326 



THE INDIA RUBBER WORLD 



[March 1, 19r/. 



If it is necessary to use naphtha to remove the backing or to 

 separate the rul)ber from the plies, the naphtha shall Ix- what is 

 technically known as 76-(legrec Baume, tree from oil. 



When naphtha has been used the test pieces shall be allowed 

 to remain at rest for not less than one hour before testing. 



In all cases where backing is removed and buffing done, the test 

 pieces shall remain at rest for not less than ten minutes before 

 testing. 



Friction Test Pieces. Test pieces for friction or adhesion 

 tests shall be cut and prepared as follows : 



All kinds of hose, round packing and similar articles shall be 

 cut transversely unless the diameter is so small that a practical 

 measurement cannot be taken, in which case the test pieces shall 

 be cut longitudinally. 



Belting, packing or gasket material may be cut in any direction. 



Test pieces from washers, ferrules (sleeves) molded gaskets 

 and other odd-shaped articles shall be prepared in the manner 

 called for in the unit specification, if it is impracticable to pre- 

 pare them in accordance with these rules. 



Cotton rubber-lined hose test pieces and braided hose test 

 pieces shall be accurately cut transversely two inches wide and 

 full length of the circumference. They shall be cut through the 

 walls so that they can be laid out llat the full length of the piece. 

 One-quarter inch of the rubber lining shall be carefully and 

 cleanly trimmed off on each side, without injuring the fabric, 

 leaving a strip of rubber lining one and one-half inches wide un- 

 disturbed on a strip of cover two inches wide. A separation 

 between lining and cover of this strip shall be started for about 

 one and one-half inches. 



Test pieces of wrapped hose, round packing and similar 

 articles shall be accurately cut transversely one inch wide, and 

 left circular, to permit sliding on to a mandrel. A separation 

 between the rubber and the fabric or between the layers in ac- 

 cordance with the test to be made shall be started full width of 

 the piece and far enough distant to permit proper fastening of 

 clamps or hooks, as the case may be. 



Solid round packing and similar articles shall have a core 

 drilled out for the mandrel. 



Fabric-bailed rubber packing test pieces shall be prepared in 

 the same manner as for cotton rubber-lined hose, except that if 

 the rubber part is more than one-eighth inch thick, the test piece 

 shall be prepared exactly opposite, leaving a strip of sheeting 

 one and one-half inches wide on a strip of rubber two inches 

 wide. A separation between sheeting and rubber shall be started 

 for about one and one-half inches. 



Belting test pieces shall be accurately cut one inch wide and 

 shall be stripped down to all but two plies, and a separation of 

 the two plies started for about one and one-half inches. 



.\11 pieces of flat material such as packing gasket, belting, etc., 

 shall be cut not less than 12 inches long whenever possible. 



DETERMINATION OF TENSILE STRENGTH. 



The determination of tensile strength of the rubber compound 

 shall be made as follows : 



Apparatus. All tensile strength tests shall be made on an 

 apparatus the general design of which conforms to the Schop- 

 per machine. "'si 



Grips. When bar test pieces are used, the grips for holding 

 the test pieces shall be such that they will tighten automatically, 

 e.xerting a uniform pressure proportionate to the applied tension 

 across the full width of the piece, regardless of any variation in 

 the thickness of the rubber. 



Ring Test Pieces. These shall be placed over the revolving 

 rollers of the Schopper machine. 



Marking Bar Test Piece. The bar test pieces shall be 

 stamped in center portion with two lines two inches apart, using 

 a rubber ink pad stamp. The distance between the outside edges 

 of these stamped lines shall be accurate to one one-hundredth of 

 an inch. 



Measurement of Bar Test Piece. The width and thickness 

 of the lest pieces shall be accurately determined at three points 

 equidistant between the marks, a spring gage or ratchet stop 

 micrometer being used. 



Measurement of Ring Test Piece. The width and thickness 

 of the test ring shall be accurately determined at not less than 

 four opposite points on the ring, care being taken to get the 

 minimum cross section as near as possible, the area of which 

 shall be used in computing the tensile strength. 



Breaking. Bar test pieces shall be tightly fastened in the 

 jaws and brought just taut. The machine shall then be started 

 and the speed so regulated throughout the entire test, that the 

 jaws separate at the uniform rate of 20 inches per minute. 



The number of pounds necessary to break the test piece shall 

 be read to the nearest tenth of a pound and computed to pounds 

 per square inch, using the measurements nearest to the break. 



When breaking the ring test piece the ring shall be slipped 

 over the revolving bearing provided for it and the procedure 

 continued exactly as for the bar test piece, the speed being so 

 regulated that it will give an equivalent elongation of test piece 

 per minute. 



TENSILE STRENGTH .^iCROSS THE SEAM. 



Bar and ring test pieces shall be prepared as usual, except 

 that the seam shall not be bufifed ofif. 



In cutting, the seam shall be centered in the middle of the bar 

 test piece, at right angles to the axis, as nearly as possible. 



The center of the seam shall be made to lie along a diameter 

 of the ring test piece as nearly as possible. 



The calculation shall be based on the average cross section in 

 both kinds of test pieces in the usual manner, but excluding the 

 cross section of the seam or seams. 



ELONG.ATION AT THE BREAKING POINT. 



The elongation at the breaking point shall be accurately deter- 

 mined during the tensile strength test as follows : 



On tlie bar test a rule graduated to hundredths of an inch 

 shall be kept opposite the two marks and the distance the out- 

 side edges of these two marks are apart at the instant of break- 

 ing shall be noted. 



This distance shall be computed into per cent of elongation, 

 t. c, if the marks are twelve inches apart at the break, that piece 

 would have 500 per cent elongation. 



Ring Test Pieces. These shall have the elongation read to 

 the nearest whole per cent from the automatic record on the 

 stretch tapes. 



DETERMINATION OF SET. 



The determination of set shall be on the test piece as broken 

 in the tensile strength test not less than one nor more than one 

 and one-half minutes after breaking. Time shall be taken with 

 a stop watch. 



Bar Test Pieces shall have the distance from the outside of 

 the line to the furthest broken point measured carefully along the 

 axis on one broken portion to the nearest one-hundredth inch, 

 and in the same manner from the corresponding nearest broken 

 point on the other portion. The sum of- these two measure- 

 ments, minus two inches, is the actual set, and shall be computed 

 to percentage of the elongation at rupture to the nearest tenth 

 per cent. 



Ring Test Pieces shall have the inner circumference care- 

 fully measured around a solid disk of the same diameter as the 

 inside diameter of the original ring. The increase in length 

 (actual set) is read to the nearest half per cent, divided by the 

 per cent elongation at rupture, and the result recorded to the 

 nearest tenth per cent. 



DEFECTS. 



If the break occurs outside the gage marks on the bar test 

 piece during the tensile strength test, the specimen shall be con- 

 sidered as defective for any determination, and another test 

 made. 



