REF. 720N PENCIL SCRATCH HARDNESS TESTER

INTRODUCTION

The purpose of scratch hardness test is to determine the resistance of coating materials

or lacquers to scratch effects on the surface. This test is of particular value for furniture or

vehicle lacquers, but is also a useful aid in the development of synthetic resins or other

film forming substances.

Generally scratch hardness is measured by moving a more or less sharp object under a

known pressure over the surface of the material. The test result may either be the value

of the pressure required to scratch through the material if a scratching tool of constant

hardness is used, or alternatively the hardness of the scratching tool if this is varied whilst

constant pressure is applied.

TEST PRINCIPLE

The pencil test uses constant pressure and variable hardness of the test tool as its

fundamental principal. Pencils of varying hardness, starting with the hardest lead, are

moved over the surface under a fixed pressure of 7.5 Newtons (765 gms) and at a fixed

angle of 45 degrees to the surface. The degree of hardness of the pencil which damages

the surface is taken as a measurement for scratch hardness.

Twenty pencils in the range of grades from 9B to 9H (ISO 15184/ BS 3900-E19) are used.

The pencils can be exchanged quickly and easily. The instrument is supplied complete

with pencils, pencil sharpener, abrasive paper and carrying case.

The test method is fully described in the standards specified.

Note: ASTM D3363/ECCA T4 specifies only 14 pencils.

INSTRUCTIONS FOR USE

The test methods describe how to relative hardness of a coating is to be determined.

This is achieved using a set of pencils of known hardness.

The test surface needs to be correctly prepared and smooth. (Please refer to the relevant

test standard.) The test should be performed at 23^ðC +/-2^ðC with a relative humidity of

50 +/-5% (ECCA T4) or 25^ðC +/-2^ðC  (ASTM D3363).