Basic Parameters of Extruder Screw

Ⅰ. The diameter of the extruder screw (D)

1. It is related to the required injection volume: injection volume per mold = 1/4 × π × D² × S (injection stroke) × density × 0.85.

2. Generally speaking, the diameter D of the extruder screw is inversely proportional to the highest injection pressure and proportional to the plasticizing capacity.

Ⅱ. Conveying of extruder screw

1. Responsible for the transportation, pushing and preheating of the plastic. It should be preheated to the melting point.

2. Crystalline plastics should be longer (such as: LCP, PA), followed by non-crystalline materials (such as: PS, AS, ABS), and the heat sensitivity is the shortest (such as: PVC).

Ⅲ. Compression section of extruder screw

1. Responsible for plastic mixing, compression and pressurized exhaust. The raw materials passing through this section have been almost completely dissolved, but may not be uniformly mixed.

2. In this area, the plastic gradually melts. The volume of the screw groove must be reduced accordingly to correspond to the reduction of the entire volume of the plastic geometry, otherwise the material will not be compacted, the heat transfer will be slow and the exhaust will be poor.

3. Generally, it accounts for 25%~30% of the working length of the extruder screw, but the compression section of the nylon (crystalline material) screw accounts for about 15% of the working length of the screw. Plastic screws with high viscosity, fire resistance, low conductivity and high additives account for 40%-50% of the working length of the screw.

Ⅳ. The metering section of the extruder screw

1. It generally accounts for 20-25% of the working length of the screw to ensure that the plastic is fully melted, the temperature is uniform and the mixing is uniform.

2. If the metering section is long, the mixing effect is good. However, if it is too long, the melt will stay too long and cause thermal decomposition. If it is too short, the temperature will be uneven.

3. Heat-sensitive plastics such as PVC should not stay for too long to avoid thermal decomposition. Use shorter metering segments or no metering segments.

Ⅴ. The depth of the feeding groove of the extruder screw and the depth of the measuring groove

1. The deeper the depth of the feeding screw groove, the greater the conveying volume, but the strength of the screw needs to be considered. The shallower the measuring screw groove depth, the higher the plasticizing heat generation and the mixing performance index. However, if the depth of the metering screw groove is too shallow, the shear heat will increase and the self-generated heat will increase. If the temperature rise is too high, it will cause discoloration or burning of the plastic, which is especially bad for heat-sensitive plastics.

2. Measuring screw groove depth=KD(0.03-0.07) ★D. When D increases, the smaller value of K can be selected.

Our conveying screw element is a self-sweeping extruder screw assembly, which opens longitudinally and closes laterally and has a strong conveying effect. It has short material residence time, good self-cleaning and can build up high pressure in a short axial distance.

The conveying element is mainly of threaded construction. Its function is to transport the material and give the material a certain thrust, so that the material can overcome the resistance encountered in the flow channel. Conveying screw elements are currently the most popular extruder screw elements. It has strong conveying function, short residence time and good self-cleaning.

In terms of production specifications, LESUN not only provides general extruder screws and standard twin screw extruder accessories produced by manufacturers, but also provides design and manufacturing services for special extruder accessories according to customer requirements. At the same time, we also provide surveying and mapping business and processing business of accessories for major extrusion press companies. If you are in need, welcome to contact us.

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