What is the principle of the extrusion machine and the structure of each section?

What is the principle of the extrusion machine and the structure of each section?

1、 Extrusion machine Basic Principles of Extruder

Melt and compact the polymer, and use a constant current source, temperature control, and constant rotation workbench speed to guide it towards the mold shell, producing a mold blank in the molten state of the product based on the mold shell. But the single screw extruder is different from the single screw extrusion mechanism in terms of manufacturing, principles, and processing standards for its operation.


2、 Structure of the extrusion machinery

The entire process of plastic extrusion is achieved by using the extrusion line screw to transport, compact, and further melt the plastic in a completely uniform melting state. The plastic is then extruded from the mold mouth under working pressure, shaped by forming mechanical equipment, and cooled to produce the desired product.

Therefore, the extruder is the main equipment for plastic extrusion, which determines the quality and production capacity of the extruded product. The extruder is mainly composed of extruder screws, material barrels, heating and cooling systems, transmission devices, and control devices. The extruder screw is an important component of the extruder, responsible for the transportation, compaction, melting, homogenization, charging, and pumping of raw materials throughout the entire extrusion process.

PVC Pipe Extrusion Line

3、 The efficiency of each section of the extruder

A typical single screw extruder is a three stage extruder, which includes feeding, shrinking, and extrusion stages.

1. Feeding section: Generally, granular materials are used for extrusion forming. The feeding device is a device that ensures continuous feeding of material to the extruder barrel, resembling a Buchner funnel, with conical and square conical shapes, also known as a hopper. The connection between the bottom end and the material barrel is the feeding hole, which has a disconnection device that can adjust and disconnect the material flow. There are refrigeration clamps around the feeding holes to prevent the high temperature of the material from conducting heat to the hopper, and to prevent the plastic inside the hopper from heating and sticking, resulting in uneven feeding and obstruction of the material flow. The side of the hopper is provided with a laminated glass sight hole and a calibration, metering and verification device. Some hoppers also have heating and drying vacuum pump pressure relief devices that prevent plastic from digesting and absorbing water from the air, as well as mixing devices that overcome the “railway bridge” caused by powdered plastic, and devices that can perform quantitative analysis and fully automatic feeding at regular times.

2. Reduced section: The material barrel, also known as the material barrel, is a metal material drum that is subjected to heat and force. The melting and shrinking of raw materials are all carried out in the material barrel. The operating temperature during extrusion forming is generally between 180~290 ℃, and the internal pressure of the material barrel reaches 60MPa. Setting up heating and cooling devices on the outside of the material barrel generally divides heating into three to four stages. Common resistors or inductors for electric heaters also use far thermal radiation. The purpose of refrigeration is to avoid overheating of plastic or to quickly cool the plastic during parking to prevent its dissolution. Refrigeration generally uses air or water cooling for heat dissipation. The material cylinder must bear high pressure, have sufficient compressive strength and bending stiffness, and have a smooth inner cavity. The material barrel is generally used for wear and corrosion resistance, and the friction of plastic causes the plastic to overheat. In addition, the outer surface temperature of the extruder screw is slightly lower than the material barrel to prevent raw materials from adhering to it, which is conducive to the transportation of raw materials.

3. Extrusion section: The extruder screw is supported by a thrust bearing suspended in the middle of the material barrel, in line with the axis of the material barrel, without significant error. The gap between the extruder screw and the material barrel is not large, causing the plastic to undergo strong cutting effects and melt and push forward.

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