IMPROVING THE LIFE AND CAPABILITIES OF LUBRICANTS

A review of commonly used additives

Additives present in a lubricant improve and strengthen its life. In turn, the lubricant protects and extends the life of your equipment. Additives can improve the physical properties of the lubricant while increasing its performance. Chemically active additives are actually able to interact with metals and form a protective film with the metallic components present in the machinery.

The amount of additives present in the oil depends on its intended use. High-performance machines such as engines require superior additives.

The oil formulator must ensure that the additives present in the lubricant will not produce unacceptable side effects. If an additive is present in excessive levels or interacts in an unsatisfactory manner with other additives that are present, it can be detrimental to the equipment. Over a period of time additive packages can deplete, leaving machinery unprotected and vulnerable to failure.

The additives in a lubricant can also be referred to as the performance package. Some of the more commonly used additives include:

Anti-foam agents

Almost every lubricant foams to some extent due to the agitation and aeration that occurs during operation. Air entertainment due to the agitation encourages foam formation. The presence of some detergent and dispersant additives tends to promote foam formation. Foaming increases oxidation and reduces the flow or oil to the bearings. In addition, foaming may cause abnormal loss of oil through orifices.

Anti-foam agents are used to reduce the foaming tendencies of the lubricant. Foam inhibitors may be added to a lubricant in service if a foaming problem is detected. The lubricant and equipment manufactures should be consulted before adding foam inhibitors.

Anti-wear and EP additives

Both anti-wear and extreme-pressure (EP) additives form a protective layer on metal parts by decomposition and absorption. Anti-wear additives function in moderate environments of temperature and pressure while EP additives are effective in the more extreme environments.

Molybdenum disulfide and graphite additives are a special form of anti-wear additives known as anti-seize agents. They form a protective layer on the metal parts by deposition of the graphite or molybdenum disulfide. Anti-seize agents work independent of temperature and pressure.

Typical applications include engine oils, transmission fluids, power steering fluids, and tractor hydraulic fluids. EP additives are common in gear oils, metalworking fluids, and some hydraulic fluids.

Dispersants

The purpose of this additive is to suspend or disperse harmful products within the lubricant. Thus, the additive neutralizes the effect of these products.

Harmful products include contaminates such as dirt, water, fuel, and process material, and lube degradation products such as sludge, varnish, and oxidation products.

Typical applications include diesel and gasoline engine oils, transmission fluids, power steering fluids, and in some cases gear oils.

Detergents

Detergents, like dispersants, are blended into lubricants to remove and neutralize harmful products. In addition, detergents form a protective layer on the metal surfaces to prevent deposition of sludge and varnish. In engines, this can reduce the amount of acidic materials produced.

A detergent’s protective ability is measured by its total base number or its reserve alkalinity. The metallic basis for detergents includes barium, calcium, and magnesium and sodium. Typical applications for detergent additives are primarily diesel and gasoline engines.

Friction modifiers

Friction modifiers are lubricant additives blended with the base stock to enhance the oil’s natural ability to modify or reduce friction. Friction modifiers reduce wear, scoring, and noise.

Typical applications include gasoline engine oils, automatic transmission oils, power steering fluids, metalworking fluids, and tractor hydraulic fluids.

Anti-oxidants

Anti-oxidants, also known as oxidation inhibitors, interfere with the oxidation process by chemically converting oxidation products to benign products. In addition, some oxidation inhibitors interact with the free catalytic metals (primarily copper and iron) to remove them from the oxidation process. Almost all modern lubricants contain anti-oxidation additives in varying degrees.

Lubricants for extreme operating conditions such as diesel and gasoline engines, for high-temperature situations, and for applications that involve high lubricant agitation require higher levels of anti-oxidants than other lubricants.

Pour point depressants

The pour point is the lowest temperature at which a lubricant will flow. In order to obtain flow of oil at low temperature (fluidity), pour depressants are added to the lubricating oil to lower the pour point. These additives tend to inhibit the formation of wax at the low temperatures. In many formulations, especially those containing viscosity improvers, supplemental pour depressants are not needed since other additives also have pour point depressant properties.

Typical applications include diesel and gasoline engine oils, transmission fluids, tractor fluids, hydraulic fluids, and circulation fluids.

Rust and corrosion inhibitors

Rust and corrosion are the result of the attack on the metal surfaces by oxygen and acidic products, and are accelerated by the presence of water and impurities. Rust and corrosion inhibitors work by neutralizing acids and forming protective films. These inhibitors must work in the lubricant and on surfaces above the liquid level.

Typical applications include engine oils, gear oils, metalworking fluids, and greases.

Viscosity index improvers

Mineral lubricants tend to lose their lubricating ability at high temperatures due to viscosity reduction. Viscosity improvers are added to a lubricant to retain satisfactory lubricating capabilities at the higher temperatures. At low temperatures the viscosity characteristics of the base stock prevail while at high temperatures the viscosity improver maintains the viscosity at satisfactory levels.

In addition to these additives, there are numerous other ones such as dyes to mark lubricant types, seal-swell agents to counteract the adverse effect of other additives on seals, and biocides to retard or prevent bacterial growth. Additive packages are proprietary information and lubricant manufacturers do not offer detailed information on the additives present in their products.

There are, however, several laboratory tests available to determine additive depletion or loss in a lubricant. It is important to monitor your additive package through laboratory tests. When your additive package depletes, your lubricant’s performance decreases and your equipment is left unprotected.

as seen in:
Maintenance Technology
May 1999