718 



THE INDIA RUBBER WORLD 



[August 1, 1920. 



tween the two marks subtracted from the final distance gives 

 the increase in length or the set and this distance divided by the 

 original length multiplied by 100, expresses the set in percent of 

 the original distance. For example, if the original length is SO 

 mm., and the final length is 57.5 mm., the set in per cent will be 

 57.5 minus 50 mm., divided by 50, and multiplied by 100, equals 

 15 per cent. 



(4) Taking of Time: All measurements of time shall be by 

 means of a stop-watch or with a watch having a second hand. 

 The fundamental methods of testing are so made throughout the 

 entire rubber specifications that the following procedure shall be 

 uniform. After placing any test piece in the machine ready for 

 stretching, the piece shall be drawn just taut and the stop-watch 

 started at the instant of the beginning of the stretch. 



Then in case a piece is held for 10 minutes at a certain dis- 

 tance, the time shall be again measured at the moment the piece 

 is released. This moment is simultaneously the beginning of the 

 period of rest. The measurement is then to be taken at the 

 instant of the expiration of the second 10 minutes. 



(5) When the specification calls for a 1-minute stretch and a 

 l-minute rest, the time consumed in stretching to the specified 

 elongation shall not exceed IS seconds. 



(6) Initial Tension and Reduction in Tension after a Speci- 

 fied Elongation for a Given Length of Time: For this purpose 



Fig. 10. Apparatus for Testing Frictions. 

 the apparatus illustrated in Fig. 8 may be used. Its operation is 

 similar to that of the apparatus shown in Fig. 7. If desired a 

 spring balance may be used in connection with the apparatus 

 shown in Fig. 7. 



(7) Friction Adhesion : Definition of Friction : By friction 

 test, is meant the strength of the adhesion of the fabric plies 

 that will meet the test given in the various specifications for 

 adhesion between the fabric plies or between fabric and cover. 



(8) Method of Making the Test: A section a little over 25 

 mm. in width should be cut and raveled down to exactly 25 mm. 

 After starting the separation as previously described under 

 "Preparation of Test Pieces," the ends of the pieces are gripped 

 in the jaw of the testing machine after which separation is af- 

 fected by running the machine so that the jaws separate at a 

 uniform rate of 25 mm. per minute. The weakest point shall be 

 recorded and the average taken. 



(9) In the case of tire frictions and hose frictions it is usually 

 desirable to make a separation between every ply ; with belts the 

 tisual practice is to make a separation of two plies at a time. 



(10) Apparatus and General Method of Conducting Dead 

 Weight Tests. 



Friction : A testing frame, Fig. 10, suitable for the purpose 

 shall be used. This may consist of a wooden frame provided 

 with roller bearings at the top in which a mandrel is free to 

 revolve. Tlie total weight including the clamp suspended from 



the test piece, shall be equal to that called for in the specifica- 

 tions. 



(11) A movable platform should be provided for supporting 

 the weight while adjustments for the tests are being made. The 

 arrangement should be such that the platform may be gradually 

 lowered until the weight is carried by the test piece, after which 

 it should be dropped or swung to the side. In every case this 

 operation should be accomplished without a jerk. With the 

 weight hanging freely from the test piece a mark shall be made 

 along the line of separation of the layers, and at the same instant 

 the time shall be noted for the beginning of the test. At the 

 end of 10 minutes, or as great a part thereof as possible, a 

 second mark shall be made along the line of separation. The 

 distance between the marks, measured after the weight has been 

 removed, shall be used in computing the rate of separation. 



(12) Plied Hose: In preparing test pieces, a short length of 

 hose is pressed tightly over a slightly tapered mandrel. The 

 mandrel is put in a lathe and 2S-min. rings are cut with a 

 pointed knife. Beginning at the lap a short length of the fabric 

 is separated and the ring is pressed snugly over a mandrel which 

 is placed in the roller bearings on the test table. To the detached 

 end of the fabric is fastened a clamp provided with a hook or 

 ring from which the weight is to be supported. 



(13) Cotton Rubber-Lined Hose: In preparing a sample of 

 cotton rubber-lined hose, a S-cm. section shall be taken and cut 

 at the lap to give a strip equal in length to the circumference 

 of the hose. From this section a 40-mm. strip shall be cut 

 with as little injury as possible to the cotton jacket. The jacket 

 shall be separated from the lining for about 40 mm. at one end. 

 The detached end of the jacket is held in a stationary clamp 

 which is supported by the testing frame and the specified weight 

 is suspended from the rubber lining. 



(14) Rubber Belting: When testing rubber belting, a 2S-mm. 

 strip cut either longitudinally or transversely, shall be used. 

 The strip shall consist of two plies of fabric only, these plies to 

 be the second and third plies of the belt, numbering from the 

 top cover or from the bottom cover, as may be desired. 



(15) Packing and Gasket Material: When testing packing or 

 gasket material, the pieces shall be prepared and tested as in the 

 case of cotton rubber-lined hose, unless the thickness of rubber 

 is greater than 27 mm. under which conditions the piece shall 

 be prepared in such a way that the rubber part is to be clamped 

 at the top and held immovable while the weight is to be clamped 

 to the fabric. The test strips shall be cut in both directions. 



(16) Tuck's Packing: The friction in round Tuck's packing 

 iihall be tested by the same method as is used in plied hose, the 

 core being drilled out to permit the insertion of a mandrel. 

 Whenever the core is 5 mm. or less in diameter it shall be 

 tested in its original shape. When it is over 5 mm. in diameter 

 a piece 15 cm. long shall be separated from the fabric and cut 

 and buffed on four opposite sides to form a square section 2 mm. 

 l)y 2 mm. in the center of the test piece. The 2-mm. square 

 shall be at least 25 mm. in length. 



(17) Hydraulic Pressure Test of Rubber Hose: The hose 

 shall be stretched out for inspection, connected to the pump, and 

 filled with water, leaving the air cock open to allow the air to 

 escape. The air cock shall then be closed with a pressure of 1 

 kilogram per square centimeter applied. The test is then begun 

 by taking original measurements w-ithout releasing the pressure. 



(18) .-Ml pressure measurements shall be made with a stand- 

 ardized gage. The increase in pressure shall be at the rate of 

 715 kilograms per square centimeter per minute and the hose 

 under test shall be held for measurement not more than two 

 minutes, unless otherwise called for in the specifications. The 

 hose under test should be protected by a frame of metal or wood, 

 or of heavy plate glass so that in case a piece breaks during 

 the test the operator will not be injured. 



(19) Steam Test for Rubber Hose: The arrangement of pipe 

 connections shown in Fig. 9 is recommended. The header (1) 



