Gear Materials

Today there is a great variety of materials that are available to a gear designer. The designer can choose from a plethora of choices. Further, there are many ways to modify or process the materials. This improves the properties and side by side helps to minimize the cost of production. Actually the production process also plays a decisive role in the type of Gear Material. For example take the case of Machined gears they are most precise. Now to manufacture them only that materials could be used that show good strength characteristics.
The following table gives a good summary of the different materials used in the making of gears:

Material	Outstanding features	Applications	Precision Rating
Ferrous:
Cast Iron	Low cost, good machining, high internal damping	Big size, moderate power rating, Commercial gears	Commercial quality
Cast Steel	Low cost, high strength	Power Gears, medium rating	Commercial quality
Plain Carbon Steel	Good machining, Heat treated	Power Gears, medium rating	Commercial to medium precision
Alloy Steels	Heat treated, high strength and durability	Strict power requirements	High precision
Stainless Steel	High corrosion resistance, nonmagnetic	Low power rating	Good Precision
Non Ferrous:
Aluminium alloys	Light weight, noncorrosive, good machinability	Very light duty instrument gears	High precision
Brass alloys	Low cost, noncorrosive, good machinability	Low cost commercial equipment	Medium precision
Die cast alloys	Low cost, low strength	High production, low quality, commercial	Low grade commercial
Non Metallic:
Nylon	No friction or lubricant, high water absorption	Long life, low nose, low loads	Commercial quality
Delrin	Wear resistant, long life	Low loads	Commercial quality

Type of Gear Material

These can be divided into two types:

Metallic Gears

Non Metallic Gears

Plastic Gears

Selection of Gear Materials:

There are some very critical matters that needs to be given a consideration before selecting a gear material. They are the following:

Allowable bending and hertz stress
Wear resistance
Impact strength
Water and corrosion resistance
Manufacturing cost
Size
Weight
Reliability
Lubrication requirements
No Moisture Absorption
Dimensionally Stable
Stress-Free structure
Environmental and surface temperature-
It has been found that if there is friction the surface temperature of the gear shows a tendency to rise.

Die Cast Alloy
The process is capable of producing high-volume low-cost gears. Mostly they are produced in aluminium and zinc alloys, while others in bronze and brass.

Material Quality
As it is well known that material quality has a strong influence on factors like pitting resistance and bending strength. So for getting a high quality material, the following metallurgical variables should be properly controlled.

Chemical composition
Hardenability
Material Toughness
Hardness of Surface and core
Micro structure of surface and core
Cleanliness and inclusions
Surface defects like flanks and root fillets
Structure and size of grain
Residual stress pattern
Internal defects
Decarburization