NBSIR 80-2091

Precision Measurements on

Fibrous Glass Insulation

B. Branthover

R. Veale

Automated Production Technology Division

National Bureau of Standards

U.S. Department of Commerce

Washington, DC 20234

Building Thermal and Service Systems Division

National Bureau of Standards

U.S. Department of Commerce

Washington, DC 20234

November 1980

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

C. Siu

NBSIR 80-2091

PRECISION MEASUREMENTS ON

FIBROUS GLASS INSULATION

B. Branthover

R. Veale

Automated Production Technology Division

National Bureau of Standards

U.S. Department of Commerce

Washington, DC 20234

C. Siu

Building Thermal and Service Systems Division

National Bureau of Standards

U.S. Department of Commerce

Washington, DC 20234

November 1980

U.S. DEPARTMENT OF COMMERCE, Philip M. Klutznick, Secretary

Jordan J. Baruch, Assistant Secretary for Productivity. Technology, and Innovation

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Director
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CONTENTS

Page

1. Introduction 1

2. Material 2

2.1 Repeatability 3

2.2 Thickness Profile Procedure 3

3. Force Determination 4

3.1 Procedure 4

3.2 Graphs 4

3.3 Different Density Materials 5

3.4 Deformation Under Extreme Loads 5

4. Actual Thickness Profiles 6

5. Stacking 6

6. Concluding Remarks 7

Tables 1 and 2 8

Table 3 9 & 10

Appendix - Conversion Table 11

Figure 1 12

Figure 2a 13

Figure 2b 14

Figure 2c 15

Figure 3 16

Figure 4a 17

Figure 4b 18

Figure 4c 19
Figure 5a

Figure 5b

Figure 5c

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Page

20

21

22

23

24

25

26

27

28

29

30

References 31
PRECISION MEASUREMENTS ON FIBROUS GLASS INSULATION

by

Brian Branthover and Ralph Veale

ABSTRACT

This paper is concerned with the technique in measuring the thickness

of low density fibrous glass materials. The results will aid in the

development of a Standard Reference Material for thermal resistance measurement systems.

1. INTRODUCTION

The recent emphasis on energy efficient homes and offices has inspired much

research in the field of fibrous glass insulation. However, the persistent

question still exists as to how much to use. Manufacturers want to maximize the

thermal resistance of their product and at the same time use a minimum amount of

materials. Thus, a standard thickness measurement procedure must be established

to insure uniformity in production. Using the thickness data, one can more

precisely determine the thermal conductivity. Recently, the Building Thermal

and Service Systems Division of NBS undertook the task to develop low density

fibrous glass as a Standard Reference Material (SRM) for thermal resistance

measurement systems. They requested the assistance of the Dimensional Metrology

Group in developing a measuring technique and determining the thickness of

several samples.

Proper characterization of fibrous glass material as an SRM requires

information as to its thermal resistance, R, and factors affecting R. Not only

are the factors in question important but also how the information for each was

obtained. The thickness of a sample of fibrous glass prior to mounting in a thermal resistance system is one such important parameter in SRM characterization. The existing method for determining the thickness (ASTM C167)^ does not

possess the accuracy required by NBS for SRM. Since the force had been left

undefined, it became necessary to discuss an alternate technique. This report

briefly describes a procedure for measuring the thickness of low density fibrous

glass material. The application of this technique will aid in developing an

SRM.
2. MATERIAL

The low density fibrous glass material selected for development as an SRM was obtained from a domestic manufacturer* who provided the following brief

description of the process of fabrication:

"The glass melt is fed into perforated rotors. As the rotors spin at a very high velocity, the glass is extruded through the perforations into

primary fibers. The fibers are further attenuated into very fine fibers by

application of high temperature jets of gas in combustion. A solution of

phenolic resin and water is applied to the fibers before they are collected

on a moving chain conveyor. This conveyor carries the mat of glass fibers

and uncured resin into a curing oven. The cured blanket is then sliced and

cut into the required dimensions. The density of the final product is

controlled by the speed of the conveyor and the degree of compression

during the cure. To provide the most desirable characteristics, the material selected for this program was cut from the central part of the total

blanket. The outer skins were discarded."

These were screened for homogeneity and five hundred (500) samples,

24" X 24" X 1 1/4", were sent to NBS. Table 1 summarizes some of the information provided by the manufacturer. Ten samples were randomly selected from the

lot of 500 for characterization.

The first thing which had to be established for this type of measurement

was what procedure to follow. It must be uniform and precise, and easily re- constructed in another laboratory. The process which was used throughout this

project was that which made use of an LVDT (linear variable differential transformer) indicator and a height gage. However, in order to properly use the

indicator a smooth hard surface must be in contact with the probe. Also, a constant force must be applied for each measurement. All measurements were made

in an environmentally controlled laboratory in which the temperature was

20® + .5°C and the relative humidity was between 30 and 40 percent.

To meet these two prerequisites (smooth hard surface. and constant force),

ten aluminum discs varying in weight from 1/2 to 8 ounces were made (2 each of

1/2, 1, 2, 4 and 8 ounces. Each disc was three inches in diameter and each

differed in height according to its weight (see Table 2). The discs represented

numerous loads which could be applied to the surface of a sample. The discs

also solved the problem of a smooth surface necessary for the indicator. The

indicator, when set to zero, exerts a force of .107 ounce; therefore, the total

force is 0.1 ounce greater than the weight of the discs.

*Material by Johns-Manville Corp.**

**Certain commercial equipment, instruments, or materials are identified in this

paper in order to adequately specify the experimental procedure. In no case

does such identification imply recommendation or endorsement by the National

Bureau of Standards, nor does it imply that the material or equipment identified

is necessarily the best available for the purpose.

^Conversion to SI Units are given in the Appendix.

2
A small circle was marked on each disc. Each disc was measured at this

spot for its thickness to an accuracy of + .0001 inch (see Table 2). The precision needed for this measurement demanded that a specific area be marked off

so that readings would be taken at a constant location. This would eliminate

any trouble encountered due to thickness variation of any one disc.

2.1 Repeatability

Before any meaningful measurements could be taken it was necessary to

determine the repeatability of the measurement system. A disc was placed on a test sample so that it was not too close to the edge where it would tip or slant

toward the side. The 2 ounce disc was used for a series of twenty readings at

that one spot. (The 2 ounce disc was arbitrarily chosen for these measurements.)

The disc was placed on the sample and then the indicator probe brought down on top of the disc. The probe was then centered inside the marked area which had

been previously measured for its thickness. The meter was then zeroed. The

probe was moved away to allow the disc to be raised. The disc was then placed

back on the fiber glass at the same point. The probe was brought back on the

mark and a reading was again taken noting any variation from zero. A total of

twenty readings were taken. The standard deviation of a single reading was

0.0002 inch which indicated the system was capable of measuring the fiberglass

to the desired +0.001 inch accuracy.

2.2 Thickness Profile Procedure

In order to have an accurate picture as to the thickness of each test

piece, a good profile must be made for each. To do this, enough points must be

taken into consideration. It was agreed that twenty-five locations would be

sufficient. Five readings were taken at each of the twenty-five spots using the

method described above. During all thickness profile measurements, the height

gauge and the indicator were used to produce true thickness values.

Since the test samples were nominally 24” x 24", a grid system was set up as shown in figure 1 to aid in uniformity of measurements. The readings were

taken at the twenty-five intersecting points and the identification number was

placed at the top left above the origin as shown in figure' 1. A co-ordinate

system (i,j) was formed: point A corresponds to (1,1), point B to (4,3), etc.

By using the two devices mentioned, the actual thickness of each piece was

measured. One disc was used for preliminary profile measurements. However,

through hypothesis and further data analysis, we concluded that two discs should

be used for the measurement, i.e. one on top and one on the bottom. The disc on top would be directly above the one below for each reading. The reason for two

discs is to cut down the error introduced by the variability of the test sample.

The two discs would allow a measurement to be made between two flat and parallel

three-inch contacts. This should make for a more accurate measurement since one disc does not take into account any undulations in the contour of the underside

of the test piece. The lateral dilation caused by stretching the material over

the bottom 3 inch disc could possibly cause measurement errors exceeding the

desired 0.001 inch accuracy; therefore, to counteract the imbalance, cork board,

slightly lower than the height of the disc, was inserted beneath the fiber glass

3
sample. The cork board simply acted as a surface for the test piece to rest on and had no effect on the desired compression of the test piece. From that point

on all thickness profile measurements were conducted with two dies.

Before further measurements were made, it was suggested that flipping the

test sample might make a difference. Through several series of observations it was concluded that flipping had a very small affect on the thickness and thus it was not necessary to measure the samples both top up and bottom up.

3. FORCE DETERMINATION

3.1 Procedure

Up to this point, little has been said about what force should be used,

only about different forces available. The question of force must be dealt with

so that a standard testing procedure may be established.

Taking a fiber glass piece (.8 Ib/ft^) with an approximate known profile,

three points were selected such that none were high or low contour areas. At

the first point, each of the five weights, (.5, 1, 2, 4, and 8 ounces) in that

order, was placed there and a thickness measurement was taken. Then at that same location, the preceding procedure was repeated, but this time the order of

the weights was reversed (8, 4, 2, 1, and .5 ounces). Similar data was taken at

the other two points.

3.2 Graphs

Referring to Figures 2a, 2b, and 2c, (one for each of the three selected

points,) it is seen that the thickness dependence upon weight curves act as would be expected-greater thicknesses for lighter weights and smaller thickness

for heavier weights. However, a difference between the thicknesses for increasing weights (forward direction) and that for decreasing weight (reverse

direction) is evident. The average difference for the three figures was approximately .006 inch. An explanation for this might be that permanent deformation

was caused by the heavier weights. This suggests that the 4 & 8 ounce weights

might have caused the difference. The experimental verification of this hypothesis will be discussed later in this paper.

Before discussing permanent deformations under heavy loads consider the

material behavior under the lighter discs. Looking at the .5 ounce disc plotted

value on the curve, there seems to be a turning point where the curve starts to

level off. The desire for more information at a lighter weight required a 0.25 ounce disc. The data taken from measurements using this new disc was plotted on each of the three graphs. Through examination of the data and by

looking at the interface of the sample and the disc using an optical projector,

we concluded that the lighter discs were resting on the peaks of surface irregularities. Figure 3 is a picture of the surface of the sample, magnified 20

times. The measurement values obtained from these weights reflected the amount

of irregularities present and not the actual thickness of the test piece. From

these observations the 0.25 and 0.5 ounce discs are too light for the purpose

4

k
desired. Also, 4 ounces & 8 ounces would be too heavy because of deformation.

Therefore, the 1 or 2 ounce discs were appropriate selections for the force to

be used for standard measurements. The two ounce disc was arbitrarily chosen to

be the one we would use. Coupled with the probe force this made a measuring

force of 2.1 ounces.

3.3 Different Density Materials

Force graphs were also constructed using data taken from two different

nominal bulk densities (1.0 Ib/ft^ and 0.5 Ib/ft^). The graphs for the 1.0 Ib/ft^

material (Figures 4a, 4b and 4c) were similar to the graphs for the 0.8 Ib/ft^

except the thickness values were somewhat larger. This was probably because a more rigid material was being used. The graphs for the 0.5 Ib/ft^ material

(Figures 5a, 5b and 5c) are somewhat different from the other two graphs.

Because the material was lighter, an increasing load drastically changed thickness readings, and the leveling off found on the graphs for the other two densities

is not present. Therefore, it should be noted that when working with lower

density materials, a lighter weight probably will be necessary to avoid possible

permanent deformation.

3.4 Deformation Under Extreme Loads

As the load is increased, deformation is more likely to occur. Such is the case for all materials, but especially when working with such a non-rigid test

material as fiber glass. It has already been shown that deformation is evident

when only a four ounce weight was used. We were interested in determining the

extent of the deformation at heavier loads and if the deformation was permanent.

test proceeded as follows:

1) place the 4 ounce disc at

thickness measurement.

arbitrary point (x,y) and take

2) place the 8 ounce disc at (x,y) and take reading.

3) repeat (2).

4) repeat (1)

.

The series of measurements took 20 minutes. The difference between (1) & (4) was the short-term permanent deformation caused by the heavier weight in (2) & (3). This test kept 4 ounces as a base weight for steps (1) & (4), but varied

the heavier weight in increments of 4 ounces. Looking at the graph (see Figure 6),

the points are positioned such that the force was plotted vs. the observed

deformation (l)-(4). From the graph and its data table, one notes the steady

increase in deformation, also the steep rise as the force increased from 16 to

20 ounces and from 32 to 36 ounces. The value obtained for the 8 ounce force is

almost exactly that obtained from the force curve of the .8 Ib/ft^ density when

comparing the difference between cycles. Because of the short time intervals

between steps (1) and (4) for each weight, a recheck of the data was done to see

5
if the test piece regained any of its original thickness. After a two week

period, test results on one piece showed a slight increase in thickness; however,

not enough data was taken to make the measurements statistically meaningful.

4. ACTUAL THICKNESS PROFILES

In section 2, the thickness measurements procedure was outlined. However,

it failed to specify any exact force to be used as a standard. Making use of

the force data accumulated, we chose the two ounce disc as the standard (total

force = 2.1 ounces). With all preliminary tests completed, we then measured

seven samples of fiber glass nominally 0.8 Ib/ft^ (see Figures 7-13). The

nonuniformity in thickness is clearly shown in these figures. Differences in

thickness for a given specimen may be as large as 0.150 inch over the entire

24" X 24" piece and 0.080 inch over the central 8 inch square.

5. STACKING

The test samples were nominally 11/4 inches thick. For certain thermal

resistance measurements it may be necessary to use a thicker piece, or a combination

of pieces. In order to meet such a demand, a stacking measurement was carried

out. Various combinations of pieces allowed measurements to be made on two to seven pieces stacked on top of each other. The procedure was the same as for

regular profile determination. Of the twenty-five locations only five randomly

selected points were chosen for measurement. The purpose of this was to see what the relationship between the stacked value and the sum of the individual

pieces. There were 4 possible outcomes:

I

I

1)

The total thickness would be equal to the sum of individual thicknesses,

2)

surface undulations and irregularities would cause a large positive

(+) difference.

3)

as more samples were stacked a larger negative (-) difference may be

present because the bottom pieces were being crushed.

4 ) a combination of 2 and 3 would leave little difference.

It was hoped that case 1 would be the outcome, but that was not so. Noting

Table 3 the difference between the stacked and the individual sums was about

+0.053 inch for each interface of fiberglass-on-fiberglass; i.e., two stacked

pieces gave one interface, three pieces gave two interfaces, etc. A large

positive number was present and thus supported case 2. But as more and more

pieces were stacked case 3 came into play (bottom pieces crushed) since the

difference per interface dips to about 0.047 inch. Thus, the results of this

test dictate the need for a correction to be introduced when stacking the pieces.

6
6. CONCLUDING REMARKS

Measurements of the thickness of low density fiber glass can be made with

precision and accuracy at selected locations. For thickness measurements,

applied pressures between .009 Ibin^ and .018 Ib/in^ are considered adequate.

Errors, especially with very low density material, are introduced when applied

pressures are below .009 Ib/in^. Pressures much greater than .018 Ib/in^ may

result in deformation of the material.

Results of measurements show a nonuniformity in thickness over a given

specimen. The variation in thickness is large enough to require that measurements be made at several locations of the specimen.

7
Table 1 - Summary - Manufacturer's Data on Low Density Fibrous

Glass Samples Under Development as an SRM.

Density 0.8 + 0.1 kg/m^

Fiber Diameter

Micronaire^ 4.5 ym(7.2%)*; 4.1 ym (5.0%)

Optical Count

Average 5. 7 ym 5.0 ym

Range 1.6-12.4 ym 1.5-11.7 ym

Standard

Deviation 2.4 2.4

*Flgure in parenthesis

material.

is percentage phenolic resin binder

Table 2 - Thickness and Weight of Aluminum Discs

Weight Thickness

(ounces) (inches)

0.25 0.0202

0.50 0.0420

1.00 0.0880

2.00(a)

2.00(b)

0.1763

0.1759

4.00 0.3540

8.00 0.7060
Table 3 - Thickness Values of Stacked Samples

Number of

Pieces

2

3

4

Summation of

Location Stack Sum Individual Pieces Difference

(inches) (inches) (inches)

(1,1) 2.351 2.300 0.051

(2,2) 2.331 2.288 0.043

(2,4) 2.321 2.286 0.045

(4,2) 2.341 2.269 0.078

(4,4) 2.318 2.257 0.061

Mean 0.055

(1,1) 3.455 3.366 0.089

(2,2) 3.542 3.449 0.093

(2,4) 3.488 3.401 0.087

(4,2) 3.598 3.480 0.118

(4,4) 3.532 3.415 0.117

Mean 0.101

Mean/Number of Interfaces 0.050

(1,1) 4.696 4.413 0.203

(2,2) 4.766 4.608 0.158

(2,4) 4.737 4.577 0.160

(4,2) 4.774 4. 641 0.133

(4,4) 4.767 4.602 0.165

Mean 0.164

Mean/Number of Interfaces 0.054

(1,1) 5.960 5.663 0.297

(2,2) 6.000 5.818 0.182

(2,4) 5.988 5.775 0.213

(4,2) 5.999 5.830 0.169

(4,4) 5.986 5.781 0.205

Mean 0.213

Mean /Number of Interfaces 0.053

(continued)

9
Table 3 - (Continued) page 2

Number of Summation of

Pieces Location Stack Sum Individual Pieces Difference

(inches) (inches) (inches)

(1,1) 7.118 6.813 0.305

(2,2) 7.174 6.966 0.208

(2,4) 7.165 6.925 0.240

(4,2) 7.207 6.995 0.212

(4,4) 7.194 6.954 0.240

Mean 0.241

Mean/Number of Interfaces 0.048

(1,1) 8.283 7.951 0.332

(2,2) 8.332 8.079 0.253

(2,4) 8.345 8.057 0.288

(4,2) 8.379 8.130 0.249

(4,4) 8.394 8.132 0.262

Mean 0.277

Mean/Number of Interfaces 0.046

10
Appendix - Conversion Table

To convert to multiply by

inch cm 2.54

-2

oz kg 2.834952 x 10

lb/ft3 kg/m^ 1.601846 X 10

11
FIGURE 1 - GRID SYSTEfl SHOWING HEASUREHENT POSITIONS

12
13

Figure

2a

-

Variation

of

Specimen

(nominal

0.8

Ib/ft^)

Thickness

with

Applied

Load.
S3H3NI5 SS3N>l3IHi

Figure

2b

-

Variation

of

Specimen

(nominal

0.8

Ib/ft^)

Thickness

with

Applied

Load.
S3H3NI> SS3N>l3IHi

15

Figure

2c

-

Variation

of

Specimen

(nominal

0.8

Ib/ft^)

Thickness

with

Applied

Load.
Figure 3 - Picture illustrating the surface irregularities present on each

fiber glass test sample. (20X magnification).

16
CS3H0Ni:> SS3N>I3IH1

17

Figure

4a

-

Variation

of

Specimen

(nominal

1.0

Ib/ft^)

Thickness

with

Applied

Load.
CS3H3Ni:> SS3N>l3IHi

18

WEIGHT

COUNCES>
CS3H0NI> SS3N>l3IHi

WEIGHT

COUNCES!)
.25

-r ®

CS3H3NI> SS3N>I3IH1

20

Figure

5a

-

Variation

of

Specimen

(nominal

0.5

Ib/ft^)

Thickness

with

Applied

Load.

CS3H3NI:) SS3N>l3IHi

22

Figure

5c

-

Variation

of

Specimen

(nominal

0.5

Ib/ft^)

Thickness

with

Applied

Load.
Force (ounces)

Figure 6 - Change in fiber glass thickness after application of a large load.

Measurement using a four ounce force was used as reference.

(0.8 Ib/ft^ sample)

23
FIGURE 7 - THICKNESS PROFILE OF FIBER GLASS SPECIMEN NUMBER 813A1

(FOR ACTUAL THICKNESS ADD 1 INCH TO EACH NUMBER)

24
FIGURE 8 - THICKNESS PROFILE OF FIBER GLASS SPECI’IEN NUflEER 818A3

(FOR ACTUAL THICKNESS ADD 1 INCH TO EACH NUfIBER)
FIGURE 9 - THICKNESS PROFILE OF FIBER GLASS SPECIHEN NUfiBER 82251

(FOR ACTUAL THICKNESS ADD 1 INCH TO EACH NUMBER)

26
FIGURE 10 - THICKNESS PROFILE OF FIBER GLASS SPECIMEN NUMBER 8A018

(FOR ACTUAL THICKNESS ADD 1 INCH TO EACH NUMBER)

27
FIGURE 11 - THICKNESS PROFILE OF FIBER GLASS SPECIflEN NUMBER 8AAA2

(FOR ACTUAL THICKNESS ADD 1 INCH TO EACH NUMBER)

28
FIGURE 12 - THICKNESS PROFILE OF FIBER GLASS SPEClflEN NUMBER 8A612

(FOR ACTUAL THICKNESS ADD 1 INCH TO EACH NUMBER)

29
FIGURE 13 - THICKNESS PROFILE OF FIBER GLASS SPECIflEN HUflBER 86218

(ACTUAL THICKNESS ADD 1 INCH TO EACH NU(IBER)

30
REFERENCES

1) American Society for Testing and Materials, Thickness and Density

of Blanket or Batt-Type Thermal Insulating Materials , ANSI/ASTM

C167-64. Philadelphia; American Society for Testing and Materials,

1967.

2) American Society for Testing and Materials, Measuring Compressive

Properties of Thermal Insulations , ANSI/ASTM C165-77. Philadelphia:

American Society for Testing and Materials, 1977.

31

NBS>114A (REV. 0-78)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 80-2091

2.Gov’l. Acccssi(jn No. $. Recipient's Accession No.

4. TITLE AND SUBTITLE

PRECISION MEASUREMENTS ON FIBROUS GLASS INSULATION

5. PuDiicaiion Date November 1980

6. Performing Organization Code

7. AUTHOR(S)

B. Branthover, R. Veale, and C. Siu

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AiND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

10, Project/Task./Work Unit No.

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS fSfreer. City, st^te, ziP) 13. Type of Report & Period Covered

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 200~word or less factual summary of most significant information. If document includes a significant bibliography or

literature survey, mention it here.)

This paper is concerned with the technique in measuring the thickness of low

density fibrous glass materials. The new method of measurement described provides

a higher degree of accuracy than previously accomplished. The new procedure

determined a specific force to be used for measuring. Also, a stacking technique

was carried out to see what effect placing a number of test samples on top of each

other would be. The results of the entire testing will -aid in the development of a

standard reference material to be used for thermal resistance measurement systems.

17, KEY WORDS (six to twelve entries; alphabetical order; capi talize only the first letter of the first key word unless a proper name;

separated by semicolons)

Fiber-glass; fibrous glass; insulation; measurement; R value; standard reference

material; thermal resistance

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