Injection molding machine electrical operation

An injection molding machine is operated by hydraulic power and equipped with an dectric motor and hydraulic pump. The maximum hydraulic oil pressure is ca 14 MPa (2000 psi). A hydraulic cylinder opens and closes the mold and holds the mold dosed during injection another cylinder forces the screw forward, thereby injecting the mdt into the mold. A separate hydraulic motor turns the screw to plasticate, homogenize, and pressurize the mdt. Control of these movements is a combined function of the hydraulic and electrical systems (35—37). 

Safety device All machines are equipped (or should be equipped) with applicable electrical, hydraulic, and/or mechanical safety devices. Some of them, such as injection molding machines, have all three modes for safety operations. 

The operation of the injection and clamp units and other components of the injection molding machine (opening and closing of the mold and melting and injection of the polymer material) requires power, which is supplied by an electric motor. The orderly delivery of this power depends on auxiliary systems the hydraulic and control systems. The hydraulic system, the muscle for most maehines, transmits and controls the power from the electric motor to the various parts of the maehine. Maehine functions are regulated by a careful control of the flow, direction, and pressure of the hydraulic fluid. The elements of the hydraulic system for most injection molding machines are essentially the same fluid reservoir, pumps, valves, cylinders, hydraulic motors, and lines (Figure 11.8). 

Injection molding machines are equipped with guards around the barrel, which protect the operator from bums and electric shocks. Never operate a machine without the guards in place. 

Before operating your new injection molding machine for the first lime, check all wiring to see that it has been done correctly. All exposed wires and terminals must be covered. The machine should only be plugged into a GFI outlet. GFI stands for ground fault interrupter. GFI outlets have a circuit breaker as part of the outlet. An electrical short or other problem in the wiring of your machine will flip the circuit breaker off and cut the power to the machine. 

To mold micron-scale precision parts with shot weights of only 0.0022 g, electrical operating IMMs are being used. Those who desire precise shot size (dosing) can buy electric injection machines with servomotors capable of very accurate screw positioning. With hydraulic IMMs, molders can install a valve gate that shuts when the correct amount of plastic has been injected into the mold. 

Polysulfones have been used satisfactorily in a wide range of products, including consumer, medical, automotive, aircraft, aerospace, industrial, electrical, and electronic applications. Like other engineering thermoplastics, they are replacing metals in a variety of applications because they can be injection molded into complex shapes at reduced cost since costly machining and finishing operations can be avoided. Table 15.15 lists some of the applications of polysulfones. 

Automatic press n. Hydraulic press for compression molding or an injection machine which operates continuously, being controlled mechanically, electrically, hydraulically, or by a combination of any of these methods. 

Since injection molding clamping functions are fast and can be dangerous to the operator, certain safety features are required. An interlocked sliding gate at the front of the machine protects the operator. The interlocks are electrical, hydraulic, and mechanical. 

Melting (plasticating) the plastic is accomplished in a plasticator (screw in barrel as described in Chapter 3). This melt is forced into a clamped mold cavity. The liquid, molten plastic from the injection cylinder of the injection machine is transferred through various flow channels into the cavities of a mold where it is finally shaped into the desired object by the confines of the mold cavity. What makes this apparently simple operation complex is the limitations of the hydraulic or electrical circuitry used in the actuation of the injection plunger and the complicated flow paths involved in the filling of the mold (Chapter 17). Finally opening the mold to eject the plastic after keeping the material confined under pressure as the heat in the melt is removed to solidify the plastic into the shape desired. 

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