Tham khảo tài liệu 'plastic product material and process selection handbook part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 6 Blow molding 299 blowing operation that provides radial stretch and orientation Figure . Blowing pressures range up to about 40 bar. The blow mold temperature is relatively high at 35 to 65 c in order to minimize strain in the bottle. For a given bottle size the degree of orientation is determined principally by the parison length and diameter. Stretch ratios are relatively high. In the wall thickness of the bottle body the amount may be as high as 15 1. Axial stretch is about 4 1 diametrical stretch ranges about 1 Figure Example of stretched injection blow molding using a rod left and example of stretched injection blow molding by gripping and stretching the preform With the two-stage process processing parameters for both preform manufacturing and bottle blowing can be optimized. A processor does not have to make compromises for preform design and weight production rates and bottle quality as done on single-stage equipment. One can either make or buy preforms. And if one chooses to make them one can do so in one or more locations suitable to the market. Both high-output machines and low out-put machines are available. The two-stage process which permits injection molding of the preform and then shipping to BM locations has allowed companies to become preform producers and to sell to BM producers. Thus companies that wish to enter the market with oriented containers can minimize their capital requirements. Extrusion stretch blow molding ESBM is a one-stage or two-stage process using two mold mandrel sets where one is for pre blow and the other for final blow. An extruded parison is first pinched off and blown 300 Plastic Product Material and Process Selection Handbook conventionally in a relatively small preblow mold to produce a closed-end preform. The preform is then transferred to the final blow mold where usually an extending stretch rod within the blowing mandrel bears on the closed preform end to stretch it axially. The stretched preform is .
