But two centuries have elapsed since rubber was known only as a curiosity; today it is in common use in nearly every industry and household.

Young rubber tree.

The system by which crude rubber is brought down to merchantable condition, is a simple method of kneading by steam rollers. First the crude rubber is soaked in hot water for several hours. After this operation, it is cut up into pieces of convenient size and run through a washer, which is a machine equipped with heavy corrugated steel rollers. Here it passes through and through until it is crushed and mangled, all the time being washed clean of bugs and other impurities, that get into the rubber tree. The rubber is very sticky and after the washer has completed its work, one sees nothing but a sticky mass in long sheets. These are allowed to dry and then are run through heavier rollers.

After this process the rubber is run through the "mixers," which consist of large hollow steel rollers having steam pipes inside of them, to furnish heat in the operation of mixing, and also a set of water pipes by which the rubber may be cooled when necessary. Through the rollers the rubber passes. So adhesive is it that it sticks fast to the rollers and has to be constantly cut off by means of a sharp knife, and thrown back, for another rolling. Great power is needed for this process because the sticky mixture retards the rollers. When the kneading is all but completed, a coloring compound is added to the mass to give it the tint desired in certain kinds of uses for which it is intended.

After this, the rubber is run through four polished steel rollers, one above the other, and here it gets its proper thickness. These rollers or "calenders" are used also for crushing the rubber into cotton ducking, for making rubber cloth, etc.

Manufactured rubber goods are made by this method of compression instead of by melting and pouring into molds.

Charles Goodyear discovered the process of vulcanizing rubber, a process which consists in changing the chemical composition of rubber by heat, whereby its sticky and elastic properties are removed and the rubber is given greater durability. This process consists in submitting the rubber to a great pressure under heat, by means of hydraulic presses. Generally, about 2,000 pounds are brought to bear, and the presses are connected with steam so as to secure the desired heat.

An odd method is employed to vulcanize rubber belts. A stretcher is used to take the stretch out of the belts. This is made up of two sets of heavy clamps, and a great hydraulic ram which exerts a pressure of 2,000 pounds to the square inch. In this manufacture, the belting has already been made by pressing the rubber into the cotton duck. This is now cut into strips of desired length, and the strips are laid, one over the other, until the thickness of the desired belt is obtained. Then a strip of thin, pure rubber is wrapped about the several folds. The whole belt may then be put into a steam press and vulcanized.

Rubber trees in US barracks, Key West, over 100 years old.

When rubber hose is made, a rubber tube is first slipped over a mandrill, and cotton-duck stripping is wrapped about it until the desired thickness is attained. Then, a thin sheet of rubber is rolled about it all. This is covered with strips and sent to the vulcanizing press. The press consists principally of an iron pipe which is thrust into the hose. Steam is admitted to the pipe and the hose is heated. When the process is over, compressed air is blown between the hose and the pipe to remove it. Firemen's hose, with its cotton outside, is made by drawing a rubber tube within the cotton tubing, and then the whole is charged with steam.

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© 1998, 2002 by Lynn Waterman