Localized fretting that occurs when the rolling elements of a bearing vibrate or oscillate with small amplitude while pressed against the bearing race. The mechanism proceeds in stages: 1) asperities weld, are torn apart, and form wear particles, which may then be oxidized; 2) the wear particles are abrasive and accelerate wear. The resulting wear depressions appear similar to Brinell depressions obtained with static overloading. (See also Fretting). Note: Asperities are microscopic â€œbumpsâ€ or â€œpeaksâ€ on surfaces.
The ability of lubricating grease to flow under suction in a dispensing pump at a rate at least equal to pump delivery capacity. (Some lubricating greases do not feed satisfactorily and cause cavitation at the inlet to a dispensing pump. In such cases, feedability can often be improved by the use of follower plates).
Soap thickeners form microscopic fibers in lubricating grease. Some soaps crystallize in the form of threads, which are 20 or more times as long as they are thick. (Most soap fibers are microscopic in size, so that the grease appears smooth to the eye). Some greases have a fibrous appearance when fiber bundles are large enough to be seen by the unaided eye. The most common fibrous lubricating greases contain sodium based thickeners, although not all sodium base greases are fibrous. (See also Appearance and Texture).
An extremely small fiber, barely visible even at maximum magnification of an electron microscope. Fibrils may collect in bundles to form larger fibers.
A material added to a grease to increase bulk or density. Dependent on type and amount, a filler may contribute to, detract from, or have no effect on the lubricating properties of the grease. Examples of fillers are talc, pigments, and carbon black.
The ability of a film of lubricant to resist rupture due to load, speed, and temperature.
A plate fitted to the top surface of lubricating grease in a container and designed to assist delivery of grease to the inlet of the dispensing system.
A food grade lubricant is one suitable for use when incidental food contact may occur. It is given the H1 designation by a certifying body such as NSF International or InS Services. Food grade lubricants are formulated to minimize risks associated with unplanned trace contamination in food and beverages. Components for H1 lubricants often carry the HX1 designation.
In ASTM D2596, the applied load at which the lubricant can no longer prevent metal-to-metal contact, and the standard steel balls used in the test weld together.
Fretting corrosion occurs between a bearing inner ring and shaft or the outer ring and housing. The corrosion occurs at points where the fit is too loose. When the fit is too loose, the metal oxide film can be worn away, allowing oxygen from the air to attack the underlying metal. The build-up of corrosion products can cause severe bearing damage, including cracking of bearing rings.
A form of wear caused by vibratory or oscillatory motion of limited amplitude and characterized by the removal of fine particles from the rubbing surfaces. Fretting wear is often followed by localized oxidation, hence the term Friction Oxidation. In the case of ferrous metals, the oxidized wear particles are abrasive iron oxide (Fe2O3) that resemble rust, which has led to the term Fretting Corrosion. (See also False Brinelling). Note: Wear is damage that removes material from a surface.
The force resisting relative motion between two surfaces that are in contact.
See Fretting Wear.