The outer diameter of the screw is easy to be roughly ground flat, so one of the most commonly used methods for refurbishing screws is the fine grinding process. Fine grinding is also known as fine grinding. It is an important process between the two major processes of rough grinding and polishing. The purpose of fine grinding is to ensure that the workpiece achieves the required surface shape accuracy, dimensional accuracy and surface roughness before polishing. Therefore, the quality of fine grinding has a very significant impact on polishing. The methods of fine grinding are divided into…

When the injection molding screw has difficulty pressing the material at the feeding port or fails to form sufficient adhesion along the length of the barrel to convey the material, the screw will slip. During the pre-plasticizing stage of the screw, as the screw rotates in the barrel, conveying the material along the screw direction and retreating to accumulate the material for the next injection molding, the screw…

1. Feeding zone: The depth of the fixed screw groove is determined, and its function is to be responsible for preheating, solid plastic conveying and pushing. It is necessary to ensure that the plastic begins to melt at the end of the feeding section – that is, it needs to be preheated to the melting point.

The screw barrel of an injection molding machine operates for a long time under high pressure, high temperature, high mechanical torque and high friction conditions. The first few factors are required by the process conditions, but the wear and tear caused by friction is inevitable. Generally, screws undergo surface nitriding treatment to enhance surface hardness, that is, to improve wear resistance…

An injection molding machine injects molten plastic into a mold, and after cooling, it becomes the product. It has a very wide range of uses. Depending on the type of plastic, it is used in different places. Injection molding machines are the most widely used processing machinery in the plastic processing industry. Not only can a large number of products be directly produced by injection molding machines, but they are also the key equipment that constitutes the injection stretch blow molding process.

When extruding thermoplastic composites, the design of the screw and the structure of the screw and barrel are of vital importance. If these issues are considered in advance. This will ensure the successful completion of the processing of thermoplastic composites. Generally, the design of screws for thermoplastic composites mainly involves two different aspects. One is the mixing of materials; The second is the processing of thermoplastic composites.

The main factors affecting plasticizing quality are: length-to-diameter ratio, compression ratio, back pressure, screw speed, barrel heating temperature, etc.

1. Length-to-diameter ratio: It is the ratio of the effective working length of the screw to its diameter.

A. a larger length-to-diameter ratio makes it easier to feed evenly.

For plastics with better thermal stability, longer screws can be used to enhance mixability without burning. For plastics with poorer thermal stability, shorter screws or screws without threads at the end can be used. Considering the characteristics of plastics, the general flow rates are as follows: for thermosetting plastics, it is 14 ’16; for heat-sensitive plastics such as rigid PVC and high-viscosity PU, it is 17 ’18; for common plastics, it is 18 ’22; and for high-temperature stable plastics such as PC and POM, it is 22 ’24.

2. Compression ratio: It is the ratio of the depth of the last screw groove in the feeding section to that of the first screw groove in the metering section.

A. Considering the compressibility of the material, the degree of filling, reflux and other influences, the products should be dense, heat-conductive and well-ventilated.

B. An appropriate compression ratio can increase the density of plastics, making the molecules combine more closely with each other, which helps to reduce the absorption of air, lower the temperature rise caused by pressure, and affect the difference in output. An inappropriate compression ratio will damage the physical properties of plastics.

C. The higher the compression ratio, the greater the temperature rise generated during the plasticizing process of the plastic in the barrel pipe, which results in better mixing uniformity for the plasticized plastic and a significant reduction in the corresponding discharge volume.

D. High compression ratio is suitable for plastics that are not easy to melt, especially those with low melting viscosity and thermal stability. Low compression ratio is suitable for fusible plastics, especially those with high melting viscosity and heat sensitivity.

3. Back pressure

A. Increasing back pressure can enhance the work done by the screw on the molten resin, eliminate unmelted plastic particles, and increase the density and uniformity of the raw materials in the feed pipe.

B. Back pressure is used to increase the temperature of the barrel, and its effect is the most significant.

C. Excessive back pressure can cause decomposition of heat-sensitive plastics and may lead to salivation of low-viscosity plastics. If the back pressure is too low, the injection-molded products may have bubbles.

4. Screw speed

A. The rotational speed of the screw directly affects the shear of the plastic in the helical groove.

B. The small screw groove is relatively shallow and absorbs heat sources quickly, which is sufficient to soften the plastic during the compression period. The frictional heat energy between the screw and the barrel wall is low, making it suitable for high-speed rotation and enhancing the plasticizing capacity.

C. Large screws should not be rotated rapidly to avoid uneven plasticization and excessive frictional heat.

D. For plastics with high heat sensitivity, if the screw speed is too high, the plastic will decompose very easily.

E. Generally, screws of various sizes have a certain speed range, typically ranging from 100 to 150rpm. If it is too low, the plastic cannot be melted; if it is too high, the plastic will be burned.

5. Electric heating temperature setting

A. Melt the cold hard plastic retained in the barrel and screw to facilitate the rotation of the screw and provide part of the heat required for the plastic to be melted.

B. Set the temperature 5 to 10 degrees Celsius lower than the melt temperature (partly provided by frictional heat energy);

C. The adjustment of the nozzle temperature can also be used to control issues such as drooling, condensate (nozzle plug), and wire drawing.

D. General temperature control for crystalline plastics.

Due to the certain thickness of the coating layer, after the surface treatment of the parts, it is inevitable that the dimensions of the parts will change. The dimensions and tolerances of parts specified on the design drawings usually refer to the final dimensions and tolerances of the parts. If there are no fit requirements for the parts, electroplating or electroplating shall be carried out on the final dimensions of the parts…

Plastic extruders can be classified into single-screw extruders, twin-screw extruders and multi-screw extruders according to the number of screws they have. At present, single-screw extruders are the most widely used and are suitable for the extrusion processing of general materials. The twin-screw extruder is characterized by less heat generated by friction and a relatively lower shear rate on the material…

1. Excessive back pressure: If the back pressure is set too high, the screw may not be able to generate sufficient forward pressure to transport the melt to overcome the reverse pressure of the back pressure. The screw will rotate in a certain direction without retreating, which will do more work on the melt and significantly increase the melt temperature, thereby affecting the quality of the finished product and the cycle period…