The causes and countermeasures of mould scale after plastic injection molding
The causes and countermeasures of mould scale after plastic injection molding
1. The forming of the mold is almost all the thermoplastic plastic injection molding. When the final product function requirements must be mixed with additives (such as modification agent, fire prevention agent, etc.), molding process, these additives are very may remain in the cavity surface, lead to form scale. Die scale formation and other reasons, the most common reasons are as follows: ? raw material thermal decomposition products; ? injection molding, melt flow extreme shear force; ? inappropriate exhaust; As above model scale is often caused by a combination of different factors, and seek to find these mould scale what causes and how to prevent, very trouble, and the model scale form in a few days before. 2. Category 1 of mold scale 1) various additives produce the scale of specific categories. Fire retardants react at high temperatures to form decomposition and may produce scale products. Under the influence of excessive high temperature or extreme shear force, the anti-impact agent will be separated from the polymer and residue on the surface of the molds. 2) the pigment in thermoplastic engineering plastics is melted at high temperature, which will reduce the thermal stability of the molding material, resulting in the formation of scale of the degradation of the polymer and the decomposition of pigment. 3) special hot parts (such as molds) on the mold, the modifier/stabilizer and other additives may adhere to the surface and cause the scale. In this case, measures must be taken to achieve better mold temperature control or use special tranquilizers. The following table lists may cause of model scale and prevent measures: 3, sudden die scale measures if sudden die scale, may be due to the change in the molding conditions, change or because different batch of molding material. The following Suggestions help to improve the scale. First, the melt temperature and the visual inspection of the melt adhesive are dissociation (e.g. charred particles). Also check whether the molding material is contaminated with foreign material and whether the same cleaning material is used. Check the exhaust condition of the mould. Again, check the operation of the machine: using dye forming raw materials (except black), about 20 minutes after close the injection molding machine, demolition of nozzle, connection, and if possible with screw removed, check whether the raw material is burning in the grain, raw material color comparison, quickly find out the source of scale. In many cases there is a surprising cause of scale defects. This technique is most suitable for the smaller injection molding machine and the maximum diameter of 40mm screw. The removal of molds also makes the quality of the parts made clear and improved when other raw materials are formed. The above countermeasure also applies to the forming of hot runner system. Mold scaling causes the appearance defects of the injection molding, especially the making of surface etching, which can be patched by sandblasting. 4. The mould maintenance and maintenance shall be strengthened in the maintenance of the mould. The mould surface is easy to clear in the initial stage, so the cavity and exhaust channels must be cleaned and maintained regularly (for example after each batch of molding production). It is very difficult and time-consuming to remove the mold after forming thick coating. The injection mould maintenance and maintenance of injection mould mainly include: mold release agent, anti-rust agent, top - needle oil, adhesive cleaning agent, mould cleaning agent, etc. The chemical composition of molds is very complex, and it must be used and tried out new methods, such as general solvents and various special solvents, oven sprays, caffeinated lemonade etc. Alternative strange ways of using clean model track rubber. 5. When it is recommended to use heat flow path forming and heat-sensitive raw materials, the melt residence time will be longer, which increases the risk of the decomposition of raw materials to form the scale. Clean the screw of injection molding machine. When the raw material of the shearing force is sensitive, it can reduce the flow distance and reduce the risk of forming the mould scale by using the larger runner and gate. The effective mold exhaust can reduce the possibility of forming the mold, and set the appropriate mold exhaust in the design stage of the die. Automatic purge and exhaust system, or the exhaust mode that can easily remove the scale is the best choice, the improvement of exhaust system often results in the reduction of mold scale. A special non-stick coating is covered on the surface of the cavity to prevent the formation of the mold, and the effect of the coating should be evaluated. The surface of the mould can be treated with titanium nitride to avoid mold forming.
