The Classification of the Plastic Gear (Part one)
The molding materials of plastic gears can be divided into general-purpose plastics, engineering plastics, special engineering plastics, and fiber-reinforced plastic composite materials based on them. With the continuous emergence of new materials, plastic gears have better advantages compared with metal gears. Different fillers can also be added to the gears to change the properties of pure plastic gears and improve the performance and service life of the gears.
Universal plastic gears
Common general-purpose plastics used for gears are polyethylene, polyvinyl chloride, polystyrene, etc. They have great output, low prices, and a wide range of applications. However, there are many disadvantages, such as low surface hardness and being easy to be scratched, cracks under the action of environmental stress, resulting in failure. In the process of gear meshing, a large amount of heat will be generated due to the great coefficient of thermal expansion, and creep and permanent deformation are more likely to occur. Therefore, general-purpose plastic gears are not suitable for applications with high load-carrying but are suitable for manufacturing gears for toys and medical devices.
Engineering plastic gears
Engineering polymer is a special, high-performance synthetic plastic with excellent comprehensive performance, high rigidity, small creep, high mechanical strength, good heat resistance, good electrical insulation, and can be used in harsh environments for a long time.
Polyamide gears
Polyamide (PA) has the hardness of thermoplastic material, and has good impact resistance and impact toughness. In some cases, it performs better than metal and has been widely used in the manufacture of gears, cams and bearings. However, its thermal deformation temperature is relatively low; the product has greater water absorption after being kept for some time, and the residual stress generated will cause defects on the surface of the product, change the thickness of the surface, increase the yield strength, and reduce the toughness. Creep will also occur. Therefore, to improve the performance of PA, blending modification can be carried out to generate copolymerized PA with different properties.
In terms of crystallinity, PA gears are semi-crystalline materials that allow for a sharp transition from solid to melt. PA is affected by crystallinity in the injection molding. There is a problem of thermal stress in the meshing and wear process of PA gears. The key factor determining the service life of the gear is the heat accumulation on the gear tooth side. It is necessary to predict the thermal stress of the gears and dissipate the accumulated heat to reduce the meshing temperature of the gears.
When gears of different driving materials mesh with PA gears, different forms of wear will occur on the PA gear tooth surfaces. When the acetaldehyde material is used as the driving wheel, the PA gear tooth surfaces will have great thermal wear, resulting in an increase in the gear pressure angle and aggravated wear. Drive gear materials play a critical role in wear.
PA gears have good lubricity, but under high load conditions; the service life of the gears will be reduced, and the failure will increase. Therefore, it is not enough to rely on the lubricity of the PA gear. To reduce the meshing wear between gears, using polytetrafluoroethylene (PTFE) as a lubricant will significantly reduce the meshing friction coefficient. After adding PTFE to PA, it is observed that the friction is significantly reduced, and a friction coefficient reduction of more than 60% is realized and 41 % of the working temperature is reduced, which can increase the service life and obtain greater torque power, but in the combined application of PTFE and polyoxymethylene, it is found that it cannot significantly improve the tribological properties of the gear.
POM gears
Polyoxymethylene (POM) has good mechanical properties and can be applied to injection molding of gears integrating precision and load bearing. As a highly crystalline linear polymer, it is a model for heat-resistant plastics. Through injection molding, POM can be made into hard, compact, anti-fatigue and anti-wear gears, which have the advantages of good impact resistance, small friction coefficient and good self-lubricating performance. Therefore, POM is the preferred engineering material for polymer gears. Its disadvantage is that it tends to shrink when forming products and is prone to defects.
In terms of the molding process conditions of POM gears, the injection speed, mold temperature, mold clamping pressure and cooling time have an important influence on the injection molding of POM gears in the injection molding process. In terms of wear and failure of POM gears, wear of the gear will affect its service life, and is closely related to the wear coefficient between gears. However, many factors affect the evaluation of the wear coefficient which needs to be considered comprehensively.
Universal plastic gears
Common general-purpose plastics used for gears are polyethylene, polyvinyl chloride, polystyrene, etc. They have great output, low prices, and a wide range of applications. However, there are many disadvantages, such as low surface hardness and being easy to be scratched, cracks under the action of environmental stress, resulting in failure. In the process of gear meshing, a large amount of heat will be generated due to the great coefficient of thermal expansion, and creep and permanent deformation are more likely to occur. Therefore, general-purpose plastic gears are not suitable for applications with high load-carrying but are suitable for manufacturing gears for toys and medical devices.
Engineering plastic gears
Engineering polymer is a special, high-performance synthetic plastic with excellent comprehensive performance, high rigidity, small creep, high mechanical strength, good heat resistance, good electrical insulation, and can be used in harsh environments for a long time.
Polyamide gears
Polyamide (PA) has the hardness of thermoplastic material, and has good impact resistance and impact toughness. In some cases, it performs better than metal and has been widely used in the manufacture of gears, cams and bearings. However, its thermal deformation temperature is relatively low; the product has greater water absorption after being kept for some time, and the residual stress generated will cause defects on the surface of the product, change the thickness of the surface, increase the yield strength, and reduce the toughness. Creep will also occur. Therefore, to improve the performance of PA, blending modification can be carried out to generate copolymerized PA with different properties.
In terms of crystallinity, PA gears are semi-crystalline materials that allow for a sharp transition from solid to melt. PA is affected by crystallinity in the injection molding. There is a problem of thermal stress in the meshing and wear process of PA gears. The key factor determining the service life of the gear is the heat accumulation on the gear tooth side. It is necessary to predict the thermal stress of the gears and dissipate the accumulated heat to reduce the meshing temperature of the gears.
When gears of different driving materials mesh with PA gears, different forms of wear will occur on the PA gear tooth surfaces. When the acetaldehyde material is used as the driving wheel, the PA gear tooth surfaces will have great thermal wear, resulting in an increase in the gear pressure angle and aggravated wear. Drive gear materials play a critical role in wear.
PA gears have good lubricity, but under high load conditions; the service life of the gears will be reduced, and the failure will increase. Therefore, it is not enough to rely on the lubricity of the PA gear. To reduce the meshing wear between gears, using polytetrafluoroethylene (PTFE) as a lubricant will significantly reduce the meshing friction coefficient. After adding PTFE to PA, it is observed that the friction is significantly reduced, and a friction coefficient reduction of more than 60% is realized and 41 % of the working temperature is reduced, which can increase the service life and obtain greater torque power, but in the combined application of PTFE and polyoxymethylene, it is found that it cannot significantly improve the tribological properties of the gear.
POM gears
Polyoxymethylene (POM) has good mechanical properties and can be applied to injection molding of gears integrating precision and load bearing. As a highly crystalline linear polymer, it is a model for heat-resistant plastics. Through injection molding, POM can be made into hard, compact, anti-fatigue and anti-wear gears, which have the advantages of good impact resistance, small friction coefficient and good self-lubricating performance. Therefore, POM is the preferred engineering material for polymer gears. Its disadvantage is that it tends to shrink when forming products and is prone to defects.
In terms of the molding process conditions of POM gears, the injection speed, mold temperature, mold clamping pressure and cooling time have an important influence on the injection molding of POM gears in the injection molding process. In terms of wear and failure of POM gears, wear of the gear will affect its service life, and is closely related to the wear coefficient between gears. However, many factors affect the evaluation of the wear coefficient which needs to be considered comprehensively.
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