There are five plastic blow moulding methods: extrusion blow moulding, injection blow moulding, stretch blow moulding, multilayer blow moulding and foam blow moulding. The process of blow moulding products is generally: the preparation of raw materials and the production of i-shaped blanks for transportation. The i-shaped blanks are inflated, moulded, and cooled. Once the moulding method is selected, the moulding process is basically determined. In addition, in the mass production of blow-moulded products, the operation method of moulding and the auxiliary equipment that should be equipped should also be considered.
The operation modes are: manual operation, semi-automatic operation, and fully automatic operation.
The following issues should be considered when equipping auxiliary equipment:
(1) Whether the raw materials are dry, technical measures should be taken.
(2) Treatment method, reuse method and technical requirements of corner waste.
(3) The temperature control of the parison reheating device.
(4) Temperature control of blow moulding or injection mould.
(5) Drying of compressed air and selection of pressure.
(6) Cooling system for products after blow moulding.
(7) Surface treatment and surface printing methods of blow moulded products.
(8) Inspection methods, methods and tools for the quality of blow moulded products (dimensions, pressure resistance, leakage prevention, environmental stress cracking resistance, etc.).
Compared with injection moulding, extrusion blow moulding has the following advantages:
(1) The cost of blow moulding machines (especially blow moulding moulds) is relatively low (when moulding similar products, the cost of blow moulding machines is about 1/3-1/2 of that of injection machines), and the production cost of products is also low .
(2) In blow moulding, the parison is formed under a lower pressure through the die and inflated under low pressure (mostly 0.2-1.0 MN), so the residual stress of the product is small, and it is resistant to stretching, impact, and bending. It has high performance against various strains such as the environment, and has better performance in use. In injection moulding, the melt must pass through the mould runner and gate under high pressure (15-140yPa), which will cause uneven stress distribution.
(3) The relative molecular mass of blow moulding grade plastics (such as PE) is much higher than that of injection grade plastics. Therefore, blow-moulded products have high impact toughness and high environmental stress cracking resistance, and are suitable for the production of containers or vats for packaging or transporting detergents and chemical reagents.
(4) Since the blow mould is only composed of a female mould, the wall thickness of the product can be changed by simply adjusting the gap between the die orifice of the die or the extrusion conditions. This is very beneficial for products that cannot accurately calculate the required wall thickness in advance. The cost of changing the wall thickness of the product for injection moulding i is much higher.
(5) Blow moulding can produce products with very small wall thickness, which cannot be produced by injection moulding.
(6) Blow moulding can produce products with complex, irregular and integral shapes. When using injection moulding, after producing two or more products, they should be combined together through buckle fitting, solvent teaching or ultrasonic welding.
However, the accuracy of blow moulded products is generally not as high as that of injection moulded products.