Crumb Rubber

May 18, 2006

Vincent Corporation recently placed two CP-4 screw presses at the largest volume tire manufacturing facility in the United States. Their purpose is to dewater crumb rubber.

This facility performs all functions of the tire manufacturing process, from the receipt of raw materials (such as rubber bales, chemicals, textiles, and steel) to x-ray inspection of the finished tire.

The rubber compound is composed of two major components, the raw rubber and the filler. The most popular fillers are carbon black and silica. Carbon black usually comprises one third of the rubber by weight, giving it its strength and characteristic black color. Rubber for whitewalls and white letters does not require the same strength, thus the absence of carbon black.

Steel and fabric cords are calendered - an operation in which the rubber compound is pressed onto and into the cords - to form steel belts and plies. The inner liner is also calendered. Then, after preparation of the bead component and extrusion of the tire tread and tire sidewall components, the tire building process begins.

The tire building process is complicated and highly mechanized. Of most relevance to Vincent is the method by which whitewalls and raised white letters are created. A ply of white rubber is laid just below a thin layer of black rubber wherever the white is to show through. After the tire is cured - a high-temperature, high-pressure operation during which the rubber flows to form the tread pattern and sidewall details - the thin layer of black is ground off to expose the whitewall or white letter. The resultant crumb rubber is pneumatically conveyed to a Rotoclone, which uses water as its filter media. The discharge from the Rotoclone is saturated and must be disposed of.

Current disposal costs are quite high at $37 per ton to landfill. With up to 40 cubic yards to dispose of per week, annual landfill costs easily exceed $62,000. The CP-4 presses achieve a greater than 50% reduction in weight, or a greater than $30,000 per year savings in landfill costs. Press liquor is returned to the Rotoclone to reduce make-up water requirements.

Better yet, the dewatered crumb now has a market value, and the current plan calls for an end user to pick up the crumb at no cost. There is even a possibility the plant may be able to sell the crumb.

This is a high torque application and the standard speed presses use 2 hp motors. A moderately tight slot screen (0.015" or less) is desirable.

Issue 173