The NTN Corporation (hereafter, NTN) has succeeded in developing a "New MQCJ Oil Jet System For Machine Tool Spindle Angular Ball Bearings". This new commercial use product is designed for machine tools and delivers the world's fastest operating speed. At the Japan International Machine Tool Fair (JIMTOF2006) held on November 1st, actual machine tool cutting was performed using a machining center on display whose spindle was assembled with bearings using this lubrication method. NTN calls this new lubrication method "MQCJ" an abbreviation for "Minimum Quantity and Cooling Jet" to show that this is different from conventional lubrication method
In recent years, the main spindle in multipurpose machine tools and machining centers has been required to operate at higher speeds in order to boost machining efficiency and improve the surface quality of the machined piece. The usual method for reaching high speeds is to force-feed lubricating oil to internal bearings in large amounts via jet lubrication and under-race lubrication. However this method has the problem that supplying large quantities of lubricating oil increases the agitation resistance in the oil.
NTN solved this problem by injecting lubricating oil into the inner race, supplying a small but optimal amount to the bearing internally by using most of the remaining oil in the new "MQCJ lubrication method" to cool the inner races. This method also helped attain the world's fastest speed at a fixed pre-pressure load of 5 million dmn and index pre-load of 3.6 million dmn while also reducing moving part wear loss to figures equivalent to air-oil lubrication.
In machine tool spindles, the heat emitted from the motor and the heat from the bearings are usually cooled separately by outer cylinder cooling from a section in the external housing. The lubricating mechanism developed by NTN however jointly cools both the bearing lubricating oil and the outer cylinder cooling oil without requiring separate lubricating oil supply systems. It is effective in reducing costs.
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