Gears can be produced by the various casting processes. Sand casting is economical and can take up large size and module, but the gears have rough surfaces and are inaccurate dimensionally. The gears are used in machinery where operating speed is low and where noise and accuracy of motion can be tolerated, for instance, farm machinery and some hand operated devices. Sand casting is suitable for one-off or batch production.
Large quantities of small gears are made by “Die casting”. These gears are fairly accurate and need little finishing. However, the materials used are low melting ones, such as an alloy of zinc, aluminum, and copper. So, these gears are suitable for light duty applications only, for example, gears used in toys, cameras, and counters, etc. gears made by investment casting may be accurate with good surface finish. These can be made of soft materials to withstand heavy loads. Moderate-sized gears are currently being steel cast in metal molds to produce preforms which are later forged to size. Light gears of thermoplastics are made by injection molding. This method is suitable for large volume production. However, gear tooth accuracy is not high and initial cost is high. These gears find their use in instruments, household appliances, etc.
For phosphor bronze worm wheel rims, centrifugal casting is used far more extensively than any other method. Centrifugal casting is also applied to the manufacture of steel gears. Such gears perform well as rolled gears and are usually less expensive.
Shell molding is also sometimes used to produce small gears and the product is a good cast gear of somewhat lower accuracy than one made by investment casting but much superior to sand casting.
The methods of forming gears include:
Gear roll forming method
Gear extrusion method, &
Gear cold forming method.
These three methods are the popular ones, the details of each of them will be discussed in our subsequent articles, while the other methods not mentioned will also be treated.
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