Grease Lubrication Flashcards
Lubricating grease
Two components: fluid lubricant (mineral oil, 80-95%) and oil-insoluble thickening agent (usually soap, 2-15%).
Plus additives 0-10%
What affects the properties of grease?
The nature and amount of thickening agent
The characteristics of the mineral oil
Additives or not
Method used to produce the grease
Where is grease used?
Primarily where oil lubricant would not work:
- Where oil would easily leak out
- Where it would not properly seal the lubricated part
- Where it would not reach the point of application
What are the 7 advantages of grease?
- When grease is used, there is a decrease in dripping and spatter as the grease acts as an additional seal to reduce leakage
- Grease is useful for hard to reach points that require lubrication
- Use of grease may decrease the frequency of lubricant application
- Grease seals in the lubricant and seals out the contaminants such as dirt and water.
- Grease will seal the bearing from corrosive materials.
- Grease will cling to a part and not flow away like that.
- Grease has a better ability to suspend additives (e.g. graphite and moly) than mineral oil.
7 properties of grease
- Consistency
- Temperature range and load conditions
- Dropping point
- Miscibility
- Rust protection
- Mechanical stability and wear protection
- Sealing
- Consistency
Consistency is the stiffness of grease; dependent on the type and quality of thickener used, the operating temperature, and the type of mechanical conditions present
- Temperature range and load conditions
Must be suited to the temperature range in which the machine operates. At high operating temperatures, grease will soften and may leak out of the machine and at low temperatures they will become stiff and lubricated poorly. Heavy loads require greases that provide a strong lubricating oil film. If the load exceeds what the capability of the grease, then the metal surfaces of the bearing and journal may come into contact. If the surfaces contact, there is a high change that they will fuse or weld together momentarily, destroying the finish of the bearing and journal.
- Dropping point
Temperature at which the grease softens enough to flow; a factor for evaluating the high temperature capabilities of grease. Grease with a dropping point below the operating temperature would not provide proper lubrication since it would flow from the bearing surfaces. A dropping point above operating temperature may not guarantee proper lubrication since the grease may be too hard to properly form a film between the bearings and the journal.
- Miscibility
Also known as compatibility, the ability to be mixed with other types of greases. When different types of greases are mixed, there is a possibility of extreme softening, lots of leakage, and subsequent loss of lubricant. This is a concern when packing bearing with grease. The bearing should be thoroughly cleaned of old grease to ensure that the new grease will not be contaminated.
- Rust protection
Important when there is a risk of water contamination. It is not enough for a grease to resist being washed away by water but it must also prevent rusting of the metallic parts. Rust inhibitors are often included in grease formulation to enhance the natural rust protecting properties of grease.
- Mechanical stability and wear protection
Certain greases have a tendency to soften during mechanical working and this will result in excessive leakage. Therefore in machinery that experiences high vibration, it is important to choose grease with good mechanical stability. Wear results from excessive metal to metal contact, either from the rolling or sliding action of the parts. The combination of lubricating oil and the metallic soaps used to make grease gives good anti-wear properties, however additional additives may be used to increase this capability
- Sealing
It is important for a bearing or gear assembly to be protected from the environment so that no contaminants or moisture will enter the rotating parts. Grease can only provide this protection if it remains secure within the parts
7 types of grease
- Sodium based grease
- Barium soap grease
- Lithium soap grease
- Calcium soap grease
- Aluminum soap grease
- Multi-purpose grease
- Synthetic grease
- Sodium based grease
Often used as general-purpose greases, and because of a higher dropping point, often used to lubricate machine parts operating near heat. Made with lighter oils are used for ball and roller bearing lubricants. Because of their working stability and intermediate melting point, they are used for lubricating wheel bearings and for general-purpose industrial applications. Example: rough, heaving bearings operating at low speeds
- Barium soap grease
General-purpose type greases, valued for their ability to work over a wide temperature range. Chosen for a high variety of jobs and for nearly all types of bearing lubricants. High soap content, so less suitable for use at low temperatures and in very high-speed applications
- Lithium soap grease
Handles extremes of temperatures quite well, highly suitable for both high and low temperature applications. Those used at higher temperatures have a different composition than those used at a lower temperature, the difference being the viscosity of the mineral oil used. Very good stability, water resistance and easy to pump
- Calcium soap grease
Also called lime-soap grease, most commonly used grease and usually relatively inexpensive. Commonly used as axle grease, water pump grease and for general machinery applications. Isn’t suited for applications with temperatures above 160F because the water content will dry out and the soap and oil will separate.
Will not dissolve in water.
Not suited for high speed bearings.
- Aluminum soap grease
Special-purpose lubricants. Very sticky making them perfect for applications requiring surface lubrication
- Multi-purpose grease
Combine the properties of two or more specialized greases and permits the use of a single type of grease for a variety of applications. It is possible to replace as many as 6 specialized greases with a single multi-purpose grease and get better results at the same time. Most have a soap base of barium, lithium or calcium complex.
High melting point, operate well at continuous temperatures of 250F or more. Good resistance to water and exceptional stability
- Synthetic grease
Lubricant of choice for extreme temperatures, loads and speeds. Becoming a more viable option for bearings and other components facing medium-duty operating requirements.
Increased popularity because:
1. Availability of new products and formulations (additional viscosities and consistencies, even come in green or biodegradable varieties)
2. Affordability (cost has not increased as rapidly as conventional petroleum-based greases, reducing the cost differential between the two categories)
Thickeners
Made of a metallic substance, such as lithium or calcium. Can be formulated with additives to meet extreme pressures, excessive vibration, or other challenging requirements.
Conventional greases employ a petroleum-based product.
Synthetic greases use a synthetic lubricant such as silicone and can withstand temperature extremes and maintain lubricating effectiveness better than conventional greases
4 specialized roles of synthetic greases
- High temperatures
- Low temperatures and low torque
- High speeds
- Outdoor and harsh environments
- High temperatures
Conventional petroleum-based greases may soften at high temperatures, leading to lubricant leakage. The upper temperature limit for conventional greases is appox 285 F / 140 C. However, synthetic greases exhibit better mechanical stability in these conditions. As a result, they are traditionally used in automotive engine and other automotive applications
- Low temperatures and low torque
Synthetic greases excel at the opposite extreme, performing in low temperature, low torque applications. A typical example is wheel bearings, which must rotate smoothly even at low temperatures. In contract, conventional grease can become stiff and lose effectiveness at low temperatures. This can prevent bearing rolling elements from rotating especially at start up and under light loads
- High speeds
Machine tool spindles, industrial fans and other high-speed applications often require synthetic greases, which run quieter than standard greases at high speeds
- Outdoor and harsh environments
Because of their temperature and performance properties, synthetic greases are often employed in equipment operating in outdoor conditions. They can also be specially formulated to withstand exposure to excessive moisture.
