GB2181959A

GB2181959A - Improvements in or relating to tennis balls

Info

Publication number: GB2181959A
Application number: GB08526459A
Authority: GB
Inventors: Robert Christopher Haines
Original assignee: Dunlop Ltd
Current assignee: Dunlop Ltd
Priority date: 1985-10-26
Filing date: 1985-10-26
Publication date: 1987-05-07
Also published as: GB2181959B; FR2589068B1; GB8526459D0; FR2589068A1

Abstract

A tennis ball comprises a spherical core covered by means of twelve pentagonally-shaped identical cover pieces. Adjacent edges of adjacent cover pieces are in spaced parallel relationship so as to define a continuous channel (30) extending, in a geometrically symmetrical manner, over the spherical surface of the core. No bonding agent is present in the channel. The degree of hysteresis loss in the ball attributable to the cloth is reduced in comparison with a tennis ball having a bonding agent present in the channel. <IMAGE>

Description

SPECIFICATION Improvements in or relating to tennis balls This invention relates to tennis balls and in particular to tennis balls wherein a plurality of discrete, substantially identical, polygonally-shaped cover members are adhered to the surface of a spherical core member.

Our U.K. Patent No. 2,124,504 describes a method for making a tennis ball wherein twelve pentagonally-shaped cover members are adhered to the surface of a spherical core member, adjacent edges of adjacent cover members defining a seam channel which is filled with a bonding agent prior to the said adjacent edges being urged into abutment.

It has now been found that an improved tennis ball can be achieved by omission of the bonding agent filling the seam channel described in the aforesaid U.K. Patent.

Surprisingly, it has also been found that a tennis ball made according to the present invention possesses lower hysteresis loss (i.e. greater elasticity) than a ball made in accordance with the aforesaid U.K. Patent.

Accordingly, the present invention provides a tennis ball comprising a spherical core member and a plurality of discrete, substantially identical, polygonally-shaped cover members, in which the cover members are adhered to the surface of the core member so that adjacent edges of adjacent cover members are in spaced parallel relationship, whereby a continuous channel is defined between said adjacent edges and no bonding agent is present in said channel.

Preferably, the channel extends in a geometrically symmetrical manner over the spherical surface of the core.

In a particularly preferred embodiment of the present invention, the ball is provided with twelve cover members, each cover member having the shape of a regular pentagon.

Suitably, each cover member is made of a needle-punched cloth.

It has been found, according to the present invention, that the use of a needle-punched cloth for the cover members ensures deep penetration of the cloth by an adhesive and therefore improved adhesion of the cover members to the spherical core. Thus, the cover members show little or no tendency to "lift" at edges or corners and the need to seal adjacent edges by means of a bonding agent is avoided.

It has also been found that the absence of a bonding agent in the channel allows the cover members to react individually when the ball is subjected to distortion when in play. Although it is not intended that the present invention be construed with reference to any particular theory, it is believed that the continuous, geometrically-symmetrical channel may act as a "grid" of elasticity extending over the whole surface of the ball. In other words, each cover member may be regarded as an area of decreased elasticity on the flexible surface of the core, with the channel acting as a pattern of enhanced elasticity.

The present invention will be illustrated, merely by way of example, in the following description and with reference to the accompanying drawing, the single figure of which is a schematic perspective view of part of a tennis ball according to the present invention.

In the drawing, a tennis ball consists of a spherical elastomeric core 10 having twelve substantially identical pentagonally-shaped cover members (six are shown; 20, 21, 22, 23, 24 and 25) adhered thereto.

Adjacent edges of adjacent cover members are in spaced parallel relationship so as to define a channel 30 which extends, in a geometrically symmetrical manner over the whole spherical surface of the ball.

Comparison of the properties of a ball according to the present invention with a similar ball in which the channel is filled with a bonding agent (so that adjacent cover members are sealed together at adjacent edges) produced the results shown below.

To establish the properties of a ball made according to the present invention it is necessary to describe the manner in which tennis balls are tested and the interpretation of this test data.

It is desirable to make tennis balls of improved performance and this is done according to the present invention by attempting to reduce hysteresis loss in the ball. Hysteresis loss is traditionally measured* by applying a static force of 18 Ibs weight (7.17 Kg weight) to the ball and measuring the associated deformation of the ball (termed "Forward Deformation"), continuing to apply a force until the ball is deformed through one inch, (25 mm) progressively reducing this force until again 18 Ibs weight (7.17 Kg weight) is applied and measuring the deformation* (termed "Return Deformation"). The difference between the Forward and Return Deformation values is a measure of hysteresis loss of the ball the greater the difference, the greater the hysteresis loss.For perfect elasticity, i.e. zero hysteresis loss, the Forward and Return Deformation values should be identical but this is never achievable in practice.

However, it is possible to move towards this ideal by attention to tennis ball design.

The application of a textile covering to the ball core greatly increases hysteresis loss and it is desirable to reduce this as much as possible. Textile covering is necessary to provide a tennis ball with desirable aerodynamic and wearing qualities.

The present invention reduces the degree of hysteresis loss attributable to the cloth and this is demonstrated by the following test data. Hysteresis loss is measured first for the core of the tennis ball and * See Rules of Tennis : Lawn Tennis Association Official Handbook then forthe tennis ball itself when covered with cloth in the manner described herein and then by the manner described in U.K. Patent No.2,124,504.

HYSTERESIS LOSS (.001") Cloth Increased Core only Covered Ball Hysteresis Loss 1. Ball made 121 128 7 according to 124 141 17 the present 121 150 29 invention 112 143 31 117 140 23 Mean 119.0 140.0 21.4 2. Ball madeas 128 163 35 above but with 119 147 28 seam bonding 110 141 31 accordingto 112 142 30 U.K. Patent 113 148 35 2,124,504 Mean 116.4 148.2 31.8 It will be seen that hysteresis loss is increased to a lesser degree by omitting the seam bonding material.

Claims

1. Atennis ball comprising a spherical core member and a plurality of discrete, substantially identical, polygonally-shaped cover members, in which the cover members are adhered to the surface of the core member so that adjacent edges of adjacent cover members are in spaced parallel relationship, whereby a continuous channel is defined between said adjacent edges and no bonding agent is present in said channel.

2. Atennis ball according to Claim 1, in which the channel extends in a geometrically symmetrical manner over the spherical surface of the core.

3. A tennis ball according to Claim 1 or 2, in which the ball is provided with twelve cover members, each cover member having the shape of a regular pentagon.

4. A tennis ball according to Claim 1, 2 or 3, in which each cover member is made of a needle-punched cloth.

5. A tennis ball, substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawing.