BACKGROUND ART For the purposes of explanation, reference will be made to the use of the present invention with respect to the casting of aluminium. It should be understood by those of ordinary skill in the art that the invention is not limited to use in casting aluminium, and that it can be used in the casting of other materials.

It is common practice in the automotive industry in particular to keep the weight of the component parts of a vehicle to a minimum if possible, as this has benefits associated with both the handling and fuel consumption of the complete vehicle.

Thus while many vehicle components were for long periods cast from cast iron, the use of aluminium has become prevalent, due to the associated weight savings.

While the weight and thermal conduction rates of aluminium offer big advantages over cast iron, the actual casting of liquid aluminium is problematic. Conventional gravity pouring of aluminium alloys results in turbulent flow and the manifestation of oxides dispersed through the casting. These oxides often become the failure points for the casting in service.

To overcome this problem with oxide formation, counter gravity filling of the liquid aluminium from the bottom of the mould has become the preferred method of casting. A typical casting apparatus for counter gravity filling comprises a tower or reverbatory melting furnace in which the aluminium is melted, from here it is then laundered to a holding furnace, from which the liquid metal is pumped either by an electromagnetic or pneumatic system, to the mould.

The consistency of the molten metal feed rate provided to the mould is critical to the quality of the casting, and the efficiency of the operation. A major factor in the consistency of electromagnetic pump counter gravity filling systems is the level of

the metal in the holding furnace system. In well-controlled systems the metal level in a holding furnace can be maintained at +/-3mm.

A method used to offset fluctuations in the holding furnace is to change the power supplied to the electromagnetic pump. The operating technique is for the molten metal to be held at the discharge point of the pump assembly. It is maintained at this point by applying energy to the electromagnetic pump, known as the pump bias voltage (PBV). When the metal level in the holding furnace and pump drops it requires more PBV to keep the metal at the same discharge point. While controlling the level using the PBV is effective, it also has an affect upon the fill rate of the mold, as electromagnetic pumps are not linear over the voltage range. If the starting point for a given program is at a higher voltage it will either reduce or increase the fill rate depending on where the voltage in the program falls on the power flow rate curve. As outlined above, any irregularity in fill rate can have a detrimental effect on the quality of the casting.

It is an object of the present invention to provide a means and method for feeding fluid to a casting application that overcomes or at least substantially ameliorates the problems associated with the fluid feed systems of the prior art.

Other objects and advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed.

DISCLOSURE OF THE INVENTION According to one form of the invention there is a fluid feed system for a casting application, including a furnace, a transfer launder drawing fluid from said furnace, a charging well, fluid communication means between said furnace and said charging well, sensing means for measuring the fluid level in said furnace, and fluid displacement means incorporated in the charging well, which are adapted to effect displacement of the fluid between the charging well and the furnace, wherein the fluid displacement means is actuated in response to inputs from the sensing means.

Preferably, a control system is used to continuously control the fluid displacement means in response to inputs from the sensing means.

Preferably, the fluid is molten metal.

Preferably, the furnace is a holding furnace.

Preferably, the sensing means is a laser.

Preferably, the fluid displacement means includes a body attached to manipulation means, which is lowered into the charging well, thereby displacing the fluid.

Preferably, the manipulation means is a linear actuator.

In a further form of the invention, the fluid displacement means includes a gaseous pressurising means, that increases the pressure in a region enclosed above the fluid in the charging well, thereby displacing the fluid.

Preferably, the gas is nitrogen.

Preferably, the charging well is enclosed by a steel lid.

Preferably, the gaseous pressurising means is a portable device adapted for use with a variety of fluid feeding systems.

Preferably, the portable gaseous pressurising means includes a hollow ceramic tube, and a steel lid incorporating the gas fittings, adapted for insertion in an open portion of the holding furnace, such as the charging well.

In a further form, the invention may be said to lie in a method of controlling fluid levels in a fluid feed system for a casting application, the fluid feed system including a furnace, a transfer launder drawing fluid from said furnace, a charging well, fluid communication means between said furnace and said charging well, sensing means for measuring the fluid level in said furnace, and fluid displacement means incorporated in the charging well, wherein if the level of the fluid in the holding furnace departs from a desired level, the level sensing means generates the appropriate signal as an input signal to the control system, which will control the fluid displacement means as required, in order to restore fluid levels in the furnace to the desired level.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of this invention it will now be described with respect to the preferred embodiment which shall be described herein with the assistance of drawings wherein; Figures 1 and 2 are cross-sectional views through the feeding system according to the preferred embodiment, and Figures 3 and 4 are cross-sectional views through a feeding system according to a second embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Now referring to the illustrations, there is a feeding system 1 having a holding furnace 2, and charging well 4, containing molten metal 5. The holding furnace 2 and charging well 4 are separated by a common wall 6, which has a molten metal communication passage 7 therein, at its top.

The holding furnace 2 has a plurality of heating elements 10 suspended above it, so as to keep the molten metal at a desired temperature. There is a transfer launder 15 drawing molten metal from the holding furnace 2 via a suction pipe 20, which incorporates an electromagnetic pump 25, that is immersed in the molten metal 5, thereby forming a supply system.

The holding furnace 2 is provided therein with a level sensing means 40 for detecting the level of the molten metal in the holding furnace. The level sensing means is a laser, using triangulation, and which reads the metal level at a frequency of 250Hz and a resolution of 0.025mm. It is to be understood by a person skilled in the art, that there are other devices which may be used for this purpose however.

The metal displacement means takes the form of a ceramic, or metal block 30 suspended above the charging furnace via an actuating means, such as a hydraulic or pneumatic cylinder 35.

When the level of the molten metal in the holding furnace 2 departs from the desired level, the level sensing means generates the appropriate signal as an instruction signal to the pneumatic cylinder, which will in turn manipulate the ceramic block 30 accordingly. If the level in the holding furnace 2 drops, the actuating cylinder 35 will lower the block 30 into the charging furnace 4, thereby displacing molten metal over the common wall 6 into the holding furnace.

Referring now to Figures 3 and 4, which illustrate a further embodiment of the present invention, wherein the charging furnace 40, is a closed vessel provided with a gas inlet 45 and outlet 50; the charging furnace is provided with a gas that will applies pressure to the to the interior of the charging well, thereby forcing molten metal through a passage in the common wall 55 in the bottom of the furnace. In the same fashion as before, this gas charging system, can in response to inputs from the metal level sensing laser, control the molten metal level in the holding furnace.

A significant advantage of the furnace according to the present invention is that the holding furnace will keep a constant level (+/-0. 5mm) even as metal is fed to the holding launder and mould, resulting in greater control of the filling of the mould.

Another advantage of the present invention is that the electromagnetic pump is situated in the furnace, and the molten metal is drawn directly from the furnace.

Given the critical effects of temperature on metal and casting characteristics, this is a significant advantage.

The feeding system according to the present invention is ideally adapted to facilitate ease of maintenance operations. The pump is made from ceramic materials, and is removably immersed in the furnace, such that it can be quickly and easily removed from the molten metal if maintenance is required. Consequently, there is no need to remove any molten metal from the furnace in order to carry out maintenance.

It is considered therefore that a feeding system such as that described herein would prove to be of considerable benefit to those using counter gravity techniques to cast aluminium in particular.

Although the invention has been herein shown and described in what is conceived to be the most practical and preferred embodiment, it is recognised that departures can be made within the scope of the invention, which is not to be limited to the details described herein but is to be accorded the full scope of the appended claims so as to embrace any and all equivalent devices and apparatus.