Equipment Lubrication

Proper lubrication is essential to keeping industrial equipment operating. Almost every machine and tool requires lubrication to protect its moving parts and ensure smooth operation. Every maintenance technician should have a strong working knowledge of lubrication principles and procedures to diagnose or better yet, to prevent equipment failures.

An article by Duke Electric revealed that over half of industrial motor failures are due to failed bearings, with 80% of bearing failures being caused by improper lubrication. While not every machine is driven by an electric motor, these statistics reveal that equipment lubrication is improperly performed on a wide scale.

Why is Lubrication Important?

Lubricants perform the following functions:

• Reduces work
• Reduces wear
• Reduces shock
• Removes heat
• Cleans and seals components
• Minimizes corrosion

Reducing work and wear and removing heat are the result of minimizing friction. Resistance (in the form of friction) results in more energy required to create motion or to do work. A major role of lubricants is reducing the energy needed to cause that motion. Without lubrication, the energy from work is converted to heat between the two surfaces, which can result in damage.

The machined surfaces of industrial equipment appear smooth to the naked eye. However, this is misleading. Machined surfaces contain peaks and valleys that will wear away without proper lubrication. In general, increased wear increases friction, resulting in more heat.

Excessive wear on a machine shaft causes imbalance. This can cause the shaft to become out-of-round. An imbalanced shaft increases the wear rate and creates additional problems with the machine. In extreme scenarios, improper lubrication of rotating equipment creates enough heat to melt (wipe) the bearing material and seize (weld) the equipment shaft to the bearing housing.

Reducing Friction

Separating the machine surfaces with a proper lubricant reduces friction in the machine. The lubricant layer equally distributes load between the high and low points of the surfaces. In a typical journal bearing, the lubricant layer is as little as 2 to 100 microns thick. The lubricant used must have the proper viscosity and contain the correct additives for the operating conditions. If the lubricant viscosity is too high, friction generated between the lubricant molecules will generate excessive heat. Conversely, too low of a viscosity will reduce the thickness of the lubricant layer, creating the potential for metal-to-metal contact.

Causes of Improper Lubrication

With the importance of lubrication understood, the cause of improper lubrication must be investigated. Site personnel may develop the mindset that periodically adding grease to a motor or topping off a bearing with oil are effective lubrication methods. While the intention to maintain the equipment is good, the execution is poor.

Typical causes of improper lubrication are:

• Improper lubricant quantity: Too little lubricant will result in the loss of the fluid film, resulting in metal to metal contact, which rapidly increases friction and wear. Excess lubricant increases the friction between the lubricant molecules and generates heat. Adding excessive grease to an electric motor bearing can result in grease entering the motor windings, creating a fire hazard.
• Improper lubricant type: The lubricant used must meet the requirements of the equipment manufacturer. For example, adding a grease designed for gearboxes operating at low speeds and high loads to the bearings of an electric motor will yield poor results. Always compare the product data sheet for the lubricant against the lubricant requirements provided by the equipment manufacturer.
• Lubricant contamination: Contamination is the introduction of foreign materials to the lubricant. This includes adding two or more dissimilar lubricants to the same piece of equipment. Foreign material cause machinery parts to wear. Water contamination significantly diminishes a lubricants properties. Dissimilar lubricants can react and diminish the lubricating properties of each other.
• Lubricant degradation: Over time, the properties of the lubricant will degrade. The original properties of the lubricant diminish as additives separate out from the base. Following the lubrication intervals set by the equipment manufacturer is critical to the maintenance of plant equipment.
• Lubricant delivery: Selecting the correct delivery tool is critical when manually lubricating equipment. Battery powered grease guns can reach pressures of 5,000 to 25,000 psig. A standard ball bearing race is rated for 500 psig. A few extra strokes of the grease gun in a small bearing cavity can lead to high pressures that destroy the bearing.

Next Steps

The task of planning and performing maintenance at an industrial facility can be daunting. Additionally, building a qualification program for maintenance technicians with site-specific training can feel like an impossible undertaking. FCS is equipped and prepared to assist you with maintenance procedures and qualification and training programs.

References

Dukeelectric.com. (n.d.). Electric motor failure. Duke Electric. https://www.dukeelectric.com/motors/failure/guide/.

Machinerylubrication.com (n.d.). Lubrication regimes explained. Noria Corporation. https://www.machinerylubrication.com/Read/30741/lubrication-regimes

Wilson, C. (n.d.). 12 reasons why bearings fail. ReliablePlant. https://www.reliableplant.com/Read/30255/reasons-bearings-fail.