Even the ancient Egyptians in the ⅩⅠⅤ century BC used a mixture of olive oil with lime to lubricate the axes of wooden chariots. It was this composition that was the prototype of modern multicomponent greases, which are effectively used in many nodes of modern technology to reduce the wear of rubbing parts.
In the modern world, every car owner perfectly understands that grease is one of the main components that effectively affects the safe and long-term operation of both a simple and complex mechanism with friction surfaces. Therefore, knowledge of the composition and range of lubricating products is the key to their successful application.
What are they made of?
The most common type of lubricant is grease, which is a mixture of thickeners dissolved in a liquid medium. Three component systems are considered the most effective, which contain a liquid component (70-90%), thickeners (10-15%) and various additives (1-15%).
In the role of a liquid component, oils of synthetic and petroleum origin, as well as mixtures of these substances are most often used. Synthetic oils are used for critical components of mechanisms operating in large ranges of contact loads and various temperatures. The oil component is less stable when fluctuating temperature effects. Mixtures of liquid oils are created for more efficient use of greases and changes in their operational properties.
Thickeners, which take soap or solid hydrocarbons, create the necessary consistency of the product.
Improving the properties of greases is achieved by the introduction of additives in the form of additives and fillers. Each of the components performs its function.
Functional Features
The effective operation of any brand of grease is determined not only by the operating conditions of the material itself, but also by the type of technical unit that it is designed to protect. There are many criteria according to which lubricant is selected:
- The operating mode of the friction unit (variable or constant loads).
- Design features of the operated unit (size, type, nature of movement).
- Characterization of the material with which the grease contacts.
- External conditions for the functioning of rubbing surfaces.
- Timing and the possibility of replacing the protective coating.
Based on these criteria, the main purpose of greases can be formulated:
- Decrease in friction force between the conjugate elements of the mechanism.
- Reduction of noise and vibration of the unit during operation.
- Prevention of wear of rubbing parts.
- Protection of metal surfaces from the harmful effects of the environment.
- Effective sealing of gaps between mating elements.
It is necessary to correctly determine which greases to use to carry out several functions from the list that can ensure reliable operation of the mechanism. Why not everyone? Because a universal lubricant that could perform all these functions at the same time does not exist.
Lubricant Requirements
Grease is a means to ensure the effective and long-term functioning of any unit with friction surfaces. The following requirements are imposed on such materials:
- The ability to maintain their properties under various temperature effects.
- Do not destroy the structure of the surface in contact with grease.
- Withstand various types of loads without changing their properties.
- The absence of harmful effects on the human body, as well as on the environment.
- Profitability during operation and not very high cost of material.
Private requirements may also be imposed on the lubricant, for example, in some mechanisms, the optical and dielectric properties of greases are very important.
Operating principle
Why is metal soap added to the composition? It acts as a thickener, creates a container for oil. Soap in grease is a kind of sponge. It forms a lattice frame. In a simple sponge, it is foam. With a large mechanical load or an increase in temperature, oil is extruded from this molecular structure. This action effectively reduces the friction force of the mating parts.
The weakening of the load helps to restore the lubricant to a plastic state, which prevents the spreading of oil, and also holds it on an inclined and vertical surface.
Advantages and disadvantages
Qualitative determination of grease can be characterized by its advantages in comparison with liquid lubricants. Its main advantages include:
- Increased lubrication coefficient increases the wear resistance of rubbing surfaces.
- The best protective properties against corrosion.
- High coefficient of adhesion allows the grease to be held firmly in vertical and inclined planes.
- Increased sealing properties protect the mating units from foreign debris and moisture.
- Higher operating temperature range.
- Long service life of grease increase the efficiency of its use.
Along with the advantages of plastic material, there are several disadvantages of its use:
- Slows down cooling of rubbing surfaces.
- Soap greases have poor chemical resistance.
- The ability to hold foreign inclusions significantly increases the wear rate of the mating nodes.
- Difficulty delivering grease directly to rubbing surfaces.
Basic properties
Of great importance during the operation of any mechanical unit is the correct choice of lubricant. That is why it is necessary to know well the main characteristics of greases, which largely depend on the substances that make up their composition, as well as on the operating conditions of the equipment.
The main properties of plastic materials can be divided into several groups, characterized by the following indicators:
- Strength.
- Viscosity.
- Stability.
Strength
All grades of greases are characterized by a special indicator - tensile strength. This coefficient indicates the value of the minimum load at which the destruction of the molecular skeleton occurs and material is sheared.
If the load of the rubbing surfaces exceeds the tensile strength, then the lubricant begins to spread. This can lead to serious deformation of the nodes and even to accidents (if we talk about cars). When the load is reduced, the lubricant returns to an elastic state, due to which it is effectively retained even on vertical surfaces.
The strength factors are influenced by the following factors:
- Type of thickener and its concentration.
- Properties and composition of the liquid component of the material.
- The concentration and composition of the fillers.
- The mode and method of manufacturing a lubricant.
The tensile strength is significantly affected by the temperature in the assembly. When choosing a lubricant, the minimum force that needs to be applied to move the mating surfaces must be taken into account.
Viscosity
This indicator characterizes the effect of grease directly in the place of friction after its transition to a liquid state. In lubricating oils, viscosity is a constant. In plastic, it directly depends on the speed of rotation of the node and on temperature, therefore this indicator is called - effective viscosity.
An increase in the speed of movement leads to a decrease in this indicator. If the temperature is constant, then it is expressed by a viscosity-velocity characteristic. When the moving speed of the rubbing surfaces remains constant, and the temperature changes, it is determined by the viscosity-temperature characteristic. An increase in temperature in the region of rubbing nodes significantly reduces the viscosity of the plastic ligament.
Stability
This indicator means how much the material is able to maintain its properties for a certain period of time under the influence of external factors.
Depending on the type of external influence, the stability indicator can be divided into the following groups:
- Mechanical stability indicates the ability to maintain the properties of grease after deformation. It significantly depends on the exposure time and intensity. The unstable type grease is not used in not very tight units.
- The stability of the thermal property shows the ability of grease to maintain its parameters under short-term exposure to elevated temperatures. Its components can decompose into a thickener and oil at various peak temperatures.
- Chemical stability characterizes the lubricant's ability to withstand the harmful effects of various acids or alkalis. More often this property indicates the resistance of the substance against oxidation by oxygen.
- Physical stability indicates the ability of a lubricant to evaporate or to independently release a liquid component without applying a load.
There are also many other properties of greases:
- an indicator of the penetration of the composition into the material of the rubbing surfaces;
- dropping point at which the first drop of substance is released;
- properties against wear and others.
Classification
There are many parameters by which a standard classification of greases is made. On its basis, the selection of material for specific purposes.
By area of use, greases are divided into the following categories:
- Preservation - protect the surface of the metal during storage.
- Anti-friction - reduce the wear of rubbing parts.
- Rope - used to prevent wear of steel ropes.
- Sealing - used to seal valves and threaded connections.
According to the type of oil base, greases are divided into the following types:
- Based on petroleum refined products.
- Compositions using artificial oils (synthetic).
- With vegetable oil.
- Mixtures of oils.
Classification of greases by type of thickener:
- Organic They include a thickener made of polymer material.
- Inorganic. They include thickeners of inorganic origin.
- Soapy. Soap is used as a thickener.
- Hydrocarbon. They contain a thickener made of paraffin or ceresin.
Marking
In accordance with the listed properties and compositions, lubricants are marked. Previously, it was arbitrary, expressed in alphabetic or digital name, as well as by the name of the manufacturer. The labeling process was later standardized. Lubricants were denoted by the letters:
- The scope is indicated by the letters: U - universal, I - industrial, F - railway, P - rolling.
- Depending on the temperature of use, universal greases are marked with the letters: T - refractory, C - medium melting, H - low temperature.
- Specific properties are indicated by the letters: Z - protective, B - moisture resistant, M - frost-resistant, K - rope.
For example, UNZ grease means that it is universal, low-temperature, protective.
Remember that the effective performance of any mechanical equipment or machine depends on the correct lubricant. Its use will significantly reduce the friction force in the mating nodes and extend the life of the mechanical device.