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Analysis and Countermeasure of Molding Defects of Plastic Gear
Release time:
2017-08-07 13:52:51 |
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1. Overview
Plastic gears because of its light weight, low cost, low transmission noise, no post-processing, less production processes, and because of its strength and stiffness close to the metal material, can replace non-ferrous metals and alloys, so it is in industrial applications Is gradually expanding, is now widely used in machinery, instrumentation, telecommunications, household appliances, toy products and a variety of time devices. As the molding of plastic gear mold has its particularity, so the plastic gear to form a special type of injection mold.
2 .gear material
(POM), the material has excellent overall performance, strength, high rigidity, impact resistance, fatigue, creep performance is better, self-lubricating performance (including POM), the material has excellent performance, Excellent, small friction coefficient and good abrasion resistance, small water absorption, product size and stability, suitable for the manufacture of various gears, transmission parts or friction parts.
3. injection process
3.1 temperature
The temperature at the time of injection refers mainly to the temperature of the melt and the temperature of the mold, since both have an important effect on the entire injection process. To have the highest filling speed, but also to maintain the characteristics of plastic parts, you need to have the appropriate melt temperature. The higher the mold temperature, the faster the filling speed. Mold temperature control plastic filling speed, finished cooling time and finished product crystallinity.
Mold temperature on the gear forming cycle and the finished product quality (such as stress, coefficient rate, size, left, mechanical properties, etc.) have a decisive impact on the parameters of the POM material, the molding gear mold temperature control range of 90 degrees C ~ 120 degrees C.
3.2 The relationship between injection pressure and mold temperature
Injection pressure on the plastic filling a decisive role, and injection pressure and plastic temperature, mold temperature is mutual constraints. Using injection molding method to find out the best combination of finished products can be finished, through the rubber injection pressure and mold temperature diagram, you can find a reasonable combination of injection pressure and mold temperature. It can be seen from the graph, ABCD within the points, on behalf of the production of quality products can be the pressure and the combination of chess temperature. Exceeding the CD curve will cause the finished product to be burated or oversized. Below the AB curve will result in the finished product being too small or filled with dissatisfaction. The best combination at point X is that it allows the maximum range of parameters to be varied.
4. mold structure and manufacturing
To prevent gear deformation and contraction, the gear thickness of about 2 ~ 3mm. Forming gear injection mold with a uniform distribution of 3-point gate, so that one side to ensure the accuracy of gear, on the other hand can remove the point of waste. The gears are ejected with mandrels, and the cores are in the form of inserts.
In the design of gear mold cavity, to correctly grasp the shrinking of the parameters of the gear, if the calculation of shrinkage and actual shrinkage there is a big gap, you need to re-create the cavity. The machining accuracy of the cavity is the main means to ensure the accuracy of the plastic gear, the mold with high precision machining precision machining of the gear cavity. For a single part of the processing accuracy, we should pay attention to the size of parts and left and left position tolerance. The assembly of the gears requires a coaxiality of 0.003 mm.
Main Defects and Countermeasures of Forming Gear
Production practice shows that the defects of the forming gear mainly lies in the design of the mold, the manufacturing precision and the degree of wear and so on. In the more mature plastic factory, if the injection molding machine and the mold are ideal in all aspects, it is easy to obtain the qualified parts quality The The process of production process adjustment is to improve the production and quality of the necessary way. Adjust the process of measures, means all aspects, to identify the crux of the problem, can really solve the problem. The defects of the forming gears tend to cause noise, wear and tear, and reduce the efficiency of the gear transmission. |
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