Measuring the thickness of mill lining with ultrasound during operation

Purpose and goal
Mining mill linings experience continuous wear, requiring periodic inspections, and can lead to high costs in case of unplanned stoppages. In this pilot study, the feasibility of using waterflow ultrasonics to measure the thickness of rubber liners is investigated. Ultrasonic testing in lab of rubber thickness through aluminium was performed with high precision, which is an important step towards measuring through steel. For reliable measurements of rubber thickness, a more realistic experimental set-up that provides shorter reverberation that hides rubber-echoes is needed.

Structure and implementation
The project started from specification of equipment, followed by ordering, collection of materials and construction of experimental set-up. Rubber linings were delivered by Metso Minerals. The study mostly consisted of measurements in lab, but also some computer simulation was performed to determine the selection of the ultrasonic probes. The experimental set-up worked well for measurement through aluminium, but for steel, the set-up proved to be too small, and thus, give too long reverberation time. The project was then documented in a technical report.

Results
Ultrasonic measurements of rubber thickness through aluminium plates were carried out with high precision. This results in the ability to measure rubber plates and lifters through aluminium plugs/rivets with ultrasound through water. A larger test set-up is to be designed for measurement through steel. Also, new projects have been initiated as a result, regarding periodic ultrasonic testing of bricks of pelletizing plant, of conveyor belts in mining and of ReRail for railways. The pilot project is also interesting for lining in pipes and pipelines.