Instrument uses acoustic emissions to monitor bearing health

9th November 2012 By: Chantelle Kotze

As the early stages of bearing defects may not be detec- tible through condition-monitoring technologies, such as vibration, thermography and tribology monitoring, machine solutions provider Motornostix has introduced the MHC-Bearing Checker solution onto the South African market.

The MHC-Bearing Checker is a hand-held and easy-to-use device, which monitors the high-frequency acoustic emission (AE) of a rotating machine to determine its bearing condition and lubrication state.

Motornostix is the sole sub-Saharan African distributor of the solution, which was designed and developed by UK-based condition monitoring company Kittiwake Holroyd, part of the Parker Hannifin company. It can also be used to monitor the health of gearboxes, fans, pumps and motors.

“Since the product’s launch, industries and companies interested in the unit include condition monitoring service providers, original-equipment manufacturers (OEMs), maintenance service contractors, lubrication manufacturers, artisans, foremen and mining companies,” he says.

Meanwhile, State-owned power utility Eskom’s research and development team has recognised the value of AE analysis for its slow rotating conveyor pulley bearings to monitor the early stages of bearing defects.

Motornostix MD Johan Grobler says Eskom is in the process of evaluating the use of the MHC-Bearing Checker on its conveyors.

He adds that there is no current condition monitoring solution in the utility’s maintenance plan to monitor AE on pulley bearings. If the instrument is deployed, it will be used as the first line in its maintenance plan to detect the early deterioration of bearings.

Grobler explains that condition monitoring is simplified through AE technology, which makes it easy for any technician to monitor a machine’s health and assess its condition on the spot.

The MHC-Bearing Checker measures and interprets the decibel and Distress levels of roller bearings and white metal bearings.

The Distress level, a measurement trademarked by Kittiwake Holroyd, displays either a numeric or interpreted reading of the state of the bearing’s health. It is a measurement that provides an instant indication of the impacts and frictions within a bearing and the state of its health. A level below five indicates a healthy bearing, a level between five and ten is acceptable and a level above ten indicates damage and a bearing that needs attention.

The decibel level indicates the overall high-frequency AE noise of the bearing, which depends on the bearing’s speed. The level will increase with the speed of rotation and with bearing failure progression, or if there is insufficient lubrication.

Before attaching the MHC-Bearing Checker, a small amount of grease must be applied to the sensor head. The unit is then attached to the bearing through its magnetic sensor head and, in less than 20 seconds, the decibel and Distress value will be displayed, explains Grobler.

He says the MHC-Bearing Checker is a good tool for maintenance artisans and technicians, as slow-rotating bearings, with speeds from as low as 35 rpm up to 2 500 rpm, can also be checked using the unit.

The unit is powered by an internal rechargeable battery, offering up to 1 000 measurements between charges and can be recharged using a micro universal serial bus port when connected to a standard personal computer.

Grobler says using the unit is easy enough for any employee, as it gives an interpretation of the Distress measurment. Vibration monitors, which are common condition monitoring tools, are generally more difficult to use, as inputs are required and reading levels must be interpreted by the operator.

The MHC-Bearing Checker, however, does not rely on inputs or interpretation.

“Machine maintainers find it difficult to detect bearing failure at the earliest stage [as they do not use] the correct tool for the job,” says Grobler.

Vibration measurement equipment, which is used to detect causes of failure modes like imbalance or misalignment of rotating equipment, cannot detect the very early stages of bearing failure like wear, scoring due to foreign matter or inadequate lubrication.

The MHC-Bearing Checker is an entry-level on-site instrument in Motornostix’s condition monitoring portfolio that enables the detection of surface and structural failure modes that would otherwise not have been detected if other condition monitoring techniques had been used.

After using the MHC-Bearing Checker, maintenance teams can decide if they want to implement an entire condition monitoring programme at the operation to monitor the health of their machines, either through the use of an online monitoring and analysis system or a remote monitoring analysis system.

Motornostix has built partnerships with asset management- related companies, which form part of the network through which it approaches the market, says Grobler.

“We are working with a selection of OEMs and maintenance service contractors to get our products to market.”

AE technology has been in existence for many years and the application of AE condition monitoring technology in the rotating equipment market has developed and improved significantly and has been used with great success by Motornostix over the last four years, notes Grobler.

AE is not the general condition monitoring tool in the industry, as there are still many companies that only use vibration monitoring.

Motornostix’s marketing strat- egy is to create awareness of AE as an acceptable way of monitoring the health of rotating machines.

Grobler would like to see the MHC-Bearing Checker become the first line method for monitoring the health of bearings, instead of merely relying on visual inspections or the interpretation of low-frequency audible sound of the bearing.