Find out more about Industrial greases
Grease are substances whose density varies from semi-solid to solid.
In addition, the basic ingredient of industrial greases is either mineral oil or synthetic oil.
In addition, a thickener and additives are added to it to satisfy optimum lubrication.
Thus the additives present in a grease are corrosion inhibitors, anti-wear and oxidation agents, or even adhesion additives. But those are also the “extreme pressure” and water repellents, or the metal deactivators.
Advantages of grease over oils
Therefore using a grease rather than an oil provides multiple benefits.
In particular, the grease stays in place compared to the flowing oil. In this way, this leads to a decrease in the frequency of lubrication of the bearings. In addition, grease requires practically no monitoring (for example: “lifetime sealed” bearings). This allows a simplified design of the bearing frame.
Note that the grease prevents access to impurities such as humidity, steam, dust, etc.
In summary, greases offer both better protection against water and abrasives, but also good adhesion. In addition, the greases ensure good sealing, but also good accessibility to the lubrication points of the bearings. In particular, greases guarantee performance under extreme conditions such as temperature, pressure, shock loads and low speeds or immediate departures.
Finally, grease lead to the use of solid additives.
It is the addition of a thickener to each of the greases that is the differentiating element.
In summary there are two types of greases. On the one hand, fats without soap and, on the other hand, fats with soap.
In general the industry uses very little grease without soap. Indeed these are clay-based. Consequently, these clay fats are developed for high temperature applications.
Grease with soap is the addition of thickened oils to metallic soap.
In fact these soaps give the grease a semi-solid consistency.
The different soaps or thickeners
Overall grease with soap breaks down into three categories of soaps. These are simple, mixed and complex soaps.
So simple soap grease is made up of a fatty acid (a paraffin substance extracted from animal fats or vegetable oils) and a base (metal hydroxide). The common types of metal hydroxide used in the manufacture of simple soap greases are lithium, calcium, aluminum, barium and sodium.
Whereas mixed soap grease is made from a fatty acid and two bases (for example: lithium and calcium). In other words, it has better properties than simple soap grease. This is why it is the best compromise between quality and price.
Finally, the complex soap grease combines two fatty acids reacted with a base. These greases generally offer very good performance at high temperatures and against oxidation. The common types are aluminum, calcium and lithium complexes.
First of all, it must be said that the types of metallic soaps most used in industry are calcium soap, sodium soap, aluminum soap, lithium soap, barium soap and complex soaps.
For starters, calcium soap is general purpose and has good water resistance. It has low efficiency at high temperatures (<60 ° C) and needs a certain amount of water to remain stable.
Sodium soap, on the other hand, has low water resistance and is soluble in hot water. Its operating temperature is above 70 ° C.
On the other hand the aluminum soap is very sticky and is designed for special applications. It provides good rust protection. Its resistance to water is low.
Then the lithium soap is suitable for multiple uses. Its water resistance is medium. On the other hand, it offers good resistance to humidity and withstands temperatures up to 150 ° C.
Finally, barium soap offers good resistance to water but its performance is low at low temperatures. It withstands a continuous operating temperature of 135 ° C. Complex soaps have a high dropping point and good efficiency at high temperatures.
Classification of greases :
The hardness (consistency) is used to classify greases.
This is the NLGI grade from the National Lubricating Grease Institute. This determines the degree of firmness of a grease.
It is measured using a “penetrometer”
Very soft grease (NLGI = 000) has a high degree of penetration
A very hard grease, a low degree of penetration (NLGI = 6).
Here are some examples :
NLGI 2 consistency greases are widely used
NLGI 3 grade greases are often used in large bearings rotating at high speeds (electric motors).
NLGI 0 and NLGI 2 greases are used in automatic central distribution systems.
NLGI 000 and NLGI 00 greases are only used at polar temperatures.
Selection and application of greases
The most important factors to consider when choosing a lubricating grease are:
- types of machines,
- the type and size of the bearing if applicable,
- the operating temperature (viscosity of the base oil),
- charging conditions,
- the speed range,
- operating conditions (vibration, centrifugal force, pumping, etc.),
- cooling conditions,
- the effectiveness of the seal and the external environment (presence of water, acid or other substances).
It is best not to mix the kinds of fats. The reason is that some fats are incompatible. For example, greases with sodium soap, barium soap and aluminum complex are incompatible with all other greases.
When selecting a grease, it is recommended to consult:
the machinery manufacturer's maintenance manual or the grease manufacturers' lubrication guides.
Synthesis on industrial greases
- The main advantages of using a grease are that it stays in place, that it prevents access of impurities, that it offers better protection against water and abrasives and that it allows the use of solid additives.
- There are two types of grease : grease without soap and fat with soap. The industry uses very little soap-free greases which are clay based.
- Greases with soap are divided into three categories: simple, mixed and complex.
- The types of metallic soaps most used in industry are calcium soap, sodium soap, aluminum soap, lithium soap, barium soap and complex soaps.
- The properties of a grease are consistency, stability against shearing, oil separation, stability at high temperature, resistance to oxidation, the ability to be pumped at low temperature, anti properties - wear and “extreme pressure”, water resistance and corrosion resistance.
- The hardness (consistency) of the fats makes it possible to classify them. It is the NLGI grade of the National Lubricating Grease Institute which determines the degree of firmness of a grease.
- When selecting a grease, it is recommended to consult the maintenance manual of the machinery manufacturer or the lubrication guides of the grease manufacturers.