400 



THE INDIA RUBBER WORLD 



[May 



canization is pushed too rapidly the outer layers are vulcan- 

 ized before there is any action at all on the inner layers. A 

 sheet of tin-foil inserted between the layers of fabric, and just 

 as wide and as long as the fabric, will remedy this trouble and 

 bring about uniform vulcanization. Even by injecting hot air 

 under pressure into the heater good results would nut lie ob- 

 tained, because the fabric is a poor conductor of heat. Low 

 temperature and slow progressive vulcanization are therefore nec- 

 essary. Even with this method there are differences in the de- 

 gree of vulcanization of the several layers of fabric. 



The old time dry heater is better. In this the material is 

 hung in the heater and slowly and evenly vulcanizeil In 

 this connection, Worrintjtnn's contimmns vu'.cani/atiun nwii i> 

 worthy of special 

 mention. This 

 heater, which is 

 popular in Eng- 

 land, has a quad- 

 rangular cham- 

 ber 9 feet long 

 and IS feet high. 

 at the top and 

 bottom of whicli 

 geared rollers are 

 arranged. The 

 fabric is placed 

 on a drum out- 

 side of the cham- 

 ber, into whicli 

 it is drawn by 

 an endless chain 

 through a slit in 

 the walls. The 

 fabric comes out 

 of the heating 

 chamber through 

 another slit at 

 the top, and is 



again wound on a large drum. The chamber is heated by steam 

 pipes and the fabric passes slowly through it, making zig-zags 

 over rollers. It takes the fabric from 2 to 3 hours to go througli 

 this vulcanizer. 



For very fine fabrics cold vulcanization is preferable. 

 The usual process is that of a solution of chloride of 

 sulphur in bisulphide of carbon. It is commonly held that 

 fabrics vulcanized in this manner do not last. This is often 

 true, though not always. Failure should not be attributed 

 to the method but to the mixture of the solution with in- 

 gredients which do not act properly in contact with chloride 

 of sulphur. Account must be taken of the fact that chloride 

 of sulphur creates reactions with other materials than rubber. 

 Oxide of zinc and hydrated lime must be left out when chlo- 

 ride of sulphur is used, for they give bad results. The rapidity 

 with which chloride of sulphur adds itself to rubber depends 

 upon the degree of penetration of the solvent. As a solvent 

 carbon bisulphide has proven best because its boiling point is 

 constant and not too high (being below 212 degrees F.). 

 Further, it swells the rubber, penetrating it faster than the 

 chloride can vulcanize it, and thus an even, regular vulcanization 

 is obtained. 



If the boiling point of the solvent is too low the rubber may 

 not be very deeply penetrated; concentration increases very 

 rapidly and the speed of the reaction between the chloride and 

 the rubber is much increased. For this reason a homogeneous 

 vulcanization cannot be expected. A too rapid evaporation of 

 the solvent lowers the temperature of the surface, a sort of dew 

 forms on the surface of the rubber, which decomposes the 

 chloride of sulphur. Naphtha has no constant boiling point: it 

 does not penetrate the layer of rubber fast enough and should 



"Capitaine Feber" (Fbexch Xon-Riciu). 



not be used. Benzol can only be used in a very pure state and 

 then, like tetra-chloride of carbon, it is too expensive. It is im- 

 portant that the bisulphide of carbon and the chloride of sul- 

 phur be perfectly dry, for water decomposes the latter, generating 

 hydrochloric acid and sulphur. For cold vulcanization the fol- 

 lowing installation is necessary: a boxwood cylinder running in 

 a long, narrow wooden trough lined with lead. 



A short time before beginning operations for vulcanizing, this 

 trough is filled with a solution of carbon bisulphide and chloride 

 of sulphur composed of from 1 to 2"^ parts of the latter for 100 

 parts of the former. The coated fabric is stretched tight and 

 slides over the cylinder: sufficient liquid being thus taken from 

 tin cxlinilrr to cause vulcanization. Xext the fabric is passed 



over a heated 

 drum to evap- 

 orate the solvent. 

 Then the mate- 

 rial is wound up. 

 The wooden cyl- 

 inder must be 

 perfectly round 

 and smooth, and 

 must run true, so 

 that the material 

 is evenly coated. 

 Otherwise a sort 

 of marbled effect 

 will be the result. 

 Sometimes a por- 

 celain trough and 

 cylinder are used. 

 The more the 

 material is wound 

 ihe greater the 

 spec d, because 

 the circumference 

 of the roll is al- 

 ways increasing. 

 But this is of little importance, for the faster the cylinder turns 

 the more vulcanizing liquid it picks up and the shorter the time 

 of contact with the liquid. The material is thus perfectly cov- 

 ered from the beginning to the end. 



Another method of cold vulcanization is by using the vapors 

 of chloride of sulphur. The web of coated fabric is run up 

 and down on rollers which keep it constantly moving in an air- 

 tight room, just as for hot vulcanization. This room must be 

 wider than the material and provided with a perfect, controllable 

 ventilating system. 



Small heaters are placed under tanks containing chloride of 

 sulphur to vaporize it. The temperature of the vulcanizing room 

 must go above 11 degrees F. The vapors must not be gen- 

 erated too close to the material, and it is preferable that they 

 be developed to the side and near the ground. The quantity of 

 chloride of sulphur is bas?d upon the size of the room, the thick- 

 ness of the rubber coating and the time. A material with 100 

 grams (3.52) ounces) of inserted rubber is vulcanized in 30 

 minutes with chloride of sulphur at 5 per cent. When the vulcan- 

 ization is finished, ventilators are opened, or, better, hot air is 

 blown into the room to drive away the fumes. The material is 

 then hung up to dry 24 hours in another perfectly dry room. 

 Humidity must be avoided. Hydrochloric acid gas which is pro- 

 duced by dampness creates a combination that weakens the fabric 

 by the formation of hydrocellulose. It is not advisable to use am- 

 monia to neutralize the hydrochloric acid, for it has been proven 

 by experience that an excess of ammonia has an unfavorable effect 

 upon the fabric and the rubber coating. After vulcanization the 

 material is measured and its weight to the meter determined. 

 CAUSES OF DETERIORATION OF BALLOON FABRICS. 

 Copper or its alloys coming in contact with the sulphurized 



