Device for injecting compressed air into a blow mold

Abstract

The invention relates to a device for injecting compressed air into a parison, having an injection cylinder, having a hollow shaft (2) arranged inside the housing (1) of the injection cylinder in a manner so as to be displaceable along its longitudinal axis (A), one end of said hollow shaft projecting out of the housing (1) and provided with a connection head (7) for a tight connection to the parison, and having a stretching rod (3) arranged coaxially to the hollow shaft (2) in the interior of the hollow shaft (2) and displaceable coaxially with the hollow shaft (2). A double piston (21, 22) is arranged axially parallel to the hollow shaft (2). The double piston (21, 22) is connected to the hollow shaft (2) by a connection lug (25) and thereby moves the hollow shaft along its longitudinal axis (A) between a lower and an upper end position. The drive of the hollow shaft (2) therefore takes place not coaxially, but rather from the side via a piston axis (B) arranged parallel to the longitudinal axis (A) of the hollow shaft (2). In this way, the functioning of the air supply via the hollow shaft (2) and the movement of the coaxially arranged stretching rod (3) is separated from the drive of the hollow shaft (2).

Description

technical field [0001] The invention relates to a device according to the preamble of claim 1 and to a blow molding unit comprising a device of this type. Background technique [0002] For the manufacture of plastic bottles, especially PP (polypropylene) and PET (polyethylene terephthalate) bottles, blanks or preforms are normally formed in two steps in a hollow body blow molding machine. The piece is blown into its final shape. For this purpose, the blank basically already has a finished bottle head, which is fixed in the blow mold of the hollow body blow molding machine and connected to the compressed air system via a blow cylinder. The preform is blown by blowing compressed air through the head of the bottle and finally formed into its final shape. [0003] The blowing process is usually carried out in a two-stage method, wherein, as a first stage, the pre-blowing is carried out via a pre-blowing valve with a pressure value between 2 bar and 20 bar, and subsequently in ...

AI Technical Summary

Problems solved by technology

[0009] Due to the arrangement of the flange of the hollow shaft or the ring piston, the blow molding cylinder has a radially larger housing in the region of the ring piston, which is very expensive to manufacture due to the different diameters distributed in the axial direction, which lead to high production costs

The blow cylinder is therefore also heavily stepped in its axial direction and has a relatively large space requirement

Furthermore, in particular the displacement of the hollow shaft in the blow cylinder or the stop at the upper end are only poorly damped, which has a negative effect on the service life of the cushioning ring and also limits the effective operating speed

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