GB2163686A - Pressurised gas compaction of foundry mould material - Google Patents

Abstract

A method of compacting a moulding mixture comprises impacting the moulding mixture with a pressurized gas at a speed less than sonic speed, the gas having a pressure less than 8 x 10<5> N/m<2> and the pressure grandient obtained being in the range of 100 to 300 bar/s. The pressurised gas is delivered at the required speed and pressure gradient by the quick opening of valve (54) at the exits of a first pressurized gas reservoir 42. Each valve (54) is loaded to a closed position by the lower (or equal) gas pressure of a second reservoir (63) acting on the upper surface of a valve operating spool (56), on the lower surface of which acts the gas pressure of reservoir (42). The upper side of valve (54) and its underside (61) around a valve seat (58) is also loaded by the gas pressure of reservoir (42), so that there is an excess area of the spool (56) against which the first reservoir pressure acts in the valve opening direction, to quickly open the valve (54) when the pressure in second reservoir (63) is released by a quick release valve (64). <IMAGE>

Description

SPECIFICATION Improvements in and relating to a method and apparatus for compacting a moulding mixture This invention relates to a process and apparatus for compacting loosely poured moulding material.

In U.S. Patent 3659642, a device for compacting a moulding mixture is disclosed wherein a relatively high moulding pressure of 2X 106 N/m2 is used to impact the moulding mixture.

In G.B. Patent No. 2069384, an apparatus for compacting a mass of loosely poured moulding material is shown wherein a gas under excess pressure is expanded through a supersonic nozzle to supersonic speed to impact the moulding material.

Finally in European Patent Application No. 0084627, a process for compacting foundry moulding material is disclosed in which a pressure gas is expanded into the moulding chamber so as to produce a pressure rise (gradient) in excess of 300 bar/s.

In order to obtain a mould which is suitable for casting, each of the above prior art methods/apparatus resort to an extreme condition or variable. Such reliance has disadvantages associated therewith, namely problems with respect to safety, complications in design, expense, efficiency and uniformity.

In accordance with one aspect of the invention, a method of compacting a moulding mixture comprises impacting the moulding mixture with a pressurized gas having a pressure less than 8X105 106 N/m2, the gas being delivered at a speed less than sonic speed, the pressure gradient obtained being in the range of 100 to 300 bar/s.

Such a method provides a mould suitable for casting without resorting to extreme conditions or variables and consequently overcomes a number of problems associated therewith.

After the moulding mixture is compacted, the mould obtained is preferably sized down to a correct depth by removal of a top excess layer of moulding mixture.

The pressurized gas is preferably directed down over the whole surface area of the moulding mixture to provide substantial uniformity of compaction.

The pressurized gas is suitably delivered at speed with the required pressure gradient by the quick opening of the exits of the pressurized gas reservoir. Preferably such opening of the exits is practically/substantially instantaneous so as to release air from the pressurized air reservoir to the moulding chamber as quickly as possible.

The pressurized gas preferably impacts the mixture with a pressure in the range of (3.5 to 5.5)X105 N/m2, while the delivering speed is initially greater than 100 m/s and suitably in the range of 100 to 300 m/s and finally the pressure gradient is advantageously in the range of 200 to 250 bar/s.

In accordance with another aspect of the invention, an apparatus for compacting a moulding mixture comprises a pressurized air reservoir, a moulding chamber interconnected with the reservoir, and valve means operable to close an exit(s) between the reservoir and moulding chamber, the or each exit being controlled by a valve element, the or each element being movable between open and closed positions and connected to a valve operating member characterised in that the valve operating member is open to the pressures of a gas in a second reservoir, the force of this pressure acting in a valve closing direction, the arrangement being such that the resultant force of the pressure acting on the valve element and/or valve opening member due to the gas in the first reservoir is aiways in a valve opening direction, so that wheN the pressure in the second reservoir is released, the valve element is moved to the open position by the force of the pressure in the first reservoir.

Such an arrangement provides for rapid opening of the valve element such that pressurized air is delivered at speed into the moulding chamber.

Preferably, deflection means advantageously in the form of a nozzle or deflector for each exit is provided in order to direct pressurized air from the first reservoir over the whole surface area of the moulding mixture in the moulding chamber.

After the mixture in the chamber is compacted, slicing means are suitably used to remove a top excess layer of compacted moulding mixture in order to obtain a correctly sized mould.

The valve means preferably includes a quick release valve, the valve operating member and element being supported on a common axis. Suitably, the underneath surface area of the valve element is greater than the effective area of the exit(s) being controlled, at least part of the excess underneath area of the valve element being open to the pressure in the air reservoir in a valve opening direction.

Advantageously, the underneath area of the valve operating member is greater than the effective area of the valve element, the effective area of the valve element being the upper surface area of the valve element less the part of the underneath area of the valve element open to the pressure in the first reservoir.

In one embodiment, the area of the underneath face of the valve operating member is substantially equal to the upper surface area of the valve element whereby any pressurized air in the first reservoir which acts against the underside of the valve operating member tends to be equalized by any pressurized air acting against the upper surface of the valve element. The resultant force on the valve is thus the resultant of the force from firstly the pressurized air in the second reservoir or chamber acting against the upper surface of the valve operating member and secondly the force of the pressurized air in the first reservoir acting against the underneath surface of the valve element.

The valve element is suitably provided with extra support by an upstanding member adjacent the exit(s), when the valve face is engageable with the exit(s), so as to prevent damage.

In another embodiment, there is preferably provided a common pressurized air source for the first and second reservoirs, whereby the pressures in both reservoirs when fully pressurized will be substantially equal.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic representation of a moulding apparatus in accordance with the invention, Figure 2 is a schematic diagram showing the sequence of operating steps of the apparatus of Fig. 1, Figure 3 is an enlarged side cross-sectional view of one embodiment of impact arrangement for use in the apparatus shown in Fig. 1, Figure 4 is a plan view of the impact arrangement shown in Fig. 3, Figure 5 is a further enlarged side cross-sectional view of part of the impact arrangement shown in Fig. 3, as taken along the lines A-A of Fig. 4, Figure 6 is an enlarged side cross-sectional view of another embodiment of impact arrangement for use in the apparatus shown in Fig. 1, Figure 7 is a plan view of the impact arrangement shown in Fig. 6, and Figure 8 is a further enlarged side cross-sectional view of part of the impact arrangement shown in Fig. 6, as taken along the lines B-B of Fig. 7.

The moulding apparatus 10 shown in Fig. 1 basically comprises a mould support arrangement 12, a moulding mixture filling and mould lifting, lowering and removal system 14, a moulding mixture container 32 and a compacting device in the form of a pressurised air reservoir 16.

The mould support arrangement 12 comprises a pattern plate 18 with a pattern 20 mounted thereon, a moulding or box frame 22 and a filling or upset frame 24.

The lifting, lowering and removal system in the form of a draw assembly 14 includes two off draw cylinders 26 each having two off support arms 28 to support and raise/lower the upset frame 24 via shoulders 25, a squeeze or clamp cylinder 36 secured to a table 38 to support and raise/lower the pattern plate 18 and pattern 20 mounted on plate 18, and a conveyor arrangement in the form of two off roller frames 30 to initially support the box frame.

The sequence of steps for operating the apparatus of Fig. 1 is shown schematically in Fig. 2.

Firstly the mould support arrangement 12 is brought together in a starting position by moving the upset frame 24 within the arms 28 of the draw cylinder 26 to its upper and raised position, rolling into position the box frame 22 by means of the conveyor 30, securing the pattern plate 18 to the plate 38 and finally either lowering the draw cylinder 26 and/or raising the squeeze cylinder 36 until all the components of arrangement 10 are connected (see Steps 1 to 3 in Fig.

2).

Thereafter, the whole mould support arrangement 12 is raised by the clamp cylinder 36 to a filling position just under the container in the form of a sand hopper 32 and the arrangement 12 filled with moulding mixture, in particular foundry moulding mixture such as sand-clay mixtures, green sand (see Step 4).

The mould arrangement 12 full of sand, is then lowered to its original starting position, and the impact device 16 specifically an impact cylinder 40, 73 moved horizontally to a position above the arrangement 12. The arrangement 12 is then raised by the squeeze cylinder 36 such that it may be subsequently clamped to the impact cylinder. After clamping, the sand in the arrangement 12 is subjected to a pressure wave which causes the sand to be impacted and compacted to approximately 2/3rd of its original depth. The mould arrangement 12 is then unclamped from the impact cylinder 40, 73 and both arrangement 12 and cylinder 40, 73 returned to their original starting positions (see Steps 5 to 9).

The filling frame 24 is then disengaged from the box frame 22 by raising of the draw cylinders 26 and arms 28, and thereafter the frame 22 is disengaged from the pattern plate 18 and pattern 22 by the raising of the draw cylinders 26 and rollers of the conveyor 30, thereby leaving the frame 22 and compacting sand therein supported on the conveyor 30. The frame 22 is subsequently horizontally rolled out on the conveyor 30, at which time a stationary slicer 34, having a slicing blade 35-in particular a strickle, acts to cut off the layer of sand protruding above the upper surface of the box frame 22, in order to provide the correct depth and required shape of mould 39. Finally, excess sand is 'cleaned' from the blade 35, and the mould 39 removed from the box frame 22 (see Steps 10 to 13).

The whole sequence of steps (that is 1 to 13 shown in Fig. 2) is then repeated in order to produce a further identical mould 39.

One embodiment of impact cylinder 40 is shown in greater detail in Figs. 3 to 5, having an outer 'first' reservoir 42 supporting firstly six nozzles 44 and a discharge housing 45 from the bottom plate 46 and secondly siz pressure valves 48 from the top plate 50. Each valve 48 is positioned above one of the nozzles 44 to correspond therewith, the valves 48 acting to release pressurised air in the reservoir 42 onto the sand in the moulding arrangement 12, and the nozzles 44 acting to direct this air flow uniformly over the whole area of the sand surface.

The pressure valve 48 for the impact cylinder 40 is shown in greater detail in Fig. 5 having a valve housing 62 and valve arrangement comprising a longitudinal stem 52 mounted firstly with a valve element 54 on the outer end thereof and secondly with a valve operating member in the form of a spool 56 on the inner end thereof. The valve element 54 is shown having an elastomeric face seal 55 which rests on a metallic valve seat 58 provided in an exit on the bottom plate 46 above each nozzle 44, while the spool 56 provided with seals 60 about the circumference is shown co-operating with the housing 62 of the valve 48.

The underneath surface area of each valve element 54 is greater than the area of the corresponding exit being controlled, the excess area of the valve element being open to the pressure in the reservoir 42. In other words, the diameter (see Dl in Fig. 5) of the underneath surface of each valve element 54 is greater than the diameter (D2 in Fig. 5) of the corresponding exit being controlled, the excess area

being open to the pressure in the reservoir 42.

The metallic valve element 54 is provided with extra support in the form of a metallic lip 59 provided on the outer circumference of the valve seat 58, such that when a pressure acts on the valve element 54, the metallic valve seat 58 engages the elastomeric face seal 55 sufficiently to provide an effective seal whilst not damaging the face seal 55, due to the extra support afforded by the metallic lip 59. The metallic lip 59 is also provided with horizontal slots (not shown) to allow air in the reservoir 42 to pass into the space 61 which is underneath the valve element 54 and outwardly of the seal 55.

The operation of the pressure valve 48 will now be described, wherein firstly pressurized air is introduced by means (not shown) through an opened quick release valve component 64 into a 'second' reservoir or chamber 63 comprising inner chambers 66 and 68, to force and push down the valve arrangement from an upper and 'unsealing' position where the spool 56 engages an 'upper' stop 65 to a lower and sealing position (see Fig. 5) where the valve element 54 rests on the valve seat 58. At this stage the pressurized air will have completely occupied the inner chambers 66 and 68 between the upper surface of the spool 56 and the quick release valve 65.

Thereafter air, at a high pressure than that air in the inner chambers 66 and 68, is introduced into the outer 'first' reservoir 42 through the inlet port 70 (see Fig. 4) by means (not shown). In consequence thereof, this high pressure acts firstly upwards against the lower surface of the spool 56, secondly downwards against the upper surface of the valve element 54 and thirdly upwards against the excess area of the lower surface of the valve element 54 which radially extends outwards from the face seal 55. The resultant force on the valve arrangement is thus downwards as the force of the low pressure against the whole face of the upper surface of the spool 56 exceeds the force of the high pressure against the excess area of the lower surface of the valve element 54.

On actuation of the quick release valve 64 however, the low pressure in the chambers 66 and 68 is expelled therefrom through the valve 64 and the resultant force on the valve arrangement is upwards due to the force of the high pressure against the excess area of the lower surface of the valve element 54.

The valve arrangement consequently moves from the lower and sealing position to the upper and 'unsealed' position, and the high pressure in the reservoir 42 is then directed into the moulding chamber 12 by the nozzles 44.

The high speed at which the valve arrangement is opened, due to the quick release valve 64 and pressure acting on the lower surface of the valve element 54, results in the pressure in the reservoir 42 acting as a 'pressure wave' which impacts the sand in the moulding chamber causing compaction.

Another embodiment of impact cylinder 73 is shown in Figs. 6 to 8 having an outer 'first' reservoir 42 supporting a discharge housing 45 from the bottom plate 46, the housing 45 containing a deflector 72 beneath each port opening 74 in order to direct air flow. The top plate 50 supports a pressure valve 48 above each port opening 74 in order to release pressurised air in the reservoir 42 onto the sand in the moulding arrangement 12, the deflectors acting to direct this air flow uniformally over the whole area of the sand surface.

The pressure valves 48 for the impact cylinder 73 is shown in greater detail in Fig. 8 having a valve housing 62 and valve arrangement comprising a longitudinal stem 52 mounted firstly with a valve element 54 on the outer end thereof and secondly a valve operating member 76 on the inner end thereof.

The valve element 54 is shown having an elastomeric face seal 55-which rests on a metallic valve seat 58 provided in an exit on the bottom plate 46 above each deflector 72, while the valve operating member 76 is provided with a seal 60 about the circumference to co-operate with the housing 62 of the valve 48. In particular, the seal 60 prevents the passage of pressurised air and also acts as a guide for the valve 48 when operated.

The metallic valve element 54 is provided with extra support in the form of a metallic lip 59 provided on the outer circumference of the valve seat 58, such that when a pressure acts on the valve element 54, the metallic valve seat 58 engages the elastomeric face seal 55 sufficiently to provide an effective seal between the reservoir chamber and the open ports whilst not damaging the face seal 55, due to the extra support afforded by the metallic lip 59. The metallic lip 59 which ensures a predetermined sealing contact between seal 55 and seat 58 is also provided with horizontal slots (not shown) to allow air in the reservoir 42 to pass into the space 61 which is underneath the valve element 54 and outwardly of the seal 55, in order to ensure that the effective sealing diameter of the valve 54 is D4.The valve 48 is guided at the lower end by the support device 71, which is integral with the valve seat 58.

The operation of the pressure valve 48 will now be described, wherein firstly pressurized air is introduced by means (not shown) through an opened quick release valve component 64 into a 'second' reservoir or chamber 63 comprising inner chambers 66 and 68, to force and push down the valve arrangement from an upper and 'unsealing' position where the valve operating member 76 engages an elastomeric buffer 65 to a lower and sealing position (see Fig. 8) where the valve element 54 rests on the valve seat 58. At this stage the pressurized air will have completely occupied the inner chambers 66 and 68 between the upper surface of the valve operating member 76 and the quick release valve 64.

Thereafter compressed air, at the same pressure as that air presently in the inner chambers 66 and 68, is introduced into the outer 'first' reservoir 42 through the inlet port 70 (see Fig. 7) by the same means which introduces pressurized air into the 'second' reservoir 63. In consequence thereof, the pressure in the first reservoir 42 acts firstly upwards against the lower surface of the valve operating member 76, secondly downwards against the upper surface of the valve element 54, and thirdly upwards against the excess area of the lower surface of the valve element 54 which radially extends outwards from the face seal 55.The resultant force on the valve arrangement is thus downwards as the force of the pressure against the whole face of the upper surface of the valve operating member 76 exceeds the force of the pressure against the excess area of the valve operating member 76 over the valve element 54.

In particular, the pressurised air within the chamber 42 acts in relation to the following areas of the valve element 54: n Effective area in a downward/closing direction=-D42-a, 4 ('a' being the area of stem 52), Effective area in an upward/opening direction --D,Z-a, 4 n Excess area -(D32-D42).

4 The excess area is operated upon by the air pressure in an upward/opening direction since D3 is greater than D4.

The pressurised air within the chamber 63 meanwhile acts in a downward/closing direction on the upper surface of the valve operating member 76

Since the pressures in both the chambers 63 and 42 are the same, the resultant effective area in an upward/opening direction is thus:

a -- -D42 4 ie. nett downward/closing force=

The pressurised air in chamber 63 is then allowed to exhaust rapidly through release valve 64.

the air pressure rapidly decaying to a point where the pressure in chamber 63 is equal to pressure in chamber 42:

As the pressure in chamber 63 further decays, a nett upward force is experienced and the valve arrangement 52, 54, 76 will begin to lift.

As the valve arrangement begins to travel upwards, the force equations alters dramatically since the upward acting force now approximates to the pressure in chamber 42 times area of valve operating member 76,

and the valve arrangement rapidly accelerates in an upward direction from the lower and sealing position to the upper and 'unsealed' position.

As the port opening 74 is exposed to the reservoir 42, the pressurised air in the reservoir 42 rushes out and sets up a 'pressure wave' causing compaction of the moulding mixture in the moulding arrangement 12.

In the impact cylinders 40 and 73, the high but relatively low 'moulding' pressure in the reservoir 42 is delivered at high speed (but lower than sonic speed and preferably initially in the range of 150 to 250 m/s to give a 'mean' delivery speed in light of pressure degradation of approximately 130 m/s) to produce a moderate pressure gradient in the region of 100 to 300 bar/s.

For example the relatively low 'moulding' pressure used in the reservoir 42 may range from (5 to 7.5)X105 N/m2, while the impact pressure in the moulding chamber 12 may range from (3.5 to 5.5)X105Nm2. The mean gas mass throughput is preferably in the range of 15 to 35 Kg/s.

The sand after impact has been found with these conditions to produce a sand mould suitable for casting.

Claims (20)

1. A method of compacting a moulding mixture comprising impacting the moulding mixture with a pressurized gas having a pressure less than 8X105 N/m2, the gas being delivered at a speed less than sonic speed, the pressure gradient obtained being in the range of 100 to 300 barts

2. A method as claimed in Claim 1 wherein the pressurized gas is directed from over the whole surface area of the moulding mixture.

3. A method as claimed in either Claim 1 or Claim 2 wherein the pressurized gas is delivered at speed by the quick opening of the exits of a pressurized gas reservoir.

4. A method as claimed in Claim 3 wherein the opening of the exits is substantially instantaneous.

5. A method as claimed in any preceding claim wherein after the moulding mixture is compacted, the mould obtained is sized down to a correct depth by removal of a top excess layer of moulding mixture.

6. A method as claimed in any preceding claim wherein the pressurized gas impacts the mixture with a pressure in the range of (3.5 to 5.5)X105 N/m2.

7. A method as claimed in any preceding claim wherein the delivering speed of the gas is initially greater than 100 m/s.

8. A method as claimed in any preceding claim wherein the delivering speed of the gas is in the range of 100 to 300 m/s.

9. A method as claimed in any preceding claim wherein the pressure gradient is in the range of 200 to 250 bar/s.

10. An apparatus for compacting a moulding mixture comprising a pressurized air reservoir, a moulding chamber interconnected with the reservoir, and valve means operable to close an exit(s) between the reservoir and moulding chamber, the or each exit being controlled by a valve element, the or each element being movable between open and closed positions and connected to a valve operating member characterised in that the valve operating member is open to the pressure of a gas in a second reservoir acting in a valve closing direction, the arrangement being such that the resultant pressure acting on the valve element and/or valve opening member due to the gas in the first air reservoir is always in a valve opening direction so that when the pressure in the second reservoir is released, the valve element is moved to the open position by the pressure in the first reservoir.

11. An apparatus as claimed in Claim 10 wherein the underneath surface area of the valve element is greater than the effective area of the exit(s) being controlled.

12. An apparatus as claimed in Claim 11 wherein at least part of the underneath area of the valve element is open to the pressure in the first reservoir in a valve opening direction.

13. An apparatus as claimed in Claim 12 wherein the underneath area of the valve operating member is greater than the effective area of the valve element, the effective area being the upper surface area of the valve element less the part of the underneath area of the valve element open to the pressure in the first reservoir.

14. An apparatus as claimed in any one of Claims 10 to 13 including deflection means for each exit to direct pressurized air from the first reservoir over the whole surface area of the moulding mixture in the moulding chamber.

15. An apparatus as claimed in any one of Claims 10 to 14 wherein slicing means are provided to remove a top excess layer of compacted moulding mixture in the moulding chamber.

16. An apparatus as claimed in any one of Claims 10 to 15 wherein the valve means includes a quick release valve to open the exits between the first reservoir and moulding chamber.

17. An apparatus as claimed in any one of Claims 10 to 16 wherein the valve operating member and valve element are supported on a common axis.

18. An apparatus as claimed in any one of Claims 10 to 17 wherein the valve element is provided with extra support by an upstanding member adjacent the exit(s), when the valve face is engageable with the exits

19. A method of compacting a moulding mixture substantially as herein described with reference to the accompanying drawings.

20. An apparatus for compacting a moulding mixture substantially as herein described with reference to either Figs. 1 to 5 or Figs. 1, 2 and 6 to 8.