Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1993-09-17
1995-09-05
Batten, Jr., J. Reed
Metal founding
Process
Shaping liquid metal against a forming surface
164113, 164133, 164319, B22D 1712, B22D 1802
Patent
active
054471885
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a process for casting metals, in particular alloys with low melting points, during which process liquid metal is filled from the bottom to the top into a casting mold by way of a casting runner and a filling hole arranged at the lowest point of the casting mold, and to an apparatus to effect such a process.
Such processes are employed, for example, during the production of lost cores for injection molded plastic parts. During such process top casting must be avoided, so that the casting takes place by necessity at the lowest point of the mold. To date the liquid metal during the process of the aforementioned kind has been filled under pressure into the casting mold and the casting pressure has been maintained until the metal has totally solidified in the casting mold. After the metal has solidified, the resulting sprue or runner has to be removed and the filling point has to be ground smooth.
The cores produced in this manner are used, among other things, for mass producing plastic parts in the automobile industry, where it is important on account of high quantity requirements to hold the cost of production as low as possible. However, these costs are significantly increased by the requisite subsequent treatment and the additionally required machines or manual activity.
SUMMARY OF THE INVENTION
Therefore, the object of the invention is to develop a process and apparatus by which a casting can be produced without sprues or runners and can be directly further used without subsequent processing.
This object is achieved according to the invention by decreasing or turning off the casting pressure after totally filling the casting mold and only partial solidification of the metal in the casting mold, so that the liquid metal flows back out of the casting mold by way of a return flow channel having a cross section significantly smaller than the cross section of the casting runner. A ram having a face corresponding in size and shape to the outer contour of the casting in the region of the filling hole is pushed at least over the last segment of the casting runner, thus displacing the liquid metal present therein into the casting mold as far in the direction of the mold interior until the fact of the ram aligns with the inner contour of the casting mold. Due to the adaptation of the fact of the ram to the desired outer contour of the core in the region of the filling hole, the core is located now in a totally closed casting mold and solidifies without forming a casting sprue that must be subsequently processed.
When advancing the ram and closing the filling hole at the end of the casting operation, the ram displaces the liquid material, a process that would not have been possible with the conventional process since the mold with the liquid metal is filled totally without air pockets. However, a cavity, into which the ram can be subsequently pushed upon closing the filling hole of the liquid metal, is created according to the invention in the casting mold by means of the return flow of the liquid metal out of the casting mold after reducing or switching off the casting pressure. The return flow volume is controlled by the cross section of the return flow channel being significantly smaller than the cross section of the casting runner. In this manner it is ensured that until the filling hole is closed by the ram, not too much liquid metal has flowed back and the cavity within the casting mold is not too large.
Upon pressing the metal into the casting mold, the ram closes according to the invention the casting runner before the face of the ram aligns with the inner contour of the casting mold. In this manner it is achieved that the metal displaced by the ram is forced reliably into the casting mold and is not discharged partially by way of the casting runner, thus preventing a defined filling of the cavity in the casting mold.
To achieve maximum filling of the cavity produced in the casting mold by means of the return flow of the metal, it is provided in another
REFERENCES:
patent: 969539 (1910-09-01), Kitchen
patent: 4991641 (1991-02-01), Kidd et al.
patent: 5109914 (1992-05-01), Kidd et al.
Srostlik Peter
Walter Alfred
Bachmann Giesserei und Formenbau GmbH & Co. KG
Batten, Jr. J. Reed
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