GB2199523A

GB2199523A - Compacting a moulding mixture by a pressurised gas wave

Info

Publication number: GB2199523A
Application number: GB08727599A
Authority: GB
Inventors: Colin Philip Beckett
Original assignee: CF Doyle Ltd
Current assignee: CF Doyle Ltd
Priority date: 1986-11-25
Filing date: 1987-11-25
Publication date: 1988-07-13
Also published as: GB8727599D0; GB8628132D0

Abstract

The pressure of the impaction gas is reduced from its maximum delivery pressure at or immediately prior to the point of impaction of the gas on the mixture. The apparatus includes a moulding box (24) containing the moulding material around a pattern (20) on a pattern plate (18), and a pressurised gas impaction unit (14) provided with a gas reservoir (30), quick release valves (34) for releasing the gas wave, and a discharge frame (32) through which the gas is released into the box (24), the frame (32) having exhaust vents (36) which effect the reduction of the gas pressure from its maximum. The gas compacted mixture, is then additionally squeezed from its rear face, against a squeeze head (16). The mood produced by this method and apparatus is evenly compacted and has no holes therethrough. The moulding box may be laterally transported between a box filling location (A) and a position (B) at which it is raised by a piston (26b), firstly against the frame (32) for the gas compaction, and then against the squeeze plate (16). Alternatively, each of the filling (12), impacting (14), and squeeze means (16) may be transversely displaced into alignment with the mould box, or vice versa. <IMAGE>

Description

IMPROVEMENTS IN AND RELATING TO A METHOD AND APPARATUS FOR COMPACTING A MOULDING MIXTURE This invention relates to a process and apparatus for compacting moulding material.

In GB Patent Application No. 2163686, a device for compacting a moulding mixture is disclosed which does not resort to extreme conditions or variables to obtain a mould.

However in devices of this type the pressure wave employed to impact the moulding mixture is released within a space above the mixture which is, at least initially, enclosed. Therefore the pressure is maintained at a maximum for a finite amount of time which can lead to what is known as 'rat-holing'. This occurs because the gas held within the closed space will tend to act on and pass through any areas of the moulding mixture which are more loosely filled which results in holes in the final mould.

In accordance with one aspect of the invention a method of compacting a moulding mixture comprises subjecting the surface of the mixture in a moulding box to a wave of pressurised gas, the pressure of the gas simultaneously being reduced from its maximum at or immediately prior to the point of impaction of the gas on the mixture.

In accordance with another aspect of the invention an apparatus for compacting a moulding mixture to produce a mould comprises a moulding box and an impaction unit for subjecting the surface of the mixture to a wave of pressurised gas and including means for simultaneously reducing the pressure of the gas from its maximum at or immediately prior to the point of impact of the gas on the mixture.

Another problem which has been found with known compaction devices is that the mould obtained is much harder at the joint face than at the back face in other words the density of the mould is greater at the joint face than the back face therefore in order to give a mould of acceptable hardness the back face has to be removed and this can result in a wastage of upto 25%.

A solution to this problem which has been suggested is to subsequently recompact the moulding mixture by mechanically squeezing it. One way in which this has been achieved is by providing a squeeze plate within the discharge frame through which the pressurised gas passes from the pressurised gas reservoir to the moulding mixture, the squeeze plate being movable between a first position within the discharge frame and a second position where it contacts and presses the moulding mixture. However these devices have the disadvantage that the pressurised gas must pass around or through the squeeze plate to impact the sand and the full force of the pressure wave is therefore not realised rendering the process inefficient.

Preferably the apparatus includes a squeeze unit positioned to the side of the impaction unit for squeezing the moulding mixture, means being provided to bring the moulding box into contact with the squeeze unit or vice-versa.

Such an apparatus produces a mould wherein the density of the mould at the joint and back faces thereof can be controlled to any desired level and in particular can be made to be substantially equal. By separating the squeeze and impact units the full force of the pressurized gas is realised.

Preferably the moulding mixture is impacted with a pressurized gas having a pressure of less than 8 x 105 N/m2 and at a subsonic speed whereby the pressure gradient obtained is in the range of 100 to 300 bar/s.

The pressure of the delivered gas may be suitably adjusted to provide stronger or weaker impaction such that the density of the mould particularly at the joint face can be varied.

Advantageously the moulding mixture is physically squeezed at its back face. The strength of squeezing is suitably adjustable such that the density of the mould particularly at the back face thereof can be varied.

Suitably the impaction unit includes a pressurised gas reservoir and a discharge frame, the pressurised gas reservoir and discharge frame being connected by quick-release valves, the moulding mixture being subjected to the wave of pressured gas by opening the quick-release valves, the reduction of the pressure being effected by exhaust vents provIded in the discharge frame.

Suitably means are provided for raising the moulding box into contact with the supply squeeze and impaction units. Means are also provided to move the moulding box transversely below the supply unit and/or the impaction unit and/or the squeeze unit. Alternatively means may be provided to move the supply unit and/or the impact ion unit and/or the squeeze unit transversely above the moulding box.

The invention will now be described, by way of an example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic representation of a first embodiment of moulding apparatus in accordance with the invention.

Figure 2 is a diagrammatic representation of a second embodiment of moulding apparatus in accordance with the invention, and, Figure 3 is a diagrammatic representation of a third embodiment of moulding apparatus in accordance with the invention.

The moulding apparatus 10 shown in Figures l-to 3 all basically comprise a mould support arrangement, a mould lifing lowering and draw system, a moulding mixture supply unit 12, an impacting unit 14 and a squeeze head arrangement 16.

The moulding support arrangement comprises a pattern plate 18 with a pattern 20 mounted thereon, a moulding box 22 and a sand frame 24. The lifting, lowering and removal system includes at least one piston 26 to support and raise/lower the pattern plate 18 and pattern 20 mounted thereon and optionally a conveyor arrangement including a plurality of rollers 28 to support the pattern.

The impacting unit 14 comprises a pressurised air reservoir 30 which is connected to a discharge frame 32 by a series of quick release valves 34. The discharge frame 32 is provided with exhaust vents 36.

The sequence of steps for operating the apparatus of Figure 1 comprises firstly, from the position shown in A, raising the pattern 20 into engagement with the moulding box 22 and sand frame 24 and secondly raising the pattern and moulding box combination to a position just below the moulding mixture supply unit 12 by way of a first piston 26a. Moulding mixture is then discharged from the supply unit 12 into the moulding box 22 and sand frame 24 over the pattern 20, whereafter the moulding box and pattern combination is transversely moved on the rollers 28 to a position beneath the impacting device 14 (see B).

The moulding box and pattern arrangement is thereafter lifted into engagement with the impacting device 30 by means of a second piston 26b.

The quick release valves 34 are opened and pressurised air flows into the discharge frame 32 and impacts the moulding mixture causing it to be compacted.

The pressure immediately begins to fall from its initial maximum because of the exhaust vents 36 in the discharge frame. The direction of air flow is shown by the arrows in C. This impacting step is shown separately- in Figure 1 in order to fully describe the apparatus but there is no movement of any of the units between B and C.

After impaction, the second piston 26b is lowered, and the squeeze head arrangement 16 is moved transversely from its initial position at the side of the impact unit 14 to its operating position over the moulding box and pattern and thereafter the moulding box and pattern is raised by the piston 26b to engage the squeeze head arrangement and thereby squeeze the back face of the mould.

The sequence of steps for -operating the apparatus of Figure 2 comprises raising a piston 26 to engage firstly the pattern 20 with the moulding box 22 and the sand frame 24 and secondly the moulding box and pattern.

comD nation with the moulding mixture supply unit 12.

Moulding mixture is then discharged from the supply unit 12 into the moulding box 22 and over the pattern 20. The piston is then lowered, and the impacting device 14 is then moved transversely to a position over the moulding box and pattern combination. The piston 26 is raised to engage the moulding box and pattern combination with the impacting device 14, which is then operated to impact the moulding mixture in the moulding box, whereafter the piston is lowered.

Thereafter the squeeze head arrangement 16 is moved transversely to a position over the moulding box and pattern combination, and the piston 26 is raised to engage the molding box and pattern combination with the squeeze head arrangement to squeeze the top of the mould in the moulding box 22 and the piston 26 is thereafter lowered.

The moulding mixture supply unit 12 impacting unit 14 and squeeze head arrangement 16 are interconnected such that they move transversely together whereby when one of the components is moved transversely into positIon, one of the other components is automatically moved out of position.

The sequence of steps for operating the apparatus of Figure 3 comprises raising a piston 26a to engage firstly the pattern 20 with the moulding box 22 and secondly the moulding box and pattern combination with the moulding mixture supply unit 12 moulding mixture is then discharged from the supply unit 12 into the moulding box and over the pattern 20 whereafter the piston 28a is lowered disengaging the moulding box and pattern combination from the supply unit 12.

The moulding box and pattern combination is then moved transversely to a position over a second piston 26b and then raised thereby into engagement with the impacting device 14 which impacts the moulding mixture in the moulding box. The piston 26b then withdraws the moulding box and pattern combination from the impacting device 14 and the moulding box and pattern combination is then again transversely moved to a position over a third piston 26c, which raises the moulding box and pattern combination into engagement with the squeeze head arrangement 16 to squeeze the top of the mould, after which the third piston 26c is retracted and the moulding box and pattern combination moved away from the squeeze head.

The specific details of the operation of the quick-release valves of the impacting device 14 can be ascertained from GB Patent Application No. 2163686 (the contents of which are incorporated herein by reference).

In the arrangement shown in Figures 1 to 3, initial compaction of the moulding mixture is obtained by the impaction unit 14 and the mould resultIng therefrom has a density greater at the mould face than the back face thereof. The back face of the mould is thereafter further compacted by means of the squeeze head arrangement 16 such that the resulting mould has a density at the mould and back faces thereof substantIally equal. The moulding mixture is compacted by the maximum force of the compressed air since there is no obstruction between the outlet of the quick release valves and the moulding box.

The problems of 'rat-holing' are obviated by providing exhaust vents in the discharge frame so that the pressure of the gas on the moulding mixture decreases immediately from the maximum when the quick release valves are opened.

Suitably the moulding mixture is impacted by the impaction device 14 with a pressurised gas having a pressure of less than 8 x 105 N/m2 and at a subsonic speed whereby the pressure gradient obtained is in the range of 100 to 300 bar/s. The pressure of the delivered gas can be adjusted to provide stronger or weaker impaction of the moulding mixture whereby the density of the mould particularly at its face can be varied. Similarly the strength of squeezing by the squeeze head arrangement 16 can be suitably adjusted whereby the density of the mould particularly at the back face thereof can be varied.

The impaction device 14 and squeeze head arrangement 16 can thus be used to obtain a whole range of moulds having different densities throughout the depth thereof.

Claims

CLAIMS:

1. A method of compacting a moulding mixture comprising subjecting the surface of the mixture in a moulding box to a wave of pressurised gas, the pressure of the gas simultaneously being reduced from its maximum at or immediately prior to the point of impacting of the gas on the mixture.

2. The method as claimed in Claim 1 wherein after subjecting the surface of the moulding mixture to the pressurised gas the mixture is squeezed.

3. The method as claimed in either Claim 1 or 2 further comprising filling the moulding box which is supported on a pattern plate prior to subjecting the surface of the mixture to the pressurised gas.

4. A method as claimed in any preceding claim wherein the moulding box is brought into contact with an impaction unit which includes a pressurised gas reservoir and a discharge frame, the pressurised gas reservoir and discharge frame being connected by quick-release valves, the moulding mixture being subjected to the wave of pressurised gas by opening the quick-release valves the reduction of the pressure being effected by exhaust vents provided in the discharge frame.

5. The method as claimed in any preceding claim wherein the moulding mixture is impacted by a pressurised gas having a pressure of less than 8 x 105 N/m2 and at a subsonic speed whereby the pressure gradient obtained is in the range of 100 to 300 bar/s.

6. The method as claimed in any preceding claim wherein the impacting pressure of the delivered gas is adjustable so that the density of the compacted moulding material may be varied.

7. The method as claimed in any one of Claims 2 to 6 wherein a squeeze unit is provided for squeezing the moulding mixture, the moulding box being brought into contact with the squeeze unit by moving the moulding box transversely into contact with the squeeze unit or by moving the squeeze unit transversely into contact with the moulding box.

8. Apparatus for compacting a moulding mixture to produce a mould comprising a moulding box and an impacting unit for subjecting the surface of the mixture to a wave of pressurised gas and including means for simultaneously reducing the pressure of the gas from its maximum at or immediately prior to the point of impact of the gas on the mixture.

9. Apparatus as claimed in Claim 8 including a squeeze unit positioned to the side of the impaction-unit for squeezing the moulding mixture.

10. Apparatus as claimed in either Claim 8 or 9 including a moulding mixture supply unit for filling the moulding box which is supported on a pattern plate.

11. Apparatus as claimed in any one of Claims 8 to 10 wherein the impaction unit comprises a pressurised gas reservoir and a discharge frame, the reservoir and discharge frame being connected by a plurality of quick-release valves, the means for reducing the pressure of the gas comprising exhaust vents provided on the discharge frame.

12. Apparatus as claimed in any one of Claims 9 to 11 wherein the squeeze unit is a mechanically or pneumatically operated squeeze plate.

13. Apparatus as claimed in any one of Claims 10 to 12 wherein means are provided for raising the moulding box into contact with the supply, squeeze and impaction units.

14. Apparatus as claimed in any one of Claims 10 to 13 wherein means are provided to move the moulding box transversely below the supply unit and/or the impaction unit and/or the squeeze unit.

15. Apparatus as claimed in any one of Claims 10 to 14 wherein means are provided to move the supply unit and/or the impaction unit and/or the squeeze unit transversely above the moulding box.