- 发布时间：2021-05-08 20:19
- 发布时间：2021-05-08 20:19
Analysis of the causes of black spots and impurities before injection plastic pallets are formed?
1 During the processing of plastic pallet raw materials, due to various reasons, the foreign matter is not clean and the raw materials appear black spots;
2 Black spots caused by impure granulation;
3 The raw materials of plastic pallets are mixed with color masterbatch or speckled crushed pieces and scraps;
4 The plastic pallet material is not pure, and high melting point pellets are mixed into the low melting point material;
5 Impurities may be mixed in during packaging, transportation and storage. The obvious feature is that after unpacking the raw materials of the plastic pallet, carefully observe that there are foreign bodies and impurities on the surface of the material particles;
6 Except for 5 and 11, which will not directly pollute the hopper material, other parts may contaminate the raw materials of the plastic pallet during the feeding process, resulting in product black spots and impurities. Pollution sources include: dust in the air, suspended solids, foreign materials, foreign materials, powdered color masterbatches, colorants, etc. In order to prevent black spots caused by foreign matter and impurities, management must be strengthened to control all links (including the recycling process) from raw materials entering the factory to feeding. When changing materials, you must carefully clean up the parts where the original materials or chips may stay, especially the material storage box, hopper, funnel, hem clamp fastening, etc. During normal production, pay special attention to the cleaning of the feed source-the preparation box. After the production is stopped, the feeding port of the feeding pipe should be sealed at the place where the feeding system is exposed to the external environment, to prevent contamination, and achieve interlocking and closed management.
7 Carbonization of the raw materials of plastic pallets, such black spots are generally large in size, and the appearance diameter of large black spots can reach 1-2mm. Most of the "black spots" are thicker, and there are one or two layers of thinner. In this case, the raw material of the plastic turnover box is accumulated for a long time or partially subjected to high heat, decomposed, coked, and carbonized into agglomerates. The flow is formed by shearing and breaking in the screw or nozzle.
The reasons for the carbonization of raw materials are:
1 If the melt temperature is too high and the material temperature is too high, it will cause overheating to decompose and form carbides. Especially for some heat-sensitive materials, the temperature range is narrow, and the temperature of the barrel must not be too high.
2 Accumulated material coking: If the molten plastic stays in a place for too long, there will be coking accumulating material, causing black spots, areas that may cause material stagnation, such as the connection between the nozzle and the screw barrel, the wall of the screw barrel, and the melt ring. The contact part of the nozzle and the gate, the corner of the hot runner, the dead corner of the main runner, etc.
3 The gap between the barrel is too large, and the gap between the screw barrel and the screw is too large, which will cause the material to stay in the barrel, and the retained material will be decomposed after long-term overheating, and the plastic turnover box will produce black spots.
8 Additives reduce, decompose and discolor. Additives include antistatic agents, violet/infrared absorbers and general dyeing agents. Their properties are generally more active than the raw materials of the plastic turnover box. The raw materials are not decomposed under the action of the shearing force of the processing temperature. When they are decomposed, they become dark, yellow-brown or even black, forming black spots and impurities during molding.