An AFC Chain Management Strategy Extends Life and Prevents Unplanned Downtime
Mining chain can make or break an operation. While most longwall mines use 42 mm chain or above on their armoured face conveyors (AFCs), many mines are running 48-mm and some are running chain as large as 65 mm. The larger diameters can extended chain life. Longwall operators often expect to exceed 11 million tons with the 48-mm sizes and as much as 20 million tons with the 65-mm sizes before the chain is taken out of commission. Chain in these larger sizes is expensive but worth it if an entire panel or two can be mined without a shutdown due to chain failure. But, if a chain break occurs due to mis-management, mishandling, improper monitoring, or due to environmental conditions that can cause stress corrosion cracking (SCC), the mine faces major problems. In this situation, the price paid for that chain becomes moot.
If a longwall operator is not running the best chain possible for the conditions at the mine, one unplanned shutdown could easily erase any cost savings garnered during the purchase process. So what should a longwall operator do? They should pay close attention to the site-specific conditions and choose a chain carefully. After the chain is purchased, they need to spend additional time and money necessary to properly manage the investment. This can pay significant dividends.
Heat treatment can increase chain strength, reduce its brittleness, relieve internal stresses, increase wear resistance, or to improve the chain’s machinability. Heat treating has become a fine art form and varies from manufacturer to manufacturer. The aim is to obtain a balance of metal properties to best suit the products function. Differentially hardened chain is one of the more sophisticated techniques used by Parsons Chain where the crown of the chain link remains hard to resist wear and the legs if the links are softer in increase toughness and ductility in service.
Hardness is the ability to resist wear and is denoted by either the Brinell hardness number by the symbol HB or the Vickers hardness number (HB). The Vickers hardness scale is truly proportional, so a material of 800 HV is eight times as hard as one having a hardness of 100 HV. It thus provides a rational scale of hardness from the softest to the hardest material. For low hardness values, up to about 300, the Vickers and Brinell hardness results are approximately the same, but for higher values the Brinell results are lower due to distortion of the ball indenter.
The Charpy Impact Test is a measure of the brittleness of a material can be obtained from an impact test. The chain link is notched at the weld point on the link and placed in the path of a swinging pendulum, the energy required to fracture the specimen being measured by the reduction in the swing of the pendulum.
Most chain manufacturers save a few meters of each batch order to allow full destructive testing to take place. Full test results and certificates are normally supplied with the chain which is normally shipped in 50-m matched pairs. Elongation at test force and total elongation at fracture are also graphed during this destructive test.
Post time: Sep-26-2022