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Gear Casting

Gear casting is also called cast steel gear. It is because most of gears are made by cast steel. Herein, I share some information about producing gear casting and related heat treatment.

As for the weights, the gear castings are normally from several kilogram to over tons.

As for the materials, gear castings were usually made by high carbon cast steel, and some were made by alloy steel with some Cr, Ni and Mo in order to reach high tensile strength. Normally large gears have lower physical requirement than small gears.

As for the casting process, usually floor molding process is suitable and enough for the normal requirements. For cast steel gears, such as bull gear, pinion and idler, floor molding with quartz sand will be good choice. Why, because most of positions of gears need machining. So, you do not need to use the higher casting process. In addition, as for the middle and large steel castings, floor molding with quartz sand is almost the only choice.

As for the heat treatment, of course, the normalization is necessary for all steel castings in order to erase the inside stress. Some positions of gear castings are allowed welding. If the foundries weld the castings, the anneal will be necessary for the welding positions. If the hardness is too high for gear hobbing, you could do the anneal again to reduce the hardness and erase the hard spots inside. After machining and hobbing, the gears need quenching or called hardening treatment to enhance the surface hardness of gear teeth. For small gears, you could do the carburizing treatment. For large bull gears, you could do the surface quenching treatment. The gears without hardening treatment have very short lifetime, from several weeks to several months.

Since the gear castings have higher requirements to materials, defects, machining and heat treatment. Moreover, the order volume for gear castings are small relatively. Therefore, many steel foundries were not willing to make them.

Some gears are made by forging process. Forging gears have better internal organization of dense, high strength. Forged gears could be used in the more stringent working conditions. Cast gears have low intensity, but widely used in the general working conditions. Forged gears need high costs, and cast gears need lower costs comparatively. The buyers should choose the suitable manufacturing process according to the cost and conditions of use. In addition, as for the alloy steel, you should consider to use the casting process.

The following are some photos of gear castings Dandong Foundry made before, such as small gears, bull gears, pinions, idlers and large gear.


   

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