Stock material or miscellaneous articles – Structurally defined web or sheet – Edge feature
Patent
1986-07-08
1989-05-30
Swisher, Nancy
Stock material or miscellaneous articles
Structurally defined web or sheet
Edge feature
428373, 428371, 428377, 428374, 428395, A63B 5102, B65H 5500
Patent
active
048350362
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL DOMAIN
The invention relates to a method for manufacturing a string ready for supply for stringing, particularly a tennis racquet, as well as a string obtained by said method. It furthermore relates to a method for stringing racquets with said string.
STATE OF THE ART
Strings for tennis rackets are put on the racquet frame with a specified initial tension. It is a known fact that after the string is strung on the racquet frame, the string tension decreases steadily, with said decrease in tension taking place at a rate of decrease that drops with passing time. A majority of the decrease of the string tension generally takes place within a span of approximately 40 seconds after the respective string is strung on the racquet frame.
This phenomenon is known as relaxation which holds true with different intensity for gut strings as well as for the various synthetic strings. It entails that the string must always be put on the racquet frame with an initial tension that is considerably above the average string tension in the racquet over the life of the stringing. however, the extent of the initial tension is limited in that it must lie within the elastic range. This relaxation is relatively minor in gut strings. But gut strings have other disadvantages which are brought about by quality fluctuations of the gut material used, and, on the other hand, by their high absorption of moisture, which impairs the playability of racquets with gut strings due to the great change in length this causes at high atmospheric humidity. In addition, production of gut strings is relatively expensive. In the commercially available strings made of a polyamide monofilament said relaxation is somewhat greater, but still relatively small.
However, only relatively hard stringing can be effected with such polyamide strings, bringing about some disadvantes to the player. This is explained in greater detail with the aid of the graphs shown in FIG. 1.
In FIG. 1, the graph for a commercial gut string shows the dependence of the spring rate E'.A (in kN), as defined by the product of the modulus of elasticity A and the sectional area A of the string, on the initial stressing force F.sub.v of the string (in N). As can be seen, the value of this spring rate changes very little with initial stressing force of the string. This shows the good playability properties of tennis racquets with gut strings.
Strings of polyamide monofilaments show spring rate characteristics of a kind as shown, e.g., by graph B in FIG. 1: in the eligible range of the string's initial stressing force F.sub.v of 200 to 300 N, the spring constant E'.A is greater than in comparable gut strings and, in addition, with increased initial tension it rises essentially linearly on a relatively steep incline. The result is that the deformations of the string occurring upon the ball impacting on the racquet are lesser than in comparable gut strings and that the force peaks required to brake a specific kinetic energy of the ball and which must be absorbed by the racquet are correspondingly higher than in gut strings.
The player therefore regards a racquet with synthetic strings as being "hard," which in comparison with racquet with gut strings feels even harder, the more forceful the shots have to be made.
The applicant has now discovered that, e.g., a string, in which monoaxially drawn film strips of polypropylene which has, e.g., a melt index MFI 190/5 determined according to DIN 53735 in a size of approximately 0.3 to 0.5 g/10 min., are welded together in several superposed layers, will have with graph A a spring rate characteristic similar to that of a gut string (see graph A). Such a string is described in the international patent application AT84/00014 (WO83/03998). However, this string exhibits relatively strong relaxation.
DESCRIPTION OF THE INVENTION
The invention has the object of disclosing a method for producing a string in a form ready for supply for stringing a racquet in which the relaxation of the string then strung on the racquet is reduced.
This proble
Schamesberger Robert
Woltron Herbert
Isosport Verbundbauteile Ges.m.b.H.
Swisher Nancy
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