SURFACE EVAEUATION OF MELAMINE
OVERLAID PARTICLEBOARD

Thesis for flu Degree OI M. S.
MICHIGAN STATE UNIVERSITY

Chun Young Lo
I975

 

IHESIS

LIBRAR y '

Michigan Static
University

 

ABSTRACT

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L..—

SURFACE EVALUATION OF MELAMINE OVERLAID PARTICLEBOARD

By

Chun Young L0

The objective of this study was to determine whether the results
of physical surface measurement can be correlated with the average visual
judgements by a number of observers of surface deterioration of overlaid
particleboard.

melamine impregnated papers were bonded to both faces of
particleboard with heat and pressure in a hydraulic press. Three layers
of impregnated paper sheets composed the overlays, which were overlay
sheet, pattern sheet and bonding sheet. Bonding sheet impregnated with
phenol formaldhyde resin was optional. Seven types of commercial
particleboard were used as substrates. The suitability of a substrate
for these overlays was not always apparent and must be expressed in
term of the surface quality of the overlaid products after exposure to
high humidity. All the specimens were first conditioned at 40% relative
humidity and 70° F, and then at 90% relative humidity and 70° F until
equilibrium was reached. Deteriorated surface profiles of overlaid board
without bonding sheet were evaluated by various mathematical methods and
then ranked. Visual judgements made by eight individuals resulted in a

rank of all specimens. The rank correlation between the various

Chun Young Lo

mathematical evaluations and the visual judgements was determined by
using Spearman’s formula. The test results show that the E system

was rank correlated with the visual judgements, as was the L0 method.
The Average method and the Standard Deviation method were not correlated
with the visual judgements.

The results of the evaluation based on the E system and the Lo
method revealed that surface characteristics of overlaid board were
greatly affected by the substrate. Those laminates with bonding sheet
have bettersurface quality than those without bonding sheet only under
severe moisture condition. Substrates with good surface quality need
no bonding sheet. Under this interpretation, substrate 10, 8 and l were

considered as having good surface quality.

SURFACE EVALUATION OF MELAMINE OVERLAID PARTICLEBOARD

BY

Chun Young Lo

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements

for the degree of

MASTER OF SCIENCE

Department of Forestry

1975

ACKNOWLEDGMENTS

The author wishes to express his deepest appreciation to
Dr. Otto Suchsland, of the Department of Forestry, for his guidance in
the construction of this thesis, and for his great deal of thought which
was given throughout the course of this study.

Thanks and appreciation also go to the author‘s parents, Yu Chun
Lo and Chung Chen Yao, for their continuous encouragement from thousands

of miles away.

ii

TABLE OF CONTENTS

ACKNOWLEDGMENTS. . . . . .

LIST OF TABLES .

LIST OF FIGURES. . . . . . . . .

methods

exposure to

iii

CHAPTER
1. INTRODUCTION . . . . . . . . . .
2. THE MEASUREMENT OF SURFACES. . .
2.1) General. . . . . . . . . . .
2.2) Methods and instruments. . .
2.2.1) Visual and tactile
2.2.2) Light methods. . .
2.2.3) Mechanical systems .
2.3) Evaluation . . . . . . . . . .
2.3.1) M (mean line) system .
2.3.2) E (envelope) system.
3. EXPERIMENTAL DESIGN AND PROCEDURE.
3.1) Material . . . . . . .
3.1.1) Substrate. . .
3.1.2) Overlays . .
3.2) Laminating procedure . . .
3.3) Exposure cycle . . . . . .
3.4) Design of experiment . . .
3.5) Visual observation after
3.6) Measuring surface profiles .
3.6.1) Instrument . . . . .
3.6.2) The use of the instrument.
3.6.3)
4. MATHEMATICAL EVALUATION OF SURFACE PROFILES.
4.1) E system . . . . . . .
4.2) Average method . . . . . . .
4.3) Standard Deviation method. .
4.4) L0 method. . . . . . . . . .
5. STATISTICAL ANALYSIS AND DISCUSSION OF RESULTS

The reproducibility of measurements.

high humidity .

H

Page
ii

vi

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.16

16
16
20
23
23
23
25
25

29
4O
40
43
48
48

55

CHAPTER

6.

CONCLUSION.

REFERENCES . . . .

TABLE OF CONTENTS (Cont'd.)

iv

LIST OF TABLES

TABLE ‘ Page
1. General Properties of Seven Types of Commercial Particleboard. . 19
2. Design of Experiment . . . . . . . . . . . . . . . . . . . . . . 24

' 3. Results of Analysis by Several Methods of Surface Profiles of
Group C Specimen Measured at Exposure Condition 2. . . . . . . 56

4. Qualitative Ranking of Surface Profiles of Group C Specimen
Measured at Condition 2 Analysed by Several Methods. . . . . . 57

5. Score of Individual Specimens by Visual Judgement. . . . . . . . 58
6. Limit Values for Spearmen Rank Correlation Coefficient . . . . . 60
7. Surface Roughness and waviness of Group C and Group D Specimen
Measured at Condition 1 and Condition 2 Analysed by the
E Me thOd O O O O O O O O O O O O O O O '. C O O O O O O O I O O 62
8. Surface Roughness and waviness of Group C and Group D Specimen
Measured at Condition 1 and Condition 2 Analysed by the
L0 Method. . . . . . . . . . . . . . . . . . . . . . . . . . . 71

9. Thickness, Thickness Swelling, and Water Absorption of Four
Groups of Specimen Exposed to Condition 2. . . . . . . . . . . 77

LIST OF FIGURES

FIGURE ' Page

1. Basic surface measures according to the M (mean line)
system. O O O O O O O O O O O O O O O O O O O O O O O O O O 11

2. Basic surface measures according to the E (envelope)
system. . . . . . . . . . . . . . . . . . . . . . . . . . . l4

3. Photograph of seven types of substrate. . . . . . . . . . . . 18
4. The construction of overlays. . . . . . . . . . . . . . . . . 22
5. The Bendix Microcorder stylus instrument. . . . . . . . . . . 27

6. The original profiles of overlaid substrate without
Bonding Sheet (group C) measured at condition 1 . . . .-. . 31

7. The original profiles of overlaid substrate without
Bonding Sheet (group C) measured at condition 2 . . . . . . 33

8. The original profiles of overlaid substrate with
Bonding Sheet (group D) measured at condition 1 . . . . . . 35

9. The original profiles of overlaid substrate with
Bonding Sheet (group D) measured at condition 2 . . . . . . 37

10. The reproducibility of the profiles produced from two traces
over the same surface. I-A and I-B are plain substrate.
lO—A and lO—B are overlaid substrate. . . . . . . . . . . . 39

11. The technique of evaluating E system. The radius of the

large disc is 250 mm. The radius of the small disc is

25 mm. The length of the plastic profile is 23 inches. . . 42
12. Comparison of the original profile with the reproduced

profile. I-A is the original profile. I-B is the

profile reproduced from the plastic profile . . . . . . . . 45
13. Surface measures according to the Average method. . . . . . . 47
14. Surface measures according to the L0 method . . . . . . . . . 50
15. A segment of a circle relationship between the mean line

of compensation and the average angle between roughness
intervals . . . . . . . . . . . . . . . . . . . . . . . . . 53

vi

LIST OF FIGURES CONTINUED

FIGURE Page

16. Surface roughness of overlaid substrate without Bonding
Sheet (group C) evaluated at condition 1 and 2 by the
E system. . . . . . . . . . . . . . . . . . . . . . . . . . 64

17. Surface roughness of overlaid substrate with Bonding
Sheet (group D) evaluated at condition 1 and 2 by the
E system. . . . . . . . . . . . . . . . . . . . . . . . . . 66

18. Surface waviness of overlaid substrate without Bonding
Sheet (group C) evaluated at condition 1 and 2 by the
E system. 0 O O O I O O O O O O O O O O O O O O O O I O O O 68

19. Surface waviness of overlaid substrate with Bonding
Sheet (group D) evaluated at condition 1 and 2 by the
E system. 0 O O O O O O I O O O O O O O O O O O O O O O O O 70

20. Surface roughness of overlaid substrate without Bonding
Sheet (group C) evaluated at condition 1 and 2 by the
Lo system 0 O O O O O I O O O O O O O O O O O O O O O O O O 73

21. Surface roughness of overlaid substrate with Bonding

Sheet (group D) evaluated at condition 1 and 2 by the
L0 system . . . . . . . . . . . . . . . . . . . . . . . . . 75

vii

CHAPTER 1

INTRODUCTION

Melamine overlaid particleboard consists of thin layers of
melamine impregnated papers bonded to both faces of particleboard to
provide protective and/or decorative surfaces.

Overlays are very essential to the wood industry. Most overlays
are derived from paper products, some are polymer film. They are
applied to wood products such as plywood, lumber, and composition board.

Advantages of overlaid boards are high scratch resistance, high
resistance to acids, water etc. and higher mechanical strength. In
addition, overlaid boards can be mass produced with a wide choice of
patterns and colors and require no finishing. Among the disadvantages
of board products overlaid with paper or plastic film is the instability
of the surface due to thickness swelling of the substrate. The surface
quality of overlaid boards is greatly dependent upon the substrate used
as compared with the stability of veneered boards. The suitability of
a substrate for these overlays is not always apparent and must be
expressed in terms of the surface quality of the overlaid product after
exposure to high humidity.

Overlays can be applied only to boards having special properties
such as high compression strength and very fine surface layers. .Methods
of application vary with the types of overlay used, which in turn depends

on the use of the end products. There are three basic types of overlays:

high density overlay, medium density overlay, and decorative overlay.
All three are applied to the substrate by means of heat and pressure in
hydraulic presses. Roll laminating is another method used for certain
types of film that can not be satisfactorily applied to wood substrates
in any other way. Roll laminating uses momentary pressure applied by

a resilient roll to combine the overlay with the wood substrate panel,
the adhesive having been spread on the overlay, the wood substrate or
both (11).

While the human eye is very sensitive to the slightest distortions'
of high gloss surfaces and would therefore serve as a good indicator,
classification of surfaces by visual observation could be very subjective
and therefore unreliable. Physical measurement of surface profiles on
the other hand requires special evaluation procedures.

The objective of this study is to determine whether the results
of physical surface measurement can be correlated with the average
visual judgements by a number of observers of surface deterioration of

overlaid particleboard.

CHAPTER 2

THE MEASUREMENT OF SURFACES

2.1) General

The measurement of surface characteristics has been discussed
for over 40 years. First attempts of surface evaluation involved the
use of "sight—touch" to arrange sample specimens in a qualitative manner.
Later, standards have been set with some quantitative gradation based on
surface geometry (7).

To evaluate surface characteristics, a three dimensional
measurement of the surface would be most desirable in order to represent
the total natural characteristic of the surface. However, the difficulties
involved in making such measurements are considerable so that in most
cases physical surface measurement is limited to two dimensions. Subjective
judgement by the sense of sight and touch on the other hand is of a three
dimensional nature. Unfortunately, such evaluation cannot readily be
standardized. Devices have, thus, been developed to replace "sight-touch"
methods by other indirect and direct methods based on optical, accoustical,
mechanical and pneumatic principles. All of these methods are comparative
methods, and standards based on them are more or less arbitrary (2).
Because of this fact, devices measuring the true geometry of the surface
have been popularily used. The direct measurement of surfaces is based
on the geometrical surface of the test specimen. The roughness factor
is defined as the ratio of the area of the actual surface to that of the

3

geometric surface (20). Deviation from the geometric surface is
categorized into three categories which are refered to as roughness,
waviness and lay (19).

According to the American Standard Association (19), roughness
consists of the finer irregularities in the surface texture within the
limits of the roughnessewidth cut off*. waviness is the usually widely-
spaced component of surface texture. Deviations including error of form
are macro-geometrical. Lay is the direction of the predominant surface
pattern. In the measurement of surface texture only deviations of
roughness and waviness are of interest.

Stylus type instruments are widely used for measuring surface
roughness depending on electrical amplification of the motion of a
stylus perpendicular to the surface over which the stylus is traversed.
The surface being traversed is cut by a plane which is perpendiCular
to the geometrical surface of the test specimen. The line of intersection
between the cutting plane and the real surface is the real surface profile
4(12). I

The mathematical evaluation of surface profiles has caused much
confusion and misunderstanding. There are many standards for assessing
roughness. But none of them can provide enough information to represent
functional qualities of the surface (15). In this study, it was not
attempted to determine which is the best method to evaluate surface

profiles based on mathematical consideration. Rather, it was

 

* roughness!width cut off: The greatest spacing of repetitive
irregularities to be included in the measurement of average roughness
height.

attempted to find out the most applicable method which can serve as an
alternative to visual judgement, which in many practical circumstances
is the only criterion for the consumer to determine surface quality.

Such a method would be a valuable tool for the manufacturer in predict-

ing consumer reaction.

2.2) Methods and instruments

 

2.2.1) Visual and tactile methods

The reliability of touch and sight in evaluating surface texture
has been studied (10, 1, 17). The human eye can detect very small
variation of the angle of reflection on polished wood and nice smooth
surfaces. A roughness of 0.5 u* or even 0.1 u with some training, can
be sensed by touch. Optics of reflection deal with the relationship
between the incident beam of light and the reflected beam of light.

A change in angle of the incident light will cause an intensity
variation of the reflected beam. The degree of change will be greater
at large incident light angles than at smaller incident light angles.
The human eye is capable of recognizing differences in light intensity
of one percent.

Two components of light can be distinguished when a beam of light
strikes an irregular wood surface covered with a transparent film. The
diffuse component is responsible for the color of the surface, the

specular components for its gloss.

 

* .—
111 = 10 3mm

The relative intensity of both components depends on the geometry of the
surface, refractive index and coefficient of absorption of the film.

In the case, where light is incident on a wavy surface, the intensity

of the reflected light will be considerably higher at the crests and
troughs than at the slope of the waves. This is the principle of glossy
surfaces which will show very small irregularities or unevenness. The
observability depends not only on depth or height of the irregularities
but also to a large extent on the ratio of wave, depth: wave length.
When normal light is not adequate to discriminate surface roughness, the
use of tactile cues is necessary. However, by using oblique light to
illuminate a surface, the visual observation is as good as tactile
judgements, and more rapid. Judgements made by skilled operators

showed only a little more sensitivity in judgement than those made by

unskilled operators under the familiar inspection condition.

2.2.2) Light methods

Several other methods are described (4) using light to analyze
surfaces. One is based on image reflection, the other is the so called
"light sectioning" method. The image reflection method evaluates the
surface quality of a high gloss highly reflective surface by observing
the distortion suffered by the reflected image of either a straight line
or a regular grid pattern. Quantitative evaluation of such observation
is difficult, however. In the so called "light sectioning" method, a

narrow beam of light formed by a slit is focused on the surface at an

acute angle. The intersection of the light beam with the surface is
then observed from a position directly above the surface. Pictures of
the elongated waves can be analysed and the true wave height can be

calculated.

2.2.3) Mechanical systems

Devices measuring the true geometry of the surface were developed
from simple mechanical systems to electrowmechanical systems by way of
optical mechanical systems.

Timms (17) described an instrument in which a simple mechanical
linkage is used to connect the stylus to the recorder pen, the
magnification being controlled by the lever ratio in the system;

Schmalz (13) studied surface texture using a sharply pointed stylus
to trace the profile and record its movements by an optical method.

I In the Forster apparatus (4) manufactured by Ernst Leitz, the test
Specimen moves under an oscillsting stylus, connected mechanically to a
tilting mirror. As the stylus oscillates, a beam of light is reflected
from the mirror. The exposed portion is the air above the-surface, the
unexposed portion is the material, and the interface is the surface
profile.

Ernest Abbott (13) in 1936, devised the "Profilometer" which
converts the movements of the stylus into a corresponding alternating
current and assesses the current representing the deviation of the
profile from its mean line.

R. A. Mann (6) devised an apparatus consisting of three basic
components: the pick up arm, the amplifier recorder and the feed

mechanism. The pick up arm is fitted with strain gages which are mounted

on the beam. They are so connected that vertical deflections are
magnified. The probe on the pick up arm consisting of a steel ball
touches the surface being studied. The size of the steel ball, 1/4 inch
in diameter, is considered satisfactory for studies of finished panels,
machined surfaces, and particleboard. The amplifier recorder magnifies
the strain in the pick up arm and records it on a moving paper chart.
The speed of the chart and the amplification can be adjusted to give
varying degrees of vertical and horizontal magnification. Hann found
that the results were reproducible, and that the apparatus could detect
differences in surface contours of wood panels due to humidity change.
The currently used stylus instruments transfer the motion of the
stylus electrically to the recording system. There are two types of
transducer. One is a direct displacement type using the same principle
as that employed in a phonograph. Another type integrates the rate of
stylus motion to give the displacement (13). When the stylus tracer
moves over the specimen at a constant speed, two components resiSt the
motion. Horizontal movement of the stylus is resisted by friction force,
requiring a greater driving force. The vertical component results in
the stylus moving upward. The magnitude of this vertical component
depends on the cone angle of the stylus and the coefficient of friction
between the stylus and the surface. Small cone angles of the stylus will
result in no vertical lifting component no matter how much horizontal
force is applied. In addition, dynamic inertial forces are generated in
the vertical direction which may lead to surface damage and erroneous
indication of the surface profile. Therefore, the weight and cone angle

of the stylus should be appropriate for the surface to be traced (l3).

2.3) Evaluation

 

The two types of references used in the stylus type measuring
technique are the true-datum method and the surface-datum method. In
the true-datum method, the reference line is a straight line. In the
surface-datum method, the oscillation of the stylus on the surface occurs
relative to a skid or shoe of certain dimension which as it moves over
the surface, does not necessarily describe a straight line but follows
a second order surface characteristic which depends in part on the
dimensions of the shoe. The difference between the surface and the
second order curve described by the shoe is indicated by the
variation of the trace from a straight line.

Two basic evaluation systems based on mathematics have been
considered as national standards, namely the M (mean line) system and the

E (envelope) system (12).

2.3.1) M system

In this system the deviation of the profile from the mean line is
measured. The mean line is defined by British Standard 1134 as a line
conforming to the prescribed geometrical form of the profile and so
placed that the sum of the squares of the ordinates between it and the
profile is a minimum. A number of roughness values are defined, based on
the M system, which are illustrated in Fig. 1.

a) The peak to valley value, R, is the distance between the upper
and lower reference line L¢ and LH'
b) The center line average Value, Ra, is the arithemetic average

value of the departure of the whole of the profile both above

and below its mean line throughout the prescribed roughness-

10

FIGURE 1. Basic surface measures according to the

M (mean line) system.

ll

 

 

 

 

 

 

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12

width cut off in a plane substantially normal to the surface.

The mathematical expression is:
l i
Ra ‘3 Ifolyldx

c) The root—mean—square value, RMS, is the geometric average value
of the departure of the whole of the profile both above and below
its mean line throughout the prescribed roughness-width cut off,

in a plane substantially normal to the surface. The mathematical

RMS -1’%J§y2dx

n
v

expression is:

The main defect of the M system is the difficulty in determining
the actual position of the mean line. In addition, the M system does
not offer a clear separation of roughness, waviness and error of form.
None of the above single measurements can describe the surface
characteristics completely. In some cases, the center line average

fails to distinguish between two different surface characteristics.

2.3.2) E system

The E system is described in Fig. 2.Two circles with different
radii are rolled across the surface to be evaluated. The center of each
circle produces a curve. The curve generated by the center of the large
circle is called "curve of form". The curve generated by the center of
‘the small circle is called "contacting envelope". Both the "curve of
form" and the "contacting envelope" are displaced in a direction
perpendicular to the geometrical profile to a position where they are

contacting some of the highest peaks in the effective profile which is

13

FIGURE 2. Basic surface measures according to the E

(envelope) system.

14

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15

the actual surface trace. The area between the geometric profile and
the "curve of form" represents the "error of form", the area between
the "curve of form" and the "contacting envelope" represents the
waviness and the area between the "contacting envelope" and the
effective profile represents the roughness.

The main defect of the E system is that the radii of the discs
chosen for the determination of roughness and waviness are arbitrary.
The advantage of the E system is that it offers a clear and unambiguous
separation of roughness, waviness and error of form.

This ability of the E method to separate the three components of
the surface profile makes it appear very suitable for the treatment of
the problem at hand. It can readily be verified that surface distortions
percieved by the eye as undesirable and detracting are those of relative
short wavelength or period. Distortions of longer wavelength on which
the former may be superimposed do not necessarily affect the value
judgement of the observer. It would, therefore, be desirable to measure
the objectionable deviation of the surface profile from a possibly
percievable but not objectionable trend curve or curve of form. Such
an evaluation could indeed simulate the judgement based on visual
observation.

For these reasons, the E system was employed in the present study.
In addition, several other methods, namely the Average method, Standard
Deviation method and the method which was developed by the author

(Lo method) were also used and are described in the following chapter.

CHAPTER 3

EXPERIMENTAL DESIGN AND PROCEDURE

3.1) Material
3.1.1) Substrate.

Several commercial particleboards which have previously been
described by Suchsland (18) were used as substrates (see Fig. 3 and
Table 1). Of the ten types used in the previous study, three had to be
eliminated because of the following reasons: No. 6 and No. 7 of the
boards used before are flake boards which are not considered to be very
suitable for the application of overlays. Board No. 9 developed steam

blisters in the laminating process and was, therefore, eliminated.

3.1.2) Overlays

Laminating papers were obtained from Resopreg Products, Division

of Pioneer Plastics Corporation.

a) Overlay Sheet:

This paper is a long fibered alpha cellulose paper weighing
20 lbs per 3,000 square feet, saturated with a specially
formulated melamine formaldehyde resin designed for this purpose.
The resin content is 75% by weight.
b) Pattern Sheet:

This is a "saturating grade" alpha cellulose pigmented paper,

16

17

FIGURE 3. Photograph of seven types of substrate.

18

 

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65 lbs basis weight, the resin is the same type of melamine
formaldehyde resin as used in the overlay. Resin content is
40% by weight. The amount of pigment varies from
approximately 10% up to 25% of the weight of the paper prior
to saturation. The pigment is put into the paper in the
original pulping stage prior to forming on the paper machine.

Its function is to provide color and to increase Opacity.

c) Bonding Sheet:

This is a natural kraft paper blending unbleached
hardwood kraft for saturating capability with softwood fiber
for strength and is referred to as a saturating kraft. Basis
weight varies from 97 lbs to 128 lbs. The resin is a phenol

formaldehyde resin. Resin content is 45%.

3.2) Laminating procedure

 

Twelve by twelve inch pieces were cut from each type of
particleboard. Laminating papers having the same size as the
substrate were arranged as shown in Fig. 4. The same construction
was used on both surfaces of substrate. The laminating procedure
followed the recommendations for industrial application. In a
single opening oil heated press, a press cycle of 10 minutes at
2500—290o F and 300 psi pressure was used. Temperature was
measured by themocouple, reading taken at the laminating surface.
The same treatments were used for the laminates without using

bonding sheet and also for the plain substrate of each type. The

21

FIGURE 4. The construction of overlays.

 

22

 

 

 

 

 

 

 

FIGURE 4.
Press at n I
I Gaul Plate I
Overlay.

 

 

 

 

 

 

.Jmtive Sheet

 

 

 

 

, Bonding Sheet optional"

 

 

 

 

 

Bonding Sheet optional

 

 

 

 

Decorative Sheet

 

 

 

 

Overlay

I anl,P1ate

[ Press Platen _I

 

 

.L._.I,

 

 

 

23

treated plain substrates are called compressed substrates. It should
be noted here that the press cycle used caused considerable thickneSs
compression of all specimens except type 1 which has a higher density

than the others (see Table l).

3.3) Exposure cycle

 

All the Specimens were first conditioned at 40% relative humidity
and 700 F (condition 1), and then at 90% relative humidity and 700 F
(condition 2) until they reached equilibrium. Surfaces were measured

at both conditions, at the same locations on the specimen.

3.4) Design of experiment

 

The experimental design is shown in Table 2.

3.5) Visual observation after exposure to high humidity

 

As explained earlier, the judgement of surface equality is
basically a subjective sensation by human's sight and touch. In the
case of a commercial product where appearance is an important property,
visual judgement of surface quality must be recognized as an important
quality control element. Any objective method which correlates well
with visual evaluation results would therefore have important practical
application. 4

Eight individuals were asked to pick the Specimen with superior
surface quality from randomly selected pairs of specimens. They were

instructed to view the specimens at an acute angle. A certain number of

24

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25

such comparative judgements resulted in a ranking of all Specimens based

On the surface quality as percieved by each individual.

3.6) Measuring surface profiles

 

The surface profiles of four groups of specimens were
measured 3 inches along the central line of each specimen with a

Bendix Microcorder (see Fig. 5) at condition 1 and condition 2.

3.6.1) Instrument
This instrument consists of five major units.

a) The tracer:

The tracer translates the surface irregularities into
voltage changes. The tracer has a stylus which follows the
irregularities of the surface. The stylus is attached to
one end of a pivoted beam, the other end being connected to
a transducer which transforms the physical displacement of the
stylus into electrical signals which are fed to the amplimeter.
The movement of the stylus is relative to a shoe. The size

of the shoe is .25 in. in length.

b) The pilotor:

The pilotor drives the tracer over the surface being
tested. The pilotor provides a system for driving the tracer
at a speed of .005 inches per second. The pilotor consists of

a drive screw mechanically driven and a ram that is free to

26

FIGURE 5. The Bendix Microcorder stylus instrument.

 

27

 

.m NMDOHh

 

 

If... .7 °.NI 3.1.. .7 .

28

move in a vertical direction, but is controlled in the horizontal

direction by the motion of the ram,
c) The amplimeter:

The amplimeter amplifies the voltage from the tracer and
feeds the amplified signal to the recorder. The amplimeter is
housed in a portable case and consists of the electronic system.

and a control panel.
d) The recorder:

The recorder draws the amplified profile on a translucent,
reproducible chart. The recorder is contained in a separate
case and features a Horizontal Sensitivity Selection Wheel.

The chart-drive switch is also a paper feed switch to allow
the feeding of paper when the recorder is not drawing a

profile.
e) The linkarm:
The linkarm provides for attaching the tracer to the
pilotor.
3.6.2) The use of the instrument

The selection of the magnification scale is based on the
surface characteristics to be traced. In order to reveal enough
variation of the surface on the chart, it is desirable to keep

both the vertical and horizontal magnification at a maximum.

29

Limitation should be such that the drawing is kept on the chart.
Sometimes, for the convenience of evaluation, a smaller scale of
magnification is chosen to produce a smoother curve. Precaution must

be taken to make sure that the same scales of magnification can be used
at different moisture conditions without exceeding the range of the chart.
The vertical magnification can be chosen from the following: 2.5, 10,

25, 100, 250, 1000, microinches per chart paper division from which 250
was chosen for this study which is a magnification of 1000 times or 4000
microinches full scale. The horizontal selection can be made from the
following: .001, .002, .005, .010, .020, .050 inches per division.

.050 inches per division was selected for this study which is a magnification
of 10 times. The length of the trace was approximately 3 inches.: Fig.
6‘9 Show the original profiles of group C & D specimens at condition

1 and 2.

3.6.3) The reproducibility of measurements

The reproducibility of the profiles produced from two traces over

the same surface is demonstrated in Fig. 10.,

30

FIGURE 6. The original profiles of overlaid substrate without

Bonding Sheet (group C) measured at condition 1.

wit!
III

31

FIGURE 6.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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32

FIGURE 7. The original profiles of overlaid substrate without

Bonding Sheet (group C) measured at condition 2.

33

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34

FIGURE 8. The original profiles of overlaid substrate with

Bonding Sheet (group D) measured at condition 1.

35

FIGURE 8 .

 

 

36

FIGURE 9. The original profiles of overlaid substrate with

Bonding Sheet (group D) measured at condition 2.

37

FIGURE 9 .

 

38

FIGURE 10. The reproducibility of the profiles produced from
two traces over the same surface. I-A and I-B are
plain substrate. lO-A and lO-B are overlaid

substrate.

39

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CHAPTER 4

MATHEMATICAL EVALUATION OF SURFACE PROFILES

The purpose of this evaluation is to find out suitable methods
which correlate well with visual observation. Evaluation of the surface
profiles of group C at condition 2 (see Table 2) is described in the
following. The E system, The Average method, The Standard Deviation
method and The L0 method are used. Group D profiles were not used for
evaluation at this time because the Bonding Sheet reduced the surface
deterioration to a point where the effects of the various substrate

types was greatly obscured.

4.1) E System

The following simple procedure was used for E method analysis
(see Fig. 11).

(a) Transfer original profile to plastic sheet.

(b) Cut with scissors along profile on plastic sheet.

(c) Place large diameter disc (250 mm radius) which is made
from same plastic sheet material in contact with plastic
profile and generate curve of form with pencil through
center of disc.

(d) Place small diameter plastic disc (25 mm radius) in
contact with plastic profile and generate contacting

envelope with pencil through center of disc.

40

41

FIGURE 11. The technique of evaluating E system. The radius
of the large disc is 250 mm. The radius of the
small disc is 25 mm. The length of the plastic

profile is 23 inches.

42

 

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43

(e) Move both generated curves downward without allowing any
lateral slipping until they contact the plastic profile
at at least two points.

(f) The following two areas are now defined and integrated.
with planimeter.

(1) Area between curve of form and contacting envelope.
This is called the waviness of the surface and is
expressed in square centimeters.

(2) Area between contacting envelope and plastic profile.
This is called the roughness of the surface and is
expressed in square centimeters.

(g) The transfer of the original profile to the plastic sheet
did not result in any significant distortions of the

original (see Fig. 12).

4.2) Average method

 

The principle of this method is to pick up points on the
effective profile (original profile) at uniform intervals along the
horizontal base. The vertical distance of these points from the
average value of all points is each point's deviation. The area of
deviation can thus be determined.

As shown in Fig. 13, the intersections between the numerous
parallel vertical lines and the effective profile are the points called
ordinates. The horizontal distance between vertical lines were chosen
to be .5" based on the actual scale. The ordinates (Y values) were

measured from an arbitrary base line (X axis). Forty-seven ordinates

44

FIGURE 12. Comparison of the original profile with the reproduced
profile. I-A is the original profile. I-B is the

profile reproduced from the plastic profile.

45

 

.NH MMDUHh

46

FIGURE 13. Surface measures according to the Average method.

47 A

 

 

 

 

 

 

 

 

 

 

 

 

3?..th N

 

 

 

 

 

 

 

 

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48

were measured throughout the effective profile. The resulting y values
were obtained by subtracting each ordinate value from the average value.

The formula used to calculate the area is as following:

Area (inz) = %f§|y|dx, where dx = .5"
1: length of trace (approx. 3 in.)

The precision of this method depends upon the horizontal interval between

points, the smaller the interval, the better the results.

4.3) Standard Deviation method

 

This method calculates the standard deviation of the ordinates
described in the Average method instead of calculating the area deviation

from the average.

4.4) L0 method

The former two methods, Average method and Standard Deviation
method, use a straight line reference whereas the E method tries to
exclude from analysis a certain acceptable trend line. The advantage of
that technique was discussed earlier. The L0 method is another attempt
to calculate the deviation of the profile from a non-linear compensating
line rather than from a straight line.

The idea of this method is to eliminate the effect of gross
deviation to which the human eye is less sensitive. The means of
removing gross deviation is to construct a mean line of compensation.
The mean line is established by measuring uniform intervals along the

profile with a divider (see Fig. 14). A straight mean line would result

49

FIGURE 14. Surface measures according to the L0 method.

 

 

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51

if the measured surface was flat. The mean line will take the form of a
polygon in the case of a non-flat surface. The elements of the polygon
are called Roughness Intervals. The length of the Roughness Interval is
arbitrary. It should be selected to accent either the roughness or the
gross deviation. The average amplitude and wave length of the profile
are the factors to be considered when determining the Roughness Interval.
In this study, intervals of .5" were marked out on the effective profile
with a divider to fulfill this goal.

The trend of the mean line of compensation goes along with the
profile curve. As the Roughness Interval becomes shorter and shorter
and approaches zero, the mean line of compensation will coincide with
the curve. The characteristic of the curve is thus described by two
things, namely, the length of the mean line of compensation and the
angle between the Roughness Intervals (the angle is measured between the
n th. Roughness Interval and the elongation of the n-I th. Roughness
Interval. The angle measured to the right of the elongation line is
taken as positive, to the left of which is taken as negative). It is
apparent that the longer the mean line and the larger the angle, the
rougher the surface would be. In order to assess roughness, all the
measured angles either positive or negative have to be changed to those
angles based on the base line which is chosen to be the first Roughness
Interval. Positive or negative angles being changed are on either side
of the base line. As shown in Fig. 15, the average of the positive
angles is m. The average of the negative angles is n. A segment of a
circle relationship is established to combine the length of the mean

line of compensation and the average angle between Roughness Intervals.

52

FIGURE 15. A segment of a circle relationship between the mean
line of compensation and the average angle between

roughness intervals.

53

FIGURE 15 .

 

 

average of positive roughness interval angles
average of negative roughness interval angles

the length of the mean line of compensation
roughness factor

 

 

 

54

The length of the mean line of compensation which is R can simply be
measured by adding up Roughness Intervals plus the last one which may
equal to or less than one Roughness Interval. The roughness factor, K,

can be calculated using the following formula:

6

K a 360° ‘

ZflR (in.), m + n = e, K = c + d

If >> I then the profile would have a generally concave character.

If >> I then the profile would have a generally convex character.

ole. ado

CHAPTER 5

STATISTICAL ANALYSIS AND DISCUSSION OF RESULTS

Results of the mathematical evaluation of surface profiles of group C
specimen at condition 2 (see Table 2) are listed in Table 3 which
includes the four evaluation methods described in the previous section.
A transformation of the results shown in Table 3 into qualitative rank
is shown in Table 4. The ranking of the roughness and of the waviness
according to the E system do not quite agree with each other. This
may be due to the different sizes of the disc used to generate the so
defined as roughness and waviness. The Average method and the Standard
Deviation method have the same ranking. The E method (roughness) and
the L0 method have the same ranking also.
The results of eight people's ranking by visual observation are listed
in Table 5. The agreement of these eight ranks was tested by calcul-
ating Kendall's coefficient of agreement~(5).

= 122(5 - §)2

KZN (NZ-I)

W: coefficient of agreement
K: number of observers
N: number of ranks
5: sum of rank numbers for each specimen

5: N+I)K
2

55

56

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57

TABLE 4. Qualitative Ranking of Surface Profiles of Group C Specimen
Measured at Condition 2 Analysed by Several Methods.

 

 

 

 

 

SPECIMEN lON' 4N 8N 1N 2N 5N 3N
Average 1 2 3 4 5 6 7
Method
Standard
Deviation l 2 3 4 5 6 7
Method
Lo Method 1 3 2 4 6 5 7
E Method -
(Roughness) 1 3 2 4 6 5 7

 

 

 

 

 

 

 

 

 

 

*The smaller the number, the higher the ranking.

TABLE 5.

58

Scores of Individual Specimens by Visual Judgement.

 

 

 

 

 

 

 

 

 

 

 

SPECIMEN NO. lON 8N 5N 2N 1N 4N 3N
Rank 1 2 3 4 5 6 7

1 2 3 6 4 5 7

2 1 3 6 4 5 7

1 2 3 6 4 5 7

1 2 3 6 5 4 7

1 2 4 6. 3 5 7

1 2 3 6 5 4 7

1 2 5 6 4 3 7

Sun (5) == 9 15 27 46 34 37 56

 

*
The smaller the number, the higher the rank.

 

59

In this test, K=8, N=7, §=32, the coefficient was found to be .917.

The significance of W was tested as follows:

(K—I)W =
F "7E3?“ 77.34
n = N—I-Z.= 5.75
l K
n2 = (K—I)nl = 40.25

According to the F Table, the test result is significant.' This means
that the ranking by the eight individuals can be considered to be in
agreement. '

The correlation between the visual observation and the various analy-

tical evaluations was determined by using Spearman's formula (5).

2d12
N(N2 - I)

rS = I - 6
r : rank correlation coefficient
Xi: The rank of visual observation
Y1: The rank of E method (or Lo method) or the rank of Average
method (or standard Deviation method).

di: The difference between Xi and Yi'

N : number of ranks

If N < 9, the significance of r is tested according to Table 6. Form
Z(di)2, if smaller than A, the correlation is significant at the
indicated level. In the test between the visual observation and the
E system (or L0 method), rS = .857, di = 8<16, the rank correlation

is significient at the 95 percent level. In the test between the

visual observation and the Average method (or the Standard Deviation

60

TABLE 6. Limit Values for Spearmen Rank Correlation Coefficient.

 

 

95% 0 2 6 16 30

 

 

 

 

 

 

 

 

 

61

method), rS = .643, Edi = 20>l6, the rank correlation is not signifi-
cant at the 95 percent level.

The test results show that the E system is rank correlated with the
visual observation, as is the L0 method. The Average method and the
Standard Deviation method are not correlated with the visual
observation.

The conclusion is both the E system and the L0 method could be
recommended for the evaluation of profiles of the type described in
this article. The E method and the Lo method possess some similar-
ities which were discussed separately in an earlier chapter. However,
the L0 method would be preferable because of greater simplicity and
would introduce less errors if the angles could be measured more
precisely than using a simple device like a protractor.

Table 7 and Table 8 list the surface characteristics of group C and
group D specimens at condition 1 and condition 2 (see Table 2) as
determined separately by the E system and the L0 method. Fig. 16 and
17 and Fig. 18 and 19 are graphical illustration of Table 7. Fig. 20
and 21 are graphical illustration of Table 8. Surface quality may be
indicated by the difference in roughness or waviness before and after
exposure to severe moisture conditions. It is interesting to see
from the graphs that both methods agree that the surface quality of
melamine overlaid particleboard deteriorates much more severely at
extreme exposure conditions when no bonding sheet is used.

In other words, the bonding sheet has the ability to mask the surface
instability of the substrate to a considerable extent. When no

severe exposure conditions are encountered, the use of the bonding

62

TABLE 7. Surface Roughness and waviness of Group C and D Specimen
Measured at Condition 1 and 2 Analysed by the E Method.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CONDITION 1 CONDITION 2
SEESEEEN GROUP
Roughness waviness Roughness waviness
(cmz) (cmz) (cmz) (cmz)
c 9.6 11.3 ~ 16.4 22.8
10
D 7.3 9.6 15.7 29.2
c 11.0 11.6 16.4 21.4
8 D 8.0 11.1 15.8 26.6
c 13.1 17.6 ' 21.6 30.9
4 D 10.8 14.3 13.0 22.4
C 13.4 17.6 21.8 25.7
1 D 11.6 15.2 20.0 26.6
c 12.5 12.3 22.0 30.0
5 D 9.5 10.3‘ 13.0 18.5
c 12.7 14.8 27.1 39.0
2 D 10.2 14.7 14.0 26.3
c 14.4 15.5 54.1 67.6
3 C 12.1 16.2 23.3 30.7

 

 

 

 

 

 

 

 

FIGURE 16.

63

Surface roughness of overlaid substrate without

Bonding Sheet (group C) evaluated at condition 1

and 2 by the E system.

 

 

 

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64

FIGURE 16 .

 

 

 

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Board Type (group C)

FIGURE 17.

65

Surface roughness of overlaid substrate with
Bonding Sheet (group D) evaluated at condition

1 and 2 by the E system.

 

66

FIGURE 17.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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67

FIGURE 18. Surface waviness of overlaid substrate without
Bonding Sheet (group C) evaluated at condition

1 and 2 by the E system.

 

68

FIGURE 18.

 

 

 

 

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[J condition 2

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Board Type (group C)

69

FIGURE 19. Surface waviness of overlaid substrate with
Bonding Sheet (group D) evaluated at condition

1 and 2 by the E system.

70

FIGURE 19.

 

 

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70

condition 2

 

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Board Type (group D)

TABLE 8. Surface Roughness of Group C and D Specimens Measured

71

at Condition 1 and 2 Analyzed by the L0 Method.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CONDITION 1 CONDITION 2
835$? GROUP
Roughness (in.) Roughness (in.)
C 1.087 1.524
10
D .588 1.444
A c 1. 016 1 .617
8 D .662 1.546
C .965 1.873
4 D .724 1.132
C 1.372 2.118
1 D 1.554 1.823
C .908 2.681
5 D .893 1.222
C 1.467 2.923
2 D .883 1.503
C 1.134 4.036
3 D 1.195 2.390

 

 

72

FIGURE 20. Surface roughness of overlaid substrate without
Bonding Sheet (group C) evaluated at condition

1 and 2 by the L0 system.

73

 

FIGURE 20.

 

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L—

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Board Type (group C)

74

FIGURE 21. Surface roughness of overlaid substrate with
Bonding Sheet (group D) evaluated at condition

1 and 2 by the L0 system.

75

FIGURE 21.

 

 

 

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76

Sheet is not justified. Under those conditions, substrates can be
considered as having good surface quality. Comparing Fig. 16 with
Fig. 17, Fig. 18 with Fig. 19 and Fig. 20 with Fig. 21, laminates 10,
8 and 1 do not gain much advantage by using bonding Sheet under
severe exposure conditions. It can therefore be concluded that
substrates 10, 8 and 1 must have good surface quality. Surface
quality is determined by several factors, one of them is the dimen-
sional stability of the substrates. Due to the fact that substrate

1 is the only one not having been compressed down in thickness, it
showed less thickness swelling (see Table 9, group A and B) and a
better quality of the overlaid surface. Substrate 10 and 8 possess
some other properties besides the dimensional stability, which make
them deteriorate even less than substrate 1. Substrate 10 is fiber-
board with fine surfaces. Substrate 8 has very fine particles on

its surfaces.

Table 9 lists thickness, thickness swelling and water absorption of
four groups of specimen exposed to condition 2. When comparing the
thickness swelling of substrate having been compressed (group B) with
those not having been compressed (group A), the former show a greater
thickness swelling than the latter. This can be explained by internal
failures occurring in the compressed particleboard. Substrate l and
its laminates are the only exception. It had not been compressed
significantly during the laminating operation and therefore the
difference between group A and group B in thickness swelling is small.
Table 9 also indicates that overlaid particleboards (group C and D)

swell less than substrates (group B) and absorb less water. This could

77

 

 

 

 

 

 

 

 

 

TABLE 9. Thickness, Thickness Swelling, and Water Absorption
of Four Groups of Specimen Exposed to Condition 2.
THICKNESS THICKNESS MOISTURE
SPECIMEN GROUPS (in) SWELLING (Z) ABSORPTION (%)
A .744 9.0 10.49
10 B .640 17.0 10.56
C .610 13.6 8.00
D .673 11.0 9.26
A .748 11.6 9.46
8 B .656 17.4 10.39
C .689 12.8 8.46
D .673 13.7 9.56
A .755 15.9 10.73
4 B .591 25.0 11.25
C .600 20.2‘ 8.53
D .628 16.1 8.40
A .757 9.6 8.46
1 B .736 10.3 9.15
C .770 6.1 6.90
D .785 4.3 6.15
A .754 15.4 11.51
5 B .654 22.8 11.98
C .685 15.5 9.18
D .681 15.9 9.36
A .744 11.8 9.23
2 B .581 27.0 11.81
C .614 16.8 8.51
D .644 15.2 8.17
A .746 15.5 10.64
3 B .669 23.0 12.04
C .665 19.4 9.25
D .717 13.1 8.58

 

 

 

 

 

 

78

be explained by the reduced water permeability of the overlaid boards
and by some swelling restraint caused by the overlays.

General properties of the seven types of commercial particleboard are

listed in Table l (18).

CHAPTER 6

CONCLUSION

The melamine impregnated paper can improve the surface quality of
the substrate by restraining the thickness swelling, masking imperfections
and providing a smooth surface. On the other hand the overlay accentuates
small imperfections because of its high gloss.

Both the E system and the L0 method are used in this test to evaluate
effective profiles of melamine overlaid particleboard, because both have
good correlation with visual observation which is considered a good indi-
cator of surface quality. The E system provides a clear separation of
roughness, waviness and error of form, while the Lo method eliminates the
effect of gross deviation by constructing a non-linear compensating line.
The determination of the radii of the discs in the E system and the
length of the roughness interval in the L0 method should be studied
further.

The results of the evaluation based on the E system and the Lo
method reveal that surface characteristics of overlaid board are greatly
affected by the substrate. Those laminates with bonding sheet have better
surface quality than those without bonding sheet only under severe
moisture conditions. Substrates with good surface quality need no bonding
sheet to add to the cost instead of improving surface quality. Under this
interpretation, substrate 10, 8 and l are considered as having good surface

quality.

79

80

The melamine overlay can only be applied to substrates having,
densities higher than 45 pounds. Otherwise, the long press cycle will
cause compression of the substrate resulting in internal failures, and

excessive thickness swelling.

REFERENC ES

10.

ll.

12.

13.

14.

REFERENCES

Brown, I.D. 1960. Visual and Tactual Judgements of Surface
Roughness. Ergonomics 3(1):31—61.

Bryan, J.B. 1963. Measuring Surface Finish, Mech. Eng., Dec.,
43-46.

Ehlers, W. 1958. Uber die Bestimmung der Gute Von Holzoberflachen
Holz als Rohund Werkstoff l6(2):49-60.

Elmendorf, A. and T. W. Vaughan. 1958. Survey of Methods of
Measuring Smoothness of Wood. For. Prod. J. l3(10):275-282.

Graf, U. and H.J. Henning. 1952. Statistische Methoden Bei
Textilen Untersuchungen. Springer-verlag, Berlin.

Hann, R.A. 1957. A Method of Quantitative Topographic Analysis of
Wood Surfaces. For. Prod. J. 7(12):448-452.

Heebink, B.G. 1955. Some Potentialities of Overlaid Lumber. For.
Prod. J. April 97-101.

Heebink, B.G. 1960. Showethrough of Particleboard Cores. For.
Prod. J. 10(8):379-388. '

Marchessault and Skaar. 1967. Surfaces and Coatings Related to
Paper and Wood. First Edition, part 3, chapter 15. C.E. Roger,
Polymer Films as Coatings. 463-489.

Marian, J.E. and O. Suchsland. 1956. waviness of Lumber and
Chipcore Board. Paperi ju Puu 38(6/7):291-302.

Mottet, A.L. 1963. Roll Gluing of Exterior Overlay. For. Prod. J.
5:175.

Olsen, K.V. 1961. On the Standardization of Surface Roughness
Measurements. Bruel and Kjaer Tech. Rev. (B & K Instruments,
Inc.) Copenhagan, Denmark No. 3, 3-32.

Peter, C.C. and J.D. Cumming. 1970. Measuring Wood Surface
Smoothness: a review. For. Prod. J. 20(12):40-43.

Reason, R.E. 1960. Orderly Progress in Surface Measurement.
Engineering 12, February 230-231.

81

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l7.

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82

Rubert, M.P. 1959. Confusion in Measuring Surface Roughness.
Engineering, October 23, 393—395.

Stensrud, R.K. and J.W. Nelson. 1965. The Important of Overlay to
the Forest Products Industry. For. Prod. J. 5:203.

Stumbo, D.A. 1963. Surface Texture Measurement Methods. For.

Suchsland, Otto. 1973. Hygroscopic Thickness Swelling and Related
Properties of Selected Commercial Particleboards. For. Prod. J.
July 26—30.

United States of America Standards Institute, Asa B46. 1-1962.
Surface Roughness, Waviness and Lay. Pub. The American Society
of Mechanical Engineers.

Wenzel, R.N. 1949. Surface Roughness and Contact Angle J. of
Physical and Colloid Chem. 53, 1466-1467.

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