GEAR MATERIAL

Gear Materials

• The selection of gear materials depends upon:

1. Type of service
2. Method of manufacture
3. Wear and shock resistance
4. Space and weight limitations
5. Safety and other considerations
6. Peripheral speed
7. Degree of accuracy required
8. Cost of material
9. High load ,impact loads,and longer life requirements

• The gear material should have the following properties:

1. High tensile strength to prevent failure against static loads
2. High endurance strength to withstand dynamic loads
3. Low coefficient of friction
4. Good manufacturability

•  The gears may be manufactured from metallic or non-metallic materials. The metallic gears with cut teeth are commercially obtainable in cast iron, steel and bronze. The non-metallic materials like wood, rawhide, compressed paper and synthetic resins like nylon are used for gears, especially for reducing noise
• The following  shows the some of commonly used gear materials.

1.METALLIC MATERIALS

a)STEEL:

• So far  the most widely used material in gear manufacture is steel. Almost all types of steel have been have been used for this purpose.
• To combine the property of toughness and tooth hardness ,steel gears are heat treated.
• Steels with brinell hardness number(BHN) <  350 are used  in light and medium duty drives.But steels with BHN > 350 are used in heavy duty drives and also where compactness is required.The plain carbon steels used for medium duty applications are 50 C 8 , 45 C 8 ,  50 C 4 , and 55 C  8.For heavy duty applications ,alloy steels   40 Cr 1 ,30 Ni 4 Cr 1 ,and 40 Ni 3 Cr 65 Mo are used.
• For cast steels the tensile strength ranges from 650 N/sq.mm to 1020 N/sq.mm/

b)CAST IRON

• It is used extensively  as gear material because of its low cost ,good machinability, and moderate mechanical properties.
• Generally ,large size gears  are made up of grey cast of iron of grades FG 200 , FG 260 ,or FG 350.
• Its main disadvantage  is its low tensile strength.

c)BRONZE:

• It is mainly used in worm gear drives because of their ability  to withstand heavy sliding loads.
• Bronze gears are also used where corrosion and wear  are a problem .
• Its main disadvantage is its high cost.

2.NON-METALLIC MATERIALS

• The non-metallic materials like wood ,rawhide, compressed paper and synthetic resins like nylons are used for gears .
• Its advantages are              

1. Noiseless operation;
2. Cheaper in cost;
3. Damping of shock and vibration;

• Its disadvantages are 

1. Low load carrying capacity;
2. Low heat conductivity;

It also has to be noted that the material for pinion should always be better than material of the mating gear because the teeth of pinion undergoes more number of cycles than those of gear and hence quicker wear.