lubrication

Lubricant Types | Oils and Base Fluids | Lubrication Methods | Speed Factor | Lube Specs

Lubricant Types

Oil is the basic lubricant for ball bearings. NHBB offers both petroleum-based and synthetic oils such as diesters, silicone polymers and fluorinated compounds. In general, diesters have better low temperature properties, lower volatility and better temperature/viscosity characteristics than petroleum-based oils. Silicones and fluorinated compounds possess even lower volatility and wider temperature/viscosity properties.

Grease is an oil to which a thickener has been added to prevent migration from the lubrication site, resulting in longer life. It is used in situations where frequent replenishment of the lubricant is undesirable or impossible. The operative properties of grease depend almost wholly on the choice of base oil. Other factors being equal, the use of grease instead of oil results in higher starting and running torques and can limit the bearing to lower speeds.

Solid film lubricants are any non-fluids used to prevent wear and reduce friction. They can range from simple sacrificial cages to graphite powder and ion sputtering. Each type must be engineered for the specific application.

Solid film lubricants have definite advantages. They are very useful in areas of temperature extremes, vacuum, radiation, pressure or harsh environments where conventional lubricants would fail. In addition, these lubricants do not deteriorate in storage.

Oils and Base Fluids

Petroleum Lubricants:

• Excellent load carrying abilities
• Moderate temperature range (-25° to 250°F)
• Greases with petroleum oil bases have high dN capability (recommended for light to heavy loads and moderate to high speeds)

Synthetic Lubricants:

• Wide temperature range (-65° to 350°F)
• Resist oxidation
• Less film strength than petroleum oils

Silicone Lubricants:

• Wide temperature range (-100° to 400°F)
• Less film strength than diesters
• Tend to migrate

Perfluorinated Polyether:

• Wide temperature range (-112° to 400°)
• Stable at high temperatures
• Chemically inert
• Low vapor pressure

Lubrication Methods

Centrifuging an oil-lubricated bearing removes excess oil and leaves only a very thin film on all surfaces. This method is used on very low torque bearings and can be specified for critical applications.

Vacuum impregnation, used with ball bearings containing porous cages, forces lubricant into the pores, using the cage as an oil reservoir. When this method is used with a greased bearing, its purpose is to prevent the cage material from leaching oil from the lubricant. Normally, the base oil of the grease is used in the cage to prevent incompatibility.

Grease packing approximately 1/4 to 1/3 of a ball bearing’s internal free volume is one of the most common methods of lubrication. Grease quantity can be controlled by the use of special lubrication equipment.

Grease plating consists of mixing a quantity of grease and solvent to the desired consistency, lubricating the bearing with this mixture, then evaporating the solvent at a moderate temperature, leaving a thin film of grease on raceways and balls.

Operating Speed

To determine whether a particular bearing will operate satisfactorily at the required speed, multiply that bearing's value (Nmax/fn) by the proper factor taken from the fn vs Cage table shown. Note that the table takes into account lubricant and cage type. When petroleum or synthetic ester oils are used, the maximum speed Nmax is dictated by the ball cage material and design or centrifugal ball loads rather than by the lubricant.

For full ball complement types, the listed Nmax values apply regardless of lubricant type or whether the inner ring or outer ring rotates. For speed limit values Nmax, the Nmax/fn values shown in the product listings must be multiplied by the fn values tabulated as shown.

Table of fn vs Cage, Lubricant Types and Ring Rotating

Speed Factor

The maximum usable operating speed of a grease lubricant is dependent on the type of base oil. The speed factor is a function of the bore of the bearing (d) in millimeters (mm) and the speed of the bearing (N) in revolutions per minute (RPM) where:

dN = d (bearing bore, mm) x N (RPM)

Lubricant Specifications

We have included a table of Commercial and Military Lubricants and their recommended uses. When ball bearings are ordered without a specified lubricant, it is the policy of NHBB to lubricate with MIL-L-6085 oil.

Company standard lubricants are LO1 Winsor Lube L-245X oil and LG68 Royco 27 grease. The standard quantity of oil varies with bearing size, but is approximately one drop (3–6mg) per bearing up to R-2 size and two drops (6–12mg) for larger sizes. The standard quantity of grease is 30% (±5%) of the bearing’s internal free volume.

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