Posted at 09-Sep-2020

Reliability starts at the very beginning, with your bearings

Paul Skade
By Gareth Pollard
Product Manager, Bearings

I started work at ERIKS UK in March 2001 after being on a temporary contract at Ball Packaging Europe. 

My life at ERIKS began as a Junior Inside Sale...

Read full bio

Reliability is a popular buzzword in industry but can have different meanings for different businesses and engineers. But when it comes to your bearings, reliability is summed up in two main areas – quality and operating environment.

 

Firstly, we must consider the bearing itself. To put it simply, the higher quality the materials, the better the bearing. The higher purity of steel, the overall quality and reliability of the bearing is increased.

Now we must consider the production of the bearing. The process itself can be particularly challenging as it requires high accuracy turning and grinding, followed by a super finish to the raceways, ensuring that they present the lowest possible friction – exactly what you want to see from your bearings.

 

This process must be undertaken in a controlled manner as repeatability is essential. Repeatability and accuracy go hand in hand, and it’s the only way to ensure that the last bearing your produce, is as good as your first.

Production complete. What’s next?

Now that the physical bearing has been produced, to the highest standards of course, you need to assess any external factors which may affect its operating life, with the main two regarded as load and speed.

The demand for high volume production, particularly in high cost environments, continues to grow. But as production levels are increased, seemingly, little regard is given to how this will significantly impact the quality of your bearings. Increasing operational speed or quantity may seem feasible but increasing the applied load can be disastrous.

Here’s some food for thought: It’s not only the big things that can cause bearing failures, sometimes smaller issues over time lead to dramatic consequences.

AIP to the rescue

A large automotive manufacturer was experiencing regular failures on their tool spindles, leaving the maintenance department to replace the bearings every 4 months. Not only was this disastrous on the uptime targets of the plant, but also had a significant bearing on cost implications.

 

The current bearings in use were NSK Super Precision Bearings – high accuracy and specifically designed for the demanding and high-speed world of machining centre spindles.

Specially trained to find the cause of production pain by utilising their experience and knowledge, NSK experts introduced the innovative Asset Improvement Program (AIP). By implementing the AIP value cycle, which is a standardised tried and tested process, coupled with viewing the working practices, production processes and a choice of different bearings, NSK were about to identify the areas which required improvement.

The initial visual inspection of the application offered very little insight to the problems, as there were no obvious signs of mistreatment load or excess speeds. Essentially, the bearings appeared to be suitable for the job. In-depth full bearing failure analysis was completed, and the results left little doubt as to the cause of these repeated failures – metal-to-metal contact of the balls to the raceway.

This type of failure increased the bearing temperature, resulting from an increase in friction, which caused the bearing steel to expand and cause seizure. However, this failure was a symptom and not the root cause. Further analysis of the grease lubrication displayed a strong presence of cutting fluid within the bearing, that was emulsifying the lubricant grease causing it to become ineffective, inadequate and unreliable.

Knowing this detail, the solution was simple – keep the grease from emulsifying. A solution was required quickly with limited modification to the application itself. The cutting fluid source could not be changed due to the spindle design. Luckily, NSK has just the right solution for the job – Sealed Super Precision Bearings.

Problem identified. Problem solved

NSK Sealed Super Precision Bearings are factory filled with the exact quantity of high-quality grease lubricant required to fulfil the task at hand. The innovative seal design is non-contact ensuring that the speed capability isn’t compromised. The seal also offers the benefit of keeping cutting fluid contamination out of the bearing, whilst ensuring that the lubricating grease is retained within the bearing.

 

With the added benefit of pre-lubrication, fitting time is also reduced, increasing productivity. There was now no longer the need for the regular lubrication technique of carefully and systematically filling the bearing with the desired amount, which can more often than not become a difficult and messy job.

Additionally, grease lifecycle has been extended by 50% as a result of switching to a high grade NSK grease.

The summary of this simple, yet effective change was staggering.

  • Bearing Lifetime improved from 4 months to over 12 months, a massive achievement that allowed the automotive plant to marry this into the annual maintenance of each machine.
  • Bearing purchases for these machines were now 1/3 of what they were, £7k instead of £21k.
  • The major factor was the massive reduction in unplanned downtime, saving nearly £150k per year.

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