GB2121177A

GB2121177A - Measuring tool

Info

Publication number: GB2121177A
Application number: GB08225728A
Authority: GB
Inventors: Wilhelm Vogel
Original assignee: MTU Motoren und Turbinen Union Muenchen GmbH
Current assignee: MTU Aero Engines GmbH
Priority date: 1981-09-09
Filing date: 1982-09-09
Publication date: 1983-12-14
Also published as: DE3135585A1; CH657451A5; FR2512542A1; FR2512542B3

Abstract

The tool, e.g. a plug or snap gauge, is made of a ceramic or fibre- reinforced material, such as an organic plastic reinforced with carbon fibres alone or with glass fibres. Compared with measuring tools made of metal, the tool of the present invention is substantially more resistant to abrasion and has a much lower coefficient of expansion; it shows little if any distortion, normally provides greater rigidity, is non-corroding, light in weight and non-magnetic. <IMAGE>

Description

SPECIFICATION Measuring tool This invention relates to a measuring tool, particularly but not exclusively for use in sensing or testing the diameter, length, angle or shape of a body, e.g. gauge, gauge block or dial gauge feeler.

Measuring tools, especially tolerance gauges, normally consist of steel, preferably an ailoyed steel or hard metal. Setmasters often come in lengths of 300 mm to 1200 mm (and longer) with a tolerance of about +0.006 mm and normally consist of low-alloy steel, where the alloying additions (amounting to normally less than 5% altogether) particularly are manganese and vanadium, or manganese and chromium.

The disadvantages of such tools is that thermal expansion and/or abrasion or wear in use and, perhaps with measuring tools of some length, distortion will cause changes in dimensions or shape. Distortion of the measuring tool occurs especially in hardening, grinding and measuring and with variation in temperature especially when the measuring tool has already been warped by a hardening process. It is because of such distortion that long setmasters-exceeding 500 mm in length-are difficult if not impossible to manufacture within the required tolerance limits.

Distortion changes the length of the dimension, the measuring section, the gauge length or the setting length of the setmaster.

An object of the present invention is to provide a measuring gauge in which the changes in shape and size are reduced if not eliminated.

The invention provides a measuring tool formed from ceramic or fibre-reinforced material.

Compared with measuring tools of steel or similar materials, the differences are these: the measuring tool made of a ceramic material will show substantially less expansion when heated (lower coefficient of thermal expansion), which makes it less sensitive to temperature, and it is substantially better resistant to wear and abrasion. The measuring tool made of a fibrereinforced material will expand even less when heated. Also, little if any distortion occurs and this, more particularly, keeps measuring, gauge or spaced surfaces or the measuring or gauge jaws of the measuring tools parallel for all practical purposes. The measuring tools of ceramic materials and occasionally also the measuring tools made of fibre-reinforced material, are more rigid (higher modulus of elasticity).Also, the measuring tool does not corrode and it weighs less if ceramic, and generally still less if it is made from fibre-reinforced material. Additionally, it is a non-magnetic and it so reduces if not eliminates measuring error; adjusting errors, etc.

The measuring tool of the present invention accordingly exhibits greater accuracy in terms of shape and/or dimension. This is to say that, e.g., there will be no pronounced, intolerable or appreciable changes in the dimension which the inspection of sensing body is intended to represent and/or in the shape which the inspection or sensing body is intended to represent. This now enables also long measuring tools, e.g. setmasters for gauge lengths exceeding about 500 mm, to be manufactured with great ease and within the specified tolerance requirements. The long tool, whether distorted or not, will retain for all practical purposes its shape and gauge section, e.g. during measurements or in the absence of temperature changes, especially because, unlike measuring tools of steel or similar materials, it will bend very little if at all.

The tool may be a plug gauge, such as a go nogo plug gauge or cylindrical gauge, or a snap gauge. The prism is a sensor body having a chute of acute or obtuse angle section offered said cylinder body for a snug fit inside it by means of bilateral linear contact. The invention ensures that the shape of the chute and its angle of section are maintained or are practically retained in the intendment of the present invention.

Compared with the measuring tools of steel or similar materials a measuring tool made of silicon carbide is recommended especially on account of its substantially reduced thermal expansion and because of its resistance to wear and abrasion. A measuring tool made from organic material reinforced with carbon fibres has even less pronounced thermal expansion.

A measuring tool made of organic material reinforced with carbon fibres and glass fibres has a virtually insignificant thermal expansion. Even when the measuring tools are long, they undergo little or no distortion. The coefficients of thermal expansion of the carbon fibre is negative, that of the glass fibre positive.

The ceramic material of the measuring tool may alternatively be silicon nitride (Si3N4). The measuring tool may consist of e.g., a fibrereinforced metal or a fibre-reinforced alloy of smaller coefficients of thermal expansion in either case than those of steel or similar materials. The ceramic measuring tool is more particularly made by a sintering process from, preferably, silicon carbide (SiC) or by hot isostatic pressing.

The measuring tool may be a gauge, e.g., a measuring tool for verifying at least one dimension of a part, machine component or the like, or especially a gauge block having precisely planar, parallel gauge surfaces, which serves as a standard linear dimension. By adding a number of gauge blocks together, linear gauge dimensions can be formed that are 0.001 mm within true dimension. The measuring tool, may, however, be a caliper rule or its long guide arm carrying the sliding member, or a protractor.

The embodiments of the invention will now be described with reference to the accompanying drawings wherein: Figure 1 is a side view taken in the direction I of Figure 2 of a setmaster in accordance with the invention for setting inside calipers; Figure 2 is a plan view taken in the direction II of Figure 1; and Figure 3 is a side view of a go no-go plug gauge in accordance with the invention.

The setmaster shown in Figures 1 and 2 is a single-piece construction comprising a straight rail 10 of rectangular section and two gauge cheeks 11 and 12 at either end, which give the setmaster its U-shape. The rail 10 and the cheeks 11 and 12 are made of an organic plastic reinforced with carbon fibres and glass fibres.

The two gauge cheeks 11 and 12 exhibit two opposed parallel gauge surfaces 13 and 14, the distance between which is the dimension represented by the setmaster. The inside calipers 15, shown diagrammatically in dash-dotted line, have two pins 17 and 18 extending along a common axis 16; the pins are movable along the axis 1 6 away from or towards the centre line 19 and symmetrically to it when the inside calipers 1 5 are adjusted. As shown in Figure 1, the pins 17 and 18 are touching the gauge faces 13 and 14, and the measurement is being taken.

This arrangement is used, e.g., for verifying or inspecting the inside diameter of a turbine casing.

The gauge faces 1 3 and 14, their parallelism and their spacing are produced with a maximum of precision. This spacing or measure is 1100 mm, the tolerance being +0.006 mm.

If the fibre-reinforced material is used for the setmaster, the setmaster firstly exhibits very little thermal expansion, that is, it is rigid and resists distortion and thus the spacing will be maintained to better effect and, secondly the setmaster is nonmagnetic, free from corrosion and very light in weight. The rail 10 and the gauge cheeks 11 and 12 being nonmagnetic, setting errors are alleviated or prevented for the normally rather small pins 1 7 and 18.

The go no-go plug gauge of Figure 3 is made of silicon carbon. It is a single-piece construction composed of a short cylinder 20 representing the go side, a short cylinder 21 representing the nogo side, and a longer, intermediate cylinder 22 of smaller diameter. As a result, firstly, the circumferential surfaces of the cylinders 20 and 21 will better resist wear and the cylinders 20 and 21 will expand less when heated, so that the diameters of the cylinders 20 and 21 will be maintained to better effect. Secondly, the go nogo plug gauge is non-magnetic, non-corroding and rather light in weight.

It will occasionally be advantageous to give the rail a cylindrical or tubular section. Compared with the rail of rectangular section made of fibrereinforced material, the rail of tubular section made of fibre-reinforced material is easier to manufacture and gives the same rigidity in any direction. Occasionally a rail or square section will afford a greater advantage. At a rail length of about 500 mm, the square section of the rail will more particularly be about 30 to 40 mmx 10 to 13 mm.

Claims

1. A measuring tool formed from ceramic or fibre-reinforced material.

2. A measuring tool as claimed in claim 1, wherein the ceramic material is silicon carbide (SiC).

3. A measuring tool as claimed in claim 1, formed from organic plastic reinforced with carbon fibres.

4. A measuring tool of claim 1, formed from organic plastic reinforced with carbon fibres and glass fibres.

5. A measuring tool substantially as herein described with reference to Figures 1 and 2 or Figure 3 of the accompanying drawing.