It is difficult to imagine a machine or engine running without fat, since most of the operations of machines and dynamic motors are carried out on bearings or bearings, who need a lubricant grease. Historically, the use of grease to lubricate wheels and axles took place immediately after the discovery of the wheel.
Composition of lubricating greases
The lubricating greases They essentially consist of a base oil (80 to 90%), a thickener (from 10 to 15%) and additives (from 5 to 10%). By far, the lithium greases dominate 75% of the current market, outperforming the calcium fats Y sodium. Although various types of grease may be required in an industrial plant, from an economic and logistical point of view, efforts have always been made to rationalize and minimize their quantity, which has led to the development of multipurpose greases.
In simple terms, a multipurpose lubricating grease is a product that combines the properties of two or more specialized greases and can be used in more than one application. For example, lithium greases can be applied both to the chassis and to the wheel bearings or bearings of transport vehicles. Traditionally, they have been used calcium fats for chassis and sodium fats for the bearings. Calcium greases have good water resistance, but poor performance at elevated temperatures. In contrast, sodium greases work better at high temperatures, but have less resistance to water.
High performance multipurpose greases
In modern machinery design and construction, equipment operates under more severe conditions in search of higher productivity and less downtime. Given these demands, it is difficult for lithium greases to satisfactorily meet these requirements. This is why superior products have been developed, such as lithium complex greases, calcium sulfonate, aluminum, aluminum complex, polyurea Y clay. However, due to their compatibility with most widely used lithium greases, lithium complex and calcium sulfonate greases appear to be the best candidates of these. high performance multipurpose greases.
The following table shows a comparison between the properties of lithium complex and calcium sulfonate multipurpose greases.
The only limitations of calcium sulfonate fats are its high cost and its lower pumpability, that is, the property that allows the lubricant to flow satisfactorily to and from the oil pump and adequately lubricate all moving components. However, recent technological advances have placed these fats on a par with lithium complex greases. A calcium sulfonate grease it can also be applied in a wider variety of industries, making it the preferred choice for a high performance multipurpose grease.
How to choose the right multipurpose lubricating grease
Given the wide range of characteristics that can exist in fats, it is best to first characterize the equipment and working conditions, and then select a grease to meet those conditions.
Equipment considerations and working conditions must take into account the size and type of machinery or motor, the load to which they are subjected, the working speed, the lubrication intervals Y weather conditions What temperature, humidity Y solid contaminants airborne. The selection of the grease base oil viscosity and the quantity/quality of polymers Y additives that it should contain.
Once these conditions are analyzed, the lubricating grease properties to choose. To do this, the following must be taken into account:
Grease base oil viscosity: Since this reduces under load because fluid friction produces heat that locally reduces the base oil viscosity, it is best to initially choose a grease whose base oil has the highest viscosity that the machine can tolerate, then progress to lower viscosities as the machine grows. consider high speed conditions.
base oil type: the synthetic base oils offer a wider range of operating temperatures than petroleum derived oils, but even within the family of synthetics there are variations. The paraffinic mineral oils often have a viscosity index (VI) of approximately 95. With few exceptions, synthetic base oils offer greater flexibility, with an IV of 120 to 175. The higher the VI, the wider the temperature range in which the product can function effectively.
Oxidation resistance: if the application is high temperature and difficult to access to the machine, then it is preferable to select a product with a base oil and thickener that can resist temperature and breakdown over extended lubrication intervals. Oxidation resistance is largely related to base oil selection, because the type of base oil has a significant influence on oxidation resistance. But the selection of thickener and the additive system are also important.
Behavior against wear: where there is a strong probability shock load Y extreme load, additives anti-wear and of extreme pressure they can be useful in supplementing the properties of the base oil to provide additional protection against wear and failure. Inorganic additives such as molybdenum, graphite and PTFE are often used in addition to chemical additives to provide mechanical load support.
Waterproof: applications where the process employs water-based coolants or process chemicals have multiple issues to address. Water resistance is characterized by the grease’s ability to withstand one of four water-related problems:
- resistance to washing: is the ability of the lubricant to remain in the bearing while running partially or fully submerged.
- Water absorption: is the ability of the grease to withstand the presence of water, either by absorption or by resisting washing and the diluting action of water.
- corrosion resistance: is the ability of the grease to prevent surface corrosion in the presence of water.
- Resistance to projections: is the capacity of the grease to resist displacement in the event of a direct impact of water on the greased surface.
Oxidation/corrosion resistance: As in the previous case, if the operating conditions are constantly exposed to water, process chemicals or high humidity, it is advisable to consider elements that provide additional resistance to corrosion. Some thickeners, such as aluminum, have good corrosion resistance. If the thickener is water resistant, such as lithium or calcium soaps, then rust and corrosion inhibitors are added to protect the surfaces from the action of water.
thickener type: Generally, the selection criteria of the type of thickener for the multipurpose grease are the compatibility with other used greases and the drop point that the thickener imparts to the fat. The lithium thickeners are compatible with other lithium thickened greases, lithium complex thickeners are compatible with lithium complex thickened greases, etc. Another peculiarity is that complex thickeners can be used for higher temperature ranges and up to 204 °C, with frequent relubrication. The thickener must remain stable over a wide enough temperature range so that an incidental spike in temperature will not dilute the grease or cause it to drip.
As we have seen, selecting a multipurpose lubricating grease meeting broad operational requirements requires an understanding of how the equipment works and how the grease will respond to those operational factors. A well-reasoned and planned selection of a multipurpose grease can be very beneficial in reducing complexity and risk of contamination, as well as improving overall lubrication conditions.
However, the reliability of the machine or engine must not be compromised by using a multipurpose grease in an application for which it is not suitable.
