Nbvi \n<m 1, 1914. | 



THE INDIA RUBBER WORLD 



69 



The Testing of Balloon Fabrics. 



By K. A. D. Presli, 



TESTING balloon fabrics may be considered as comprising 

 first the routine testing of the fabric and its component 

 parts during manufacture, and secondly testing of a re- 

 search nature to determine the behavior of the fabric under 

 special conditions. The principal routine tests made at the 

 Goodyear Tire & Rubber Co. are tensile tests and resin deter- 

 mination of rubber to be used in the proofing compound, tensile 

 and stretch test and determination of sizing in the unproofed 

 cloth and tensile and permeability tests of the finished fabric. 

 The specifications of a balloon fabric usually consist of maximum 

 weight and maximum permeability to gas per unit of area and 

 minimum tensile strength per unit width in the direction of 

 warp and weft of the principal ply of fabric (in case of "bias" 

 fabric). 



Considering these in the order named, a sample of the rubber 



is washed w'ith spe- 

 cial care, dried, com 

 pounded to a stand- 

 ard formula and a 

 specially shaped 

 sample mold-cured 

 and tested for ten- 

 sile strength, stretch 

 and set on the H. 

 W. Cooey machine 

 ( Fig. 1 ) which reg- 

 isters a graph of 

 these properties. 

 "Hie resin content is 

 determined by ex- 

 tracting with ace- 

 tone, using the well- 

 known underwriters' 

 apparatus. 



Tensile and stretch 

 tests of the un- 

 proofed cloth are 

 made on the ( llsen 

 fabric testing ma- 

 chine (Fig. 2). The 

 standard sample <li 

 mensions for warp 

 and weft strength 

 have been the sub- 

 ject for considerable 

 study. Test pieces 

 2 inches wide and 

 " inches long are 

 cut carefully with 

 their length parallel 

 to the warp and u efl 

 respectively. Three 

 tests are made in 

 each direction and 

 one-half the average value of the breaking load taken as the 

 tensile strength per inch. That this width sample gives the most 

 representative value of tensile strength is confirmed by tests on 

 specimens of varying width and length made at the English 

 National Physical Laboratory. In making tensile tests of fabrics 

 it is desirable to keep the samples for several days in a room of 

 constant relative humidity (usually 65 per cent.). The amount 

 of moisture in the fabric considerably influences its tensile 



Fig. 1. Cooey Rubber Testing Machine. 



strength, the difference between dryness and saturation often 

 reaching 40 per cent, of the normal strength. 



The bare cloth is also tested for traces of starch sizing by 

 boiling out a small sample in distilled water and testing the solu- 

 tion with iodine. Any appreciable quantity of sizing prevents the 

 proper impregnation of the fabric on the spreading machines. 



The strength and stretch of finished fabric is determined in 

 the same manner as in the case of the bare cloth. Considerable 



Fig. 2. Olsen Fabric Testing Machine. 



attention has been given to tests of fabric seams and standard 

 specifications have been adopted which make the joint stronger 

 than the fabric itself. 



The most interesting and practically the only test in the 

 series for which special apparatus other than that customarily- 

 used in the rubber and textile industries is required, is that 

 for permeability to gas. Although illuminating gas is nearly 

 always used for spherical balloons, the permeability of balloon 

 fabric is expressed in volume of hydrogen (the gas exclusively 

 employed for the inflation of dirigible balloons) which under 

 specified pressure (usually the equivalent of 2 inches water) 

 will leak through a unit area of the fabric in 24 hours. 



There are several methods of determining hydrogen diffusion. 

 That of most historical interest is the Renard-Surcouf balance. 

 The apparatus consists essentially of an ordinary balance to 

 one arm of which is attached a bell jar dipping into a water 

 tank. Across the top of the jar the test piece is held by two 

 metal rings with a rubber gasket, the whole being well bolted 

 together. The bell jar is fitted with connections so that pure 

 hydrogen may be passed through it. This is done until the air 

 is eliminated. The bell jar is then weighted to give the desired 

 pressure, when the stop cocks are closed and connections de- 

 tached, balanced with weights on the other arm of the balance 

 and allowed to remain 24 hours. Due to diffusion of hydrogen 

 through the test fabric, the equilibrium will be destroyed and the 

 bell jar will drop slightly. This will be indicated by the balance 

 pointer, and with proper corrections expresses the leakage per 

 24 hours. 



Another apparatus somewhat used in France is that of Josse. 

 From the sketch (Fig. 3) it will lie seen the essentials are a 



