We were discussing the selection procedure of right grease for our application and components of grease with the help of our previous posts. Let us discuss the key properties of grease here in this post.
Grease
Grease is a semi-solid lubricant that is used to reduce friction and wear between two surfaces that are in relative motion.
Grease is a type of lubricant that is commonly used in a variety of applications to reduce friction, protect surfaces from wear and tear, and prevent corrosion.Â
Key properties of grease
Let us see some of the key properties of grease as mentioned below.
Consistency of grease
The consistency of grease means its degree of firmness or solidity. It is basically the measure of the grease's resistance to deformation or flow under pressure, temperature, or shear.Â
Consistency is basically one of the most important properties of grease lubricant, because it affects the ability of the grease to lubricate and protect moving parts efficiently. Grease consistency is classified on the basis of the National Lubricating Grease Institute (NLGI) scale, from 000 (very fluid) to 6 (very hard).Â
In general, higher consistency greases are basically used in applications where there are high loads, shock loads, or high temperatures. Lower consistency greases will be used in applications where there is low-temperature performance, low starting torque, or high-speed performance will be required.
The selection of grease consistency will be determined by the application's specific requirements and also the equipment manufacturer's i.e. OEM recommendations.Â
Dropping point of a greaseÂ
The dropping point is a very important property of a grease lubricant. It basically is the temperature at which the grease lubricant changes from a semi-solid state to a liquid state. It could be considered as the temperature at which the grease lubricant will no longer support its structure, and hence it starts to flow or drip.
The dropping point of a grease, as mentioned above, is an important property, because it indicates the ability of grease to maintain its lubricating properties and structure at high temperatures. Grease lubricants with high dropping points will be preferred for high-temperature applications, because they will not evaporate or break down at elevated temperatures.
The dropping point of a grease lubricant will be determined by ASTM D-2265 or any similar standard procedure. During the testing, a sample of grease lubricant will be heated in a standard apparatus and will be under observation in order to record the temperature at which the first drop falls from the test cup. The temperature at which it happens will be considered as the dropping point of grease.Â
The dropping point of a grease lubricant is basically reported on the product data sheet and is an important criteria during selecting a grease for high-temperature applications.
Water resistance of greaseÂ
Water resistance is also an important property of grease lubricant, because many industrial applications usually involve exposure to water or some other liquids or fluids. Grease lubricants that are not water-resistant will be washed away or break down, which will result in inefficient lubrication and will further cause the potential damage to equipment.
The water-resistance of grease lubricant is typically evaluated by a water washout test. It involves measurement of the amount of grease lubricant remaining on a surface after it has been exposed to a specific amount of water spray or immersion. This test is basically performed according to the standard ASTM D1264 or similar standard procedures.Â
Grease lubricants with good water resistance properties will retain their lubricating properties and will remain in place on the surface, even when subjected to water or other fluids. Grease lubricant will not wash away or break down, and it will continue to provide efficient lubrication and also protection to the equipment.
The level of water resistance needed for a specific application will be depending on the equipment's operating environment and the severity of the conditions. We can say that applications where there is frequent exposure to water or other fluids will certainly require grease lubricants with higher water-resistance properties.
Oxidation stability of greaseÂ
The oxidation stability of grease lubricant is a very important property that specifies the ability of the grease lubricant to resist the chemical breakdown due to exposure to oxygen over a period of time. When a grease lubricant is exposed to oxygen, it will react with the additives or grease base and will lead to the formation of acidic by-products and also the breakdown of the grease structure. This process is known as oxidation.
Oxidation stability is basically very important for grease lubricants used in applications where the equipment is exposed to long periods of storage or operates at elevated temperatures. In these applications, the grease lubricant will be subjected to more significant oxidative stress, and its performance can deteriorate quickly if it is not protected adequately.Â
The oxidation stability of grease lubricant is basically determined by several different test methods, for example ASTM D2893, ASTM D942, or ASTM D6185. These tests determine the amount of acid produced during the oxidation or the time needed for the grease lubricant to reach a specific level of oxidation.
Grease lubricant with high oxidation stability will surely resist breakdown and will remain efficient over a longer period of time. It will also help to avoid the formation of harmful deposits and will protect the equipment against corrosion and wear. We can say that synthetic and high-performance grease lubricants will provide better oxidation stability as compared with conventional mineral oil-based greases.
Load-carrying capacity of greaseÂ
Load carrying capacity is basically a very critical property of grease lubricants that refers to the ability of the grease lubricant to withstand pressure and support loads without losing its lubricating properties or breaking down. The load-carrying capacity of grease lubricant is critical in those applications where the equipment faces shock loads, high loads, or extreme pressures.Â
The load carrying capacity of grease lubricant is basically determined by different test methods, for example the Four-Ball EP Test (ASTM D2783) or the Timken OK Load Test (ASTM D2509). These tests determine the amount of load that the grease lubricant may support without failure.
The load-carrying capacity of a grease lubricant is influenced by a few factors, including the thickener type and concentration, the base oil viscosity, and the additives type and concentration.Â
Higher viscosity base oils and more concentrated thickeners basically lead to the higher load carrying capacities. Additives e.g. extreme pressure (EP) additives will also increase the load-carrying capacity of grease.
Grease lubricants with higher load-carrying capacities are preferred for those applications where shock loads or high loads are present, because they will help to protect the equipment from wear or damage. Hence, we can say that grease lubricants with high load-carrying capacities will be more expensive and also have more complex formulations as compared with standard greases.
Corrosion protection characteristics of greaseÂ
Corrosion protection is one of the most critical properties of the grease that basically refers to its capability to protect metal surfaces against corrosion. Corrosion may result from exposure to acids, moisture, salts, and also some other chemicals, and it may lead to equipment failure or damage.
Grease lubricants having good corrosion protection properties form a very useful protective film over the metal surfaces, that helps to avoid the metal from corroding. This film will act as a barrier between the metal and corrosive substances present, avoiding them from coming into contact with the surface of the metal.
The corrosion protection of grease lubricant is basically determined by different test methods, for example the ASTM D6138 test or the ASTM D1743 test. These tests determine the ability of the grease lubricant to protect metal surfaces from corrosion or rust.
The corrosion protection of a grease lubricant will be influenced by a few factors, including the base oil type and viscosity, the type and concentration of additives used, and the equipment operating conditions. Additives e.g. anti-wear agents, rust inhibitors, and antioxidants may improve the corrosion protection ability of grease.
Next Post-Â Functions of Grease lubricant
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