Ugra Abrasion Tester

The device is basically a construction of the following four elements:

• a guiding slide-frame equipped with screw-fitted counter
• an abrasion sled gliding on the frame
• a metal block (weight 520 g) supported freely by the guiding frame, the lower side covered by a foam rubber coating
• a smooth Plexiglas board (size approx. 14 x 26 cm) serving as abrasion base

The metal block has a surface area of 50 x 50 mm which causes an abrasive pressure of 2 mN/mm2 or 0.2 N/cm2. The friction path measures 2 x 10 cm per double movement (to-and-fro) and is registered automatically by the counter.

Preparation of the Test Sample

Normally the printed test sample is placed on the abrasion base and unprinted paper serving as the element of counter-friction is laid on the abrasion sled and moved backwards and forwards. The only exception of this basic rule of testing is in the case of the test sample being of a size smaller than 20 x 7 cm. Above all it is important that the test sample is long enough: The rear and front rubber cushions of the guiding frame should rest on the printed sample in order to avoid displacement of the printed sample during the abrasion test.

Generally a sample of unprinted paper out of the same staple to be tested is used as counter-friction element. Care should be given to choosing the correct side of the paper: Usually it is the printed side, but it may happen that a preference is given to the reverse side of the paper, for example if the abrasion characteristics in the staple are to be tested.

In case there is no possibility to cut out a sufficiently large piece of unprinted paper, the test should be implemented using a similar paper. As an alternative the result of friction between two printed sides may be of interest. Therefore it is important that the material applied as the element of counter-friction is always exactly specified.

The cut out counter-friction sample should always be f at least 5.2 cm x 10 cm. It is particularly important that the width is not less than 5.2 cm; otherwise there is a risk that the foam rubber coating of the friction stamp will be taken along.

Carrying out of the Abrasion Test

First of all the printed test sample is placed on the Plexiglas board. It is not necessary to fix the printed paper, as the rear and front rubber cushions of the metallic guiding frame will clamp the sample onto the base. Then the counter-test paper (element of friction) is placed, test side face down, on the printed sample. Finally the abrasion tester is placed on the test sample in a way to make sure that the friction stamp exactly covers the counter-test paper. The counter is adjusted to the zero position by turning the button of the counter. For the actual testing process, the left hand holds the guiding frame of the device, pressing it against the front plate (counter side) while the right hand grips the two grey handles at the side of the abrasion sled and moves it smoothly from one end to the other.

The duration of friction is recommended at 20 strokes (to-and-fro). This standard number of motions must be consistent to each test, independent of the abrasion resistance of the test print. It assures the comparison of the results with previously carried out tests or evaluations made by other users of the device. This number of 20 strokes has been determined as a way of obtaining similar results to the scale applied with abrasion testers of other manufacturers. In order to produce similar results with other manufactures the following values regarding pressure and duration of friction have to be maintained.

Evaluation of the Abrasion Test

The result of the abrasion test is to be judged visually, the most interesting often being the color transfer to the counter-test sample. Notwithstanding whether only the test piece or also the counter-friction sample is qualified, the result of the abrasion test should be one single qualification based on a three-stage scale. A different scale has to be applied however if a comparison can be made between the test piece and a reference sample.

In this case the test sample, compared to the reference sample is:

• better
• the same
• worse

In case there is no reference sample available, the test result is qualified according to the following scale:

• good
• sufficient
• bad

In addition each evaluation of the abrasion resistance should be accompanied by the following specifications:

• abrasion device used
• description of the examined print
• specific description of the tested sample (i.e. full-tone, text, autotype, etc.)
• specification of counter-friction sample (i.e. type of paper, which side of paper, etc.)
• number of samples tested
• duration of friction (number or duration of strokes)
• climatic test conditions