Bearing up: how to choose miniature bearings for medical devices

Chris Johnson, managing director of medical bearing manufacturer SMB Bearings, explains what medical device manufacturers should consider before selecting a bearing. 

The inner, outer and width dimensions — often, customers are under the impression that these are the only bearing specifications they need to consider. But, that’s not the case. Bearings have many different specifications; materials, retainers, load ratings and lubricants, to name just a few.

Some bearings can be a relatively cheap investment, so manufacturers may overlook the specific requirements of the application and opt for the first bearing that fills the void. However, just because it fits, it doesn’t mean you should use it. Aside from the basic dimensions, an instrument manufacturer should fully understand the other bearing specifications and, importantly, how they impact the effectiveness of the bearing.

Beyond choosing a bearing that fits, it is also necessary to consider the application in which it will be used. Even in niche industry sectors such as medical device manufacturing, there is a wide variety of bearings with significantly different properties. For example, is the bearing lubricant compatible with the materials it may contact? Should the bearing have low starting and running torque?

Some applications, such as MRI scanners, require non-magnetic or non-conductive bearings and are therefore likely to use full ceramic bearings. Conversely, stainless steel miniature bearings are the most common type used in handheld medical equipment.

Generally, medical device manufacturers have limited space in their equipment, particularly for handheld devices, so they require the smallest possible bearings to fit.  At SMB Bearings, a miniature bearing is defined by the inner diameter being under 10mm. However, the smallest bearing in SMB Bearings’ miniature range is designed to fit a shaft just 0.6 millimetres in diameter — comparable to the head of a pin.

For rotational handheld medical equipment, such as dental drills, bearings may need to work at high speeds. A bearing with a 0.6 millimetre bore can deliver 160,000 revolutions per minute (rpm), giving an impressive capacity for rotational speed, while some larger bearings can have their speed rating increased by the use of ball retainers, made from materials such as torlon or reinforced polyamide.

If rotational accuracy is important to the application — usually the case with medical instruments — manufacturers must consider choosing a precision branded bearing. There are plenty of low-cost bearings on the market, but their accuracy and inconsistent quality makes them dangerously unsuitable for high precision applications.

There’s much more to choosing a bearing than simply making it fit. That’s why, at SMB Bearings, we don’t provide an option to purchase bearings online. With so many variations and possibilities, it’s important to treat every application on a case-by-case basis.

As the worldwide medical device market continues to prosper, medical manufacturers must ensure their devices are safe, accurate and up to the task. This means choosing bearings that don’t just fit, but are the perfect fit.