Applications are site specific and conditions vary throughout the coal business. Large western U.S. surface mines, such as those operating in the Powder River Basin (PRB) are looking at high volume applications, processing a friable subbituminous coal with little rock. At the other end of the spectrum, coal operators in the eastern U.S. are processing coals that are much harder and oftentimes accompanied with a significant amount of rock.
One prominent roll crusher provider, McLanahan Corp., has invested quite a bit of time into extending the wear elements on its roll crushers and the research is now beginning to pay nice dividends for its customers. Working with Kennametal, the company developed weld-on carbide teeth for its crusher segments. “The new carbide teeth have been a very hot product for us,” said Bruce Daskivich, general manager-mineral division, McLanahan. “In the PRB, we have increased the capacities for crusher segments by more than twice what they were getting with regular cast segments. In this application, the segments would normally average 18 to 20 million tons. We have now increased that to 50 million tons at some operations.” The new teeth also reduce the change-out times for the mines.
The mines stock the weld-on teeth on site. If a piece of tramp steel passes through the crusher and breaks off teeth, they grab replacement teeth from the warehouse shelf, weld them on and are quickly back in operation without replacing the complete segment. “This extends the life of the segment saving time and money,” Daskivich said. “They are getting a lot of value out of this product.”
The mines do not normally replace the primary and secondary rolls at the same time. The secondary rolls, the ones with the smaller teeth, see the most wear. For some of the larger triple roll machines, they can change a set of roll segments in about 16 to 24 hours, Daskivich explained. “To reduce segment changeout from annually to every two to three years, again, saves money and prevents downtime,” Daskivich said.
The engineers at McLanahan had been working on these improvements for a while. Initially, they designed cast roll teeth to include a piece of carbide as a tooth cap. The tooth was cast with a step and then the carbide cap was welded into the face of the tooth. “That was our first attempt at improving wear life with carbide and it worked well,” Daskivich said. “However, we found through field trial that when the weld wore away or the tooth cap broke, the cast parent-tooth would wear rather quickly, leaving a void in the segment. Operators were left without much recourse for in-place repair and therefore had to replace the entire segment. ”
That thinking led the company to pursue a replacement tooth that, if it was worn or broken, the mine could weld the tooth back in place. “We worked with Kennametal to develop a replaceable tooth with carbide granules impregnated into the base metal of the tooth itself on the leading face on the top edge,” Daskivich said. “These teeth maintain their profile much longer resulting in a tremendous amount of wear life and the replaceable design means a longer lasting base segment. We are providing similar technology for other brands of roll crushers. We have an agreement with Kennametal on the tooth. If mine operators want these teeth, they have to work with McLanahan.”
McLanahan has started to use the same technology in more eastern U.S. applications with more rock. “We have introduced it slowly in the East and we are experiencing similar success,” Daskivich said. “ The teeth are holding up fairly well calming our initial fears that we would be breaking teeth left and right with some of the harder sandstones that these mines encounter. That has not been the case.”
When Lee Doyer, vice president, sales and marketing, Pennsylvania Crusher, considers some of the more recent trends for coal crushers, he talks about a shift from roll crushers to sizers, particularly for coal operators based in the Illinois Basin and Appalachia. That should make for lively internal dialogue for the K-Tron Size Reduction Group, a subsidiary of Hillenbrand Inc., which acquired Pennsylvania Crusher and Gundlach. Gundlach builds some fairly large roll crushers.
Pennsylvania Crusher has also been looking at ways to extend wear life for its sizers. “Initially, we provided primary sizers with Kennametal mining bits,” Doyer said. “More recently, we have started to provide rotors with a specially-developed hardfacing to improve wear. For primary crushing applications, we have started supplying rotors with segmented tooth castings. From a maintenance perspective, it’s a lot easier to change these teeth. Occasionally with the really strong teeth, the bit block would get knocked off and the maintenance technicians in field are not normally equipped to properly replace those blocks.” The bit blocks require special procedures with preheat and post-heat welding specifications.
Pennsylvania Crusher is now stocking parts at its Ohio plant and the company has embarked on a warehouse in West Virginia, which also carries supplies for Gundlach’s machines.
Every piece of equipment has its own application, explained Phil Schaefer, regional sales manager-Western USA & Canada, Gundlach Equipment. “If a mine can manage with a roll crusher and a v-belt drive, they can save quite a bit of money over buying an expensive sizer,” Schaefer said. Gundlach has been supplying the 8030 carriage mounted units or the 5000 series double stage machines for high-volume PRB applications. Some of those mines are crushing as much as 6,000 to 7,000 tons of coal per hour.
The two major environmental concerns associated with crushing coal are dust and noise. “We have been looking for more ways to better seal the equipment for fugitive dust,” Schaefer said. “We have been looking at a better seal arrangement to control dust inside the crusher housing. We are always looking at how to improve roll configuration and roll design to give the mines a better product yield for their facility.”