Agitating – Rubber or heavy plastic working – Stirrer is through-pass screw conveyor
Patent
1996-12-17
1998-08-25
Cooley, Charles E.
Agitating
Rubber or heavy plastic working
Stirrer is through-pass screw conveyor
366331, 403358, 425192R, B29B 748, B29B 758
Patent
active
057976775
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a screw-type extruding machine for processing materials, in particular for the processing of plastics, having at least one drivable shaft that is arranged inside a housing, onto which wear-resistant screw-type elements can be inserted in an optional sequence.
BACKGROUND OF THE INVENTION
Nowadays, screw shafts for screw-type extruding machines are designed in accordance with the prior art in a modular fashion. For that, screw-type and kneading elements for the most varied functions such as conveying, plastifying, mixing and cutting, homogenizing, degasing and building up pressure are fitted in a freely selectable sequence onto a shaft. An interlocking connection secures the screw elements against twisting and permits the transfer of the rotational moment from the rotating shaft to the screw element.
The different process functions require that the work material be adapted to these functions, e.g. that it be wear-resistant, anticorrosive or a combination of both. Conditional upon the respective connecting systems for the shaft/hub (feather key, six-spline, multi-spline or involute tooth system (e.g. DE-OS 15 02 337)) stress concentrations tend to occur at the notches or grooves of those connecting systems. In particular with through-hardened elements made of wear-resistant materials (tool steels, cold-working steels, rapid-machining steels) these stress concentrations can lead to a breaking of the element, which can result in considerable damage in a screw-type extruding machine.
The use of spring-actuated keys as transfer elements for the rotational moment between shaft and screw elements to increase the load capacity of the shaft is known from DE 42 06 219 A1.
Apart from the fact that this measure can be used only when using feather keys as transfer elements for the rotational moment and a groove as a longitudinal recess (and not when using multi-spline, involuted tooth system etc.), it is not possible to purposely reduce the stress peaks (hub edge stresses) that occur at the screw elements in the above arrangement because the deformation of the feather key always occurs along its total length.
In order to reduce the danger of breaking, screw elements used primarily in practical operations are made from a composite material comprising a ductile core material into which the profile of the composite system is inserted, and a jacket material that serves as a wear and/or corrosion resistant material. This composite material is typically manufactured with methods such as those used for manufacturing melt-metallurgical cast materials, soldered composites or hot-isostatically produced PM composites.
The manufacture of these composite materials is very cost-intensive and frequently no longer economical for a wear-resistant part.
SUMMARY OF THE INVENTION
The object upon which the invention is based involves designing the connection between the shaft or shafts of a screw-type extruding machine and the insertable screw elements in such a way that the risk of breakage during the transfer of the rotational moment, particularly for screw elements made of through-hardened material, is reduced considerably.
The above object is achieved by providing a screw-type extruding machine which includes a housing; a drivable shaft disposed inside the housing and including a rotational moment transfer element; and at least one screw element. The screw element has two ends and defines a longitudinal groove therein for receiving the rotational moment transfer element of the shaft, the shaft thereby transferring its rotational moment to the screw element. The groove is configured such that it defines two expansion regions, each expansion region having an axial extent, the groove having side surfaces which diverge with respect to a longitudinal axis of the groove along the axial extent of each expansion region in a direction toward a corresponding one of the two ends of the screw element, a width of the groove thereby increasing in a direction toward its two ends along each expansio
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Sauter Rainer
Weihrich Gerhard
Woerz Wolfgang
Wuttke Reinhard
Cooley Charles E.
Werner & Pfleiderer GmbH
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