Agitating – Rubber or heavy plastic working – Stationary mixing chamber
Reexamination Certificate
1999-04-19
2001-05-22
Soohoo, Tony G. (Department: 1723)
Agitating
Rubber or heavy plastic working
Stationary mixing chamber
C366S241000, C366S348000, C366S144000
Reexamination Certificate
active
06234660
ABSTRACT:
This application claims Paris Convention priority of German patent application number 198 21 072.8 filed May 12, 1998, the complete disclosure of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The present invention concerns a method for the Production of an intermediate product, which can be inject-on moulded, from a dry, pasty or fluid raw material and at least one binding agent.
Known in the art is the production of intermediate products, which can be injection moulded, by kneading of raw materials together with a binding agent in a device.
In the conventional methods, the raw materials are processed together with the binding agent within the device (kneading device) with the assistance of knead elements, warmed by a separate heating device and kneaded into a paste after melting of the binding agent. The paste can then be removed from the device, and the extracted intermediate product, designated as “feedstock” (paste), can be injection moulded into a product to be produced. This object must still be subjected to baking or sintering processing for curing and is referred to as a “green body”. The intermediate product must optionally be further processed prior to injection moulding. This further processing can consist essentially of a granulation or a grinding of the cooled paste.
In order to manufacture the intermediate product, it is necessary for the raw materials and the binding agent to disadvantageously be kneaded for 2 to 20 hours.
Due to the low mixing effectivity of the kneading device, the produced paste has a limited degree of homogeneity. This low or absent homogeneity affects the recycling process or the utilization of the waste products occurring from injection moulding which are once more introduced into the device. It has turned out that there is a strong difference in flow properties between the pure raw materials and the recycled product wastes. The inadequate homogeneity of the paste also leads to the need for post-processing the paste optionally in an extruder or in a cylinder mill.
The kneading processing of a mixture comprising raw materials and at least one binding agent is only possible in dependence on the mixture utilized by selecting an appropriate mixture. Not all types of kneading devices are suitable for each mixture so that, under certain circumstances, the mixture must be changed.
It is the purpose of the present invention to develop a method for as effective production as possible of a high quality intermediate product which can be injection moulded.
SUMMARY OF THE INVENTION
This purpose is achieved by a method with which the raw material and the at least one binding agent are initially processed in a mixing container using rapidly rotating mixing elements to generate a powder mixture and, subsequent thereto and with the assistance of mechanical processing of the powder mixture by the mixing elements and/or of additional components (break-up tools, rod-shaped elements, knives, etc.), the powder mixture is warmed and processed into the intermediate product.
The designation—rapidly rotating mixing elements—refers to a motion of the mixing elements which is capable of producing a swirl or a circulating ring of mixed products within the device. The mixing elements should have a peripheral velocity in excess of 20 m per second.
The components of the mixture are introduced into the mixing container either simultaneously or sequentially. Processing of the mixing components with the assistance of the mixing elements generates frictional heat to warm up the mixing components. In exceptional cases, the heating-up process can be supported or initiated by heating-up the wall of the mixing container. During this processing step, an intense pre-mixing of the raw material and the binding agent occurs. A pourable powder mixture having high mixing quality normally results.
In the same mixing container, an intermediate product in the form of an agglomerate or a paste can be generated from the powder mixture which can be extruded in a mold to generate an object. Both the agglomerate as well as the paste have high homogeneity. This mixing quality improves the quality of the final product which can be produced from the intermediate product.
Mixing elements disposed on a rapidly rotating mixing shaft facilitate limitation of the processing duration, in most cases, to 10 to 20 minutes.
Processing of the raw material and the binding agent in the device with the assistance of the rapidly rotating mixing elements can be carried out independent of the mixture of raw materials and binding agent introduced into the device. A rate of rotation of the mixing shaft adapted to the mixture can be adjusted in such a fashion by controlling the device that the desired pre-mixture and heating-up of the mixture occurs. The mixing elements can cooperate with fixed or movable components in the mixing region to shorten the mixing and/or breaking-up and warming times.
The method in accordance with the invention advantageously leads to a reduction in the investment and operating costs and has positive effects on the lifetime of operation of the device for carrying out the method.
In a preferred embodiment, the mixture comprising the raw material and at least one binding agent is heated and agglomerated through mechanical processing to below the melting point of the binding agent. The frictional heat occurring in the vicinity of the mixing elements leads to a melting of the surfaces of the binding agent particles which can then bond to the raw material particles to effect agglomerate generation. For certain mixture conditions, the agglomerate can already be removed from the device as an intermediate product capable of injection moulding.
In another embodiment, the binding agent is melted through the mechanical processing in the mixing container, wherein a paste is produced from the mixture comprising the raw materials and the at least one binding agent. The raw material particles form, together with the binding agent particles, a viscous mass of pasty consistency. The binding-together of the raw material particles and the binding agent particles leads to an intermediate product which can flow. The ductile paste is likewise highly homogenized through processing by the mixing elements.
The paste can be cooled down and thereby once more agglomerated prior to further processing of the agglomerate using an injection moulding machine.
Bulk products, solids as well as fluid raw materials of the most differing kinds can be utilized as raw materials. The method can also be used with metallic powder or ceramic powder as raw materials. The method can thereby be utilized for the production of intermediate products suitable for powder-injection moulding (PIM) technology. A modified plastic injection moulded machine thereby produces the “greenhorn” out of a raw material powder and binding agent mixture. The extruded and cured “greenhorn” can then be further processed in differing manners.
An organic binding agent can preferentially be utilized as at least one binding agent. Binding agents can be considered which react with the raw materials and/or which can accelerate the combining of the raw material particles among themselves. The organic binding agent can effect sufficient flow capability in the injection moulding machine and can impart a large degree of shape stability to the extruded and cured slug (greenhorn). The binding agent can be removed from the greenhorn using baking or sintering methods.
The method in accordance with the invention is simultaneously applicable for MIM (metal injection moulding) and CIM (ceramic injection moulding).
Further features and advantages of the invention can be extracted from the subsequent description of an embodiment of the invention with regard to the drawing, showing details important to the invention, and from the claims. The individual features can be utilized in embodiments of the invention individually or collectively in arbitrary combination.
REFERENCES:
patent: 4057227 (1977-11-01), Cruff et al.
patent: 4197118 (1980-04-01), Wie
Hullmann Hans-Dieter
Schaer Ulrich
Schuermann Ludger
Wulf Burkhard
Gebrueder Loedige Maschinen-gesellschaft mit beschraenkter Haftu
Soohoo Tony G.
Vincent Paul
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