Casting control method

Abstract

A casting control method comprises the steps of supporting a mould on a support structure; sealing the mould to a launder system; measuring the weight of the mould to obtain a base ‘tear’ reading; operating the launder system to cause liquid casting material to flow into the mould; monitoring the change in weight of the mould due to the in-flow of liquid casting material; and controlling the rate of flow of the liquid casting material into the mould so that the change in weight monitored follows a predetermined optimum or substantially optimum path. Mould supporting apparatus, which can be used in the above casting control method, comprises a support structure which includes a support plate for supporting the mould, and one or more load cells which support the support plate in a floating arrangement. A launder system, a mould, and a casting are also provided.

Description

This invention relates to a casting control method, a mould supporting apparatus which is preferably, but not exclusively, intended for use with the casting control method, a mould for use with the casting control method and/or the mould supporting apparatus, a launder system used in conjunction with the casting control method, mould supporting apparatus, and/or the said mould, and a casting produced using the casting control method, mould supporting apparatus, mould, and/or launder system.

It is necessary to produce castings which are correctly formed. If the liquid material used to form the casting flows too slowly, cold-shots are formed preventing a complete casting being produced, and if the liquid material flows too quickly, the flow becomes chaotic and gaseous bubbles are entrained. Both cases are undesirable.

It is also preferable to produce a casting which requires a minimum amount of post-casting attention, such as grinding and polishing to produce the required finish. This enables savings in both costs and time.

Furthermore, by optimising the flow of liquid material, wastage is prevented, further reducing costs.

Casting control methods are known which attempt to monitor or detect the presence of liquid material in a mould, and thereby attempt to optimally control the flow rate of the liquid material to produce an optimum casting. A common type of casting control method is a capacitive method, and the ‘Cosworth’ method employs a well-known type of capacitive method.

The capacitive method works on the basis of transmitting a sinusoidal waveform of 32 KHz, 20 volts pk-pk, through an antenna plate into the mould. When the radiated signal comes into contact with the liquid metal material, such as aluminium, which is at ground potential, a current flows through the notional 50 ohms resistor of the coaxial cable feeding the sine wave to the antenna plate assembly. This current results in a voltage potential which is filtered to remove predominate stray parasitic values and the resultant signal is then amplified into the format of a 0-10 Vdc control signal or similar industry standard control signal.

A problem occurs with this method in that the output of the signal is non-linear and requires further computation to extract any meaningful signal. If metallic objects are placed inside the mould, such as cast in liners, when the molten metal comes into initial contact with the liner the signal from the antenna jumps to a value relating to the height of the liner. Hence, an erroneous signal is generated, which consequently effects the control process.

The present invention overcomes the deficiencies associated with the hitherto known methods.

According to a first aspect of the invention, there is provided a casting control method comprising the steps of:

a. supporting a mould on a support structure;

b. sealing the mould to a launder system;

c. measuring the weight of the mould to obtain a base ‘tear’ reading;

d. operating the launder system to cause liquid casting material to flow into the mould;

e. monitoring the change in weight of the mould due to the in-flow of liquid casting material; and

f. controlling the rate of flow of the liquid casting material into the mould so that the change in weight monitored in step (e) follows a predetermined optimum or substantially optimum path.

Preferable and/or optional features of the first aspect of the invention are set forth in claims 2 to 7, inclusive.

According to a second aspect of the invention, there is provided mould supporting apparatus for use with a method according to the first aspect of the invention, the apparatus comprising a support structure which includes a support plate for supporting a mould, and one or more load cells which support the support plate in a floating arrangement.

Preferable and/or optional features of the second aspect of the invention are set forth in claims 9 to 22, inclusive.

According to a third aspect of the invention, there is provided a mould used in a casting control method, in accordance with the first aspect of the invention, and/or used with mould supporting apparatus, in accordance with the second aspect of the invention.

Preferably, the mould is a sand mould.

According to a fourth aspect of the invention, there is provided a launder system for use with a casting control method, in accordance with the first aspect of the invention, for use with mould supporting apparatus, in accordance with the second aspect of the invention, and/or for use with a mould, in accordance with the third aspect of the invention.

Preferably, the launder system is a metal launder system.

According to a fifth aspect of the invention, there is provided a casting formed using a casting control method, in accordance with the first aspect of the invention, using mould supporting apparatus, in accordance with the second aspect of the invention, using a mould in accordance with the third aspect of the invention, and/or using a launder system in accordance with the fourth aspect of the invention.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of part of mould supporting apparatus, in accordance with the second aspect of the invention;

FIG. 2 is a view similar to FIG. 1, and shows a mould supported by the mould supporting apparatus in a first condition;

FIG. 3 is an enlarged view of part of FIG. 2;

FIG. 4 is a further enlarged view of part of FIG. 3;

FIG. 5 is a partially-sectioned side view of part of the mould supporting apparatus;

FIG. 6 is a perspective detailed representation, from behind, of part of the mould supporting apparatus;

FIG. 7 is a view similar to FIG. 2, but with the mould supporting apparatus in a second condition; and

FIG. 8 is an enlarged view of part of FIG. 7.

Referring firstly to FIGS. 1 to 6, there is shown mould supporting apparatus 10 which comprises a support structure 12 adapted to support a sand mould 14.

The support structure 12 includes a rotatable cage 16; a clamp plate 18 positioned parallel to the bottom face of the cage 16, when the cage 16 is in a first condition; a first actuator mechanism 20 mounted externally on the cage 16 for moving the clamp plate 18 towards and away from the cage 16; and a plurality of bearing elements 22 mounted on the interior of the bottom face 24 of the cage 16 adjacent to the clamp plate 18.

The bearing elements 22 are spaced to enable loading of a mould by a forklift or other suitable lifting device (not shown), whilst allowing the mould to be positioned thereon.

The support structure 12 also includes a support plate 26 positioned parallel to the top face 28 of the cage 16, when the cage 16 is in the first condition; a plurality of main load cells 30, in this case two, which support the support plate 26 in a floating arrangement; and a second actuator mechanism 32 mounted externally on the cage 16 for moving the support plate 26 relative to the cage 16.

As can best be seen in FIG. 5, the second actuator mechanism 32 comprises a mounting plate 34 held to the cage 16 via two elongate beams 36 (see FIGS. 3 and 4). A reduction gearbox 38 is mounted on the mounting plate 34. Drive is provided by a servo motor 40 mounted on the gearbox 38, and a ball screw shaft 42 is driven through the gearbox 38. Two telescopic guide shafts 44 are mounted on the mounting plate 34 either side of the gearbox 38. The guide shafts 44 extend in parallel with the ball screw shaft 42. The end of the ball screw shaft 42 opposite the gearbox 38 engages a drive plate 46. The drive plate 46 is also supported by the guide shafts 44. The main load cells 30 are mounted on the drive plate 46, and are equidistantly spaced about the longitudinal axis of the ball screw shaft 42 and between the ball screw shaft 42 and the guide shafts 44. The support plate 26 is supported by the main load cells 30, and also loosely engaged with the end of the guide shafts 44. The loose engagement of the support plate 26 with the guide shafts 44 prevents the support plate 26 from being dislodged from the support structure 12, but does not interfere with, or has a negligible impact on, measurements being taken through the main load cells 30. In this way, the support plate 26 can be said to be ‘floating’, and as such has a suitable amount of freedom to move or tilt in any direction.

When the gearbox 38 is operated, the ball screw shaft 42 is rotatably driven causing the drive plate 46 to be moved along the longitudinal axis of the ball screw shaft 42. Movement of the drive plate 46 results in corresponding movement of the main load cells 30 and support plate 26. Through the engagement of the support plate 26 with the guide shafts 44, the guide shafts 44 thus telescopically extend or retract in accordance with the direction of movement of the support plate 26.

Returning to FIGS. 1 to 4 and 6, the support structure 12 includes a cage support frame 48 which supports the cage 16 for rotation and relative lateral movement. The frame 48 itself is movably mounted on a bed 50, which in turn is mounted for movement on tracks 52. The tracks 52 allow the entire apparatus 10 to be moved for cleaning and maintenance purposes.

The frame 48, as best seen in FIG. 6, includes wheels 54 to enable travel along the bed 50. Movement of the frame 48 along the bed 50 is performed through a first rack-and-pinion arrangement 56, the pinion 58 is driven through a motor 60 mounted on the frame 48. The rack 62 is only schematically shown in FIG. 1.

The frame 48 includes a face plate 64 having a central aperture (not shown), a slew ring 66 mounted on the back of the face plate 64, and a tubular cage support shaft 68 held by the slew ring 66 for axial and angular movement relative to the slew ring 66. the tubular shaft 68 enables convenient access to the cage through the frame 48, for example for cables (not shown).

The cage 16 is mounted to one end of the cage support shaft 68. The axial movement of the cage support shaft 68 is achieved via a pair of diametrically opposite rack-and-pinions 70. The rotational movement of the cage support shaft 68 is achieved using a race (not shown) on which the rack 72 of each rack-and-pinion 70 rides. The axial and rotational movement of the cage support shaft 68 is controlled using a third actuator mechanism 74, mounted on the frame 48 adjacent the slew ring 66.

The frame 48 also includes a supplementary load cell 76 which monitors the lateral force applied by the third actuator mechanism 74, reasons for which will become apparent hereinafter.

Controlling means, such as computer control apparatus (not shown), energise and control the first, second and third actuator mechanisms 20, 32 and 74. Monitoring means, incorporated as part of the computer control apparatus, monitor the outputs of the main load cells 30 and the supplementary load cell 76 to enable feedback control.

The mould supporting apparatus 10 and computer control apparatus form part of a casting control system (not shown). The casting control system also includes a metal, in this case aluminium, launder system and electromagnetic pump for pumping the liquid aluminium. The metal launder system and pump are both common and well known, and are therefore not shown.

In use, and with additional reference to FIGS. 7 and 8, the cage 16 is initially in the first condition with the clamp plate 18 lowermost and the support plate 26 uppermost. See FIG. 1. The clamp plate 18 and support plate 26 are both initially in a retracted state relative to the cage 16. A ‘chill’ member 78, which requires insertion into the sand mould 14 prior to casting, is first positioned on the clamp plate 18. The sand mould 14 is then loaded onto the bearing elements 22, and the first actuator mechanism 20 is operated to raise the ‘chill’ member 78 up and into the sand mould 14. The second actuator mechanism 32 is also operated to clamp the sand mould 14 securely between the support plate 26 and the clamp plate 18.

The cage 16 is then inverted through operation of the third actuator mechanism 74. The cage 16 adopts the second condition whereby the support plate 26 is lowermost and the clamp plate 18 is uppermost. See FIG. 7. The first and second actuator mechanisms 20 and 32 are then operated to retract the clamp plate 18 and the support plate 26 by a small amount. With the mould supporting apparatus 10 in this second condition, the sand mould 14 along with inserted ‘chill’ member 78 are solely supported by the support plate 26 (i.e. in the orientation as shown in FIGS. 5, 7 and 8), and the mould is spaced from the bearing elements 22. For the remainder of this embodiment, the sand mould 14 with inserted ‘chill’ member 78 is simply referred to as the ‘sand mould 14’.

The main load cells 30 are used to measure the weight of the sand mould 14 while the sand mould 14 is only acted upon by gravity, i.e. prior to the sand mould 14 being sealed to the launder system. This enables a quality check to be performed on the sand mould 14. If the weight of the sand mould 14 does not match, or does not fall within acceptable tolerances of, the weight of a previous mould that is known not to contain defects, then this indicates that the present sand mould 14 may have imperfections, such as missing sand cores.

Once the quality check has been completed, the third actuator mechanism 74 is operated to advance the cage 16 laterally relative to the slew ring 66 to seal the opening 80 of the sand mould 14 to the metal launder system (not shown). The supplementary load cell 76 indicates the lateral force being applied by the third actuator mechanism 74 to seal the sand mould 14 to the metal launder system, and the computer control apparatus monitors and regulates this force so that it does not exceed or fall below predetermined limits throughout the rest of the casting operation.

Prior to operation of the metal launder system, and with the sand mould 14 sealed thereto, a base or ‘tear’ weight reading of the sand mould 14 is taken using the main load cells 30. The tear reading is necessary in order to take account of the lateral force being applied by the third actuator mechanism 74 on the sand mould 14, and the effect that this has on the measured weight of the sand mould 14.

The electromagnetic pump (not shown) is then operated to pump liquid aluminium from the metal launder system into the sand mould 14.

The change in weight of the sand mould 14 from the tear reading, due to the influx of liquid aluminium, is continuously monitored simultaneously through the main load cells 30. Since the liquid casting material is relatively viscous, the dispersion of the liquid casting material is not immediate, and therefore the weight distribution across the sand mould 14 is not uniform. The main load cells 30, being spaced from each other, thus output readings which indicate the changing weight of the sand mould 14 at different positions, and, through these outputs, provide an indication of the dispersion of the liquid aluminium within the sand mould 14.

The computer control apparatus monitors the change in weight of the sand mould 14, which is a simple first order equation, through the output readings of the main load cells 30, and controls the electromagnetic pump/metal launder system to adjust the flow-rate of the liquid aluminium into the sand mould 14. This closed-loop feedback control of the flow-rate of the liquid aluminium by the computer control apparatus is based on a predetermined and prestored optimum flow-rate profile, which is derived through calculation and prior testing. The optimum flow-rate is, generally, one which is not too low, causing cold-shots and mis-runs within the cores of the sand mould 14, and one which is not too high, causing entraining of air, chaotic flow and cavitation.

Although the above embodiment has been described as requiring inversion of S the cage, this is only a requirement when using certain moulds. In the above case, the sand mould requires insertion of a ‘chill’ member in order to form an engine casting. However, if the sand mould is a unitary mould, then inversion is not necessary and the cage only needs to be laterally movable. The cage can thus remain permanently in the second condition, with the support plate being permanently lowermost.

The cage may also be dispensed with, if inversion is not required, and a simple bed or platform arrangement could be utilised instead.

Also, the quality check could be omitted.

The above described apparatus and method could be used in conjunction with any suitable type of mould, not just a sand mould, and with any type of suitable liquid casting material and/or launder system, such plastics or other types of metal.

The number and positioning of main and supplementary load cells may vary. In the present case, the main load cells can each measure up to 250 kg. Therefore, with heavier moulds, more than two main load cells will be utilised. It is also possible to simply utilise one main load cell.

Multiple load cells having lower rated capacities can also be utilised to raise the accuracies of the readings.

Although the above embodiment has been described as simply having computer control apparatus, the means for monitoring the output of the load cells can be separate from the means for controlling the actuator mechanisms, instead of being combined into a single control system. The term ‘computer control apparatus’ is intended to cover any suitable electronic control apparatus.

It is thus possible to provide mould supporting apparatus which provides a simple and accurate indication of the weight dispersion within a supported mould at any instance, which has hitherto not been possible. It is also possible to provide mould supporting apparatus which enables a quality check to be simply and accurately performed, while also allowing straightforward insertion of a chill. A method of controlling casting is also provided which enables accurate control of the flow-rate of a liquid casting material into a mould through closed-loop feedback. The method employs linearly variable feedback through the use of load cells and utilises simple first order equations to determine the state of the casting at any instance. This enables optimisation of casting material used, and a reduction in the amount of post-casting finishing.

The embodiments described above are given by way of example only, and other modifications will be apparent to persons skilled in the art without departing from the scope of the invention as defined by the appended claims.

Claims

1-29. (canceled)

30. A casting control method comprising the steps of: a. supporting a mould on a support structure; b. sealing the mould to a launder system; c. measuring the weight of the mould to obtain a base ‘tear’ reading; d. operating the launder system to cause liquid casting material to flow into the mould; e. determining the dispersion of the in-flowing liquid casting material in 10 the mould by simultaneously monitoring at different positions on the mould the change in weight of the mould due to the in-flow of liquid casting material; and f. controlling the rate of flow of the liquid casting material into the mould based on the dispersion of the casting material determined in step (e), so that the change in weight monitored in step (e) follows a predetermined optimum or substantially optimum path to provide an optimum or substantially optimum dispersion of casting material in the mould.

31. A casting control method as claimed in claim 30, wherein the weight of the mould in step (c) and the change in weight in step (e) are determined using one or more load cells.

32. A casting control method as claimed in claim 30, further comprising a step (g) between steps (a) and (b) of rotating the support structure to invert the mould.

33. A casting control method as claimed in claim 30, further comprising a step (h) between steps (a) and (b) of measuring the weight of the mould to determine the quality of the mould.

34. A casting control method as claimed in claim 30, wherein, in step (b), a sealing force by which the mould is sealed to the launder system is monitored.

35. A casting control method as claimed in claim 30, wherein the mould support structure includes a support plate for supporting the mould, and one or more load cells which support the support plate in a floating arrangement.

36. A casting control method as claimed in claim 35, wherein the support structure further includes a cage which supports the support plate and the or each load cell.

37. A casting control method as claimed in claim 36, wherein the support plate is supported indirectly by the cage.

38. A casting control method as claimed in claim 35, wherein the cage is rotatably supported by the support structure to enable inversion.

39. A casting control method as claimed in claim 35, wherein the support structure further includes a clamp plate, supported by the cage opposite the support plate.

40. A casting control method as claimed in claim 39, wherein the clamp plate is indirectly supported by the cage.

41. A casting control method as claimed in claim 40, wherein the support structure includes an actuator by which the clamp plate can be moved relative to the cage.

42. A casting control method as claimed in claim 35, wherein the support structure further comprises means for laterally moving the support plate so that the mould can seal against the launder system.

43. A casting control method as claimed in claim 42, wherein the lateral moving means includes a slew ring in which a support shaft can move axially to move the support plate laterally.

44. A casting control method as claimed in claim 43, wherein the support shaft is angularly movable relative to the slew ring.

45. A casting control method as claimed in claim 35, further comprising means for monitoring the output of the load cells.

46. A casting control method as claimed in claim 45, further comprising means for controlling the launder system based on the output of the load cells monitored by the monitoring means.

47. A casting formed using a casting control method as claimed in claim 30.