Black spots and impurities are characterized by small particles, dark brown in color, and generally non-reflective. When the particles are large, the impurities are layered, brittle, fragile, and porous after being broken. There are two characteristics as below.
1. Some are distributed randomly and scattered as a whole, some are distributed randomly and scattered partially, and sometimes there are occasionally scattered in a certain section of the plastic profile extrusion product;
2. This kind of black spots and impurities sometimes only appear on the surface of plastic profile products, sometimes regardless of the depth of the surface and the inside, but the inner black spots closer to the surface are lighter in color than the surface black spots, and the deeper black spots can’t be seen at all. What is interesting is that if you link these two points together, you will find that impurities that only appear in a certain section area which must be black spots on the surface, and the distribution of black spots, regardless of the depth or depth of the surface, must be the overall irregular and scattered distribution.
This is because the internal impurities exist before the plastic profile is extruded, and the impurities that only appear during extrusion only be distributed on the surface. In this way, impurities are divided into two categories: before plastic profile extrusion and during the extrusion process.
The causes of black spots and impurities before plastic profile extrusion:
1. During the processing of raw materials, there are some black spots in the raw materials;
2. Black spots caused by impure granulation;
3. The raw material is mixed with color masterbatch or speckled crushed pieces and scraps;
4. The material is impure, and high melting 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 the raw materials are opened, carefully observe that there are foreign bodies and impurities on the surface of the material particles;
6. Except for 5, which will not directly pollute the hopper material, other may pollute the raw materials during the feeding process, causing black spots and impurities in plastic products. Pollution sources include dust in the air, suspended solids, foreign material scraps, foreign material pellets, 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 the raw material entering the factory to the 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 the preparation box. After stopping production, seal the feeding port of the feeding pipe where the feeding system is exposed to the external environment to prevent contamination, and achieve interlocking and closed management.
7. The raw material is carbonized. This kind of black spots is generally larger in volume, 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 materials are accumulated for a long time or locally subjected to high heat, decomposed, coked, and carbonized into agglomerates. The flow is formed by shearing and breaking in the screw or nozzle. ,
Dongguan H.D.Plastics Products specializes in the production of extruded (extruded) plastic profile extrusion products. We can customize and process a variety of plastic profiles, PVC profiles, abs profiles, pp profiles, PC lampshades, transparent plastic profiles, and other profiles. Self-built mold room, specializing in providing solutions for all kinds of profiled materials with more than 10 years of experience in designing extrusion dies processing as well.