Materials
Tennis rackets are most often made out of aluminum and composite materials. Aluminum rackets are made of one of several alloys, including a 2 percent silicon alloy with traces of magnesium, copper and chromium, and a 10 percent zinc alloy, with magnesium, copper and chromium. Composite rackets contain a range of materials, including graphite, fiberglass, boron or Kevlar. The strings are made of nylon, twisted sheep, cow gut or synthetic gut, but nylon is the most commonly used.
Aluminum Rackets
The frames of aluminum rackets are formed by one of two methods. Either the alloy is melted and then fed through a die cast in the shape of a racket frame or the alloy is melted and inserted into a tube, which is then fed through a die. After the frame has been formed, holes are drilled by a drilling machine for the yoke, which is the piece at the bottom of the racket that holds the ends of the strings. During this process, the racket is kept in place in the drilling machine and all the holes are drilled at once by several drill bits. Afterward, the racket is sanded to remove any rough spots from drilling. Next, the rackets are tempered by a heating and cooling process, which makes the aluminum even stronger. The rackets are heated to a high degree and then submerged in water. Then they are treated with a sulfuric acid solution and an electric current is passed through the acid solution, making the aluminum surface shiny.
Stringing is the next step, however some top rackets are sold unstrung so that the purchaser can have the racket strung to her liking. Rackets that are sold strung go through the stringing process, which includes laying a plastic grommet strip in the inner groove that goes around the head of the racket. The grommet has been drilled to fit over the existing holes in the racket head. Rackets are strung individually by a technician using a stringing machine. The racket is secured in the machine, and the technician inserts the strings--horizontal strings first, and then the vertical strings. They are then tightened.
Finally, the racket goes through the finishing process, in which the handle is cut and a butt cap is inserted into the end. Double-stick tape and vinyl grip tape are wrapped around the handle, strings are imprinted with a logo, an inspector checks it over for imperfections, and then the racket undergoes a final cleaning.
Composite Rackets
Composite rackets are formed out of layers of materials in a solid sheet, which is then cut into strips. The strips are wrapped around a flexible, hollow tube, which is then inserted into a mold that's shaped like a racket. The tube connects to a pump, which either pumps air or foam core into the center of the racket. The pressure of air pumped into the tube, combined with high heat, melds the layers of the racket. If foam is pumped in, it expands with heat and causes the layers to bond together.
Next, the string holes are drilled in the rackets with a drilling machine similar to that used for aluminum rackets. After the holes are drilled, the rackets are coated in polymer and put in a dryer. This step is performed several times.
Stringing of composite rackets is the same as it is for aluminum rackets. If it is a high-end racket, it will sometimes be sold unstrung. If not, a plastic grommet with drilled holes is inserted into the groove in the inside of the racket head and a technician feeds stringing material into the stringing machine, which attaches the racket strings, first horizontally and then vertically. The strings are tightened, and then the handle of the racket is finished with grip tape and a butt cap.
Member Comments