POM black recycled pellets usually need to be pretreated before processing. Although POM material itself has low water absorption, recycled pellets stored in a humid environment still need to be dried to remove possible absorbed moisture. This is because moisture will react with POM, causing bubbles or cracks in the product, affecting product quality. Drying is usually carried out at a temperature of about 80°C for no less than 2 hours to ensure that the recycled pellets are fully dried.
The processing temperature range of POM is relatively narrow, generally between 0 and 215°C. When the residence time in the barrel is slightly longer or the temperature exceeds 220°C, POM will decompose and produce irritating formaldehyde gas. Therefore, the temperature needs to be strictly controlled during processing to avoid overheating and decomposition of recycled pellets. The barrel temperature should usually be controlled at 150-180°C. This temperature range can ensure the full plasticization of POM and avoid its decomposition. At the same time, the nozzle temperature should be slightly lower than the barrel temperature to prevent the melt from overheating at the nozzle.
Mold temperature is an important factor affecting the strength and dimensional stability of POM products. Generally speaking, the higher the mold temperature, the longer the crystallization time, which is conducive to the growth of crystals and the complete crystallization of products. However, too high mold temperature will also cause the cooling time of the product to be too long, affecting production efficiency. Therefore, the mold temperature should be controlled between 75 and 120 ° C, and the specific temperature needs to be adjusted according to the thickness, shape and performance requirements of the product. In order to reduce the shrinkage rate after molding, a higher mold temperature can be selected.
The size of the injection pressure mainly depends on factors such as the melt fluidity of POM, the thickness and width of the runner and gate, and the thickness of the plastic product. For the injection molding of POM black recycled particles, the injection pressure is usually 40 to 130 MPa. For thick-walled products, the injection pressure can be a small value; conversely, for thin-walled products, a large value should be taken. The injection speed should be selected at a medium or high speed to ensure that the melt can quickly fill the mold cavity.
In the injection molding process of POM black recycled particles, the screw speed cannot be too high and the residual volume should be small. This is because too high a screw speed will cause the melt to stay in the barrel for too long, increasing the risk of decomposition. At the same time, the back pressure should also be kept at a low level, generally not exceeding 200 bar, to reduce the pressure drop and shear heat of the melt at the screw head.
After the molten POM enters the mold, it will quickly cool and harden to form a preset shape. This process requires precise control of the cooling time and cooling rate to ensure the dimensional stability and performance of the product. Generally speaking, the cooling time depends on the size and thickness of the product, as well as the cooling effect of the mold. During the molding process, it is also necessary to avoid problems such as internal stress or deformation of the product.
After the product is pushed out, some post-processing operations may be required, such as trimming burrs or flashes, grinding, drilling or assembly. These operations should be carried out according to the specific requirements of the product. Finally, the product needs to be quality inspected, including appearance inspection, dimensional measurement and performance testing, to ensure that it meets the design requirements and quality standards.
The processing conditions and molding process of POM black recycled particles require strict control of multiple parameters such as temperature, pressure, speed, etc. to ensure the quality and performance of the product.
