Plastic parts of the wall thickness of the impact of a great impact on the wall thickness is too small, the flow resistance, large and complex plastic parts will be difficult to fill the cavity.Plastic parts of the smallest wall thickness should meet the following requirements:
1, with sufficient strength and stiffness;
2, stripping can withstand the impact of the stripping mechanism and vibration;
3, when the assembly can withstand tightening force.
Injection molding plant provides a minimum wall thickness, due to the plastic pieces of various varieties, grades and products vary the size of the plastic parts of the wall thickness is not only a waste of raw materials, thermosetting plastic molding processing, but also increased the molding Of the time, and easy to cause curing is not complete; and for thermoplastic, then increase the cooling time. Also affect the quality of plastic parts processing, the same injection molded body wall thickness should be as uniform as possible, otherwise because of cooling and The unevenness of the curing rate produces additional stress.
A wide range of plastic, but many small plasticity, large crystallinity, small surface tension, poor wetting, smooth surface, in order to improve the coating of plastic adhesion, reduce the surface of the various defects, thereby improving the quality of plastic coating , Plastic parts before painting to be surface treatment. The pretreatment methods of plastic parts are: annealing; degreasing; electrostatic dusting; wetting and coarsening.
Annealing: plastic in the formation of easy to form internal stress, stress concentration in the Department of easy cracking, in order to ease the internal stress generated when forming to prevent cracking, to be annealed.
Degreasing: plastic surface must be degreased when oil and degreasing. Degreasing method and metal similar to alkaline washing solution can be used, such as surfactants.
Electrostatic dust: most of the plastic is the insulator, easy to produce static electricity and adsorption of dust, so the mass production of parts, commonly used compressed air through the electrostatic generating device, electrostatic dust.
Wet and coarser: chromic acid,Plastic Parts sulfuric acid mixture solution, is a more convenient traditional method, it can make the plastic surface of the wettability significantly improved. Impregnating the plastic with an organic solvent can remove various amorphous parts of the plastic surface, roughenize or have multiple reactivity, and improve the adhesion of the coating.
The temperature will affect the degreasing speed, in general, high temperature to speed up the oil removal rate, but the temperature is too high will cause decomposition of the surfactant, affecting the oil removal effect.
Alkaline solution degreasing is usually carried out in the steel tank, the temperature is between 50 ~ 80 ℃, the number of degreasing depends on the amount of production and oil pollution, usually 1 to 2 times,Plastic Parts for large quantities of parts can be used pressure spray emulsifier Oil: the use of emulsifier wetting, emulsification, solubilization and dispersion capacity, remove the surface of the oil, such as OP emulsifier. Solvent degreasing: the use of organic solvents on the grease solubility, remove the surface of the oil, commonly used organic solvents are gasoline, kerosene, rosin and so on.