The case for timely sealing inspections: How to prevent damage to your mill’s main bearings

In my role as a technician for Metso, I have spent over ten years working in and around grinding mills. I noticed some areas of the mill often get the most attention from maintenance teams such as the gear, pinions and liners. However, other components can also be critical to maintaining the uptime of the mill. One area that is often overlooked is the seals that protect the bearings and the bearing housing.

I once came across a mill which had an accumulation of 10 cm of slurry in the bearing housing, clearly posing a serious risk of damage to their once maintenance-free bearing, due to the slurry contaminating the oil. This risk could easily have been avoided with timely inspections and correct maintenance of the mill’s bearing seals. Read on to learn about timely sealing inspections and the three things to consider when it comes to the planning and execution of audits.

Make time for inspections 

The first thing to think about is allocating sufficient time, especially as inspecting the bearing housing seals is often done when the mill is down for relining or larger service work. In many cases, there may be multiple crews performing different tasks around the mill at the same time, which can lead to certain tasks being neglected in the rush to get the mill back up and running. Exactly how much time you will need to allocate to properly inspect the seals depends on how much experience and familiarity your maintenance engineers and service team have in terms of servicing this section of the mill. In the absence of time pressure, your crew can take advantage of the opportunity to carry out other small repairs and adjustments during the inspection. 

The risk involved in not planning sufficient time for the inspection of the seals is that problems are often missed or not properly dealt with. This can give rise to serious issues later on, including excessive oil leakage, poor seal stability and sealing adaptability to misalignments, damage to the bearing journal and seal orientation and rotation, which can lead to grooving, defined as marks and imperfections on the bearing surface. In turn, these can lead to bearing oil contamination, premature bearing failures, environmental infractions and increased operational and maintenance costs. That’s a pretty long list of things you want to avoid!

Plan inspections to coincide with shut-downs

When deciding on the best time for your main bearing seal inspection, it makes sense to check if there’s a planned stop you can take advantage of. For example, if there’s already a mill reline booked in the company calendar, the sealing inspection could be carried out on the same day. There are no safety issues associated with inspecting the main bearing sealings during a mill reline, so this is an ideal opportunity to do so.

What’s more, the necessary shutdown will undoubtedly have been planned a long time ahead, giving you the chance to get organized and order spare parts in advance. Shutdowns are complex projects to plan and the more tasks are added to the event can easily cause it to go overtime, leading to lost production. This is why some sites are reluctant to add many extra steps to a planned shutdown event, fearing that problems will creep in.

It is important to remember that you are in control of the timing of the service tasks. Even if inspections are often bundled together, there’s nothing stopping you from carrying out a single item inspection whenever it works the best for your operation. It is important to understand your crew’s capabilities and find a balance between what your crew is focused on and where you might need assistance.

For peace of mind, consider bringing on external resources to complement your own team with specialists who know how to make the process more efficient, for instance by combining steps or taking care of certain aspects of the service work. This will ensure that other tasks, like sealing inspection, are not neglected.

Right inventory at the right time

Last but not least, it’s advisable to keep the right spare parts in stock. There’s nothing more frustrating than unnecessary stops or delays while waiting for new parts to arrive. Since seals are made up of four different pieces around the mill trunnion and each piece has a different wear life, it’s easy to get caught without the right sealing component handy. By keeping the right mix of spares, you avoid putting your operations at the mercy of an unpredictable logistics chain.

Storing your seals properly is also an often-overlooked factor. Most seals are made of rubber or other material, and if not stored properly, can lose their integrity or shape, leading to leakage. Typically, storage areas should be cool and dry and the seals protected from dust and stored in suitable packaging, to avoid issues. I have even seen seals stored next to a mill in an open and unprotected environment which is not a practice to recommend. A final point to remember is to check whether your seals are the latest design. Some newer seals may bring advantages in terms of durability or life.

A stitch in time saves nine

To conclude, timely inspection of your main bearing sealings is a classic example of preventive maintenance. To apply an old adage: a stitch in time saves nine! Allocating enough time for your seal inspection, coordinating timing with other service events, and ensuring you have the right parts ready, are all part of solving the puzzle.  If your crew is less experienced in changing the main bearing seals, one way to avoid issues and achieve peace of mind is to consider bringing on a professional partner to execute the work or complement your crew. Metso offers a full range of mill inspection and component replacement services. Get in touch if you’d like to explore your options.