November i, 1901.] 



THE INDIA RUBBER W^ORLD 



35 



THE ACID AND VAPOR CURES. 



By a Superintendent, 



EVER since the days of Charles Goodyear more or less has 

 been done in the vulcanizing of rubber by what is known 

 as the cold cure process. At times certain lines of 

 work have adopted this method on a very large scale 

 and have been fairly successful. For example, there was a time 

 when a factory in Providence made large quantities of rubber 

 shoes, all cured in this manner. Later the American mackin- 

 tosh business went very largely into the vapor cure, but for a 

 variety of reasons this was not particularly successful, and it 

 was entirely dropped in favor of dry heat vulcanization. For 

 certain puregum goods, however, the process has always been 

 followed with more or less success — perhaps in European coun- 

 tries with a greater degree of success than in the United States, 

 until within the last three years, when there has been noted a 

 large increase in goods produced in this way and a much 

 finer product. 



Indeed, American goods of this sort to-day are rapidly cap- 

 turing the foreign markets. Experts in this line predict a 

 great future for cold cured goods. Among them are those who 

 claim that nearly every variety of rubber work can be cured 

 by it as now used, or by adaptations of it. Whether this is true 

 or not, it certainly has been proved that goods are turned out 

 that are long lived, elastic, and of a most beautiful finish. It 

 is also to be noted that cheaper stocks are being successfully 

 treated than was possible in the past. Little by little the 

 dipped goods manufacturers are coming into the field of gen- 

 eral druggists' sundries, but that they will some day monopo- 

 lize it, as the more enthusiastic predict, is hardly likely. 



The acid cure, pure and simple, is used only on thin dipped 

 work. That is, a cement that will flow easily, is made and forms 

 of porcelain, glass, or wood are dipped into this cement and with- 

 drawn slowly so that it drains off evenly and without air bub- 

 bles. A number of secret compounds are used in the making 

 of this cement, as it is necessary to have the blend so smooth 

 that it will drain oflf smoothly and yet not too quickly. After 

 the solvent has evaporated and the rubber has hardened upon 

 the forms the vulcanization takes place. A mixture of ^ 

 pound of chloride of sulphur to 4 pounds of bisulphide of car- 

 bon is the ordinary vulcanizing solution. Into this the dipped 

 goods are submerged from ten to fifteen seconds, when they are 

 stripped from the molds and again dipped. The rubber is then 

 placed in a bath made of 20 gallons of soft water, \i pound of 

 chipped borax soap, and i ounce of ammonia. The goods are 

 allowed to soak in this for about two hours and then rinsed 

 with clear water. Of course, this process is only used for arti- 

 cles made up of an even thickness of rubber not over )i inch. 



It is to be noted that heavily compounded stocks are not 

 generally suitable for this sort of work, nor stocks that contain 

 oil or rubber substitutes ; also that silk is the only fabric that 

 will withstand the acid cure. Where the dipped work is used 

 it is customary to have the employ6s protected from the fumes 

 by having the work in aclose covered cabinet in which the dip- 

 ping is done, an exhaust fan drawing the fumes away. 



A very interesting part of the acid cure is that which applies 

 to "blown goods," such as toy balloons. These goods are 

 dipped in the vulcanizing solution and at once inflated to about 

 seven times their normal size, the object being to allow the 

 fluid that still adheres to the surface of the rubber an oppor- 

 tunity to cure it more evenly. After this expansion the bal- 



loons are thrown into a basket and the air is allowed to leak 

 slowly out through the valve by which it was admitted, which 

 by the way is made so that it is just leaky enough for the pur- 

 pose. Only a small portion of the dipped work is blown, how- 

 ever, some manufacturers claiming that the expansion of the 

 rubber during the cure is wholly unnecessary and that rubber 

 properly cured without expansion is far more dense and every 

 way desirable, while others hold just the reverse opinions. It 

 may be noted, however, that both schools make excellent goods. 



The vulcanizing of goods by acid fumes, a process that is 

 often used, is done in a vaporizing room made of clear kiln 

 dried white wood boards, the ordinary size being 7 feet wide, 7 

 feet high, and 12 feet deep. This room is made with the frame 

 on the outside, the sheathing being on the inside, and is put 

 together with galvanized nails, screws, and hinges, the steam 

 fittings being also galvanized. This is lined with ^ inch as- 

 bestos board and has for heating about 180 feet of i inch pipe 

 placed inside of the room about 6 inches above the floor. The 

 pipe, by the way, is arranged in two coils, one on each side of 

 the room, leaving a clear space in the middle. A % inch board 

 is then cut into 1% inch strips, 7 feet long, with round corners, 

 which strips are placed crosswise in the heater, two inches apart 

 and 6 inches below the ceiling. All the uncovered woodwork 

 is then covered with shellac. The heater is then fitted with 

 four small sliding doors, one on each side, the bottoms of the 

 doors being level with the steam pipes. A ventilator with a 

 damper is then placed at the rear of the room and as near the 

 top as possible. The front of the room should have folding 

 doors the entire width of the room. This vulcanizing chamber, 

 o"f course, is arranged for the curing of coated cloths which 

 are festooned from between the cross bars, already described, 

 the bottom folds hanging about 12 inches from the floor. A 

 heater of this size will hold about 400 yards. A small china 

 dish is then placed on the pipes at each of the sliding doors 

 and in each one is poured >g of an ounce of chloride of sulphur. 

 The doors are then closed and the room kept tight for from 15 

 to 20 minutes, depending upon the thickness of the goods. The 

 ventilator is then opened, as are the small doors, and about 20 

 minutes are allowed for the fumes to pass off. In the mean- 

 time clean plates are put upon the pipes, in each of which is 

 an ounce of ammonia. After 20 to 30 minutes, with the venti- 

 lator opened about half the time, the goods may be removed. 



In the vulcanization of dental dam the same process is fol- 

 lowed, except that it takes about i )i. hours to vulcanize, and i 

 ounce of chloride of sulphur is used, the heat being turned off 

 after the first hour. The amount of heat used in this vulcani- 

 zation never exceeds 150 F. In building a vulcanizing cham- 

 ber, it should be on the top floor of the building, away from all 

 mixture of oils, and where the fumes cannot come in contact 

 with sheet zinc, or other easily corroded metals. 



In the vulcanization of dress shields in a chamber of this 

 sort, a tumbling barrel is made with cross bars running from 

 one end to the other. This is covered with }i inch galvan- 

 ized or nickel wire. A very good size for a barrel of this sort 

 is lYi feet in diameter by 5 feet in length, so set that it will 

 make 27 revolutions a minute. This will hold a number of 

 gross of dress shields and the vulcanization very easily accom- 

 plished. Cloth covered shields will vulcanize in 20 minutes 

 and pure gum shields 1% hours. 



