Grease According to The Practical Handbook of Lubrication
OK, MKTEF requested some information on grease types and thickners. Here's some information that I received in July at the AMSOIL University. AMSOIL provides dealers with training and written information that the dealers can use and pass on to folks to better educate them about lubricants and filtration. I have removed any reference to the AMSOIL products so that this information is informative, not advertising. That's what this forum is about is right, sharing information?
According to The Practical Handbook of Lubrication, grease is a lubricant composed of a fluid lubricant thickened with a material that contributes a degree of plasticity. With their high retentive properties, greases are used in applications where a continuous supply of fresh lubricant is not provided, and/or where an oil would not be retained. Many bearings not supplied by circulating or bath systems are lubricated with grease.
The three main components of any grease are: 1.) The base oil 2.) An additive package 3.) A thickener.
A simple way to understand how grease is made is by relating it to gravy. In making gravy, we start with the warm juices from the bottom of the roasting pan. Lets think of the juices as our base oil and any small meat pieces as additives. To this, flour is mixed in. The more flour added, the thicker the gravy becomes. One thing that is noted when the gravy cools, is that a small amount of the juice separates out. The same holds true for lubricating grease.
Soap Based Organic Thickeners - Soap thickeners can be enhanced by adding a complex agent, which converts the soap thickener to a soap salt complex thickener. These thickeners and greases are called complexes. When a grease is considered complex, it takes on enhanced performance attributes and include higher dropping points, better water-resistance and in some cases, improved low temperature performance.
Organic Non-Soap Based Thickeners- Polyureas are the most widely used non-soap organic thickener. Polyurea greases are characterized by good water resistance and good thermal stability. Because of their durability, polyurea greases are frequently used in sealed-for-life bearings which are filled during assembly, permanently sealed and operated without relubrication for the normal life for the bearing. They are also often found in electric motor bearings. Experience has shown that these greases have average mechanical stability and are not compatible with most other greases. These greases tend to be more costly than conventional soap-based greases because they require more sophisticated processing and their raw materials are more expensive. The special characteristics of greases based on inorganic thickeners – primarily clays and silica –
have made them useful in specific, demanding applications.
Clays (Bentone) are the most common inorganic thickening agents. Clay-based greases are functional over extremely wide temperature ranges because they lack melting points and resist other phase transformations. In general, clay based greases are only compatible with themselves.
Silica is a natural occurring substance commonly in the form of sand. However, a very fine form of silica thickens many fluids to form high melting point greases. Silica greases are inherently sensitive to water. These greases have a high tolerance for radiation and are often used for lubricating rolling element bearings in nuclear power plants.
The chart I posted in this forum is meant only to serve as a guideline for determining compatibility. For the purposes of changing products in the field, the compatibility of greases in question should be determined by testing.
NLGI definition of incompatibility: Two lubrication greases show incompatibility when a mixture of the products show physical properties or service performance which are markedly inferior to those of either of the greases before mixing. Fluid separation is the first sign of incompatibility. When ever in doubt regarding compatibility, always remove all traces of the old grease before applying new.
Like engine oils, grease additives are used to impart new or differing characteristics of a particular product. Oxidation inhibitors for example, are used mainly to improve the life expectancy of a lubricant at elevated temperatures. Their use reduces thickening of the oil and minimizes the formation of sludge and other deposits. Typical oxidation inhibitors are zinc dithiophosphates, hindered phenols, aromatic amines and sulfurized phenols.
Dyes are typically added mainly for identification purposes and to give a uniform appearance to a particular product. While certainly not a fool-proof method, dyes can aid in the differentiation between products, thus helping to avoid compatibility issues.
Anti-wear and extreme pressure additives are used to provide wear protection when the oil film alone is not capable of preventing contact between components. These additives work by providing a sacrificial wear surface or by changing the surface metallurgy of the components. Anti-wear additives or their reaction products form thin, tenacious films on loaded parts to prevent metal-to-metal contact. They assist in the reduction of friction, wear, scuffing and scoring under boundary lubrication conditions. Typical anti-wear additives are zinc dithiophosphate and polar molecules such as fatty oils, acids and esters. Extreme pressure additives are also commonly referred to as EP additives. Like anti-wear additives, they or their reaction products also form thin, tenacious films but on heavily loaded or shock loaded components. They may be persent in the form of solid additives such as molybdenum.
Greases are graded by their National Lubricating Grease Institute (NLGI) Consistency number – as indicated by the chart above. This system is designed to grade a particular grease according to its consistency…firmness or softness based upon worked penetration. The most commonly used consistency number is NLGI 2. Softer grades, such as 0 & 1, are often used for increased pumpability and low temperature application. Higher consistency numbers are used in highspeed bearings, worn parts or where leaks and sealing are particular concerns.
Greases can also be classified by a system that, again, has been developed by the NLGI. First used in 1991, this classification system relates to automotive applications (chassis & wheel bearings); but is widely recognized throughout the industry. The highest classifications that can be achieved are NLGI GC/LB, which carry the following requirements:
1) Penetration (consistency) 220-340 (#1 or #2 grease)
2) Dropping Point 428 F. Minimum
3) High Temperature bearing life is 80 hrs minimum
4) Water washout 15% max
5) Rust & Corrosion Pass
6) Oil Separation 6% max
7) Leakage 10 grams max
8) 4 Ball Wear .6 mm max
9) Fretting Wear 10 mg max
10) 4 Ball EP 200 kg min. LWI 30 min.
11) Low Temp Torque 15.5 n.m max
I hope this helps posting helps to answer some of your questions about greases, thickeners and compatibility. If there is anything else that I can assist you with, let me know and I'll get it posted or emailed to you. Thanks for the questions.
OK, MKTEF requested some information on grease types and thickners. Here's some information that I received in July at the AMSOIL University. AMSOIL provides dealers with training and written information that the dealers can use and pass on to folks to better educate them about lubricants and filtration. I have removed any reference to the AMSOIL products so that this information is informative, not advertising. That's what this forum is about is right, sharing information?
According to The Practical Handbook of Lubrication, grease is a lubricant composed of a fluid lubricant thickened with a material that contributes a degree of plasticity. With their high retentive properties, greases are used in applications where a continuous supply of fresh lubricant is not provided, and/or where an oil would not be retained. Many bearings not supplied by circulating or bath systems are lubricated with grease.
The three main components of any grease are: 1.) The base oil 2.) An additive package 3.) A thickener.
A simple way to understand how grease is made is by relating it to gravy. In making gravy, we start with the warm juices from the bottom of the roasting pan. Lets think of the juices as our base oil and any small meat pieces as additives. To this, flour is mixed in. The more flour added, the thicker the gravy becomes. One thing that is noted when the gravy cools, is that a small amount of the juice separates out. The same holds true for lubricating grease.
Soap Based Organic Thickeners - Soap thickeners can be enhanced by adding a complex agent, which converts the soap thickener to a soap salt complex thickener. These thickeners and greases are called complexes. When a grease is considered complex, it takes on enhanced performance attributes and include higher dropping points, better water-resistance and in some cases, improved low temperature performance.
Organic Non-Soap Based Thickeners- Polyureas are the most widely used non-soap organic thickener. Polyurea greases are characterized by good water resistance and good thermal stability. Because of their durability, polyurea greases are frequently used in sealed-for-life bearings which are filled during assembly, permanently sealed and operated without relubrication for the normal life for the bearing. They are also often found in electric motor bearings. Experience has shown that these greases have average mechanical stability and are not compatible with most other greases. These greases tend to be more costly than conventional soap-based greases because they require more sophisticated processing and their raw materials are more expensive. The special characteristics of greases based on inorganic thickeners – primarily clays and silica –
have made them useful in specific, demanding applications.
Clays (Bentone) are the most common inorganic thickening agents. Clay-based greases are functional over extremely wide temperature ranges because they lack melting points and resist other phase transformations. In general, clay based greases are only compatible with themselves.
Silica is a natural occurring substance commonly in the form of sand. However, a very fine form of silica thickens many fluids to form high melting point greases. Silica greases are inherently sensitive to water. These greases have a high tolerance for radiation and are often used for lubricating rolling element bearings in nuclear power plants.
The chart I posted in this forum is meant only to serve as a guideline for determining compatibility. For the purposes of changing products in the field, the compatibility of greases in question should be determined by testing.
NLGI definition of incompatibility: Two lubrication greases show incompatibility when a mixture of the products show physical properties or service performance which are markedly inferior to those of either of the greases before mixing. Fluid separation is the first sign of incompatibility. When ever in doubt regarding compatibility, always remove all traces of the old grease before applying new.
Like engine oils, grease additives are used to impart new or differing characteristics of a particular product. Oxidation inhibitors for example, are used mainly to improve the life expectancy of a lubricant at elevated temperatures. Their use reduces thickening of the oil and minimizes the formation of sludge and other deposits. Typical oxidation inhibitors are zinc dithiophosphates, hindered phenols, aromatic amines and sulfurized phenols.
Dyes are typically added mainly for identification purposes and to give a uniform appearance to a particular product. While certainly not a fool-proof method, dyes can aid in the differentiation between products, thus helping to avoid compatibility issues.
Anti-wear and extreme pressure additives are used to provide wear protection when the oil film alone is not capable of preventing contact between components. These additives work by providing a sacrificial wear surface or by changing the surface metallurgy of the components. Anti-wear additives or their reaction products form thin, tenacious films on loaded parts to prevent metal-to-metal contact. They assist in the reduction of friction, wear, scuffing and scoring under boundary lubrication conditions. Typical anti-wear additives are zinc dithiophosphate and polar molecules such as fatty oils, acids and esters. Extreme pressure additives are also commonly referred to as EP additives. Like anti-wear additives, they or their reaction products also form thin, tenacious films but on heavily loaded or shock loaded components. They may be persent in the form of solid additives such as molybdenum.
Greases are graded by their National Lubricating Grease Institute (NLGI) Consistency number – as indicated by the chart above. This system is designed to grade a particular grease according to its consistency…firmness or softness based upon worked penetration. The most commonly used consistency number is NLGI 2. Softer grades, such as 0 & 1, are often used for increased pumpability and low temperature application. Higher consistency numbers are used in highspeed bearings, worn parts or where leaks and sealing are particular concerns.
Greases can also be classified by a system that, again, has been developed by the NLGI. First used in 1991, this classification system relates to automotive applications (chassis & wheel bearings); but is widely recognized throughout the industry. The highest classifications that can be achieved are NLGI GC/LB, which carry the following requirements:
1) Penetration (consistency) 220-340 (#1 or #2 grease)
2) Dropping Point 428 F. Minimum
3) High Temperature bearing life is 80 hrs minimum
4) Water washout 15% max
5) Rust & Corrosion Pass
6) Oil Separation 6% max
7) Leakage 10 grams max
8) 4 Ball Wear .6 mm max
9) Fretting Wear 10 mg max
10) 4 Ball EP 200 kg min. LWI 30 min.
11) Low Temp Torque 15.5 n.m max
I hope this helps posting helps to answer some of your questions about greases, thickeners and compatibility. If there is anything else that I can assist you with, let me know and I'll get it posted or emailed to you. Thanks for the questions.
