The ASIA Miner - Reporting Important Issues to Mining Companies in the Asia Pacific Region
Issue link: http://asiaminer.epubxp.com/i/786114
VDMA 62 VDMA MINING SUPPLEMENT • 2017 The forces introduced into powered roof supports are increasing considerably along with longwall face lengths and the depth of min- ing. As a result, the hydraulic pressures and cylinder diameters of the shields are increasing as well. The higher cutting speeds of the shearer loaders additionally require a faster advance of the shield supports. All these factors are setting high requirements for the effi- ciency of the hydraulic stations in use. Adding to this are new, more stringent requirements for the en- ergy efficiency and noise levels. The pump stations are located more and more often in the immediate vicinity of the longwall controls in the headgate. While total cost of ownership and energy costs are a concern, longwall operators are also looking for more compact design because of the confined space. KAMAT understands these conditions and has successively de- veloped a new pump series that features a new drivetrain. It is based on the high-pressure plunger pumps, which have been used by the mining industry for decades. "The reduced noise level requirement was difficult to meet with the existing drive concept of the KAMAT pumps because the crank- shaft, which moves the plunger via crossheads, had to be asymmet- rical to accommodate it in the previously undivided housing," said Dr. Andreas Wahl, CEO, KAMAT. "The asymmetry resulted in stronger vibrations, which made it difficult to achieve acoustic decoupling by means of damping elements." The new drivetrain features a split housing in which a sym- metrical, balanced crankshaft takes over the power transmission between the drive and the plunger. "The newly designed dou- ble-helical gearing also helps to improve the smoothness in op- eration and to reduce the noise emission from the pumps," Wahl said. The new design is now incorporated in the triplex pumps of the performance classes from 80 kW to 400 kW. It also forms the basis for the design of the quintuplex pump drives in the performance classes from 530 kW to 800 kW, which KAMAT has developed for series production and has the potential to bring about significant cost savings from an operator's point of view when large volume flows are requested. The mechanical part of the drive creates the prerequisite for a demand-oriented, variable speed control of the pumps, which is one of KAMAT's core competencies. The power transmission de- sign details include large surfaces for a low surface pressure and the amply dimensioned crosshead. "They ensure an excellent, hydrodynamic lubrication of the pump drive at the spots with the highest loads even at a low rotational speed," Wahl said. "Since KAMAT plunger pumps are working at full operating pressure over a speed range from 10% to 100%, the plunger pumps are oper- ated in an energy-efficient and demand-oriented way at partial flow." The first KAMAT quintuplex pumps for pressures up to 3,500 bar were another development stage on the basis of the rede- signed, energy-efficient triplex plunger pumps, Wahl explained. "This development was initiated in response to the fact that the (water) hydraulic systems of various high-pressure plunger pump applications — and notably those on longwalls in the mining in- dustry and descaling systems in the steel industry — are getting larger and larger," Wahl said. Today, the operators are using multiple large triplex pumps given that the volume flow of these pumps is limited by design, but also for reasons of the high pressures involved. The cylinder volume is limited by cavitation, which implies that it only makes sense to produce triplex pumps with ratings of "only" about 400 kW. The basic design of the new triplex pumps then opened up the option to develop, on their basis, the first quintuplex (five-cylinder) pumps with a rating of 530 kW or 800 kW and the capability to reliably deliver distinctly larger volume flows than triplex pumps. The advantages for the operator result from the "economy of scale." A large pump is working far more cost-effectively than two or three smaller ones, and clearly needs less space — an import- ant argument in most modernization projects. A lot of detailed design work was, however, required to trans- fer the basic concept of the triplex design to the quintuplex pump. The crankshaft, for example, is supported by multiple bearings, and the crossheads are oil-spray lubricated rather than splash lubricated so that sufficient lubrication of the center crossheads is ensured as well. The crankshaft is supported in special split bearings. KAMAT has managed to keep spare parts stocking eco- nomical by using many common triplex pump parts. The new quintuplex pumps offer the same advantages as the redesigned triplex pumps. They operate at extremely low noise and low-vibration levels and they work at full operating pressure over a speed range in conjunction with speed-controlled drives. Thus, they can ideally be adapted to the respective volume flow re- quirements, and one single pump is sufficient due to a very large speed control range. "This is primarily achieved through the pump's capability to rotate slowly without affecting the hydrodynamic lubrication of the highly loaded drive elements of the crosshead in particular," Wahl said. "The corresponding design prerequisites are, among others, amply dimensioned crossheads with large surfaces, which absorb a high-surface pressure and preserve the continuity of the lubricant film." Operators see another advantage in the fact that the flow rate of KAMAT pumps is not controlled through circulation valves in on/off technique but through an electronically controlled speed change of the pump. As a result, wear is significantly reduced since the pump, the pipes and the valves are subjected to far less load. Since the New double-helical gearing reduces the noise emissions from the pumps.