The development of steel cord belting

The early steel-cord belts experienced problems with crooked running, cable corrosion and cover separation. Various measures were tried to overcome these, but the breakthrough came with the development of the modern method of manufacture (Wingfoot Patent, USA 1957). 

The method and plant in use at BTR are described in detail in Section 21.5. However, the principle employed is similar to all manufacturers. It entails tensioning the longitudinal web of cords so that each has the same tension, applying the rubber covers and vulcanizing the tensioned belt. The completed vulcanized belt is wound up at the end. A step-by-step method of operation allows the tension to be maintained until vulcanization is complete. The cords are nowadays galvanized, not brass plated. 

The top and bottom covers comprise laminated layers. The inner one which contacts the cords is compounded to give a high level of adhesion to the metal. The outer one is compounded to give appropriate service, e.g. wear, heat, oil, fire resistance. 

One of the most important provisions of DIN 22131 concerns the level of adhesion between the rubber and the steel cords. The test involves pulling a single embedded cord from the matrix, using a test piece containing five cords (Fig. 21.3). 

Values are expressed in kg cm length of embedded cord, and the specification states minimum values. The minimum values approximate to 8D + 38 where D is cord diameter in millimetres. This derives from a (simplified) curve of pull-out strength against cord diameter. Fig. 21.4. 

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Lancaster J., The Development of Steel Cord Belting, Internal BTR report. 

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