October 1, 1920.] 



THE INDIA RUBBER WORLD 



25 



showing the various ingredients and the proportions used in 

 practice. 



Dental — Light Pink Dental — Red Palate 



Fine Para 16.0 Fine Para 62.S 



Lithopone (green seal) 56.0 Lac sulphur 12.5 



Lac sulphur 6.0 Dark vermilion 22.0 



Lime 2.0 Lime 3.0 



Pale vermilion 20.0 ^ „ ,,^ 



Ultramarine blue Trace Dentai^-Black Weighted 



Dental— Black Palate F'"e Para 20.5 



Lac sulphur 15.5 



Fine Para 77.0 Lime 1.0 



Lac sulphur 15.0 Pure tin foil 615 



Lampblack 4.0 Raw linseed oil 1.5 



Lime 4.0 



After the mixing operation is complete, the rubber is trans- 

 ferred to a refining mill, the rolls of which are set closely 



NEW RUBBERIZED AIRSHIP FABRICS 



Method of Equally Dividing Glazed Hollands by Tearing 



together and between which the rubber is passed seven times 

 in order to attain the desired results. 



Calendering dental rubber differs from ordinary practice in 

 that absolute smoothness is not required in the soft calendered 

 sheets, as they are piled on a special smoothing table where any 

 unevenness is removed. Another difference is the use of glazed 

 Hollands, running 85 yards to the roll, on which the dental rubber 

 is calendered. The selvage of the hollands is removed by tear- 

 ing, and the width of the sheet divided, also by tearing, into equal 

 widths of 18 or 20 inches. It is not practical to sheet dental 

 rubber on full width goods. 



The calendering operation consists in feeding the rubber stock 

 in small quantities from the warming mill to the calender, the 

 thickness of the calendered sheet being regulated by the adjust- 

 ment between the center and top rolls, while the width is gov- 

 erned by two cutting knives. An average batch of dental rubber 

 is 60 pounds. 



As the sheet of hollands passes between the center and bottom 

 rolls, the rubber sheet is laid continuously on the fabric by pres- 

 sure of the middle roll, and wound up on the stock shell. As 

 soon as possible after calendering, the roll is removed to the 

 cutting room and eight-foot lengths are cut from it and piled 

 one upon the other on the smoothing table where any unevenness 

 in the sheets will disappear, due to the softness of the calendered 

 stock. 



This special table for cutting dental rubber is provided with a 

 plate-glass top, 10 feet long, 18 inches wide, and .^j^-inch thick. 

 A 10-foot straight-edge, a T-square, a cutting knife, and dividers 

 complete the equipment. Two sheets of rubber are then removed 

 from the smoothing table and placed rubber side down on the 

 cutting table. The width and length of cuts to be made are laid 

 off on the sheet with the dividers and the cutting is done with 

 the hand knife guided by the straight-edge in the longitudinal 

 cuts and the T-square in the cross-cuts. 



When the two-ply sheet has been cut into the required sizes 

 they are removed from the cutting table and a sheet of hollands 

 is placed on the exposed rubber surface of each sheet for pro- 

 tection. The sheets of dental rubber are then stamped, weighed, 

 boxed, and delivered to the shipping room. 



Fabrics for the gas envelopes of lighter-than-air craft usually 

 consist of cotton cloth coated with rubber. The requirements 

 are high strength, light weight, low diffusion, water resistance 

 and durability. The most important of all is durability, and ex- 

 tended observations show that the intensity and time of exposure 

 to sunlight varies the life of rubberized fabric to a great extent. 

 Dirigibles operating off the Florida peninsula and using envelopes 

 made with a fabric that a year ago was considered to be of 

 standard quality have had a useful period of not over thirty days. 

 At the end of that time replacement of gas is necessary, which 

 reduces the operating period. Envelopes made of the same fabric 

 and operated off waters adjacent to Long Island have shown an 

 average useful life of fifty days before deflation was necessary. 



The Manufacturers Aircraft Association has learned that a 

 study of British and other foreign practice in fabric manufac- 

 ture, combined with the results of extended exposure tests car- 

 ried out under various climatic conditions with fabric made 

 experimentally in this country, has led to the formulation and 

 adoption of what are believed to be improved rubberized fabrics 

 that withstand the sun's action. 



The cloths that are used to the greatest extent are known as 

 AA, BB and DD, respectively 2-ounce, 2.5-ounce and 4.5-ounce. 

 All are of long-staple Sea Island, Egyptian or Arizona-Egyptian 

 cotton, 40.5 inches wide when finished, with a tolerance of ^- 

 inch. The other specifications follow : 

 Cloth AA. 



Weight: 2.1 ounces, maximum per square yard. 



Tensile strength; 30 pounds minimum for either the warp or filling 

 finished. 



Count: 118 threads minimum per inch either way, finished. 

 Cloth BB. 



Weight: 2.65 ounces maximum per square yard, finished. 



Tensile strength: 45 pounds minimum for cither warp or filling, 

 finished. 



Count; 128 threads minimum per inch either way, finished. 

 Cloth DD. 



Weight: 4.6 ounces maximum per square yard, finished. 



Tensile strength; 65 pounds minimum for either warp or filling, fin- 

 ished. 



Count: 95 threads minimum per inch in the warp and 105 threads 

 minimum per inch in the filling finished. 



After weaving, a careful inspection is made of the cloth, both 

 before and after desizing and washing. All slubs and imperfect 

 spots are marked so that they may be cut out before rubberizing. 

 The cloth is then passed through spreaders which apply thin 

 coats of Para rubber solution containing only a very minor per- 

 centage of sulphur and litharge without the usual organic cure 

 accelerators previously used. This thin rubber solution fills up 

 the interstices of the weave. Much heavier rubber dough is then 

 applied as the process proceeds. 



After twenty to twenty-five coats are spread and dried, a con- 

 tinuous, gas-tight film is produced. High count cloth and heavy 

 proofing give the minimum diffusion. For instance, with a 2-ply 

 BB cloth having a gas film of 3H to 4 ounces there is obtained 

 very low diffusion, .^dded weights of proofing applied to higher 

 count cloth would probably induce but slightly better results 

 than are obtained with the above construction. Two plies of the 

 treated cloth are stuck together by means of roll ply machines. 

 The fabric is then wound on drums, wrapped and steam cured 

 at carefully controlled temperatures, pressures and periods of 

 time. Colored proofing is then added which, it is believed, con- 

 stitutes an important factor in reducing tlie action of light. The 

 exterior of the fabric is faced with an aluminum coat which acts 

 as a continuous light reflecting coat. 



The inner or gas side of the fabric is coated with one-half to 

 one ounce of pure rubber per square yard which helps to keep 

 the cloth moistureproof, reduces diffusion and makes a good 

 sticking coat for successful taping. The tape is applied both 

 to the exterior and interior. 



Declared exports of rubber to the United States from Lis- 

 bon, Portugal, totaled $194,825 for the quarter ended June 30, 

 1920. 



Replete with information for rubber manufacturers — H. C. 

 Pearson's "Crude Rubber and Compounding Ingredients." 



