Many engineer in industry increase the use of grease lubricant in many engineering product for particular feature of grease. Grease lubricants are relatively easy to manage and need only the simplest securing devices. For these reasons, grease is the most extensively used lubricant for rolling bearings. It is applied a bearing that is pre-sealed with grease (sealed/shield bearing), or if working with an unsealed bearing, fill the bearing and housing with the proper amount of grease, and replenish or change the grease regularly.
Types and characteristics of grease Lubricating grease are consisting of both a mineral oil base or a synthetic oil base. To this base a thickener and other additives are added. The properties of all greases are primarily determined by the kind of base oil employed and by the mixture of thickening agent and various additives. As performance characteristics of even the same type of grease will vary widely from brand to brand, it is needed to check the manufacturers' data when selecting a grease.
Base oil
Mineral oil or synthetics for example ester or ether oil are applied as the base of the grease. Mainly, the properties of any grease is identified by the properties of the base oil. Generally, greases using low viscosity base oil are best suited for low temperatures and high speeds; Grease using high-viscosity base oil has superior high-temperature and high-load characteristics.
Thickening agents
Thickening agents are compounded with base oils to maintain the semi-solid state of the grease. Thickening agents comprise of two types of bases, metallic soaps and non-soaps. Metallic soap thickeners involve: lithium, sodium, calcium, etc.
Non-soap base thickeners are divided into two groups; inorganic (silica gel, bentonite, etc. ) and organic (poly-urea, fluorocarbon, etc. ). The various special characteristics of a grease, such as limiting temperature range, mechanical stability, water resistance, etc. depend largely on the type of thickening agent used. For example, a sodium based grease is generally inadequate in water resistance components, while greases with bentone, poly-urea and other non-metallic soaps as the thickening agent are generally superior in high temperature properties.
Additives
Different additives are included to greases to improve various properties and efficiency. For example, there are anti-oxidents, high-pressure additives (EP additives), rust preventives, and anti-corrosives.
For bearings subject to heavy loads and/or shock loads, a grease featuring high-pressure additives should be used. For comparatively high operating temperatures or in job applications where the grease cannot be replenished for long time periods, a grease with an oxidation stabilizer is best to use.
Consistency
Consistency is an index that indicates hardness and fluidity of grease. The greater the number, the softer the grease is. The consistency of a grease is determined by the quantity of thickening agent used and the viscosity of the base oil. For the lubrication of rolling bearings, greases with the NLGI consistency numbers of 1, 2, and3 are used.
Mixing of greases
When greases of different kinds are mixed together, the consistency of the greases will change (frequently softer), the running temperature range will be lowered, and other changes in characteristics will occur. As a rule, grease should not be combined with grease of any other brand. However, if distinct greases must be mixed, at least greases with the same base oil and thickening agent need to be determined.
Types and characteristics of grease Lubricating grease are consisting of both a mineral oil base or a synthetic oil base. To this base a thickener and other additives are added. The properties of all greases are primarily determined by the kind of base oil employed and by the mixture of thickening agent and various additives. As performance characteristics of even the same type of grease will vary widely from brand to brand, it is needed to check the manufacturers' data when selecting a grease.
Base oil
Mineral oil or synthetics for example ester or ether oil are applied as the base of the grease. Mainly, the properties of any grease is identified by the properties of the base oil. Generally, greases using low viscosity base oil are best suited for low temperatures and high speeds; Grease using high-viscosity base oil has superior high-temperature and high-load characteristics.
Thickening agents
Thickening agents are compounded with base oils to maintain the semi-solid state of the grease. Thickening agents comprise of two types of bases, metallic soaps and non-soaps. Metallic soap thickeners involve: lithium, sodium, calcium, etc.
Non-soap base thickeners are divided into two groups; inorganic (silica gel, bentonite, etc. ) and organic (poly-urea, fluorocarbon, etc. ). The various special characteristics of a grease, such as limiting temperature range, mechanical stability, water resistance, etc. depend largely on the type of thickening agent used. For example, a sodium based grease is generally inadequate in water resistance components, while greases with bentone, poly-urea and other non-metallic soaps as the thickening agent are generally superior in high temperature properties.
Additives
Different additives are included to greases to improve various properties and efficiency. For example, there are anti-oxidents, high-pressure additives (EP additives), rust preventives, and anti-corrosives.
For bearings subject to heavy loads and/or shock loads, a grease featuring high-pressure additives should be used. For comparatively high operating temperatures or in job applications where the grease cannot be replenished for long time periods, a grease with an oxidation stabilizer is best to use.
Consistency
Consistency is an index that indicates hardness and fluidity of grease. The greater the number, the softer the grease is. The consistency of a grease is determined by the quantity of thickening agent used and the viscosity of the base oil. For the lubrication of rolling bearings, greases with the NLGI consistency numbers of 1, 2, and3 are used.
Mixing of greases
When greases of different kinds are mixed together, the consistency of the greases will change (frequently softer), the running temperature range will be lowered, and other changes in characteristics will occur. As a rule, grease should not be combined with grease of any other brand. However, if distinct greases must be mixed, at least greases with the same base oil and thickening agent need to be determined.
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