WO1999004241A1

WO1999004241A1 - Improvements in and relating to durometers

Info

Publication number: WO1999004241A1
Application number: PCT/GB1998/001944
Authority: WO
Inventors: Adrian Redwood Miller; Alan Garratt
Original assignee: Hampden Test Equipment Ltd.
Priority date: 1997-07-18
Filing date: 1998-07-02
Publication date: 1999-01-28
Also published as: GB9715272D0; AU8228498A; GB2327504A; GB2327504B

Abstract

The present invention provides improvements in and relating to durometers. More specifically, the invention provides a durometer comprising an indentor (7), means (9) for applying a predetermined force to the indentor (7), and means for measuring the extent to which the indentor (7) indents a material being tested in response to the predetermined force. The characterising feature of the invention is a self contained module (4) which is formed by the indentor (7) and the force applying means (9). The module (4) can be removed from the measuring means so as to allow an alternative module having a different indentor and/or force applying means to be substituted. A modified durometer may be thereby provided which is capable of operating on an alternative hardness scale. The present invention thus enables a single durometer, provided with a multiplicity of interchangeable heads, to operate in different hardness scales.

Description

IMPROVEMENTS IN AND RELATING TO DUROMETERS

This invention provides improvements in and relating to durometers .

A durometer is an instrument used for the hardness testing of non-metallic materials. A durometer includes an indentor, means to apply a predetermined force to the indentor, and means for measuring the extent to which the indentor indents the surface of the material being tested in response to the predetermined force.

There are a number of different recognised hardness scales for non-metallic materials, the most common scales being designated A,B,C,D,0 and 00. Heretofor, durometers have been designed such that each individual durometer operates in only one of the standard scales. Hence, if an organisation requires hardness testing in, say, three of the standard scales, it must have three separate durometers. The object of the present invention is to address this problem and to enable a single durometer, provided with a multiplicity if interchangeable heads, to operate in a multiplicity of hardness scales.

According to one aspect of the present invention a durometer comprising an indentor, means for applying a predetermined force to the indentor, and means for measuring the extent to which the indentor indents a material being tested in response to the predetermined load is characterised in that the indentor and the means for applying a predetermined force to the indentor form a self contained module which can be removed from the measuring means to allow an alternative module having a different indentor and/or different force applying means to be substituted and thereby allow the resultant modified durometer to operate on a different hardness scale from that of the original durometer.

Preferably, the means for applying a predetermined force to the indentor comprises a spring which is housed within the module and is substantially isolated from the surrounding environment. Preferably, means are provided to adjust the pre-load of the spring. Preferably, the indentor is mounted on a shaft which is moved axially as the indentor is applied to a material to be tested. In this case, the displacement of the end of the shaft remote from the indentor may be used to drive the associated measuring device. In this case, each module is designed so that when the indentor is in its starting position prior to application to an item to be tested, the position of the end surface of the indentor displacement shaft is a fixed distance from a datum surface provided on the body of the module. This fixed distance will be constant for each module so that when each module is installed with the associated measuring device, it is only necessary to bring the datum surface of the module into engagement with a corresponding datum surface of the measuring device in order to place the end of the indentor shaft at a predetermined zero deflection position. Accordingly, when the modules are interchanged no or substantially no zeroing of the instrument is necessary.

In the particularly preferred embodiment each module is provided with screw threads which engage mating threads on -the body of the measuring device when the module is installed. Under these circumstances, the datum surface can conveniently be the surface of a flange located at one end of the module, the flange being brought into engagement with a corresponding datum surface defined on the measuring device as the module is screwed home. Preferably, the flange defines the presser foot of the module and the datum surface is the surface of the flange opposite to that which, in use, engages the item to be tested.

The measuring device may be an analogue or a digital device and may be of any appropriate design. In the preferred embodiment of the invention in which the module defines a presser foot which is brought into engagement with the surface of the item to be tested in order to effect hardness measurement, the measuring device is merely required to measure the movement of the indentor as the presser foot is brought into engagement with the surface of the item to be tested. The movement of the indentor provides a direct measurement of the hardness of the material .

The above and further features and advantages of the invention will be understood from the following description of a preferred embodiment thereof, given by way of example only, reference being had to the accompanying drawing wherein:

Figure 1 shows schematically a durometer according to the present invention; and

Figure 2 illustrates, on a larger scale, the indentor module of the durometer of Figure 1.

Referring to the drawings, and firstly to Figure 1 , there is illustrated a durometer 1 having a digital readout 2. Although the illustrated durometer includes a digital readout it is to be understood that the present invention is not limited to such applications, and is directly applicable to durometers having a conventional mechanically driven analogue readout.

The durometer 1 is formed of two assemblies, namely a measuring device 3 and an indentor module 4. The two assemblies are connected to provide a complete durometer, but are readily separable, for example by unscrewing the module 4 from the body of the measuring device 3. For this purpose, mating screw threads are preferably provided on the exterior surface of the module 4 and on the internal surface of the neck 5 of the measuring device 3.

The indentor module is shown in more detail in Figure 2. It comprises a body 6 which has, on the exterior surface thereof, the screw threads necessary to connect the module to the measuring device. An indentor 7 is secured to an indentor displacement shaft 8 and is movable axially relative to the body in use of the instrument. The exact form of the indentor 7 will depend on the hardness scale for which the module is intended to be used. A spring 9 is located within the body 7 and operates between a flange 10 provided on the indentor displacement shaft 8 and a ring 11 which is in screw-threaded engagement with threads provided on the inside of the body 6. After assembly of the various components the ring 11 is tightened down in order to apply a preload force to the spring and accordingly to bias the flange 10 into engagement with a corresponding shoulder 12 formed in the body 6. During calibration, the indentor 7 is adjusted so that, with the flange 10 held in engagement with the shoulder 12 the tip of the indentor projects by a known distance from the surface 13 of a presser foot 1 defined by the body.

The module components are precision machined such that, when assembled as described above, the end 14 of the indentor displacement shaft 8 is at a known and precisely controlled distance from a datum surface 15 provided by the rear surface of the presser foot 1 . A range of modules all having the same datum distance from the end surface 14 of the indentor displacement shaft to the rear surface 15 of the presser foot are produced, each module being fitted with a particular indentor 7 and a particular spring 9 intended for the measurement of hardness on a particular hardness scale.

In use, an operative wishing to measure a particular hardness scale will select the module corresponding to that scale and screw the module into the displacement measuring device 3 until the datum surface 15 is firmly engaged with a corresponding datum surface provided on the end of the measuring device neck 5. This action will automatically place the end 14 of the indentor displacement shaft 8 in contact with the displacement measuring element of the device 3 with the displacement element device reading "0". If desired, means may be provided for setting the measuring device to read zero when this datum state is achieved, but in general it is envisaged that little or no such zeroing will be required after manufcture. The device is then used to measure the required hardness by pressing the indentor against the material to be measured until the surface 1 comes into engagement with the material. The reading on the display 11 will then be a measure of the hardness of the material on the scale corresponding to the particular module 4 being used.

If it is required subsequently to measure hardness on a different scale, the module 14 may be removed by unscrewing it from the neck 5, and a module corresponding to the other scale is inserted. Because the distance between the end face 14 of the indentor displacement shaft and the datum surface 15 will be the same in the replacement module, the instrument may immediately be used without re-zeroing.

The above described durometer may be factory assembled with the module 4 secured in place. In this case, the technique of the present invention will be used by a durometer manufacturer to provide a durometer for a particular range from a selection of stock modules 14 which he holds. Alternatively, a single display device 3 and a range of modules 4 may be supplied as a kit to users to enable them to change the module as necessary to measure any particular scale.

It will be appreciated that, as well as enabling a user to have available an instrument which is capable of measuring several durometer scales, the present invention means that in the event of indentor wear or damage, only the module 4 need be returned to a specialist for service and re-calibration. Accordingly, the user of an instrument may choose to have more than one module calibrated for a particular range to enable one module to be returned to a specialist for repair or re-calibration whilst the other module remains in use.

Claims

CLAIMS:

1. A durometer comprising an indentor, means for applying a predetermined force to the indentor, and means for measuring the extent to which the indentor indents a material being tested in response to the predetermined force, characterised in that, the indentor and the means for applying a predetermined force to the indentor form a self contained module which can be removed from the measuring means to allow an alternative module having different indentor and/or different force applying means to be substituted and thereby allow the resultant modified durometer to operate on a different hardness scale from that of the original durometer.

2. A durometer as claimed in claim 1, wherein the means for applying a predetermined force to the indentor comprises a spring which is housed within the module and is substantially isolated from the surrounding environment.

3. A durometer as claimed in claim 1 or 2, wherein means are provided to adjust the magnitude of the predetermined force.

4. A durometer as claimed in any of the preceding claims, wherein the indentor is mounted on a shaft adapted to move axially in use as the indentor is applied to a material being tested.

5. A durometer as claimed in claim 4, wherein displacement of an end of the shaft remote from the indentor drives the associated measuring means.

6. A durometer as claimed in claim 5, wherein, when the indentor is in a starting position prior to application to a material to be tested, the position of said end of the shaft is a predetermined distance from a datum surface provided on a body of the module, said predetermined distance corresponding to a measurement of zero indentation determined by the measuring means.

7. A durometer as claimed in claim 6, wherein the module datum surface is the surface of a flange located at one end of the module, the flange engaging a corresponding datum surface defined on the measuring means when the module is installed with the measuring means.

8. A durometer as claimed in claim 7, wherein the flange defines a presser foot on the module and the module datum surface is the surface of the flange opposite to that which, in use, engages the material to be tested.

9. A durometer as claimed in claim 8, wherein the measuring means measures the displacement of the indentor as the presser foot is brought into engagement with the surface of the material to be tested.

10. A durometer as claimed in any of the preceding claims, wherein the module is provided with screw threads which engage mating threads on the measuring means when the module is installed.

11. A durometer substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.