1. Program control of injection speed. The program control of the injection speed of the JTT-850R disc vertical injection molding machine
is to divide the injection stroke of the screw into 3 to 4 stages, and each stage uses its own appropriate injection speed. JTT-850R disc vertical injection molding machine slows down the injection speed when the molten plastic just passes through the gate, adopts high-speed injection during the filling process, and slows down the speed at the end of the filling process. This method can prevent flashing, eliminate flow marks and reduce residual stress of products. When filling the mold at low speed, the flow rate is stable, the fluctuation is small, the internal stress of the product is low, the product size is relatively stable, and the internal and external stress of the product tends to be consistent. Under relatively slow mold filling conditions, the temperature difference of the material flow, especially the large temperature difference between the material before and after the gate, helps to avoid the occurrence of shrinkage holes and dents. However, due to the long filling time, it is easy to cause delamination and poor welding weld marks on the part, which not only affects the appearance, but also greatly reduces the mechanical strength. When high-speed injection, the material flow speed is fast. When the high-speed mold filling is smooth, the molten material fills the cavity quickly, the material temperature drops less, and the viscosity drops less. Lower injection pressure can be used, which is a hot material filling state. High-speed mold filling can improve the gloss and smoothness of the parts, eliminate the phenomenon of seam lines and delamination, have small shrinkage depressions, uniform colors, and ensure fullness for larger parts of the parts. High-speed and high-pressure injection can be considered in the following situations: 1. Plastics have high viscosity and fast cooling speed, and long-process parts using low pressure and slow speed cannot completely fill all corners of the cavity. 2. For parts with too thin wall thickness, the molten material will easily condense and stay at the thin wall. A high-speed injection must be used to make the molten material enter the cavity immediately before a large amount of energy is consumed. 3. Plastics reinforced with glass fibers, or plastics containing a larger amount of filler materials, have poor fluidity. In order to obtain a smooth and uniform surface, high-speed and high-pressure injection must be used. For high-grade precision products, thick-walled parts, parts with large wall thickness changes, and parts with thicker flanges and ribs, it is best to use multi-level injection. 2. Program control of injection pressure. JTT-850R disc vertical injection molding machine usually divides the control of injection pressure into one injection pressure, two injection pressure (holding pressure) or more than three injection pressure control. Whether the pressure switch is appropriate is very important to prevent excessive pressure in the mold, prevent flash or lack of material, etc. The specific volume of the molded product depends on the melt pressure and temperature when the gate is closed during the pressure holding stage. If the pressure and temperature are the same every time when switching from the holding pressure to the product cooling stage, the specific volume of the product will not change. At a constant molding temperature, the most important parameter that determines the product size is the holding pressure. The most important variables that affect product dimensional tolerances are holding pressure and temperature. For example, after filling the mold, the holding pressure is immediately reduced. When the surface layer is formed to a certain thickness, the holding pressure rises again. In this way, low clamping force can be used to form large thick-walled products and eliminate craters and flash. The holding pressure and speed are usually 50%-65% of the highest pressure and speed when the plastic is filled in the mold cavity, that is, the holding pressure is about 0.6-0.8MPa lower than the injection pressure. Third, the program control of the plastic filling amount in the injection mold cavity. Program control of the amount of plastic injected into the mold cavity. JTT-850R disc vertical injection molding machine adopts a pre-adjusted certain metering, so that near the end of the injection stroke, there is still a small amount of melt at the end of the screw (buffering amount) , According to the filling situation in the mold, further apply injection pressure (two or three injection pressure) to add a little melt. In this way, the product can be prevented from sinking or the shrinkage of the product can be adjusted. 4. Program control of screw back pressure and speed. The high back pressure can make the melt material get strong shear, and the low speed can also make the plastic get longer plasticizing time in the barrel. JTT-850R disc vertical injection molding machine mostly uses the program design control of back pressure and rotation speed at the same time. In the screw metering full stroke, first high speed and low back pressure, then switch to lower speed and higher back pressure, then switch to high back pressure, low speed, and finally plasticization under low back pressure and low speed. In this way, most of the pressure of the molten material in the front of the screw is released, and the rotational inertia of the screw is reduced, thereby improving the accuracy of screw measurement. Excessive back pressure tends to increase the degree of discoloration of the colorant, increase the mechanical wear of the pre-plastic mechanism and the barrel and screw, extend the pre-plastic cycle, and reduce production efficiency. The nozzle is prone to drooling, and the amount of recycled material increases. Therefore, when using JTT-850R disc vertical injection molding machine, the back pressure must be adjusted properly. Recommended reading: How to calculate the injection volume and clamping force of a vertical injection molding machine based on plastic products?
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