Brief Introduction of Extruder Molding Control

Heating and cooling systems

The heating and cooling system of the extruder mainly refers to the heating and cooling of the barrel (including the molding die and screw) in the extrusion plasticizing system.The purpose of heating or cooling the barrel (molding die and screw) is to control the process temperature of the raw material during extrusion machine plasticization, so that it is limited to a certain range to ensure the normal production of plastic products made by the extruder.

Heating of the barrel

The heating methods for the barrel (molding die) in the extruder include resistance heating, induction heating and heating medium heating.

Resistance heating

The structure of the resistance heating method is relatively simple. It mainly allows the current to pass through a wire with relatively large resistance (resistance wire) to generate heat and conduct it to the barrel that needs to be heated.The cast aluminum sleeve resistance heater is to install the resistance wire in a metal tube, fill the tube with insulating materials such as magnesium oxide powder, and then cast the metal tube in an aluminum alloy.This kind of resistance wire heating cast aluminum sleeve resistance heater has magnesium oxide insulation powder in the tube, which is well sealed and prevents premature oxidation of the resistance wire, and has a long service life; the aluminum alloy sleeve has a large contact area with the outer circle of the barrel and has good heat transfer performance.

Electric induction heating

Electric induction heating device, when the barrel is heated by electric induction, a coil is installed on the outer circumference of the barrel, and a magnetic silicon steel sheet is installed on the outer circumference of the coil.When current passes through the coil, the silicon steel sheet and the barrel form a closed magnetic circuit. The alternating magnetic flux induces current in the barrel, and the barrel generates heat due to a certain resistance value.The barrel adopts the electric induction heating method to heat up quickly, and the inductor application materials have a long working life, but the inductor application devices are more complicated.

Heating by heat carrier

Using steam or oil as a heat carrier to heat a simple machine requires pipeline transportation and a heating source for the heat carrier (boiler or resistance heat source). The equipment is complex, the cost is high, and the temperature control is difficult, so it is very difficult to use.However, this heating method has a gentle and uniform temperature, which is very suitable for heating heat-sensitive plastics.

Barrel cooling

The cooling of the barrel in the extruder,  the cooling of the extrusion plasticizing part in the cylinder, the cooling of the hopper seat and the cooling of the screw.The cooling of the plasticizing part is mainly a cooling measure to prevent the temperature of the machine from being too high during operation.There are two cooling methods: water cooling and air cooling.At present, the most widely used method is air cooling.It uses a fan to directly blow the part of the barrel that needs to be cooled, and the cold air takes away the heat of the barrel, thereby achieving the purpose of cooling the barrel.The fan cooling barrel method is simple, the equipment structure is simple, the thermal shock to the barrel is small, the cost is not high, and the maintenance and production operation are relatively convenient.

Cooling of the hopper seat

The cooling of the hopper seat is mostly carried out by cooling water.The purpose of cooling is to prevent excessive heat from being generated in the hopper due to forced feeding.In addition, it is also to prevent the temperature of the screw feeding section from being too high. If the temperature of these two parts is too high, it will mainly affect the feeding of the hopper and the forward transportation of the material entering the screw feeding section.

Cooling of the screw

The screw is usually cooled with heat transfer medium oil. A rotary joint structure is used to connect the rotating screw center hole to the oil pipeline, allowing the heat carrier oil to pass into the screw body through the rotary joint, taking away the heat of the screw and achieving the purpose of cooling the screw.

Control system

The control system of the extruder mainly refers to the control of the screw speed, the heating temperature of each section of the barrel, the temperature of the molding die and the pressure required for the molten material to form the product.The function of these position control devices is to ensure that the extruder works within the set process conditions so that the extruder can produce plastic products stably and smoothly.