- Lubricants are expected to function problem-free over a long period of time, and in many cases, over the entire lifespan of a component.
- Pneumatic drives and control systems incorporate a variety of elements such as cylinders, motors or valves, which are made of different materials, so the tribological system that results is often highly complex.
Selecting the proper speciality lubricant for pneumatic components, drives and control systems may involve complex factors that require extensive tribological expertise to understand. That’s because pneumatic equipment incorporates a variety of different elements — such as cylinders, motors or valves — which are comprised of different materials that make the tribological system highly complex.
A decisive factor for ensuring maximum service life and proper equipment function is selecting the right pre-start lubrication for all components that move relative to one another, e.g. piston rod, cylinder wall, valve slide and sealing elements. Furthermore, the lubricants used for reducing friction and wear must also be tuned to the ambient temperature, sliding speed and normal forces, just to name a few factors.
As operating pressures, temperatures, sliding speeds and stroke frequencies rise continuously, design engineers and tribologists must carefully 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
Additionally, environmental factors act on the components and the friction points, e.g. low and/or high temperatures or aggressive media in liquid, gaseous or abrasive form, such as sand, etc.
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.
Preventing leakage means less energy consumption
Preventing leakage is key to developing successful pneumatic components. While a component is in operation, some leaks may go unnoticed, for example when water leaking from a pump evaporates on the spot. There are less trivial types of leakage, though, which have to be remedied with considerable outlay in terms of time and costs. Compressed air, for instance, is expensive to generate, and therefore, fixing leaks in the field are extremely costly.
There’s a rule-of-thumb saying that it costs a nickel 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 percent. This means costs can rise enormously, especially when leakages go undetected in connecting lines, check- and control valves, quick-fitting pipes, maintenance units or the terminal equipment, such as pneumatic units.
Besides professional maintenance, high-quality design elements — such as materials, sealing elements and lubricants — are indispensable to ensure economical operation and extended or eliminate the need for component replacement.
Consequently, when looking at cost, what matters is not so much the cost of air compression as such, but rather how much energy is needed to make the compressed air available at the point of use. On average, approximately 33 percent of compressed air is generated only to vanish through a large number of small leaks that combine into a huge loss.
A simple calculation reveals the expected losses – and the potential for improvement. For example, a medium-sized company operates a 100 kW compressor station with a total runtime of all compressors of about 6,000 hours a year. At a rate of approximately $0.082 per kWh, the annual energy costs is about $48,700. If typical leakages can be prevented, however, the operator will need 30 percent less of compressed air, saving roughly. $15,000 on energy alone.
How collaboration identifies savings
To prevent leakages from being caused by brittle seals, it is essential that the seal and the lubricant be compatible. In a recent case, both hydrologic and lubrication manufacturers cooperated in using mechano-dynamical test rigs for tests that closely resembled application and component realities. By combining knowledge, both parties identified opportunities for improvement. With the development of seal-and-lubricant combinations for the various tasks encountered in pneumatic systems, operators benefitted from improved pneumatic drives, valves and seals. As a result, the machinery was able to operate reliably for long periods while cutting energy costs considerably — a significant competitive advantage resulting from early cooperation that identified the relevant tribological and operational factors.