Rock picks come of age

LATEST tests conducted using new rock pick technology on a longwall shearer demonstrate major improvements on conventional pointed bits. The most noticeable benefits were a 30% reduction in respirable coal dust and a 33% reduction in fines.
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AGE picks on left showing greater clearance than industry standard, right.

Staff Reporter

Published in Australia's Longwalls

The tests, conducted in October last year at the Kestrel longwall mine in central Queensland, showed the Dawood Cutting System performed substantially better across all measured key performance indicators, including respirable dust, fines generation and power usage.

The innovative Dp4 rock pick is the brainchild of Dr Albert Dawood who completed a PhD at the University of New South Wales in pick tip geometry and coal cutting mechanics in the mid 1980s. He formed NSW-based AGE Mining Services in 1996 to further develop chisel-shaped pick technology as an alternative to conventional conical bits.

The company’s first trials were conducted in 2000 at Myuna colliery, near Newcastle in NSW, on a Joy continuous miner. However, the Kestrel tests have taken the concept further with the picks being tested on the shearer over eleven 12-hour shifts to compare the performance of the Dp4 rock picks with conventional pointed bits.

The main difference between the Dp4 and a pointed bit lies in the tip geometry. The Dp4 is designed with a clearance angle of 10 degrees in the cutting plane, compared with no clearance in the industry standard pick. This serves to keep the cutting forces as low as possible and normalise the gap between normal and cutting forces. Typically, as a standard bit wears the ‘normal’ forces generated are higher than the ‘cutting’ forces, requiring more specific energy.

Furthermore, the Dp4 is sharp while the pointed bit is round. This makes the striking action slightly different with the Dp4 acting as a wedge to split the coal. The tests showed 14% less specific cutting energy was required with the sharp rock pick.

“This reduction is attributed to the sharpness of the tip as cutting progresses and the unchanged rake angle. The reduction is also well reflected in an increase in the coarseness index and a decrease in fines,” Dr Dawood said.

Conventional bits have a larger contact area, so as they strike coal the action is more a crushing and grinding force. The fines and airborne dust generated by the conventional pointed bit were 51% and 55% higher respectively than the Dp4. The lowered levels of fragmentation of the Dp4 improved product coarseness by 5%.

The grinding action of conventional bits is also thought to be the reason these bits generate a quartz content of 2%, while the Dp4 rock picks generate less than 1%.

Measurements of comparative wear rates, conducted by the University of NSW’ School of Mining Engineering, found the Dp4 had a 21% improvement in wear.

More importantly though was the impact of wear on the risk of frictional ignition. The probability of frictional ignition decreases with sharp picks, Dawood said.

As the contact surface area of pointed bits increases over time, along with a negative clearance angle, the risk of developing hot spots and frictional ignition increases. In addition, these factors generate dust, greater specific energy requirements, greater noise and machine vibration.

Another important safety result was a reduction of over 50% in machine noise, measured by SIMTARS as part on an ongoing monitoring program at the mine.

This finding has been applauded by Warwick Williams, senior research engineer at the National Acoustic Laboratories.

Williams said the tests showed it was possible to engineer out noise related hazards in mines, rather than accepting them as inherent to the process and managing them by modifying worker behaviour.

AGE has faced some industry scepticism about the chisel-picks and the company has gone to great lengths to offer verifiable proof of its claims. AGE has recently completed a comprehensive risk assessment of the Dawood Cutting System, conducted by Hawcroft Miller Swan Consultants, which will be audited by PricewaterhouseCoopers. Also, various independent experts (SIMTARS, ACIRL, Power Solutions and Unisearch) provided impartial measurements of the cutting parameters for the Kestrel tests.

Each AGE pick is turned and milled, not drop forged, and is therefore more expensive than industry standard picks, but the proven benefits would seem to more than compensate for any price premium.

“In the conditions the picks were tested, the Dp4 picks could reduce costs by up to $2.50 per tonne,” said AGE chief corporate officer George Wawryck.

In May the company demonstrated the picks in the US, on a Joy 14CM continuous miner at the Peabody Energy bord and pillar mine, Willow Lake mine, in Missouri.

“The mining industry is on the threshold of a new and exciting advancement in coal and rock cutting technology and the opportunity is now available,” Wawryck said.

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