Screw Barrel Assembly and Melt (Gear) Pump

       The main purpose of screw and barrel assembly is to melt the plastic and ten pump the molten plastic through a narrow opening of the die. Injection molding machines have a good injection mechanism to pump the molten plastic into the cavity of the mold. In injection molding machine screw of machine cam move to and fro like reciprocating pump and pumps the plastic with very high pressure.

In plastic extrusion machines (Extruders) to achieve high pressure some time not possible. Dies with complex profile design required high pressure that an extruder cannot generate in this case a device is used to increase the pressure of molten plastic that is called melt pump. Extruders with more than two screws have high through put but lesser pressure. To achieve high pressure is not the only cause of use melt pumps. Gears are used for pumping the melt that is why melt pumps also called as gear pump. The second function of the gear pump as a component of the extrusion equipment is to keep the flow and pressure of the plastic melt flow to the die at a continuous and constant level. The quality of the extruded material is thus highly increased.

The feed fluctuations of the extruder screw are thereby compensated by the pump. The output of the extruder can usually be increased. The results of older extruders are thus also highly improved.

Advantages of Melt Pump

More accurate gauge control

Fluctuations in melt pressure can be minimized by adding melt pump. Poor melt pump design can be more adverse and increases the pressure fluctuations. Straight teeth gear are replaced with gears having teeth in angle.

Increased output rates

Addition of melt pump can increase the output rates of melt without any additional load on the machine.

Increased life on extruder screw & barrel

Screw and barrel are the main and expensive parts. When high forces are applied to these parts wear and tear starts. High shear forces means high rate of wear.

Lower energy consumption

Energy consumption in high when a single screw has to perform two jobs. When we add a melt pump stress on screw decreases and less energy required.

Lower shear stress

When melt pump is attached then screw not need to generate high pressure. High pressure means more shear stress. Shear stress in very simple words is a force which resist the screw to rotate in the barrel.

Faster start-ups and Reduced scrap

Fluctuations at the start can be minimized and hence scrape generated at the start is also reduced.

Lower processing temperatures

Disadvantages of Melt Pump

Disadvantage of melt pump is limited like more capital cost and maintenance cost