MRO Magazine

Feature

The impact of lubricants on machine performance

Everything works better with lubrication. But with the huge variety of lubricants available, it can become a challenge to select the right lubricant for the application. Making a good decision requires knowledge of the application and its...


Everything works better with lubrication. But with the huge variety of lubricants available, it can become a challenge to select the right lubricant for the application. Making a good decision requires knowledge of the application and its requirements – load, speed, temperature, environment, etc. It also requires knowledge of lubricants – types and their functions.

In a recent maintenance conference organized by the Plant Engineering & Maintenance Association of Canada (PEMAC), Mario Tammaro, a senior advisor at Petro-Canada Lubricants, Mississauga, ON, provided some useful information on lubrication fundamentals, rules, and key fluids for manufacturing and processing applications.

Tammaro prefaced his remarks by pointing out that in today’s manufacturing and processing plants, equipment must work harder, at higher temperatures and extreme pressures, and at higher speeds, often in harsh environments. Under these circumstances, proper lubrication and correct choice of lubricants have become even more paramount.

The fundamental purpose of a lubricant is to reduce friction and heat by preventing metal-to-metal contact. All lubricants will do this, but at widely varying degrees of efficiency. Finished lubricants consist of base fluids plus specially chosen additives. The performance characteristics and applications of a lubricant depend upon the type, quality and proportions of base fluids and additives.

While mineral lubricants are still in use, synthetic lubricants are becoming more prevalent. These include alkyl benzenes, organic esters, phosphate esters, polyalkene glycols, polyalpha- olefins, silicones, silicate esters, and others.

Additives enhance the properties that the oil already has and enable it to do things that it could not accomplish by itself. But keep in mind that additives can sometimes counteract each other. Each finished lube is a finely balanced blend of additives whose porportions must not be disturbed by adding aftermarket ‘miracle’ additiives.

Of vital importance is the lubricant’s viscosity, the measure of ‘thickness’ or resistance to flow. Viscosity varies with temperature – oils gets thicker when colder and thinner when hotter. That is why viscosity of industrial lubricants is always measured at a fixed temperature: 40°C.

ISO standards list viscosity grades from 10 to 1500. The viscosity index (VI) is an inherent property of the base oil, used to blend a lubricant. The higher the VI, the less the viscosity changes with temperature.

Oxidation is a chemical deterioration that affects all hydrocarbons. The further it progresses, the faster it will go. As a rule of thumb, every 10°C rise in temperature over 80°C decreases oil life by about half. Oxidation alters the composition of the oil, produces acids, sludge and gums, and is accelerated by contaminants – metals, dust, water. It can be greatly reduced with the right base oils and additives.

Anti-wear additives minimize wear caused by metal-to-metal contact, but they only function when load, pressure and/or temperature are high enough to activate them.

Heat generated at points of metal-to-metal contact causes additives to chemically react with metal surfaces. In this case, extreme pressure (EP) additives can be used. They prevent welding and excessive wear of contacting parts under high load conditions by producing a compound that forms a slick layer between metal surfaces and reduces friction and heat.

The cardinal rule for maximum lubrication efficiency is the right lubricant, at the right time, in the right amount, at the right place.

Key lubricating fluids for manufacturing and processing plants comprise hydraulic fluids, gear oils, heat transfer fluids and greases. Choosing the correct one for the application is a bit of an art.

Hydraulic fluids must resist oxidation and have a long service life. They require excellent anti-wear properties to protect moving parts (pumps, valves, etc.) and should not emulsify water, but have good rust-protection properties.

Gear oils must have adequate film strength and are recommended for industrial gears. They, too, must resist oxidation and have a long service life.

Heat transfer fluids are unique lubricants that transmit heat to operations. They must be absolutely resistant to oxidation, because if they do oxidize, they become more viscous, which results in a significant reduction in the fluid’s thermal efficiency and in costly premature fluid change-outs.

Greases are used to reduce loss in open-system equipment, to seal against corrosion and entry of abrasive fluids, and to protect bearings and gears against the effect of shock loads at low speeds.

Greases are solid or semi-solid lubricants produced by the dispersion of a thickening agent in a liquid lubricant. They are commonly classified according to their stiffness, or lack of it, and are referred to by their NLGI number – 6 to 1, 0, 00 and 000.

When looking for a high-temperature grease, determine the temperature range, whether the equipment performs continuously or intermittently, what the relubrication intervals should be, and whether the grease can drip onto and contaminate products.

The proper selection of lubricants will enhance equipment performance, extend machine and component life, reduce downtime and costly repairs, and improve the overall bottom line. 

Steve Gahbauer is an engineer, a freelance writer, and a contributor of technical articles to MRO Magazine. You can reach him at gahbauer@rogers.com.