What Is Grease? Industrial and automotive greases are blends consisting of liquid oil and other additives, plus a soap thickener. The oil and additives do the lubricating; the soap thickener simply holds them in place.
Grease typically does not provide the cooling, flushing and cleaning capabilities offered by liquid lubricants. However, grease keeps the lubricant from draining away and forms an effective barrier to help keep contaminants out of bearing housings and related components.
Common thickeners used in automotive and industrial greases are calcium, sodium, lithium, aluminum, barium, polyurea, and bentonite. Complexes of these thickeners are also commonly used.
The most common grease in the automotive and fleet market is a lithium or lithium complex grease. Lithium complex grease normally offers a higher usable temperature range. The buttery smooth texture and resistance to water washout have made lithium complex grease the industry standard.
Grease-vs-Oil: When the specifications or the application allow a choice as to whether to use a liquid oil or a grease, use the liquid oil and add 15% MILITEC-1 Metal Conditioner by weight for ultimate lubrication. However, in applications where liquid oil is inappropriate, as in a sealed bearing housing, use MILITEC-1 GREASE, or use another high-quality grease of the recommended NLGI grade, thoroughly blended with 15% MILITEC-1 Metal Conditioner by weight.
Grease Compatibility: Sometimes mixing different greases is acceptable. As a rule, greases of the same soap base are compatible. If some question exists concerning the compatibility of the new grease with the one being replaced, there are two choices:
Grease incompatibility is revealed by a change in the consistency of the mixed greases. Most commonly, the mixture of incompatible greases will become soft and runny, but occasionally they will harden instead. In either case, grease incompatibility will cause the resulting mix to be out of parameter. The only solution is to flush and reapply.
Solid Lubricants In Grease: Sometimes solid lubricants (in the form of powders) are added to grease. These powdered solids include polytetrafluoroethylene (PTFE), graphite, molybdenum disulfide, zinc oxide, and others. These powders act as friction modifiers for the grease. Because the grease is thick, the solid particles can be suspended and uniformly distributed throughout the grease.
Grease Characteristics and Terminology:
General: Greases possess many of the same qualities that are common to liquid lubricants. The additives used in the oil portion of the grease improve the natural characteristics and provide new, desirable characteristics. Greases typically contain extreme pressure compounds (EP), anti-wear additives, anti-corrosion packages, and tackifiers.
Tackiness: An often-misunderstood characteristic is the tackiness of grease. Grease must be cohesive (stick to itself) and adhesive (stick to metal surfaces). Too much of either characteristic is undesirable.
The ability to produce a long strand of grease when stretched between thumb and forefinger does not necessarily mean the product is a quality grease. Very tacky grease can offer too much resistance to movement because of its extreme stickiness. This can actually be very detrimental. It can increase internal friction to the point where reduced efficiency and increased wear are the result.
Dropping Point: The dropping point of grease is the temperature at which the grease starts to melt. This is normally above the maximum recommended usable temperature for the grease.
Oil Separation: Oil separation, also called "bleeding," is often a concern to maintenance personnel. Separation is usually noticed when oil forms on the surface of the grease in storage. While excessive bleeding can be a concern, slight bleeding is regarded by some as a desirable characteristic for enhanced lubricating ability, specifically in roller element bearings. Stirring the top few inches of the grease prior to use will eliminate most of the free oil.
Viscosity: A vital characteristic of oil is its viscosity. For grease, viscosity is equivalent to hardness, which is determined by measuring with a penetrometer. This apparatus drops a weighted cone into a prepared sample of grease. The depth of cone penetration into the grease determines its hardness, or NLGI Grade.
NLGI: The National Lubricating Grease Institute (NLGI) has established a grading system for grease hardness. The grades range from a semi-fluid "triple ought " (000) grease to a rating of six, which is considered a block grease.
The usually specified hardness of chassis grease is NLGI 2. During the winter in certain climates, a NLGI 1 or 0 is sometimes recommended.
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GREASE - MSDS
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