65 extruder

Extruder is one of the types of plastic machinery that originated in the 18th century.

The extruder can be divided into right angle and oblique angle heads based on the direction of the material flow in the head and the angle between the screw centerline.

Screw extruder relies on the pressure and shear force generated by the rotation of the screw, which can fully plasticize and uniformly mix the material, and form it through the mouth mold. [1] Plastic extruders can be classified into twin-screw extruders, single screw extruders, as well as rare multi screw extruders and non screw extruders.

Mechanical principles

Principle of single screw extruder

A single screw is generally divided into three effective lengths, determined by the diameter, pitch, and depth of the screw, with each segment accounting for one-third of the total effective length.

The last thread of the material mouth is called the conveying section: the material here is required not to be plasticized, but to be preheated and compressed. In the past, the old extrusion theory believed that the material here was loose, but later it was proven that the material here is actually a solid plug, which means that the material here is a solid plug after being compressed. Therefore, as long as the conveying task is completed, it is its function.

The second section is called the compression section, during which the volume of the screw groove gradually decreases from large to small, and the temperature needs to reach the degree of material plasticization,Spiral feeding machineThe compression generated here is from the third conveying section, where it is compressed to one, which is called the compression ratio of the screw -3:1. Some machines also have changes, and the material that has been plasticized enters the third section.

The third paragraph is the metering section, where the material is maintained at the plasticizing temperature, just like a metering pump that accurately and quantitatively delivers molten material to the machine head. At this time, the temperature cannot be lower than the plasticizing temperature, usually slightly higher.

Energy saving extruder

The energy-saving of extruders can be divided into two parts: one is the power part, and the other is the heating part.

Energy saving in the power part: Most of them use frequency converters, which save energy by reducing the residual energy consumption of the motor. For example, the actual power of the motor is 50Hz, but in production, you only need 30Hz to produce, and those excess energy consumption are wasted. Frequency converters change the power output of the motor to achieve energy-saving effects.

Heating energy-saving: The energy-saving of the heating part is mostly achieved by using electromagnetic heaters, with an energy-saving rate of about 30% to 70% compared to old-fashioned resistor coils.

Working process

Plastic materials enter the extruder from the hopper and are transported forward by the rotation of the screw. During the forward movement of the material, it is heated by the barrel, sheared and compressed by the screw, causing the material to melt, thus achieving a change between the three states of glass state, high elasticity state and viscous flow state.

In the case of pressurization, the material in a viscous flow state is passed through a mold with a certain shape, and then becomes a continuous body with a cross-section similar to the shape of the mold according to the mold. Then cool and shape to form a glassy state, thereby obtaining the desired processed product.