December i, 1903.] 



THE INDIA RUBBER WORLD 



77 



PAPERS ON AIR BRAKE HOSE— I. 



THE MANUFACTURE OF AIR BRAKE HOSE. 



THE problem of how to make the best air brake hose in 

 short lengths with capped ends has been the subject o( 

 much careful study, both by the manufacturers and the 

 railroad experts. The first expedient of making hose 

 in the usual 50 foot lengths, cutting into short pieces, and cap- 

 ping the ends, is no longer practiced by the more progressive 

 makers of these goods. It, however, illustrates the general 

 principles of rubber hose making, and will be described here 

 for the information of those unfamiliar with the process. 



The duck selected for air brake hose is generally 22 ounce, 

 40 inches wide, of long fiber cotton, and made " open " weave ; 

 1. e„ — not woven compactly as in the case of belting duck. 

 This weight of duck gives the strength required to insure a hose 

 of high bursting test, while the open texture affords the finished 

 hose the desired flexibility or freedom to bend short without 

 kinking, and also furnishes a better foundation for the applica- 

 tion of the " friction " than a close texture duck. The term 

 " friction " is used in a special sense in the rubber industry, and 

 refers to that mode of application of the rubber stock to any 

 fabric whereby it is made to penetrate the interstices of the 

 weave, filling them with the gum compound, and also impreg- 

 nating the surface fibers of the fabric. When applied to both 

 sides of a fabric the goods resemble the well known adhesive 

 tape, which is merely frictioned sheeting rolled and cut into rib- 

 bon-like width. The adhesiveness of frictioned fabric is derived 

 from the tacky nature of raw or unvulcanized rubber and to no 

 property of the friction process. 



Vulcanization changes the tacky rubber stock into the famil- 

 iar form of cured rubber. By this property surfaces that have 

 been brought into close contact in the raw state are merged 

 into each other without any seam or surface of union being ap- 

 parent, or indeed existing. An open weave duck thus wrapped 

 together in several bias plies is practically embedded in the 

 rubber stock and held together, when cured, in a very effective 

 way. To secure a still more secure binding of the plies the 

 duck is often skim coated over the friction surface of one side. 

 This causes a film of rubber to intervene between the plies when 

 the fabric is wrapped upon itself as in building up a hose. 



The method of applying a friction coat on a fabric consists 

 simply of passing the material through the calender at a slower 

 speed than that at which the thoroughly softened rubber mass 

 is being carried around on the middle roll of the machine. This 

 difference of speed results in a " friction" between fabric and 

 rubber, with the effect of crowding the gum into the structure 

 of the cloth. The application of a skim or even motion coat is 

 accomplished by passing the fabric through the callender at 

 the same speed as the rubber. In this case the lay of rubber on 

 the middle roll is simply transferred to the surface of the cloth 

 without penetrating it. If the goods have previously been fric- 

 tioned the skim coat has a very secure attachment. Turning 

 now to the preparation of the material for the tube. If it is to 

 be machine made the stock is forced from a tubing machine 

 and received on an endless apron conveyor which conducts it 

 away from the machine ready for slipping onto the hose mandrel. 



If the tube is to be hand made of a number of superimposed 

 layers, the sheet is produced by coating the stock the requisite 

 number of times on an apron passed through the calender. 

 From this apron the sheet is stripped in the cutting room and 

 cut into strips of appropriate width for the various sizes, then 



rolled in clean, narrow linings for the convenience of the hose 

 makers. The tube is formed around the mandrel by joining 

 the overlapping edges of the tachy raw stock upon itself. The 

 side of the sheet which forms the inside of thetube having first 

 been dusted with soapstone to assist, as a lubricant, in the sub- 

 sequent removal of the hose from the mandrel. Generally in 

 hand work a second tube sheet is applied over and breaking 

 joint with the first and both are carefully rolled into union to 

 exclude all air and consequent danger of blisters. 



The friction duck having been cut diagonally into suitable 

 width to provide the requisite number of plies, these diagonal 

 pieces are joined end to end, with seams overlapping about 

 three quarters of an inch, to form a bias strip fifty feet in 

 length. The object of applying the weave of the fabric diagon- 

 ally to the length of the hose is to secure flexibility and balance 

 the strength of the warp and filling of the duck in the structure 

 of the hose. It would be impossible to coil smoothly— t, e., 

 without kinks, a length of hose made straightway of the fabric. 

 One edge of the bias duck strip being attached to the tube on 

 the mandrel it is rolled down by hand for the first ply around, 

 using concave rollers. The completion of the wrapping is 

 further accomplished by power rolling in a 50 foot three roll 

 machine. 



A cross section of this hose machine would show the rolls 

 disposed in an equilateral triangle separated by the hose man- 

 drel in the center. The ply of rubber forming the cover is 

 generally wrapped around the hose as an attachment to the 

 outer edge of the last duck ply. A few moments combined 

 compression and rolling is sufficient to exclude the air and 

 effect an intimate union of the respective parts of tube, duck 

 and cover. The next operation, if air brake hose is to be the 

 product, is to cut the long hose into short pieces while it is re- 

 volving, as in a lathe, in the hose machine. Being then with- 

 drawn from the mandrel, the ends receive an application of rub- 

 ber cement in order to attach the raw gum washers which form 

 the capping to exclude the moisture from the duck. Next 

 comes the attachment of the various brands or labels for the 

 identification of the hose. These labels are preferably made by 

 applying thin sheets of raw colored rubber backed with thin 

 embossed sheet metal negatives. These metal negatives are 

 easily removed from the hose after curing and leave the col- 

 ored label with its markings sharply defined. The labeled 

 short lengths, still uncured, are mounted on a 50 foot man- 

 drel, each section separated by a metal or hard rubber ring to 

 prevent the sections curing together end to end. Thus ar- 

 ranged the goods are wrapped first with a straight narrow wet 

 strip of sheeting and subsequently cross wrapped with a two or 

 three inch wide wet strip of sheeting applied spirally. This 

 process of wrapping takes place in a similar three roll machine 

 to that used in making the original 50 foot hose. 



The object of wrapping is not only to hold the parts of the 

 hose compactly together, and in close contact with the man- 

 drel which determines the internal diameter, but it also serves 

 to prevent damage and adhesion of the hose when piled to- 

 gether in the car in which they are cured in the vulcanizing 

 chamber. The vulcanization or " cure " is effected in an at- 

 mosphere of steam and varies in length and temperature with 

 the nature of the goods and the compounds entering into them. 



The chief objection to cutting up long hose for making air 

 brake lengths, is that of expense. The more progressive com- 



