Bearings

Designers beat the biggest bearings test of all

One of the biggest challenges ever faced by a bearing designer was the support systems for the 880mm diameter solid aluminium alloy wheels used in the ThrustSSC for its supersonic land-speed record attempt.

The SKF bearings team applied expertise gained from high-speed machine tool design for the front wheels, and from Formula One cars for the rear wheels.

It came up with two wheel bearing designs to cope with the imbalance from front and rear loadings – two thirds of the vehicle’s 10.4 tonnes weight is carried on the front axle. High G-forces from deceleration by parachute would break up conventional axle or spindle bearings.

Instead, the team developed a three-part wheel and bearing housing assembly that depends on accurate alignment and fit. Overheating is avoided by a floating-cartridge design.

To meet load demand, each front wheel has two sets of two ceramic bearings in a face-to-face arrangement. These eight assemblies are universally matched with similar pressure centres, so each pair acts as a single bearing. Each rear wheel has two bearing assemblies with a back-to-back configuration for stability.

Spacers with adjustable shimming allow the bearings to be preloaded for stiffness. Ceramic is tougher than steel but less prone to sticking from friction, so it is used in all the ball bearings.

Balls were chosen instead of taper rollers because of the ceramic content. And as ceramic is 60% less dense than steel, it produces lower centrifugal forces and less wear on bearing races.

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Higher speeds without chatter are being claimed by NSK for highly accurate ballscrew positioning systems based on a new damped, hollow shaft construction.

The design overcomes vibration and noise caused by resonance at the natural frequency of the screw shaft as it rotates.

The way to beat vibration at higher rotational speeds has been to increase the natural frequency of the shaft by increasing its diameter, or by providing extra support along its span.

NSK’s solution to the demand for higher speed is to increase the damping capacity of the screw shaft.

Faster ballscrews are needed typically in laser equipment and chip mounting machines.

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Ina is introducing an `economic’ bearing series for machinery.

PE versions of its existing bearing types are made to less stringent manufacturing tolerances, says the company, but provide the same load capacity, rigidity, limiting speed and ease of assembly as the standard item at lower cost.

Axial angular contact ball bearings are the first to be offered with flange mounting as an option.

Available for shaft diameters from 12mm to 60mm, the SKLF/SKLN series has a run-out tolerance of P5 to DIN 620 compared with P4 for the standard bearing.

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Water lubricated rubber-lined shaft bearings have been chosen by GEC-Alsthom subsidiary, Bergeron, to provide environmentally-friendly lubrication on specialist vertical water pumps.

The Silverline bearings work by encouraging a film of water to form between the revolving shaft and the bearing surface, eliminating the need for oil lubrication, which is a pollutant.

They will be fitted to pumps with bore sizes from 15-240mm.

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Bearings developed by Cross & Morse for the brewing and beverage manufacturing industries have a thin, dense coating of chrome applied to the races to improve wearability and provide up to 15 times better corrosion resistance than standard bearings.

Beverage Bearings also have three fluoropolymer coatings on the cast iron housings which resist peeling, abrasion and cleaned solvents up to pH 11 acidity, and prolonged exposure to moisture.

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Self-aligning cam roller units from linear motion specialist Star compensate for uneven mounting surfaces or other alignment errors.

Units are available in 20 and 25mm sizes. A U-type cam roller guide provides quiet, smooth linear motion in high-end flying optic and camera imaging applications.

Less engineered, more cost-sensitive units are also available.

Customers for standard products can now deal directly through its new Star Direct service.

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