Bearing Technical Information – Load Ratings

Measuring Operating PV
The load carrying ability of the plastic bearing material is listed as a PV (pressure/velocity) factor.

P      =   Listed as pounds per square inch over the projected bearing area.
V      =   The velocity in feet per minute of the shaft at the surface.
PV   =   P x V

Example:

Shaft OD:           5/8”
Bearing Length: 1-1/32”
Bearing Load: 35 lbs.
Shaft RPM: 120

P (PSI)
Bearing Load / (Bearing Dia.) x (Bearing Length)
=  35 lbs. / .625” x 1-1/32”
= 54.3 PSI

V (FPM)
= .2618 x (Shaft Dia.) x (Shaft RPM)
= .2618 x .625” x 120 RPM
= 19.635

PV
= V (FPM) x P (PSI)
= 19.635 x 54.3
= 1066.2

Use the Material “PV Table” to see if the selected material is within the PV limits.

Note:  The PV value of any material may be affected by many variables, such as low or high temperatures, shock loads, shaft material, hardness of finish, etc.  Lubrication can increase the capacity as much as 100%.

Plastic bearings must be designed around their own abilities and characteristics, then proven by actual performance.  Field testing under actual conditions is strongly recommended.

Clearance:
Plastic bearing clearances should be much greater than those recommended for standard precision steel bearings.  The additional clearance is required to compensate for expansion or contraction of the plastic material due to frictional heat or cold environments which can cause significant changes in the bearing dimensions.

Lubrication:
The use of lubricants can decrease the static and dynamic coefficients of friction and permit the plastic materials to operate at higher PV’s  than a bearing that is not lubricated.  Most plastics listed in the selection table on page TP 01 do not require lubrication but some lubricant will usually increase the material performance.  In most cases water will provide sufficient lubrication during bearing operation.  It is good practice to apply a light coating of grease to the bore of the bearing during the installation of the bearing.

Shaft Hardness and Shaft Material:
Shaft hardness and material is a major factor in the operation of the plastic bearings.  The bearing and shaft will last much longer as the hardness increases and the finish is smoother.

Chemical Resistance Data:
Due to the number factors involved in material selection for chemical resistance information please consult factory.  You will need to supply the chemical name, concentration and operating temperatures for evaluation.

Disclaimer
All statements, technical information and recommendations contained in this publication are presented in good faith, based upon tests believed to be reliable and practical field experience.  The reader is cautioned, however, that BNB Industries, Inc. cannot guarantee the accuracy or completeness of this information, and it is the customer’s responsibility to determine the suitability of these products in any given application.  BNB Industries, Inc. recommends actual field testing of the material and application under actual conditions for evaluating suitability for use.