■0 DEPARTMENT OF COMMERCE Technologic Papers OF THE Bureau of Standards S. W. STRATTON. Director No. 147 AN apparatus for MEASURING THE RELATIVE WEAR OF SOLE LEATHERS, AND THE RESULTS OBTAINED WITH LEATHER FROM DIF- FERENT PARTS OF A HIDE BY R. W. HART, Assistant Physicist R. C. BOWKER, Assistant Mechanical Engineer Bureau of Standards ISSUED NOVEMBER 22.1919 oy-Z'6'H'Sl PRICE, 5 CENTS Sold only by the Superintendent of Documents, Government Printing OflSce, Washington, D. C. WASHINGTON GOVERNMENT PRINTING OFFICE 1919 ".lonograph of J. 9 m /f >i^ A -Ix < AN APPARATUS FOR MEASURING THE RELATIVE WEAR OF SOLE LEATHERS, AND THE RESULTS OB- TAINED WITH LEATHER FROM DIFFERENT PARTS OF A HIDE By R. W. Hart and R. C. Bowker CONTENTS Page I. Introduction ^ II. Wearing-test machines 3 III. Methods ^ IV. Results of tests ^ V. Conclusions I. INTRODUCTION The quality of sole leather is affected by many factors, such as the breed of the animal, its mode of life, the time of killing, the method of preserving the hide, and the kind of tannage. A very important factor which influences the durability of any particular sole is the part of the hide from which it is cut. It is a difficult problem to measm-e the wear of sole leather and gen- erally it is accomplished by actual service tests on individuals. Such a method takes considerable time, and the value of the results obtained is often uncertain on account of the many imcon- trollable variables occurring in the types of service and among the individuals \\ earing the soles. The development of a simple method for quickly determining the durability of sole leather seemed desirable, and this paper discusses a laboratory apparatus designed for this purpose and also presents the results of tests made to date to determine the relative wear of leather from different parts of a hide. n. WEARING-TEST MACHINE A machine has been developed at the Bureau for testing the durability of sole leather with the idea of subjecting the leather to shearing action during the wear similar to that occurring in service on shoes and at the same time accelerating the actual wearing away of the material so that an indication of the dura- bility of the specimen might be obtained in about 24 hours. The 137325°— 19 3 4 Technologic Papers of the Bureau of Standards machine as first designed (Fig. i) embodied a cam of clover-leaf shape, to which the samples were attached, and which rested on a horizontal disk having an abrasive smiace of cement. The difficulties with this design were that the samples were submitted to a bumping action which caused the wear of each sample to be so localized that it was often worn through on one end before the other end showed appreciable wear, that no means was pro- vided for removing the material worn away, and that the abrasive material soon wore smooth which caused a longer time to be necessary for a test. The machine (Fig. 2) as later developed and as now used is described as follows: A wheel of 15 -inch diameter carries on its face 12 test pieces. The wheel revolves at the rate of 30 revolutions per minute about a horizontal, axis with its bearings in two parallel metal bars which are pivoted at one end, the other end being free. The wheel carrying the weight of the bars (and any additional weight that may be suspended from their free ends) , rests on a horizontal disk of 16-inch diameter, the point of contact being ^}4 inches from the axis of the disk. This disk has a surface of carborundum, and rotates about a vertical axis on which is a brake wheel provided with a brake strap, by means of which any desired resistance to rotation may be secured by the application of dead-weight. The wheel is driven by a chain and in turn drives the horizontal disk with which the test pieces are in contact. The apparatus is designed with the view of subjecting the test piece to (i) a driving (shearing) action tmder pressure, and (2) a slight abrasive action resulting from the circular path of contact between the wheel and disk. The conditions of pressure and shear may be adjusted as desired. A circular brush is shown resting on the carborundum disk. This brush in connection with a small exhauster tends to keep the surface of the wearing disk clean. A test usually consists of 40 000 revolutions of the wheel which corresponds with 40 000 steps, or approximately 40 miles of walking. The substitution of a wheel for the cam eliminated the bimiping action but retained the shearing action and resulted in a more even and smoother operation. The use of a wheel allowed more specimens to be tested at one time, the entire surfaces of which were subjected to the wearing action. By using carborundum for an abrasive, a material was obtained which did not become dull or smooth quickly and which could be resm-faced with an emery- wheel dresser. Bureau of Standards Technologic Paper No. 147 P"iG. I. — Wearing test machine as fust used Fig. 2. — Wearing test viachine as used at present Jureau of Standards Technologic Paper No. 147 ^\S\ i 7 8 9\fo II -^ ,^\t^ IS II '^\f^ l9'\^o\ll j2a 23 ^-r mP^ 37\38 39^(^4lW2n^f^^^^Y'^ d/9\50 S-ASZ 5-5 54^5V5 5-7 SS 59 &0 61 \6Z 63 6^ 65 ^& 67 6d\69\7o\7f \7Z No.2 pjQ_ 2. — A 6e%c^ marked off for machine wearing test Wear Resistance of Sole Leather 5 A small suction fan and circular brush were added to the equip- ment in order to remove the dust caused by abrasion. These improvements permitted the wearing conditions to be more uni- formly maintained, m. METHODS Sole leather is generally sold in the form of bends. A bend is a half of a hide with the shoulder and belly portions trimmed off, the remaining portion being suitable for soles. In the tests con- ducted samples of leather from different locations on a bend were used to determine their relative durability or resistance to wear. When a whole bend was tested the general scheme was to divide it into blocks, as illustrated in Fig. 3. Each block was stamped with a code number, which fixed its location on the bend. When using the clover-leaf-shaped cam for holding the samples, test pieces approximately 24 by 5 cm were required and they were attached to the cam by a clinching device. Test pieces for use with the wheel were about half as long and were attached by means of four countersunk screws. In either case the samples were first weighed and then placed on the machine. After the test was completed the samples were again weighed and the loss in weight determined. The relative durability was obtained by determining the loss in volume from the loss in weight and the specific gravity. The sample showing the greatest loss in volume was considered as the least durable. A small sample adjacent to the test specimen was used in de- termining the specific gravity. Since only the grain portion was worn away during the test, it was thought desirable to use the specific gravity value for the grain portion only. Accordingly the flesh portion of the sample was removed and the grain portion was then coated with cellulose nitrate to render the sample water- proof. The determinations were then made using a direct-reading gravitometer (Fig. 4). IV. RESULTS OF TESTS Test No. I. — This series of tests was conducted on an oak-tanned bend using the machine with the clover-shaped cam to carry the samples and an abrasive disk of cement. The length of the test was 40 000 revolutions except that in some cases one of the test pieces was entirely worn through before the 40000 mark was reached; in these cases the machine was stopped and the results figured on a proportional basis. 6 Technologic Papers of the Bureau of Standards The foiir pieces tested at the same time were all taken from the same colimm across the bend and equidistant from each other so that each nm gave an indication of the relative wear across the bend. The exact location of each test piece is shown in Fig. 3. The results show that in general the resistance to wear is greater at the backbone edge and decreases gradually toward the belly edge of the bend. This is shown in Fig. 5. In studying these results it should be remembered that the best wearing portions of the bend are represented by the lowest points on the ciirves. In Fig 4. — Direct reading gravitometer diagrams B, C, and D the results of each individual run may be distinctly seen as one continuous curve, and the general tendency in regard to the wear as stated above is shown in each case. In diagram A , all the points in the other three diagrams are plotted, which gives a broken curve, showing that tests of practically the same material made at different times did not check. This failure of the machine to check itself caused the changes previously discussed to be made. Test No. 2. — A scoured oak bend was used in this series of tests. The samples in this case were 10 by 5 cm. in size, and when placed rr.'. \\ 137326°— 19. (TofacopascO.) Fig. 5. — Results of test No. i (ordinales indicate loss in ieear'"9 '"'^' Wear Resistance of Sole Leather 7 on the wheel were made to an apparent even thickness by backing the thinner ones with sheets of metal so that the outer circumfer- ence of the wheel, after all the test pieces were in place, presented a smooth surface. Twelve pieces were tested at one time. The same general scheme of placing the samples on the machine for this test was carried out as in Test No. i. The results of the tests are given in Fig. 6 and show that the best wearing portions of the bend are along the backbone edge and Ctitkeeiifmtltn. Fig. 6. — Results of test No. 2 (ordinates indicate loss in wearing tests) over the kidney. The resistance to wear decreases as the belly edge is approached and also toward the shoulder end of the bend. Test No. 3. — Test No. 3 differs from the preceding test mainly in the fact that the leather was of hemlock tannage instead of oak tannage, and that the conditions of pressure and shear were chang- ed, so that no comparison can be made between the relative wear of the oak and hemlock tannages. The tests were made along the bend with samples of composition material placed alternately on the machine with the leather. The general tendency of the de- creasing resistance to wear as the belly edge and the shoulder end Technologic Papers of the Bureau of Standards Wear Rssistance of Sole Leather 9 are approached is shown in Fig. 7. This test also shows that the portion on the extreme butt end near the tail is inferior in wearing quality. ) ' 11 21 31 f ' 12 22 32 \ ' 13 23 33 \'\* 14 •24 34 \ ^ 16 35 35 w- Fig. 8. — Method of dividing a bend for service and machine tests Test No. 4. — Several bends of sole leather were divided into blocks as shown in Fig. 8. From each block a sole was cut which was used in an actual service test. A sample for the wearing-test 11 13 13 15 21 82 Location 23 24 25 31 on the Hide Fig. g.-Chart showing relation between actual service tests and laboratory machine tests in test No. 4 machine was also secured from each block adjacent to the toe end of the sole. A comparison of the results obtained in service and on the machine is shown in Fig. 9. lO Technologic Papers of the Bureau of Standards The upper curve represents the average wear in days per iron^ for all the soles from each location. The lower curve represents the wear as indicated by the machine tests expressed as the average loss in volume of the test pieces as compared with a standard speci- men of composition material, a sample of which was tested with each group of six samples of leather. The two curves show the same general tendency as regards wearing quality with the excep- tion of location No. 3 1 , No cause can be assigned for this apparent discrepancy, but it is expected that subsequent investigations will correct this difference. V. CONCLUSIONS The results of these tests show that the machine indicates a decided difference in the wearing quality of leather taken from different parts of the hide, the portion near the back and over the kidneys having the best wearing quality and those portions near the belly edge, shoulder end, and extreme butt end having con- siderable less durability. These indications are in accord with the opinion and experience of many tanners and leather manufactiurers. The results obtained on the machine in Test No. 4 also agree quite closely with those obtained in service tests. In view of these facts it seems reasonable to believe that the ma- chine may properly be used to indicate the relative resistance to wear of different leathers. Washington, May 26, 191 9. 1 The iron is a unit of measure used in the leather trade to designate the thickness or gage of leather and is equal to approximately one-half millimeter in the metric scale, and equal to one forty-eighth inch in the EngUsh scale. ^ LIBRARY OF CONGRESS IllllllllllllllliJiil 018 455 019 2