Bearings - 2011-10-14
The drive to cut costs prompted ever-increasing machining volumes and therefore higher cutting speeds. A new sphere of application was born: high-speed cutting (HSC). This meant it was necessary to develop corresponding cutting and clamping tools, cooling lubricants and more. Special attention had to be paid to the bearing assembly for spindles – the heart of any machine tool spindle.
The job done by these components, which have developed into the top of the range of bearings, is absolutely crucial for smooth operations. Based on the requirements to absorb both radial and axial forces at high levels of rigidity – with running accuracy equivalent to just 1/50th of the diameter of a human hair – sets of angular-contact ball bearings have become established as the most common solution.
In this application, the rolling elements are subject to peripheral velocities of up to 600 km/h. Supplying the working surfaces with constant, reliable lubrication is a major challenge. Without it, the bearings would be unable to operate.
NSK’s newly developed Robust Shot series of angular-contact ball bearings complies with these requirements in full. Conventional oil-air lubrication methods attempt to inject lubricant into the side of the bearing using a nozzle. However, this is made difficult by the air vortex generated around the bearing by rotating parts such as the cage and the balls. The injection speed has to be much higher than that of the air vortex for the lubricating oil to make it into the bearing at all.
The Robust Shot series of bearings avoids this problem altogether. The lubricating oil is routed straight to a point right by the working surfaces on the outer ring via a circular groove and a through-hole in the outer ring. This guarantees a reliable, even supply of lubricant, enabling speeds of over 3 million n x dm to be achieved. In addition to this, two O-rings in the outer ring ensure that the through-hole in the housing is securely sealed. This means that any fit can be selected to suit the application.
As there is no need for injection nozzles between the bearings, spindle designers can realise very compact spindles. Since the Robust Shot angular-contact ball bearings have the same dimensions as grease-lubricated bearings, it is easier to make modular use of the spindle components for a range of different spindle series. This enhances economic efficiency from a spindle manufacturer’s point of view.
The dimensions of the Robust Shot bearings also comply with DIN-ISO standards and match conventional bearings, making it easy to retrofit NSK bearings in existing constructions.
NSK has been one of the world’s leading manufacturers of high-precision bearings for many years. A large number of major German machine tool manufacturers also choose NSK as a supplier and development partner. With its Robust Shot series of bearings, the company has now further expanded its range of high-performance bearings for the machine tool industry.
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