On a belt conveyor transfer point, wear liners are sacrificial layers that protect the skirtboard. Otherwise, friction and the shifting of material will cause dents and holes through which spillage and dust can escape, Daniel Marshall, Process Engineer, Martin Engineering, says.
Removal and replacement of wear liners can be gruelling, requiring multiple workers and days of scheduled downtime. Conventional wear liners have historically been installed inside the chute, but modern designs are now placed on the outside, improving skirtboard sealing and preventing spillage.
Most transfer chutes are “permit-requiring confined spaces”, mandating that an “authorised entrant” perform the work inside the chute. An attendant must also stand outside monitoring the safety of the person inside while assisting in the removal of material from the chute. In some cases, a supervisor further oversees this procedure.
The goal of the external design is to significantly cut the installation and service time while reducing risk and improving safety. The result is excellent performance with fewer labour hours, no required maintenance certification and lower operating costs.
Taking a pounding
For the most punishing applications, urethane skirtboard liners might be required. They absorb impact and abrasion by creating a dam to shield the wall and other sealing accessories from the weight of the material load. They can be retrofitted and attached to the structural sides of the transfer point enclosure to contain dust and spillage.
Commonly also called “canoe liners”, some urethane skirtboard liners feature a steel plate, moulded and encased in thick urethane, to prevent bond issues. A unique T-slot mounting interface allows the liner to be adjusted from outside the chute wall, eliminating the need for confined space entry.
The strip and its bottom edges should be machine-cut to the trough angle and the length of the transfer point to help seal the enclosure. The angle helps the unit better protect the skirting from larger material and spillage, allowing the skirting to focus on sealing in turbulent, dusty air. This prolongs the life of the skirting, reducing maintenance and downtime.
Rethinking chute design
Not all transfer chutes can accommodate a urethane skirtboard liner, so a metal liner is required. Wear liners are typically ¼-inch (6.35 mm) sheets of metal welded to the inside of the chute, with the skirt seal mounted on the outside. Instead, Martin Engineering designers came up with the idea of raising the chute work about 4 inches above the belt, out of the way of the material, then putting the wear liner on the outside. Using this approach, the material still hits the liner without damaging the chute. This configuration allows for service outside of the enclosure.
After elevating the chute box above the material flow, a 3/8 inch or 1/2 inch (9.5 mm or 12.7 mm) thick abrasion-resistant liner plate (AR500) is mounted on the outside of the chute, followed by the skirt seal. Mounting brackets with jackscrews provide a tight hold, with precision adjustment of the wear liner to reduce spillage.
This system closes the gap between the liner and the sealer, thus eliminating abrasion from trapped material without interfering with existing supports. When accompanied by skirting and clamps, the system forms a tight belt seal, delivering outstanding fugitive material control.
Installing an external wear liner
An external liner can be installed and adjusted more quickly and easily, without the need for a grinder or torch, using special mounting tabs. Clips for bolting the liner are initially welded in place and do not need to be removed when the liner wears out. Since the work is done from the outside, without any grinding sparks or torch flame, the hazard of explosive dust from tool usage is greatly reduced. Replacement liners come in a standard length of 72 inches (1,829 mm), and Martin Engineering uses laser cutting technology to create the complex geometries necessary for a custom fit.
The new liner is easily retrofitted onto existing equipment. Installers simply cut back the chute wall on existing chute boxes to accommodate the external wear liner. On new installations, the chute is easily engineered to work with the new liner design, as well as other Martin Engineering components such as dust curtains, track-mounted idlers and cradles.
Case study – coal plant, USA
A coal-fired power plant in Illinois run by Dynegy Inc. with a bulk transport volume of 907 t/h was experiencing spillage issues due to ageing equipment at two of its main bulk material transfer points. Located side by side, the transfer chutes suffered from belt tracking and sagging issues, allowing material to escape the chutes and build up around the work area. Moreover, the old wear liners were difficult to remove and replace, requiring torch work. Operators sought a solution to the excessive equipment maintenance, regular clean-up around a running belt and system downtime that increased the cost of operation.
After reviewing the most essential components needed to control material flow and improve working conditions, Martin Engineering technicians installed Martin® Wear
Liners and Martin Tracker™ systems
Designed to protect the chute wall from material impact while keeping a tight seal on the belt to stop fugitive material, the external wear liner is bolted on from the outside, making replacement of worn sections a one-person job with no need for a torch. To mitigate spillage along the belt path, the Martin® Tracker utilises extended arms with roller sensors and a troughed idler to detect slight variations in the belt path and train it quickly.
Nearly one year after installation, operators have seen a significant reduction in spillage and fugitive dust around the transfer points. Labour costs for clean-up and maintenance have been reduced, and the area around the loading zones and along the belt path is considerably safer.
“We are very pleased with the results of the solution,” a Fuels Supervisor close to the project said. “We set a goal to create a cleaner, safer, and more productive material handling process, and Martin helped us successfully achieve that.”
Source: im-mining.com
