Lubrication is essential for any mechanism that moves. It cools, reduces friction, and prevents wear. The challenge is to decide the best way of providing it. Here we'll address the main considerations influencing industrial equipment lubrication.
A lubricant keeps moving surfaces apart. Without it, they’ll come into contact, causing friction that resists motion. Friction also creates heat, which leads to expansion, and the surfaces wear. The resulting particles, plus thermal expansion, increase the wear rate, and sooner rather than later, the equipment will fail.
Oils, greases and dry lubricants
Oils are liquid, although viscosity can range from thick-as-syrup to thinner-than-water. Synthetic oils are engineered through chemical processes. They're typically more pure and uniform than mineral oils, so they last longer. They're also more expensive.
Oil is an effective way of removing heat and wear particles, but it needs a delivery method. This is usually a recirculating system with a pump and filter, plus pipes and valves that move it around.
Grease is a semi-solid composed of oil mixed with a metallic 'soap'. Its strength, and also its weakness, is that it doesn't flow. Instead, it sticks to surfaces, even those that are vertical.
Closely related to grease are lubricating pastes and waxes. These will be solid at low or ambient temperatures, transitioning to liquid as they warm up. Greases, pastes, and waxes don’t need complex delivery systems the way oil systems do.
Dry lubricants also avoid the need for pumps, pipes, and valves. Instead, these form a long-lasting film over one or both surfaces. PTFE is one such material, although it's less durable than graphite and molybdenum disulfide.
· Motion: Consider if the movement is sliding or rolling. Sliding friction can be addressed with greases and dry lubricants, while rolling motion is better with oil.
· Load: The lubricant's job is to separate two surfaces, but it can be squeezed out as one pushes down on the other. Assessing the load is important because it determines the viscosity needed.
· Viscosity: A more viscous lubricant can handle higher loads but takes more energy to move. Generally speaking, choose the lowest viscosity compatible with the expected loads. Note that higher viscosity oils need more powerful pumps and perhaps also larger diameter pipes.
· Temperature: Oil becomes less viscous at higher temperatures. Consider loads and the viscosity needed under operating conditions, not at ambient.
· Cost: Lubrication can be expensive, but the cost of not lubricating is often far higher. The key is considering and minimizing total lubrication costs.
The cost of lubrication
Adding pipes and valves for a recirculating system increases machine cost and complexity; plus, oil wears out and needs periodic replacement. That means taking equipment out of service, so cost of downtime should be a primary consideration. Using a higher quality lubricant, or switching from mineral to synthetic oil, can save money by reducing replacement frequency. When equipment access is difficult or expensive, it may be worth looking at lifetime lubricant options.
Consider what's needed
Effective lubrication lowers operating costs and extends equipment life. By considering the operating environment and internal loads, it's usually possible to determine the best approach for every piece of equipment.