Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Patent
1989-11-17
1993-11-30
Heitbrink, Jill L.
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
26432817, 425200, 425543, 366 76, 366178, 366193, 366303, B29B 724, B29B 726
Patent
active
052662616
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the production of molded articles from hot-setting plastics of several components, in particular resins, fillers and hardeners, by low-pressure casting, in which the components fed for the formation of a homogeneous plastic compound are mixed before leaving the casting device.
Such a process is used, i.a., for the production of high-quality components, especially those for insulation of electric lines and equipment.
Especially dynamic mixers, used for this purpose, because of their high speed cause in the different resin components a sedimentation, great shear forces and too great a warming. The turbulence thus reached leads to inclusion of gas in the casting compound, which entail a quality loss in the molded articles.
The object of the invention therefore is to eliminate these defects.
According to the invention as a way of achieving this object a process of the type initially mentioned stands out, in which the components, flowing laminarly, are brought together before mixing. As a result a sedimentation of the fed components can be largely prevented. At the same time, by the premixing effect achieved a remarkable reduction of the speed of the mixer and thus a smaller degree of shear forces is reached. The additional warming during mixing is reduced and the absorptive capacity of the pipes conducting the components can be improved, briefly a more subtle operation meeting the high requirements for quality and an economical production can be performed.
In such a procedure it proves particularly favorable if the components are fed to a chamber upstream from the mixing device, as a result of which an additional smoothing phase and a premixing, at selectable metering, of the individual components in the plastic compound occurs.
For performing the initially mentioned process there is particularly suitable a device for low-pressure casting of molded articles from hot-setting plastic compound of several components, such as resins, fillers and hardeners, consisting of housing receiving a drivable rotor for forming a mixer, a housing which is connected to the feed pipes for the components and exhibits an outlet for the plastic compound.
Known mixers of this type, in the processing of multicomponent systems, are subject to the drawbacks that the flow conditions, changing by the changes of temperature, viscosity and amount, make difficult or prevent achieving a homogeneous mixer contents or of a plastic compound to be cast in the end, even epoxy resins mentioned above, since these changes of conditions in the pipes and spaces that are passed through lead to turbulences, which result in undesired inclusions of air.
A device for performing the process according to the invention is distinguished by a special configuration of a feed device for the components use upstream from the mixer, by being placed by a chamber on the back end of the mixer, concentrically to the axis of rotation of the rotor, adjacent to the housing, a chamber which is surrounded with spacing by several annular feed ducts, assigned to the individual components, and connected to the ducts by pipes.
The feed device allows a laminar uniform flow of the components into a chamber, in which they flow into one another under a premixing effect before they are picked up by the dynamic mixer and changed into a homogeneous plastic compound. The laminar flow condition and the premixing effect achievable by flowing into one another favor the necessary homogeneity of the plastic compound to be cast and the uniformity of the casting process.
The component feed ducts emptying into the chamber advantageously exhibit, relative to their longitudinal extension, through openings placed axially offset so that the individual components, mixing in a flat manner, penetrate into the chamber and there flow into one another on a prolonged flow path under expansion action before the final mixing procedure.
The through openings are suitably distributed on the downstream end of the annularly designed feed ducts so that already a mixing effec
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Heitbrink Jill L.
Jaskiewicz Edmund M.
Suter & Co.
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