Plastic and nonmetallic article shaping or treating: processes – With step of cleaning – polishing – or preconditioning...
Patent
1993-12-16
1995-10-24
Heitbrink, Jill L.
Plastic and nonmetallic article shaping or treating: processes
With step of cleaning, polishing, or preconditioning...
249 79, 26432816, 264335, 425552, 425437, B29C 4573
Patent
active
054607612
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF INVENTION
The present invention relates to a method for tempering a moulding tool intended for production of products of natural or synthetic polymers, which moulding tool comprises one or more moulding parts made of sintered metal with communicating pores. The moulding parts are obtained by pressing a powdered material at a high pressure and sintering at a high temperature. A moulding cavity has then been made in the moulding part or parts. Preferably the outer envelope surface of the moulding tool is tight.
DESCRIPTION OF PRIOR ART
From the Swedish publication SE-P-454247 it is known before to produce moulding parts of sintered metal, whereby the moulding parts get communicating pores. A moulding cavity is produced in the moulding parts, which together constitute a mould intended for production of products of natural or synthetic polymers by injection moulding.
When the moulding cavity has been completed the envelope surfaces are tightened. The center of said known invention consists in the formation of a reservoir in the pore system of the mould for temporary reception of air or another gas formed at the injection moulding. When the mould is opened after each production cycle the gas i released again from the reservoir.
The known process disclosed above works very well. At some applications there are, however, difficulties in regulating the temperature in the different parts of the moulding tool. Moreover, in certain cases the pores will be clogged by by-products formed at the moulding of the polymer products.
For instance at injection moulding of thermoplasts in steel moulds, often about 80% of the production cycle, consists of cooling time. The thermoplast is injected via a gate or another nozzle into the moulding cavity at a temperature of about 90.degree. C.-300.degree. C. The plastic product is cooled in the moulding cavity by conduction and the heat is removed by water cooling in channels situated outside the moulding cavity or drilled into the mould steel.
When cooling channels are placed in the mould steel, you often get the problem that they make the mould construction weaker. Of course, this is especially true for small areas. A weak mould construction cannot be accepted. Therefore, certain areas of the mould are not provided with cooling channels, which of course results in an insufficient cooling.
Another considerable problem is to be able to arrange cooling channels in connection with a complex moulding cavity. This results in an uneven cooling or tempering of the moulding cavity and also a deterioration of the quality of the plastic product.
Another very frequent problem, especially at the production of big products, is that the flow paths i.e. the distance from the injection site to the middle of the product is so long that the plastic is cooled to much before it has filled the whole cavity. Then, often certain inner parts of the cavity will get defects in respect of the moulded plastic.
Thus, an uneven tempering of the moulding cavity is a big problem both at the moulding of thermoplasts and thermosets.
In the U.S. Pat. No. 5,021,203 a method for solving the above tempering problem and the problem with clogging of the pores is disclosed. Then the temperature is regulated in a moulding tool intended for the production of products of natural or synthetic polymers.
The moulding tool comprises one or more moulding parts made of sintered metal with communicating pores obtained by pressing a powdered material at a high pressure and sintering at a high temperature. A cavity has then been made in the moulding part or parts. The pores are open towards the moulding cavity while the outer envelope surface of the moulding tool is tightened against leakage.
A heating buffer is arranged in the moulding tool by filling the communicating pores with a liquid with a high vaporizing temperature. The pressure on the liquid in the pores is regulated by means of a suitable pressure producer connected with the communicating pores in the moulding tool. The pressure is arranged to be automatica
REFERENCES:
patent: 4139177 (1979-02-01), Hanning
AGA Aktiebolag
Heitbrink Jill L.
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