When Westwind Air Bearings Ltd began marketing air lubricated
spindles capable of speeds in excess of 100,000 rpm in 1963, it was not
long before the company started receiving requests from both public and
private research centres to produce high speed rotating devices to meet
diverse special needs. These ranged from tiny, finger-tip size, infrared
choppers running on helium gas in skin cancer detectors to much larger
machines capable of testing centrifugally-arming artillery shell fuses
at speeds up to 30,000 rpm. One of the most challenging, as well as
long-lived projects, however, was undertaken under contract to Britain's
National Physical Laboratory (NPL). This involved developing machines
to rotate glass prisms at the highest possible speeds for use in laser
research.
The design of the NPL prism spinners posed a range of interesting problems for the Westwind engineers. The prisms were made of special quality glass, cut with high precision, about 2 cm long and of hexagonal cross section. The specification required that the prism rotate about its longitudinal axis, open at both ends to light rays incident throughout an unobstructed conical angle of 120 degrees. These limitations meant that the whole rotor, including turbine drive and air lubricated bearings, could be only marginally longer than the glass prism. The solution lay in locating the prism in a hollow metal cylinder, with a central turbine and symmetrical bearings on either side on the outer surface.
Another restriction on the design came from the requirement that the glass prism should not be unevenly stressed, either by the method of holding in the rotor or by the effect of rotation. This requirement was achieved only after testing alternative methods of holding and required specially shaping the ends of the prism. The final arrangement is shown schematically on the dust cover of the book The Design of Aerostatic Bearings published by the Machinery Publishing Co. Ltd. in November 1970.
The first prism spinner delivered to NPL ran at 80,000 rpm. Good results were reported and published in international scientific journals. Westwind were happy to receive a second order for this first model from a research laboratory in the USA.
NPL wanted to press on to higher speeds. Westwind pointed out that the maximum speed was limited by the mass of the glass prism and the physical dimensions of the bearings. By using a light alloy for the rotor, the rotating mass was kept as low as possible but the mass of the prism was fixed by the customer. The specification strictly limited the bearing parameters, leaving little scope for improvements in this area. NPL were told that significantly higher speeds would only be possible with a smaller prism.
In due course a smaller prism was produced and this was carried in a spinner at 130,000 rpm. Once again good results were reported and once again a second order came from the customer in the USA. The 1960s was an exciting decade for Westwind engineers with their gas bearings keeping them in touch with cutting-edge developments in many fields of science and technology. Hopefully, their efforts contributed to some of the advances in laser applications that were achieved at that time.
The design of the NPL prism spinners posed a range of interesting problems for the Westwind engineers. The prisms were made of special quality glass, cut with high precision, about 2 cm long and of hexagonal cross section. The specification required that the prism rotate about its longitudinal axis, open at both ends to light rays incident throughout an unobstructed conical angle of 120 degrees. These limitations meant that the whole rotor, including turbine drive and air lubricated bearings, could be only marginally longer than the glass prism. The solution lay in locating the prism in a hollow metal cylinder, with a central turbine and symmetrical bearings on either side on the outer surface.
Another restriction on the design came from the requirement that the glass prism should not be unevenly stressed, either by the method of holding in the rotor or by the effect of rotation. This requirement was achieved only after testing alternative methods of holding and required specially shaping the ends of the prism. The final arrangement is shown schematically on the dust cover of the book The Design of Aerostatic Bearings published by the Machinery Publishing Co. Ltd. in November 1970.
The first prism spinner delivered to NPL ran at 80,000 rpm. Good results were reported and published in international scientific journals. Westwind were happy to receive a second order for this first model from a research laboratory in the USA.
NPL wanted to press on to higher speeds. Westwind pointed out that the maximum speed was limited by the mass of the glass prism and the physical dimensions of the bearings. By using a light alloy for the rotor, the rotating mass was kept as low as possible but the mass of the prism was fixed by the customer. The specification strictly limited the bearing parameters, leaving little scope for improvements in this area. NPL were told that significantly higher speeds would only be possible with a smaller prism.
In due course a smaller prism was produced and this was carried in a spinner at 130,000 rpm. Once again good results were reported and once again a second order came from the customer in the USA. The 1960s was an exciting decade for Westwind engineers with their gas bearings keeping them in touch with cutting-edge developments in many fields of science and technology. Hopefully, their efforts contributed to some of the advances in laser applications that were achieved at that time.
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