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Reaping the rewards of bearing and machine tool spindle reconditioning

Large size bearing remanufacturing
Machine tool spindle refurbishment

2012 August 01, 09:00 GMT

The causes of wear and failure in bearings and machine tools, and how efficiency and sustainability can be maximised by remanufacture and reconditioning are explained by Phil Burge, Country Communication Manager for SKF.

Bearings and machine tools are so familiar in the manufacturing industry that they are often largely forgotten until they go wrong. Indeed, it is true that, with little more than basic lubrication, spindles can potentially continue to function day after day and provide excellent service for long periods of time. A similar point can be made about rolling bearings; if operating conditions are ideal and the fatigue load limit is not reached, they can, technically, go on rotating forever. So why should either need to be replaced at all? The answer of course, is that in practice, conditions are rarely ideal and imperfect installation and maintenance can further compromise both bearings and machine tools.  However, replacement is no longer the only option available.

The remanufacture and reconditioning of bearings and machine tools has become increasingly popular and it’s easy to see why. The option exists to not only restore but exceed the original quality specifications of rolling bearings through remanufacture, which presents a significant opportunity to increase efficiency.  Meanwhile, the reconditioning of machine tool spindles offers an efficient way to ensure the spindle precision that is critical in defining the accurate manufacture of the end product.

The benefits of remanufacture
Remanufacturing services offer an extremely cost-effective option for worn or damaged bearings. In fact, cost-benefit analysis has shown that remanufacturing can exact a saving of as much as 80% against the cost of a new bearing. And there are further advantages; for example, a major benefit of remanufacture is that it enables engineering firms to sidestep the potentially costly delays to production that can be incurred when orders for replacement bearings are subject to long lead times. Remanufacture also allows facilities to maintain better machine availability and stock reduction, while the damage analysis data gathered during the remanufacturing process can identify recurring areas of high maintenance and failure that can then be addressed as part of an on-going preventative maintenance programme.

The process
The process of assessing a bearing for remanufacture begins with disassembly and cleaning. This is followed by both a visual and a microscopic inspection, after which ring hardness is measured.  A dimensional inspection completes the assessment phase, which is then concluded by the submission of a report and a recommendation for treatment. Recommendation for reworking is categorised into classes, from Class I – Reclassification, which encompasses all of the operations of inspection described above and any appropriate additional work such as buffing, polishing, grinding of scratches and grooves, and demagnetisation, through to Class IV, with each stage adding further levels of component replacement and refurbishment to the remanufacturing process.

Having outlined the process, let’s take a closer look at the type of work that is typically carried out during remanufacture. Depending on the findings of the initial assessment, reworking can result in the grinding or polishing of bearing side faces, bore diameter and outside diameter, while a nickel or chrome plating may be applied to allow the surfaces to be reground or polished to their original dimensions; this can result in a surface finish that is even better than that specified by the original blueprint.  Bearings are then typically refitted with new rolling elements, while cages are inspected for cracks and potentially remanufactured by replating.  With all issues assessed and addressed, the bearing is then reassembled.  In the case of larger bearings, remanufacture may involve a deeper grinding of inner and outer ring raceways, while further machining methods such as hard turning may also be applied.

Coupled with a robust predictive and preventative maintenance regime, a programme of bearing remanufacture can significantly extend component lifespan and maximise efficiency.  As for sustainability, SKF estimates that the remanufacturing of 100 kg of used bearings leads to a reduction of about 350 kg of CO2 emissions.

Machine tool spindle reconditioning
Similar advantages can be gained by reconditioning machine tool spindles. It is not uncommon to discover that spindle components are damaged through incorrect use, such as errors during tool changes, or the ingress of particles or coolant, which can result in damage to bearings, taper run-out /wear, clamping malfunction, imbalance and alignment errors.  Infrequent and/or inappropriate volumes of lubricant are a common cause of failure in many types of moving machinery, and machine tools are no exception.  Contamination, too, is a constant threat in many manufacturing industries and spindles can be especially vulnerable.  However, by capitalising on some of the reconditioning services that are now available, operators can improve machine tool reliability and maximise the quality of their manufacturing output.

The process
Following a general visual inspection, a reconditioning process follows an intensive and extensive itinerary of analysis and action. To give a summary of some key stages in this comprehensive operation, the reconditioning process begins with inspections, tests and disassembly before moving towards a detailed review, including failure mode determination, coolant permeability check and inspections of lubricant and sealing.  The process culminates in spindle re-assembly and run-in.

Reconditioning services bring peace of mind, as work on every reconditioned spindle can be verified with documentation. And if each asset and individual action is logged within a data management system, every spindle can be traced throughout its life cycle, enabling effective management of assets and offering vital data that can be used to optimise plant operations in the future.

Owing to the high degree of accuracy and repeatability required by machine tool applications, reconditioning or upgrading requires a high level of precision, so operators of plant-critical machine tool equipment may benefit from outsourcing to a partner that offers dedicated facilities with capacity for precision machining. Ideally, choose an operator that not only develops and produces precision equipment for spindles but which also operates a range of machine tools with spindles. That way, you can be sure that your partner understands your needs and appreciates what it takes to keep production running at a high level of reliability. The advantages of working with a partner can also include an extended warranty and preventive maintenance input.

SKF Spindle Service Centres repair and recondition over 6,000 machine tool spindles worldwide every year, handling all brands and all defects and offering added value services such as consultancy, field support, performance upgrading, statistics reports and partnership frames for machine tool end-users.

Summary
The need to cut costs and reduce waste has led many operators to consider remanufacture and reconditioning, and calculating the potential savings in both cash and emissions that can be made results in some attractive figures and percentages.  The opportunity to increase efficiency and sustainability through remanufacturing and reconditioning now sits alongside the provision of good lubrication and the establishment of preventative maintenance programmes as a powerful tool with which to protect profitability.

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