Like most working chocks, Kenmare’s roof supports have been subject to the usual wear and corrosion dished up by the harsh underground environment. Joy Mining Machinery has been assigned the huge task of overhauling the roof supports and is using the services of specialist subcontractors HVOF and Laser Technologies to assist.
HVOF will reclaim the static seal surfaces and threads on the damaged inner and outer cylinders with its LaserBond technology.
HVOF’s LaserBond process allows just about any worn or corroded component to be coated with a high performance surface and reclaimed. It provides superior corrosion resistance to chrome, making it suitable for the refurbishment of the outer (or dynamic) seal surfaces of any hydraulic cylinder.
HVOF said it couldn’t be sure how many seals it needed to repair until job completion, however it estimated there were 110 two-leg chocks being overhauled and each leg had two stages, so there were potentially 440 stages being repaired. Each stage has a static seal area which must be in excellent condition to ensure a good seal.
In the Dendrobium case, HVOF will carry out the repairs by machining the damaged areas, applying LaserBond cladding and finish machining to the required tolerances, leaving a smooth, corrosion resistant surface.
The LaserBond process uses precisely controlled energy from a high power laser to simultaneously melt a powdered metal feedstock and a very thin layer of the component being repaired. The feedstock material sets as a high performance coating that is metallurgically bonded or welded to the substrate. However, the low, precisely controlled heat input also means there is no risk of distortion or other undesirable metallurgical effects on the substrate. In this way, LaserBond can be used where welding is not suitable. In the case of the static seal areas of the chock legs, conventional welding would lead to distortion of the shape of the cylinder.
In addition, unlike welding, the LaserBond process results in very low dilution with the substrate, so high performance, corrosion resistant or very hard surfaces can be applied in a thin layer.
LaserBond allows components to be economically reclaimed and returned to service rather than being scrapped. It can also be used to provide “tailored” high performance surfaces, such as nickel alloys for corrosion resistance.
HVOF director Wayne Hooper said a LaserBond treated component would often last longer in the longwall environment than the original part.
HVOF’s LaserBond technology differs from its competitors in its ability to access hard to reach areas. For the Dendrobium overhaul, HVOF are reclaiming the corroded static seal area and damaged threads on the hard to reach inside of the leg supports.
HVOF also offer thermal spraying processes such as High Pressure HVOF, plasma and arc spraying to the longwall sector. These spraying systems can be used to reclaim components, providing coatings with a mechanical bond rather than a metallurgical bond to the substrate.
These thermal spray systems are suitable where the component is not subject to high impact loads and/or where corrosive attack under the sides of the coating may cause spallation. Typical examples are the repair of bearing journals or seal areas on gearbox and motor shafts, or restoration of critical flame path dimensions.
HVOF uses all of its processes, including LaserBond and the various thermal spray systems to assist a number of companies supplying the longwall mining sector with high performance surfaces for component reclamation and resistance to wear and corrosion.