Making the matters needing attention of injection q | | dynamic plastic
in the process of plastic doll, the highest pressure of injection molding machine nozzle, to overcome the melt flow resistance of the whole. Followed by pressure along the flow length to melt the front wave front place gradually reduce, if cavity internal exhaust is good, the melt front end pressure is atmospheric pressure.
there are many influence factors in the melt filling pressure, has three categories: (generalizing 1) The type of material factors, such as plastic, viscosity, etc. ; ( 2) Structural factors, such as the type of gating system, the number and position, the mould cavity shape and thickness of products; ( 3) Molding process elements.
2. Injection temperature
injection temperature is an important factor to affect the injection pressure. Injection molding machine cylinder have 5 ~ 6 heating period, each material has its appropriate processing temperature ( The detailed data processing temperature can refer to the material suppliers) 。 Injection temperature must be controlled in a certain range. Adverse effects, low temperature, molten material plasticizing quality, increase the difficulty of the process, Temperature is too high, the raw material easy to decompose. In the process of practical injection molding, injection molding temperature are often higher than the cylinder temperature, higher values associated with injection rate and material performance, up to 30 ℃. This is because the melt through the material when the mouth of the high heat generated by shear. When a mold flow analysis can to compensate for the difference in two ways, one is trying to measure molten material on the temperature at which the air injection, the other is a when modeling the nozzle is also included.
3. Injection time
here injection time refers to the time required for full of plastic melt ininjection mould cavity, not including mold open, close and other auxiliary time. Although the injection time is short, for the influence of the molding cycle is very small, but the injection time of adjustment for the sprue, runner and cavity pressure control is a big role. Reasonable injection time helps to melt the ideal filling, and to improve the surface quality of the product and reduce the size tolerance has very important significance.
injection time is far below the cooling time, cooling time is about 1/10 ~ 1/15, this rule can be used as the basis for all plastic parts molding time. When a mold flow analysis, it is only when the melt is entirely driven by the screw rotating fill the cavity of the case, the results of the analysis of the injection time is equal to the process conditions of injection time. If before the cavity is filled with the screw of the pressure switch, then the results will be bigger than the setting of process conditions.
4. The holding pressure and time
at the end of the injection molding process nearly, stop rotating screw, just move forward, the injection into the holding stage. Pressure to the mold filling nozzle of the injection molding machine in process of the material, to fill the vacated due to shrinkage of fabrication capacity. If you don't to the holding cavity is filled, the parts will shrink about 25%, especially the reinforcement due to the large shrinkage and forming shrinkage mark. The holding pressure is usually about 85% of the maximum pressure filling, according to the actual situation to determine, of course.
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