Clamping units

Cost-effective production of high-quality plastic products is the prime target of the plastic processor. As an example, the continually growing pressure from the competition demands the choice of IMMs with the smallest possible injection and clamping units in order... 

The assembled cell was put between two metal collectors and pressed to the level of operating pressure for purposes of reduction of the contact resistance of assembly parts between power covers of the clamp unit. 

CIVIL ENGINEERING, 429 455 CLADDING, 272 CLAMP FORCE, 62 73 CLAMPING UNIT, 56 CLARITY, 312 454 CLAY, 21... 

Injection molding involves two distinct processes. The first is melt generation, mixing, and pressurization and flow, which is carried out in the injection unit of the molding machine. The second is product shaping, which takes place in the mold cavity. Injection molders, therefore, have two distinct parts the injection unit and the mold/clamping unit. The function of the injection unit is to melt the polymer and inject it into the mold the function of the clamping unit is to hold the mold, open and close the mold, and eject the finished product. 

Figure 3.46 Clamping unit with a toggle mechanism.

Figure 3.47 presents a schematic of a hydraulic clamping unit in the open and closed positions. The advantages of the hydraulic system is that a maximum clamping force is attained at any mold closing position and that the system can take different mold sizes without major system adjustments. 

Such RIM plants are Indeed typical of the Industry. The comparable output for a SMC operation would employ 13 clamp units. A comparable output 1n an Injection molding operation would require seven large extruders of at least 2,500 ton clamping capacity. 

In addition to the accumulator head, a number of other machine advances have taken place in the past 20 years. These are in-mold prefinish, automated flash trimming, leak detection, and conveying to filling station. Also, dual accumulators allow up to four parisons to be extruded simultaneously and molded on the clamping unit. 

Injection equipment consists essentially of two parts the injection and clamping units. The injection unit melts the polymer and injects it in the mold. The vast majority of modern injection presses use a reciprocating screw. As in an extruder, the screw rotates, melts the polymer and pumps it. Furthermore, in most injection molding units, the whole screw can also axially move forward, acting like a plunger to inject the resin into the mold cavity through runners and gates. 

These functions must be performed automatically under conditions that ideally should result in a high quality and cost-effective part. Injection molding machines have two principal components to perform the cyclical steps in the injection molding process. These are the injection unit and the clamp unit (Figure 11.4). We now describe the operation of the various units of the injection molding machine... 

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). 

The size of injection molding machines is usually specified in terms of injection capacity and clamp force. These factors are not directly related. Other important variables are the L D (length to diameter) ratio, barrel size, plasticizing rate, injection rate, and injection pressure. Major components of injection molding machines include the injection unit, the clamp unit, and the machine base which contains the power and control units. 

The main component of an injection-molding machine are (1) the injection unit which melts the molding material and forces it into the mold (2) the clamping unit which opens the mold and closes it under pressure (3) the mold used and (4) the machine controls. 

Several techniques can be used for the clamping unit (1) hydraulic clamps, in which the hydraulic cylinder operates on the movable parts of the mold to open and close it (2) toggle or mechanical clamps, in which the hydraulic cylinder operates through a toggle linkage to open and close the mold and (3) various types of hydraulic mechanical clamps that combine features of (1) and (2). 

An injection molding machine is used. The clamping unit is used as a press and preplasticizing is done in the injection unit. With this technique, much more precise feeding of the preplasticized mixture keeps the molding tolerances down. 

A further development of TM is to plasticize the mbber mixture in a screw-type extmder solidly attached to the press, heat it up and inject it into the transfer cylinder. Closing the clamping unit then fills the mold cavities as in normal TM, Fig. 44 [7]. 

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