By Steve Fiscor, Editor-in-Chief
Most western underground coal mines use wire mesh as a form of secondary roof support. It’s a well-established practice for high seams and several mines use mesh on the ribs as an extra precaution to prevent the coal from sloughing. Over the years, mines have implemented good systems for handling wire mesh. A prime example is the material handling systems developed by Fletcher for its line of roof bolters, which helps miners install wire mesh.
Wire mesh is relatively inexpensive. The miners know how to handle it and where to buy it, but there are some downsides to wire mesh as well. It’s conductive and corrosive. If it’s damaged, protruding wires can injure unsuspecting miners. The wire mesh panels are hard to handle and the bundles are extremely heavy. The miners pick up the screen panel, carry it onto the bolter, and place it on the TRS. The awkward nature of handling the panels poses potential bending, slipping, tripping and lifting type injuries.
At Oxbow Mining’s Elk Creek mine, a longwall operation located near Paonia, Colo., meshing the ribs with steel wire has been difficult. Getting the mesh up on the rib, positioning it properly and holding it in place can be a challenge. “Years ago, when Oxbow first started mining, the miners did not mesh the ribs, except in places where they thought they needed it, around the feeder-breakers, power centers, and where the miner operator stood when he made the cut,” said Jens Lange, production superintendent, Oxbow. “As we mined deeper into the mountain, that policy changed and we moved to 100% rib meshing.”
When the bolter goes into a cut, the crew likes to advance the vent tube, which is on the left side of the entry (opposite the miner operator), to get it as close to the bolter canopy as possible. “That puts an individual between the machine and the rib,” Lange said. “We kept asking ourselves, ‘How could we do that better?’”
About four or five years ago, Oxbow began to explore other options and they eventually approached Fletcher and asked them what they thought. Since that initial conversation, Oxbow has worked on three systems with Fletcher and Huesker, a company that manufacturers synthetic mesh (or grids). As it is with trial and error, each system improved progressively. “Oxbow was motivated to find a new method,” said Bill Kendall, western U.S. sales manager, Fletcher. “They were concerned about safety, yet very cooperative—willing to try anything. They had already tried several ideas on their own.” Working with Huesker, Oxbow and Fletcher devised a concept to use synthetic mesh.
Tom Bailey, marketing manager-mining, Huesker, remembers sketching the initial concept on Kendall’s kitchen table after dinner a few years ago. “We wanted to keep it as simple as possible,” Bailey said. “He told me what Fletcher’s bolting machines could do and I explained to him what we could do with the grids. We were able to meet in the middle.”
What they envisioned was a handling system to carry, dispense, and tension rolls of mesh. Mounted on the roof bolter, it would pay out mesh as the bolter trammed forward. As the mesh is unrolled and bolted to the roof, the fan-folded ends automatically unfurl for use as rib mesh. Fletcher designed new mechanical attachments for its bolters. Huesker manufactured custom rolls of grid for each cut. And, Oxbow agreed to test the prototype underground. The current protoype testing began five months ago and it proved successful—the system was easy to work with; it did tension the mesh properly; and the sides did unfold as the machine trammed forward.
The beautiful thing about this new process is that, once the first row of bolts is installed, everything is automatic, Lange explained. The miners tram the machine forward, install the roof bolts and the rib bolts, and repeat the process. “This system works well for us because it allows us to mesh the ribs as we bolt the roof,” Lange said. “When the miners advance the vent tube, the rib is fully supported.”
Meshing the Ribs
Synthetic mesh is lightweight, nonconductive, and non-corrosive. The material cost is double, but Oxbow believes the benefits of its use would outweigh the added costs. When the bolters are working with the system, they are fully enclosed by the mesh, which protects them from smaller nuisance rock falls. The unknowns are how well