Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1993-03-23
1994-09-06
Batten, Jr., J. Reed
Metal founding
Process
Shaping liquid metal against a forming surface
164113, 164313, 164342, B22D 1712, B22D 1720, B22D 2709
Patent
active
053439279
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of press casting. The invention also relates to a device, designed for press casting.
In order to in a rational way utilize the capacity of a press casting machine it is in most cases used to cast different objects. In order to cast these different objects, i.e. to change from a casting of a certain type of object to a certain other type of object, the lower piston as well as the upper piston are usually exchanged as well as the sleeve which constitutes the filling chamber and of course the mold as well as the sleeve, which surrounds the lower piston. These measures are of course always time-consuming and expensive processes and therefore objectionable. Also, the casting process is made more difficult in this way, since e.g. constantly changed diameters of casting pistons, used a little while, lead to varying pressures, which in practice is not acceptable on indeed not feasible. Consequently, a change as regards the casting piston diameter, i.e. an exchange of a casting piston, must be accompanied by a corresponding change of the compression pressure of the machine. This implies automatically a substantial risk of having the personnel make miscalculations or wrong adjustments of the pressure, resulting in a worse quality or actually a rejection of castings.
Particularly when the casting is done under relatively low pressures, e.g. between 1 and 200 bars, a few problems, so far unsolved, will appear. The rationale of such a low pressure casting is to make possible a use of sand mold cores, which in its turn makes possible a production of more complicated products or products, which are to meet high quality requirements, e.g. car rims, sand mold cores however not being absolutely required. The particular complex of problems of a low pressure casting comprises partly the necessity of continuously using strongly heated molds and a superheated metal and partly prolonged cycle periods, since the solidification times are absurdly prolonged, e.g. between 100 and 300 seconds. Thanks to the comparatively slow solidification the metal structure will be coarse and have a low strength. In case a blacking occurs, it is true that it is advantageous during the filling of the liquid metal, but it is a drawback during the ensuing solidification, because it prolongs the cycle periods and contributes to a larger grain size and hence a coarser structure and a lower strength. Thus, it has so far been necessary in many cases to oversize the products.
JP 59-130688 relates to already known techniques in this field. The lower piston according to this specification has a larger diameter than the upper piston, but no specific reasons or explanations are mentioned why this is or must be the case. The activation of the initiation of the movement of the upper piston is done, when a pressure influence has been obtained from the melt via the movement upwards of the lower piston. As regards the lower piston only a general movement upwards is mentioned. As regards the upper piston only a general movement downwards is mentioned.
The object of the present invention is to, in the above-mentioned respects, improve and develop the already known method and devices of press casting. Also, another object is to, in this field, develop the state of the art in various respects and create opportunities of a rationally useful technique and products having a high and uniform quality.
One particular object of the present invention is to improve the casting when relatively low pressures are used by achieving shorter cycle periods, improved product quality, particularly as regards a higher strength, a lower porosity and a finer material structure, namely a material structure having finer grains. Blacking normally is to be avoided and a surface with finer grains obtained, if possible.
It is particularly advantageous according to the invention, if the lower piston is moved upwards to a mechanical stop element in its upmost position, the upper end surface of the lower piston, when necessary, forming the lower surface o
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Abstract of Japanese Patent Publication 56-36369 Published Apr. 9, 1981.
Abstract of Japanese Patent Publication 59-130668 Published Jul. 27, 1984.
Batten, Jr. J. Reed
Tour & Andersson AB
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