Tests of Various Forms of Belt Connections

i. 1^ 4. * -•!*-- 4- ^4 TESTS OF VARIOUS FORMS OF BELT CON NECTIO jN S BY nWIGHT GRIFFIN CLARENCE SCHUCK HEISLAR THESIS FOR THE DEGREE OF BACHELOR OF SCIENCE IN MECHANICAL ENGINEERING IX THE COLLEGE OF ENGINEERING OF THE UNIVERSITY OF lELINOIS JUNE, 19 lO UNIVERSITY OF ILLINOIS .M.ay 3.1 19(2.0 THIS IS TO CERTIFY THAT THE THESIS PREPARED UNDER MY SUPERVISION BY -D-wlglit Griffin and CI.ar.e.n.c..e. S.cliu.c.k Hei.alan ENTITLED Tests of :7ar'ious .Fox-ms of .Belt Connecti.Qns . IS APPROVED BY ME AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE DEGREE OF Bachelor of . Scienc e in Ma.chani.cal Engin.e.ering Instructor in Charge. APPROVED: HEAD OF DEPARTMENT OF Ilrichanical Engineering 168117 CONTENTS Division Page I Introduction — 1 II Theory and Available Data S III Materials, Test Pieces and Methods of Testing 6 IV Experimental Data and Discussion 11 V Conclusions — — 17 TESTS OF VARIOUS PORI^S OF BELT CONNECTIONS. I INTRODUCTION. The transTTiisaion of poTver is one of the oldest problems which has confronted men interested in machinery. The ancients used bark peeled from trees in some instances to serve as belts for driving rotating parts of machines. Without doubt the fastening together of these crude devices gave them no little trouble. As the mechanical world developed the method of transmitting power grew in the same proportion, until, at the present time, we have various materials ~ the one most in favor being leather - used in the construction of belts. Numerous connections have been invented to supply the demand which this advancement in power transmission has awakened. Although the strength of the belt depends upon the weakest part, which is usually the joint, there is very little available data with respect to the relative strength and durability of belt connections. It is the object of this thesis to duplicate some work which has been done along this line and to carry on tests to a further extent, under conditions similar to those occuring in ordinary practice. Many tests have been made on belts and belt connections but usually only in tension and while both were new. Similar tests were made in this thesis which showed the relative values of the ne^T connections tested* Only four-inch belting was used since the average values for strength per inch of width should apply equally well to belts which are wider. Should an attempt to test very wide belts be nade, it is proba- ble that the difficulty In applying the load uniformly across the width of the belt would give less reliable data than tests on narrower belting. In practice it may be assumed that in belts of considerable lengths, even if the fasteners are not properly applied, the tension will be distributed almost uniformly across the belting due to it*s stretch and elasticity. On the other hand, narrower belts, if used for these tests, would not give values which would represent as these do the average strength of several gripping points between the belt and the connection. Since the strength of the fastener does not increase proportionally with an increase in thickness of belt, both single and double were tested, which should give values that could be applied with a reasonable degree of accur- acy to belts varying in thickness. These tests of new belts and connections, however, do not represent the conditions which exist in the actual use of belts. The constant bending over pulleys may cause rapid wear either of the connection itself or between the belt and the fastener. After long use it is evident that the strength of the belt connections would be much lower than when new. In order to have some means of comparing the different connections with respect to their durability, belts joined with the fasteners to be tested were run at high speed over small pulleys for a fixed length of time and then tested in a manner similar to the new connections. This work was carried on under the direc- tion of the department of Theoretical and Applied Mechanics. II. THEORY AND AVAILABLE DATA. Belt connections may be analyzed theoretically as riveted joints. There are three forms of failure which may now occur; (a) the connection itself may fail; (b) rupture may occur at the smallest cross section of the belt which is on a line with the holes for the fastener; (c) the holes may tear to the end of the belt which in riveted joints is known as "tearing out". In order to have an efficient joint, either of the three above forms should be equally liable to failure. The efficiency of a belt connection is the ratio of the breaking strength of the connection to the breaking strength of the belt. Efficiency = Strength of Connection Strength of Belt Therefore, as a concrete example, suppose a connection breaks at a tension of six hundred pounds per inch of width, and that the strength of the belt is twelve hundred pounds per inch of width, then the efficiency of the connection is equal to fifty percent. A few tension tests on new belt connections have been made by such men as Unwin, Towne, and Flint. Unwin's results which were obtained from his "Elements of Machine Design", are shown in the following table. -4- Pounds per inch of width. Double belt, copper semi — 1110 Single belt, ordinary lace joint 473 Single belt, butt laced 265 Single belt, joint scarfed and glued — 544 Single belt, grip fasteners -— 242 Single belt, Crowley*s 635 Single belt, riveted in two rows 304 Townees tests are given in his investigation of "Adhesion of Leather Belts to Cast-iron Pulleys" . The average of the trials were as follows :- Pounds per inch of width. Three-inch belts broke through lace holes 210 Three-inch belts broke through rivet holes - 382 Three-inch belts broke entire belt 675 This gives an efficiency for the laced connection of 31 percent and for the riveted 56 percent. Professoi* Flint, of Maine State College, also made a series of tests and his conclusions were that metal fastenings serving as connections fail at from 25 to 50 percent of the strength of the solid belt and that lace joints fail under a stress from 30 to 80 percent. These conclusions were obtained from an account of Professor Flint's tests in the "American Machinist" for November 14, 1895. The following table was obtained from G« F. Gebhardt^s experiments (February 11, 1909) made at Armour Institute of Technology, Chicago, and are results obtained from tensile tests of "Alligator" steel lacing. Sample Lacing Kind of Belting Pounds per inch of width. No . No A 25 Four ply stitched canvass 650 B 25 Four ply rubber 640 25 No. 1 Single Leather 575 D 45 Eight ply stitched canvass 88B E 45 Six ply rubber 840 P 45 Six ply rubber — B42 G 45 Six ply rubber 860 H 45 No. 1 Double Leather 1000 1 45 Imported woven Cotton 1110 Tables I, II, and III, which follow later, were obtained from a Thesis on "Tests of Belt Connections" made at the University of Illinois, 1908 by "Fast". These are the only available data which bears directly on the subject in hand and it is interesting to note how closely it agrees with a larger number of tests on similar connections. These tables have been slightly rearranged in order to make a direct comparison with our own results. The headings of the columns have been some- what altered but practically the same meaning is evident. The "Jewell" and the "Blake" connections used in "Fast's", thesis will be known hereafter in this thesis as the "Potter" Belt Hook and the "80th Century Belt Studs" respectively. -6- III. IIATERIALS, TEST PIECES MB METHODS OF TESTING. The belting used in all the following tests was four- inch single (3/16 inches thick) and four-inch double (3/r inches thick). This was the best oak bark tanned oxiiide manufactured by Chas. A. Schieren & Company of Chicago. There were eleven different kinds of connections tested; two styles of rawhide lacing; three of the metallic hinge type; two of wire lacing; three of the belt hook type and one of belt studs. Although these may not comprise all the different makes on the market, nevertheless representatives of all the types have been mentioned above. The rawhide lacing used was the "Royal Worcester" (3/8 inch cut lace) made by Graton & ICnight Manufacturing Company, Chicago. The Metallic Hinge, type of fastener was represented by the following makes; (a) the "Jackson" which is a machine made connection of wire having a high tensile strength; (b) and (c) the "Flexible" steel hinge and the "Alligator" steel hinge, manufactured by the Flexible Steel Lacing Company, Chicago. The wire, which is very pliable, used for the wire lacing and represented by the "A-B-C" and "Trojan", was manufactured by Kerr & Company, New York, and Leather Preserver Manu- facturing Company, Chicago, respectively. The Belt Hook fasteners consisted of ; (a) the "Cres- cent", which is composed of a steel plate and rivets and made by the Crescent Belt Fastener Company, New Yorkj (b) the "Bristol" which is a steel hook made by the Bristol Company of Waterbury, . -7- Oonneotiout; (o) the "Potter" which is a heavy hook made of malleable iron manufactured by the Jewell Belt Hook Company of Hartford, Connecticut. The "Twentieth Century Belt Studs" were manufactured by Graton & Knight Manufacturing Company, Chicago, and are made of an alloy high in tensile strength as may be seen from Table VIII.

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