Metal founding – Means to shape metallic material – Pressure shaping means
Reexamination Certificate
1999-02-09
2001-10-09
Nguyen, Nam (Department: 1722)
Metal founding
Means to shape metallic material
Pressure shaping means
C164S410000, C164S312000
Reexamination Certificate
active
06298903
ABSTRACT:
FIELD OF THE INVENTION
The present invention refers to a method for venting a diecasting mould of a diecasting machine that is provided with a casting piston located in a pressure chamber and adapted for pressing liquid casting material into a mould cavity of the diecasting mould. The diecasting mould is provided with at least one venting channel communicating with the mould cavity. It comprises a first venting valve operationally connected to an impact transmitter exposed to and moved by the liquid casting material advancing from the mould cavity into the venting channel.
Moreover, the present invention refers to a valve assembly for venting a diecasting mould of a diecasting machine that is provided with a casting piston located in a pressure chamber and adapted for pressing liquid casting material into a mould cavity of the diecasting mould, whereby the diecasting mould is provided with a venting channel communicating with the mould cavity.
BACKGROUND OF THE INVENTION
In order to avoid the occurrence of trapped air in the finished cast work piece, the diecasting mould and the mould cavity of the diecasting mould, respectively, has to be vented during the diecasting operation. Thereby, it must be ensured that not only the air contained in the cavities of the diecasting machine and of the diecasting mould can escape, but it has also to be ensured that gases escaping from the liquid casting material can be removed as well.
In venting a diecasting mould, there is a problem insofar as the venting valve should be closed as late as possible in order to ensure that the mould cavity is vented, if possible, until it is completely filled; on the other hand, it should be avoided that liquid casting material can enter the venting valve. Taking this problem into account, venting assemblies have been disclosed in the prior art having a venting valve that is operationally connected to an impact transmitter operated by the liquid casting material advancing from the mould cavity into the venting channel. With the aid of such a design, very reliable valve assemblies can be realized that can be operated very quickly. In order to be able to build up a ram pressure at the impact transmitter sufficient to perform the closing operation, the venting channel comprises returns and cross sectional area variations. Moreover, the venting channel must have a certain minimal length between the impact transmitter and the real valve body member of the venting valve, and it should be full of corners in order to ensure that the venting valve is closed before the liquid casting material has reached the venting valve. By a design of the venting channel running between the impact transmitter and the venting valve that is full of corners, moreover, it can be avoided that splashes leading the real flow of casting material can enter the venting valve and block it. In order to increase the efficiency of such valve assemblies, usually a vacuum pump is connected to the venting valve.
PRIOR ART
The document EP 0 612 573 discloses a valve assembly referred to herein for venting diecasting moulds, comprising a venting channel, a venting valve located in the venting channel and an operating means for closing the venting valve. The operating means comprises an impact transmitter that is exposed to the liquid casting material advancing from the mould cavity into the venting channel. The impact transmitter is mechanically operationally coupled to the movable closure element of the venting valve. Thereby, the impact transmitter is designed as a push member hating an operating stroke that is limited to a fraction of the stroke to be passed through by the movable element of the venting valve. Moreover, the closure element of the venting valve is freely movable along the path exceeding the operating stroke of the impact transmitter, and the operating means comprises a power transmission member for transmitting the impact impulse from the impact transmitter to the movable closure member of the venting valve.
Even if such valve assemblies operate very reliably in practice, it would be desirable to increase the venting efficiency, particularly in the case of mould cavities having a large volume. The maximal venting efficiency is limited particularly by the turns and variations of the cross sectional area in the venting channel because thereby the flow resistance for the gases escaping from the mould cavity is substantially increased.
In order to solve the problems discussed herein above, it would be obvious to increase the cross sectional area of the already present venting valve and of the venting channel. However, tests conducted with such a design have shown that an increase of the cross sectional area of the valve and the venting channel doesn't offer the desired success because the flow resistance of the venting channel, due to its design full of corners, hinders an efficient venting as was always the case. An increase of the size of the venting valve, moreover, results in an increase of the mass of the movable parts of the valve assembly. Thus, consequently, the force required for closing the venting valve increases correspondingly, and/or the closure time of the venting valve increases to an undesired high value. Moreover, an increase of the cross sectional area of the venting valve and of the venting channel results in the fact that the dimensions of the valve assembly are increased as well; this is also not desired.
OBJECTS OF THE INVENTION
Thus, it is an object of the present invention to propose a method for venting the diecasting mould of a diecasting machine by which a higher venting efficiency can be achieved, still maintaining a reliable operation.
It is a further object of the invention to provide a valve assembly by means of which the method of the invention can be optimally performed.
SUMMARY OF THE INVENTION
To meet these and other objects, the present invention provides, in a first aspect, a method for venting a diecasting mould of a diecasting machine that is provided with a casting piston located in a pressure chamber and adapted for pressing liquid casting material into a mould cavity of the diecasting mould. The diecasting mould is provided with at least one venting channel communicating with the mould cavity. It comprises a first venting valve operationally connected to an impact transmitter exposed to and moved by the liquid casting material advancing from the mould cavity into the venting channel.
According to the invention, in a first step, the mould cavity and/or the pressure chamber is vented by means of a second venting valve in addition to the first venting valve during the step of pressing liquid casting material into the mould cavity of the diecasting mould. In a second step, the second venting valve is closed before the mould cavity is entirely filled with the liquid casting material, and in a third step, thereafter, the first venting valve is closed by the casting material advancing into the venting channel and hitting the impact transmitter.
With the method as outlined above, the venting efficiency can be considerably increased, because the provision of a second venting valve that is closed before the mould cavity is completely filled results in at least a doubling of the mean cross sectional area of the channels relevant for the venting efficiency, whereby simultaneously the venting channel portion leading to the second venting valve can be optimized as far as the flow resistance is concerned.
In a preferred embodiment of the method, the criterion for closing the second venting valve is constituted by the time elapsed since the start of the filling operation, or the position of the casting piston, or the path along which the casting piston has moved, or the fill rate of the pressure chamber, or the fill rate of the mould cavity. By this measure, it is ensured that the second venting valve is closed when the cast material has advanced up to it.
According to a second aspect, the invention provides a valve assembly for venting a diecasting mould of a diecasting machine that is provided with
Guth Heinrich
Wyser Johann
Fondarex SA
Lin I.-H.
Nguyen Nam
Tarolli, Sundheim, Covell Tummino & Szabo L.L.P.
LandOfFree
Method and apparatus for venting a diecasting mould of a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for venting a diecasting mould of a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for venting a diecasting mould of a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2616236