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Shanghai blow molding is one of the important processing methods for thermoplastic materials. It uses extrusion, injection and other methods to produce tubular preforms, and then compressed air is introduced into the cavity of the thermoplastic mold to expand it into the desired shape of plastic products.
Blow molding technology began to be used in the production of low-density polyethylene small bottles during World War II. In the late 1950s, with the birth of high-density polyethylene terephthalate and the development of blow molding machines in Shanghai, blow molding technology was widely applied. The volume of hollow containers can reach several dry liters, and some production has adopted computer control.
Application of blow molding processing in Shanghai
Blow molded products are widely used in various industries, especially in the beverage and pharmaceutical packaging industry, and are also widely used in the toy industry, such as blowing baby bottles, hollow floating parts, Christmas lampshades, toy boats, children's learning car accessories, and some large toys such as sliding ladder tracks, bases, etc.
Key points of product design for blow molding processing in Shanghai:
1. Generally speaking, the corners and edges of blow molded products should be made into R-transitions because the high expansion ratio at sharp corners can easily cause uneven wall thickness, and sharp corners are also prone to pressure cracking;
2. With different product requirements, some structural designs in terms of compression, tension, and torsion can also be added;
3. In addition, for blow molded toy products, more emphasis is placed on safety and physical testing (consideration of tension, torsion, picking, and stress cracking), while for container products, more emphasis is placed on pressure resistance, corrosion resistance, and good impermeability requirements.
Troubleshooting of common faults:
1. Difficulty in membrane introduction
Fault analysis and troubleshooting methods:
(1) Improper temperature control of the machine head. When the head temperature is too high or too low, it can cause traction difficulties, and the head temperature should be adjusted appropriately.
(2) Uneven discharge from the mouth mold. The gap between the mouth molds should be adjusted to make the surrounding gaps uniform. At the same time, adjust the temperature of the nose connector appropriately to coordinate with the body temperature.
(3) The melt contains impurities of coke. Raw materials should be purified and the machine head and screw should be cleaned.
(4) Improper control of extrusion process conditions. The process conditions should be adjusted appropriately. The extrusion process conditions for several commonly used plastic blow molded films are shown in Table 3-1.
2. Analysis and troubleshooting methods for skewed bubble tubes:
(1) The temperature of the body and mouth mold is too high. It should be appropriately reduced.
(2) The temperature of the head connector is too high. It should be appropriately reduced.
(3) Uneven discharge from the mouth mold and uneven thickness of the film. The gap between the mouth mold and the temperature of the head connector should be adjusted appropriately.
3. The bubble tube is shaped like a reed
Fault analysis and troubleshooting methods:
(1) The regular gourd shape of the bubble tube is due to the clamping force of the traction roller being too small, or the speed of the traction roller being affected by the regular changes in mechanical transmission resistance. In this regard, the clamping force of the traction roller should be appropriately increased, and the mechanical transmission part of the traction device should be inspected to ensure that the speed of the traction roller is stable.
(2) The irregular gourd shape of the bubble tube is due to unstable traction speed and excessive air pressure on the cooling air ring. Regarding this, adjustments should be made
Traction speed to ensure stable operation; The wind pressure of the wind ring should be appropriately reduced.
