Blow moulding, here mainly refer to hollow blow moulding, is a common used plastic process methods. It is also one of plastic mould methods that develop relatively rapidly. Compared with injection moulding method, blow moulding method is more adaptable. The whole process can be divided into four processes.
(1) Parison forming process.
During this process, conglomerates will be transported in the extruder. They will be melted firstly. And then, all materials will be mixed together to form the parison.
(2) Parison materials added process.
During this process, the machine will pick out certain quantity of needed materials. The chosen materials will be delivered through space between the die lip and the die core. Under this circumstance, swelling or drawdown of the parison will influence the final forms of moulds.
(3) Parison pre-blow process.
This process is very necessary. It is operated to avoid internal touch or adhesion of the parison, and to improve uniformity of the product thickness. To blow inside of the parison from its bottom. In this way, the shape of parison can be remained to the greatest extent. The drawdown situation can be also improved.
(4) Parison blow process under high-pressure.
To blow the parison under high pressure. Therefore, the parison will cling to the mould cavity and realize the final form of the mould.
It should be noticed that the parison might be out of shape because of excessive or unsuitable blowing during this process. This will greatly influence the manufacture of moulds. Besides, deformation of the parison might also be caused by contact between the parison and mould cavity.
The quality of blow moulding products can be effectively improved with adjustment of technological parameters. Optimized technological parameters can upgrade the overall performance of the products while decreasing cost of raw materials and improving production efficiency.
Blow moulding technology is developing together with the growth of modern plastic industry and mechanical manufacturing technologies. The technologists should combine advanced design theory together with human’s experience to improve efficiency of every process, including design and manufacture. On this basis, the quality and competitive capacity of blow moulding products can be improved greatly.
We will continue to focus on this series. The next classical mould is cam moulds.