The use of industrial lubricants in mechanical systems is essential, as these specialised substances play a key role in ensuring the smooth operation and durability of various pieces of equipment.
Classification and characteristics of industrial lubricants
Industrial lubricants constitute a broad group of products. They can be classified into several categories, depending on their application and composition:
- Classification by physical form
- Solid greases – have a lamellar structure that prevents direct contact between two touching surfaces, even under extreme conditions. Particularly useful for applications where liquid lubricants might leak.
- Liquid lubricants – these are most often mineral or synthetic oils. They perform well in applications requiring high precision lubrication or in hard-to-reach areas.
- Semi-fluid greases – these are lubricants with a semi-solid consistency. They are characterised by high viscosity. They are used in high-temperature environments or where there is significant vibration.
- Classification by type of thickener
- Lithium greases
- Calcium greases
- Silicone greases
- Polyurea greases
- PTFE greases
- Classification by industrial application
- High-temperature greases
- Low-temperature greases
- Food-grade greases
- Biodegradable greases
NLGI consistency grades
A very important criterion in selecting a grease is its consistency, i.e. hardness, determined by the NLGI consistency classification.
The NLGI classification is an international standard defining the fluidity of grease at room temperature. The measurement is carried out using a penetration test. This involves placing a standardised cone into the grease and measuring the depth of its penetration. The deeper the cone penetrates, the softer the grease.
The NLGI scale is a numerical classification of the consistency of greases – ranging from very fluid (NLGI 000) to very hard (NLGI 6). Greases marked 000 to 1 have a consistency similar to that of liquid oils. They are mainly used at low temperatures. Greases with NLGI 2–3 are well-suited for applications such as bearings, due to their medium hardness. Hard greases are classified as NLGI 4–6 and are specifically designed for harsh operating conditions.
Types of base oils and thickening agents
Grease is made up of 95% base oil. Most modern greases use mineral oil as their liquid component. These are produced through the refining of crude oil. They provide satisfactory performance in most industrial applications. Mineral oils are relatively inexpensive but have low resistance to oxidation. In the API classification of base oils, mineral oils belong to the first three groups (Groups I, II and III).
Read about the differences between mineral and synthetic oils.
In demanding operating conditions, such as high temperatures, it is necessary to use lubricants based on more durable base oils. Synthetic oils are well suited for this purpose. They are not derived from crude oil, but are produced through chemical synthesis. Among the most important types of synthetic oils are polyalphaolefins (PAO). They are characterised by a high viscosity index and exceptional thermal stability.
In addition to base oils, thickening agents are extremely important components in the formulation of lubricating oils and machining fluids. Their role is to create a network structure within the lubricant that binds the liquid phase and additives into a uniform structure. They impart shock-absorbing properties to the lubricants.
The most commonly used thickening systems are soaps (simple: lithium, calcium; hydroxyl; complex). Other substances used include inorganic gels. These include bentonite clays, silicas, and solid hydrocarbons such as paraffins, waxes, etc. Teflon (PTFE) is also used in lubricants with the highest chemical and thermal resistance.
Base oils – PAG
Polyalkylene glycols (PAG) are popular synthetic base oils available on the market. They are a better choice compared to mineral base oils. They are characterised by good lubricity, a high viscosity index and thermal stability. The advantage of PAG oils is that, when used at high temperatures, the resulting oxidation products dissolve completely in the remaining liquid or evaporate, leaving no residue in the equipment.
In industrial applications, polyalkylene glycols are chosen not only for their stability but also for their biodegradability. Currently, there is an increasing emphasis on the use of products that are environmentally friendly. PAG base oil is one such example. It serves as an alternative to, for example, hydraulic oils or mineral oil-based lubricants. Furthermore, selected PAG base oils are biodegradable, making them suitable for use where it is essential to minimise the environmental impact of any potential spills.
The PCC Group’s portfolio includes base oils from the polyalkylene glycol group. These are products from the Rokolub series, such as Rokolub P-B-32 and Rokolub P-B-320.
Do all greases contain additives?
Lubricants are a combination of base oils and additives. The properties of the finished product depend largely on the type of base used (e.g. mineral or synthetic). Lubricant additives, on the other hand, improve performance and durability thanks to their unique physical and chemical properties.
It is worth remembering that additives are not suitable for all lubricants; for example, anti-seize additives (EP) should be used where necessary and economically justified. EP substances activate at high temperatures and under high pressure. Therefore, they are not suitable, for example, in low-speed, low-load bearings. Their importance is particularly evident in machines operating under impact loads or in metal forming processes. For such applications, EP additives from the PCC Group’s range – the EXOfos series (e.g. EXOfos PA-080S, EXOfos PB-184) provide exceptional high-pressure and lubricating properties, as well as exhibiting anti-corrosion and anti-static effects.
See the full range of lubricants and machining fluids from the PCC Group.
