GB1586562A

GB1586562A - Ceramic spacers

Info

Publication number: GB1586562A
Application number: GB3474077A
Authority: GB
Original assignee: PARK ROYAL PORCELAIN CO Ltd
Current assignee: PARK ROYAL PORCELAIN CO Ltd
Priority date: 1978-05-12
Filing date: 1978-05-12
Publication date: 1981-03-18

Description

(54) CERAMIC SPACERS (71) We, PARK ROYAL PORCE LAIN COMPANY LIMITED, of Woodlands, Cox Hill, Sandy, Bedfordshire, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to ceramic spacers.

In many applications ceramic spacers are required to be clamped up in an assembly. If their surfaces are not flat and parallel strains tending to snap them are set up when the clamping up is done, and the assemblies are likely to come apart in service dr at least be incapable of reassembly if for any reason they have to be taken apart.

We have had the idea of applying the principle of a three-point mounting to these spacers by providing them at each of three spaced positions rounded protruberances from its opposite faces, through which protruberances the spacer bears on the other members of the assembly, the total thickness of the spacer through the protuberances being the same at the three positions.

Warping in such a spacer, rather than allowing a snapping force to act for example across the whole width of the spacer, at most brings the contact points of the protuberances a little out of true axial alignment. Even this can be avoided if, according to a subsidiary feature of the invention, the protuberances at each position are parts of a common sphere.

The invention allows production of spacers by directly pressing and firing, without subsequent lapping such as is required to produce reliable spacers of the known kind, an expensive process when spacers are being produced in bulk.

The invention further extends to assemblies using the spacers, wherein one or more spacers are clamped between metal or other parts distributing an axial clamping load between the protuberances. The protuberances on successive spacers do not need to be aligned if the metal or other parts between them are sufficiently rigid to transmit the load through the protuberances rather than distort and apply the load to the web of the spacer. If necessary however alignment or substantial alignment can be given by keying the spacers or other mechanical means.

The spacers will have a shape suitable for their intended use and may be designed for a single central clamping screw or the like or for two or more. In particular spacers, when provided for use in an assembly where two or more spaced means for clamping up the assembly are used, may have shaped projections or recesses to engage such recesses or projections respectively of another such spacer to hold the spacers with their protuberances in line. Thus the clamping load alone to ensure maintenance of the relative orientation of the members of the assembly is avoided.

The shape of the protuberances depends on the nature of the material of the members to be spaced and the nature of the ceramic used for the spacers. The bearing area desirable in practice is related to the materials and to the load to be applied, so that the crushing strength of the ceramic is not exceeded and the members to be spaced are not excessively indented.

Generally a rounded protuberance on a radius about half the thickness of the spacer at the position of the protuberance or rather more is satisfactory.

The invention is illustrated in the accompanying drawings, in which: Fig. 1 is a schematic view of a domestic iron thermostat assembly with the clamped parts slightly separated for illustration and shown with spacers of known kind; Fig. 2 shows part of a similar assembly but illustrating the use of the spacers of the invention; Fig. 3 shows a single spacer in plan view (above) and in section on line X-X of the plan view (below); Fig. 4 is an exploded view of part of a toaster thermostat assembly; and Fig. 5 is a view in plan, underneath plan and elevation of a spacer as used in the assembly of Fig. 4.

In Fig. 1, the parts of the thermostat are a mounting 1, a fixed terminal arm 2, and a moving terminal arm 3. The mounting carries an adjustment spindle 4 bearing through a ceramic pin 5 on a part 6 of the moving terminal arm 3. There is also an adjustable ceramic stop 7 for the moving arm. Connecting tabs 8 (seen in end view) project sideways, each in electrical contact with one of the arms, and separated by a fibre insulating washer 9.

The assembly is held together by a screw 10 passing into a tapped end cap 11, the screw being electrically isolated from the arms and the connecting tabs by a ceramic sleeve, omitted in the drawing but running through the various parts between two ceramic spacers 12. These are spacers of the kind improved upon by the invention, essentially plane-faced and liable to fracture when the assembly is locked up by tightening the screw.

In Fig. 2 the application of ceramic spacers of the present invention is shown, separating metal thermostatic switch members 14 etc.

generally as in Fig. 1. The assembly is in this instance riveted, at 15, and three spacers 16 as also shown in detail in Fig. 3 are used with thick metal washers 17. The spacers, which are annular, show protuberances 18, which are disposed in random orientation from one spacer to the next as the members 14 spread the load. The protuberances are so designed that their curved surfaces are parts of the surface of a single sphere, and acordingly even in a warped spacer the contact points of the protuberances are still in a line coaxial with the assembly and no strains tending to snap the spacer arise.

In Figs. 4 and 5 there are shown respectively an assembly and a spacer for it in which re tention of relative orientation of the parts is ensured not simply by the clamping load as in the above, but by the shape of the parts. The clamping load can thus be reduced to that needed to keep-the parts in contact and the clamping means (two screws) from coming undone; risk of breakage of the spacers by exceeding the crushing strength of the ceramic is eliminated.

In Fig. 4 the parts are, successively, clamping screws 21, spring washers 22,-a metal plate 23 to spread the clamping load, a spacer 24, one thermostat arm 25 (working parts omitted), a second spacer 24', the other thermostat arm 26, a ceramic base block 27 and nuts 28.

The two spacers are for convenience the same. Each bears on its upper face three rounded protuberances 29 and on its lower face three similar and correspondingly placed protuberances 29'. The upper face has two recesses, one, 30, round and the other, 31, Dshaped. The iower face has corresponding projections 32 and 33 which cooperate with the recesses to ensure that the spacers will only go one way round and thus that the protuberances of successive spacers are in line.

The projections enter the recesses, clearing holes in the thermostat arms, but do not in the final assembly touch their bottoms: the load is transmitted by the protuberances.

Recesses 34 in the base block 27 are similar, though since this block is thick enough to be in no danger of breakage it has no protuberances and can go either way round; thus both recesses can be and are the same.

In assembly the screws are done up to normal vibration proof tightness. Overtightening results only in stripping of the threads, rather than crushing of the spacers as can happen if a single large screw in an assembly such as that of Fig. 1 is overtightened in the course of obtaining sufficient grip to keep the thermostat arms and other parts aligned.

WHAT WE CLAIM IS: 1. A ceramic spacer for use clamped up between other members of an assembly, the spacer having at each of three spaced positions rounded protuberances from its opposite faces, through which protuberances the spacer bears on the other members of the assembly, the total thickness of the spacer through the protuberances being the same at the three positions.

2. A ceramic spacer according to claim 1, wherein the protuberances at each position are parts of a common sphere.

3. A ceramic spacer according to claim 1 or claim 2, for use in an assembly comprising two or more spaced means for clamping up the assembly, the spacer having shaped projections or recesses to engage such recesses or projections respectively of another such spacer to hold the spacers with their protuberances in line.

4. A spacer substantially as herein described and shown in Figs. 2 and 3 of the accompanying drawings.

5. A spacer substantially as herein described and shown in Figs. 4 and 5 of the accompanying drawings.

6. An. assembly of two or more members clamped together by a bolt, rivet or other means giving an axial load distributed between the protuberances of one or more spacers according to claim 1, 2 or 4.

7. An assembly of two or more members clamped together by a bolt, rivet or other means giving an axial load distributed between the protuberances of one or more spacers according to claim 3 or 5.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

a mounting 1, a fixed terminal arm 2, and a moving terminal arm 3. The mounting carries an adjustment spindle 4 bearing through a ceramic pin 5 on a part 6 of the moving terminal arm 3. There is also an adjustable ceramic stop 7 for the moving arm. Connecting tabs 8 (seen in end view) project sideways, each in electrical contact with one of the arms, and separated by a fibre insulating washer 9.

The assembly is held together by a screw

10 passing into a tapped end cap 11, the screw being electrically isolated from the arms and the connecting tabs by a ceramic sleeve, omitted in the drawing but running through the various parts between two ceramic spacers 12. These are spacers of the kind improved upon by the invention, essentially plane-faced and liable to fracture when the assembly is locked up by tightening the screw.

In Fig. 2 the application of ceramic spacers of the present invention is shown, separating metal thermostatic switch members 14 etc.

generally as in Fig. 1. The assembly is in this instance riveted, at 15, and three spacers 16 as also shown in detail in Fig. 3 are used with thick metal washers 17. The spacers, which are annular, show protuberances 18, which are disposed in random orientation from one spacer to the next as the members 14 spread the load. The protuberances are so designed that their curved surfaces are parts of the surface of a single sphere, and acordingly even in a warped spacer the contact points of the protuberances are still in a line coaxial with the assembly and no strains tending to snap the spacer arise.

In Figs. 4 and 5 there are shown respectively an assembly and a spacer for it in which re tention of relative orientation of the parts is ensured not simply by the clamping load as in the above, but by the shape of the parts. The clamping load can thus be reduced to that needed to keep-the parts in contact and the clamping means (two screws) from coming undone; risk of breakage of the spacers by exceeding the crushing strength of the ceramic is eliminated.

In Fig. 4 the parts are, successively, clamping screws 21, spring washers 22,-a metal plate 23 to spread the clamping load, a spacer 24, one thermostat arm 25 (working parts omitted), a second spacer 24', the other thermostat arm 26, a ceramic base block 27 and nuts 28.

The two spacers are for convenience the same. Each bears on its upper face three rounded protuberances 29 and on its lower face three similar and correspondingly placed protuberances 29'. The upper face has two recesses, one, 30, round and the other, 31, Dshaped. The iower face has corresponding projections 32 and 33 which cooperate with the recesses to ensure that the spacers will only go one way round and thus that the protuberances of successive spacers are in line.

The projections enter the recesses, clearing holes in the thermostat arms, but do not in the final assembly touch their bottoms: the load is transmitted by the protuberances.

Recesses 34 in the base block 27 are similar, though since this block is thick enough to be in no danger of breakage it has no protuberances and can go either way round; thus both recesses can be and are the same.

In assembly the screws are done up to normal vibration proof tightness. Overtightening results only in stripping of the threads, rather than crushing of the spacers as can happen if a single large screw in an assembly such as that of Fig. 1 is overtightened in the course of obtaining sufficient grip to keep the thermostat arms and other parts aligned.

WHAT WE CLAIM IS: 1. A ceramic spacer for use clamped up between other members of an assembly, the spacer having at each of three spaced positions rounded protuberances from its opposite faces, through which protuberances the spacer bears on the other members of the assembly, the total thickness of the spacer through the protuberances being the same at the three positions.
2. A ceramic spacer according to claim 1, wherein the protuberances at each position are parts of a common sphere.
3. A ceramic spacer according to claim 1 or claim 2, for use in an assembly comprising two or more spaced means for clamping up the assembly, the spacer having shaped projections or recesses to engage such recesses or projections respectively of another such spacer to hold the spacers with their protuberances in line.
4. A spacer substantially as herein described and shown in Figs. 2 and 3 of the accompanying drawings.
5. A spacer substantially as herein described and shown in Figs. 4 and 5 of the accompanying drawings.
6. An. assembly of two or more members clamped together by a bolt, rivet or other means giving an axial load distributed between the protuberances of one or more spacers according to claim 1, 2 or 4.
7. An assembly of two or more members clamped together by a bolt, rivet or other means giving an axial load distributed between the protuberances of one or more spacers according to claim 3 or 5.