in Percent '

fiburs PGEBds c c-e o-e E
188.75 280.50 19.7 11.7 9.8
156.75 275.00 17.8, 9.8 7.5
159.50 278.00 17.0 9.0 125.1 7.2
9159.50 278.00 17.0 11.3 127.8 8.9
159.75 273.50 16.7 11.0 8.6
160.00 273.25 1 .6 10.9 8.6
160.25 273.00 16.5 10.8 8.5
160.50 272.50 16.3 10.6 8.3
160.75 272.25 16.2 10.5 8.2
161.00 272.00 16.1 10.8 8.2
163.00 270.50 15.5 9.8 7.7
165.00 269.50 15.0 9.3 7.3
169.50 267.00 1810 8.3 6.5
172.75 265.50 13.3 7.6 6.0
181.00 262.00 11.8 6.1 8.8
183.00 260.50 11.2 5.5 127.8 8.3

 

* Schedule Change

 

 

 

 

 

 

 

 

 

 

Equilibrium Moi sture
Moi sture Content
Dry Bulb Iet Bulb Content of
Temperature Temperature in Percent Stock
Degrees FEE . Degree st—ahr . e Percent
135 127 13 .8 116.3
135 125 12 .1 26.8
135 120 9-7 17-9
135 115 8 . 0 12 .2
135 105 5 -7 9-9
Average Original Moi sture Content (0) . . . . 116.3%
Average Final Moi sture Content . . . . . . 7 . 7%
0011‘P80 e e e e o o e o e 0 Hon.
Cupping e e e e e e e e e o e e Slight
Warping e e e e e e e e e e e 0 none
Current V
Age Weight Moi sture ' (c-e)100 _ E
of of Content ' - o-e
Run Load in Percent '
Hours Pounds o c-e o-e E
0 .00 637.00 116.3 102 .9 102 .9 100 .0
0.25 655 .00 121.8 108 .8 105.5
0.50 658.00 122.1 108.7 105.6
0.75 651.00 121.1 107.7 108.7
1.00 689.00 120 .8 107.0 108.0
1 . 25 687 .00 119 . 7 106.3 103 .3
1.50 685.00 119.0 105 .6 102.6
5.75 618.00 109.9 96.5 93 .8
9.75 600.00 103.8 90.8 87.9
26.25 582.00 88.1 70.7 68.7
30.25 529.00 79.6 66.2 68.3
38.50 16.50 3.8 62.0 60.3
7.25 5.00 .0 50.6 89.2
51.50 873.00 60.6 87.2 85.9
58.00 867.00 58.6 85.2 88.0
59-25 855-50 58.7 81.3 110-1
70.75 1158-00 117.14 38-0 33-0

(Cont ' d)

 

 

Run;

 

 

 

urrent
Age Weight Moisture
of of Content
Run Load in Percent '

Hours Pounds o W
72.50 831.00 86.8 32.1
75.00 826.50 88.8 30.5
78.00 821.75 83.2 29 29.0
82.00 816.00 81.3 27 27.1
95.00 399.00 35.5 22.1 21.5
96.50 396.50 38.6 21.2 20.6

101.25 398.00 33 .8 20.8 19.8

108.85 385.00 30.7 17.3 16.8

119.00 377.00 28.0 18.6 18.2

120.00 376.00 27.7 18.3 13 .9

128.00 373.50 26.8 13 .8 13.0

It128.00 373.50 26.8 18.7 18.1

128.25 575.00 26.7 18.6 18.0

128.50 372.50 26.5 18.8 13.8

128.75 372.00 26.3 18.2 13 .6

125.00 372.00 26.3 18.2 13.6

125.25 371.75 26.2 18.1 13 .5

125.50 371.50 26.2 18.1 13.5

130.25 368.00 25.0 12.9 12.8

182.25 360.00 22.3 10.2 9.8

188.00 358.50 21.7 9.6 9.2

186.00 357.75 21.5 9.8 9.0

189.00 356.00 20.9 8.8 8.8

158.00 353.50 20.0 7.9 7.6

167.00 388.25 18 .3 6.2 6.0

168.00 388.00 18.2 6.1 5.9

171 .25 387. 25 17.9 5 .8 5 .6

#171.25 387.25 17.9 8.2 7.7

171.50 387.00 17.8 8.1 7.6

171-75 386.25 17-5 7-8 7.3

172.00 386.00 17.5 7.8 7.3

172-25 285-75 17-8 7-7 7-2

172.50 385.50 17.3 7.6 7.1

173.00 385.00 17.2 7.5 7.0

173-25 588-75 17-1 7.8 6-9

177.75 382.00 16.8 6.7 6.3

192.50 336.00 18.1 8.8 8.1

197-75 338.25 13.5 3-8 3-6

215.50 331.25 12.5 2.8 2.6

217.50 330.75 12.3 2.6 2.8

219.00 330.25 12.2 2.5 2.3

*219.00 330.25 12.2 8.2 3.9

219.25 330.00 12.1 8.1 3.8

219.50 330.00 12.1 8.1 3.8

219.75 329.75 12.0 8.0 3.7

220.00 329.75 12.0 8.0 3.7

 

 

Run 5 (Cont'd)

 

 

ren

 

 

I
Age Weight Moisture ' sc-e)100 .
of of Content ' o-e E
Run Load in Percent '
Hours Pin-Eds o e-e o-e B
220.25 329.25 11.8 3.8 3.5
220.50 329.00 11.7 3.7 3.8
220.75 328.75 11.6 3.6 3.3
222.00 528.00 11.8 5.8 5.1
225.00 327.00 11.1 3.1 2.9
226.50 326.75 11.0 3.0 2.8
238.75 328.25 10.1 2.1 1.9
3.25 328.00 10.0 2.0 1.8
.00 323.50 9.9 1.9 108.3 1.8
9288.00 323 .50 9 .9 8.2 110 .6 3 .8
.25 323.00 9.7 8.0 0
288.50 323.00 9.7 8.0 3.6
.75 322-75 9.6 3-9 3-5
285.00 322.50 9.5 3.8 3.8
2145-25 322-25 9.8 3-7 3.3
285.50 522.00 9.3 3.6 3.3
2116-25 321-75 95 5-6 3-3
251.00 320.00 8.7 3.0 2.7
262.50 317.75 7.9 2.2 2.0
265.00 317.25 ' 7.7 2.0 1.8
267.25 317.00 7.7 2 0 110.6 1.8

 

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______.. _.—_.—.—_

 

 

 

 

 

 

Run 6
EquiIiFTr um mixture
Moisture Content
Dry Bulb let Bulb Content of
Temperature Temperature in Percent stock
Degree§3iihr. DegreesAFEhr. e Person;
135 127 13.8 111.0
135 125 12.1 29.6
135 120 9.7 21.7
135 115 8.0 13.7
135 105 5.7 8.8
Ayerage Original Moisture Content . . . . . 111.0%
Ayerage Final Moisture Content . . . . . . 6.0%
COIIaPSO e o e e e e e e e e 9 Hon.
Cupping - I e e I e o e e e e e Slight
Warping. e e a e o e e e e e 0 none
Current '
Age weight Moisture ' (c-e)100 . E
of of Content ' o-e
Run ‘Load in Percent '

Hours Pounds c c-e o-e E
0.00 612.00 111.0 97.6 97.6 100.0
0.25 628.00 116.5 103.1 105.6
0.50 628.00 116.5 103.1 105.6
0.75 626.00 115.8 102.8 108.9
1.00 623.00 118.7 101.3 103.8
1.25 621.50 118.2 100.8 103.3
1.50 618.50 113.2 99.8 102.3
7.00 586.00 102.0 88.6 90.8

12.00 566.00 95.1 81.7 83.7
23.75 525.00 81.0 67.6 69.3
28.00 511.00 76.1 62.7 68.2
50.50 500.00 72.5 58.9 60.3
35-00 837-00 67-9 514-5 55-8
147-75 1158.00 56-5 83-1 814-2
50.50 888.00 58.8 81.0 82.0
511.50 839-00 51-3 37-9 38.8
59-50 -50 148-1 514-7 35-6

 

Weight
of
Load
Po'fids

808.50
598.50
597.00
591.00
579.00
576.00
576.00
375-75

$29-50
529.00
529.00
328-75
528.50
528.00
322.00
520.00
517.00
516.50
516.25
316.00
515.50
515.50

Run 6 (Cont'd)

 

26

 

Current '
Moisture '
Content '

in Percent '

c

80.8
37-8
36.8
38-8

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Age Height

of of

Run Load
Hours Pounds c E
205.25 515.00 8.6 2.9 2.8
205.50 515.00 8.6 2.9 2.8
205.75 518.75 8.5 2.8 2.7
208.00 518.50 8.8 2.7 2.6
218.75 512.00 7.5 1.8 1.7
217.00 511.00 7.2 1.5 1.8
219.50 510.50 7.0 1.5 1.2
228.75 510.00 6.9 1.2 1.1
258.75 308.25 6.5 0.6 .6
288.25 508.00 6.2 0.5 .5
289.00 507.50 6.0 0.5 .5

 

* Scfieduie Change.

 

 

 

 

 

28

 

 

 

Run 7

Equilibrium E1 sture

Moisture Content

Dry Bulb Wet Bulb Content of

Temperature Temperature in Percent Stock
Degrees Fahr. Degrees Fahr. 6 Percent

135 127 13.8 100.0

135 125 12.1 36.5

135 120 9.7 27.6

135 115 8.0 16.0

135 105 5.7 11.7

 

Average Original Moisture Content (0) . . . . 100.0%
Average Final Moisture Content . . . . . . 8.2%
Collapse . . . . . . . . . . . None

Cupping . . . . . . . . . . . Slight

 

 

 

warping . . . . . . . . . . . None
Current '
Age Height Moisture ' (c-e)100 E
of of Content ' lo-ei g
Run Load in Percent '

Hours Pounds c c-e o-e E
0.00 605.0 100.0 86.6 86.6 100.0
0.25 620.5 105.1 91.7 105.9
0.50 622.0 105.6 92.2 106.5
0.75 621.5 105.5 92.1 106.8
1.00 619.0 108.6 91.2 105.3
1 .25 617 . 5 108. 2 90 .8 108.8
1.50 616.0 103.7 90.3 108.3
1.75 18.0 103.0 89.6 103.5
1.1-25 598.0 97-7 811-3 97-3
7-75 583-5 92-9 79-5 91-8

12.25 567.0 87.5 78.1 85.6
28.50 530.5 75.8 62.0 71 6
27.00 528.0 73.2 59.8 69.1
29.50 518.0 71.3 57.9 66.9
32-25 5116 69-1 55-7 61.1-5
36.50 501.5 65.8 52.8 60.5

 

 

 

 

 

 

 

(
29
Run 7 (Cont'd)
CTfi'rent '
Age Weight Moisture ' (c-e)100 _ E

v of of Content ' o-e
Run Load in Percent '

Hours Pounds c c-e o-e E
87.50 878.5 58.2 88.8 51.7
51.25 872.0 56.0 82.6 89.2
56.50 865.5 55.2 59.8 86.0
62.25 858.0 50.1 56.7 82.8
71.50 881.5 86.0 52.6 37.6
75-00 857-0 88-5 51.1 35-9
77.00 858-5 83-7 30-3 35-0
79.25 852.0 82.8 29.8 55.9
85.00 825.5 80.0 26.6 50.7
95.50 815.00 57.2 25.8 27.5
97.50 815.00 56.5 25.1 86.6 26.7

*97.50 815.00 56.5 28.8 87.9 27.8
97-75 812-25 36-5 28-2 27-5
98.00 812.00 56.2 28.1 27.8
98.25 812.00 56.2 28.1 27.8
98.50 811.50 56.0 25.9 27.2
99.00 811.0 55.9 25.8 27.1
100.00 809.75 55.5 25.8. 26.6

108.50 808.25 55.6 21.5 28.5
109.00 800.00 52.2 20.1 22.9
119.50 590.50 29.1 17.0 19.5

121.00 588.25 28.8 16.5 18.5
128.00 586.00 27.6 15.5 87.9 17.6

*128.00 586.00 27.6 17.9 90.5 19.8

1 .25 585.25 27.8 17.7 19.6

128.50 588.75 27.2 17.5 19.8

‘ 128.75 588.25 27.0 17.5 19.2

125.00 588.00 27.0 17.5 19.2
125.75 585.25 26.7 17.0 18.8

127.75 581.00 26.0 16.5 18.1

150.75 577.25 28.7 15.0 16.6

182.75 566.00 21.0 11.5 12.5

186.25 568.00 20.5 10.6 11.7

189.00 562.00 19.7 10.0 11.1

156.75 557.25 18.1 8.8 9.5

170.25 551.00 16.0 6.5 90.5 7.0

*170.25 551.00 16.0 8.0 92.0 8.7

170.50 550.00 15.7 7.7 8.8

170.75 550.00 15.7 7.7 8.8

171.00 589.75 15.6 7.6 8.5

171.25 589.50 15.5 7.5 8.2

171.50 589.2 15.5 7.5 8.2

175-25 387.00 18.7 6.7 7-3

179-75 388-50 13-9 5-9 6-8

190.50 580.25 12.5 8.5 8.9

 

 

 

 

 

 

 

50
Run 7(Cont'd)
Current '
Age weight Moisture ' (c-e)100 = E
.of of Content ' o-e

Run Load in Percent '

Hours Pounds c c-e o-e E
198.25 559.00 12.1 8.1 8.5
198.00 558.00 11.7 5.7 92.0 8.0
*198.00 558.00 11.7 6.0 98.5 6.8
198.25 557.75 11.7 6.0 6.8
198.50 337.25 11.5 5.8 6.2
198.75 557.00 11.8 5.7 6.0
199.00 556.75 11.5 5.6 5.9
199.25 556.50 11.5 5.6 5.9
205.50 558.00 10.8 8.7 5.0
218.25 550.50 9.5 5.6 5.8
218.25 529.25 8.9 5.2 5.8
220.75 529.00 8.8 5.1 5.5
225.50 528.00 8.8 2.7 2.9
227.50 527.25 8.2 2.5 98.5 2.7

 

*Schedule Change.

 

 

 

 

 

 

 

31
Run 7
Values of E Calculated on Basis of an
Original Moisture Content of 133.1 per cent.
Current '
Age Weight Moisture ' (c-e)100 ' E
of of Content ' c—e
Run load in Percent '
Hours Pounds c c-e o-e E
0.00 605.00 100.0 ‘TRLEV 119.7 7225‘“
.25 620.50 105.1 91.7 76.6
.50 622.00 105.6 92.2 77.0
.75 621.50 105.5 92.1 76.9
1.00 619.00 108.6 91.2 76.2
1.25 617.50 108.2 90.8 75.9
1.50 616.00 105.7 90.5 75.8
1.75 618.00 105.0 89.6 78.9
8.25 598.00 97.7 88.5 70-8
7-75 583-50 92-9 79-5 66-8
12.25 567.00 87.5 78.1 61.9
28.50 550.50 75.8 62.0 51.8
27.00 528.00 75.2 59.8 50.5
29.50 518.00 71.5 57.9 88.8
52.25 511.50 69.1 55.7 86.5
56.50 501.50 65.8 52.8 85.8
87-50 878-50 58-2 88-8 37-8
51.25 872.00 56.0 82.6 55.6
56 50 863-50 53-2 39-8 33-2
62.25 858.00 50.1 56.7 50.7
71.50 881.50 86.0 52.6 27.2
75.00 837.00 88.5 51.1 26.0
77.00 838-50 83-7 30-3 25.3
79.25 852.00 82.8 29.8 28.
85.00 825.50 80.0 26.6 22.2
95.50 815.00 57.2 25.8 19.9
97.50 815.00 56.5 25.1 119.7 19.5
*97.50 815.00 56.5 28.8 121.0 20.2
97 75 812.25 56.5 28.2 20.0
98.00 812.00 56.2 28.1 19.9
98.25 812.00 56.2 28.1 19.9
98.50 811.50 56.0 25.9 19.8
99.00 811.00 55.9 25.8 19.7
100.00 809.75 55.5 25.8 19.5
108.50 808.25 55.6 21.5 17.8
109.00 800.00 52.2 20.1 16.6
119-50 390-50 29-1 17.0 18.0
121.00 588.25 28.8 16.5 15.5
128.00 586.00 27.6 15.5 121.0 12.8
*128.00 586.00 27.6 17.9 125.8 18.5

 

 

 

   

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52
Run 7 Cont'd
Current '
Age ‘Weight Moisture ' (c-e)100 . E
of of Content ' o-e
Run Load in Percent '
Hours Pounds c c-e o-e E
”128.25 585.25 27.8 17.7 18.5
128.50 588.75 27.2 17.5 18.2
128.75 588.25 27.0 17.5 18.0
125.00 388.00 27.0 17.5 18.0
125.75 585.25 26.7 17.0 15.8
127.75 581.00 26.0 16.5 15.2
150.75 377.25 28.7 15.0 12.2
182.75 566.00 21.0 11.5 9.2
186.25 568.00 20.5 10.6 8.6
189.00 562.00 19.7 10.0 8.1
156.75 557.25 18.1 8.8 6.8
170.25 551.00 16.0 6.5 125.8 5.1
*170.25 551.00 16.0 8.0 125.1 6.8
170.50 550.00 15.7 7.7 6.2
170.75 550.00 15.7 7.7 6.2
171.00 589.75 15.6 7.6 6.1
171.25 589.50 15.5 7.5 6.0
171-50 389 25 15-5 7-5 6-0
175.25 587.00 18.7 6.7 5-8
179-75 388-50 13-9 5-9 8-7
190.50 580.25 12.5 8.5 5.6
198.25 559.00 12.1 8.1 5.5
198.00 558.00 11.7 5.7 125.1 5.0
*198.00 338.00 11.7 6.0 127.8 8.7
198.25 557.75 11.7 6.0 8.7
198.50 557.25 11.5 5.8 8.6
198-75 337-00 11-8 5-7 8.5
199.00 556.75 11.5 5.6 8.8
199.25 556.50 11.5 5.6 8.8
205.50 558.00 10.8 8.7 5.7
218.25 550.50 9.5 5.6 2.8
218.25 529.25 8.9 5.2 2.5
220.75 529.00 8.8 5.1 2.8
225.50 528.00 8.8 2.7 2.1
227.50 527.25 8.2 2.5 127.8 2.0
*Schedule Change.

 

 

 

 

 

 

THE DRYING 0F WOOD

 

Tiemann (10) states, ”That the moisture in wood may move in
two distinct ways, namely, by flow as capillary freedwater, like oil
in a wick, and by diffusion through the cell walls as hygroscopic
moisture." Both of these movements may occur in green wood. In
sapwood, most of the free water will move by capillary flow, but the
water in the heartwood may be bound up in the cells and have to pass
through such small openings as to make capillary action impossible.

The rate of drying may be controlled by temperature and steep-
ness of the moisture gradient, the moisture gradient being the dif-
ference in moisture concentrations between the center and surface of
the wood. Temperature influences the rate of drying, because heat
lowers the viscosity of water, making diffusion more rapid. The
steeper the moisture gradient, the greater will be the difference in
the concentrations of moisture at the center and at the surface of the
wood. The greater this difference, the more rapid the drying. The
steepness of the moisture gradient is controlled by the relative humid-

ity and temperature in the kiln.

PLOTTING 0F DRYING CURVES
For purposes of comparison, drying curves for the several
runs were made by plotting the percentage (on the oven-dry basis) of
evaporable water in the lumber at various times against the age of
the run in hours. The percentage of evaporable water in the lumber

was determined by the following formula:

E I (c-e)lOO
o-e

 

 

58

Nomenclature:

E - the percentage of evaporable water.

c - the current moisture content of the wood in percent.

9 - the equilibrium moisture content of the wood in percent.

0 — the original moisture content of the wood in percent.

For example, in Run 7 when the original moisture content
was 100 percent, the current moisture content was 80 percent, and

the equilibrium moisture content was 13.8 percent, E equaled

$80.0 - 13.8) 100 or 30.7 percent.
100.0 - 3.

The equilibrium moisture content must be subtracted from
the current and original moisture contents in arriving at the per—
centage of evaporable water. because wood. as previously mentioned,
will dry until its moisture content reaches the equilibrium value,
and continued exposure to conditions of temperature and humidity
giving the same equilibrium value will result in no further loss of
moisture.

For each run, the values of E for various moisture contents
were determined and plotted against age of run on semi-logarithmic
paper (see charts 1 to 7. inclusive). In calculating the points for
each change of a run, the original moisture content of the wood for
that run was used in every instance. This gave the origin of each
new curve a higher value than that of the final point of the pre-
ceeding curve. The points for each schedule change fell in approx-
imately a straight line (that is, the relationship between E and

time was linear when plotted on semi-logarithmic paper) in every case

except for the E values of the first few hours at the beginning of

 

 

 

 

4 ”hit a

J

 

 

each schedule change. These first slope values showed variable
and more steep slopes on semi-logarithmic paper in every instance
than did the values for the rest of the change which had a con-
stant and more moderate slope. This rapid drying at the beginning
of each change may be accounted for by the readjustment of the
moisture gradient in the wood. Whereas, the concentration of
moisture at the center of the wood remains approximately the same,
the concentration of moisture on the wood's surface is lovered by
changing the drying conditions so that the wood assumes a lower
equilibrium moisture content. Consequently, evaporation from the
surface of the wood is more rapid for a short time until the con-
centration of moisture on the surface of the wood is in equilibrium
with the kiln's conditions. I
Some differences in the original moisture contents of the
runs due to air seasoning of the lumber before kiln drying were
found, even though the lumber was piled without stickers. Also,

the logs from which the lumber for Runs 1 and 2 was sawed were cut

, several months prior to sawing which allowed time for some air

seasoning of the logs. To determine the effect of these differ-

ences in original moisture content on the character of the drying

curves, two sets of E values were calculated for Run 7 using, first,
100 percent as the original moisture content and then 133.1 percent,
the highest original moisture content found in any of the runs. Chart

7 shows the two sets of curves resulting from plotting the E values.

Examination of the two sets of curves shoWs that using a different

original moisture content has no effect on the slope of the curves

as corresponding curves have identical slopes. The only effect pro-

 

 

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.

1. '3,

,5. ..

    

r" .
-— - .tw'fl‘l‘ww‘cul i Sab‘ a. .‘V. w.’
t ’ I ' '.

 

 

 

56
duced by using the higher original moisture content is that it

results in lower E values, thus lowering the position of the

curves on the chart.

Table I

Slopes of the Linear Portions of the Drying Curves
for each Schedule Change of Runs 2 to 7, inclusive.

 

 

 

Equilibrium

Mbisture Slopes of Drying Curves

Content

Percent 2 7? u 5 6 7
15.h -.00523 -.00509 -.00632 -.oo725 -.00823 -.00622
12.1 -.00557 -.00522 -.OO797 -.00839 -.OlO95 -.OO775
9.7 -.00759 -.00995 -.01028 -.Ol§85 -.00957
8.3 -.00938
8.0 -.00922 -.00981 -.Oll70 -.01689 -.01135
6.7 -.00822
6.6 -.013h1
5.7 -.00882 -.01210 -.01192 -.01851 -.01105

 

 

 

 

 

 

 

 

Table I gives the slope values of the linear portions of the
drying curves for each schedule change for Runs 2 to 7, inclusive.
Slope values for Run 1 are not included in this table because a con-
stant dry bulb temperature was not used in drying. With the exception
of the slope values for the equilibrium moisture contents of 6.7
percent and 5.7 percent in Run 3, of 8.0 percent in Run h, and 5.7
percent in Run 7, there is an increase in the slope of the curves for
each successive schedule change for each run. Nelson (7) in his Work
with Douglas fir lumber found that the curves resulting from plot-
ting E against time were all of approximately the same slope when a

constant dry bulb temperature was used. He used only Douglas fir

heartWood lumber, a relatively impervious wood, and had a circulation

 

 

4’3“ a'tfi— .. .. .-m:» ml
v »r

. , .. o- §—-..

 

 

 

37
of 550 feet per minute in his kiln.

The slopes of the curves for Runs 5 and 6 are consistently
steeper than those of the other runs for each equilibrium moisture
content with one exception. For the equilibrium moisture content of
5.7 percent, the slope of the curve for Run h is .00018 steeper than
the corresponding slope of the curve for Run 5. Several reasons exist
for the steeper curves in Runs 5 and 6. Lumber of by and 6-inch
widths were used in building up the loads 10 inches high and 10 boards
wide for these runs; whereas, for Runs h and 6, boards of 10- and 12-
inch widths were used. (Runs 2 and 3 are not taken into consideration
because of the low rate of circulation used in drying them.) A
higher percentage of sapWood was contained in the boards of h! and 6-
inch widths than in the wider boards as they were cut from the smaller
logs and from the sapwood portion of the larger logs. The 10- and 12-
inch boards were cut from the center portion of the larger logs and con-
tained no, or only a small strip of, sapwood on each side of the heart-
wood. As the sapwood of cottonwood is much more pervious and ordina-
rily contains a higher percentage of free water than heartwood, the
rate of drying of sapWood is considerable faster than the rate of dry-
ing of heartwood. Also, using twice the number of boards in a load
10 or 12 inches high and 10 boards wide gives ho board edges from
which drying can take place in Runs 5 and 6 as compared with 20 edges
in Runs h and 7. This increased drying surface area results in a
greater amount of moisture being evaporated which increases the rate
of drying.

Hermann and Rasmussen (h) working with sap ponderosa pine

r‘u "Ynu “I: a...‘

usual - ‘1';

 

 

 

 

     

38
found that the rate of drying increased rapidly with an increase of
circulation up to 365 feet per minute using one—way circulation.
Sap pcnderosa pine and sap cottonwood are woods which give up their
free moisture with relative case.

That the rate of circulation, 1148 feet per minute, used in
the last four runs of this experiment was too slow for mximum rate
of drying is indicated by the temperature drop across the load as
determined by measuring the conditions of the air on the leaving side
of the load in Runs 6 and 7. 1 drop across the load of L; degrees
Fahr. with the corresponding increase in relative humidity existed
for 128 hours during Run 6 and 36.5 hours during Run 7. Thus, the
first part of the run is most affected by the slow rate of circulation;
for, after wood dries to the fiber saturation point, water moves to
the surface of the wood by diffusion rather than by capillary action.
Therefore, the water arrives at the surface at a slower rate. It is
then possible for the lower rate of circulation to remove the moisture
from the surface as rapidly as it appears. Herman and Rasmussen
()4) found that below 25 percent moisture content, the rate of circu-
lation could be reduced to 50 percent or less of that needed before
the wood dried to that point. Consequently, the slopes of the dry-
ing curves for the last schedule changes probably more nearly repre-

sent what the slopes of the curves at the begiming of the runs would

have been, providing the rate of circulation had been adequate.

 

 

EFFECT OF CIRCULATION ON THE DRYING CURVES

That the slopes of the drying curves are affected by
changes in rate of circulation is shown by examination of table II.
In every instance, for similar equilibrium moisture contents, the
drying curves for Runs h to 7, inclusive, are steeper than the
curves for Runs 2 and 3. A comparison of the average drying curve
slopes of Runs h to 7, inclusive, with those of Runs 2 and 3 is made
in table II. The greatest difference in slopes is found in the last
schedule change while the least difference is in the first schedule
change. The small sample makes impossible any conclusion other than

an increase in the rate of circulation increases the steepness of the

drying curves.

Table II

.Eff°°t of Increased Rate of Circulation on the
Slopes of the Linear Portions of the Drying Curves for
Runs 2 to 7, inclusive.

 

Awerage Drying Ayerage Drying

 

Equilibrium Curve Slopes Curve Slopes
moisture for Runs for Runs
Content 2 and 3* h to 7,inclusive Difference
13.b% -.00h66 -.00701 .00235
12.1% -.oo5ho -.ooe76 .00336
9.7% -.00759 -.01091 .00332
80 -.00922 “.012145 000321
5.7% -.00822 -.013h0 .00518

 

*Slope values for equilibrium moisture contents of 9.7%, 8.0%,
and 5.7% are for Run 3 only.

 

 

   

EFFECT OF CIRCULATION ON DRYING TIME

Table III shows the total drying time in hours from a
moisture content of 95 to hB percent for each run except Run 1.
The ages of the runs at 95 and hB percent were determined by calcu—
lating the E values for these moisture contents for each run and
locating these values on the respective charts. The two moisture
contents of 95 percent and hB percent were chosen, as they fell with-

in the limits of the first part of the schedule for the six runs.

Table III

Effect of Increased Rate of Circulation on Rate
of Drying from a Moisture Content of 95% to bB%.

 

 

 

Average Average
Time for Time for
Rate of Runs Runs h to 7,
Run Time Circulation 2 and 3 inclusive

Hours Feet/Minute Hours Hours

2 88.25 15
5 73-50 15 80-90

1:, 59-50 11:8
5 51.75 1148
6 15.00 m8

7 59-75 1148 57-140

 

Difference between average time of Runs2 and 3 and Runs h to 7,
inclusive . . . . . . 23.50 hours.

 

The effect on the rate of drying of increasing the rate of
circulation from 15 feet per minute in Runs 2 and 3 to lbs feet per
minute in Runs h to 7, inclusive, is shown by the shortening of the
average drying time 23.5 hours between the two above moisture contents

in the latter runs.

 

 

 

 

SEASONING DEFECTS

 

While cottonwood has a tendency to warp badly, this was
prevented by tightly binding the load. Cupping for the most part
was prevented; but where it did occur, it was due to the difference
in tangential and radial shrinkage in pieces out near the pith of
the log.

The most serious defect encountered was collapse which
occurred in 25 percent of the load in Run 1 and 10 percent of the
load in Run h. Tiemann (10) explains collapse as follows:

"When water is drawn out from completely filled cells
whose walls are relatively impermeable, that is when the surround-
ing cell membrane has openings so small that the water films over
their surfaces are capable of exerting a sufficient pull, the walls
of the cells may be drawn together or "collapsed“ so that certain
areas, or even the entire cross-section of the wood may appear
greatly shrunken."

A more detailed explanation of collapse is given by Koehler
and Thelen (5) as follows:

I'In very wet wood, some of the cells at least are entire-
ly filled with water. As this water leaves the cell cavities, air
should take its place, but it is very difficult for air to pass
through the wet cell walls, so in the absence of air the cells flat-
ten out as the water leaves. This is similar to what happens if
water is drawn out of a rubber tube without admitting air. It is not
the air pressure on the outside of the wood which is responsible for

this collapse, as that at the most could be only 15 pounds per

 

 

 

 

L2
square inch, but rather the force of the water pulling the wet cells
together as it leaves. This force is much greater than that due to
atmospheric pressure. (The cohesive strength of water, when it can
be effectually applied, has been variously estimated as being from
150 to h,500 pounds per square inch.)"

Collapse occurs before the lumber dries to the fiber satur-
ation point which is from 25 to 50 percent for most woods. The
collapse found in this experiment occurred in every instance at the
junction of the heartwood and sapwood.

In this area, the surface of

the boards assumed a greatly sunken appearence.

Table IV

Occurrence of Collapse in Cottonwood as Related to Temperature,
Equilibrium.Moisture Content, and Rate of Circulation.

 

 

 

Equilibrium
Temperature Moisture
Original immediately' Contentl Rate of Amount
Run Original Equi- prior to immediate y Circu- of
Temper- librium 5053/ prior to lation Collapse
ature Moisture Moisture 50%E/VMois-
Contentl/ Content ture Content
Degrees Degrees Ft. per
Fahr. Percent Fahr. Percent Minute Percent
l 155 15.h lh5 7.9 15 25.0
2 155 15.h 155 8.5 15 0.0
3 135 13 .1; 135 12.1 15 0.0
h 135 li-h 135 9-7 1h8 10.0
5 135 13-h 135 lfi-h lh8 0-0
6 135 13.1; 135 151; m8 0.0
7 155 l5.h 155 12.1 lhB 0.0

 

 

 

 

 

 

 

 

1

,d/ The equilibrium moisture contents indicated applied to entering
air conditions.
E/ Moisture content of 50 percent used as the fiber saturation point
of wood.

 

 

 

 

 

143

The relation of temperature, equilibrium moisture content, and
circulation to collapse in cottonwood is shown in table IV. In the
first three runs, due to the slow rate of circulation, the equilibrium
moisture content of the lumber actually was higher than indicated in
the table. The values in the table indicate the condition of the
air entering the load; but, because of the indisputable drop in temper-
ature across the load, the equilibrium moisture content of the lumber
on the leaving side would be considerably higher. This condition
would not be as true for the last four runs because the increased rate
of circulation caused the conditions throughout the load to be more
uniform.

Tiemann (10) states that high temperatures are the cause of
collapse rather than low humidities. The high temperatures make the
cell walls plastic, and they are unable to withstand the terrific
pull exerted on them. That even a moderate temperature of 155 degrees
Fahr. may make the cell walls sufficiently plastic to permit collapse
when subjected to rather severe drying conditions is shown in table IV.

In Runs h to 7, inclusive, where drying was more rapid because
of increased circulation, collapse was found only in Run A. In this
run, changing the entering air conditions caused the equilibrium
moisture content to drop from 15.h percent to 9.7 percent before the
lumber reached the fiber saturation point as contrasted to Runs 5, 6,
and 7 where the next lowest equilibrium moisture content was 12.1
percent with no collapse resulting. The collapse in Run h was direct~
1y due to the lowered equilibrium moisture content which set up a

steep moisture gradient causing rapid removal of the water; and the

cell walls, too weak to withstand the cohesive force of the water, were

 

 

 

 

 

 

 

 

 

 

 

 

 

 

14h

drawn together.

While an equilibrium moisture content higher than 9.7 per-
cent undoubtedly existed in Run 1 when the load reached the fiber sat-
uration point, increasing the temperature from.l55 degrees Fahr. to
1&5 degrees Fahr. made the cell walls sufficiently plastic to collapse
even with a lesser cohesive force exerted by the water on the cells.

As collapse weakens lumber and may be the cause of severe
honeycombing, extreme care should be exercised in choosing a sched—
ule for kiln drying green cottonwood. From the information gathered,
as a result of these seven runs, a safe schedule using a temperature
of 155 degrees Fahr. should use an equilibrium.moisture content of
l5.h.percent until the wood reaches a moisture content of 55 percent
and then change to an equilibrium.moisture content not lower than
12.1 percent until the lumber has dried to the fiber saturation point.
This would preclude any possibility of collapse when the rate of circu-

lation in the kiln is le feet per minute or less.
LIMITATIONS OF RESULTS

Inadequate circulation in the dry kiln and lack of material
precluded a more exhaustive study. Consequently, the results obtained

are based on a limited sample and a limited range of conditions.
SUMMARY

The study consisted of kiln drying l l/B-inch cottonwood
lumber with original moisture contents ranging from 97.1 percent to

155.1 percent. 'With the exception of one run, the lumber was dried at

a constant dry bulb temperature of 155 degrees Fahr., and the severity

 

 

 

 

of the drying conditions increased by lowering the wet bulb temper-

ature. The results of the study are summarized as follows:

1. In general, the slopes of the linear portions of the drying curves
for cottonwood lumber dried at a constant dry bulb temperature
became steeper at each schedule change as the severity of the dry-
ing conditions increased.

2. At every schedule change, very rapid drying took place for several
hours until the moisture gradient in the lumber had adjusted itself
to the new moisture equilibrium conditions in the dry kiln.

5. An increase in the rate of circulation from 15 feet per minute to
lhB feet per minute increased the steepness of the slopes of the
drying curves and, therefore, the rate of drying of cottonwood.

h. Degrade in cottonwood due to warping and cupping was reduced to a
minimum by securely binding the load.

5. Collapse in green cottonwood was found to occur when the following
conditions existed in the kiln before the lumber reached the fiber
saturation point.

A. An increase in the dry bulb temperature from 155 degrees Fahr.
to lh5 degrees Fahr. together with a change in the entering air
conditions which caused a reduction in the equilibrium moisture
content from l5.h percent to 7.9 percent while using a rate of
circulation of 15 feet per minute.

B. A constant dry bulb temperature of 155 degrees Fahr. together
with a change in the entering air conditions which caused a
reduction in the equilibrium moisture content from l5.h percent
to 9.7 percent while using a rate of circulation of lhB feet
per minute.

6. In dry kilns with circulation rate of lh8 feet per minute or less,

 

 

i. ., I

 

 

 

1L6

a safe schedule for the drying of green cottonwood using a
temperature of 155 degrees Fahr. should use an equilibrium
moisture content of l5.h percent until the stock dries to a
moisture content of 55 percent and then change to and main-

tain an equilibrium moisture content of not lower than 12.1

percent until the lumber reaches the fiber saturation point.

 

 

 

 

9.

10.

ll.

12.

1}.

LITERATURE CITED b7

Badger, W. and McCabe. W. Elements of Chemical Engineering
(McGraw-Hill. New York, 1951).

Greenhill. W. L. "The Effect of the Rate of Air Circulation on the
Rate of Drying of Timber," Journal for the Council for Scientific
and Industrial Research, (August, 1936), vol. 9, no. 3. Melbourne.
Iustralia.

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(Madison, Wisconsin, 19375.

 

 

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