Bearings are crucial to reducing noise in factories

The health and safety executive (HSE) estimates that 170,000 people in the UK suffer deafness, tinnitus or other ear conditions as a result of exposure to excessive noise at work. Here, Chris Johnson, managing director of low-noise bearings supplier, SMB Bearings explains how small changes in the machine design process, can have a huge effect on workers’ eardrums. Machine builders should take note.

Millions of people are exposed to dangerous decibels in the workplace, from musicians and farmers to industrial workers. Coming in at number one on the Top Ten Noisiest Jobs list, as compiled by the US company Acoustical Services, is airport ground staff. No surprises there — with noise levels of up to 140 decibels (dB), protecting workers’ ears is a crucial safety consideration in such an environment.

Factory and farm workers take the sixth position on the list, having to endure noise of up to 105 dB. While noise protectors, like earplugs or earmuffs, go some way to protecting workers, this arguably doesn’t get to the root of the problem.

High-force machinery may never be completely quiet. However, machine builders and design engineers can produce lower-noise machines through a more careful choice of the bearings that are used in their equipment.

In April 2006, the Control of Noise at Work Regulations came into force for all of Britain’s industry sectors. The regulation puts a duty on employers to reduce risks to their employees’ health by controlling the noise they are exposed to while at work. This includes potential causes of hearing loss or tinnitus — a permanent ringing in the ears that affects approximately six million people in the UK, alone.

Protecting employees from excessive noise in the workplace is a huge priority for health and safety professionals, who are tasked with containing or dampening the noise of loud machinery. There are three important noise levels, of which health and safety managers must be aware:

  • If average daily noise is 80 dB or over, employers must assess the risk and provide workers with training on hearing protection
  • If the average daily noise exposure is 85 decibels or over, hearing protection must be provided
  • There is also an exposure limit value of 87 decibels, taking into account any reduction in exposure attributed to hearing protection

In order for machine builders to meet health and safety obligations and keep noise levels beneath these thresholds, ball bearing noise and vibration are key design considerations. Not only do excessive vibrations drastically shorten the life of bearings, it can also produce unnecessary noise and wasted energy. So, what do machine builders need to know in order to keep noise levels to minimum?

Inspect the surface

Issues relating to smoothness or noise in bearings can be checked using accelerometers. These measure vibrations at the bearing's outer ring, as the inner ring usually rotates at speeds of 1800 rpm. This is an important measurement step and can be included in decision-making processes — for example, if a machine builder receives a sample batch of bearings and is unsure of whether to commit.

It’s worth considering that not all bearing rings and balls are perfectly round or smooth, nor are the inner and outer races on the bearing, even after extensive fine grinding and polishing. Machining imperfections, in the form of rough or uneven surfaces, can cause one ring to move or oscillate radially in relation to another. This is a principle cause of bearing vibration and noise.

These issues can be addressed at the point of purchase by opting for bearings that are known for their manufacturing quality. EZO brand bearings, by Sapporo Precision of Japan, are manufactured with particular attention paid to roundness, tight tolerances and surface finish. All EZO bearings are noise tested as part of the post-production quality check.

Another way to boost noise-reduction efforts is through the use of filtered low noise greases. These greases contain fewer, smaller solid particles that otherwise generate noise when they pass between the balls and raceway.

Noise and vibration levels can also increase because of dirt or dust contamination. Poor fitting practices or incorrect handling are sometimes to blame, causing shock loads that, in turn, create scratches or dents in the raceway. To avoid these issues, machine builders must maintain high levels of cleanliness during the assembly process, using gloves in a near-cleanroom environment.

If machine builders account for decibels during the design and assembly process, the workplace noise problem could be drastically reduced. While there may be no cure for the 170,000 Britons already affected by work-related hearing problems, improving noise levels in factories can prevent similar injuries to others.