Engineering plastics for manufacturing gears should meet the following conditions:
(1) High bending strength and contact fatigue strength;
(2) High impact strength and certain elasticity;
(3) Low friction factor, excellent wear resistance;
(4) High heat resistance and low coefficient of linear expansion
(5) Excellent aging resistance;
(6) Small tendency of stress cracking
(7) Excellent dimensional stability;
(8) Low water and oil absorption rates, small changes in size and strength after water and oil absorption
(9) Simple forming process;
(10) Good price.
At present, the following engineering plastics are mostly used to manufacture gears.
The commonly used polyamide are nylon 6, nylon 66, nylon 610, nylon 1010, nylon 11, MC nylon, glass fiber reinforced nylon, graphite or molybdenum disulfide filled nylon, etc., their respective properties and the working performance gears made with them are as below:
(1) Nylon 66:
It is with high fatigue strength and rigidity, good heat resistance, low friction factor, and excellent wear resistance, but high hygroscopicity and slightly poor dimensional stability.
Nylon 66 gears can work under moderate load, high temperature (100~120℃) and no lubrication or less lubrication.
(2) Nylon 6:
Its fatigue strength, rigidity and heat resistance are not as good as nylon 66, but with good elasticity, good shock absorption and noise reduction capabilities.
Nylon 6 gears mainly work under the conditions of light load, medium temperature (80~100℃) without lubrication or less lubrication, and requiring low noise.
(3) Nylon 610:
The strength, rigidity and heat resistance are slightly weaker than nylon 66, but the hygroscopicity is small and the abrasion resistance is excellent.
Nylon 610 gears mainly work under the conditions of light load, medium temperature (80～100℃), no lubrication or little lubrication, large humidity fluctuation, and precise gear size is required.
(4) Nylon 1010:
Nylon 1010 gears operate primarily under light loads, high humidity fluctuations, requiring low noise, and no or little lubrication.
(5) Nylon 11
The strength and rigidity are weaker than nylon 66, but with less hygroscopic.
Nylon 11 mainly works under conditions of light loads, high humidity fluctuations, requiring low noise or requiring operation in water.
(6) MC Nylon:
Its strength, rigidity and heat resistance are better than nylon 66, with low hygroscopicity, excellent wear resistance, suitable for manufacturing large gears.
MC nylon gears can work under high load, high temperature (120°C), no lubrication or less lubrication.
(7) Glass fiber reinforced nylon:
The glass fiber content is generally around 30%, the mechanical properties and thermal properties are better than that of unreinforced nylon, and the coefficient of linear expansion and hygroscopicity are lower than those of unreinforced nylon.
It can work under the conditions of high load, high temperature and certain transmission accuracy, but it needs to be lubricated with oil when the speed is high.
(8) Graphite or molybdenum disulfide filled nylon:
Good thermal conductivity and self-lubricating properties, but slightly poor strength and impact resistance.
Graphite or molybdenum disulfide filled nylon gears operate primarily at light loads, higher speeds, with no or little lubrication.
POM has better fatigue strength and rigidity than nylon, lower hygroscopicity, good dimensional stability, and better wear resistance than nylon, but the molding shrinkage rate is greater than that of nylon. Polyacetal gears mainly work under light load, moderate temperature (below 100°C), no lubrication or less lubrication.
Polycarbonate (PC) has good rigidity, low moisture absorption, good dimensional stability, small molding shrinkage, and its heat resistance is better than nylon and polyoxymethylene, but with low fatigue strength, slightly poor wear resistance, and a tendency to stress cracking. Polycarbonate gears mainly work under the conditions of higher load, higher temperature and certain transmission accuracy, but need to be lubricated with oil when the speed is high.
Alternatively, the gears can be made from glass fiber reinforced polycarbonate. It has excellent heat resistance and fatigue resistance, high strength and rigidity, while water absorption and molding shrinkage are lower than those of polyoxymethylene and nylon. The stress cracking tendency is significantly reduced, but the wear resistance is slightly worse.
Glass fiber reinforced polycarbonate gears are mainly used under conditions of high loads and temperatures and higher precision requirements, but oil lubrication is required at high speeds.
4. Chlorinated polyether (CPE)
Chlorinated polyether has outstanding corrosion resistance, low moisture absorption and molding shrinkage, good dimensional stability, high molding precision, but low strength and rigidity. Chlorinated polyethers mainly work in corrosive media and conditions requiring high dimensional precision.
In addition to the above engineering plastics, special engineering plastics such as polyvinylidene, polyarylidene and polyimide can also be used to manufacture gears. Their heat resistance and rigidity are better than nylon, polyoxymethylene and polycarbonate, but due to the high price, the application scope is not wide enough.