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GRP tile is a new type of composite material, composed of glass fiber and resin. It not only has the high strength, hardness and transparency of glass, but also has some advantages of plastic, such as...
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BMC insulation is a thermoset composite material consisting of staple fiber reinforcements, fillers, resins, and additives. These components are blended to form a flowable mixture that can be processe...
SMC mold surface dullness refers to a lack of gloss and reduced transparency in transparent products. There are many reasons for poor gloss, and below we will analyze three of them.
SMC compound mold malfunction
If there are scratches, corrosion, micro-pores and other surface defects on the surface of the SMC sheet mold, it will reflect and cause poor gloss on the surface of the plastic part. If there is oil, water, too much or inappropriate use of release agent on the surface of the mold cavity, it will also make the surface of the plastic part dark. Therefore, the surface of the mold cavity should have good smoothness, and it is best to polish or chrome plate the surface.
The mold cavity surface must be kept clean, and oil stains and water stains should be removed in a timely manner. The type and amount of release agent should be appropriate, and the mold temperature has a great influence on the surface quality of the plastic part. Usually, different types of plastics have a large difference in surface gloss under different mold temperature conditions, and too high or too low mold temperature will cause poor gloss. If the mold temperature is too low, the molten material solidifies immediately after contacting the mold cavity, which will reduce the reproducibility of the mold cavity surface.
In order to increase the gloss of SMC compound molds, the mold temperature can be appropriately increased. It is best to use the method of passing warm water into the mold cooling circuit to quickly transfer heat energy in the cavity, so as to avoid prolonging the molding cycle. This method can also reduce residual stress during molding. Generally, except for polystyrene, ABS, and AS, the mold temperature can be controlled above 100℃. However, it should be noted that if the mold temperature is too high, it will also cause the surface of the plastic part to darken.
Improper control of SMC compound molding conditions
If the injection speed is too fast or too slow, the injection pressure is too low, the holding time is too short, the booster pressure is not enough, the dispersion performance of the fiber-reinforced plastic filler is too poor, the filler is exposed or the aluminum foil-like filler is not directionally distributed, the temperature in the barrel is too low, and the plasticization of the molten material is not good, and the supply is insufficient, it will cause poor gloss on the surface of the plastic part. For this, adjustments should be made according to specific situations. If a dark area appears near the gate or at a variable cross-section, it can be eliminated by reducing the injection rate, changing the gate position, expanding the gate area, and adding a circular arc transition at the variable cross-section. If there is a thin layer of milky white on the surface of the SMC product, the injection speed can be appropriately reduced. If the poor gloss is caused by the poor dispersion performance of the filler, a resin with better fluidity or a screw with stronger blending ability should be used.
The SMC compound molding raw materials do not meet the requirements
If the water or other volatile content in the molding raw materials is too high, the volatile components during molding will condense between the mold cavity wall and the molten material in the SMC product mold, resulting in poor gloss on the surface of the plastic part. Therefore, the raw material should be pre-dried. If the colorant decomposes and changes color, materials and colorants with higher temperature resistance should be selected. If the fluidity of the raw material is too poor, the surface of the plastic part will not be tight, resulting in poor gloss. A resin with better fluidity or an appropriate amount of lubricant can be used to increase the processing temperature. If the raw material is mixed with foreign materials or incompatible raw materials, new materials should be used. If the particle size of the raw material is uneven, raw materials with too large particle size differences should be screened out. For thick-walled plastic parts, if the cooling is insufficient, the surface of the plastic part will become hairy and the gloss will be dark. The solution is to immediately put the plastic part into a cold-casting mold immersed in cold water for cooling and setting after taking it out of the mold. If the proportion of recycled materials in the raw materials is too high, it will affect the uniform plasticization of the molten material, and the amount should be reduced.
