Contour Mining Corp., headquartered in Summersville, W.Va., is experiencing firsthand the benefits of the HWM. Contour began highwall coal recovery using augers in 1985. Today the company operates three HWMs, with work sites in West Virginia and Kentucky.
Using the HWM, Contour’s Powellton, W.Va., site has produced more than 2 million tons of coal during 34 months of operation. That’s an average of more than 60,873 tons per month. “Our maximum monthly production came to 78,862 tons in March 2007, and that beat our previous monthly record by just over 600 tons,” said Dave Bundy, COO, Contour Mining. “When you consider that the seam was averaging 52 inches in height, it shows just how productive the machines can be, even when we are using a low-seam cutter module.”
Contour’s most recent accomplishment came when its HWM mined “in seam” 98 out of 132 entries, 1,000 ft deep, in a 30-inch seam, using a low-seam cutter module. The system was working four days a week and averaged about 40,000 tons a month.
The HWM can use a low- or high-seam cutter module. This provides increased flexibility, especially when operators are working in areas where two or more seams of differing recoverable thicknesses can be accessed. Low-seam cutter modules can mine seams from 30- to 64-inches thick, and high-seam cutter modules are used for seams from 50- to 120-inches thick.
Position Sensors Keep HWMs on Track
MTS Systems’ Sensors Division is providing mobile hydraulic magnetostrictive sensors for the HWM system. Because the magnetostrictive technology proved to be more durable and reliable, especially in this harsh mining environment, the sensors replaced externally mounted switches and potentiometers throughout the system.
“Our engineers did some research on MTS Sensors’ Temposonics technology in cylinders, and they seemed to be the best option,” said Stewart Myers, engineering manager, Terex Highwall Miners. “They allowed us to do away with expensive string pots, cable encoders and switches, and the MTS sensors are a better choice because they can be embedded inside the cylinders, making them more reliable and longer-lasting.”
Throughout the equipment’s original design, externally mounted pressure switches, string potentiometers, and infrared switches were providing feedback on position, but were often less than accurate due to harsh operating conditions that caused sub-par performance in components. MTS’ RH series and MH series sensors replaced parts in nine different cylinders in the SHM equipment. MTS’ sensors use magnetostrictive technology to provide the most accurate and reliable results in linear position sensing.
Before the installation of the MTS sensors, the problem areas for equipment operators and technicians were numerous, but were easily addressed with the magnetostrictive sensors:
•The high shock and vibration of the mining environment caused dust and water to seep into the externally mounted sensor originally used in the shear cylinder, requiring quite a bit of maintenance. Maintenance needs have almost been eliminated by using embedded MH sensors instead.
•The steering cylinder, traverse cylinder, and PTM cylinder were compromised due to the use of string pots, which often failed in harsh winter conditions. The embedded MH sensors have proven to be reliable in the same conditions.
•The base frame latching cylinders and base frame locking cylinders were crudely detected with pressure switches. The embedded MH sensor provides accurate positive feedback indicating where that cylinder is at any point in time.
• The powerhead latching cylinder was using infrared switches which would often cause a work stoppage so operators could clean off the lens. By replacing the infrared switches with embedded MH sensors, downtime was mitigated and productivity increased.
•The sump cylinder, which strokes 22.5 feet, was using a cable encoder that needed to be replaced once or twice a month because the cable was repeatedly pulled through 22.5 feet and susceptible to water, dust, ice and cable kinks, resulting in high incidence of downtime for maintenance and repair.
“Switching to MTS magnetostrictive sensors may have reduced our cost, but I know it’s saved our customers money, especially in downtime,” said Myers. “Downtime on these machines is huge—revenues can be in the tens of thousands of dollars per hour for these machines, so if they go down, it’s costly.”
The MH sensor, which is used in the shear, steering, base frame latching, base frame locking, and powerhead latching cylinders in the HWM, provides rugged housing and built-in electronics, a pressure-proof sensor pipe that protects the internal sensing element, and a position magnet.
Along with high shock and vibration ratings, the sensor has 200 V/m EMI protection. Designed for cylinders 2 inches in diameter (or larger), the MH sensor now provides a measuring range of 2 to 98 inches while maintaining high levels of accuracy and repeatability.
The RH sensor, which is used in the sump, PTM lift and PTM traverse cylinders in the HWM, features improved precision, with position sensing resolution as low as 1 micron. The resolution is factory-or field-adjustable from 1 to 100 mm. A built-in measurement non-linearity correction improves the sensing accuracy to as low as +/-10 mm, depending on the mechanical application package. The R-Series sensor, with current or voltage analog outputs, has options for programmable dual position and/or velocity channels with a maximum velocity range of up to 10 m/sec, and velocity resolution as low as 0.1 mm/sec.