Plastic article or earthenware shaping or treating: apparatus – Female mold and charger to supply fluent stock under... – With accumulator – trap chamber – or serially arranged valves...
Patent
1998-02-25
2000-12-05
Heitbrink, Tim
Plastic article or earthenware shaping or treating: apparatus
Female mold and charger to supply fluent stock under...
With accumulator, trap chamber, or serially arranged valves...
425563, B29C 4552
Patent
active
061558168
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a backflow blocking arrangement for an injection unit of an injection molding machine having a screw cylinder with a plasticising screw, at the front end of which is arranged the backflow blocking arrangement comprising a screw tip, a blocking bush and a blocking sleeve with corresponding sealing and friction surfaces, wherein at least a portion of at least one friction surface of the screw tip, the blocking bush and/or the blocking sleeve is formed by a protective layer comprising a fusion-metallurgical compound between the respective base body and a supplied or pre-deposited additive material.
The invention further relates to a process for producing such a backflow blocking arrangement.
Backflow blocking arrangements of that kind prevent a backflow of a part of the plastic material during the injection moulding procedure. An example of a backflow blocking arrangement is described in EU-B1-0 212 224.
Backflow blocking arrangements of that kind are subject to high abrasion and corrosion loadings. It is known for individual parts of the backflow blocking arrangement to be provided at the friction surfaces with a hard material layer. In accordance with the known state of the art various coating processes such as flame spraying, high-velocity flame spraying, plasma spraying, detonation spraying, PVD, CVD with or without subsequent heat treatment are used in the treatment of the individual parts of a backflow blocking arrangement. Welding processes, for example PTA-welding and WIG-welding were also used.
The known coatings have relatively thin anti-wear ranges (from the .mu.m range in the case of CVD and PVD up to some 1/10 mm-layer thicknesses with various spray procedures).
All known coatings have a substantially different normal electrode potential relative to the base body, which is disadvantageous from the corrosion point of view if a non-coated region has a contact surface in relation to a coated region and the assembly is subjected to the action of a medium having a corrosive effect.
Even if the coatings are sintered in position by means of a heat treatment, they always have a relatively brittle contact zone which can give rise to problems when the assembly is subjected to rough mechanical handling. Thus for example breakages, cracks and the like may occur.
In accordance with the known state of the art welding processes are used primarily for build-up welding procedures, for example PTA-welding=plasma powder build-up or transfer welding. In that operation an arc burns between a tungsten electrode and the workpiece. The additive material is generally introduced in powder form. The disadvantage of that process is that it provides for an insufficiently defined mixing effect as between the additive material and the base material. It is therefore not possible to set specific structures. Furthermore the susceptibility to cracking in the armoring is high due to the differences in heat expansion of the build-up or transfer material and the base body. Starting the procedure and stopping the procedure when using conventional welding processes represent further problems.
The known backflow blocking arrangements of this kind cannot therefore be completely satisfactory in terms of their service life. Therefore the object of the present invention is to improve a backflow blocking arrangement and a process for processing the individual base bodies of the parts of a backflow blocking arrangement of the kind set forth in the opening part of this specification, in such a way that the service life of the backflow blocking arrangement is substantially increased insofar as the invention provides a material system particularly suited to that component and a process for the production thereof.
The object according to the invention is attained in that at least the base body of the screw tip comprises a metal material, preferably a chromium-bearing steel material and additive materials such as metals, carbides, carbonitrides, borides, carboborides, silicides, sulfides and/or oxides, preferably compounds
REFERENCES:
patent: 5167971 (1992-12-01), Gill et al.
Baldinger Peter
Brandstatter Elmar
Ebner Reinhold
Pitscheneder Walther
Urbanek Otto
Engel Maschinenbau Gesellschaft m.b.H.
Heitbrink Tim
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