Key points
In the correct circumstances, repairing – or remanufacturing – a failed bearing makes more economic and environmental sense than replacing it with a new one. SKF’s Head of Service, Ian Peverill, explains.
During World War II, the British government’s ‘Make do and mend’ campaign encouraged people to repair their clothing, rather than buy new.
In our throwaway society, it seems a quaint and outdated concept. However, this kind of thinking is fundamental to the idea of the circular economy – at both a consumer and an industrial level. Later this year, for example, the UK government will introduce a ‘right to repair’ law, forcing electronics manufacturers to make spare parts available to consumers. It covers equipment such as washing machines and fridges, which typically cannot be fixed at home if they break down.
This attitude is increasingly being adopted within the manufacturing industry. Ordinarily, when a component such as a bearing fails, it is automatically replaced with a new one. The old bearing is then disposed of. While this process is more sustainable than it was – thanks to improved recycling processes – it still makes for a lot of bearings.
There is now increasing focus on the concept of remanufacturing, in which a bearing is repaired rather than replaced. This does not work in all circumstances: very small bearings – such as those in an electric motor – cannot be repaired and replaced economically, for instance. However, other types – even those as small as a spherical roller bearing – can be remanufactured, from both an economic and ecological standpoint.
Remanufacturing can reduce the life cycle cost of industrial equipment by extending its operating life and reducing maintenance costs. It also helps companies reduce consumption of natural resources and energy, to lessen their environmental impact – which is increasingly important in both society and industry.
Remanufacturing bearings principles
Remanufacturing in itself is not difficult but may require a change in attitude. It typically involves going back to your bearing supplier and having them remanufacture – rather than re-supply – a failed bearing. Historically, remanufacturing was not a feature of bearing supply. For this reason, both suppliers and users are having to embrace a relatively new concept.
Firstly, a failed (or failing) bearing must be assessed for its remanufacturing potential. As already mentioned, it is not appropriate to remanufacture very small bearings. Neither is it recommended for bearings that have suffered serious damage. Remanufacturing in this case would be akin to patching up a blown-out car tyre, rather than fitting a new one.
Many factors – from poor lubrication to contamination – can reduce the service life of a bearing. Rusting, indentations and microcracks can all cause expensive bearing failure. However, if a problem is identified early enough – before irreparable damage occurs – the bearing can be removed, remanufactured and returned to ‘factory conditions’.
Repair or replace bearings?
Remanufacturing is not always the most appropriate approach, and this will be picked up when the bearing is inspected.
Bearings that have suffered heavy damage, fractures or sub-surface initiated fatigue should be replaced. This is because the damage is too serious to repair. However, bearings that have suffered some form of surface-initiated fatigue can often be restored using techniques such as honing or grinding.
Many other types of bearings lend themselves to remanufacturing, as long as the damage is not too serious. Examples include: large bearings with an outside diameter of 420mm or more; caster bearings, such as spherical roller bearings and CARB bearings; railway bearing units; and slewing bearings.
The remanufacturing process is typically more appropriate in heavy industries, such as metals, mining, cement, pulp and paper, and marine.
In a real-world example, the operator of a coal-fired power station found that six wheel bearings needed overhauling to bring a pulveriser back online. The pulveriser is critical to maintaining peak power output.
The cost of new bearings was around €17,000, with a lead time of around seven months. Remanufacturing the bearings took six weeks, and cost around €11,000. This led to a direct saving of around €6,000 in new bearing purchases and related costs. More importantly, the faster repair avoided more than five months of potentially reduced power production – which would have led to €1 million in lost revenue.
Damage assessment
The first stage in deciding whether to remanufacture is to assess the damage to the bearing. Here, the bearing supplier will start by carrying out a visual inspection to determine the extent of the damage. This is followed by non-destructive testing to gain a more detailed picture.
The remanufacturer should be experienced in bearing manufacture – and understand exactly how the remanufactured bearing will be used. This will make sure that the work carried out is appropriate to the application. It includes taking account of factors such as lubrication conditions, bearing load and time in operation.
Remanufacturing may be seen as a ‘slower’ option than replacement – as a part must be disassembled, shipped for repair, then returned and reinstalled. However, the process can be relatively fast. In one case, SKF remanufactured a large bearing for a paper manufacturer inside 10 days. Often, these short lead times can be contained within normal line shutdowns – so there is no loss in productivity. In some cases, remanufacturing can be completed in a few hours.
Work begins with cleaning, degreasing and disassembling bearings. All components are then inspected. Then, a detailed bearing analysis report is issued. Those bearings that are not damaged beyond repair can be restored using appropriate procedures – including polishing, grinding and component replacement. As a rule of thumb, any bearing with more than 30% of its calculated service life remaining is worth remanufacturing. For this reason, the cost savings that can be generated through remanufacturing are substantial.
Bearing benefits
There are several advantages to remanufacturing – and the most significant one is cost. It is normally much cheaper to repair a damaged bearing than it is to install a new one. This helps manufacturing plants retain more of the investment in their existing bearings. Overall, remanufacturing can deliver cost savings of up to 50% compared to manufacturing a new bearing.
At the same time, a remanufactured bearing consumes around 10% of the energy of a new bearing. It can also deliver an 80% reduction in CO2 emissions. This improvement in sustainability is critical in the modern manufacturing environment. There are also associated savings in resources (no need for new steel, for instance) and waste.
At the same time, remanufacturing breathes new life into a bearing, helping to extend operating life beyond its original expected lifespan. The process can add 50% or more to the useful life of a bearing. Remanufacturing can actually be carried out more than once – if the type of damage allows it – which can further extend bearing life.
Linked to this, the process can increase the uptime of a production line by boosting asset reliability. A remanufactured bearing will also be supplied with a warranty for the components and workmanship. Remanufacturing also brings associated benefits, such as reduced maintenance costs.
Keeping track
A remanufactured bearing is just as important to an asset as a ‘new’ bearing – so issues such as traceability are equally important.
Advanced management processes can capture data of every remanufactured bearing and apply a unique code to each asset. In this way, each one can be tracked through its future life cycle. The process can also be used to add bearing feature modifications for different or higher specifications, such as mounting sensors, providing integrated lubrication or offering different sealing or coating solutions.
Once remanufacturing has been carried out, it is important to prevent the original damage from happening again. This can be done by using predictive maintenance, which provides information about the ongoing status of plant machinery using techniques such as vibration analysis. Suppliers can offer root-cause failure analysis to identify the reasons behind bearing damage – and devise a ‘corrective action’ plan to stop problems from returning.
When a bearing begins to wear down, it usually means a large bill to replace it. However, if the problem is caught early enough, it may be appropriate to remanufacture – rather than replace – the bearing. Although it cannot be applied to every situation, remanufacturing helps to reduce maintenance costs, extend bearing lifetime and help manufacturers to become more sustainable.
