to rule out more calories when molding, the mold should be designed cooling uniformity of cooling circuits, nylon, poor thermal stability of molten state prone to degradation of performance degradation plastic, so do not allow the nylon in high temperature within the cylinder for a long time. Is polyformaldehyde after nylon developed a kind of high performance thermoplastic engineering plastic, its performance as nylon, and the price is lower than nylon. Polyoxymethylene hard and smooth surface with yellow or white, translucent shape thin-walled parts.
polyphenylene oxide water imbibition is small, still have a dimensional stability in boiling water to boil, and resistant to pollution, non-toxic. Disadvantages of polyphenylene ether is plastic stress is big, easy craze, melt viscosity, liquidity is poor, low fatigue strength. Liquidity is poor, the mold should be bold runner diameter, as far as possible to shorten the length of the sprue, fully polished runner and sprue. To avoid plastic pieces of silver and bubbles, processing before dealing with plastic to fully dry, appropriate is used high temperature, anti-embrittlement temperature, high pressure, high speed injection molding, pressure maintaining and cooling time shoulds not be too long. To eliminate the stress of the plastic parts, prevent craze, annealing treatment should be made for plastic parts.
polyformaldehyde has high mechanical strength, tensile and compressive properties and outstanding resistance to fatigue strength, particularly suitable for a long time under external force of gear material over and over again. Polyoxymethylene size stability, bibulous rate is small, it has excellent antifriction and wear resistance. Polyformaldehyde ability distortion, have outstanding ability to rebound, can be used to make plastic spring products. Gasoline and oil resistant performance is very good also. Have higher electrical insulation performance. Polyformaldehyde defect is molding shrinkage rate, under the molding temperature of poor thermal stability.
polyformaldehyde molding shrinkage rate, melting point is obvious. Polyoxymethylene low melt viscosity, viscosity changes with temperature. Near the melting point of polyformaldehyde melting or solidification is very quickly, so that faster injection, injection pressure is unfavorable and exorbitant. Because of polyformaldehyde low coefficient of friction, high elasticity, so shallow lateral recess forced out are available, and can with wrinkles on the surface of the plastic figure. Due to poor thermal stability of pom, processing temperature range narrow, so we will strictly control mold temperature, in order to avoid because of the high temperature or under the allowed temperature heat for a long time and cause decomposition. Due to the cooling and solidification ruled out more calories, so should mold design uniform cooling of the cooling circuit.
in order to further the performance of nylon, always to join in the nylon antifriction agent, stabilizer, lubricant, glass fiber packing, etc. , in order to overcome the disadvantages of nylon, improve its mechanical strength. Low melt viscosity, liquidity is good, easy to produce flash, before shaping must be dry processing, easy absorption of moisture, injection molding processing large size change. Wall thickness and the thickness of gate had a great influence on molding shrinkage rate, so the plastic parts wall thickness uniform, to prevent the shrinkage cavity, when more than one module, make the gate thickness uniformity should be paid attention to.
polyphenyl ether is a deep amber color transparent thermoplastic engineering plastic, hard and tough. Polyphenylene oxide hardness higher than nylon, polyoxymethylene, polycarbonate, and small to creep, have good wear resistance, polyphenylene oxide using a wide temperature range and the long-term use of temperature was minus 127 - 121 ℃, low temperature embrittlement, da Under the condition of 170 ℃, no load continuous temperature of 205 ℃. Polyphenylene ether good electrical insulating performance. Polyphenylene oxide resistance to dilute acid, dilute alkali and salt, water and steam resistance particularly fine.
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