Industrial consumables and engineering firm Bearing Man Group (BMG) reports that its technical services team com- pleted a condition monitoring case study to assess continuous health on four rock winder headgear sheave wheel bearings at one of gold miner Goldfield’s shafts last year.

The aim of the study was to gather information to prevent unplanned failures on sheave wheel bearings and eliminate secondary and collateral damage to shaft components and injury to employees.

“The condition monitoring study entailed the monitoring of the bearing and lubrication conditions under variable loads and at variable and slow rotational speeds, as well as under several external influences,” says BMG condition monitoring manager Pieter van Zyl.

“BMG’s shock-pulse analysis technology, known as the high-definition shock-pulse method (SPM HD) provides reliable fore- warning time for plant personnel, which enables them to either perform the required maintenance or to schedule a planned component replacement, thus reducing repair costs and downtime,” he says.

The SPM HD, which accurately monitors low-speed bearing applications, from 1 rpm to 20 000 rpm, reduces unplanned stoppages and increases asset productivity.

Advanced digital techniques and rpm-based sampling frequency make the SPM HD suitable for condition monitoring on low-speed applications.

BMG recommends that condition monitoring, using the shock-pulse analysis technology, be continuously monitored through a permanently installed system that can monitor variable loads, variable speeds, slow rotational speeds and rope slap.

“The team encountered challenges during this case study, which included rope slap, variable speeds, changing loads and shifting load zones. These have also been the biggest challenges in the past, when attempting to perform predictive maintenance effectively on this application.

“These obstacles were efficiently overcome using patented filters and algorithms, such as a disturbance rejector, a symptom enhancer and HD order tracking. The slow rotational speeds of mining headgear sheave wheels make this application especially suitable for SPM HD, which monitors the bearings’ mechanical and lubrication condition,” explains Van Zyl.

Shock-pulse sensors were permanently installed on the over- and underlay sheave wheel bearings of the rock winder, in conjunction with a frame-mounted speed sensor. The sensors were all connected to an SPM Intellinova continuous monitoring system. The SPM HD, in combination with a shock-pulse transducer, is suited to monitor speed applications as low as 1 rpm.

“By monitoring the mechanical and lubrication condition of a bearing, BMG is able to integrate an automatic lubrication system with the Intellinova online computer unit to supply lubrication on demand,” says Van Zyl.

Based on the results of this case study, it was evident that the shock signal was influenced by the speed, loading and direction of rotation. This is seen in the resultant ‘double trend’ of a defective bearing. Towards the end of bearing life, the delta value between the mechanical condition and lubrication condition of the bearing decreases. The overall mechanical condition trend either increases in amplitude or continues to trend in a state of alarm.

During this study, two defective bearings were identified – one failed two months after the study and the other shortly thereafter, as a result of an inner race defect and excessive clearance.

BMG’s condition monitoring system offers continuous bearing and lubrication condition information to complement regular interruptive inspections, which are legally required, by providing the responsible certified engineer with critical information about the physical health of the sheave wheel bearings while they are in operation.

The measurement results are also presented in high definition to provide a clear picture of the bearing condition.

BMG’s condition monitoring division comprises highly skilled condition monitoring engineers and offers a combination of products and services for users of condition monitoring products at every level. The company’s portfolio of SPM condition moni- toring equipment ranges from basic hand-held instruments to high-level online systems.

“We use the latest SPM equipment, which enables us to effectively monitor applications that rotate as slow as 1 rpm,” says Van Zyl.

BMG’s field services division also uses the SPM equipment to perform corrective maintenance such as shaft alignment and rotor balancing.