Progressive Distributor - Selling housed bearing units

Selling housed bearing units

Helping customers decide when and how to select a housed unit in place of other bearing options

By Craig Etheridge

Putting a square peg in a round hole is never a good option. When it comes to inserting a shaft into a round bearing bore, however, there are many good options. One of the most reliable is housed (mounted) bearings.

This article identifies advantages, applications and options associated with housed bearings. The intent is to help create some distinction between options – thereby improving your ability to understand potential applications and make the right selection given those demands.

Which applications may be appropriate?
Mounted or housed units are the ideal friction management solution to attach a rotating shaft to a stationary object. This is particularly true when the shaft is not perfectly perpendicular with the mounting surface or when there is shaft expansion. Industries benefiting from these units include food and beverage, agriculture, fan and blower, textile and conveyor, printing and packaging, industrial equipment, consumer equipment and construction. Within these markets, applications range from combines and bottling machines to printing presses and pavers. Depending on material, sealing capabilities, size and design, housed units operate in harsh environments, with high heat and a range of duty applications.

What are the features and benefits?
Designed to maximize performance, a housed unit combines the bearing, housing, seal and locking system into one device for easy installation and operation. Installed in a sturdy housing, each bearing provides shaft support for radial, thrust or combination loads to reduce friction in applications where machined bearings are seated in equipment frames that are undesirable or impractical.

Available in a wide variety of designs and materials, the housings come in many shapes and sizes and allow for mounting shaft misalignment.

Housed units are available in a number of designs and materials including cast iron, powder metal, steel, polymer and rubber. Each material, based on the demands of the application, have unique advantages. Operational impact, space constraints, vibration, conductivity and presence of corrosives are common factors for consideration.

What are the standard design options?
Although designs can be customized to meet each customer’s unique needs, understanding the basic design is critical. First, mounted units are available for plain, roller and ball bearings.

A plain (journal) bearing mounting may consist of a bored housing with a bearing liner or a split housing with a solid or split internal bearing. Typical applications include heavy-duty fans, turbines and diesel generators.

On the other side, mounted roller bearings change depending on the rolling element. Typically, mounted ball bearings have spherical outer surfaces that compensate for angular shaft misalignment. A cylindrical outside diameter with a slip-fit in the mounting allows for axial freedom. Cylindrical, spherical and tapered roller bearings also are available as mounted units. Because roller bearings are often used for heavier duty applications than ball bearings, they may require more rigid locking to the shaft. Roller bearings are mounted to shafts by several methods, including some requiring special machining of the shaft (threads, key seat, tapers or multiple diameters), and locking collars, which require no special machining. The simplest types mount with a slip-fit collar and setscrew and are easy to assemble on site. Some are mounted with a sleeve, nut and washer (SNW).

Split roller-bearing assemblies are available for applications where replacement is difficult, such as with long shafts or shafts with tight-fitting components outside the bearing. The bearing components are split into two halves so they can be removed and assembled without disturbing other components on the shaft.

Considering the wide variety of options for plain or rolling element mounted units, the standard designs include pillow blocks (both solid and split-housing), flanged and cylindrical cartridges, and take-up units.

Pillow blocks
These are the most common type of housed units and have the plane of the mounting base parallel to the shaft. Pillow blocks are used on vertical or horizontal surfaces or on an inclined plane. Depending on the required base rigidity and available space, pillow blocks are available in two- and four-bolt mountings. It is important to work closely with the customer to understand the application and mounting requirements because the broad range of needs in the industrial marketplace makes it impossible for one size, shape or function to meet all needs.

Flanged units
Flanged units or cartridges are usually mounted on vertical surfaces where a shaft passes through the machine frame at a right angle. A four-bolt mounting is the most common. Where mounting is restricted, two- and three-bolt versions are available. Flanged units are supplied in multiple series (standard and heavy duty) and materials. Also, a complete line of pressed steel flanged units provides an economical solution for light-duty applications.

In addition to its basic design, a piloted, flanged cartridge-type bearing also is available and provides better mounting accuracy and more support than a basic unit. Cylindrical cartridges, like flanged cartridges, provide shaft support where the shaft axis is perpendicular to, and passes through, a machined housing.

Take-up units
This style is recommended where shaft alignment and belt tightening devices are required. The most common application is conveyors. Frames for take-up units provide side or top mounting. Complete take-up units with frames are available for both horizontal and vertical adjustments and top or side mounting.

Additional information
Learning and understanding housed units on behalf of your customers is important to the success of the application and the sale. In addition to understanding the basic style and concept of a housed unit, is it important to carefully assess the sealing options, locking devices and lubrication needs of a housed unit when making a recommendation. Designs vary between manufacturers so it is most important to talk to your customers, assess their needs, understand their application and then you can apply your knowledge of housed units to offer a solution.

Craig Etheridge is product manager – housed units, ball and wide inner ring, for the Timken Company. For more information on Timken Fafnir ball bearing housed units, contact your local Timken sales representative or visit www.timken.com.