Gain lubrication insight by looking a little deeper

Understand how metals and lubricants will interact.

By Helmut Seubert, Klüber Lubrication January 12, 2018
Valves, cylinders and motors present a lubrication challenge because they are comprised of different materials. The tribological system is very complex, which makes it difficult to determine the proper speciality lubricant for drives and control systems.

Plant personnel need an adequate understanding of critical tribological factors to select the right pre-start lubrication. Components that move in relation to each, such as piston rods, cylinder walls, valve slides and sealing elements, must be considered to ensure maximum service life and proper equipment function.

The lubricants used for reducing friction and wear must also must be tuned to the ambient temperature, sliding speed and normal forces, among other factors.

Variables in operating conditions

Pressures, temperatures, sliding speeds and stroke frequencies can vary dramatically in different equipment operations. Design engineers and tribologists must understand the friction factors where shafts or rods are taken through housing walls.

At the microscopic level, the tribological system that encompasses the various gaps, spaces and friction points involves such factors as:
  • Intermolecular forces
  • Thermal transmission and conduction
  • Friction and wear
  • Chemical and electro-chemical corrosion.
At the mechanical level, the tribological analysis must account for:
  • Cylinder and rod materials
  • Different seal materials and sealing edge geometries
  • Contact surface pressure and surface micro-geometry
  • Acting pressures
  • Mounting position and situation.
Environmental factors also act on the components and the friction points, as in low and/or high temperatures or aggressive media in liquid, gaseous or abrasives such as sand.

These complex factors are best handled when design and tribology engineers collaborate early in the development process to identify the benefits obtainable from proper lubrication selection.

Less leakage lowers energy consumption

For pneumatic components, preventing leakage is key to ensuring successful operation. While a component is in operation, some leaks may go unnoticed; such as when water leaking from a pump evaporates on the spot. There are less trivial leaks which must be remedied with considerable outlay of time and costs. Compressed air, for instance, is expensive to generate, and therefore, fixing leaks in the field is extremely costly.

The rule-of- thumb is that it costs 5 cents for each cubic meter of compressed air generated. Each additional 14.5 psi of compressed air can be expected to increase energy costs by approximately 10%. This means costs can rise quickly, especially when leaks go undetected in connecting lines, check valves, control valves, quick-fitting pipes, maintenance units or the terminal equipment, such as pneumatic units.
When looking at cost, what matters is not so much the cost of the air itself but how much energy is needed to make the compressed air available at the point of use. On average, approximately 33% of compressed air is generated only to vanish through a large number of small leaks that combine into a huge loss.

The eyes of experts can spot savings

To prevent leaks from brittle seals, it is essential that the seal and the lubricant be compatible.

Various operations make different demands on seal-and- lubricant combinations. Today, pneumatic system operators can benefit from improved pneumatic drives, valves and seals. As a result, the proper lubricant can help cut machinery energy costs while extending operation for longer periods.

In a recent case, both hydrologic and lubrication manufacturers cooperated in using mechanical-dynamical rigs for tests that closely resembled application and component realities. By combining knowledge, both parties identified opportunities for improvement.

Identifying the relevant tribological and operational factors—which often requires collaboration between lubricant, OEM-equipment and plant operations experts—can provide significant competitive advantages.
Helmut Seubert is manager of application engineering for Klüber Lubrication München SE & Co. KG.