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AFC Chain Reliability Study

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Published: November 11Project Number: C17011

Get ReportAuthor: David Cusack, Guan Zhiqiang, Barend J. Pienaar, Allan Boughen, Paul Lever | CRCMining

An ongoing trend in longwall mine planning is to demand longer, higher capacity and lower profile Armoured Face Conveyors (AFC).  The ACARP Landmark Automation project evaluation of downtime statistics from two Australian Longwall mines showed that AFC and BSL (Beam Stage Loader) chain related failures accounted for 27% of all downtime. A large majority of these failures can be attributed to incorrect chain tension.  To achieve the additional requirements for higher equipment reliability it is clear that mining chain designs must improve. This may include manufacturing to higher quality standards and potential changes to chain shapes.  All this means higher replacement chain costs.  Particularly in large mining blocks, an incremental improvement in chain life is meaningless.  Until the operating company can be assured that the risk of reusing a chain for an entire additional block is acceptable, many 'fit for purpose' chains will be disposed of prematurely.  Conversely, overly optimistic estimation of remaining life will result in significant downtime.  At present the industry understanding of the relationship between chain life and operating parameters is limited.

 

Currently, two techniques are used for continuous monitoring of AFC chain tensions. The first records AFC drive motor currents to infer chain tension. While this is better than nothing, it provides a very "averaged" record of the chain's loading at a single point. The second deploys an arm that measures the force required to deflect the chain. This is typically done at a single location and like the first method only measures tension at a single point on the conveyor. To solve this problem, CRCMining completed ACARP project C11036 "Longwall AFC Chain Tension Meter" whose objective was to measure the chain tensions in both strands of chain during normal production conditions. The results from the field trial did demonstrate an ability to measure meaningful chain tension data along the length of the face. The main objective of this project was to understand the chain failure mechanisms using real-time chain tension measured under different operating conditions on several longwall faces.

 

This project developed a revised version of the instrumented flight bar chain tension meter prototyped in the previous ACARP project C11036. This was necessary due to the smaller flight bar used in the field trial longwall. This required a redesign of the chain tension meter (strain gauge electronics, data acquisition system and battery pack). The revised chain tension meter was re-certified Ex ia for use in ERZO sections of Australian coal mines and was field trialled on a longwall face during production.

 

During the field trial the AFC chain tension meter was installed on an operating longwall for two shifts. The tension meter electronics and protection housing contained in the flight bar demonstrated the necessary robustness. However, the connections from the instrumented flight bar to the strain gauges mounted on the attached chain links did not survive for very long. The connection to one chain link failed after two hours of operation with the other failing two hours later. This result was a high quality but limited chain tension data set from the field trial that allowed for limited evaluation of chain tension during production.

 

A wide range of delays and unexpected issues were experienced during the project. One of the largest delays was related to access to a field trial face. The project was also unable to gain access to the additional field trial locations initially proposed. Redesign, fabrication and commissioning of the chain tension meter required significant time and cost, and the effort associated IS recertification was a major accomplishment.

 

The project did not collect the necessary chain tension data from several longwalls required to investigate the fundamental failure mechanisms of AFC chains.  A higher level of reliability is required from the existing flight bar based chain tension meter to make it a usable tool.  Post failure analysis of the system has helped us to understand its failure mechanisms and we have proposed a solution to solve this problem.  However, industry feedback now indicates that there would be more value in measuring AFC chain tension in real time, making it available for condition monitoring and as an input to a longwall control system.

 

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