The Secret to Smooth Operation for Thrust Ball Bearings

The secret is to select the correct thrust bearing for your application, install it correctly and apply proper maintenance. In this article we explore four configurations and how they are applied and in what applications. 

Types of Thrust Bearings

Thrust Bearings are normally Single Direction, Double Direction or Single Direction with Spherical support washer, or Double Direction Angular Contact Ball Thrust bearing. 

Single direction thrust bearing

Here is the typical single direction design with two grooved washers separated by balls in a retainer.

The common single direction thrust bearing is designed and intended to carry pure thrust loads only. Thrust ball bearings consist of two precision chrome steel washers, balls, and retainers. Thrust bearings can be supplied with flat washers or with ball grooves in the rings for increased capacity. 

Thrust bearings feature separable and interchangeable components. This feature enables simplified mounting and dismounting, and maintenance inspections. 

Single Direction Thrust bearings with sphered housing washers are used to accommodate initial misalignment. 

Shaft washers have a ground bore to enable an interference fit. The bore of the housing washer is turned and always larger than the shaft washer bore. 

Thrust ball bearings are classified into “flat seat” and “aligning seat” types, based on the shape of the housing washer (outer ring seat), and as single-direction or double-direction. Spherical and aligning seat washers help to provide tolerance for mounting errors. 

Here is the typical single direction design with two grooved washers separated by balls in a retainer. 

Single Direction thrust ball bearings like this one carry the thrust load in only one direction and have no radial load capability.

Applications Single Direction thrust ball bearings

Here are some examples of applications in which Single Direction thrust ball bearings are applied: 

• Industrial fans
• Industrial pumps 
• Metals 
• Industrial transmissions 
• Mining, mineral processing and cement 

Double Direction Thrust ball bearing 

As shown below the double direction thrust ball bearing has two sets of balls each essentially retaining the same design as the single direction version. The key to this design is the center ring has a ball groove on both sides, mounted on the shaft in such a fashion as to allow thrust loads to transmit in both directions. If an application has radial forces, then you can add a radial ball bearing into the design. 

The radial bearing can be mounted adjacent to the thrust bearing. In this case the housing ring of the thrust bearing is not held radially in the bearing housing. The ball set works to center the ring under load. A good example of this type of combination is the standard work lathe spindle. 

Most thrust ball bearings are mounted with a press fit into the housing. In this case the ring is prevented from taking an eccentric position which might easily happen especially with large bearings on horizontal shafts. It is necessary to machine the bearing housing so both bearing rings become concentric. 

As with all bearing applications, to ensure smooth operation you must select the most suitable bearing for the application. The installation and orientation must be correct 

Miniature and standard Thrust ball bearing load ratings are higher when the washers have raceway grooves. Raceway grooves reduce the contact between the shaft and the housing by suppressing the movement of the ball and retainer during rotation. 

Thrust bearings with Sphered Housing Washers 

1. Can accommodate initial misalignment 
2. Are available in both single and double direction designs 
3. Can be used together with a sphere seat washer adjacent to the housing washer or adjacent to a machine component manufactured with a sphere surface 

Appropriate sphered seat washers must be ordered separately (product tables). Depending on the bearing series, they have the basic designation U 2, U 3 or U 4 followed by a two-digit number, which identifies the size, e.g., sphered seat washer U 320 for bearing 53320). 

Double Direction Angular Contact Thrust Ball Bearings 

Double direction angular contact thrust ball bearings are designed to locate spindle shafts axially in both directions. These bearings are intended for mounting in combination with cylindrical roller bearings in the NN 30 K or N 10 K series in the same housing bore. This bearing combination simplifies machining of the housing bore. 

Double direction angular contact thrust ball bearings are manufactured with the same nominal bore size and outside diameter as corresponding cylindrical roller bearings. However, the outside diameter tolerance of the housing washers, combined with the housing bore diameter and geometric tolerances recommended for super-precision cylindrical roller bearings under light to normal load and rotating inner ring load (Seat tolerances for standard conditions) will result in an appropriate radial clearance in the housing bore. This clearance prevents radial loads from acting on the thrust bearing if its outer ring is not axially clamped in the housing. 

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