Figure 1. Taber Linear Abraser 5750

How Do We Evaluate Abraded Materials?

For abrasion testing, there are many ways that materials can be evaluated, such as, recording the number of cycles to reach a specific end point, comparing the appearance after a fixed number of cycles, or measuring the weight loss after testing. It should be noted that rotary and linear abrasion tests should not be thought to correlate, since the wear paths are very different.

All samples were tested until breakthrough or when 2,000 cycles had been reached. If breakthrough occurred, the number of completed cycles was recorded. Samples were also weighed before and after testing as a way to better understand how each stood up to abrasion. A high amount of weight loss, would indicate more damage was sustained.

Experimental Test Set-Up

For each material, three 1.5” x 1.5” squares were cut out. The samples were weighed before testing. Following prescribed methodology from Taber® Industries, the abradant was refaced prior to each test. Samples were tested individually by securing to a table attached to the instrument. Samples were all oriented to have the reciprocating action in the machine direction. In addition, if 1,000 cycles were reached, the abradant was refaced. For this test, the stroke length was 15.49 mm with 400g additional weight. The speed of the abradant was 55 cycles per minute. Over the course of the test, worn away abradant and material that had accumulated, was periodically brushed away. Once a material showed evidence of breakthrough, the testing was stopped and the number of cycles were recorded. For all materials, reported values were averaged from the performance of three samples.

Results

Below in Figure 1, is a plot showing the average amount of cycles completed for all eight materials at both severity levels.

Figure 2. Comparison of all eight materials of the average completed cycles with respect to abradant severity.

Upon completion of the testing, Trevira showed the worst performance at both severities. The other seven materials, all were able to resist 2,000 cycles when subjected to a mild abradant. The severe abradant showed a clear divide in abrasion resistance. 63-20 was able to withstand 2,000 cycles with the severe abradant for all three samples. Not far behind in performance were PFR and VHN(LT). FEP also showed pretty good performance as well, as two of the three samples withstood 2,000 cycles with the severe abradant.

In order to rank these materials, something other than average number of completed cycles needed to be considered, since the mild abradant ranking would be a seven-way tie for first. This is where the weights of the samples before and after come in. Using the weight loss of the samples, the materials can have wear indexes created. If we correct this wear index with the specific gravity of the samples, this account for the loss in volume. It should be noted that these samples all varied in thickness, which would not put these materials on an even playing field. By making a corrected wear index, all these materials can be fairly compared.

Below in Table 2, is the corrected wear indexes for all the materials for both abradants. Specifically, this wear index is called the Taber® wear index (WI) and is calculated as weight loss per 1000 cycles of abrasion (see Equation 1).

Once this number had been calculated, the value was then divided by the specific gravity to get the corrected wear index (CWI).

Table 2. Comparison of the average completed cycles, CWI and the relative ranking of each material.

Ranks were based on the CWI value, with lower values being more desirable, as this would indicate less material was abraded away. For the rankings of place 7 and 8 for the mild abradant, technically, Trevira should have placed 7^th, but because PVL would have been 8^th and did survive all 2,000 cycles, this was placed higher. Most of the rankings remained the same for both abradants, but some notable differences would be PFR improving from 4^th place to 2^nd place with the severe abradant. By far, 63-20 performed the best in this test with a very low CWI for both abradants.

Final Thoughts

The top contender for this test was by far 63-20. That being said, FEP-5, PFR-10 and VHNLT, were also very strong competitors. From this comparison, we can gather from this group of materials, which ones would be more likely to be suitable for applications needing abrasion resistance. It should be noted, that the severity of the abradants has not be correlated to mimic real situations, so these results should only be used as a guide, rather than as an absolute.

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