GB2159867A - Compensating support between two mechanical parts - Google Patents

Abstract

A method of compensating for temperature controlled dimensional changes between co-operating mechanical parts 12, 14 includes creating a gap 18 between the said parts at an interface, where dimensional discrepancy is expected to occur, to prevent direct contact between the parts at the interface, filling the gap 18 by means of a deformable enclosure 20 including base 22, sheet 24 and a totally enclosed void 26 and providing in the void an expansible matter of a volume sufficient to deform the shut 24 to maintain the gap 18 fully closed. Further embodiments of enclosure 20 are shown in Figs. 2-5. <IMAGE>

Description

SPECIFICATION Method of and means for compensating for dimensional discrepancy between two dimensionally co-operating mechanical parts THIS INVENTION relates to compensating for dimensional discrepancy between dimensionally co-operating mechanical parts. It relates also to a mechanical-arrangement including dimensionally co-operating mechanical parts and to a method of manufacturing such a compensator.

For simplicity, the invention will generally be described with reference to compensation for dimensional discrepancies due to differential thermal expansion of dimensionally cooperating mechanical parts. It is to be understood that the invention is not limited to that field. It can also be applied in cases of differential thermal contraction, such as in cryogenic applications, in cases where manufacturing tolerances are to be ameleorated, and the like.

In mechanical arrangements including dimensionally co-operating parts, different requirements have to be met by the parts, sometimes resulting in the parts having to be of different materials with different co-efficients of thermal expansion and/or different Young's moduli (stress/strain characteristics) and the like. The above results in dimensional discrepancies between the parts in applications involving changes in temperature and changes in stresses of the parts.

In accordance with the invention, there is provided a method of compensating for dimensional discrepancy between dimensionally co-operating mechanical parts, including creating a gap between said parts at an interface, where dimensional discrepancy is expected to occur, to prevent direct contact between said parts at said interface; filling the gap by means of a deformable enclosure defining a totally enclosed void; and providing in the void an expansible matter of a volume sufficient to deform the enclosure to maintain the gap fully closed.

Thus, in use, mutual support between the parts is maintained across the interface.

When the dimensional discrepancy is due to differential thermal expansion of said mechanical parts caused by a change in the temperature of the parts, the method may include subjecting the expansible matter to a corresponding change in temperature, the expansible matter being preselected to have temperature/expansion characteristics to cause suitable expansion thereof. Thus, when the expansible matter is a solid, it will have a suitable co-efficient of thermal expansion.

When the matter is a mixture of liquid and vapour, or a vapour or gas, it will have suitable temperature pressure characteristics.

The expansible matter may be a fluid, conveniently a compressible fluid. It may be a vaporizable liquid. The method may include evacuating the void prior to introducing the fluid into the void.

In a preferred embodiment, the deformable enclosure has a rigid base portion provided by a base, and a deformable sheet portion provided by a sheet defining the void therebetween, and deformation of the enclosure to maintain the gap fully closed is by distension of the sheet in response to expansion of the fluid.

The invention extends to a mechanical assembly including dimensionally co-operating mechanical parts which are spaced to define a gap at an interface, where dimensional discrepancy between said mechanical parts is expected to occur, to prevent direct contact between said mechanical parts at said interface; and a compensator filling the gap and including a deformable enclosure defining a totally enclosed void and an expansible matter filling the void, the compensator being adapted to deform to maintain the gap fully closed to compensate for the dimensional discrepancy in use.

The expansible matter may be in the form of a fluid, conveniently a compressible fluid. It may be a vaporizable liquid.

In a preferred embodiment, the enclosure includes a rigid base portion provided by a base and a deformable sheet portion provided by a sheet defining the void therebetween, the sheet being adapted to deform by distension in response to expansion of the fluid.

In another embodiment, the enclosure is of generally thin walled construction in the expected direction of deformation to enable the thin walls readily to elongate and contract.

Instead, the enclosure may be of generally thin walled construction in a direction transverse to the expected direction of deformation to enable the thin walls readily to bend inwardly and outwardly.

In a specific embodiment, the gap may be annular, the compensator then being in the form of a complemental ring. More specifically, the dimensionally co-operating parts may respectively be a valve body and a seat, and may be of materials having different coefficients of thermal expansion, the gap they define being annular and the compensator being in the form of a complemental ring.

The invention extends further to a compensator suitable for use to compensate for dimensional discrepency between dimensionally co-operating mechanical parts which are spaced to define a gap at an interface, where the dimensional discrepancy is expected to occur, to prevent direct contact between said mechanical parts at said interface, the compensator being of a size and shape complemental to said gap to fill it and being adapted to deform to compensate for the dimensional discrepancy in use, the compensator including a deformable enclosure defining a totally enclosed void, and an expansible matter filling the void, the enclosure being of generally thin walled construction in the expected direction of deformation to enable the thin walls readily to elongate and to contract.

The invention extends still further to a compensator suitable for use to compensate for dimensional discrepency between dimensionally co-operating mechanical parts which are spaced to define a gap at an interface, where the dimensional discrepancy is expected to occur, to prevent direct contact between said mechanical parts at said interface, the compensator being of a size and shape complemental to said gap to fill it and being adapted to deform to compensate for the dimensional discrepancy in use, the compensator including a deformable enclosure defining a totally enclosed void, and an expansible fluid filling the void, the enclosure including a rigid base portion provided by a base and a deformable sheet portion provided by a sheet defining the void therebetween, the sheet being adapted to deform by distension in response to expansion of the fluid the enclosure being of generally thin walled construction in a direction transverse to the expected direction of deformation to enable the thin walls readily to bend inwardly and outwardly.

The invention extends also to a method of manufacturing a compensator comprising a rigid base portion providing a rigid base and a deformable sheet portion providing a deformable sheet, which rigid base and deformable sheet are joined to define a totally enclosed void therebetween, and an expansible fluid in the void, the method including forming a hollow in a side or edge of a portion of rigid material, which is to provide the rigid base; joining a sheet of deformable material, which is to provide the sheet, to the rigid base over the hollow to enclose it, the hollow providing the void; forming a hole into the hollow; introducing expansible fluid into the hollow; and closing the hole.

Conveniently, the rigid base and the sheet are of metal, in which case the sheet is joined to the base welding, the method including machining the compensator after welding. The hole may be formed into the hollow by drilling, the method then including tapping the hole, and closing the hole by means of screwing a screw threaded stud into the hole and welding over the stud to seal it.

The invention is now described by way of examples with reference to the accompanying diagrammatic drawings. In the drawings Figure 1 shows, fragmentarily, in axial section, a mechanical arrangement in accordance with the invention; Figure 2 shows, fragmentarily, in part sectional three dimensional view a second embodiment of a compensator in accordance with the invention; Figure 3 shows, fragmentarily in axial section a third embodiment of a compensator in accordance with the invention; and Figures 4 and 5 show, fragmentarily, in axial section manufacturing of a fourth embodiment of a compensator in accordance with the invention.

With reference to Figure 1 of the drawings, a mechanical arrangement in accordance with the invention is generally indicated by reference numeral 10.

The arrangement 10 comprises a valve body 1 2 and a valve seat 14 mounted within the valve body 12. The valve seat 14 has a valve seat surface 1 6. Both the valve body 1 2 and the valve seat 14 are round. An annular gap indicated at 18 is provided between the valve body 1 2 and the valve seat 14, i.e. at their interface, to prevent contact therebetween over the interface. The gap 18 is formed by a rebate 30 in the valve body 1 2.

The gap 1 8 is filled by means of a complementally annular compensator 20. The valve seat 14 is axially supported from underneath by a support 28.

The compensator 20 has a rigid base portion provided by a rigid base 22 and a distensible sheet portion provided by a sheet 24. The base 22 and sheet 24 are joined together to form a totally enclosed void 26, which is annular in shape, therebetween. The void 26 is filled with an expansible matter such as a fluid, conveniently a vaporizable fluid which is compressible when in vapour or partly in vapour form.

The mechanical arrangement 10 forms part of an ashlock of a coal gasification plant. In use, abrasive particle laden gas at high temperature passes through the ashlock. The valve seat 14 and especially the valve seat surface 1 6 is prone to high rates of wear.

Thus, the valve seat 14 is of an abrasion resistant material such as tungsten. The valve body 12, on the other hand, for cost purposes and for ease of manufacture, is of steel. The co-efficient of thermal expansion of the steel is about twice that of the tungsten. Thus, when the temperature of the arrangement 10 increases, a clearance gap tends to form between the valve body 1 2 and the seat 14.

This is undesirable as it results in the valve seat 14 being supported peripherally inadequately, or not at all. Especially under arduous working conditions when a valve closure is repeatedly hammered onto the valve seat, as is sometimes necessary to do, there is a substantial risk that the brittle tungsten of the valve seat 14 will fracture. It is thus very important to support the valve seat peripherally very well.

The rigid base 22 of the compensator 20 is also of steel. Thus, if it was well fitted origi nally in the rebate 30, it will remain to be well fitted and this will support it even at elevated temperatures. The valve body 1 2 and the rigid base 22 will thus expand in unison.

The expansible matter in the void 26 is selected to have a suitably high co-efficient of thermal expansion or to have suitable pressure-temperature characteristics to enable it to expand, thus to distend the deformable sheet 24 inwardly to keep it in contact with the valve seat 14, thus maintaining the gap 18 fully closed and supporting the valve seat 14 peripherally.

The dimensions of the compensator 20 and especially the thickness and length of the sheet 24 and the width and length of the void 26 will be adapted to suit every application.

For example, for use in ashlocks as described above, it is believed that a sheet having a thickness of about 2 mm and a void having a width of about 2 mm will prove satisfactory.

The expansible/compressible matter has to be selected bearing in mind the characteristics of the materials of the mechanical parts involved, and also the expected operating circumstances. In the case of a valve body of steel, and a valve seat of tungsten carbide, operating at temperatures up to about 600"C, it has been found that a fluid in the form of a mixture of about 80% water and about 20% of a specific hydraulic fluid is acceptable. The hydraulic fluid is water based and is currently available in South Africa under the trade name: "SENFLUIO HF7A/750".

With reference to Figure 2, another embodiment of a compensator in accordance with the invention is generally indicated by reference numeral 20.2. The compensator 20.2 is in the form of a ring and has a rigid base portion provided by a rigid base 22.2, and a deformable sheet portion provided by a sheet 24.2.

The rigid base 22.2 and the sheet 24.2 are joined together to define a totally enclosed void 26.2 therebetween. The rigid base 22.2 and the sheet 24.2 are welded together along adjacent corners as indicated at 32.

It is to be appreciated that the sheet 24.2, which is relatively thin, extends at right angles to the expected direction of discrepancy.

Thus, to compensate for the discrepancy, it will, in use, bulge outwardly to a desirable degree.

With reference to Figure 3, yet another embodiment of a compensator in accordance with the invention is generally indicated by reference numeral 20.3. The compensator 20.3 is of ring shape. It includes radially spaced, rigid outer and inner rings 22.3, 24.3 and axially spaced annular expansion sheets 34, 35 which are interconnected to define amongst them a totally enclosed void 26.3 filled by an expansible fluid/vapour mixture. The expansion sheets 34, 35 undulate in concertina- or bellows-fashion. The expected direction of discrepancy which has to be compensated for is indicated at 36. Thus, the expansion sheets 34, 35 extend generally in the expected direction of discrepancy. In use, the expansion sheets 34, 35 will elongate or contract to compensate for the discrepancy.In this regard it is to be appreciated that the inner ring 24.3 will be of a material allowing it to expand and contract in unison with a mechanical part corresponding to the valve seat 14 of Figure 1. Similarly, the outer ring 22.3 will be of a material allowing it to expand and contract in unison with a mechanical part corresponding to the valve body 1 2 of Figure 1. Furthermore, it may be necessary to support the expansion sheets 34, 35 from their outsides to prevent or restrict outward bulging. It is believed that the embodiment of Figure 3 can be used where large amounts of discrepancies are expected and where the pressure inside the void 26.3 will be modest.

With reference to Figures 4 and 5, another embodiment of a compensator in accordance with the invention, is generally indicated by 20.4 and is shown in two stages of manufacture.

The compensator 20.4 includes a ringlike rigid base portion provided by a rigid base 22.4, and a ringlike deformable sheet portion provided by a deformable sheet 24.4. Both the rigid base 22.4 and the deformable sheet 24.4 are hollowed along corresponding sides as indicated respectively at 40 and 42. Furthermore, along the top and bottom edges, each of the base 22.4 and the sheet 24.4 are profiled as indicated at 38 to provide a welding preparation. When married up as shown in Figure 4, the base 22.4 and sheet 24.4 provide between them a void 26.4. To close the void 26.4, they are welded together at 38 as shown in Figure 5 at 44 and 46.

To fill the void 26.4 with an expansible fluid, a hole 48 is drilled into the void 26.4.

The hole 48 is tapped. The void 26.4 is then filled with an expansible fluid indicated at 56 via the hole 48. The hole 48 is then closed firstly by screwing a stud 52 into the hole 48 and then by applying a layer of welding 54 for sealing purposes.

The fluid 56 is a vapourizable fluid and will, in use, generally be in the form of a mixture of liquid 58 and vapour 60.

Manufacture of the compensator 20.4 includes also a step during which final machining is done. This can be done at a convenient stage, such as after the welds 44 and 46 have been done and prior to charging the void 26.4. It may then be necessary to grind the final spot of welding 54 afterwards. Alternatively, if the fluid 56 allows welding, machining can be done as a final step.

It is an advantage of the invention that it allows dimensions of dimensionally co-operating mechanical parts to change differentially while maintaining contact or support between the parts via a compensator in accordance with the invention.

It is a further advantage, in the case of parts having different co-efficients of thermal expansion, that discrepancy due to changes in temperature is compensated for by causing the expansible matter in compensators to respond to the changes in temperature to cause suitable compensation.

Claims (22)

1. A method of compensating for dimensional discrepancy between dimensionally cooperating mechanical parts, including creating a gap between said parts at an interface, where dimensional discrepancy is expected to occur, to prevent direct contact between said parts at said interface; filling the gap by means of a deformable enclosure defining a totally enclosed void; and providing in the void an expansible matter of a volume sufficient to deform the enclosure to maintain the gap fully closed.

2. A method as claimed in Claim 1, when the dimensional discrepancy is due to differential thermal expansion of said mechanical parts caused by a change in the temperature of the parts, the method including subjecting the expansible matter to a corresponding change in temperature, the expansible matter being preselected to have temperature/expansion characteristics to cause suitable expansion thereof.

3. A method as claimed in Claim 1 or 2 in which the expansible matter is a fluid.

4. A method as claimed in Claim 3 in which the fluid is compressible.

5. A method as claimed in Claim 3 or 4 which includes evacuating the void prior to introducing the fluid into the void.

6. A method as claimed in Claim 3 in which the deformable enclosure has a rigid base portion provided by a base, and a deformable sheet portion provided by a sheet defining the void therebetween, and in which deforming the enclosure to maintain the gap fully closed is by distension of the sheet in response to expansion of the fluid.

7. A mechanical assembly including dimensionally co-operating mechanical parts which are spaced to define a gap at an interface, where dimensional discrepancy between said mechanical parts is expected to occur, to prevent direct contact between said mechanical parts at said interface; and a compensator filling the gap and including a deformable enclosure defining a totally enclosed void and an expansible matter filling the void, the compensator being adapted to deform to maintain the gap fully closed to compensate for the dimensional discrepancy in use.

8. A mechanical assembly as claimed in Claim 7 in which the expansible matter is in the form of a fluid.

9. A mechanical assembly as claimed in Claim 8 in which the fluid is compressible.

10. A mechanical assembly as claimed in Claim 8 in which the enclosure includes a rigid base portion provided by a base and a deformable sheet portion provided by a sheet defining the void therebetween, the sheet being adapted to deform by distension in response to expansion of the fluid.

11. A mechanical assembly as claimed in Claim 7 or 8 in which the enclosure is of generally thin walled construction in the expected direction of deformation to enable the thin walls readily to elongate and contract.

1 2. A mechanical assembly as claimed in claim 7 or 8 in which the enclosure is of generally thin walled construction in a direction transverse to the expected direction of deformation to enable the thin wall readily to bend inwardly and outwardly.

1 3. A mechanical assembly as claimed in claim 7 or 8 in which the gap is annular and in which the compensator is in the form of a complemental ring.

14. A mechanical assembly as claimed in any one of Claims 7 to 1 3 in which the dimensionally co-operating parts are respectively a valve body and a seat, and are of materials having different co-efficients of thermal expansion, and in which the gap they define is annular, the compensator being in the form of a complemental ring.

1 5 A compensator for dimensional discrepency between dimensionally co-operating mechanical parts which are spaced to define a gap at an interface, where the dimensional discrepancy is expected to occur, to prevent direct contact between said mechanical parts at said interface, the compensator being of a size and shape complemental to said gap to fill it and being adapted to deform to compensate for the dimensional discrepancy in use, the compensator including a deformable enclosure defining a totally enclosed void, and an expansible matter filling the void, the enclosure being of generally thin walled construction in the expected direction of deformation to enable the thin walls readily to elongate and to contract.

1 6. A compensator for dimensional discrepency between dimensionally co-operating mechanical parts which are spaced to define a gap at an interface, where the dimensional discrepancy is expected to occur, to prevent direct contact between said mechanical parts at said interface, the compensator being of a size and shape complemental to said gap to fill it and being adapted to deform to compensate for the dimensional discrepancy in use, the compensator including a deformable enclosure defining a totally enclosed void, and an expansible fluid filling the void, the enclosure including a rigid base portion provided by a base and a deformable sheet portion provided by a sheet defining the void therebetween, the sheet being adapted to deform by distension in response to expansion of the fluid, the enclosure being of generally thin walled construction in a direction transverse to the expected direction of deformation to enable the thin wall readily to bend inwardly and outwardly.

1 7. A method of manufacturing a compensator comprising a rigid base portion providing a rigid base and a deformable sheet portion providing a deformable sheet, which are joined to define a totally enclosed void therebetween, and an expansible fluid in the void, the method including forming a hollow in a side or edge of a portion of rigid material, which is to provide the rigid base; joining a sheet of deformable material which is to provide the sheet to the rigid base over the hollow, the hollow providing the void; forming a hole into the hollow; introducing expansible fluid into the hollow; and closing the hole.

1 8. A method as claimed in Claim 1 7 in which the rigid base and the sheet are of metal, joining the sheet to the base being by way of welding, the method including machining the compensator after welding.

1 9. A method as claimed in Claim 1 8 in which forming the hole into the hollow is by drilling; which includes tapping the hole; and in which closing the hole is by means of screwing a screw threaded stud into the hole and welding over the stud to seal it.

20. Methods of compensating for dimensional discrepancy between dimensionally cooperating mechanical parts substantially as herein described with reference to the accompanying drawings.

21. A mechanical assembly including dimensionally co-operating mechanical parts which are spaced to define a gap at an interface, where dimensional discrepancy between said mechanical parts is expected to occur, to prevent direct contact between said mechanical parts at said interface comprising a compensator as claimed in claim 1 5 or 16, or a compensator substantially as herein described and illustrated in Figure 1, or Figure 2 or Figure 3 or Figures 4 and 5 of the accompanying drawings.

22. Methods of manufacturing a compensator substantially as herein described with reference to the accompanying drawings.