POM (also known as Saigang, Trane). It is obtained by polymerizing formaldehyde and the like as raw materials. POM-H (polyoxymethylene homopolymer), POM-K (polyoxymethylene copolymer) is a high density and high crystallinity thermoplastic engineering plastics. It has good physical, mechanical and chemical properties, especially excellent friction resistance.

POM is a crystalline plastic with a clear melting point. Once the melting point is reached, the viscosity of the molten material decreases rapidly. Decomposition occurs when the temperature exceeds a certain limit or the melt is heated for too long.

Copper is a catalyst for POM degradation, and copper or copper materials should be avoided from contacting the POM melt.

1, Plastic processing

POM has low water absorption, usually 0.2% -0.5%. Under normal circumstances, POM can be processed without drying, but the wet material must be dried. The drying temperature is higher than 80 ° C for more than 2 hours. Specific conditions should be based on the provider's data.

The proportion of recycled materials usually does not exceed 20-30%. However, depending on the product type and end use, it can sometimes be as high as 100%.

2, choose plastic machine

In addition to the requirement that the screw has no stagnation area, POM has no special requirements for the injection molding machine and can usually be injection molded.

3, mold and gate design

Common mold temperature control is 80-90 ° C] C, flow 3-6mm channel diameter, door length 0.5mm, door size and wall thickness depend on a given gel, should be at least 0.5 -The width of 0.6 times rectangular door is usually 2 times or more than the thickness, the depth is 0.6 times the thickness of the wall and the angle is between 40'-1 ° 30 ' Exhaust system

4, POM-H thickness 0.01-0.02mm width 3mm POM-K thickness 0.04mm width 3mm

As shown in Figure 4, the temperature of the melt can be measured by air-to-air method

POM-H can be set to 215 ° C (190 ° C -230 ° C) POM-K can be set to 205 ° C (190 ° C -210 ° C)

5, injection speed

The average speed is usually too fast, too slow to produce fluctuations, too fast and prone to shooting and shearing overheating.

6, back pressure

The lower the 越, the better, generally not more than 200 bar

7, permanent time

If the device has no glue retention points.

POM-H can be kept at 215 ℃ for 35 minutes

POM-K can be stored at 205 ° C for 20 minutes without serious decomposition. At the injection temperature, the melt cannot remain in the cylinder for more than 20 minutes. POM-K can be stored at 240 ° C for 7 minutes. If the machine is switched off, the temperature of the bucket can be reduced to 150 ° C. If a long shutdown is required, the machine must be cleaned and the heater switched off.

8, shutdown

The cleaning cylinder must be turned off with PE or PP and the screws pushed to the front position. The barrel and screws must be kept clean. Impurities or dirt can alter the thermal stability of POM, especially POM-H. Therefore, when halogen-containing polymers or other acidic polymers are depleted, POM materials can be used after cleaning with PE, otherwise explosion will occur. Pigments, lubricants or inappropriate materials containing nylon GF can cause plastic degradation. 9, post-processing

Hot parts and high quality requirements require heat treatment.

The effect of the annealing treatment can be performed by immersing the product in a 30% strength hydrochloric acid solution for 30 minutes, and then visually discriminating whether the crack has residual stress.