Ever wonder to yourself, "How is a tennis ball made?" The International Tennis Federation has strict rules about the size, bounce and amount of air inside a tennis ball that must be followed. If these tennis balls are tested and they do not pass, that company is not included on the ITF's list of approved tennis balls for use in tournaments. Here is a look at how tennis balls are made:
- Readying the rubber compound. Rubber is brought into the factory in large bales of up to 250 pounds. The rubber is kneaded like dough to make it softer and easier to work with. It is then placed in large vats with a petroleum mixture and left to sit for a few hours. After that time has passed, the rubber becomes more like sticky dough and is ready to be worked with.
- Cutting the rubber compound. The rubber is heated and then squeezed out into a long tube shape. The ITF says it is like squeezing toothpaste from a tube. The long tube of rubber is then cut into pellet shapes of a certain size. Those pellets are then left to cool down.
- Making half of the tennis ball. Each pellet is then put through a machine that molds it into a bowl shape. This is one half of the tennis ball. The edge of the half is then buffed and made rougher with another machine. This roughness will allow the glue to fall between the cracks and allow for a tighter hold. Two halves are then pressed together to make one tennis ball. This is the halfway point for making the tennis ball. According to ITF rules, tennis balls should be more than 2 1/2 inches in diameter, but less than 2 5/8 inches.
- Filling the tennis ball with air. ITF rules state that when a tennis ball is dropped from 100 feet it should bounce more than 53 inches but less than 58. To make this bounce happen, the tennis balls are filled with a certain amount of air when being made. When the tennis balls are made, they are generally pressurized to 12 pounds per square inch.
- Covering the tennis balls. The rubber balls are buffed and then uniformly coated with a type of glue solution. The cloth for the tennis balls arrives at the factory in long sheets. Those sheets are sent through a stamping machine and shapes are cut out. The shapes look similar to a bowling pin. Two of the shapes are wrapped around the rubber ball with the glue. One is placed vertically and the other horizontally so that the shapes hug each other.
- The tennis balls are tested. The now covered tennis balls are heated again. This allows the glue to seal so that the cover does not fall off. The tennis balls then go through rigorous testing to make sure they follow the ITF rules. They have to be the right size, bounce right and have a certain stiffness, too. If the tennis balls pass the test they get the company's logo stamped on them and are ready to be packaged and shipped.
- A little something extra. There is always a slight difference between tennis balls depending on how they are made, the amount of air used, bounce, pressure, etc. Tennis players can tell the difference by just handling the ball a little. This is why they are so picky about which balls to use during a match. Those slight differences can affect how the ball flies or bounces. Also, tennis balls are stored in pressurized containers because the pressure inside the ball is gradually lost once it hits air. That is why tennis balls are not used for very long and lose their bounce over time.