Traditionally, the hardness of coal was believed to be a measure of its cuttability. This however, was based on very little scientific evidence, but rather on conceptions. In the past, the prevailing notion linked coal hardness solely to its physical toughness, without thorough consideration of scientific measurements. The assumption rested on intuitive beliefs rather than empirical data, shaping the understanding of coal cuttability without a solid foundation in scientific analysis.

The hardness of coal is a measure of its Unilateral Compressive Strength (UCS), determined by the compressive load that a sample of coal, of specific dimensions, can withstand before collapsing. Tests have shown that brittle coal with a plethora of microcracks could have a relatively high UCS, while lumpy coal with very few microcracks have a low UCS value. It was therefore assumed that the fractured coal was harder to cut than coal with minor cracks.

A correlation between cuttability and pick consumption, however, proved that this assumption is incorrect.  It was found that more ton per pick was produced when cutting coal with a high UCS  than coal with a low UCS.  Further investigation showed that the pick grooves made in “hard coal” were quite wide, with a large internal angle, while the grooves made in “soft coal” was visibly smaller.

A study was done where the groove angles that were made by continuous miner cutter picks, were measured over the whole face (approximately 50 measurements per coal face), of different headings, in each production section.  A total of 53 sections on 5 different mines, were included in the study.  The pick usage of each section was obtained from miner reports, checked against stores issue records, and compared against the average coal break-out angle of each individual production section.

The results were clear and undeniable.  The larger the average internal angle of the grooves, the lower the pick consumption of that production section.  Results from some of the production sections were then double-checked, where coal samples were presented to an independent research laboratory, to have the UCS of each sample measured.  It was found that most samples with high UCS values, correlated more to coal that had a large break-out angle, and low pick consumption, while samples with low UCS results, were mostly from production sections that had small break-out angles and high pick consumption.

In summary, this study on coal cuttability overturns traditional beliefs about coal hardness and its effects on mining efficiency. The link between coal’s breakout angle, UCS and pick consumption provides critical insights for improved mining practices.

Numerous field tests in South African underground coal mining operations have shown that DaltronX cutting picks have delivered a 20-30% performance improvement. This translates to greater tonnage per pick, reduced downtime, and higher overall productivity.