Chain expert Dr Geoff Price from Parsons Chain UK outlined some future developments in chain technology at AJM’s sixth longwall conference in March.
Price said the need for stronger chain usually means bigger chain but this increases weight, size and cost. The ideal solution would be stronger chain in smaller sizes with more reliability. This requires toughness and strength.
Strength is derived from alloying elements while toughness comes from hardening and tempering. But strength declines and toughness increases as tempering temperature is raised. This means increased strength has to be traded off against reduced toughness. Future developments are that new steel alloys are being investigated to offer higher strength levels but these must retain adequate toughness.
Price said a common problem related to toughness was when rubbing cracks formed on the chain link sides as a result of short moments of contact with the deck plate at speed and under load. In some cases forces are powerful enough to cause the chain to be briefly welded to the plate before the strength of the chain pulls it free.
Stress corrosion cracking (SCC) is a phenomenon in which existing cracks grow rapidly in aggressive environments. Price said the Parsons Chain had developed the COR-X alloy to balance conflicting requirements. This alloy gives excellent resistance to SCC at a strength level higher than DIN, he said.
COR-X chains are particularly suitable for conditions where mine water is acidic (pH less than 7) and contains high levels of chloride.
Price said at the US operation Oak Grove conventional high tensile strength chain did not last for more than half million tons. SCC was identified as the culprit and COR-X chain was installed. It was still fit for use after 6 million tons.
The Bowen Basin Moranbah North mine identified SCC when 42mm chain broke up after three months of use. COR-X chain was installed and is now on its 6 million ton panel with a fresh chain being made for the fourth panel.
Price said other mines with previous corrosion problems now using COR-X were Ziemowit, Poland with 38mm chain, Dugout, USA with 42mm, and San Juan, New Mexico with 48mm.
In conclusion, Price noted that 52mm chain is under development for future applications.
