Makch 1,,1921 



THE INDIA RUBBER WORLD 



m? 



RELATION BETWEEN STATE OF CURE AND HYSTERESIS LOSS 



It is commonly held by tire technologists that the state of 

 cure of the friction and skim coat of the carcass has a lot to 

 do with the early or late occurrence of ply separation. 



Fig. 3 does in fact show that the state of cure has an intluence 



on hysteresis. What is 

 shown as the noniial cure 

 on this chart is the op- 

 timum cure as determined 

 by the tensile product. An 

 under-cure of 50 per cent, 

 for example, means that if 

 the optimum curing time is 

 90 minutes at 40 pounds of 

 steam pressure, the sample 

 was cured for 45 minutes. 

 Similarly with over-cures. 

 Curves A and B are typical 

 skim coat compounds. 

 Curve C is a breaker com- 

 pound. It will be observed 

 that minimum hysteresis 

 It must, of course, be kept 



percent cure 

 Fig. 3 



occurs in the over-cured region, 

 in mind that these data apply only to cycles of 200 per cent 

 elongation, whereas the rubber stock in question has an ulti- 

 mate elongation of over 900 per cent. Attention must also 

 be called to the danger of assuming that a slight over-cure is 

 therefore desirable. Aging conditions must be taken into con- 

 sideration, and the writer is of the personal opinion that the 

 optimum cure or, in many cases, an even shorter cure is the 

 correct condition. It is also noteworthy that the actual magni- 

 tude of the hysteresis values characteristic of high-grade, pure 

 gum frictions is very low, and that we must look elsewhere 

 for the true cause of ply separation. 



(To be Continued) 



AMERICAN RAILWAY ASSOCIATION, MECHANICAL 



DIVISION, MASTER CAR BUILDERS' AND 



MASTER MECHANICS* SPECIFICATIONS 



STANDARD AIR-BRAKE AND TRAIN AIR-SIGNAL HOSE 



Adopted, 1903; Revised, 191S 

 I. MANTTFACTTJEE 



1. Scope. These specifications supersede all previous specifica- 

 tions for air-brake and signal hose, including that for "woven and 

 combination woven and wrapped air-brake hose." Air-brake hose 

 of the woven and combination woven and wrapped type shall meet 

 all tests of these specifications except that of friction, section 4, 

 on those constructions where friction cannot be made. 



2. Physical Properties. All hose shall be soft and pliable and 

 not less than four-ply. They shall be made of rubber and cotton 

 fabric, each the best of its kind for the purpose. 



n. TESTS 



3. Tests. Hose shall be subjected to the following tests, which 

 shall be made with the temperature of the air not lower than 65 

 or higher than 90 degrees F., and the samples shall be kept at 

 a temperature within these limits for at least one-half hour pre- 

 vious to the time of test. 



4. Friction Test. The quality of friction shall be determined 

 by suspending a 20-pound weight from the separated end of the 

 duck of one of the 1-inch test specimens described in Section 

 9, the force being applied radially. The separation shall be 

 uniform and regular, and the average speed shall not exceed 

 8 inches in 10 minutes, the distance being measured while the 

 weight is still in place. 



5. Stretching Test. Test specimens from tube and cover will 

 be quickly stretched until the 2-inch marks are 10 inches apart 

 and immediately released. They will then be remarked as at 

 first within 10 seconds after starting to release and again stretched 

 to 10 inches between the new marks, remaining so stretched for 

 10 minutes. The specimens shall then be completely released, 

 and within 30 seconds after starting to release the distance be- 

 tween the marks last applied will be measured, and the initial set 

 must not he more than i<4-inch. At the end of 10 minutes the 

 distance between the marks will again be measured, and the 



final set must not be more than ^s-inch. These test specimens 

 may be cut from the tube and cover of the friction-test specimen, 

 but shall not be used for tensile test. 



6. Tensile Strength. Test specimens from tube and cover 

 shall be pulled in a tensile machine with a test speed of 20 inches 

 per minute. The inner tube must have a tensile strength of not 

 less than 800 pounds or more than 1,200 pounds per square inch 

 and the cover not less than 700 pounds or more than 1,100 pounds 

 per square inch. The elongation shall be such that the marks, 

 originally 2 inches apart, stretch to at least 10 inches before speci- 

 men breaks. If the tensile strength in pounds per square inch is 

 greater than that required, the sample may be accepted, providing 

 the per cent increase in elongation is equal to or greater than the 

 per cent increase in tensile strength in pounds per square inch 

 above the maximum figure. 



7. Porosity Test. The remaining 17 inches shall be mounted 

 and placed in a test rack, the circumference will be measured and 

 the hose filled with air at 140 pounds pressure per square inch, 

 the rubber cover shall be cut from clamp to clamp (taking care 

 not to injure the duck) and this pressure maintained for 5 minutes. 

 At the end of this time the hose will be submerged in water to 

 determine whether the inner tube is porous. The escape of air 

 through the tube shall be distinct enough so that the porosity will 

 not be confused with the escape of air which is confined in the 

 structure of the hose. In the event the hose fails on bursting test 

 at the point at which cut was made for porosity test and a satis- 

 factory hydraulic test is not obtained, the porosity and hydraulic 

 test will be repeated on another piece of hose. 



8. Bursting Tests. The section of hose which was used for 

 porosity test shall then be subjected to a hydraulic pressure of 200 

 pounds per square inch, under which pressure it shall not expand 

 in circumference more than J<}-'nch for air-brake hose and 11/16- 

 inch for air-signal hose, nor develop any small leaks or defects. 

 After the above test this section shall then stand a hydraulic pres- 

 sure of 500 pounds per square inch for 10 minutes, without burst- 

 ing or developing any small leaks or defects, after which the hy- 

 draulic pressure shall be increased to a minimum of 700 pounds 

 per square inch without bursting, at the rate of not less than 100 

 or more than 200 pounds per five seconds. 



9. Test Speomen. (a) A hose shall be selected at random 

 and a 5-inch section cut from one end. Two sections, each 1 inch 

 long, shall be cut from the 5-inch section for making friction, 

 stretching and tensile tests, the remaining 3-inch section shall be 

 used for making additional tests, which may be desired on the 

 tube and cover. Stretching and tensile test specimens shall be cut 

 from the tube and cover with a die having the dimensions shown 

 in Fig. 1. 



(b) In measuring the thickness of the test specimen shown in 

 Fig. 1 to determine the strength per square inch, a micrometer 

 graduated to 0.001-inch having a shoe 0.24 to 0.26-inch in diameter, 

 exerting a pressure of from 8 to 10 ounces on the test specimen, 

 shall be used. 



Fig. 1 



10. Number of Tests. For each lot of 200 pieces of hose one 

 extra hose shall be furnished free of cost for test purposes. 



in. PEEMISSIBLE VARIATIONS 



Thickness of 



Outside Inside Cap Vul- 



Length, Diameter, Diameter, canized on. 



Inches Inches Inches Inches 

 Air-Erake Hose: 



Maximum 22V5 2'/4 lA A 



Minimum 22 2tV IH A 



AiR-SiGNAL Hose: 



Maximum 225^ 1% lA A 



Minimum 22 Hi VA A 



IV. WORKMANSHIP AND FINISH 



11. Workmanship, (a) Tube. The tube shall be made either 

 by hand or machine. It shall be free from holes and imperfec- 

 tions, and in joining must be so firmly united to the cotton fabric 

 that it will meet the friction tests prescribed in Section 3. The 

 tube shall be of such a composition and so cured as to successfully 



