THE Bureau Standards...thisleatherwasused,sothat,whensplit,eachsinglebackcould be given its special finishing treatment andwhen tests were made theleather of …

DEPARTMENT OF COMMERCE

Technologic PapersOF THE

Bureau of StandardsS. W. STRATTON, Director

No. 160EFFECTS OF OILS, GREASES, AND DEGREE OF

TANNAGE ON THE PHYSICAL PROPERTIESOF RUSSET HARNESS LEATHER

BY

R. C. BOWKER, Assistant Mechanical Engineer

Bureau of Standards

in cooperation with

J. B. CHURCHILL, Director

American Leather Research Laboratory

April 17,1920

PRICE, 5 CENTS

Sold only by the Superintendent of Documents, Government Printing Office

Washington, D. C.

WASHINGTONGOVERNMENT PRINTING OFFICE

1920

EFFECTS OF OILS, GREASES, AND DEGREE OF TAN-NAGE ON THE PHYSICAL PROPERTIES OF RUSSETHARNESS LEATHER

By R. C. Bowker and J. B. Churchill

CONTENTSPage

I. Introduction 3

II. Methods 41. Selection of the leather 4

(a) Description of the leather selected 4

(b) Preparation of samples 6

2. Physical tests 7

(a) Tensile strength 7

(b) Stretch 7

(c) Buckle strength 8

3. Chemical tests 8

(a) Stuffing content 8

(b) Complete analysis 8

III. Data and results obtained 9

1. Physical tests 9

(a) Tensile strength 9

(b) Stretch 12

(c) Buckle strength 13

2. Chemical tests 14

(a) Stuffing content 14

(b) Complete analysis 15

3. Comparison of physical and chemical tests 16

(a) Effect of the amount of stuffing content on the physical

properties 16

(b) Effect of the degree of tannage on the physical properties. . 17

(c) Effect of animal and mineral oils on the physical properties

.

18

IV. Conclusions 18

I. INTRODUCTION

During the war physical and chemical tests of the equipment

leather purchased by the War Department were made at the

Bureau for the purpose of controlling the quality of the leather

furnished by the various tanneries. An opportunity was thus

offered for a study of the variations in the physical properties

and in the chemical constituents of many kinds of leather. Onaccount of the large quantities used the values of the various

3

4 Technologic Papers of the Bureau of Standards

properties for both russet and black harness leathers were of special

interest. Russet harness leather is not a regular commercial

product in this country and finds little use except for military

purposes. Black harness leather, however, is a regular commer-cial product and is widely used. Besides the difference in color,

there are three distinct differences between these two leathers

caused by the process of manufacture. The first of these differ-

ences occurs in the length of the tanning operation. It is general

practice to give hides for black harness leather a short-time

tannage, while those for russet harness leather are tanned for a

longer time. The average degree of tannage as determined from

the chemical analyses of black and russet harness leathers madeduring the war were 46 and 61, respectively. The second point

of difference between these two kinds of leather is shown by the

amount of stuffing used. The average amounts found in the

above-mentioned black and russet leathers were 29.3 and 15.5,

respectively. The third difference is caused by the general prac-

tice of adding to black harness leather small amounts of such filling

materials as glucose and salts. This procedure is not generally

followed in the case of russet harness leather. A better selection

of hides is generally used for the latter leather, since the coloring

of black harness readily conceals many surface imperfections

which do not affect the quality. In order to study more definitely

the effects of the amount and kind of stuffing content and also the

degree of tannage on the physical properties of harness leather,

this investigation was made.

II. METHODS1. SELECTION OF THE LEATHER

Russet harness leather was used in this investigation. Three

hides were prepared, marked butt Nos. 1,2, and 3, to study the

effects of different amounts of stuffing content, of animal and

mineral oils, and of medium and heavy tannage, respectively, on

the physical properties.

The method of using whole hides or double backs in preparing

this leather was used, so that, when split, each single back could

be given its special finishing treatment and when tests were madethe leather of the two sides compared would come from the same

hide. Each side was given a code letter.

(a) Description oe the Leather Selected.—The hides from

which the leather was produced were treated in the usual manner,

Harness Leather 5

which consisted of soaking, fleshing, liming, unhairing, handling,

and then laying away in the yard. The tanning materials used

were liquors made from chestnut-oak bark, chestnut wood, and

quebracho. After the tanning was completed the hides were

split, shaved, scoured, and bleached with a solution of soda and

water, sulphuric acid and water, and sumac and water. Theleather was then stuffed and later oiled. The finishing was done

by hand.

Butt No. 1.—This hide received the regular tannage for this type

of leather and, after being split, one side (B) was stuffed with a

mixture of cod oil and tallow, using the amount ordinarily used

in the particular tannery where the leather was made. The other

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Fig . 1.—L~)ivisior, of a side into blocks

side (A) was stuffed with a larger amount of the mixture, equal

approximately to that used by some tanners of black harness

leather. These two sides were used to study the effects of different

amounts of stuffing content on the physical properties.

Butt No. 2.—The leather produced by this hide was used to

study the effects of a medium and heavy tannage on the physical

properties. The hide, after receiving the regular tanning treat-

ment, was split and one side (C) removed, while the other side

(D) was allowed to remain in the vats a month longer in order to

receive a heavier tannage.

Butt No. j.—This hide, after being tanned as regular russet

harness leather, was split and one side (E) was stuffed with a

mixture of 50 per cent cod oil and 50 per cent tallow. The other

side (F) was stuffed with a mixture of 50 per cent Breton mineral

oil and 50 per cent tallow. This leather was prepared to deter-

mine, if possible, the effects of the use of mineral and animal oils

on the physical properties of leather.


(6) Preparation of Samples.—Each side of leather was di-

vided into 40 blocks, as shown in Fig. 1 , beginning at the butt end,

near the root of the tail, with block No. 1 and running across the

hide from back to belly. The blocks running from the butt end

to the shoulder end were numbered in steps of four. The size of

each block was approximately 8 inches in length and 7 inches in

width. Each was divided into samples for the various tests, as

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Fig. 2.

—

Division of a block into samplesfor the different tests

shown in Fig. 2. Three samples from each block, designated byTiy T2, and T3, were prepared for the tensile strength and elon-

gation tests, and three samples, designated by Bi, B2, and Bj,

were used for the buckle tests. That part of each block used for

the chemical tests is designated by the letter C. Each sample

cut from any block carried the code letter of the bend, the numberof the block, and the letter representing the test for which the

sample was to be used.

Harness Leather

2. PHYSICAL TESTS

The physical tests generally made on samples of harness leather

for determining the quality are for tensile strength and percentage

elongation. In addition, a buckle or shearing test was made.

(a) Tensile Strength.—This is the test most commonly made,

the results being expressed in pounds per square inch. Test

pieces were cut with a metal die from each individual strip. Theshape and size of the resulting sample are shown in Fig. 3. Theends are enlarged and the central portion is reduced to a wMthof one-half inch over a gage length of 2 inches. This shape usually

insures that the sample will break within the reduced section and

prevents tearing in the grips of the testing machine. The break-

ing strength, in pounds, of each sample was determined with a

tension machine the jaws of which separated at a rate of approx-

FiG. 3.

—

Shape and size of tensile strength specimens

imately 6 inches per minute. With this value and the area, as

determined by the width and thickness of the reduced section, the

tensile strength in pounds per square inch was calculated.

The breaking strength, in pounds per inch of width, was also

determined. There were three values for each of these properties

for each block and an average of the three for each property was

used as representing the value for the particular location on the

side indicated by the block number.

(6) Stretch.—The stretch, or percentage elongation, of each

tension test piece was determined at the breaking strength. Themethod consisted of first marking on the reduced section parallel

lines 2 inches apart. A convenient method of noting the stretch,

used in this test, consisted of following the parallel lines on the

test pieces, as they separated under the tension, with a pair of

dividers. The elongation was then measured with a scale and the

percentage increase calculated. In this case also the average of

three values represented the value for the block.


(c) Buckle Strength.—There are many parts of a harness

which are used in conjunction with a buckle. It is commonknowledge that the failure of a particular strap or part of a har-

ness often occurs at one of the holes through which the tongue

of the buckle passes. It was thought desirable to study the

variation on the hide in the buckle or shearing strength of new

harness leather with the idea in view of showing what portions

of the hide might be most suitable for those straps which are

used with a buckle. Three samples for this test were prepared

from each block, as shown in Fig. 4. A hole of the proper size

for the buckle tongue was punched 1 inch from the end of the

test piece. An ordinary i^-inch harness buckle with a tongue

approximately eighteen-hundredths of an inch in diameter was

secured to a strap which was placed in one jaw of the testing

Fig. 4.

—

Shape and size of buckle strength specimens

machine. The punched end of the test piece was then inserted

in the buckle and the free end secured in the other jaw of the

machine. The number of pounds required to pull the test piece

through the buckle was then noted.

3. CHEMICAL TESTS

(a) Stuffing Content.—It was considered possible that the

variation in the amount of stuffing content over the hide might

have some effect on the physical properties. For this reason,

and also to study the distribution of the stuffing content over the

hide, a chemical determination was made of this property for

each block of each side.

(b) Complete Analysis.—In order to aid in the interpretation

of the physical results, and also to have all the data possible for the

identification of the several sides, a complete chemical analysis

was made of each, using a composite sample prepared by taking

an equal quantity from each block.

Harness Leather 9

III. DATA AND RESULTS OBTAINED

1. PHYSICAL TESTS

(a) Tensile Strength.—The results of the tensile-strength

tests, expressed in pounds per square inch, are shown graphically

in Figs. 5,6, and 7 . Each individual curve of the graphs represents

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Variation of tensile strength in pounds per square inch over the side for samples

A and B

the values obtained from four blocks running from the backbone

edge to the belly edge. The values for the tensile strength, in

pounds per inch of width, are shown graphically in Figs. 8, 9, and

10. For that portion of any side represented by blocks 1 to 28,

inclusive, the strength is generally greater on the backbone edge,

decreasing in value toward a point near the belly edge, beyond

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C and D

which it generally increases to either an equal or greater value

than occurred on the backbone. That portion of the sides repre-

sented by blocks 29 to 40, inclusive, is the shoulder area. The

strength in that part is more irregular than in the other portion,

but has a general tendency to be greater at the backbone edge

162023°—20 2

IO Technologic Papers of the Bureau of Standards

and to decrease steadily to the belly edge. A glance at Figs 8,

9, and 10 will show that the average tensile strength, in pounds

per inch of width, for any given section of four blocks across a

side is generally low at the butt end, increasing in value up to

locations 17 to 20, or about half the length of the side, then de-

creasing in value, ending with the first shoulder section 29 to 32,

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E and F

where it is lowest, and then slightly increasing in value again for

the remaining two sections. This same variation applies to the

values for tensile strength, in pounds per square inch, but is not

so marked, due to the fact that the thickness is variable, which

greatly affects these values. As an illustration, considering

Fig. 5, it appears that there is a large difference between sides Aand B in tensile strength in pounds per square inch. Fig. 8 shows

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Variation of tensile strength in pounds per inch of width over the sidefor samples

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the values of the tensile strength, in pounds per inch of width, for

these two sides, and it will be noted that there is#not such a

marked difference between the values as in the case of Fig. 5.

The difference shown in Fig. 5 is due to the fact that the average

thickness over the side was greater for one than for the other.

Harness Leather ii

Thus, it is conceivable that the products of two different tanners

might have equal strength per inch of width, but due to the

different methods used the thickness of one tanner's leather might

be considerably less or greater than that of the other tanner, and

the results would be that, although the amount of fiber substance

was the same, the tensile strength as expressed in pounds per

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C and D

square inch would be quite different for the two leathers. Thefunctions of the various parts of a harness are to withstand a

definite strain or pull in tension which depends more upon the

strength of the leather per inch of width than upon the strength

per square inch of cross section. One tanner might furnish a

thick leather of the required strength and another a thinner

leather of the same strength. Both would have the same work

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E and F

to do. In view of these facts, it would seem desirable for specifi-

cations to require a strength in pounds per inch of width rather

than in pounds per square inch.

The graphs show that there is a great variation in the strength

in pounds per square inch over the hide, and for this reason it is

difficult to set a standard value. The generally accepted require-

ment has been 4000 pounds per square inch and these tests iustifv


the choice, although in the two butt-end sections of all the sides

the value is somewhat less. The results also show that the strength

of the more open texture, looser, long-fibered belly and shoulder

portions is equal to or greater than the strength of any other

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Fig. ii.—Variation in per cent stretch over the sidefor samples A and B

portions of the side. The quality of the leather from these por-

tions, however, is inferior to the more closely fibered and firmer

area extending approximately 15 inches on either side of the back-

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Fig. 12.

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Variation in per cent stretch over Hie sidefor samples C and D

bone. Thus it will be seen that high tensile strength alone does

not insure the best quality of leather.

(6) Stretch.—The results of the stretch tests are shown graphi-

cally in Figs. 11, 12, and 13. The value of this property was

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Fig. 13.

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Variation in per cent stretch over the sidefor samples E and F

lowest along the backbone edge of the sides and increased toward

the belly edge, although in some cases it dropped slightly in value

on the extreme belly edge. An interesting fact regarding the

Stretch shows that in many cases it increases when the strength is

Harness Leather 13

low and decreases when it is high. This does not occur in propor-

tion to the difference in strength, but is clearly shown by the fact

that the strength curves for any section of a side generally appear

to be concave, while the stretch curves are more convex.

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Fig. 14.

—

Variation in buckle strength over the sidefor samples A and B

(c) Buckle Strength.—The results of the buckle strength

tests are shown graphically in Figs. 14, 15, and 16. It will be

seen that the value for this property is generally low on the back-

bone edge, increasing slightly in value toward a point near the

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Fig. 15.

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Variation in buckle strength over the sidefor samples C and DJ

belly edge, after which it decreases to a minimum at the bellyêdge

for any section of four blocks running across the bend% ^The aver-

age value for the buckle strength for any section is greatest in the

butt end and decreases steadily to the shoulder end.

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Fig. 16.

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Variation in buckle strength over the sidefor samples E and F

An effort was made to establish a percentage relation betweenthe buckle strength and tensile strength per inch of width. Thisrelation was subject to a variation of from 10 to 50 per cent in

one side, so that no satisfactory figure could be accepted as stand-

ard. The results, however, show that the bellv and shoulder oro-


tions are inferior to the remaining portion of the side for use in

straps which are to be used with a buckle. The best portion of a

hide for this purpose, as shown by these tests, would be that in-

cluded in an area about 1 5 inches either side of the backbone and

30 inches in length from the root of the tail. This test would

not be of much value when examining samples of sides for general

use as harness leather, but would be valuable in testing a lot of

straps cut for use with a buckle. Table 1 gives the average values

resulting from the tests.

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Fig. 17.

—

Variation of stuffing content over the sidefor samples A and B

TABLE 1.—Average Values for Thickness, Tensile Strength, Percentage Stretch

and Buckle Strength for each Side

SideThickness,

inches

Tensile strength

Per-centagestretch

IIIw

ten

Butt Poundsper inchof width

Poundsper square

inch

1 ABCD£F

0.196

.178

.180

.198

.175

.172

740

806

865

810

815

795

3835

4600

4920

4130

4705

4605

30.8

29.0

31.6

31.1

23.3

28.2

201

1 195

2 170

2 205

3 163

3 180

2. CHEMICAL TESTS

(a) Stuffing Content.—The values for the amount of stuffing

content found in each block are shown graphically in Figs. 17,

18, and 19. The average amount for any section is least at the

Harness Leather 15

butt end and then gradually increases to the shoulder, where

the stuffing content is greatest. The general tendency is for the

stuffing content to be greatest in the more open belly and shoulder

portions. In the case of all except bend A the average stuffing

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Fig. 18.

—

Variation of'stuffing content over the sidefor samples C and D

content runs from 10 to 15 per cent and is shown to be fairly

evenly distributed over the side, except in the shoulder. Whena larger amount of stuffing was used, as in the case of bend A,

the distribution over the hide was less uniform, and the greater

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Fig. 19.—Variation of stuffing content over the sidefor samples E and F

part of the stuffing was absorbed by the belly and shoulder por-

tions of the hide.

(6) Complete Analysis.—A complete chemical analysis was

made of each side, and the results are given in Table 2.

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6

Technologic Papers of the Bureau of Standards

TABLE 2.—Results of Complete Chemical Analyses for all Sides

[Calculated to 10 per cent moisture]

Butt No. 1 Butt No. 2 Butt No. 3

Side A SideB Side C SideD SideE SideF

10.00

.32

.23

23.35

32.74

10.05

2.06

7.99

(a)

.12

23.74

72.51

.50

10.00

.27

.23

10.70

39. 92

10.20

2.07

8.13

(a)

.14

29.03

72.73

.52

10.00

.43

.21

13.30

40.24

9.88

2.58

7.30

(a)

.14

26.44

65.71

.35

10.00

.35

.22

11. 46

39.81

10.66

2.16

8.50

(a)

.14

27. 93

70.16

.32

10.00

.31

.23

13.72

37.32

10.92

2.27

8.65

(a)

.14

27.90

74.93

.55

10.00

Total ash .31

MgS047H2 ... .22

15.70

Hide substance 36.10

Water soluble 9.77

Nontans

Tans

2.20

7.57

Glucose (a)

.22Insoluble PRh

28.20

Degree of tannage b 78.12

Acidity .37

a None. 6 Degree of tannage is in each, case calculated from the figures given in corresponding table.

3. COMPARISON OF PHYSICAL AND CHEMICAL TESTS

(a) Effect of the Amount of Stuffing Content on thePhysical Properties.—The two sides A and B from the same

hide were prepared to show the effect of different amounts of

Stuffing content on the physical properties. Side A contained

23.35 per cent of grease, while side B contained 10.70 per cent.

It is apparent from Fig. 5 that side A , which contains the higher

percentage of grease, is uniformly lower in tensile strength expressed

in pounds per square inch than is side B. The average difference

in strength is nearly 20 per cent and since the two sides are as

nearly equal in quality in every respect, except grease content,

as is possible to obtain it might be assumed that the difference in

strength is caused by the different grease contents. The higher

stuffing content in side A, however, caused another effect that

must be considered, which was to increase materially the thickness

of the side so that its average thickness throughout was 10 per

cent greater than that of side B. Hence the cross-sectional areas

of the various test pieces were greater for side A than for side B.

This fact, assuming that the same breaking load would be obtained

for test pieces from the same relative location on each side, would

cause one test piece from side A to have a lower strength per unit

of cross section. Thus, it would appear that about one-half, or

10 per cent, of the difference in strength indicated in Fig. 5 is

due to the difference in thickness of the two sides which was caused

by the different stuffing contents. The remaining 10 per cent

Harness Leather 17

difference in strength may be attributed directly to the grease

content.

In the case of the tensile strength in pounds per inch of width

(Fig. 8) side B has an average value 9 per cent greater than that

of side A. Since the tensile strength per square inch for side Bwas 20 per cent greater than that for side A, half of which was

apparently caused by the difference in thickness of the two sides,

the remaining 10 per cent can be attributed to the difference of

the two sides in the strength per inch of width.. The strength in

pounds per inch of width is a more nearly true indication of the

comparative strength of different leathers, since it does not take

into account the thickness, which might vary for leathers on

account of any difference in the methods of tanning and finishing

by different manufacturers, and expresses the result for the same

amount of original hide substance regardless of the treatment of

the hide.

The effect of the grease content on the stretch was not appreci-

able, and the difference between the average values for the two

sides was only about 3 per cent.

There did not appear to be any appreciable effect, because of the

grease content, on the buckle strength. The difference between

the average values for the two sides was about 3 per cent.

It can not be definitely stated from the results of these tests

whether the variation in the grease content over the hide has any

effect on the strength. It is more likely that any effect produced

by the variation is secondary to the effect on the strength caused

by the location on the hide from which a sample is taken.

(b) Effect of the Degree of Tannage on the PhysicalProperties.—Sides C and D were prepared for this test. Side Dwas tanned the longer time, but the analysis of both show that

side C had reached that stage in the tanning process beyond which

the increase in the degree of tannage is slow. This is shown bythe fact that the difference in the degree of tannage figures for

the two sides was approximately 5.

The tensile strength in pounds per square inch (Fig. 6) for side Cwas uniformly greater throughout than for side D. This result

is what would be expected, since side C, having the lighter tannage,

was relatively nearer to the raw-hide condition in which condition

the strength would be greatest. The average strength, in poundsper square inch, for side C was approximately 20 per cent greater

than for side D, but, as was the case with sides .4 and i?, side Dwas also 10 per cent thicker than side C, thus causing its average

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8

Technologic Papers oj the Bureau of Standards

tensile strength in pounds per square inch to be considerably less

for the same amount of original hide. The average strength per

inch of width for side C was 7 per cent greater than for side D.

Although the degree of tannage values for these two sides was not

very different, it would appear that the lower strength of side Dis due to the longer time in the tanning process.

The stretch of the leather did not appear to be materially

affected by the different lengths of tannage, the average value

for the stretch being nearly the same in both cases.

The average buckle strength for side D (Fig. 15) was approxi-

mately 20 per cent greater than the value for side C. Thus, it

would appear that a long-time tannage would produce a moresolid and firmer leather, which would resist a shearing action to

a greater degree than a leather tanned for a shorter period of time.

(c) Effect of Animal and Mineral Oils on the PhysicalProperties.—Sides E and F were prepared for this test. Theaverage tensile-strength and stretch values were nearly the samefor both sides, but the average buckle strength of side F wasapproximately 10 per cent greater than the average value for

side E. This may be on account of the fact that, although both

sides were tanned for the same length of time, side F had a higher

value for the degree of tannage. The results indicate that there

is no essential effect upon the physical properties of new leather

caused by the use of mineral instead of animal oils in the stuffing

content.IV. CONCLUSIONS

Although this investigation was somewhat limited in its scope,

the following general conclusions have been drawn, based upon the

results obtained with the material used in these experiments:

i. That the amount of stuffing content affects the tensile

strength of the leather and that there is a point beyond which

the amount of stuffing content used does not add to the strength

and may actually serve to decrease it.

2. That the tensile strength is greater for leather tanned a

short time than for leather given a long-time tannage, and that

the degree of tannage also affects the firmness of the leather, the

longer-time tannage producing leather more resistant to shear whenused with a buckle.

3. That the use of the type of mineral oil with which side Fwas stuffed does not affect the physical properties of new leather

in a manner different than that caused by the use of cod oil.

Washington, October 27, 191 9.