1. Plastic treatment
POM has little water absorption, generally 0.2% - 0.5%. In general, POM can be processed without drying, but wet materials must be dried. The drying temperature shall be above 80 ℃, and the time shall be more than 2 hours. The details shall be in accordance with the supplier's data.
Generally, the proportion of recycled materials shall not exceed 20-30%. But it depends on the type and end use of the product, sometimes up to 100%.
2. Selection of plastic machine
POM has no special requirements for injection molding machine except for the requirement of no stagnation area of screw. Generally, injection molding is OK.
3. Mold and gate design
The common mold temperature is controlled at 80-90 ℃, the runner diameter is 3-6mm, the gate length is 0.5mm, and the gate size depends on the thickness of the rubber wall. The diameter of the round gate should be at least 0.5-0.6 times of the thickness of the product, the width of the rectangular gate is usually 2 or more times of the thickness, the depth is 0.6 times of the wall thickness, and the demoulding slope is between 40 '- 130'.
Exhaust system:
Pom-h thickness 0.01-0.02m, width 3mm
Pom-k thickness 0.04mm, width 3mm
4. Melt speed
It can be measured by air injection method:
Pom-h can be set to 215 ℃ (190 ℃ - 230 ℃)
Pom-k can be set as 205 ℃ (190 ℃ - 210 ℃)
5. Injection speed
It is common that medium speed is too fast, too slow is easy to produce ripples, too fast is easy to produce striations and shear overheating.
6, back pressure
The lower the better, generally no more than 200bar.
7. Retention time
If the equipment has no glue retention point, pom-h can stay for 35 minutes at 215 ℃, pom-k can stay for 20 minutes at 205 ℃, without serious decomposition, and the melt cannot stay for more than 20 minutes in the barrel at the injection temperature.
Pom-k can stay for 7 minutes at 240 ℃. If the machine is shut down, the barrel temperature can be reduced to 150 ℃. If the machine is to be shut down for a long time, it is necessary to clean the barrel and turn off the heater.
8, shutdown
PE or PP must be used to clean the barrel, turn off the electric heating, and push the screw in the front position. The barrel and screw must be kept clean. Impurities or dirt can change the overheating stability of POM (especially pom-h). Therefore, when the halogen-containing polymer or other acid polymer is used up, the POM material can only be punched after PE cleaning, otherwise explosion will occur. Improper use of pigments, lubricants or materials containing GF nylon can cause degradation of plastics.
9. Post treatment
Heat treatment shall be carried out for the parts used at abnormal temperature with high quality requirements.
The annealing effect can be checked by immersing the product in hydrochloric acid solution with concentration of 30% for 30 minutes, and then observing with naked eyes to determine whether there is residual stress crack.
