GB2068121A - A measuring body having a protective coating - Google Patents

Abstract

The measuring surface is provided with a hard protective coating to reduce wear. The coating has a thickness which is at the most equal to the tolerance of the measuring body, and the colour of the coating differs from the colour of the base so that when the coating wears away it is apparent that the gauge needs replacing. The coating is preferably opaque and deposited in vacuum. Particularly advantageous are coatings of (a) a nitride of Ti, Zr, Hf, V or Ta, (b) a carbide of Ta or Nb or (c) a carbonitride of Ti, Zr, Hf, V, Ta or Nb.

Description

SPECIFICATION A measuring body having a measuring surface The invention relates to a measuring body having a measuring surface; such bodies are e.g. end gauges or parts of measuring instruments, e.g. limit gauges.

It has already been suggested to provide delicate measuring surfaces with a protective coating in orderto reduce their wear, e.g. by the application of hard oxide layers which do not change the appearance of the measuring surface. Such protective coatings could considerably increase the useful life of the measuring body, but their accuracy had to be regularly checked.

The aim of the present invention is to form a coating on the measuring surface of a measuring body in such a way that together with the protective effect it also enables a reliable checking in that wear beyond an admissible tolerance limit may be easilyspotted and not found only after re-measurement This according to the invention achieved in that the coating has a thickness which is at the most equal to the tolerance of the measuring body, and that the colour of the coating differs from the colour of its base.

Wear beyond the tolerance limit is then immediately noticeable, because in the areas where the coating is worn off the colour of the base appears.

The tolerance is in most applications of the order of a micrometer (1 ,am).

Particularly suitable are opaque layers having their own colour, e.g. layers of hard material made by deposii-,on in vacuum, e.g. by evaporation coating or cathodic deposition. Coatings made of nitrides, par tics marly of Ti, Zr, Hf, V and Ta and also carbides of Ta and Nb and also carbonitrides of the said metals proved to be successful. All these coatings are at the same time hard and coloured yellow up to brownish.

Layers which are particularly hard and resistant to wear are obtained inter alia by ion-supported evaporation coating described in Swiss PatentApplications Nos. 006 688177 and 7092/79/0. But also layers made by other methods e.g. non-absorbent hard Oxide layers made by reactive evaporation are suitable in certain circumstances for the purpose according to the invention, if their thickness is so chosen that a suitable interference colour results and the corresponding thickness is not greaterthan a wear which is just about tolerable. Layers in interference colours have however the disadvantage that their colour may be changed not only by wear but also by other influences, namely by layers of foreign sub stance, additionally deposited on the measuring sur face during manipulation, e.g. layers of fats (which are practically unavoidable in workshops).

The coating deposited according to the invention on the measuring body, may be also in several layers. If e.g. a material which is well suitable as a protective layer differs in colour only slightly from the base material of the measuring body an inter mediate layer the colour of which is considerably different may be deposited on the measuring surface which must well adhere but need not meet higher requirements as to its hardness or stretch resistance.

The actual protective layer of a thickness within the tolerance may then follow. This protective layer is gradually removed in use until finally the coloured intermediate layer appears, which indicates that the tolerance limithas been reached. For instance a measuring body of steel may first be provided with a yellowish intermediate layer of TiN 0.2 m thick and onto that may be deposited a layer of TiC the thick- ness of which equals the tolerance. TiC is harder than TiN, so that by this two-layercombination is at the same time achievedan excellent protective effect.

By "base" as used in this specification is understood a measuring body, possibly together with all those layers which are already present on the measuring surface, on which is already deposited a protective coating related to the tolerance (in the sense of the claim). In the last example the measuring body of steel forms together with the yellowish layer of TiN the base, while the layer of TiC representsthe coating related to'tolerance.

1. A measuring body having a measuring surface, the measuring surface being provided with a protective coating to reduce wear, wherein the coating has a thickness which is at the most equal to the tolerance of the measuring body, and that the colour of the coating differs from the colour of the base.

2. A body according to Claim 1 wherein the coating is opaque.

3., A body according to Claim 2 wherein the coating consists of a layer of hard material made by deposition in vacuum.

4. A body according to Claim 3 wherein the coating is of a nitride of Ti, Zr, Hf, V ar Ta.

5. A body according to Claim 3 wherein the coating- is of carbide of Ta and Nb.

6. A body according to Claim 3 wherein the coating is of carbonitride of Ti, Zr, Hf, V, Ta or Nb.

7. A body according to Claim 1 wherein the coating is in several layers.

8. A measuring body having a measuring surface, the measuring surface being provided with a protective coating to reduce wear, constructed, arranged and adapted to operate substantially as herein described.

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

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION A measuring body having a measuring surface The invention relates to a measuring body having a measuring surface; such bodies are e.g. end gauges or parts of measuring instruments, e.g. limit gauges. It has already been suggested to provide delicate measuring surfaces with a protective coating in orderto reduce their wear, e.g. by the application of hard oxide layers which do not change the appearance of the measuring surface. Such protective coatings could considerably increase the useful life of the measuring body, but their accuracy had to be regularly checked. The aim of the present invention is to form a coating on the measuring surface of a measuring body in such a way that together with the protective effect it also enables a reliable checking in that wear beyond an admissible tolerance limit may be easilyspotted and not found only after re-measurement This according to the invention achieved in that the coating has a thickness which is at the most equal to the tolerance of the measuring body, and that the colour of the coating differs from the colour of its base. Wear beyond the tolerance limit is then immediately noticeable, because in the areas where the coating is worn off the colour of the base appears. The tolerance is in most applications of the order of a micrometer (1 ,am). Particularly suitable are opaque layers having their own colour, e.g. layers of hard material made by deposii-,on in vacuum, e.g. by evaporation coating or cathodic deposition. Coatings made of nitrides, par tics marly of Ti, Zr, Hf, V and Ta and also carbides of Ta and Nb and also carbonitrides of the said metals proved to be successful. All these coatings are at the same time hard and coloured yellow up to brownish. Layers which are particularly hard and resistant to wear are obtained inter alia by ion-supported evaporation coating described in Swiss PatentApplications Nos. 006 688177 and 7092/79/0. But also layers made by other methods e.g. non-absorbent hard Oxide layers made by reactive evaporation are suitable in certain circumstances for the purpose according to the invention, if their thickness is so chosen that a suitable interference colour results and the corresponding thickness is not greaterthan a wear which is just about tolerable. Layers in interference colours have however the disadvantage that their colour may be changed not only by wear but also by other influences, namely by layers of foreign sub stance, additionally deposited on the measuring sur face during manipulation, e.g. layers of fats (which are practically unavoidable in workshops). The coating deposited according to the invention on the measuring body, may be also in several layers. If e.g. a material which is well suitable as a protective layer differs in colour only slightly from the base material of the measuring body an inter mediate layer the colour of which is considerably different may be deposited on the measuring surface which must well adhere but need not meet higher requirements as to its hardness or stretch resistance. The actual protective layer of a thickness within the tolerance may then follow. This protective layer is gradually removed in use until finally the coloured intermediate layer appears, which indicates that the tolerance limithas been reached. For instance a measuring body of steel may first be provided with a yellowish intermediate layer of TiN 0.2 m thick and onto that may be deposited a layer of TiC the thick- ness of which equals the tolerance. TiC is harder than TiN, so that by this two-layercombination is at the same time achievedan excellent protective effect. By "base" as used in this specification is understood a measuring body, possibly together with all those layers which are already present on the measuring surface, on which is already deposited a protective coating related to the tolerance (in the sense of the claim). In the last example the measuring body of steel forms together with the yellowish layer of TiN the base, while the layer of TiC representsthe coating related to'tolerance. CLAIMS

1. A measuring body having a measuring surface, the measuring surface being provided with a protective coating to reduce wear, wherein the coating has a thickness which is at the most equal to the tolerance of the measuring body, and that the colour of the coating differs from the colour of the base.

2. A body according to Claim 1 wherein the coating is opaque.

3., A body according to Claim 2 wherein the coating consists of a layer of hard material made by deposition in vacuum.

4. A body according to Claim 3 wherein the coating is of a nitride of Ti, Zr, Hf, V ar Ta.

5. A body according to Claim 3 wherein the coating- is of carbide of Ta and Nb.

6. A body according to Claim 3 wherein the coating is of carbonitride of Ti, Zr, Hf, V, Ta or Nb.

7. A body according to Claim 1 wherein the coating is in several layers.

8. A measuring body having a measuring surface, the measuring surface being provided with a protective coating to reduce wear, constructed, arranged and adapted to operate substantially as herein described.