Method of producing strings for ball rackets, particularly for t

Details Method of producing strings for ball rackets, particularly for t Method of producing strings for ball rackets, particularly for t

1984-01-11

1986-02-04

Simmons, David

Adhesive bonding and miscellaneous chemical manufacture

Methods

Surface bonding and/or assembly therefor

57310, 156190, 156195, 156229, 428377, B65H 8100

Patent

active

045684154

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The invention relates to a method of producing a string for ball rackets, particularly for tennis rackets, wherein a plurality of winding layers of helically wound plastics sheet bands are applied to a continuously fed core, one over the other, along at least approximately concentric cylindrical surfaces, and the winding layers are joined to one another and to the core. The invention further relates to a string produced by the method according to the invention.


PRIOR ART

A method of the kind described above is known from U.S. Pat. No. 3,024,589. In this method a continuously fed nylon thread, serving as core, is for example impregnated with a liquid binder and then wound helically in two superimposed winding layers, wound in opposite directions, and the excess binder is stripped off. The resulting wet strand then passes through heated tubes, is thereby dried, and finally is drawn off and wound up as a finished string. According to modifications of the method additional pairs of winding layers may be applied to the wet strand, while however before each addition of a pair of winding layers the strand must be once again impregnated with the liquid binder. Instead of nylon threads, extruded bands may also be used as winding material.
The string known from the abovementioned U.S. Pat. No. 3,024,589 should have properties approximating to those of the customary gut strings used for stringing ball rackets. For the production of these gut strings the starting material is sheep or cattle gut, which is cut into narrow bands and subjected to treatment by chemical processes. A plurality of these narrow bands are then twisted together to form the strings. These gut strings now have the property that the dependence of their extension on the tensile force applied is substantially linear, that is to say the modulus of elasticity of the string material is substantially constant, and therefore is also not dependent on the prestress with which the string was fitted on the racket.
In FIG. 1 the curve A shows, for an ordinary commercially available gut string, the spring constant E.A. (in kN) defined by the product of the modulus of elasticity E and the cross-sectional area A of the string, plotted against the prestress F.sub.v (in N) of the string. As can be seen, the value of this spring constant E.A. varies only slightly with the prestress of the string. This gives rise to the good playing properties of tennis rackets strung with gut.
A disadvantage of stringing with gut consists on the one hand of the differences in quality which are unavoidable in manufacture and which are caused by fluctuations of the quality of the gut material used, and on the other hand of their high capacity to absorb moisture, which because of the consequent considerable variation of length, for example with high atmospheric humidity, impairs the playing properties of rackets strung with gut. In addition, the production of gut strings is relatively expensive.
For some years tennis rackets have now also been strung with strings of plastics materials. Ordinary commercially available plastics strings, which generally consist of a plastics monofilament, now have spring constant characteristics of a kind indicated, for example, by curve B in FIG. 1. In the applicable range of string prestress from 200 to 300 N, the spring constant E.A. is higher than that of comparable gut strings and in addition increases substantially linearly with a relatively steep gradient with increasing prestress. Consequently, the deformations of the strings which occur when the ball hits the racket are less than those occurring with comparable gut strings, and the force peaks which are required for braking a determined kinetic energy of the ball, and which have to be absorbed by the racket, are correspondingly higher than in the case of gut strings.
The player therefore feels that a racket strung with plastics strings is "hard" and that, in comparison with rackets strung with gut strings, it has a harder action, the more forcefully the strokes have to be made

REFERENCES:
patent: 3024589 (1962-03-01), Vaughan
patent: 3050431 (1962-08-01), Crandall
patent: 3164952 (1965-01-01), Neale et al.
patent: 4168603 (1979-09-01), Reich et al.
patent: 4168606 (1979-09-01), Callander
patent: 4300343 (1981-11-01), Nakamura et al.

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