Views: 38 Author: Site Editor Publish Time: 2020-12-22 Origin: Site
POM is a linear polymer with high density and high crystallinity. It has good physical, mechanical and chemical properties, especially excellent friction resistance and strong rigidity. The processing and forming are simple, the production cost is low, and the material performance is similar to that of metal.
Polyoxymethylene (POM) plastic injection molding process
1. Plastic treatment
The water absorption performance of POM is relatively small, reaching 0.2%-0.5%, so in general, POM does not need to be dried and can be processed directly. If the processing requirements are relatively high, the POM needs to be dried. It only needs to be dried for 2 hours at a temperature above 80°C for processing.
2. Selection of plastic injection molding machine
POM is injection-molded. There is no special requirement for the plastic injection molding machine. General injection molding machines can be used for injection molding.
3. Mould and gate design
POM is injection molded. Generally, the temperature of the mold is controlled at 80-90℃. The size of the gate depends on the thickness of the rubber wall. The diameter of the round gate should be at least 0.5-0.6 times the thickness of the product. The width of the rectangular gate is usually It is 2 times or more the thickness, and the depth is 0.6 times the wall thickness.
4. Melting temperature can be measured by air shot method
POM-H can be set to 215℃ (190℃-230℃) POM-K can be set to 205℃ (190℃-210℃)
5. Injection speed
It is common that the speed is too fast, too slow to produce ripples, and too fast to produce ripples and shear overheating.
6. Back pressure
The lower the better, generally not more than 200bar.
7. Detention time
If the equipment has no glue retention point
POM-H can stay at 215℃ for 35 minutes
POM-K can stay at 205℃ for 20 minutes without serious decomposition. The melt cannot stay in the barrel for more than 20 minutes at the injection temperature. POM-K can stay for 7 minutes at 240°C. If the machine is shut down, the temperature of the barrel can be reduced to 150°C. If it is to be shut down for a long time, the barrel must be cleaned and the heater turned off.
You must use PE or PP to clean the barrel, turn off the electric heating, and push the screw to the front position. The barrel and screw must be kept clean. Impurities or dirt will change the overheating stability of POM (especially POM-H). Therefore, when the halogen-containing polymer or other acidic polymer is used up, the POM material can be used after the PE is cleaned up, otherwise it will explode. Improper use of pigments, lubricants or materials containing GF nylon will cause degradation of the plastic.
For parts that are used at very warm temperatures and require high quality, heat treatment is required.
For the effect of annealing treatment, the product can be immersed in a 30% hydrochloric acid solution for 30 minutes for inspection, and then visually observed to determine whether there are residual stress cracks.
POM is used more and more widely in the automobile manufacturing industry. It is very suitable for manufacturing automobile pumps, carburetor parts, oil pipes, power valves, universal bearings, motor gears, cranks, handles, instrument panels, automobile window lift devices, switches, seat belt buckles, etc. Manufacturing bushings, gears, sliders and other wear-resistant parts is the strength of modified POM. These parts have less metal wear, reduce the amount of lubricating oil, and enhance the service life of the parts. Therefore, it can widely replace copper, zinc and other metals to produce bearings, gears, tie rods, etc.