The difference between plastic gear and metal gear

(1) One fundamental difference between molded plastic gears and metal gears lies in the different manufacturing methods. Almost all metal gears are machined by cutting and grinding, while molded plastic gears are machined by molds. The die cavity of spur gear can reach 2.5 by wire cutting μ M, but because this method is not generative machining, its cutting error may occur at any position. Therefore, the whole internal gear cavity must be detected. Unlike the metal gear machined, only a few representative teeth need to be detected. On the other hand, because the shrinkage rate of each part of the molded plastic gear is different and abnormal modulus value may occur at any part, it is also necessary to detect each part of the gear. The advantage of molded plastic gears is that any special gear can usually be molded as long as it can be drawn in CAD. The challenge is how to measure and adjust the shrinkage and molding abnormalities of molded plastic gears. Metal gears may also benefit from molded plastic gears in the application of full tooth profile detection technology and its advantages compared with the generation method. 

(2) there are differences between plastic gear and metal gear due to different processing methods. Metal gears are made by cutting or grinding and are rotary machining. Therefore, they have high coaxiality and easy to ensure diameter accuracy. Shrinkage compensation does not need to be considered in manufacturing. Plastic gears are molded, and the coaxiality is difficult to ensure, but the tooth shape is more accurate than metal gears, because the precision of gear cavity processed by wire cutting is higher than that processed by rolling electrode.

(3) the strength of plastic gear is worse than that of metal gear, but it has the advantages of self lubrication, light weight and low noise that metal gear lacks. The large, continuous and repeatable shrinkage characteristics of engineering plastics in the mold cavity need to be considered and compensated when molding gears. Generally, the diameter tolerance of plastic gear is larger than that of metal gear. The tolerance and transmission ratio of plastic gears are formulated and recommended according to the structure of metal gears, but these standards are unreasonable for plastic gears because they can not accurately predict the function and service life of plastic gears, even according to the plastic characteristics provided by resin material dealers, It is also impossible to accurately determine the real parameters of the material when the plastic gear enters or exits the mesh at high speed. The characteristics of traditional plastics are obtained in long-term practice.