Plastic Blow Molding
Plastic blow molding is an engineering technology that involves the process of processing various plastics into products. Mainly including processes such as extrusion, injection, and stretching, the products produced have unique advantages of uniform wall thickness and small quality tolerances.
What is Blow Molding？
The blow molding process is one of the important processing methods of thermoplastic plastics. It uses extrusion, injection, and other methods to produce a tubular parison, and then passes compressed air into the inner cavity of the parison in a thermoplastic state to expand it into a shape. Plastic products in the desired shape.
Blow Molding Process Classification
According to the production method of the embryo, plastic blow molding can be divided into film blow molding and hollow blow molding.
Hollow blow molding can also be divided into extrusion blow molding, injection blow molding, and injection stretch blow molding.
Blow Molding Process Application
Blow molding products are widely used in various industries, especially in the beverage and pharmaceutical packaging industries. They are also widely used in the toy industry, such as blown baby bottles, hollow floating parts, Christmas lampshades, toy yachts, and children’s learning driving accessories. As well as some large toys such as slide tracks, bases, etc.
Key Points of Blow Molding Process Design
- Generally speaking, the corners and edges of blow-molded products must be made into R-angle transitions, because the inflation ratio at sharp corners is relatively large, which is more likely to cause uneven wall thickness. In addition, pressure cracking is also prone to occur at sharp corners.
- With different product requirements, some structural designs in terms of compression resistance, tensile resistance, and torsion resistance can also be added.
- In addition, for toy blow molded products, more emphasis should be placed on safety and physical testing (considerations of pulling, twisting, throwing, throwing, and stress cracking).
- When it comes to container products, more attention is paid to the requirements of pressure resistance, corrosion resistance, and good barrier properties.
Film Blow Molding
Film blowing is to extrude molten plastic into a cylindrical thin tube from the annular gap in the die of the extruder head. At the same time, compressed air is blown into the inner cavity of the thin tube from the center hole of the extruder head to inflate the thin tube into a diameter of Larger tubular films (commonly known as bubble tubes) are a forming process that is curled after cooling.
Features of film blow molding process:
- It has strong adaptability to raw materials;
- The film has a certain biaxial orientation after stretching and blowing, and has high mechanical strength;
- Product waste is less and cost is low;
- The product width is wide, there are few welds, and it is easy to make bags;
- The film thickness uniformity is poor. Compared with the calendering method, the casting method, the stretching method, and the production line speed, the output is lower.
Hollow Blow Molding
Hollow blow molding is a secondary molding technology that uses gas pressure to inflate the rubber-like parison closed in the mold cavity into a hollow product. It is a method of producing hollow plastic products.
Hollow blow molding depends on the manufacturing method of the parison, including extrusion blow molding, injection blow molding, and stretch blow molding. In addition, there are special processes such as multi-layer blow molding, compression blow molding, dip blow molding, foam blow molding, and three-dimensional blow molding. Among blow-molded products, about 75% are formed by extrusion molding, 24% are formed by injection blow molding, and 1% are formed by other blow molding.
Features of hollow blow molding process:
- High production efficiency, with an average cycle time of 1-2 minutes, suitable for mass production;
- High quality and precise dimensions, no secondary processing is required after the product is made;
- Surface treatment is suitable for smooth, frosted, and textured;
- The weight and size of the hollow products are repeatable, easy to adapt, and easy to connect to the canning line;
- It has a certain biaxial orientation effect, which can improve the transparency and strength of many different materials.
- Extrusion Blow Molding
Extrusion blow molding is a method of manufacturing hollow thermoplastic parts. It is mainly used for processing unsupported parisons. Common blow molding objects include bottles, cans, barrels, boxes, and all containers for packaging food, beverages, cosmetics, medicines, and daily necessities.
Extrusion blow molding process features:
- High production efficiency, low equipment cost, a wide selection of molds and machinery, which can be used to produce products of various shapes, a wide selection of materials, and its containers can be processed as a whole or multiple layered effects can be achieved;
- The scrap rate is high, the recycling and utilization rate of waste materials is poor, the thickness of the products is controlled, and the dispersion of raw materials is limited;
- Trimming operations must be performed after molding, and are often used to process containers with volumes ranging from 3 ml to 220 liters.
- Injection Blow Molding
Injection blow molding is a parison processing mainly used for metal core support. It is a more precise process than extrusion blow molding and is used for higher-precision FMCG packaging and medical packaging.
1.Injection blow molding process features:
- No waste is produced during processing;
- It can well control the wall thickness of the product and the dispersion of materials;
- Thin-neck products have high molding precision and smooth product surfaces;
- Ability to economically produce small batches;
- The cost of molding equipment is high, and to a certain extent, it is only suitable for small blow-molded products. It is often used to process containers with a volume between three milliliters and one liter.
2.Injection Stretch Blow Molding
Injection stretch blow molding is the highest quality and cost-effective process in blow molding and is particularly suitable for packaging beverages, pesticides, and personal care products.
3.Injection stretch blow molding process features:
- High precision, especially reflected in the details of the bottle mouth;
- Can be used to produce containers with more details;
- The cyclic stretching method can provide superior mechanical properties;
- Among the three subdivision processes of blow molding, the cost is the highest;
- Mainly used to process containers with solvents between 50 ml and 5 liters.
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