The invention provides ingot feeding apparatus for a diecasting machine, comprising means for feeding an ingot into a bath containing, in use, molten metal for use in the diecasting process, means for detecting the level of molten metal in the bath, and means for operating the ingot feeding means in response to signals from said level detecting means, wherein the level detecting means comprises means for measuring temperature in said bath above the surface of the molten metal therein.

The invention also provides ingot feeding apparatus for a diecasting machine, comprising means for feeding an ingot into a bath containing, in use, molten metal for use in the diecasting process, means for measuring the temperature of the molten metal in the bath, and means for controlling the rate of feed of the ingot into the bath in dependence upon the measured temperature of the molten metal.

By way of example, an embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a general assembly view of an ingot feeding apparatus according to the invention, and

Figure 2 is a diagrammatic illustration of the apparatus together with a bath for holding molten metal.

In a typical diecasting machine, the stock of base metal to be used in the casting process is kept in a molten state in a heated bath. The level of liquid in the bath is monitored, typically by a device such as a carbon float switch. The device is arranged to trigger the introduction of a fresh ingot into the bath when the liquid level falls below a certain point.

The ingot feeding apparatus 10 seen in the drawings comprises a magazine for holding a supply of fresh ingots. Ingots are typically supplied in the form of a bar with a "C" shaped hook at one end. Here, the magazine conveniently takes the form of a rail 12 on which a number of ingots can be hung by their hooks. The rail 12 feeds each successive ingot onto a peg 15 on a carriage 13, which lowers them into the heated bath 1 1, one by one. The apparatus 10 has a pair of parallel rods 14 that are arranged to extend down into the bath 1 1. The rods 14 form a track for guiding up and down movement of the carriage 13. The carriage 13 is connected via a chain 17 trained around pulleys 18, 19 to a winder 20, which is driven by a motor 21. The motor 21, conveniently an AC electronic or stepping motor, drives the winder 20 forwards or backwards for raising or lowering the carriage 13.

The apparatus 10 incorporates sensors for monitoring the level of molten metal in the bath 1 1. Unlike conventional systems, the sensors in the apparatus 10 here are in the form of temperature sensors, conveniently thermocouples. There is one sensor 22 which is arranged to measure temperature in the bath 11 above the surface of the molten liquid. The surface sensor 22 is able to give an indication of the liquid level 30 in the bath 11, because the temperature measured by the sensor will depend on its proximity to the surface of the liquid.

There is another sensor 23 which is arranged to measure temperature below the surface of the molten liquid. The sub-surface sensor 23 essentially measures the temperature of the body of molten liquid in the bath 11.

A further sensor 24 is mounted on the carriage 13. The carriage sensor 24 gives an indication of the proximity of the carriage 13 to the surface of molten liquid in the bath 1 1.

The bath 1 1 contains a further sensor 25 which serves as a safety switch to prevent the bath 11 from overflowing. The measurements from all the temperature sensors 22, 23, 24, 25 are fed to a processing unit 26 which controls operation of the apparatus 10. The processing unit 26 also conveniently controls operation of the heating elements 40 that heat the molten liquid in the bath 11. The basic idea is for the processing unit 26 to control the ingot feed so as to achieve a balance between the energy going into the bath and the energy going out, whilst providing a steady supply of molten metal to the casting process.

The processing unit 26 is set with lower and upper temperature limits, which effectively act as on/off switches. Essentially, when the temperature measured by the surface sensor 22 falls to the lower limit, indicating that more molten stock is required, the processing unit 26 activates the motor 21 to lower a fresh ingot 16 into the bath 11 via the carriage 13.

The ingot 16 continues to be fed into the bath until the temperature measured by the surface sensor 22 reaches the upper limit, at which point the carriage

13 is halted. The carriage sensor 24 senses the proximity of the carriage 13 to the molten liquid level 30 and holds it in this position whilst the hook of the ingot 16 melts or falls away into the molten liquid. The carriage 13 is then raised to its home position to be loaded with a fresh ingot from the magazine, ready for the next cycle.

Generally, when a fresh ingot is introduced into a heated bath of molten metal, the overall temperature of the liquid will be caused to fall, as energy is used up initially melting the ingot, and it takes time for the temperature of the molten stock to re-establish. The casting process requires molten metal to be supplied at a specified temperature within a fairly narrow range. If the casting process is allowed to continue despite a fall in temperature of the molten stock, this can cause problems with the quality of the finished cast product and/or operation of the casting machine. It is therefore desirable to avoid excessive drops in temperature of the molten stock occurring. The processing unit 26 is arranged to use feedback from the various sensors to permit as fast a feed rate of fresh ingots into the bath as can be achieved, whilst maintaining the temperature of the molten stock within acceptable limits. For example, if during the feeding of a fresh ingot into the bath the sub-surface sensor 23 indicates a drop in temperature, the rate of feed may be reduced or, if necessary stopped altogether, until the temperature recovers.

The processing unit 26 controls the feed rate of the ingot by regulating operation of the motor 21 that drives the winder 20. Depending on the nature of the motor, this might be arranged to drive the carriage in a slow continuous manner and/or by means of a number of small incremental steps.

Ideally, the processing unit 26 will be set up to provide continuous adjustment to the motor control in response to temperature fluctuations. In this way the processing unit 26 provides proportional control.

The carriage sensor 24 can conveniently be used for an additional function. When metal ingots are melted in a bath, impurities, usually known as dross, tend to gather on the surface of the molten liquid. The dross needs to be removed from time to time, so that the operation of the machine and/or quality of the finished casting is not adversely affected. This is typically achieved by sweeping the dross away with a device such as a doctor blade (not shown). The temperature measured by the carriage sensor 24 here will be indicative of the extent to which dross has accumulated on the surface of the molten liquid, as the dross affects the temperature differential at the surface. Therefore, the carriage sensor 24 can additionally be used to control the dross clearance operation.