Thermography Takes the Drag out of Dragline Condition Monitoring

Adrian Botes
Condition Monitoring (Engineering)
NEW VAAL COLLIERY
A division of Anglo Operations Ltd
South Africa

Dragline excavation systems are heavy equipment used in civil engineering and surface mining. In civil engineering the smaller types are used for road and port construction. The larger types are used in strip-mining operations to extract coal and these are amongst the largest mobile equipment (not water-borne), and weigh in the vicinity of 2000 metric tons, though specimens weighing up to 13,000 metric tons have also been constructed.

About Draglines

A dragline bucket system consists of a large bucket which is suspended from a boom (a large truss like structure). The bucket is maneuvered by means of a number of ropes and chains. The hoist rope, powered by large diesel or electric motors, supports the bucket and hoist-coupler assembly from the boom. The dragrope is used to draw the bucket assembly horizontally. By skillful maneuver of the hoist and the dragropes the bucket is controlled for various operations. A schematic of a large dragline bucket system is shown below.

Dragline Bucket System

A large dragline system used in the open pit mining industry costs approximately US$20-50 million. A typical bucket has a volume ranging from 30 to 60 cubic meters, though extremely large buckets have ranged up to 168 cubic meters. The length of the boom ranges from 45 to 100 meters. In a single cycle it can move up to 450 metric tons of material.

A notable feature of mining draglines is that they are not fuel powered like most other mining equipment. Their power consumption is so great that they have a direct connection to the high-voltage grid at 11 kV. Many (possibly anecdotal) stories have been told about the blackout-causing effects of mining draglines. For instance, there is a long-lived story that, back in the 1970s, if all seven of Peak Downs (a very large coal mine in central Queensland, Australia) draglines turned simultaneously, they would blackout all of North Queensland.

In all but the smallest of draglines, movement is accomplished by "walking" using pontoons, as caterpillar tracks place too much pressure on the ground, and have great difficultly under the immense weight of the dragline. Maximum speed is only up to a few hundred meters per hour. If traveling medium distances, (about 30-100 km), a special dragline carrier can be brought in to transport the dragline. Above this distance, disassembly is generally required.

Bucyrus Erie 1570w Dragline

Using an IR Window or Sight glass for Inspection

Due to the subsequent failure of a slip ring assembly on a Bucyrus Erie 1570w Dragline, it was then contemplated to install IR windows into the Dragline’s revolving slip ring cabinet to assist in detecting hot connections on the 6.6kv supply line via the slip ring assembly. Each phase has its own slip ring with 2 shoes per slip ring connected in parallel.

A thorough investigation was performed to determine if the IR windows would be the desired solution to our dilemma. Due to strict safety regulations & precautions it was subsequently decided to fit three IR windows into the panel to enable access to the slip ring assembly without putting oneself at risk or contravening any safety regulations.

Due to Infra Red radiation not being able to penetrate through glass or Perspex, a special type of crystal is used to manufacture these IR windows, which allows up to 95% of thermal radiation through.

A tungsten carbide hole saw was used to drill out the required hole to fit the IR windows to enable us to inspect the slip ring assembly without interfering with the Draglines operational requirements.

A FLIR E4 IR camera with a 45-degree lens was used with excellent results. Within a month of installation of the IR windows a fault was detected on one of the lugs, which could have resulted in severe catastrophic failure of this component. The lug was replaced immediately to prevent further damage or subsequent unnecessary downtime.

 
Slip ring Cabinet with IR windows installed                                                            Hawk IR sight glass

 
Thermal and visible images before IR window installation

The following figure is from a report showing an anomaly with a slip ring electrical connection looking through an IR window. The estimated cost avoidance for this problem was $20,154 USD. The cost to repair the problem was $2.50 USD for spares and 1.5 hours engineering downtime.

Report showing anomaly with a slip ring electrical connection, click to enlarge

        
Dragline slip ring assembly: front view (left) and top view (center), and panel view (right), click to enlarge

For his article contribution, Adrian receives an InfraMation Executive attaché case. Published articles earn credit towards IR recertification.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Dragline excavator".