Injection machine barrel design

Injection Machine Barrel Design Each heated zone of the barrel (feed, transition, metering) should be controlled independently and should provide for accurate closed-loop feedback control. A bimetalUc barrel is recommended (an abrasive resistant carbide particle liner material inside an alloy steel outer shell). 

Plasticator A very important component in a melting process is the plasticator with its usual specialty designed screw and barrel used that is used in different machines (extruders, injection molding, blow molding, etc.). If the proper screw design is not used products may not meet or maximize their performance and meet their cost requirements. The hard steel shaft screws have helical flights, which rotates within a barrel to mechanically process and advance (pump) the plastic. There are general purposes and dedicated screws used. The type of screw used is dependent on the plastic material to be processed. 

In the injection molding process, setting the temperature involves optimization of the temperature profile of the plasticating unit (extruder barrel), temperatures of the mnners and gates, (aU these determine the molten polymer temperature) as well as the mold temperature. The temperature setpoints depend on the material type (viscosity profile, thermal and shear stability, thermal properties) as well as machine or process considerations (machine capacity to shot size ratio, screw design, mold and part design, cycle time, etc.). Temperatures of the two basic units, the injection system and the mold, should be discussed separately since their selection stems from very different considerations. 

While injection molding machines designed specifically for processing thermoset materials are available, a number of manufacturers offer replacement screw and barrel assemblies and stuffer hoppers to convert conventional thermoplastic injection moulding machines to process thermosets. 

The relationship between these variables is complex and needs to be fully understood through use of factorial experiment design for each type of machine used in the factory. The unit must allow the rubber to be processed uniformly without scorch. There must be a smooth pathway for the rubber, free from dead zones where there is little or no rubber flow. Rubber that collects in these zones will soon cure to form hard nibs that will grow in size until they re-enter the material flow, impede the injection, and produce moulding faults. This problem exists in many existing machines where the first rubber to pass into the injection barrel is the last to be injected, and may be partially retained for many cycles. The design of the injection unit is therefore crucial to the operation of the machine. 

The basic design of an injection molding machine is shown in Figure 1.3. As heart of the machine the heated barrel of the injection unit can be taken containing a... 

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