The Main Factors that needs to be considering while selection of greases are “LETS”.

L-Load

E-Environment

T-Temperature

S-Speed

Grease is made up of three main components: a base oil, a thickener and additives that enhance performance. This combination enables grease to be “squeezed” between surfaces, gradually releasing oil into the areas requiring lubrication — not unlike squeezing a sponge to release fluids held in suspension. The greater the sheer force applied to the grease, the faster the oil and additives are released.

The viscosity of the base oil used in a particular grease plays a role in determining the grease’s load carrying ability and how well it will perform under extreme pressure and temperature. Load carrying ability ratings are reported on data sheets as the four-ball weld load and the Timken “OK” load. The higher the numbers, the greater the load carrying capacity, and the greater the grease’s ability to withstand heavy loads without breaking down.

Heavy-duty construction-type greases generally have higher oil viscosities, making them suited to applications such as hinge pins, dump beds, bucket pins and pivot points subjected to higher weight loads. The heavier the load, generally the higher the viscosity of base oil needed to minimize metal-to-metal contact. Lighter oil viscosity, multipurpose greases can be more easily squeezed out between surfaces. However, they are capable of working in a broad spectrum of climates.

Grease is classified according to National Lubricating Grease Institute (NLGI) grades, which rate its thickness or fluidity — in other words, how well it will stay in the joint. The difference between grades largely depends on how much soap, or thickener, is added to the base oil.

The soap in grease essentially acts as a holding agent that traps droplets of oil. When force is applied to the grease, the soap releases the oil to lubricate the metal surfaces. As such, the type of soap is a determining factor in grease selection. Although many different thickeners can be used, the most common are lithium or lithium complex soaps, which are generally fairly compatible with each other. Lithium complex greases tend to be the most popular due to their broader high- and low-temperature properties, water washout resistance and stability. Other common thickener types include a poly urea-based soap, which provides good high-temperature and water resistance, as well as aluminium complex or calcium soap, both of which offer high resistance to water washout. However, these thickeners tend to have compatibility issues with lithium and lithium complex-based products.

Note that the Grease Thickener compatibility needs to be tested Before shifting from existing grease. The table below shows the compatibility of the Grease Thickeners.

The thickness of a grease can be determined by the NLGI grade. The higher the grade number, the greater the amount of soap used, and the greater the tendency for the grease to stay put in heavily loaded components. The most fluid grease, Grade 000, has a consistency similar to molasses or heavy gear oil, while a Grade 6 resembles a bar of soap. The grades used most often in the construction industry fall into the 0 to 2 range. Grade 0 grease is commonly used in auto lube systems where the grease has to be fluid enough to circulate through several feet of hose. Grade 1 grease is thicker and can be a good choice for cold climates in winter, since it maintains sufficient pump ability when temperatures plummet. Grade 2 is typically used in the summer in colder climates and in warmer climates year round. It provides a good balance between pumpability and cling ability.

It’s also important to be aware of how the dropping point of a particular grease applies to your application. The dropping point is the temperature at which the grease becomes too fluid to remain in place. Although the dropping point listed on a product information sheet might lead you to believe you can run the grease at this temperature, this is not the case. Lithium complex greases tend to have higher dropping points than straight lithium greases, making them better suited for mixed fleet applications.

An additive is any substance added to a lubricant to modify its properties. A number of different additive types may be used in grease to enhance desirable properties and suppress those that are less desirable. Typical examples include antioxidants, corrosion inhibitors and anti-wear and extreme pressure (EP) additives. One of the most common additives found in grease is molybdenum disulphide, or moly. This additive enhances durability by creating a more solid lubricating film around heavily loaded joints. It also provides an added layer of protection by staying in place even if the grease is forced out of the joint. Corrosion and rust inhibitors do as their name implies — protect against corrosion and rust. Greases with these properties are especially beneficial in wet and/or harsh work environments. Other additive types, such as synthetic polymers and tackifiers, tend to resist water washout and spray-off, while still others are designed to provide added temperature resistance. Some additives don’t necessarily affect grease performance, but help to make managing a lubrication program easier. Dye is one such ingredient. While the colour of the grease has no effect on performance, it can be used to quickly identify the grease being used, if it is coming out of the application and if the grease is dirty/contaminated.

Because there’s more to grease than what it seems, discuss your specific needs with your lubricant supplier. They can help you select the types of grease that will provide the appropriate combination of properties and performance for your equipment and its applications.

Content Taken From :

1. https://www.machinerylubrication.com/Read/1865/grease-compatibility

2. https://www.forconstructionpros.com/equipment/fleet-maintenance/oils-lubricants-greases/article/12091270/proper-grease-selection-is-not-as-simple-as-it-seems

3. https://www.efficientplantmag.com/2009/09/grease-basics-part-ii-selection-a-applications/

Lubrication professionals often become very familiar with the base oil viscosity of their lubricants. After all, viscosity is the most important property of a base oil. Baselines for incoming oils are set and the health of the lubricant is monitored based on viscosity alone. However, there is more to lubricants than just viscosity. It’s crucial to understand the role of additives and their function(s) within the lubricant.
Lubricant additives are organic or inorganic compounds dissolved or suspended as solids in oil. They typically range between 0.1 to 30 percent of the oil volume, depending on the machine.

Additives have three basic roles:

• Enhance existing base oil properties with antioxidants, corrosion inhibitors, anti-foam agents and demulsifying agents.
• Suppress undesirable base oil properties with pour-point depressants and viscosity index (VI) improvers.
• Impart new properties to base oils with extreme pressure (EP) additives, detergents, metal deactivators and tackiness agents.

When using oil additives, more is not always better. As more additive is blended into the oil, sometimes there isn’t any more benefit gained, and at times the performance actually deteriorates. In other cases, the performance of the additive doesn’t improve, but the duration of service does improve.
In addition, increasing the percentage of a certain additive may improve one property of an oil while at the same time degrade another. When the specified concentrations of additives become unbalanced, overall oil quality can also be affected. Some additives compete with each other for the same space on a metal surface. If a high concentration of an anti-wear agent is added to the oil, the corrosion inhibitor may become less effective. The result may be an increase in corrosion-related problems.

These include the following general types of additives:

1. Viscosity Index Improvers:

Viscosity index improvers are very large polymer additives that partially prevent the oil from thinning out (losing viscosity) as the temperature increases.  These additives are used extensively when blending multi-grade engine oils such as SAE 5W-30 or SAE 15W-40. They are also responsible for better oil flow at low temperatures, resulting in reduction in wear and improved fuel economy.  In addition, VI improvers are used to achieve high-VI hydraulic and gear oils for improved start-up and lubrication at low temperatures.

2. Anti-wear (AW) Agents:

These additives are typically used to protect machine parts from wear and loss of metal during boundary lubrication conditions.  They are polar additives that attach to frictional metal surfaces. They react chemically with the metal surfaces when metal-to-metal contact occurs in conditions of mixed and boundary lubrication. They are activated by the heat of contact to form a film that minimizes wear.  They also help protect the base oil from oxidation and the metal from damage by corrosive acids.

3. Extreme Pressure (EP) Additives:

These additives are more chemically aggressive than AW additives.  They react chemically with metal (iron) surfaces to form a sacrificial surface film that prevents the welding and seizure of opposing asperities caused by metal-to-metal contact (adhesive wear).  They are activated at high loads and by the high contact temperatures that are created.  They are typically used in gear oils and give those oils that unique, strong sulphur smell.  These additives usually contain sulphur and phosphorus compounds.

They can be corrosive toward yellow metals, especially at higher temperatures, and therefore should not be used in worm gear and similar applications where copper-based metals are used.  Some chlorine-based EP additives exist but are rarely used due to corrosion concerns

4. Detergents:

Detergents perform two functions. They help to keep hot metal components free of deposits (clean) and neutralize acids that form in the oil. Detergents are primarily used in engine oils and are alkaline or basic in nature.

5. Dispersants:

Dispersants are mainly found in engine oil with detergents to help keep engines clean and free of deposits. The main function of dispersants is to keep particles of diesel engine soot finely dispersed or suspended in the oil. The objective is to keep the contaminant suspended and not allow it to agglomerate in the oil so that it will minimize damage and can be carried out of the engine during an oil change.

6. Anti-foaming Agents:

The chemicals in this additive group possess low interfacial tension, which weakens the oil bubble wall and allows the foam bubbles to burst more readily. They have an indirect effect on oxidation by reducing the amount of air-oil contact.

7. Friction Modifiers:

Friction modifiers are typically used in engine oils and automatic transmission fluids to alter the friction between engine and transmission components.  In engines, the emphasis is on lowering friction to improve fuel economy. In transmissions, the focus is on improving the engagement of the clutch materials. Friction modifiers can be thought of as anti-wear additives for lower loads that are not activated by contact temperatures.

8. Pour Point Depressants:

The pour point of an oil is approximately the lowest temperature at which an oil will remain fluid.  Wax crystals that form in paraffinic mineral oils crystallize (become solid) at low temperatures.  The solid crystals form a lattice network that inhibits the remaining liquid oil from flowing. The additives in this group reduce the size of the wax crystals in the oil and their interaction with each other, allowing the oil to continue to flow at low temperatures.

9. Demulsifiers:

Demulsifier additives prevent the formation of a stable oil-water mixture or an emulsion by changing the interfacial tension of the oil so that water will coalesce and separate more readily from the oil.  This is an important characteristic for lubricants exposed to steam or water so that free water can settle out and be easily drained off at a reservoir.

10. Biocides:

Biocides are often added to water-based lubricants to control the growth of bacteria.

Content Taken From : https://www.machinerylubrication.com/Read/31107/oil-lubricant-additives#:~:text=Additives%20have%20three%20basic%20roles,viscosity%20index%20(VI)%20improvers..

There are three components that form lubricating grease. These components are oil, thickener and additives. The base oil and additive package are the major components in grease formulations, and as such, exert considerable influence on the behaviour of the grease. The thickener is often referred to as a sponge that holds the lubricant (base oil plus additives).

Base Oil

Most greases produced today use mineral oil as their fluid components. These mineral oil-based greases typically provide satisfactory performance in most industrial applications. In temperature extremes (low or high), a grease that utilizes a synthetic base oil will provide better stability.

Thickener

The thickener is a material that, in combination with the selected lubricant, will produce the solid to semifluid structure. The primary type of thickener used in current grease is metallic soap. These soaps include lithium, aluminium, clay, polyurea, sodium and calcium. Lately, complex thickener-type greases are gaining popularity. They are being selected because of their high dropping points and excellent load-carrying abilities.

Complex greases are made by combining the conventional metallic soap with a complexing agent. The most widely used complex grease is lithium based. Non-soap thickeners are also gaining popularity in special applications such as high-temperature environments. There is a misconception however, that even though the thickener may be able to withstand the high temperatures, the base oil will oxidize quickly at elevated temperatures, thus requiring a frequent re-lube interval.

Additives

Additives can play several roles in a lubricating grease. These primarily include enhancing the existing desirable properties, suppressing the existing undesirable properties, and imparting new properties. The most common additives are oxidation and rust inhibitors, extreme pressure, anti-wear, and friction-reducing agents. In addition to these additives, boundary lubricants such as molybdenum di-sulphide (moly) or graphite may be suspended in the grease to reduce friction and wear without adverse chemical reactions to the metal surfaces during heavy loading and slow speeds.

Content Taken From : https://www.machinerylubrication.com/Read/1352/grease-basics

Two main types of industrial lubricants are oils and greases.  Both aim to lubricate equipment and prevent damage that happens from metal to metal contact.  However, there are a few key differences in how they are used. To put it simply, grease is oil mixed with a thickener and other additives.  These thickeners impact grease capability and compatibility.  They also impact grease consistency, which is measured in NLGI (National Lubricating Grease Institute) Grades.  The NLGI grade is a measure of a grease’s consistency.  The higher the grade, the thicker the grease.

At the most basic level, oil and grease both perform the same general function: to prevent metal-on-metal contact and protect your equipment from wear. However, there are many ways components move and the kind of environment they endure inside your equipment. Greases are engineered to stay in place and provide a longer lasting barrier between metal components, such as wheel-bearings. Greases also act as an excellent seal, protecting moving parts that are exposed to the elements, and act as a welcome mat for dirt and debris waiting to contaminate your equipment. Greases therefore seal out harmful contaminants, keeping your equipment protected for maximum performance and minimum downtime.
Benefits of Oil and Grease:
Grease :

1. Does not require a lubrication circulating system, i.e., pump, filter, sump, piping
2. Better for leakage control
3. Provides better seals against contaminants
4. Can remain in equipment longer
5. Lowers the risk of a dry start
6. Worn seals and connectors can retain grease better, which lowers the risk of lubricant starvation and leakage
7. Many grease lubricated bearings can operate for years without the need to repack the bearings.
8. A better choice where a continuous supply of oil cannot be maintained
9. Less consumption of the lubricant over time

Oil : 

1. Easier to drain and replace oil lubricants.
2. Oiled bearing life can last longer than grease lubricated bearings.
3. Easier to control the amount of lubricant to use
4. Cleaner than grease due to capacity to carry away contaminants
5. Better cooling properties
6. Larger volume available allows for more available additive performance
7. Avoids the problems associated with proper re-greasing at proper frequencies
8. Less energy consumption during operation
9. Better cold start properties

Consider the above points when selecting an oil or grease to lubricate your equipment.

Content Taken From : https://www.cenex.com/about/cenex-information/cenexperts-blog-page/agriculture-and-farming/Grease-vs-Oil#:~:text=The%20biggest%20difference%20setting%20grease,syrup%2Dlike%20consistency%20of%20oil.

There are several factors to consider when selecting the right industrial lubricant. A manufacturer’s recommendation is a great starting point, but it doesn’t have to be the only option. Most manuals are written for ideal conditions, but these guidelines don’t address the real environment in which the equipment is being used. It’s best to use an industrial lubricant that meets the specific demands of your operation. There are new advancements in lubrication that could prove to be more reliable or extend equipment life further if you are willing to do the research and understand the basics.

We recommend customers understand the “4 C’s to Lubrication” :

• Correct Technology
• Correct Quantity
• Correct Frequency
• Correct Procedures

Correct Lubrication Technology

• Temperature determines lubricant base oil type
• Speed determines viscosity required (at operating temperature)
• Load, vibration, and moisture determine the additive package

There are three (3) classifications of a lubricant:

1. Fluid (Liquid)
2. Semi-Solid (Grease)
3. Solids (Dry)

Correct Lubrication Quantity and Frequency
It’s important to understand the damage that over or under greasing can cause your equipment. Manually re-greasing too often and/or with the incorrect amount, or automatically lubricating with the incorrect lubricant can cause harm. Whether you choose an automated system or manual, the goal should be to provide the right type of lubricant, in the right amount, at the right time. This approach allows for a constant level of protection.
Frequent bearing failure is a prime example of damage caused by over or under greasing. According to the American Bearing Manufacturers Association (ABMA), improper or insufficient lubrication is the cause of 64% of bearing failures. It is important to understand the various parameters surrounding the operation of any given bearing to properly select re-lubrication intervals. Over greasing will lead to increased operating temperatures, resulting in energy losses and eventual bearing failure. Similarly, using too little grease will not allow the grease to properly carry the load applied to it, which will also result in bearing failure.

Correct Lubrication Procedures
Once the correct lubrication has been determined, procedures should be put in place to maintain a lubrication program. This will ensure that the proper lubrication procedures for each piece of equipment throughout the plant. These factors should include :

• Reviewing storage and handling conditions
• Maintaining records of the correct lubricant type for each application
• Determining the proper amount of lubrication per day and frequency of re-lubrication

Content taken From – https://blog.chesterton.com/lubrication-maintenance/best-practices-industrial-lubrication/