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VARNISH HARDNESS EN ISO 15184 - 1998 (adapted)

1.1 Mechanical “trolley” consisting of a metal block fitted with 2 wheels one on each side. In the middle of the block, there is a cylindrical hole inclined at a 45 (+/-1) °. A clamp ensures that pencils are always fixed into the hole in the same way. Mounted on top of the instrument, there is a level which is used to ensure that the test is carried out with a horizontal “trolley”. The “trolley” shall be designed so that, with the instrument in the horizontal position, the tip of the pencil exerts a load of 750 (+/-10) g on the varnish surface

1.2 Set of DERWENT drawing pencils meeting the following scale of hardness:

1.3 Mechanical sharpener, draftsman-style, which will remove the lead only, leaving the cylindrical pencil lead intact

1.4 Abrasive paper, grit No. 400
1.5 Soft cloth or swab of cotton wool, to clean the sample after the test, using a solvent to which the coating is inert

Any conveniently sized sample, coated as agreed between the purchaser and the seller

Condition the sample for minimum 16 hours in the following environment:
Temperature: 23 (+/- 2) °C
Relative humidity: 50 (+/-) 5%
Perform the test in the same environment

4.1 With the mechanical sharpener, remove approximately 5 to 6 mm of wood from the point of each pencil. Make sure the resulting tip is an undisturbed, unmarked, smooth cylinder of pencil lead
4.2 Square the lead tip by holding the pencil in a vertical position and moving the pencil back and forth over abrasive paper, maintaining an angle of 90°. Continue until a flat, smooth, circular cross-section is obtained, free from chips or nicks in the edges. Repeat this procedure each time a pencil is used
4.3 Place the sample on a level, firm and horizontal surface
4.4 Place the pencil on the trolley and make sure the trolley sits horizontally on the sample, with the pencil tip resting on the varnish surface

4.5 Push the sample in the direction away from the operator, at a speed of 0.5-1 mm/s and for a distance of at least 7 mm

4.6 After 30 seconds, inspect the sample with the naked eye for defects (plastic deformation, cohesive fracture or a combination thereof)
4.7 The damage can be assessed more clearly after cleaning the varnish surface with a soft cloth or swab of cotton wool and an inert solvent which does not affect the varnish hardness
4.8 If no marking has occurred, repeat the test, without overlap of the test areas, moving up the hardness scale until marking occurs over a distance of at least 3 mm
4.9 The hardness of the hardest pencil which does not mark the varnish is the so called pencil hardness
4.10 By agreement, the test can also be carried out to determine the minimum pencil hardness which does not cause a cohesive fracture (the so-called “gouge” hardness as defined in ASTM D 3363:1992 a )
4.11 Carry out the test in duplicate. If the 2 results differ by more than one unit of pencil hardness, discard them and repeat the test

Passing requirement per the sales contract

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