Cast Gear Blanks

Before venturing on to the casting process of the gear blanks, there is one vital point here about the material. Selecting the correct material solves half the problems. To give a very easy example, generally four types of bronzes are used for casting of worm wheel blanks. They are aluminum bronzes, tin bronzes, nickel-tin bronzes, and lastly manganese bronzes. Now every single type has properties that are different from each other. Thus making them each suitable for only a specific gear application.

Selection of Right Casting Material
Choosing the best casting material type is dependent on a number of factors like:

• If the application will be on a continuous duty.
• If it would be subjected to conditions of shock or impact loads.
• What would be its operating temperature.
• What will be the input speed.

Comparison Between Gear Blanks
A comparison is here drawn between the four types of Bronzes discussed above. Tin bronze display a good wear property. Nickel-tin bronzes displays even better wear properties. Ideally they are just the right one for applications that involves continuous duty.
Aluminum bronzes are very strong materials, in fact more than 50 percent stronger than tin and nickel-tin bronzes. That is the reason they are best for application involving high shock or impact loads. Bucket trucks, Cherry pickers are suitable for aluminum bronze worm wheels. But they have inferior wear properties.
Manganese bronzes are even more stronger than the aluminium bronzes. Almost to the extent of 50 percent but strength wise the properties are not that good.

Casting Process of Gears
It has been seen that different types of casting leads to results that are altogether different. That is the reason why so much care is been given to the right casting approach. It should kept in mind that Gear properties are influenced not only by material alone. Discussed here are few of those approaches.

Centrifugal Casting
Taking the example of worm wheel, blanks of bronze are stronger if made by centrifugal casting than other types like spin, chill or sand casting. Centrifugal casting gives excellent results in tin or nickel-tin bronzes in context of overall strength or grain size. Which has a significant impact on wear. Moreover a tin bronze that is centrifugally cast, can have a tensile strength that is 50 percent greater than the one that is sand-cast.

Further Centrifugal casting can be done at gravitational forces which is 40 to 60 times more than a normal gravitational force. This can result in gear blanks that are denser along the rim, where gear teeth cutting takes place. Centrifugal casting is a perfect folly for rims or shaped gears, requiring production in moderate to low volumes.

Spin Casting
The Spin casting of composite worm wheel blanks can be a bit expensive. This is because of the tooling costs. Another factor is that the design of the blank can bar it from being spin cast. For example, the blank may be so much small in size that spin casting won’t be a viable option.