Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Including application of internal fluid pressure to hollow...
Patent
1997-08-27
1999-10-12
Timm, Catherine
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Including application of internal fluid pressure to hollow...
264540, 425532, 425534, B29C 4904
Patent
active
059650826
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for producing a blow-molded body having multiple dimensions and to a device for performing the method.
It is known that it is possible to blow-mold asymmetrical parts having a complicated shape, which have, for example, an axis that is first orientated in one dimension, then in a second one and finally in a third one, thus involving multiple dimensions, such as forced ventilation ducts of cars.
The simplest way to mold these parts is to extrude a very large tubular component whose diameter is sufficient to cover the entire profile of the part that must be molded. In this case, obviously the molded part can have a diameter that is much smaller than the diameter of the tubular component from which it is obtained; accordingly, waste is very high, up to 300-1000%. This entails serious problems, since the waste material must not only be ground again, mixed, and cleaned, with obvious burdens, but during all of these treatments its quality degrades considerably, so much that only virgin material is required for many productions, excluding recycled waste material. Furthermore, in this manner heat-sealing seams necessarily form along two opposite edges of the finished blow-molded body which can be more or less satisfactory, depending on various molding parameters that are difficult to control and particularly depending on the shape of the mold, but in any case constitute a severe weakness factor for the finished body. Finally, a machine that is several times bigger than the one required to mold a straight part of the same diameter is obviously necessary. In this manner, costs for the machine, the material, consumption, electricity, et cetera rise sharply.
Battenfeld Fisher and Krupp Kautex have developed a system in which the extruded tubular component is placed inside a mold that can be disassembled by virtue of a series of robotized mechanical devices that are arranged so as to deform the tubular component, which is still in the plastic state, to adapt it to the shape of the mold. In this manner, the problem of waste is solved at the outset, but a very expensive mold must be used. In particular, the modular mold is extremely expensive because it is composed of various parts that must close gradually as the tubular component is bent by the mechanical devices into the desired shape.
Placo Co. has developed a system in which the mold assembly is movable, so that it can follow a preset path that corresponds to the final shape of the part to be produced. Obviously, in this case, too, the movement of the mold assembly is extremely complicated and very expensive. Moreover, in view of the enormous moving masses, inertia problems arise that force to slow down the process. Slowness does not obviously just limit productivity but also produces intrinsic problems for this type of production. If the times are too long, the extruded tubular component deposited on half of the mold tends to cool before blow-molding, and furthermore does so unevenly. This obviously produces problems, especially for thin parts, which are subject to quick cooling. One should in fact consider that the mold is cooled and is made of metallic material; accordingly, it is an excellent heat conductor. In this manner, during blow-molding, the colder parts of the tubular component certainly cannot have the same expandability as the hotter parts, and therefore the colder parts will maintain a relatively excessive thickness, whereas the hot parts will be subjected to considerable drawing and to a corresponding reduction in thickness that weakens the finished body. Furthermore, it is rather difficult to obtain small radii of curvature. Finally, there are difficult problems in adjusting the machine, on a case-by-case basis, in order to synchronize the speed of the movement of the mold assembly with the descent speed of the tubular component.
IHI and Sumitomo have developed a machine in which the tubular component is drawn by suction into the mold, which is already closed. This system can work only in certain favorable c
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Coleman Henry D.
S.T. Soffiaggo S.R.L.
Sudol R. Neil
Timm Catherine
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