How condition monitoring protects rotating plant

By investing in online condition monitoring systems to automatically detect early damage to gearboxes, cement manufacturer Spenner Zement has prevented unplanned downtime and avoided costly repairs to transmission gears and gearboxes at its cement mill in Erwitte, Germany.

Spenner Zement produces a range of cement, lime and dry mortar products. The company also develops disposal concepts for different industry sectors whose waste products can be used for secondary raw materials and fuel. The company operates several cement mills (tube mills) at its Erwitte site.

In 2002 Spenner faced a production problem on a cement mill at Erwitte. One of the tube mills had to be shut down for three weeks because of damage to a gearbox that was driving the mill. At the time, the three-stage gearbox was being monitored by a temperature sensor, which failed to give Spenner's maintenance team enough warning of damage to the gearbox.

The gearbox damage and subsequent failure not only resulted in three weeks of unplanned downtime on the tube mill, but also resulted in costly repairs, which included a completely new shaft and refurbishment of parts of the gearbox housing.

Spenner then called in experts from FAG Industrial Services (F'IS), the maintenance and condition monitoring company within The Schaeffler Group, to help eliminate any future unplanned stoppages to its tube mill.

Online vibration monitoring

F'IS recommended its online vibration monitoring system, FAG DTECT X1, along with four permanently-installed sensors positioned on the main gearbox and reduction gear. Three sensors were installed on the main gearbox to monitor the gear bearings and gear mesh, with one sensor installed at the reduction gear to monitor gear rim and pinion condition.

In addition to installing the FAG DTECT X1 system and sensors, F'IS also provided three months' vibration monitoring training. Spenner maintenance engineers were trained to analyse the condition monitoring data and are now capable of monitoring and analysing the data on their own.

In 2004, around 18 months after installing the new condition monitoring system, the FAG DTECT X1 system detected damage to the gear teeth in the gear mesh. Initially, yellow alarms were displayed on the system, followed by temporary red alarms, indicating potential serious damage. Visual inspection from Spenner engineers confirmed that tooth damage had occurred in the second-stage gears. The gearbox was subsequently replaced during the next scheduled shutdown period, without causing any disruption to production. However, had the tooth damage been left undetected, damage to other parts of the gearbox may have occurred, causing costly repairs and further delays to production.

In 2006 Spenner equipped another two of its cement tube mills at Erwitte with FAG DTECT X1 systems. Five sensors are installed on each system, with three monitoring the vibration on the rolling bearings and the gear teeth. The other two sensors monitor vibration at the reduction gear bearings, girth gear and pinion.

Centralised data collection

All data is transmitted directly to Spenner's central control room at the plant, automatically triggering an alarm if deviations from preset parameters are detected. Although several Spenner engineers are now fully trained to analyse the collected data, when initial signs of complex problems are detected, data can be emailed direct to F'IS experts who can carry out in-depth analysis on the data and recommend the appropriate action to be taken.

By analysing the data sent to them, the F'IS experts not only detect the problem but also can pinpoint the damaged component. For example, the type of damage and how quickly the damage progresses, provides valuable clues for maintenance planning teams. Thanks to early detection, special replacement parts can be purchased in time and replacement can be carried out during routine, planned maintenance intervals.

Condition monitoring training at MHI

Other manufacturers are also benefiting from the maintenance and condition monitoring expertise of F'IS. Take German company MHI AG (Mitteldeusche Hartstein Industrie), for example, a natural stone mining company and leading producer of asphalt and concrete based in Hanau, Germany.

MHI recently set up a central workshop for its 16 plants, which is to become the Condition Monitoring (CM) Centre of Excellence for the group. Up to that point, vibration analysis had not been utilised at the plants and F'IS was invited to the CM group to present its expertise in this area.

The initial meeting F'IS had with the management team and maintenance staff at MHI included a presentation of the complete F'IS range of condition monitoring products and services. A contract was concluded covering a two-year vibration monitoring training programme for MHI employees. This training included: fundamentals; FAG Detector II (handheld vibration monitor) product training; regular on-site support from F'IS experts on offline measuring projects at the plant; and data analysis support from F'IS both on site and via e-services.

During this two-year contract, F'IS was commissioned to conduct a plant-wide check, which involved commercial, organisational and structural analysis of the operational procedures at MHI. Weak points were identified and suggestions for improvement developed.

Belt conveyor drives, vibrating screens and crushers at MHI's Gross-Bieberau plant are now being monitored. A total of 70 measuring points are being monitored, with permanent sensors installed at 20 of these points. Even a defect in a small bearing can cause the complete destruction of a gearbox (worth EUR50,000) driving this plant and machinery. Production losses due to gearbox failure cost EUR500 per hour and any unscheduled downtime means repair work that takes at least one to two days to complete.