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What are the common defects of plastic injection products?

  The quality of plastic products includes internal quality and apparent quality. Internal quality includes internal stress, impact strength, product shrinkage, fusion strength, etc. We describe the various apparent defects commonly found in plastic products:
     Plastic products include: plastic injection (TPU, TPR, ABS, NYLON and other shoes, trademarks, plastic products), spray paint (TPU, TPR, ABS, NYLON, rubber outsole, PU midsole painting, rubbing, lacquer, leather Materials, finished shoes, color processing, etc.) Plastic mold development and production, TPR Hongbao rear lining, 3D foam printing, UPU products, jelly body, KPU trim.
   1. Depression, shrinkage, and porosity
   1. Causes: The moisture absorption of the raw material is too large, the drying is not good, the wall thickness of the product is uneven, the cavity pressure is insufficient or the air stored in the cavity is not removed to form a barrier so that the melt cannot be completely touched with the surface of the mold, or Due to the lowering of the material cooling rate, it causes severe depression on the surface of the product, and the shrinkage hole position occurs mostly on the surface of the rib and away from the gate.
   2. Prevention method: In the design of products, it is necessary to prevent the wall thickness from being uneven due to the ribs. In the selection of materials, materials with small shrinkage rate are selected, and the molds are opened in the wall thickness, and the mold temperature is lowered in the process. Increase the injection pressure, dwell time and injection volume, strengthen the cooling where the shrinkage is likely to occur, and increase the gate cross-sectional size.
   Second, dull, cold white, bruises and wrinkles
   1. Causes: The defects are mostly caused by the mold temperature being too low, the polymer melt temperature is too high, and the cooling is too fast. When the melt is still filling, it is formed on the cavity wall. Hard shell. The shell is subjected to various forces to make it white and sturdy. In severe cases, the shell may be torn and wrinkled. Another reason for this phenomenon is that the melt has irregular pulsations in the mold. Flow, such as when the gate size is small and the injection speed is large, the fine flow of the polymer melt is injected into the cavity, and the fine jet appears after a period of time when the surface is cooled and then fused with the subsequent melt. .
   2, prevention methods: increase the mold temperature, increase the flow channel, gate.
     Third, silver wire and peeling layer
   1. Cause: When full, the wave front peaks out volatile gases. These gases are often decomposed by heat. The gas is distributed on the surface of the product, leaving silver streaks. When the moisture content of the material is too high, heating will occur. Water vapor is generated. Due to the unfavorable operation of the screw during plasticization, the air carried by the material cannot be discharged, and silver streaks are also generated. In some cases, large bubbles are elongated into flat bubbles to cover the surface of the product, so that the surface of the product is peeled off. Layer. Sometimes the temperature gradient from the barrel to the nozzle is too large to cause too much shear to produce silver.
   2. Prevention method: Select the drying equipment and drying process to reduce the moisture content to the lowest value. Reduce the melt temperature in the process, increase the mold temperature, stabilize the nozzle temperature, increase the back pressure, and open the exhaust groove in the mold.
   4. Charred, dark lines and dark spots
   1. Causes: Dark lines or dark spots are mostly caused by overheating decomposition of materials. Some are due to uneven plasticization. They are dark spots from the appearance, some are caused by foreign matter, and the air in the mold is compressed during the die. High scorch, which occurs mostly at the fusion joint.
   2, prevention method: the material is dry enough, reduce the melt temperature, improve the back pressure, improve the exhaust in the mold.
   5. Warping, deformation
   1. Cause: The corresponding force of the polymer structure, mechanical stress, thermal expansion and contraction stress (temperature stress) are caused by the residual inside the product, and the general crystal form is larger than the amorphous type.
   2, prevention methods: reduce the orientation, increase the size of the gate, properly reduce the melt and mold temperature, increase the injection rate, properly extend the injection pressure holding time, reduce the pressure at the gate, the structure of the product is reasonable, improve the demoulding Slope surface roughness. Ejection position, area, etc.
   6. Cracks
   1. Cause: The cracks arranged in the direction of the force of the molecular chain under the action of stress, when the demolding force is unbalanced, the mold release causes the vacuum suction to cause cracking.
   2, prevention methods: the use of methods to eliminate internal stress, such as increasing the melt temperature and mold temperature, reducing the injection force, using annealing, etc.
   Seven, fusion joints
   1. Cause: When two or more melts are closed, the wave front is formed by foreign matter blocking gas impurities.
   2, prevention methods: appropriate increase of mold temperature and melt temperature, increase injection force and injection speed, mold on the open exhaust, add cold wells, adjust the film and so on.
   Eight, overflowing edge
   1. Cause: The overflow edge is overflowing from the mold parting surface when filling the mold, and the flash is formed after cooling. Due to insufficient clampingforce of the injection molding machine or poor system rigidity, the precision of the mold is poor, the process is unreasonable, etc. .
   2, prevention methods: select the clamping force is sufficient, the system is rigid equipment, improve the mold; process, the clamping force is adjusted reasonably, reduce the mold temperature, melt temperature, injection temperature, pressure and pressure holding switch position and so on.