Metal founding – Means to shape metallic material – Pressure shaping means
Reexamination Certificate
1999-09-22
2002-10-08
Dunn, Tom (Department: 1725)
Metal founding
Means to shape metallic material
Pressure shaping means
C164S309000, C164S319000, C164S321000, C164S337000
Reexamination Certificate
active
06460603
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an apparatus for the uphill low pressure casting of metals, particularly light metals, in split sand moulds with a gate or sprue in one of the two moulds, to which is connectable the casting tube of a melt container and which is connected with the lowest area of the mould cavity, and with a sealing plug integrated into the mould and which following the filling of the mould cavity by means of an external drive engaging in the mould can be brought into the closed position.
2. Description of the Prior Art
In the uphill casting of metals the melt is placed under an overpressure in the melt container or a holding furnace, in order to force the melt via the casting tube and the sprue in rising manner into the mould cavity. Following the filling of the mould the melt column in the casting tube and in the mould sprue must be interrupted, in order to convey away the poured off mould and to be able to dock the next mould with the casting tube. Before this the melt must be returned in the casting tube. In addition, precautions must be taken with respect to the mould so that during the further conveying on of the mould the sprue is closed at least until the melt has solidified in the sprue. This takes place e.g. by moving the mould onto cooling plates or cooling plates carried along with the mould.
For sealing the mould after filling, sealing slides integrated into the mould and located at the sprue are known (WO 93/11892, WO 95/32826), which can be moved from an open position during casting into a closed position shutting off the sprue. In the case of sand moulds, either with or without boxes or flasks, the problem arises that the slide made from a different material must be segregated during the processing of the mould sand. Frequently there is an adhesion thereof to the solidified metal in the sprue and removal must take place through a separate operation.
In a known construction (WO 95/32826, DE-journal “Giesserei”, 1998, pp 57 to 62) following the filling of the mould by means of an external drive engaging in the sand mould from the side, moulding sand is displaced from the area alongside the sprue into the latter and is intended to displace the sprue in a plug-like manner. Considerable abrasion occurs, which is displaced into the melt both in the direction of the casting tube and in the direction of the mould cavity. The moulding sand particles displaced towards the casting tube remain in the melt on return or resetting and are conveyed into the mould cavity during the next casting process, which leads to considerable quality losses with respect to the casting, particularly if it is made from light metal, e.g. aluminium alloys.
An attempt is made to prevent the displacement of moulding sand into the melt in that downstream of the sealing plug is positioned a particle filter (DE-journal “Giesserei”), or in that (WO 95/32826), the sprue is initially guided downwards by the casting tube neck and in this falling area of the sprue the drive engages in the mould in order to displace the moulding sand in plug-like manner into the falling portion of the sprue. This construction is counter to the fundamental requirement of a very short sprue path. The falling portion is also opposed to the principle of uphill casting and can lead in this area to undesired turbulence during the pouring off of the mould. Although both constructions have the advantage that the mould contains no type-foreign components, because the sealing plug is made from the same moulding sand as the mould and consequently can be processed with the moulding sand of the mould, the disadvantage remains in both cases that sealing takes place in a completely uncontrolled manner and the quality of the seal is dependent on the shape stability, the pressing-out force acting on the moulding sand through the drive and the time force gradient. It is in particular not ensured that an intact, sealed plug is formed and that the mould does not break off laterally of the forced-out plug. These risks are particularly high with large sprue cross-sections for high casting capacities.
SUMMARY OF THE INVENTION
On the basis of this prior art, the problem solved by the invention is to provide an apparatus in which, whilst maintaining the type-pure composition of the sand mould, a completely satisfactory seal is possible in the vicinity of the sprue and also, even in the case of a high casting capacity and large sprue cross-sections, the quality of the seal remains in a reproducible manner and finally the risk of carrying moulding sand particles into the melt is minimized.
According to the invention this problem is solved in that between the sprue and the mould cavity is provided at an angle to the sprue a casting duct or channel linking the same and that the sealing plug is constructed as a sand mould body and is displaceable in a shaped-in guide of the mould between an open position and a closed position, where the sealing plug closes the casting channel and the metallostatic pressure of the melt in the mould acts perpendicular to the guide on the sealing plug.
In the construction according to the invention, the sealing plug is pre-shaped as a sand mould body. In the sand mould there is both a guide for the sealing plug and also a casting channel at an angle to the sprue, namely in the vicinity of the mould parting plane. The casting channel is preferably at right angles or under a steep, obtuse angle to the flow direction in the sprue. In the case of high castings, which consequently extend correspondingly deeply into said mould, the casting channel must also be correspondingly deep. The final cross-section of the casting channel can be determined by an inserted core.
The melt is deflected within the mould from the sprue into the casting channel. In the vicinity of the deflection is provided the guide with the sealing plug and the sealing plug is initially located in the open position freeing the transition between sprue and casting channel. Following mould filling, the sealing plug constructed as a sand mould body is displaced by means of the external drive engaging in the mould inside the guide into the closed position, in which the transition between the sprue and the casting channel is displaced away from the sealing plug. In the closed position the metallostatic pressure of the mould acts transversely to the guide on the sealing plug, so that the latter remains in its position.
As the sealing plug is a separate moulding, there is only minimum abrasion on the guide or sand mould body, so that the risk of carrying moulding sand particles into the casting tube on returning the melt is very small. It is also possible to produce the sealing plug from the same moulding sand as the mould, so that it can be processed during the preparation of the moulding sand. As a result of the separate prefabrication, the hardness of the sand mould body can be optimized in accordance with the intended use.
In a preferred development the sealing plug is held in the open position in self-locking manner in the guide. The self-locking action can be brought about by a correspondingly close fit of sealing plug and guide, optionally assisted by frictional forces due to surface roughnesses.
With horizontally positioned moulds and a roughly vertical sprue, the sealing plug can also be placed with clearance in the guide and e.g. rest on a step or the like. When filling the mould, the sealing plug is raised into the open position as a result of the melt buoyancy force and in this position it seals in the guide, e.g. engages against an annular step or is sealed against the guide surface by a conical construction of the guide. Instead of being made from moulding sand, in the manner indicated hereinbefore, the sealing plug-forming sand mould body can also be produced from core sand. In both cases a surface smoothing by the application of a blackwash is recommended.
In an other preferred development, the guide is constructed as a bush from a core sand and is inserted in prefabricated receptacles of
Damm Norbert
Zulauf Herbert
Dunn Tom
Georg Fischer Disa AG
Lin I.-H.
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