The right choice of industrial oil is the foundation of reliable and efficient machine operation. The article provides a comprehensive overview of the classification of oils used in hydraulics, gears, turbines and compressors – taking into account two key technical parameters: viscosity and quality standards.
Understanding the classification of industrial oils not only allows the right lubricant to be selected for a specific application, but also reduces the risk of failure, reduces operating costs and extends the life of equipment – which translates directly into the efficiency and safety of industrial processes.
Hydraulic oils are lubricants that act as a working medium in control systems, high-pressure hydraulics and bio-hydraulics, among others. They must meet a number of technical requirements, such as thermal stability, good filterability, wear protection for mating parts and effective corrosion protection.
A key performance parameter for hydraulic oils is their viscosity. The optimum viscosity, determined in accordance with ISO 3448 (ISO VG – viscosity grade), ensures that the system operates correctly under the conditions designed by the manufacturer. The most common viscosity range is from approximately 10 to 68 mm²/s.
DIN 51524 defines the quality requirements for hydraulic oils used in different types of hydraulic systems. The classification takes into account the presence of additives and the oil’s resistance to operating factors such as ageing, corrosion and mixed friction. Selecting the right type of oil is key to ensuring reliable system operation, durability and energy efficiency.
The ISO 6743 standard introduces an international labelling system for hydraulic oils, taking into account their basic applications and the type of additives. These classes reflect the level of technological sophistication of the product, as well as its resistance to mechanical loads, varying temperature conditions or ageing processes. Below are the basic oil classes according to this standard:
Gear oils are lubricants that play a key role in ensuring the smooth operation of power transmission and torque transmission systems. Their main functions are to reduce the coefficient of friction between mating components, dissipate heat (cooling), protect against corrosion and transport contaminants.
The basic viscosity classification is ISO 3448 (ISO VG), where the number assigned to the ISO VG class is the average kinematic viscosity of the class within a range of +/- 10%. Other viscosity standards are SAE J306, API GL 1-5, AGMA 9005 (American Gear Manufacturing Association).
DIN 51517 divides gear oils into classes according to their chemical composition and the additives that affect their performance properties. This classification makes it possible to select the right lubricant for the specific operation of the gearbox – both in terms of load conditions and protection against wear or corrosion.
ISO 6743 introduces a detailed classification of gear oils based on their composition, physico-chemical properties and end use. The individual classes are designated by the abbreviation ‘CK’ with a letter identifying the specific property or application, so that the lubricant can be precisely matched to the operating conditions of the gearbox.
Thermo-oxidative lubricants, due to extended operating time and operation due to disease-related effects. The basic division of dependent lubricants is the main type of turbine ISO 6743/5:
The ISO 6743/5 classification does not include lubricants intended for aircraft turbines or wind turbines. Turbine oils are qualitatively categorized according to the ISO 8068 standard, which specifies minimum requirements for turbine equipment (gas, steam, combined cycle).
Due to the operating conditions, compressor oils are classified as a separate group of lubricants. They are subject to categorization depending on the operating temperature, compression ratio and compression pressure. Compressor oils for devices compressing air, technical gases, and generating vacuum are classified by the following standards:
For example:
Oils categorized mainly according to their operating temperature, e.g. VCL – lubricants for systems with an operating temperature of up to 160°C.
The correct choice of lubricants is crucial to the reliable operation of industrial equipment. Whether hydraulic, gear, turbine or compressor oils, they must meet specific quality and viscosity requirements adapted to the operating conditions. Standards such as DIN 51524, ISO 6743, DIN 51517 or DIN 51506 enable precise classification and selection of products in accordance with the technological requirements of the respective system. The right lubricants not only protect components from wear and corrosion, but also affect the efficiency of machines and extend their service life.
The article was prepared by Paweł Pyszny, junior diagnostics specialist at Ecol.
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