Injection molding北京赛车 parameters you should know
Dalian injection moldingManufacturer to introduce you to what are the parameters of the injection molding:
1, the injection pressure
The injection pressure is provided by the injection system of the hydraulic system.The pressure of the hydraulic cylinder by injection molding machine screw is passed on to the plastic melt, under the impetus of the plastic melt in the pressure, the injection molding machine nozzle into the mold of the vertical flow channel (for part of the mould is also the mainstream way), mainstream channel, distributary channel, and the gate into the mold cavity, the process is the injection molding process, or filling process.Pressure exists to overcome resistance in the process of melt flow, or conversely, exist in the process of flow resistance need to offset the pressure of the injection molding machine, to ensure that the filling process smoothly.
In the process of injection molding, injection molding machine nozzle has the highest pressure, in order 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.
Many factors influencing the melt filling pressure, summarized up to three categories: (1) material factors, such as the type of 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) the molding process elements.
2, injection temperature,
Injection molding temperature is one of the important factors influence of injection pressure.Injection molding machine cylinder have 5 ~ 6 heating period, each material has its proper processing temperature (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.
北京赛车3, the back pressure
Back pressure refers to the screw reversed back to overcome the pressure needed for the loading。High back pressure is advantageous to the pigment dispersion and the melting of the plastic, but at the same time to extend the time of the screw retraction, reduce the length of the plastic fiber, increase the pressure of injection molding machine, and so the back pressure should be lower, generally no more than 20% of the injection pressure。Injection molding foam plastics, the back pressure should be higher than the pressure of the gas, otherwise will be launching cylinder screw。Some injection molding machine back pressure can be programming, to compensate the shrink of screw length during melting, it will lower heat input, cause a decrease in temperature。But as a result of this change is difficult to estimate, therefore not easy to make corresponding adjustment on the machine。
4, injection time
Injection time here 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。
5, 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.