WO1995013153A1

WO1995013153A1 - A control system for a casting machine

Info

Publication number: WO1995013153A1
Application number: PCT/AU1994/000680
Authority: WO
Inventors: Noel Francis Matthews; Michael Patrick Mckenna
Original assignee: Tasmanian Electro Metallurgical Company Proprietary Limited
Priority date: 1993-11-08
Filing date: 1994-11-08
Publication date: 1995-05-18

Abstract

A control system for a casting machine for casting ferrous and non-ferrous materials is disclosed. The control system comprises: a) a means for monitoring the width or the depth of pigs that form in each mould (8) as the moulds (8) move along the path from the mould filling station (9) to the discharge station (11); and b) a means responsive to the monitoring means for ensuring that each mould (8) receives substantially the same amount of ferrous or non-ferrous material.

Description

ACONTROLSYSTEMFORACASTINGMACHINE

The present invention relates to controlling the operation of a casting machine for casting ferrous and non- ferrous materials.

In general terms, a known type of casting machine for casting ferrous and non-ferrous materials is based on the use of a train of moulds. The moulds are arranged to be transported past a mould filling station at which molten material from a furnace is teemed into the moulds. The molten material in the moulds progressively solidifies to forms pigs as the moulds move away from the mould filling station. When solidified, the pigs are discharged from the moulds at a discharge station, and the moulds are then recycled to the mould filling station. Optionally, the known type of casting machine comprises water sprays for spraying water onto the moulds to cool the pigs.

The present invention has particular, although by no means exclusive application, to the casting of ferroalloy materials into moulds to form pigs and, as a conseςmence, the following description of the invention is directed particularly to casting ferroalloy materials.

A particular form of the known type of casting machine which is used for casting ferroalloy materials comprise an inclined conveyor assembly which supports and transports the train of moulds along a path between:

(a) a mould filling station at which molten ferroalloy material from a furnace is teemed into the moulds; and

(b) an elevated discharge station at which solidified pigs are released from the moulds and fall into a discharge bunker and fracture into smaller pieces.

The known casting machine further comprises at least one water spray for spraying water onto the moulds to cool the pigs as the moulds move along the path.

The casting machine is manually operated, whereby the parameters which control the rate of cooling of the molten ferroalloy material, such as the speed of the moulds along the path and the activation of the water sprays, are subject to the judgement of the operators.

As little instrumentation is provided, and usually the flow rate of molten ferroalloy material from the furnace is uncontrolled and variable, it is difficult for operators to accurately control the parameters in such a manner as to produce consistent, high quality, cast product. As a consequence, it is often the case that excessive fines are generated.

In many instances, the same difficulties are experienced by operators controlling other forms of the known type of casting machine for casting ferroalloy materials, other ferrous materials, and non-ferrous materials.

An object of the present invention is to provide a control system for the known type of casting machine described above which allows consistent production of high quality cast pigs of ferrous and non-ferrous materials.

According to one aspect of the present invention there is provided a control system for a casting machine for casting ferrous and non-ferrous materials described above, the control system comprising:

(a) a means for monitoring the width or the depth of pigs that form in each mould as the moulds move along the path from the mould filling station to the discharge station; and

(b) a means responsive to the monitoring means for ensuring that each mould receives substantially the same amount of ferrous or non-ferrous material.

It can readily be appreciated that in a situation where the moulds in the casting machine are substantially identical and hold the same volume the width of each pig is related directly to the amount of molten ferrous or non- ferrous material teemed into the moulds.

It can also readily be appreciated that the size of cast pigs is one factor which affects the consistency of the metallurgy of the solidified ferrous or non-ferrous material and, therefore, maintaining uniform the pig size in each mould is important in terms of producing consistency in product quality.

It is preferred that the means responsive to the monitoring means comprise, a means for adjusting the speed of movement of the moulds along the path to adjust as required the time that each mould can receive molten ferrous or non-ferrous material so as to maintain at least substantially uniform the amount of molten ferrous or non- ferrous material received in each mould.

In one embodiment it is preferred that the monitoring means be adapted to monitor the depth of the pigs.

In another embodiment it is preferred that the monitoring means be adapted to monitor the width of the pigs.

It is preferred particularly that the width determining means comprise, a temperature sensor located above the path of the moulds between the mould filling and the discharge stations, and a means to calculate the width of each pig as the moulds pass beneath the sensor which is based on:

(a) the time that the temperature recorded by the sensor exceeds a threshold temperature which indicates the presence of ferrous or non-ferrous material in a given mould; and (b) the speed of the moulds along the path at that time.

It is preferred that the temperature sensor be a pyrometer.

According to another aspect of the present invention there is provided a control system for cooling a ferrous or non-ferrous material in each mould of the casting machine described above in accordance with a predetermined temperature profile for producing a required metallurgy in the solidified pigs formed in the moulds as the moulds move along the path from a mould filling station to a discharge station, the control system comprising:

(a) a temperature sensor for determining the temperature of the ferrous or non-ferrous material in each mould at a position on the path upstream of a water spray;

(b) a means responsive to the temperature sensor determinations for predicting the temperatures at a series of points along the path downstream of the temperature sensor that the ferrous or non-ferrous material should reach in order to comply with the predetermined temperature profile; and

(c) a means responsive to the predictions made by the predicting means to selectively operate the water sprays along the path to achieve the predetermined temperature profile.

The present invention is described further by way of example with reference to the pig casting machine for the ferromanganese output of Furnaces 1 and 2 at the Tasmanian Electro Metallurgical Company Pty. Ltd. (TEMCO) plant, Georgetown, Tasmania, Australia and to the accompanying drawings, in which:

Figure 1 is a top plan of the plant layout showing the casting machine, Furnaces 1 and 2, and the furnace tapping launders supplying molten ferromanganese to the casting machine;

Figure 2 is a side elevation of the casting machine shown in Figure 1;

Figure 3 is a top plan of one of the moulds of the casting machine shown in Figures 1 and 2;

Figure 4 is a section of the mould along the lines 4-4 in Figure 3 which also illustrates the coupling together of the mould shown in Figure 3 and a downstream mould in the train; and

Figure 5 shows in schematic form the instrumentation and system architecture of a preferred embodiment of a control system in accordance with the present invention.

With reference to Figures 1 to 4, the casting machine 3 for Furnaces 1 and 2 at TEMCO comprises a series of 206 moulds 5 (Figures 3 and 4) which are coupled together as shown in Figure 4 and mounted on an inclined chain conveyor 7 (Figures 1 and 2) which is arranged to transport the moulds 5 along an upwardly inclined path between:

(a) a mould filling station 9, at which the moulds 8 are filled with molten ferroalloy material teemed from the furnaces at a temperature in the order of 1400°C and distributed to the moulds 5 via a metal launder system 10; and

(b) an elevated discharge station 11, at which the solidified pigs are released from the moulds 5 and fall into a discharge bunker 13 and on impact fracture into smaller pieces.

With reference to Figures 3 and 4, each mould 5 has a corrugated upper surface 15 which defines 5 generally semi-cylindrical mould cavities 17. The mould cavities 17 are arranged side by side so that the long axis of the mould cavities 17 is perpendicular to and the short axis of the mould cavities 17 is parallel to the direction of travel of the mould chain, as indicated by the arrows A in Figures 3 and 4. Each mould cavity 17 has the approximate dimensions of 40 x 70 x 1500 mm.

With further reference to Figure 1, the casting machine 3 comprises 5 banks of water sprays 21 spaced along the inclined chain conveyor 7 which are operable selectively to cool the molten ferroalloy material as the moulds 5 move along the path between the mould filling station 9 and the discharge station 11.

The path between the mould filling station 9 and the discharge station 11 is 59 metres and the discharge station 11 is 8.5 metres above the floor of the discharge bunker 13. The speed of the inclined chain conveyor 7 is variable, with a maximum speed of 0.38 m/s.

When operated in accordance with conventional practice the casting machine 3 is operated manually whereby the speed of the inclined chain conveyor 7 and the activation of the water sprays 21 are controlled in accordance with to the judgement of the operators. As indicated previously, even skilled operators find it difficult to determine by visual monitoring the size of the pigs being teemed into the mould cavities 17 and to keep a mental log of the history of the pouring conditions of each mould 5 to determine appropriate activation of the water sprays 21. As a consequence, inconsistent filling of the moulds 5 and uncontrolled cooling rates can result in poor quality product.

The preferred embodiment of the present invention is based on a control objective for the TEMCO pig casting machine, derived from experimental work, that in order to minimise fines generation (and therefore optimise production quality) :

(a) cast pigs should be of uniform size and as large as possible;

(b) the temperature of the ferroalloy material at the discharge end of the casting machine 3 should be above 700°C; and

(c) the use of water sprays 21 should be kept to a minimum.

The preferred embodiment of the control system of the present invention comprises:

(a) a control loop to adjust the speed of the inclined chain conveyor 7 to maintain optimal mould fullness; and

(b) a control strategy which includes the use of a temperature model to predict the temperature of each mould 5 at the downstream end of each bank of water sprays 21, assuming normal heat transfer from the ferroalloy material without operation of the water sprays 21, and includes operating the water sprays 21 as required to obtain a predetermined temperature of each mould 5 at each point.

With reference to Figure 5, the preferred embodiment of the control system of the present invention is based on a Siemens 135U PLC, a personal computer mounted on board the PLC, and 4 optical pyrometers PI, P2, P3 and P4 and a tachometer 25. The purpose of each pyrometer and the tachometer 25 is summarised below.

Pi - Pyrometer 1 measures initial teemed ferroalloy material temperature and is used for determining pig size.

P2 - Pyrometer 2 measures ferroalloy material temperature before the first water spray bank.

P3 - Pyrometer 3 measures ferroalloy material discharge temperature.

P4 - Pyrometer 4 measures initial mould temperature

Tachometer - Tachometer 25 measures the motor speed driving the inclined chain conveyor 7.

With reference to Figure 5, the Siemens 135U PLC is coupled to controllers (not shown) of each of the water sprays S₁ S₂, S₃, S₄, and S₅ and to the motor (not shown) driving the inclined chain conveyor 7. With further reference to Figure 5, in addition, the control system (optionally) provides extensive data logging, an operator interface, and a data link to the plant metallurgist's office.

As shown in the figure, the operator interface may be provided in the casting machine control room and arranged to display information on pig size, number of moulds cast, product tonnes, casting machine speed and the status of the water sprays.

The pig size may be plotted on a scrolling graph and when in manual mode the operator can use this graph to control the speed of the casting machine 3 to maintain pig size at an optimum level. The graph may be provided with a setpoint with upper and lower limits marked on it.

In accordance with the preferred embodiment, the fullness of the mould cavities 17 is determined by measuring the width of the pigs solidifying in the mould cavities 17. The width is calculated by using the pyrometer PI to detect the presence of ferroalloy material, by reference to a threshold temperature selected to be approximately 50°C below the temperature of the teemed ferroalloy material, and integrating the speed of the casting machine 3. The pig size is calculated as an average over the 5 mould cavities 17 of the mould 5 at that time being surveyed.

In view of operational/environmental constraints, the pyrometer Pi is mounted two moulds from the pour point. A slow responding proportional + integral + derivative (PID) controller is used to effect changes in the speed of the inclined chain conveyor 7 to control the pig size to a predetermined set point.

On each mould pulse the temperature of the ferroalloy material in the moulds 5 between the pyrometers PI and P3 is updated by the PLC. A closed loop estimator is used to adapt model parameters with a high degree of uncertainty, by feeding back the difference between the measured signal at the pyrometer P2 and the estimate at location P2.

In accordance with the preferred embodiment, as each mould 5 enters a spray zone 21, a predicted exit temperature is calculated based on the current speed of the inclined chain conveyor 7. If the predicted temperature is greater than the desired exit temperature to comply with a predetermined temperature profile to provide required metallurgy for the cast product, the water sprays 21 are activated to make a required adjustment to the temperature of the ferroalloy material.

The results of experimental work carried out at TEMCO show that the preferred embodiment provides scope to reduce the variation in quality of product generated by manual control.

In particular, with automatic feedback control of pig size a significant improvement in size distribution was achieved with approximately 80% of the pigs being cast falling within 20 mm (0.79 in) size distribution. This was achieved by more active control of the speed of the inclined chain conveyor 7.

The results of the experimental work carried out at TEMCO also indicate that once control of pig width is achieved it is possible to activate the water sprays 21 in a useful manner in accordance with predictions generated by the temperature model.

Many modifications may be made to the preferred embodiments described above without departing from the spirit and scope of the present invention.

By way of example, whilst the present invention is described in the context of casting ferroalloy materials into pigs, it can readily be appreciated that the present invention is not so limited and extends to casting any ferrous or non-ferrous materials.

Furthermore, whilst the preferred embodiment includes the use of a pyrometer to detect the width of the pigs, as a measure of the fullness of the mould cavity 17, it can readily be appreciated that the present invention is not so limited and any measurable parameter of the pigs, such as the depth, could be measured in this context by any suitable means.

Furthermore, whilst the preferred embodiment includes adjusting the speed of movement of the moulds, to ensure that the cast pigs are a uniform size, it can readily be appreciated that the present invention is not so limited and any suitable means may be used to ensure that each mould receives substantially to same amount of ferrous or non-ferrous material.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A control system for a casting machine as defined herein for casting ferrous and non- ferrous materials, the control system comprising:

2. The control system defined in claim 1 wherein the means responsive to the monitoring means comprise, a means for adjusting the speed of movement of the moulds along the path to adjust as required the time that each mould can receive molten ferrous or non-ferrous material so as to maintain at least substantially uniform the amount of molten ferroalloy material received in each mould.

3. The control system defined in claim 1 or claim 2 wherein the monitoring means is adapted to monitor the depth of the pigs.

4. The control system defined in claim 1 or claim 2 wherein the monitoring means is adapted to monitor the width of the pigs.

5. The control system defined in claim 4, wherein the width determining means comprise, a temperature sensor located above the path of the moulds between the mould filling and the discharge stations, and a means to calculate the width of each pig as the moulds pass beneath the sensor which is based on:

(a) the time that the temperature recorded by the sensor exceeds a threshold temperature which indicates the presence of ferrous or non- ferrous material in a given mould.

6. The control system defined in claim 5 wherein the temperature sensor is a pyrometer.

7. A control system for cooling a ferrous or non-ferrous material in each mould of a casting machine as defined herein in accordance with a predetermined temperature profile for producing a required metallurgy in the solidified pigs formed in the moulds as the moulds move along a path from a mould filling station to a discharge station, the control system comprising:

8. A control system for a casting machine for casting ferrous or non-ferrous material as defined herein substantially as described with reference to the accompanying figures.

9. A control system for cooling ferrous or non-ferrous material in each mould of a casting machine as defined herein in accordance with a predetermined temperature profile substantially as described with reference to the accompanying figures.