Tennisball

The tennis ball is the game device, is played with the tennis. It is made with the help of the tennis racket.

History

Already the direct ancestor of today's tennis, the so-called lawn tennis, the spread in 1870 from Britain, balls were used in solid natural rubber, on a fabric layer was sewn from flannel. Later it turned out that balls filled with a hollow core with compressed gas, to have better playability. To the skin was punched into cloverleaf shape of rubber, placed in spherical containers and filled with a chemical in the manufacture. This chemical formed during the subsequent heating in the oven gas, which resulted in the ball core was an overpressure. However, since the balls produced in this way were very different in their characteristics, was developed by and by modern production methods.

Previously, tennis balls, depending on the surface of the pitch, usually black or white. Today's traditional bright yellow color sat until 1972, when it was found that this can be seen best on a color TV. At the Wimbledon Championships was played until 1986 exclusively with white balls.

Specification

The Tennis rules of the International Tennis Federation ( ITF) Write balls for the following:

• The outer shell of the ball must be uniform and seamless, its color can be white or yellow.
• The ball shall have a mass of more than 56.7 g and less than 58.5 g.
• The diameter must be greater than 6.54 cm and less than 6.86 cm. For slow balls (Type 3 ) there are 7.00 cm to 7.30 cm.
• There are several types specified ball. Each ball must have a jump of more than 135 cm but less than 147 cm if it is left from a height of 254 cm, falling on a flat, hard surface such as concrete.

Then there will be rules to ball styles on different kinds of space.

Manufacturing process

The ball is surrounded by a densely woven and durable felt layer. This consists of a mixture of wool and nylon, which is spun into a yarn and then woven with a cotton thread. The felt is formed, characterized in that the fibers are shortened to a subsequent impregnation. To obtain the desired strength, the felt is dried under tension. After the back was coated with a hot melt adhesive, two dog-bone -shaped pieces are cut out of the felt, glued to the rubber bladder of the ball and dried per ball. The final evaporation ensures that hyping the felt.

The dividend is exploiting under the felt rubber bladder, also called ball core, is made of natural rubber and up to eleven different chemicals, including alumina, quartz, sulfur, zinc oxide and magnesium carbonate. These raw materials are mixed in so-called extruders with continuous kneading and at high temperature, so that a homogeneous mixture is obtained. This leaves the machine in the form of a strand which is cut into the portions necessary for a ball. These so-called pellets are pressed and vulcanized to make the mass elastically forms to hemispherical shells. The hemispheres are then bonded under heat to one another to form a hollow sphere, the ball core. In the case of pressure balls the core halves are under pressure - often nitrogen is used - together, pressureless balls on the other hand are bonded under normal pressure.

Around 240 million tennis balls are produced globally each year in this way.

There are two types of tennis balls: Balls pressure and non-pressure balls.

Pressurized balls

In the production of a small pressure ball rubber bladder ( 1.6 to 2.2 bar overpressure) filled with gas, in order to improve the jump property. With time, the gas escapes and the jump characteristic is decreased, so that the balls must be replaced frequently. In order to prevent escape before the first match, the gas, the balls are stored in an airtight tin, in the same pressure as inside the ball.

In the event area is played with a few exceptions with pressure balls. In professional tournaments the balls are replaced after a specified rhythm 7-9 games within a match. If a ball at an early stage lost, then he is not replaced by a new ball, but the completed number of games played since the last exchange by one, with the before the match. This ensures that all the balls is located at a point in the match have the same number of games and therefore have similar properties jump.

Pressureless balls

In preparing the pressureless balls the two rubber halves are easily assembled. Air composition and pressure in the ball inside thus correspond to the environmental conditions during production. In contrast to the pressure jump over the properties of the pressureless ball are determined solely by the rubber composition, which determines the elasticity and the wall thickness of the ball. Since there is no pressure loss may arise, the jump or play characteristics are retained much longer than in pressure balls. Pressureless balls have to be replaced when the rubber material is fatigued under the strong deformation of stresses and the clamping force is released. Should be up the felt worn out, the ball is long gone playable in the usual sense. Disadvantage of the non-pressurized balls is usually a harder jump property.