Courtesy of the United States Rubber Co.
How is Rubber Prepared for Use?
Now that we have rubber so that it can be used, we find there are a great many operations necessary between gathering the crude rubber and finally the finished rubber coat or shoe. These various operations are called washing, drying, compounding, calendering, cutting, making, varnishing, vulcanizing and packing and each one of these main operations requires several smaller operations.
The grinding and calendering department is the one in which the crude rubber is washed, dried, compounded and run into sheets ready to be cut into the various pieces which constitute a boot or shoe.
Rubber Market in Manaos
Courtesy of the B. F. Goodrich Co.
The cultivated rubber comes practically clean, but the crude rubber “biscuits” contain more or less dirt and foreign vegetable matter which have to be removed. The rubber is softened in hot water for a number of hours and then passed through the corrugated rolls of a wash mill in which a stream of water plays on the rubber as it is thoroughly masticated and formed into thin sheets. These sheets are taken to the drying loft. Here they are hung up so that the warm air can readily circulate through them and are allowed to remain from six to eight weeks, until every trace of moisture has been removed. The vacuum dryer is used where rubber is wanted dry in a short space of time. This is a large oven containing shelves. The wet sheets of rubber are cut in square pieces, placed on perforated tin pans and loaded into the dryer, which will hold about eight hundred pounds of rubber. The doors are closed, fastened, and by the vacuum process the water is extracted, leaving the rubber perfectly dry in about three hours’ time.
