GB2146129A

GB2146129A - A scratch hardness tester

Info

Publication number: GB2146129A
Application number: GB08321387A
Authority: GB
Inventors: Michael Charity
Original assignee: FURNITURE IND RES ASS
Current assignee: FURNITURE IND RES ASS
Priority date: 1983-08-09
Filing date: 1983-08-09
Publication date: 1985-04-11
Also published as: GB8321387D0

Abstract

A device for testing the hardness of a surface, comprises a scratching head with a graver 3 adapted to be moved over and in contact with the surface, guide means 1 adapted to constrain the movement of the graver along a predetermined path and resistance means 4, 7 adapted to resist the pressing force of the surface against the graver while it is being moved along the predetermined path, whereby the resistance of the resistance means to the force increases or decreases progressively as the graver is moved along the predetermined path. The resistance means may comprise a resilient member 4 and a pair of bearers 7 whose spacing or height above the test surface varies along their length. <IMAGE>

Description

SPECIFICATION A scratch hardness tester The invention relates to a device and method for testing the hardness of a surface.

Testing the hardness of a surface or its resistance to scratching, particularly a painted, lacquered, foil- or paper-covered surface as occurs in furniture is important and standards exist to define the downward load varying with a linear stroke applied to an edge or point drawn along such a surface. This is normally carried out by means of an electric motor driving such a point along a line with the force varied as the moment arm changes.

Such a device is expensive and cumbersome.

The invention provides a device for testing the hardness of a surface, comprising a graver with a scratching head adapted to be moved over and in contact with the surface, guide means adapted to constrain the movement of the graver along a predetermined path and resistance means adapted to resist a force applied to the graver to press it towards the surface while being moved along the predetermined path, whereby the resistance of the resistance means to the force increases or decreases progressively as the graver is moved along the predetermined path.

The progressive increase or decrease of the resistance may be stepwise or continuous.

By means of the invention it is possible to apply a constant force, for example by means of a fixed load, to the graver, yet by reason of the resistance means the pressure of the scratching head against the surface is not constant but varies progressively as the graver moves along the predetermined path. The resistance means "diverts" part of the force from the scratching head.

The resistance means may comprise biassing means tending to bias the scratching head away from the surface, the biassing effect of the biassing means varying progressively as the graver is moved along the predetermined path.

The invention is particularly valuable in that it provides as a preferred embodiment a portable and inexpensive device which is capable of performing accurate and easily repeatable tests. A particularly preferred embodiment is described below.

It consists of an edge or point mounted upon a spring strip. The point is loaded onto the surface by means of the strip being forced downward towards the surface by two bearers, typically of hard steel wire. The distance between these bearers decreases as the point is pulled along and thus the force increases.

The point is pulled along by means of the spring strip in turn pulled by a handle, the locations from the handle are arranged not to load the strip towards the surface and always to pull rather than push. This ensures that the spring strip always takes up the same position relative to the point or edge, surface and the bearers.

Because an existing standard calls for a minimum force of N/N and a maximum of 26N it may be necessary to supplement the changes in downward force on the pointer produced by varying the distance between the bearers. Clearly the minimum distance between the bearers is fixed by the slot width at the top of the housing and the forces and deflections convenient to use may lead to an unacceptable distance between bearers at the other end. This additional variation to enable the bearers to be within the housing and the slot is readily obtained by a slight slope of the surface carrying the bearers. For reasons of simplicity this slope will normally be linear, but variations are possible.

In order to avoid the need to secure the housing relative to the surface by one hand, whilst moving the handle with the other, the handle when depresed by hand presses on the housing through rollers or slides. The handle during the test always moved on one direction relative to the housing. A stop may be provided at the end of the stroke (and hence maximum downward force) to enable fine adjustment.

The test reading is the measurement of the scratched length and a scaie may be provided on the side of the housing to enable this to be made easily. Various notes may be inscribed on the housing. The point may be a hardened metal one or a natural or artificial mineral such as diamond or carborundum. Applications are envisaged beyond the furniture industry.

An embodiment of the invention is illustrated in the accompanying drawings.

Figure 1 is a general view of a device of the invention.

Figure 2 is a horizontal section through the body of the device, with the graver removed.

Figure 3 is a longitudinal vertical view (partially in section) of the graver and part of the body of the device.

Figure 4 is a partial transverse sectional view of the graver and part of the body of the device.

Figure 5 is a partial transverse sectional view corresponding to part of Fig. 4, when the force is applied.

Figure 6 shows various springs forming part of the resistance means.

In the drawings, a device comprises a body 1 and a graver comprising a grip portion 2 and a scratching head 3, carried on a flat leaf spring 4. The scratching head and spring move in a slot 5 in the body 1, such movement being effected by moving the grip portion 2 which is supported on rollers 6 through the leaf spring 4 (as shown in Figs. 3 and 4) or which is biassed downwardly by bearers 7 as shown in Fig. 5. By means of bearers 7 or 8, which may be either angled relative to each other or of progressively thicker section, the scratching head may be increasingly pressed against a surface 9 as the grip 2 is moved along under a constant load (not shown).

Claims

1. A device for testing the hardness of a surface, comprising a graver with a scratching head adapted to be moved over and in contact with the surface, guide means adapted to constrain the movement of the graver along a predetermined path and resistance means adapted to resist a force applied to the graver to press it towards the surface while being moved along the predetermined path, whereby the resistance of the resistance means to the force increases or decreases progressively as the graver is moved along the predetermined path.

2. A device according to claim 1 in which the progressive increase of the resistance is stepwise.

3. A device according to claim 1 in which the progressive increase of the resistance is continuous.

4. A device according to any of claims 1-3 in which the resistance means comprises biassing tending to bias the scratching head away from the surface, the biassing effect of the biassimg means varying progressively as the graver is moved along the predetermined path.

5. A device according to any of claims 1-4 comprising an edge or point mounted upon a spring strip and adapted to be forced on to the surface by the pulling of a handle attached to the spring strip under the action of two elongated bearers orientated so that the distance between them decreases as the handle is pulled along.

6. A device according to claim 1 substantially as hereinbefore described with reference to the drawing.

7. A method of testing the hardness of a surface which comprises contacting the surface with one scratching head of the device of any of claims 1-6 and causing it to move along the predetermined path while the force is applied, and measuring the length of the resulting scratch.