Fine steel cord with a low structural elongation

Abstract

A fine steel cord for the reinforcement of synchronous belts is presented. The fine cord has a distinct load elongation curve characterized by a very low structural elongation (below 0.09% preferably below 0.06%), and a high equivaslent modulus between 0.2 and 20% of the breaking, load. The favorable results are maintained when the cords are coated with an elastomer coating. Such a fine steel cord reduces the geometrical spread on the tooth pitch of the synchronous belts during use. A method to produce such a fine steel cord is also presented.

Description

FIELD OF THE INVENTION [0001] The invention relates to a fine steel cord for reinforcing a synchronous belt. BACKGROUND OF THE INVENTION [0002] Synchronous belts have found their way in many precision machines; in automobiles, in computer peripheral apparatus such as printers and copying machines, in positioning systems and in many other applications. In the art they are also known under other names such as ‘toothed belts’, ‘transmission belts’ or ‘timing belts’. In what follows, the terms and definitions according the standard ISO 5288-1982 will be adhered to. Industry standards DIN 7721-1989 and ISO 5296-1: 1989 define the sizes and tolerances of commercially available synchronous belts. Synchronous belts are applied where power transmission or precise longitudinal continuous or stepped displacement of the belt or precise angular positioning over a longer distance is of the essence. One of the main requirements posed to a synchronous belt is the tolerance on the pitch length (see ...

AI Technical Summary

Benefits of technology

[0011] The inventors have found a different solution to solve the ‘dimensional control problem’ of synchronous belts, which is a first object of the invention. Surprisingly their solution also solved the ‘curling’ and ‘sabre’ effect. In addition their solution also increased the overall modulus of the cord in the working region of the belt thus reducing the elongation of the belt between loaded and unloaded part of a belt cycle without having to use more reinforcement material: a second object of the invention. The inventors have found a method to produce the multi strand cords in an efficient way: a third object of this invention.

Problems solved by technology

In practice the tolerances as set forth by the DIN 7721 standard are not longer sufficient as uses of synchronous belts are spanning longer distances or require better precision control.

Any misfit during engagement of the tooth into the gear recess will lead to premature wear of the belt or even teeth jumping out of the gear.

The problem of ‘dimensional control’ has thus emerged for synchronous belts.

These forces are not high enough to completely eliminate the structural elongation.

Upon pre-tensioning the synchronous belt between the toothed wheels the remaining structural elongation of the cords will lead to out of specification tooth pitch and the problems associated with this.

Both of these solutions have their drawbacks in terms of more rejects and / or more expensive belts.

However, with increasing width the synchronous belt production is more susceptible to the ‘curling’ effect (when hanging a piece of the belt freely, the free end turns with respect to the fixed end) or the ‘sabre’ effect (a piece of the belt laid down on a flat surface is not straight, but curved).

Both effects are very detrimental in the use of the belt, as they tend to derail the belt from the gear wheel.

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