Getting to the root of machinery failures

A prime example of successful root cause analysis is highlighted by AVT's investigation into premature pinion gear failure on a 12 head carousel keg cleaner at a UK brewery.

There is much publicity lauding the benefits of predictive maintenance and condition monitoring programmes.

These certainly improve equipment reliability and plant productivity, while pouring scorn on the old adage "if it ain't broke don't fix it".

However, what happens when things do go wrong; when despite "best efforts" equipment breaks down through unforeseen critical component failure?.

In these situations, understanding as quickly as possible why something has failed is vital.

It would be all too easy for maintenance to replace a particular worn part and then several months down the line complain that "that same damn bearing has failed again".

Root cause analysis (RCA) is now becoming well established as a structured method for investigating equipment failure and coming up with a sustainable solution which automatically brings direct savings to bottom line profitability.

AVT's Senior Engineer Andrew Mellor firmly believes that RCA methods should be used in every factory, plant and facility in the UK and does not excuse his passion for the subject.

"I mean, what are the alternatives?", he asks.

"RCA is all about a logical, disciplined approach to solving chronic problems that are hurting profits throughout UK industry".

"It's about dealing in facts - once you have uncovered the facts you can start developing solutions that address the real causes of problems".

"If you don't deal in facts, what do you use?".

"Traditionally we've had 'witch-hunts' where we've assigned blame but that just causes people to keep quiet about mistakes for fear of punishment".

"It drives the problems underground but they're still there, hurting profits".

AV Technology has a broad experience in finding sustainable solutions in industrial situations involving some form of persistent equipment failure.

As independent consultants the company has no "axe to grind" with any of the parties involved, thereby allowing them to look at the problem in an unbiased way.

Problems may be as simple (on the surface) as a broken spring on a mould compacting table or far more complex involving component wear and failure in a complex piece of rotating equipment.

AVT engineers have developed a blend of excellent observational skills, analytical capabilities and mechanical engineering skills, together with the wherewithal to use different external resources as necessary to arrive at a conclusion.

Coupled with this is a pragmatic understanding of tribological and metallurgical principles.

A prime example of how AVT carries out successful root cause analysis is highlighted by the company's investigation into premature pinion gear failure on a 12 head carousel keg cleaner at a UK brewery.

On inspection in January 2006, the final drive pinion was observed to be severely worn.

AVT was asked to investigate the cause of the keg precleaner pinion failures as part of a proactive response supporting a condition monitoring programme being carried out on the site.

The precleaner had been commissioned in 2005 and at the time of the problems had been operational for only eight months, albeit operating 160 hours per week under very arduous conditions.

In addition to its own grease and vibration analysis, AVT based its investigation on information available from the brewery, the equipment manufacturer - including its subcontracted metallurgical analysis - and the lubricant supplier.

AVT's analysis identified specific deficiencies in the lubrication, manufacture and choice of material for the gears, potentially exacerbated by questionable gear alignment.

Ingress of contaminants from caustic washing was excluded.

As Andy Mellor explains: "We determined that the severe wear of the pinion was caused by adhesive wear, usually described as 'smearing', or 'cold scuffing'".

"Both the pinion and gear were made from stainless steel, presumably to counter corrosion in an environment where the gears are subject to regular washdown".

"Unfortunately it is well known and comprehensively documented that stainless steel teeth are prone to scuffing at low speeds".

"In this case the situation was made worse by a poor surface finish on the pinion teeth, which was evident on inspection of the nonloaded face".

AVT found out that when the keg precleaner was installed, the brewery requested the original grease to be changed to a food grade equivalent.

Lubrication is carried out via an automatic self-lube system which pumps the same grease type to all of the six grease nipples so all components receive the same lubricant.

Investigation showed that the OEM maintenance manual recommended a lubricant for the gear teeth which was withdrawn from the UK market in the 1990s.

No information was available to confirm whether another suitable lubricant was recommended.

The failure to replace the original lubricant with a suitable alternative was a significant contributory factor to the rapid wear.

The final report from AVT came up with a number of key recommendations involving all parties concerned.

Succinctly summarised, these focused on improving the lubricant type and lubrication regime for the gear teeth, improving the gear set's resistance to smearing and introducing best practice installation standards and start up procedures.

As Andy Mellor concludes: "Having presented our findings, we chaired a meeting with the client, the lubricant supplier and the keg manufacturer".

"The fact based approach and our neutrality took significant heat out of the situation".

"All parties admitted mistakes had been made and the meeting was conducted in an excellent atmosphere".

"The manufacturer admitted to quality problems with the one of their two suppliers of the pinion and agreed to supply and install replacement pinions on each of the three carousels in the keg filling line on a free of charge basis".

"Structured lubricant trials were agreed and changes to the lubrication system planned into production windows".

"Looking at the deeper issues, the client is considering a change management system".

"The supplier could well examine the design process leading to the choice of material selection and surface finish in that application".

Following AVT's findings and subsequent actions by the equipment supplier and the brewery, the keg cleaner is now back in full operation.

AVT is confident the solution will ensure improved long term reliability for the equipment and bring associated cost benefits for all concerned.

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