Blast pipes, also extruding blisters mentioned, is a method for the production of hollow bodies from thermoplastics.
First continuously or also intermittent a hose from hot, ductile plastic from a flanged on tool is discharged perpendicularly downward as preform (extruded). Material thickness in the hose is regulated thereby according to the form of the finished workpiece.
Then a thorn from above or down brings in into the hose. At this time still opened split tool drives then to and coats the hose with the thorn. Compressed air is then pressed by the thorn into the hose, with which this is blown up and pressed and cooled down against the outline of the blow tool. The plastic adapts so to the given form and hardens.
At the neck portion, at the soil and at the seam between the two tool halves Butzen from plastic, which are cut partly directly when opening, develop partly are necessary a rework. This waste is reused (recycling).
By variation of material thickness in the hose the thickness of the plastic in the finished product can be steered. With symmetrical things such as barrels this can be precalculated, with more complex forms in a so-called preproduction material thickness is varied, until the result fits.
A characteristic of the blowing figuration in relation to the injection moulding is that hollow parts and also Hinterschnitte without slidegate valves (see building of forms) in limited extent are manufactured to be manufactured to be able. The variation of the wall thickness is larger in relation to the injection moulding only indirectly possible, attainable tolerances therefore.
Market leader in the production of hollow body blowing machines is the enterprise BEKUM engine works GmbH from Berlin with world-wide approx. 600 coworkers at home and abroad in 5 production locations.
Polyolefins (above all polyethylene (PE) and polypropylene (PP)) to most finished plastics are. In addition, plexiglass (PMMA), polycarbonate (PC), PP (Pa) and some mixtures are processed.
One preferably meets the products developed in such a way in the everyday life as packing article such as bottles, cans or barrels. The volume varies between 0,05 and 10.000 litres. In addition, technical parts such as air ducts, luggage half shells, roof luggage carriers or fuel tanks can be blown. Larger Kinderspielzeuge (for example slide vehicles) are manufactured likewise frequently with this technology.
For pressure-loaded containers (for example char-acid beverages) usually spraying blisters one uses.