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CLOSED LOOP CONTROLLED INJECTION MOLDING M/C.
The advent of electronics and developments in the hydraulics over the last few years has revolutionized the Injection Moulding machine controls and improved the overall performance of the machine as well as the productivity. Although such high technology machines have been largely imported, many Indian machine manufacturers are now offering technology closer to overseas manufacturers.
One of the debated points in the controls is Open-loop and Closed-loop controls. By and large the machines offered by Indian manufacturers are open-loop control. When we talk about Closed-loop controls, we have to clearly differentiate between process control and machine control. The reason is that some of the hydraulic valves used in machine controls are Closed-loop and the machine manufacturers can easily claim that the machine offered is with Closed-loop controls. As far as the machine controls are concerned this statement is correct, however it is not the closed-loop process control.
It is therefore necessary to understand what is closed-loop process control and how does it help the processor in his operations.The processor has to monitor and control the following parameters for the best results of moulding.
1. Barrel and nozzle temperatures
2. Screw stroke and screw speed
3. Injection speed and pressure
4. Melt pressure at the nozzle tip
If all this parameters are continuously monitored and corrected, the machine will then said to have a closed-loop process control. In this case, the machine controls are dynamic and are monitoring and correcting the various parameters to achieve the right mouldings.
Once the two halves of the mould are closed, injection of the plastic material begins. It is important to ensure that the injection of the previously plasticized material into the cavity is exactly controlled. Depending on the requirements defined by the cavity shape, the plastic material flows through the mould cavity resulting in a corresponding injection speed profile. After the mould is filled, an additional quantity of metered plastic material is fed into the mould cavity during cooling phase to ensure shrinkage free and completely filled moulding.
The injection moulding machine-MPFC series - now offered by U.A.Poly Plast are designed by the moulder for the moulder. The machine uses dedicated electronics in conjunction with high response hydraulic valves to control.
1. Injection speed control (during filling phase) with super imposed melt pressure control
2. Holding pressure or follow up pressure control
3. Back pressure & suck back control
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