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:
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
