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Conveyor Belt Adhesions
Adhesion is firm or steady contact between two surfaces. In rubber, it generally applies to the "grab" of rubber to rubber or rubber to metal, fabric, plastics, or the other components of a finished product.
Because most synthetic fabrics are slick and will not stick to most rubber compounds, they must be treated with a "go-between." The most commonly used treatment for rubber to fabric adhesions is Resorcinol-Formaldehyde-Latex (RFL). However, sometimes you must use other coatings such as special resins or isocyanates. This RFL coating is applied at the fabric mill, where they dry and heat set the fabric at the same time.
Mills heat set the fabric between 325º-375ºF while under tension. Such heating can shrink nylon and polyesters as much as 15% from their woven dimensions, both width and length. The mill must keep this shrinkage in mind throughout the manufacturing process.
The Scott Tester is widely used to measure and record the force necessary to separate two surfaces, usually in pounds per inch of width. This information is critical for deciding the quality of a product, and the expected life in actual use. In conveyor belting, common Styrene Butadiene Rubbers (SBR) are compounded to yield an adhesion between the covers and plies in the 60 to 70 lb. range. Nitrites, EPDM, coal stocks, and Chlorobutyl will measure somewhat less.
Natural rubber compounds, high grade truck tread stocks, and specially treated fabrics can produce test figures as high as 150 to 200 lbs. per inch of width on the Scott Tester. Industrial hoses and OEM tires are usually made with lower adhesions, where tests as low as 24 lbs. per inch of width may be considered adequate. As a rule, thicker rubber compounds will produce higher adhesions, both between the rubbers and between rubber and metal, fabric, or plastic. Thin rubber layers do not test as well.
Rubber & Plastics, Inc. continues to recognize the original conveyor belting specifications and provides complete details of all rubber belting components. We show the comparative grades of belts common to the industry on the Conveyor Belt Cross Reference Chart, listing the current trade names of various belts in each category.
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