Equipment Reliability Improvements in the Pulp & Paper Industry: Part 1 of 3
Bearing Protection and Bearing Health for the Pulp & Paper Industry
Achieving optimal bearing life has been a historical headache for engineers and maintenance departments, especially within the pulp and paper industry. Constant harsh conditions create the perfect storm that directly impacts the lifespan of bearings. From unexpected breakdowns to reduced capacity, improving bearing life is always challenging. Here, we will investigate three key questions:
- Why do bearings fail?
- What are the root causes of bearing failure?
- What mechanisms can we use for bearing protection?
Why do bearings fail?
Manufacturers claim that bearings should achieve 50,000 hours or approximately 5.7 years of constant operation. However, this is under lab conditions. In the real world of pulp and paper, bearings are subjected to multiple stresses, including water, dust, heavy loads, vibrations, abrasive contaminations, corrosive vapours, and human error. This leads to unreliability and, very often, a far shorter bearing lifespan.
Equipment bearings generally have lip seals (mostly made of some type of elastomeric material, like rubber) as a first line of defence. However, this only provides protection for around 3,000 hours (125 days/24×7 operation). This certainly doesn’t equate to the designed bearing lifespan claimed.
Once this first line of defence is breached, liquid from the surrounding environment enters the bearing housing. This washes away the second line of defence – the grease – exposing the bearing metal to corrosion. This is further accelerated by heat, load, and environment. If we understand that corrosion means ‘the failure of the grease film to protect the bearing’ and that this occurs after only 3,000 hours of use, we begin to see the problem.
Root causes of bearing failure
We’ve now defined the two root causes of the problem:
- The failure of the lip sealing system
- The water ingress that washes away the grease
Solving these two issues is key. By developing and improving both layers of protection, it should be possible to extend the MTBF (Mean Time Before Failure), attaining a lifespan closer to the manufacturer’s claim.
Enter the Polymer Labyrinth Seal (PLS) – a split construction that addresses the inefficiencies of lip seals. Simple to install, this provides a far more robust and long-lasting solution to traditional seals.
Chesterton 30K Lip Seal Chesterton Polymer Labyrinth Seal
For the second line of defence – the grease – there are three issues to overcome:
- The grease must have low water washout
- It must have excellent corrosion inhibition
- It must maintain a high-lubricating film even when loads increase due to process upsets
This can satisfactorily be achieved by increasing the water resistance of the grease and upping the load-bearing capability.
However, no two bearing applications are the same, requiring a more targeted greasing approach, whereby the grease meets individual lubrication needs. While many plants use the same grease across the board, this isn’t conducive to bearing longevity. The different loads, exposures and environments of each bearing means that pairing the correct grease with application positively impacts bearing lifespan.
The Lubrication Challenge
In addition, incorrect lubrication is the single greatest cause of bearing failure – 80% of premature failure is the result of lubrication issues, such as over or under-lubrication, and poor-quality lubrication*.
With most operations working around the clock and assets in hazardous and/or hard to reach locations, this is tricky to solve. Contaminated areas, constant interruptions, staff shortages etc, means that lubrication often becomes a casualty of outside influences, leading to the following:
- Over and under lubrication: Over lubricate and this raises pressure, increasing friction and temperature. Too little and the lubricant becomes ineffective and bearings start to starve.
- Sticking to a strict timescale: Lubricating because it’s ‘on the to-do list’ rather than necessity often leads to over-zealous greasing and associated problems.
Automatic grease and oil dispensers are the answer. This innovative solution solves many challenges, providing a precise amount of industrial grease or oil exactly when needed. Such automated systems add a valuable dimension to the process, ensuring reliable bearing lubrication, no matter what the situation.
Chesterton Lubri-Cup EM Series
In Part 2 of this series, we will discuss concepts used to reduce flush water usage in a pulp and paper plant, while improving equipment reliability and increasing plant profitability.
Chesterton is a leading international provider of industrial fluid sealing systems, high-performance protective coatings and premium industrial lubricants. From their patented Lubri-Cup automatic grease dispenser to the renowned Polymer Labyrinth Seal (PLS), Chesterton offers world-leading equipment solutions. Such expertise makes Chesterton the ideal procurement partner, working with global operations to bring effective tools and maintenance requirements to the pulp and paper industry.
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*Ciprian Radu, ‘The Most Common Causes of Bearing Failure and The Importance of Bearing Lubrication’, Bearing News, March 17 2020.