Games using tangible projectile – Projectile – per se; part thereof or accessory therefor – Having hollow core or bladder enclosed within cover
Patent
1998-09-02
2000-08-22
Wong, Steven
Games using tangible projectile
Projectile, per se; part thereof or accessory therefor
Having hollow core or bladder enclosed within cover
473594, A63B 3900
Patent
active
06106419&
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a ball for use in playing games, especially to a pressureless ball, such as a pressureless tennis ball.
Conventional tennis balls as well as many other balls for playing games, have a wall or shell of elastomeric material which is usually a composition of rubber or rubber-like materials. The wall forms a hollow sphere or core defining a cavity which is filled with gas, usually air, at a required pressure.
In case the cavity contains a gas at a pressure above that of the atmosphere, the ball is called a pressurized ball. In case the cavity contains a gas having substantially the same pressure as that of the atmosphere, the ball is called a pressureless ball.
Both the above types of tennis balls can be made to meet the requirements of the International Lawn Tennis Federation as regards diameter, weight, rebound and deformation. In addition to meeting these requirements, a tennis ball should have a long life as well as good and consistent play behaviour.
Pressurized balls have a relatively short life as a result of the gas permeating through the wall of rubber or rubber-like materials. On the other hand, pressureless balls have a substantially longer life but are difficult to produce with the desired play behaviour.
There is therefore a need for an improved ball, especially a tennis ball, which will address these problems.
According to the invention, there is provided a ball having a wall of elastomeric material defining a cavity that contains a filling which comprises a plurality of substantially closed cells.
By introducing such a filling in the cavity of the ball, the deformation behaviour, and especially the dynamic deformation behaviour of the ball may be controlled, such that the play behaviour of the ball may be easily determined as desired.
It should be noted that the deformation behaviour of a pressurized ball to a large extent depends on the pressurized gas in the cavity, while the deformation behaviour of a conventional pressureless ball is mainly due to the characteristics of the elastomeric material forming the wall of the ball.
Thus, the force needed to compress the pressurized ball increases continuously, with increasing compression, along a curve primarily determined by the elevated pressure in the cavity of the ball and increasing progressively. In the conventional pressureless ball, the compression force follows an increasing curve which is more complex as a consequence of the major influence of the characteristics of the material of the elastomeric wall which also control the rebound of the ball.
By being able to modify both the characteristics of the elastomeric material forming the wall of the ball, and the characteristics of the filling comprising closed cells, the compression behaviour and, consequently, the play behaviour of the ball, especially the pressureless tennis ball, may easily be adapted to various requirements.
Preferably, the cavity is substantially filled with the substantially closed cells in order that the compression behaviour shall be affected. However, it is possible to let the substantially closed cells fill only a peripheral part of the cavity adjoining the inner side while some other material is used in the central part thereof, and still obtain a desired compression behaviour.
In a preferred embodiment, the substantially closed cells are elastomeric in order to be able to adapt to the changing shape of the cavity during compression of the ball, For the same reason, the substantially closed cells can be separate hollow bodies which may move relative to each other during the change of shape of the cavity of the ball.
Of course, neither do all the closed cells need to be separate hollow bodies nor do all the hollow bodies need to be separate.
Microspheres, especially polymeric microspheres are a preferred form of hollow bodies. They have the preferred elasticity and may be used in unexpanded as well as in expanded form. Further, microspheres have a low weight, such that they do not adversely affect the weight of the ball. In addition,
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Friel Michael
Hall Bengt
Tretorn Research and Development Limited
Wong Steven
LandOfFree
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