Rubber Heels
Rubber heels are generally made for boots and shoes as follows. The compounded rubber is sheeted on a calender roll, on a drum, until several layers are obtained, thus making a sheet of about one inch in thickness. The heel is cut out from this sheet by means of a die and placed in a mold. It is there subjected to an extremely high pressure, generally obtained by hydraulic power. The plates of the press are heated with live steam. The heels are removed at the end of nine or ten minutes and the sheet which was formerly nearly an inch in thickness is now only about half an inch and has by pressure been molded into the shape of the heel desired, is semi or partially vulcanized, and also is imprinted upon the bottom with the name or other brand of the company.
The cup-shaped portion of the heel is now coated with a layer of rubber cement, and firmly placed on the boot ready to go to the vulcanizer, where vulcanizing of the heel is then completed.
Heel-making Department.
Many articles of rubber are vulcanized by the use of chloride of sulphur, which process is sometimes known as “cold cure.” The action of sulphur chloride itself is so violent that it must be diluted, and for this purpose carbon bisulfide is often used. In some cases, as, for example, the manufacture of tobacco pouches, the articles are submerged for from one to two minutes in the liquid, then removed and washed thoroughly. In another case, as in the manufacture of some kinds of rubber cloth, such as hospital sheeting, the coated cloth is suspended in a suitable room and the chloride of sulphur and carbon bisulfide mixed and evaporated by action of heat so that the cloth is subjected to the action of vapor alone. Only articles with comparatively thin walls can be successfully vulcanized by the cold cure, as at best the vulcanizing action of the chloride is only superficial.
No account of vulcanization processes as employed in the manufacture of rubber goods is complete without the mention of “steam cure.” A great variety of rubber goods under the general term of mechanical sundries are cured by this method. This includes rubber matting, door mats, water bottles, druggists’ sundries, etc. This process consists in brief of submitting the articles to be vulcanized to the action of live steam for from half an hour to an hour, or until the goods are thoroughly vulcanized. The temperature and duration of time required depend to a considerable extent upon the thickness of the walls of the article. In order to prevent the goods from being pitted and damaged by the action of steam, they are wrapped with cloth or imbedded in pans of soapstone. A great variety of rubber tubing is cured by this method.
In rubber cloth making, the crude rubber is put through the washing process, dried and mixed with sulphur, litharge, coloring matter, etc., and then is taken to the cement room, where it is “cut” with naphtha, forming a thick paste or dough. This is taken to the spreading room in large tubs and fed into the roller machine, which is like a long table made of steam pipes placed horizontally in a single layer. Below one end is a roll of cloth, which is passed between two iron rollers on the end. The dough is fed in between these rollers and is spread smoothly over the cloth, which is rolled up and removed to a heating room, where it is unrolled and hung on racks, and then subjected to sufficient heat to cause the combination of the sulphur and rubber.