Thursday 18th Aug, 2022

New technology to improve longwall chain tension testing

A new system suitable for all types of chains is set to transform longwall chain tension testing and measurement.

A new system suitable for all types of chains is set to transform longwall chain tension testing and measurement.

Developed by Wollongong-based consulting mechanical engineers PHD Engineering, the new system is the result of almost 12 months of designing, modelling and testing to arrive at what is arguably a real breakthrough in technology for the underground coal mining sector.

Longwall chains must be tested weekly for tension and a chain at the correct operating tension is a priority.

A typical longwall chain assembly is around three hundred metres long and includes some 2000 individual flight bars – one every 150mm – linking the parallel chains.

Chains are manufactured to strict tolerances to account for the tough conditions they operate in but even the best quality product has been shown to wear. As the chain wears, it elongates and its tension drops. The automatic tensioning facility in the longwall assembly is designed to account for tension variations however most miners prefer to manually check the tension weekly.

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That current manual testing equipment is cumbersome, heavy – usually more than 85kg – and, in the restricted confines of a longwall assembly, difficult to manhandle and operate.

Bob Davey who led the design team at PHD said there were a number of design factors to take into account.

“Obviously the geometrical and physical constraints due to the proximity of the chains were leading influences but also critical to the project were the safety of personnel, the ease of transporting the equipment to and from the test site and a testing protocol that is compatible with ribbed AFC chain,” Davey said.

Some AFC chain is structurally different in that it has a steel rib across the middle of each link, which makes in incompatible with existing chain tensioners. The new tensioner is designed to clamp over the chain – rather than the traditional hook-the-link method – making this bespoke system suitable for both types of AFC chain.

“This new testing equipment meets all the criteria,” Davey said.

In practice, two unique high-tensile steel blocks fit over the chain and are hydraulically driven toward each other until the centre link between them is loose. Under normal operating conditions it takes about 20 tonnes of pressure to compress the chain but the new system had to have a safety factor of four – 80 tonnes.

“That was one of the early hurdles we had to overcome,” Davey said. “We had a system that would work at 25 tonne pressure but when we analysed the impact at 80t the stresses on the components were too high – which necessitated some redesign.”

The designers also needed robust hydraulic cylinders to suit the new connections designed for the equipment and would also fit within the physical constraints of the project. PHD Engineering called in CRAM, the hydraulic specialist arm of Motion Australia.

The cylinder from an existing testing unit was reverse-engineered, and with the data gained CRAM used the key characteristics – stroke, barrel internal and external diameter, rod diameter and pin-to-pin distance – to develop a design that replicated the existing arrangement but took into the account the structural/mechanical changes to the new tension testing unit.

The design was reviewed and approved prior to manufacture and supply to PHD Engineering for assembly and final testing before installation and commissioning at site.

The first unit is now in use in an underground mine in the Illawarra region of New South Wales, with a second currently being commissioned. All tests and analytics – including FEA analysis and a 200 per cent proof-load test – have been passed and approved and certified by an NATA-accredited testing authority. The industry-oriented regulations and requirements of the NSW Mines Department have also been satisfied.

Anecdotal evidence from the mine is positive. The new testing equipment working to design and specification and generally exceeding expectations of the underground personnel.

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