INDUSTRIAL AND MARINE LUBRICANTS AND GREASES

A grease is a lubricant that has the properties of a semi-solid body, is subjected to plastic stress and begins to flow as a liquid under a certain load. Once the load reaches its critical point and is removed, the grease regains its properties as a solid body.

It consists of a base oil, a thickener or soap and specific additives. This mixture forms a matrix that gives the product a solid character to resist changes in position.

A grease may contain antioxidant additives, corrosion and anti-wear inhibitors, extreme pressure additives, solid additives and others.

The thickener is the element that forms the matrix of the fat. It causes the lubricant to be contained in it and only released when there is certain pressure, so that it permeates and lubricates. When the force ceases, the matrix absorbs the lubricant again.

This is the temperature at which the matrix that forms the thickener loses its chemical structure, becomes permeable and begins to release the lubricant it contains even if no force is exerted. This process cannot be reversed, so a grease suitable for the application temperature must be used.

Each chemical component has various advantages. Among others, there are:

- Lithium: mechanical stability, water and temperature resistant
- Anhydrous Calcium: mechanical stability, water and shear resistant, temperature resistant.
- Lithium-calcium: very good water resistance, high thermal stability, mechanical stability.
- Lithium complex: good pumpability, oxidation, shear and thermal resistance, and withstands high loads.
- Calcium: exceptional load capacity, thermal stability and shear strength. Poor pumpability.
- Aluminum complex: good pumpability, water and oxidation resistance. Good thermal capacity.
- Bentonite: exceptional at high temperatures, good pumpability at low temperatures.

The main capabilities of greases are corrosion inhibition and lubricating, sealing and load-carrying capacity. In addition, they protect against dusty and humid atmospheres, maximizing drain intervals and retaining the oil so that it stays exactly where lubrication is required.

Consistency is the stiffness provided by the matrix that forms the grease. It is measured in NLGI grades, determined from the distance in mm that a cone penetrates the grease sample. Depending on its consistency, the cone will penetrate to a greater or lesser extent.

The most important characteristics when choosing a grease, in addition to its consistency, are the viscosity of the base oil, the thickener, and its field of application.

A grease with a specific base oil viscosity will be used depending on the application speeds. Low viscosities provide better heat transfer and good low temperature performance, while high viscosities provide better adhesion and water resistance.

The application temperature range is given by the dropping point, where the grease permeabilizes and starts to leak from the base oil and eventually leaks out of the matrix. Resistance to adverse environmental conditions, also determined by the scope of application, is conferred by the additives added to the grease mixture for anti-corrosion, extreme pressure, water resistance, biodegradability purposes and more.

To mix two greases, you must first make sure that both the base oil and the thickener are compatible with each other. If you are not sure, you should consult a lubrication specialist.

Siloxanes are organosilicon compounds (elements containing silicon and carbon). They come from silicones present in shampoo, soaps and other sanitary products, which undergo anaerobic digestion in treatment plants. These substances accompany the biogas produced, entering the combustion chamber of the cogeneration engines.

No oil can prevent the formation of siloxanes, as they are produced in the anaerobic digestion that precedes the generation of energy. Various biogas filtration treatments are available to obtain a cleaner gas.

If not filtered, the siloxanes in the biogas combust in the engine, generating crystalline silica. This silicon is an extremely abrasive substance, which can cause serious engine wear.

Cogeneration engine technologists have optimized combustion so that more power is produced at higher piston pressures and temperatures. The traditional metallurgy of these elements, normally based on aluminum, does not withstand the severe operating conditions of this production.

Steel pistons have been developed for this purpose. Previous lubricants are not formulated to withstand the thermal stress to which they are subjected in new cogeneration equipment, so they are now much more specifically additized.

Water can come from the humid atmosphere or from the degradation of insulation. If the water content exceeds the saturation of the oil, the insulating properties may be affected. In addition, water increases oxidation, reducing the useful life of the oil.

A dielectric oil must have sufficient dielectric strength, adequate viscosity for circulation and cooling and high oxidation stability to extend its life.

A gear lubricant must reduce friction and wear between teeth, cool mechanical parts, mitigate the effects of sudden shocks and overloads, ensure effective lubrication in critical operations and more.

Depending on the application, antioxidant, anti-rust and extreme pressure additives are formulated.

There are four main factors: the type of gear, its speed, temperature and applied load.

In gears moving at high speeds, it is advisable to use low viscosity lubricants. A lubricant with an excessively high viscosity may not be able to adapt to such rapid movements, and there will be absences of lubricating film due to the physical impossibility of the oil reaching all parts of the equipment.

However, in gears moving at low speeds, the use high viscosity oils is ideal. For gears operating at different speeds, dual-viscosity systems or temperature variation systems should be used.

Micropitting is the result of fatigue produced in the metal by cyclic contact stresses. Micro-cracks form in the metal, resulting in metal flaking.

The difference with pitting is the size of the cracks caused by fatigue. Cracks due to micropitting reach up to 10 μm in depth.

The main function of a hydraulic oil is to transmit power. In general, viscosities 32, 46 and 68 cSt (at 40ºC) are used.

Depending on the application, antioxidant, anti-foam, antiwear and viscosity index improvers are formulated.

This is true to a certain extent. Although volumetric efficiency increases with viscosity, mechanical efficiency decreases. This means that the oil, being more viscous, is more difficult to move mechanically. The intermediate solution would be an oil that does requires no effort to move (medium viscosity) and transmits as much power as possible (maximizing viscosity). The optimum operating range is between 20 and 100 cSt.

Bearing play in turbines are usually between 10 and 20 microns, and those in hydraulic servo valves between 3 and 5 microns. This means that the oil used must be as clean as possible to avoid wear in these critical elements.

In general, dusty environments promote oil fouling. Poor sealing, deterioration of seals or incorrect maintenance of the filtration units are some of the main reasons.

A turbine oil must lubricate the bearings of all the equipment, perform cooling functions, act as a hydraulic fluid for the control regulators, lubricate the gearbox of turbines with gears and prevent the formation of foam, rust, sludge and varnish.

In general, ISO grades 32 and 46 are used. Viscosity is important, as an excessively high viscosity will increase friction losses. In high-speed machines, this factor can become a major cause of power and heat loss for the lubricant.

Oxidation causes the formation of sludge, varnish, deposits and corrosive acids. To avoid this, the oil must be formulated with the highest quality base stocks and oxidation-inhibiting additives.

Marine engine lubricants are highly dependent on the sulfur content of the fuels due to the acid neutralization additive (TBN) content. Under IMO regulations, this sulfur content in fuels may not exceed 0.5% unless vessels are equipped with scrubbers, nor 0.1% in ECA areas. Therefore, this measure will lead to a generalized lowering of TBN in oils for vessels that are not equipped with scrubbers and so use low-sulfur fuels.

Marine 2-stroke engines are lubricated with two different types of oil. Cylinder oil is responsible for lubricating engine cylinders. The main requirements are:

- Sufficient alkalinity to neutralize acids formed during combustion.

- High thermal stability and anti-oxidant capacity to lubricate the piston ring and skirt area without deposits.

- Ability to coat a large area of the housing, without producing film breakage.

- Prevent corrosion and rust.

Its main characteristics are SAE 50 and TBN 25/100.

Certain 2-stroke engines tend to have cylinder housing corrosion. It is called cold corrosion due to the fact that it usually occurs in metal areas that are at lower temperatures. The sulfur oxides present in the cylinder condense together with the water vapor on the metal walls, reacting to form sulfuric acid that corrodes the metal. This is accentuated when using fuels with high sulfur content.

ECA stands for "Emission Control Area". The purpose of these zones is to prevent air pollution caused by ships by establishing areas where the emission of sulfur and, in some cases, nitrogen oxides is severely limited. They are located in northern Europe and along the North American coasts.

Marine 2-stroke engines are lubricated with two different types of oil. System oil lubricates auxiliary engine components. The main requirements are:

- Lubricating crankshaft and crosshead bearings

- Cooling piston heads

- Working as a hydraulic fluid to move the valves

- Lubricating auxiliary equipment and gears

- Lubricating turbocharger bearings

- Its main characteristics are an SAE 30 and a TBN of 5/10.