Industrial lubricants are used in a large variety of equipments and applications.
This deals with all types of products destined for the lubrication of industrial machines, such as hydraulic systhems, turbines, compressors, bearings, open and closed gears, machine tool slideway, pneumatic tools and industrial transmissions.
In all these categories, the one which has the most volumes is represented by the hydraulic oils which are used in the hydraulic controls of building machinery, industrial plants, etc.
Usually these fluids are containing antiwear agents to minimize wear of the pumps.
In general, the inserting of additives in industrial lubricants, except for products with special applications, is not very high (maximum 5%), but that which is fundamental is the balance between the various additives in order to reach some particular performance.
These products, besides satisfying certain chemical-physical requirements, in many cases must also pass tribological rig test (with reference to friction and wear) or test on equipment which simulates the real life use and on which a critical component is installed (for example, pumps for hydraulic circuits).
In the area of industrial lubricants are also classified other products with special applications such concrete mold oils, transform oils (insulating oils), heat treatments and heat transfer oils.
The specifications of the sector are from institutions (ISO, IEC, DIN, BS etc.) or from manufactures of components or machines (EATON VICKERS, DAVID BROWN, Denison, Alsthom, Siemens, etc.).
Composition
A lubricant is a mix of different components, carefully balanced, in which there are 'base oils' and 'additives' which together contribute to determining the behaviour when working, both in terms of performance and in terms of duration.
Base Oil
Represent the predominant component in the majority of lubricants. The finished product may contain from 70% to 99% base oil.
The quality of base oils is closely linked to the type of crude oil and the process used. The base oils can be of different natures:
Minerals: mix of hydrocarbons obtained from crude by a conventional refinery process or by a standard hydrogenation process.
The number of stocks and the relative viscosimetric characteristics depend on the producer and the type of process. Normally, these are produced:
A very fluid stock (SN 80 / 100 or spindle)
A fluid stock (SN 125 / 170 typically 150)
A medium stock (SN 350 / 600)
A BrightStock (BS 150 / 200)
Non-conventional: Mix of hydrocarbons obtained from petroleum stocks by conversion processes which include a forced hydrogenation phase.
Synthetic: all base types obtained by synthetic processes. Obtained by oligomerization and hydrogenation of olefins, they are of higher quality, as seen by the price (from two to ten times higher); the use is rising, above all in the motor oil sector.
Re-refined: obtained by efficient and modern re-refining processes of the used oils; correct management of the supplies and of the process phases makes obtaining products of a quality identical to virgin bases possible. Unfortunately, considerable prejudices still exist about the massive use of re-refined bases, which wrongly consider the products to be of inferior quality.
Additives Additives are components of lubricant oils organized in complex mixes (packages) which when united with the base mix make it possible to achieve the requested performance levels. The interaction between the various additives can be synergic or antagonistic: the study of these interactions is the basis for the acquisition of know-how.
The additives can be classified on the basis of the fact that
They improve the intrinsic characteristics of the bases (Viscosity Index improvers, pour-point depressants, foam inhibitors/friction modifiers)
They impart new properties (anti-wear/EP, detergent, dispersants, anti-corrosion)
They extend the life of the lubricant (antioxidants)
Classifications of Oils Based on Viscosity Various viscosimetric classification systems exist which indicate, generally with a number, a more or less limited viscosity interval. Their aim is to supply, together with the Viscosity Index (V.I), a quick indication for the choice of a lubricant most suitable for a given application.
For industrial oils, the ISO VG (International Organization for Standardization) classification is widely used, while that of SAE (Society of Automotive Engineers) is fundamental for automotive lubricants. The AGMA (American Gear Manufacturer’s Association) is valid for transmission oils, while that of SUS is, in essence, only used to classify the various base oils. SAE J300
Classification for Engine Oil Viscosity Lubricant oils must be commensurate to different lubrication needs resulting from operating conditions and therefore they differ, and considerably, in characteristics and performance. The SAE J300 (Society of Automotive Engineers) classification is used to establish the differentiation between automobile lubricant oils based on their viscosity.
The oils are grouped in different grades which fall within certain viscosity limits. These limits refer to different temperatures which reproduce the extreme conditions which can occur during the engine operation. The lower limit identifies the dynamic viscosity at low temperatures; it defines SAE grades “W‘ (Winter) from 0W to 25W based on the measured viscosity values at temperatures from -35oC to -10oC: the temperature represents the minimum at which the engine can be started. The upper limit defines the kinematic viscosity measured at 100oC and defines SAE grades from 20 to 60 with increasing viscosity values. The viscosity values established by SAE are expressed in centiPoises for the cold temperature (W) and in centiStokes for the temperature at 100oC.
Friction and Lubrication
Between two bodies in contact and in motion, a force which opposes the movement is always created: the force of friction.
This force is seen in every type of machine in the form of mechanical energy loss and wear; the work used to overcome friction is transformed into heat and it must be considered lost.
The friction between the metallic surfaces must therefore be avoided due to the loss of mechanical energy and the wear which would rapidly incapacitate the moving parts.
In order to reduce these inconveniences to acceptable levels, lubrication must be used, which consists of inserting special substances, called lubricants, between the moving parts. These resist direct contact between the surfaces, limiting the consequences of friction.
Lubricants can be liquid, solid or semi-solid; but the use of liquid lubricants is much more prevalent.
Liquid lubricants, also called lubricating oils, are made with an oil base (mineral or synthetic) to which is added additives, in appropriate proportions to components, whose function is to improve the characteristics of the lubricant.
In order to perform a proper lubrication of the mechanical bodies, an oil must have the following requisites
keep the moving surfaces separate, creating a continuous film between them, impeding contact in all load, temperature and speed conditions.
Act as a cooling fluid.
Possess a thermal and oxidation stability so as not to undergo degradation phenomena during the operational life.
Protect the surfaces from attacks of atmospheric agents or aggressive products which form during operation.
Impede the formation of deposits and/or keep them dispersed in the fluid.
Viscosity
The most important property, typical of a lubricant, is its viscosity. Viscosity, by definition, is a measure of the resistance to flow of a fluid. In the simple case of two surfaces in relative motion separated by a fluid, to maintain the mobile surface at a constant speed it is necessary to apply an F force which is necessary to overcome the viscous resistance exerted by the fluid. The viscosity of a lubricant increases as the temperature decreases and vice versa. The variations of viscosity, always a relevant entity in the temperature interval which is verified in motors, differ based on the types of oil and are measured by a specially defined magnitude, called Viscosity Index (V.I.). The viscosity index is a number which indicates how the viscosity of a certain oil changes when the temperature changes; it takes on much higher values when the viscosity variations are smaller as the temperature changes.
