Lubes and seals

Productivity is a shared goal in industrial applications involving designers, component makers, and end users. Everyone plays a role. In this report, Motion System Design editors polled lubes and seals experts for advice on optimizing productivity. Here are their responses, which we believe you'll find most helpful.

What design/construction features in lubes and seals contribute to higher productivity, and why?

Colin/Busak: Application-specific seals offer short-term benefits such as low friction and leakage and long-term benefits such as increased MTBF and reduced abrasion of mating components. Typical features include:

Proven, robust design
Materials developed and tested in the intended environment
Manufacturing integrity
Installation ease for reduced damage

What can designers do to ensure higher productivity from the lubes and seals they place in machines?

Colin/Busak: Designers can involve suppliers early in seal discussions, which allows for the best gland-geometry selection, surface finishes, and low-risk assembly sequence. In addition, machine designers should understand the environment, specifically working temperature and pressure ranges. Underestimating these points causes early failure; overestimating leads to overengineered seals, higher cost, and unbalanced performance. Lastly, designers must be realistic about optimization. For example, tighter leakage control on dynamic seals usually means accepting higher friction.

What can end users do to ensure higher productivity from the lubes and seals on their machines?

Colin/Busak: End users can develop close relationships with machine suppliers to clearly understand service conditions. Pushing a machine beyond its design limits may yield short-term productivity gains while risking long-term catastrophic failure. When seals fail in service, operators should record the conditions, check mating components for adherence to specs, and discuss early/repeated failures with the supplier. Observing scheduled service intervals for seals and fluid conditions prevents chemical and mechanical failures.

What are the failure modes and weak links in lubes and seals? What design/ construction features are most susceptible to early failure, and why?

Jeffrey/Nye: The most common lube failure is machine components that are inadequately or irregularly relubricated. Too little lubricant between seal surfaces causes failure. In addition, external contaminants such as dirt, debris, dust, water, chemicals, and other foreign material may induce early seal failure. When machinery is cleaned frequently, high-pressure washing can cause external contaminants to collect near the seals. Water, solvents, or chemical cleaning solutions also wash out or contaminate lubricants. Designing systems that prevent contamination from external sources, as well as eliminating high-pressure washing, helps reduce these common failures.

Todd/Dichtomatik: Reasons for seal leaks at the lip include excessive wear from contamination, high shaft speed, or pressure; cracks, due to heat; coked oil because of thermal overloading; cuts, nicks, or scratches resulting from burrs on shaft chamfer; and inverted lips or missing springs, owing to poor installation. Leaks at the bore arise from burrs on chamfers (cutting or scraping seal OD), rough surface finishes, and seals cocked in the bore during installation.

What are some common mistakes (leading to less productivity) designers make when selecting lubes and seals?

Jeffrey/Nye: A common error designers make is choosing incompatible lubricant and seal materials, which causes premature component failure. Design elements to consider include operating temperature, speed, and load of the components or systems to be lubricated. Pre-selected materials — such as seals — should agree with recommended lubricants, which can eliminate relubrication, reduce wear, and increase machine life. In turn, downtime decreases and productivity increases.

Todd/Dichtomatik: Many times seals are the last components considered in an assembly, which can limit their space. Designers must consider shaft speed, material, finish, hardness, cold-start pressure spikes, and operating pressures. In addition, a seal's location during assembly or exposure to external contamination can reduce its life.

What are some mistakes end users make regarding lubes and seals, and how do they affect productivity?

Jeffrey/Nye: Many end users neglect or postpone relubrication intervals and use the wrong lubricant. Instead, they should follow product manuals and consult the OEM for relubrication intervals, requirements, and seal selection.

Todd/Dichtomatik: Exceeding equipment design specifications reduces seal life or causes leakage. This includes rpm, pressure, temperature, and lubricants. Seal replacements must use the proper type, installation tools, and procedures.