How to control the parameters of vertical injection molding machine?

The parameters of vertical injection molding machine mainly include injection speed and injection pressure control, PVT pressure maintaining process control, buffer control, back pressure control and so on.

Injection speed refers to the speed of screw advance, which will affect the injection pressure, melt flow rate and other parameters, and directly affect the quality of products. The control of the injection speed includes two meanings: one is the open-loop or closed-loop control of the speed of the screw (or plunger) to push the material. The other is the multi-stage switch of the position and the value of the speed of the screw propulsion, which is called the multi-stage switch or control of the injection speed.

For the control of injection pressure, the traditional vertical injection molding machine generally carries out pressure switch based on stroke and time, and its control also includes two meanings: one is the open-loop or closed-loop control of the pressure of the screw propulsion material. The other is the multi-stage switch of position and pressure value of the screw propulsion pressure, which is called multi-stage injection pressure switch or control. In the traditional injection molding machine, the position switch from the injection pressure to the holding pressure is adopted, and the control method of switching from the position to the multi-stage holding pressure with time in the stage of holding pressure is adopted. The injection pressure control of the advanced injection molding machine relies on the detection of the cavity pressure to achieve the pressure switch, that is, through a preset program to control. In other words, the pressure value of the switching point is first stored in the control system and then converted into a logical control signal. If the pressure in the mold cavity is the same as the set value, it will be immediately switched to the pressure-maintaining control.

Modern injection molding machine pressure control with high accuracy and stability of PVT pressure control, namely with pressure and temperature sensors on the cavity pressure and the nozzle material and cavity temperature testing, and as a feedback signal input to the control unit to “PVT” (T – the temperature of the material in cavity, V – specific volume, P – cavity pressure) logic operations, and then issue instructions to proportional control of proportional pressure solenoid valve, so that the injection and pressure maintaining system of hydraulic can change according to the PVT characteristics curve of the command. The temperature of the melt in the mold is a function of time, which is obtained by continuous detection of the sensor.

Buffer control is the control of the screw head residual material, it plays a buffer and control the injection precision. It detects the screw position by the displacement sensor and obtains the set value of the next screw position by calculating the memory signal of the previous screw position detection.

When the screw is premolded, the pressure of the melt in the measuring chamber is called the back pressure. Back pressure control is to reduce the axial temperature difference, which is beneficial to melt compaction. It is realized by multi – stage control of preselected oil pressure. When the screw is premolded, it will retreat under the action of materials, which will cause the return oil of the injection cylinder chamber to flow back to the oil tank through the back pressure valve. Therefore, the pressure of the melt at the head of the screw (shear heat) can be adjusted by adjusting the oil discharge pressure of the back pressure valve at different positions of the screw, so that the axial temperature difference can be adjusted.

youngstrong
Dongguan Taiwang Machinery Co.,LTD
Add:NO.127,longyan road,Chongkou Industrial district,Dongguan city,China.
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