 Bearings
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We offer a large variety of Rollers and Bearings with Expedient Deliveries. We have included the following General
Information for your use. Please feel free to Contact Us if we can assist you with your requirements.
Types of Bearings
Bearings can be divided into 4 groups: Non-precision, semi-precision, precision and journal bearings.
Non-Precision Bearings
These bearings have hardened steel balls and raceways. They are often referred to as "full compliment," meaning they do not have a ball
retainer. The outer race is either stamped or machined. Non-precision bearings are used where speeds and loads are moderate.
Semi-Precision Bearings
These bearings have hardened steel balls and raceways along with a ball retainer or "cage" to separate the balls.
These bearings are suitable for speeds up to 400 RPM.
Precision Bearings
These bearings have hardened and ground balls, raceways and ball retainers. They are normally shielded and sealed.
Precision bearings are suitable for speeds above 400 RPM and for heavier loads.
Journal Bearings
These bearings consist of a housing and a bushing. They have no balls or seals. The housing is generally plastic or wood. Journal
bearings are used in washdown or similar conditions.
Bearing Components
Races
Races are the inner and outer surfaces that are in contact with the balls. Non-precision and semi-precision bearings have a machined
inner race and a machined or stamped outer race. Both races are hardened steel. Precision bearings have inner and outer races made of higher
quality steel which are machined, hardened and ground to a fine finish.
Balls
Balls are the medium between the inner and outer race which allows the outer race to rotate while the inner race is held stationary.
Balls in non-precision and semi-precision bearings are hardened steel. Balls in precision bearings are hardened chrome alloy steel.
Ball Retainer
A ball retainer, or "cage," separates the balls from each other, minimizing noise and contact friction between balls.
This enables higher operating speeds.
Shields and Seals
Shields and seals help keep contaminants out of the bearing. A shield is generally made of steel. it "shields"
contaminants from falling directly onto the balls. A shield can be used by itself or in conjunction
with a seal, in which case, the shield will also protect the seal from damage. Seals are available in teflon, felt, rubber, nylon and mylar.
Seals affixed to the outer race also contact the inner race. They create a slight frictional drag, but seal out contaminants while helping to
retain grease within the bearing. Standard seals are suitable for temperatures up to 225° F.
Lubrication
Non-precision and semi-precision bearings are available with three lubrication options: oiled, grease packed or regreasable.
Precision bearings are standard with grease.
Oiled
These bearings are generally used in gravity applications requiring a low coefficient of friction. The temperature range of
standard oil is 0° to 200° F.
Grease Packed
These bearings are generally used in powered applications. The temperature range of standard grease is -10° to
+255° F. They are also suitable for higher humidity applications.
Regreasable
These bearings share the same features as grease packed bearings and, in addition, are designed to accept more grease through a grease fitting
located on the end of the axle. Regreasable bearings have either a drilled inner race or an extended back closure.
Shot Guards 
When excessive dirt and grit exist, such as in a foundry, shot guards may be used to help keep out contaminants. Shot guards slide over the
shaft and fit up against the bearing. They are used only on bearings without flanges and where the tube is counter bored so the bearing and shot guard
can be recessed slightly inside the tube. Shot guards are made of steel.
Tolerance on Bearing Body Diameter
The tolerance on body diameter dimensions is generally +/- .006. This is only a guideline. Bearing dimensions should be
verified with a micrometer.
Bearing Load Rating and Life
Non-precision, semi-precision and precision bearings are compared on the basis of a given load rating over a specified period of time or
number of revolutions. Material type of the races and balls, ground or unground races, RPM, load type and duration, lubrication, temperature and
humidity all play a role in the life of a bearing. Non-precision bearings are rated differently then semi-precision and precision bearings. Journal
bearings are rated based on a PV factor which is rated pressure times velocity, dependent upon material type.
Non-Precision Bearings
Load ratings of non-precision bearings are difficult to predict because of the nature of their design; stamped outer races, carbon steel
balls, unground raceways, etc... They have, however, proven to be successful for use in conveyors where loads and speeds are moderate.
They are also an economical alternative to a precision bearing. Most bearing manufacturers use the following CEMA equation to determine a load
rating based on a minimum life of 1 million revolutions (Basic Dynamic Load Rating).
| C = f Z2/3 D1.8 |
| Where: |
| C |
= |
Basic Dynamic Load Rating |
| f |
= |
A factor which depends on the geometry of the bearing components,
the accuracy to which the bearing parts are made and the material |
| Z |
= |
The number of balls |
| D |
= |
The ball diameter in inches |
Minimum life refers to the number of hours or revolutions that 90 percent of bearings under the rated load will
survive. Load ratings for non-precision bearings are based on the manufacturer's ratings.
Semi-Precision and Precision Bearings
Load ratings for precision bearings are easier to predict because the bearings are constructed with closer tolerance control, ground races,
uniform ball loading and quality bearing steel. Semi-precision bearings do not have ground races or bearing type steel, but do have a ball
retainer and are rated like precision bearings. Load ratings for semi-precision and precision bearings are based on a minimum life of 3
million revolutions. To calculate the minimum life for loads other than the rated load, use the following equation:
| L10 = ( C / Pe ) 3 x
3 million revolutions |
| Where: |
| L10 |
= |
Minimum Life |
| C |
= |
Rated Capacity |
| Pe |
= |
Applied Radial Load |
Journal Bearings
These bearings are rated on a PV factor where "P" represents the total load over the projected area of the bearing I.D. and "V" represents
the surface velocity of the shaft in FPM. This PV factor is a "rule-of-thumb" for limiting the amount of heat that is generated per
square inch of bearing surface. It is not an exact value because of variations in the coefficient of friciton and the heat dissipation rate.
PV factors for several materials and a formula to predict bearing load ratings are as follows:
| PV Factor |
| Delrin® or Celcon® |
3000 |
| Nylatron® GS |
4000 |
| Teflon filled Acetal |
8000 |
| Teflon filled Nylon |
10,000 |
| Wood |
12,000 |
| P V = ( W / L x D ) x V |
| Where: |
| D |
= |
Shaft Diameter |
| L |
= |
Bearing Length |
| V |
= |
Shaft Velocity |
| W |
= |
Applied Radial Load |
| PV |
= |
PV Factor from above |
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