6 minute read
Mining operations............................................................... 5
Mining operations
Advertisement
It is presumed that the operator of this machine is experienced in continuous mining techniques. This section of the manual will present some basic rudiments of Continuous Miner mining operations, but should not be considered in any way as a complete how-to of mining techniques. It is recognized that each mine will have their own methods and techniques which work best for him.
One of the keys to good productivity with a Continuous Miner is to know the correct depth of sump which, when the cutting cycle is completed with shear-down, gives enough coal to adequately fill one haulage vehicle.
Another important factor is to do as much advance cutting as possible, while awaiting the haulage vehicle, to load up the gathering head pan. When the vehicle arrives, the gathering head can then work at maximum efficiency to load out the accumulated coal while the remainder of the cutting cycle is being completed.
The following discussion outlines the various steps of an efficient Continuous Miner mining cycle.
Preparation of the face for the next cut
The first view in Fig. 35 shows Continuous Miner approaching a freshly cut face. The operator has the cutter head lowered to prepare for making a 2’ to 3’ deep sump cut at the bottom of the face. This is done to make clearance for the gathering head blade when the miner is sumping at the top of the face. In this manner, the miner can make a deeper sump into the top of the face.
Fig. 35: Preparation of the face for the next cut
Approaching a freshly cut face
The next view in Fig. 36 depicts the miner having made a 30 in. sump cut at the bottom of the face. The operator will now back the miner out of the cut and raise the cutter head to the mine roof.
Fig. 36: Sump cut at the bottom of the face
30” sump cut at the bottom of the face
In the final view in Fig. 37, the operator has backed out of the bottom cut and raised the cutter head to the roof, positioning the miner for making a top sump.
Fig. 37: Positioning for top sump
Positioning for top sump
The next face cut
Having cut bottom clearance for the gathering head blade, the operator can now make a deep sump at the top such as a full drum diameter as shown in the first view of Fig. 38. He can commence his down-cut until his gathering head pan is full. Optimally, all this is being done while awaiting the next haulage car so that maximum loading rate can be achieved when the car arrives.
While loading the haulage car, the operator completes the down-cut to the mine bottom as shown in the second view of Fig. 38.
Depending on the depth of the top sump, a small cusp of coal will be left behind the drum on the mine bottom. This cusp is removed by backing the miner out of the face a small distance while the cutter head is running.
The miner is now in a similar position as shown in the first view of Fig. 35 and the operator can proceed with the next cutting cycle.
Using the stabilizer shoe
The stabilizer shoe is located under the rear deck of the main frame and beneath the conveyor. It is hinged at its front edge and is lowered by a hydraulic cylinder.
The stabilizer shoe serves two purposes:
■ To elevate the rear of the miner for maintenance work.
■ To provide a higher down-cut force at the coal face while shearing down during mining operations.
The advantage of increasing down-cut force at the face while shearing down is important particularly when cutting hard coal seams. Fig. 38 illustrates the advantage of the stabilizer shoe in the down-cut application.
Fig. 38: The next face cut
Miner sumps in at top and begins downcut Miner completes downcut with small cusp remaining
The miner is shown in the middle of its shearing down cycle in Fig. 39. Without the stabilizer shoe deployed, the machine will tend to rock back on the rear of the crawlers. The distance from the miner’s center-ofgravity to the rear of the crawlers is noted as “Lever Arm w/o Stab Shoe”.
Conversely, with the stabilizer shoe deployed, the miner will now tend to rock back on the shoe, providing a longer lever arm. In the case of this miner, the lever arm with the stabilizer shoe down is more than twice the lever arm without the stabilizer shoe, thus doubling the down force available for shearing down. This increase in down-cut force will improve the speed and efficiency of the shear down portion of the cutting cycle.
The miner is configured with an optional automatic stab function which will lower the stab during the shear down cycle and raise it again automatically.
Fig. 39: Effect of using stabilizer shoe on downcut force
Downcut Force
Machine Weight
Lever Arm W/O Stab Shoe Lever Arm With Stab Shoe
Shearing up and down
Most Continuous Miners have their center-of-gravity located forward of the center of the crawler footprint. This weight distribution makes the miner inherently more effective in shearing down rather than up because shearing down takes advantage of the miner’s weight to maximize down-cut force.
Shearing only downward requires the cutter head to be raised without cutting during each mining cycle, and a non-productive dead time is introduced in the mining cycle.
An alternative particularly useful in softer, easier cutting coal seams is to shear both up and down while advancing, thus maximizing the time spent actually cutting coal in the total cycle. This sequence is illustrated in Fig. 40.
The first view in Fig. 40 shows the miner having sumped in at the top of the coal face. If the operator intends to shear down and up, the depth of sump should be no more than half a drum diameter; otherwise, a cusp will be left at the bottom or top after shearing which will require trimming.
The second view shows the miner in the middle of the downcut.
Having completed the downcut, the third view shows the miner sumped in about half a drum diameter at the mine bottom.
Fig. 40: Shearing up and down
Finally, the last view shows the miner in the middle of the upcut. The technique of successively shearing up and down is particularly productive when the miner is working in conjunction with a continuous haulage system.
Miner shearing down
Miner sumping in at mine bottom Miner shearing up
