Bearing Design Features of Kaydon Corporation Bearings-Large Diameter Bearings

Whether used in heavy-duty off-road vehicles, precision medical equipment or high accuracy military radars, large diameter Kaydon bearings share many design features. There are important differences however, which often dictate the optimal bearing selection for a given application. These pages outline the primary features of each bearing type.

Turntable bearing advantages

Over the years demands have increased for equipment economy, performance, and reliability. As a result, four-point and eight-point contact ball bearings have replaced the older, less efficient hook rollers and kingpost assemblies. Turntable bearings provide smooth rotation and high radial, thrust and moment load capacity in a compact dimensional envelope. With a Kaydon turntable bearing there is no need for a center shaft or kingpost, so the bearing center space is open and available for hydraulic piping or conduit runs.

Additionally, turntable bearings incorporate many special features such as integral gearing, through-drilled or tapped mounting holes and contact seals. These features simplify the job of the equipment designer, lower manufacturing costs, and facilitate system maintenance. Importance of proper selection, installation and use. Turntable bearing applications are typified by heavy loading and slow, intermittent or partial rotation.

Bearing failure is therefore seldom due to classic rolling contact fatigue. In other words, calculated bearing life is not usually a major consideration in turntable applications, especially in construction equipment.

Turntable bearings are usually selected on the basis of static load capacity, suitable integral gearing, and other special features. Turntable bearing failure is often the result of practical considerations not covered by classical rolling bearing theory—such as non-uniform support structure design, lack of lubrication, improper selection or application of fasteners, overloading beyond equipment specifications, or other abuses.

The purpose of this manual is to provide guidelines for system design and turntable bearing application, and to caution equipment designers and users of one principle: Large-diameter bearings are not commodity products. Each bearing is a custom design or a custom application of an existing bearing design. In either case, the bearing manufacturer should be involved in the design stage.

Four-point contact ball bearings

Four-point contact ball bearings can accept combinations of radial, thrust and moment loads. This is possible due to the unusual geometry of the raceways (or ball grooves). The ball groove in each race has two radii that are larger than the ball radius. The centers of these two radii are offset from the center of the ball radius. This results in a “Gothic Arch” configuration in each of the raceway grooves, making it possible for the two grooves to contact the ball at four points.

High thrust and moment capacity is obtained in a four-point contact ball bearing by its deep raceway grooves. These allow high initial contact angles between the balls and raceways and increase the thrust and moment capacity. The deep grooves also accommodate the contact angle increase which results from ring stretch and ball deflection under load.

Precision grinding of raceways is necessary to control accuracy of contact angles, close ball to raceway conformity, diametral clearance and raceway finish. These design features, along with proper material selection, assure the proper function of the four-point contact ball bearing.

Eight-point contact ball bearings

The eight-point contact ball bearing was developed by Kaydon to satisfy requirements for maximum load capacity within a given envelope, especially in larger size bearings.

As shown in our diagrams, the eight-point contact ball bearing is an annular bearing with two rows of balls. The unique feature of this bearing lies in the utilization of the “Gothic Arch” or four-point contact internal geometry in both rows.

Functionally, the bearing may be considered to be two single row, four-point contact bearings with adjacent faces.

The four points of contact permit each row of balls to accept radial, axial, or moment loads, or a combination of the three. Through precise grinding techniques, raceways are closely matched for parallelism and size, providing a high degree of load sharing between rows. Test results have confirmed that the second row of balls provides and additional 80% capacity over that provided by a single row.

Biangular roller bearings

Biangular roller (cross roller) bearings will support the same types of load as the four-point and eight-point contact ball bearings.

To accomplish this universal load carrying capability, the bearing is designed with V-groove raceways, providing two roller paths in each ring. The rollers have a length slightly less than their diameter and are positioned so that adjacent rollers contact different sets of raceways, with the axes at right angles to each other. Positioned in this manner the rollers transmit load along perpendicular sets of 45° contacts. The action of the bearing under various types of loading is thus analogous to that of the four-point contact ball bearing.

While a roller of length and diameter approximating a given diameter of ball has more load carrying capacity, the static thrust and moment capacity of a biangular roller bearing is less than that of a four-point contact ball bearing of comparable size. The reason for this is that only alternate rollers resist a uni-directional axial load. In some cases, capacity in one axial direction may be increased by orienting more rollers along one axis than the other, with a resulting decrease in capacity in the opposite direction.

The main advantages of biangular roller bearings are greater stiffness and consequent superior spring rate, as well as tolerance of mounting surface irregularities and resulting deflections. When deflection under load must be minimized, or when bearing turning torque is critical this bearing may be given preference over a four-point contact ball bearing.

WireX® inserted raceway bearings

WireX® bearings are generally used in applications requiring maximum weight reduction and corrosion resistance. They are generally custom designed to support specific combinations of radial, thrust and moment loads. Gear teeth can be cut in the inner or outer ring, and bolt holes provided for mounting.

The bearing rings have machined seats to position the inserted wire raceways, which are held in place by bearing loads transmitted through the rolling elements. The rolling elements (usually rollers) and wires are usually made of stainless steel.

Bearing rings can be made of many different materials. When aluminum is used the complete bearing can be made of corrosion resistant material and may result in weight savings of up to 50%. The use of aluminum rings may also eliminate thermal expansion problems when the bearing is mounted to aluminum structures.

Another advantage of WireX® bearings is their high tolerance of non-rigid and out-of-flat mounting structures. Irregularities can be accommodated by the free movement of the wire inserts in their circular seats.

WireX® bearings can often be rebuilt— a substantial savings when compared to complete bearing replacement.

Three-row roller bearings

Three-row roller bearings offer the highest capacity, using three separate rows of rollers. The top and bottom rows absorb thrust loading, each row in the opposite direction, and operate together to handle moment loading. The intermediate row handles radial loads. Because each row is independent, frictional torque is low.

Plastic ball bearings

Large diameter bearings with plastic balls are provided for light duty, low load applications. Raceways are V-grooves machined in aluminum or steel bearing rings.