The Importance of Lubrication Management and its Applications
The past and present of lubrication management
From the invention of the wheel, and the discovery that animal fat smeared on axles would ease movement, right through to the cutting-edge machines of today’s heavy industry, lubrication has been integral to the story of humanity’s innovation and development. The scientific discovery of friction; the rise of petroleum lubricants; and the advent of synthetic solid, semisolid, and liquid lubricants are all part of the story. Lubrication management is the latest advancement improving the performance of the machines that make the world turn.
Today, lubrication and sealing are critical to the performance of the total machine. And it’s widely recognized that the fundamental challenges in sealing moving machine parts are establishing a good sealing system and ensuring long service life. Inextricably linked, solving these challenges is crucial to effective application performance. However, sealing and lubrication are often overlooked by plant management, whose maintenance budgets may be allocated elsewhere. Focusing on these though has positive benefits; lack of effective lubrication is identified as the primary cause of premature machine bearing failure.
Lubrication management is more than simply choosing and applying a lubricant. It’s managing and adjusting the lubrication conditions of all elements within a sealing system that reduces the load on each element and optimizes performance in terms of friction-wear lifetime. This holistic approach to machine maintenance focused on the friction points of the seals and bearings is necessary because the interfaces between surfaces in motion are constantly subjected to pressure and wear.
Effective lubrication management begins with the end in mind. Given the complexity of today’s industrial machines, suitable lubrication management takes a strategic, problem-solving approach. Reducing unplanned downtime and cost, while maintaining the integrity of the sealing system, requires assessment of potential issues before devising a solution comprising of materials, application, and maintenance.
The world is dynamic, and because of this, products are subject to failure. Energy continually shifts from one state to another, while prevention of perpetual motion is by friction, wear, and resistance at the atomic level. In this physical universe, lubrication is one way of holding back the tide of entropy, the lack of available energy to do mechanical work. Lubrication makes equipment run smoother, perform more efficiently, and last longer. The battlefronts for lubrication are a machine’s seal contact areas, or friction points; effectively lubricating these can be the difference between costly repairs and smooth running.
The exponential growth of technology, and resultant demands of an ‘always-on’ world, mean that today’s machinery is increasingly dynamic, more intricate, precision-engineered, and efficient. But this doesn’t mean machinery can break the laws of physics. Friction, wear, and pressure all pose threats to this machinery, potentially causing part failure, service downtime, and cost. And in applications in which seals, from O-Rings to rotary shaft seals, play a critical safety and operational role, the challenge of friction and wear is multiplied exponentially.
Friction is the great enemy, impacting hydraulic systems and seals in a variety of ways. Therefore, when designing a lubrication management system, it’s important to consider all factors, including:
Pressure and speed: Smaller and lighter machines have led to an increase in pressure and speed of hydraulic applications, pushing polyurethane materials to their sealing limits.
Coating of counter surfaces: When chosen for mechanical and functional reasons, often no consideration of the sealing system is given in selection of coatings. This can severely limit the lifespan of both the seals and the machinery.
Rough surfaces: Tiny imperfections, embedded holes, uneven textures, and friction-creating characteristics in the interfacing surfaces of high-speed applications may abrade the seal as it passes.
Modifications and post-processing: Making seal modifications in isolation of the system overall to extend seal life and prevent wear can be costly.
Applying lubricants to seals under pressure loads can extend the life of the seal and mitigate the effects of friction and wear. However, this is a simplistic view, given the previously mentioned speed and pressure challenges of modern machinery, as well as the mandatory need for redundancy in critical industrial applications.
In fluid power and hydraulic sealing applications, best practices involve the use of primary and secondary seals in tandem. The primary seal does the grunt work, maintaining integrity for as long as possible; the secondary seal is a redundancy measure, ready to step in when needed.
Conventional seals have high contact pressure with the rod, meaning an adequate amount of oil fails to be in the contact zone of the primary seal and cannot go through to the second seal, which is left in a dry running situation. This leads to high friction and wear.
Though seemingly simple, a focused lubrication management approach can potentially revolutionize fluid power performance. Lubrication management balances the risk of lubricant leakage to ensure both the performance of the primary seal and the extended life of the secondary seal.
To facilitate lubrication management, new innovative seal designs incorporate rounded sealing edges to give a neutral/ inverse contact pressure. In this sealing arrangement the primary seal still takes the pressure load in the hydraulic system but it is lubricated much better, so it has an easier life in terms of friction and wear. This lowers contact pressure against the rod, which allows just enough lubricant to enter the hydraulic system to efficiently lubricate the piston rod, reducing friction and wear. The secondary seal is no longer dry running and operating under better conditions. If there was a pressure build up there is a ventilation function built into the seals.
This type of lubrication management technology has been rigorously tested by Trelleborg Sealing Solutions. The tests included wear tests of a polytetrafluoroethylene (PTFE) sealing system against a laser clad (an alternative to chrome) counter surface. Being soft and sensitive, it is not an easy surface to seal against as it wears easily. In the tests, standard sealing configurations caused significant wear on the rod, while with the lubrication management technology, there was virtually no wear on the rod or seals.
Friction tests for the PTFE system followed a standard procedure, where on a test rig the sealing system is run at different velocity and pressure combination for 86,000 cycles, and at temperatures of +30 °C and +50 °C. The result showed a dramatic reduction in both constant and break out friction, as well as a consequential wear reduction.
In the standard system, without lubrication management, loss of radial heights for the primary seal during the test period was between five and six percent. Using lubrication management, the wear was virtually halved to less than three percent reduction of the radial heights. Wear on the secondary seal for the standard system was around six per cent. Using lubrication management this was reduced even more than for the primary seal, to below one percent. This means lubrication management technology can significantly extend seal life for the whole system.
Similar tests were undertaken for a polyurethane sealing system and this yielded comparable results. In addition, a short stroke endurance test took place that mimics pitch control cylinder applications in wind turbines. There was only a stroke length of 10 millimeters, so the primary seal never covered the same area as the secondary seal, making the lubrication conditions for the secondary seal very poor. The test ran at a velocity of just four millimeters per second, at constant pressure of 250 bar over one million double strokes.
After the one million double strokes, both the primary and secondary seals were in very good condition. Much more impressive was the wear on the counter surface. With standard systems, there are issues with run in of the secondary seals. After the endurance test, the sealing system based on lubrication management technology showed only slight discoloration where there was contact between the seal and counter surface and the wear was zero.
The demands of the modern world are placing increased pressure on machinery to work reliably for longer periods of time, while ongoing economic pressures are fueling a never-ending quest for cost-effectiveness. To meet these demands, it’s essential to keep things running smoothly and a focusing on lubrication management for sealing systems can help do this. To develop effective sealing systems, it is important to work with an experienced sealing solutions partner.
For more information on lubrication management and application examples, download the free Introduction to Lubrication Management whitepaper by Trelleborg Sealing Solutions by going to: https://www.trelleborg.com/en/seals/resources/technical-library/whitepapers/wp-lubrication-management