Solid plastic raw materials enter the screw channel through the feeding funnel, and due to the high-speed rotation of the screw, they produce a shear effect with the barrel, causing the plastic raw materials to be mixed and transported along the screw groove. The solid plastic raw materials are heated by the electric heating plate on the outside of the barrel and the shear heat generated by the screw, causing the internal temperature of the barrel to rise and melt into a molten state.
What is the injection screw of a plastic machine? What are the characteristics of screws?
The application of plastic products is closely related to our daily lives, and injection molding and extrusion molding are currently the economical and energy-saving processing methods. Among them, plastic plasticizing screws are the important key components, and each plastic has its physical characteristics, which makes the design of plastic plasticizing screws different. The design of plastic plasticizing screws has always been based on empirical rules, which have high costs and may not necessarily solve problems. Therefore, some details in the design of plastic plasticizing screws are worth exploring and analyzing.
Plasticizing screws can be divided into four zones according to their functions:
1. Solid conveying zone
This section is connected to the feeding funnel, where solid plastic particles are tightly compressed to form a solid bed. Under the shear effect of the glue cylinder, the plastic is gradually transported forward, in addition to increasing the temperature of the plastic.
2. Delay of melting
This section is the area from the end of the solid conveying area to the formation of the melt pool. Its main feature is the formation of a thin film layer composed of molten glue on the surface of the solid bed and the melt cylinder. The molten glue in the thin film layer is subjected to the drag force of the melting cylinder and accumulates in the screw groove of the front screw. The pressure formed at the end of this area is large enough to deform the solid bed and gradually forms a melt pool in the screw groove of the front screw.
3. Melting zone
This section is from the end of the melting delay zone to the complete melting of the plastic. This zone can be further divided into two parts for discussion, one is plasticization, which mainly comes from the shear effect of the glue cylinder, and the other is melt conveying, which transports the glue to the melting pool.
4. Melt conveying zone
When all plastics are completely melted, they begin to enter this section and end at the end of the plasticizing screw, maintaining a uniform temperature of the melt and a stable flow rate of melted plastics.
Plastic plasticizing screws are divided into three sections based on their geometric shape:
1. This section is the depth of the fixed screw groove, which is responsible for preheating, conveying plastic solids, and pushing. It is necessary to ensure that the plastic begins to melt at the end of the feeding section (meaning it needs to be preheated to the melting point). The length of this section is divided into crystalline (POM, PA, etc.)>amorphous (PS, PU, ABS, etc.)>thermosensitive (PVC, etc.).
Generally:
Amorphous: approximately 48-58% L. (AS, ABS, PS, etc.)
Crystallinity: approximately 48-58% L. (PA, POM, PE, PP, CA, etc.)
Additive glass properties: approximately 45-55% L
2. Measuring zone
This section is the fixed groove depth of the screw screw groove. In addition to its main functions of mixing, glue conveying, and metering, it must also provide sufficient pressure to maintain a uniform temperature of the glue and stabilize the flow rate of the molten plastic.
The general length is:
Amorphous: approximately 15-58% L. (AS, ABS, PS, etc.)
Crystallinity: approximately 48-58% L. (PA, POM, PE, PP, CA, etc.)
Additive glass properties: approximately 45-55% L
3. Compression zone
This section is a gradually decreasing screw groove with deep teeth, and its function is to melt, mix, shear and compress plastic raw materials, and pressurize exhaust. Plastic will completely dissolve at this stage and its volume will shrink, so the design of compression degree (compression ratio) is important.
The general length is:
Amorphous: about 25-35% L... (AS, ABS, PS, etc.)
Crystallinity: approximately 22-32% L. (PA, POM, PE, PP, CA, etc.)
Glass addition property: about 28-40% L
