This is misleading as there are no “tricks” with horizon control.

The scenario: the longwall is functioning perfectly, the face is straight, support pressures are good, the equipment is well maintained and the conditions are excellent.

The question: what is the quickest and most effective method of bringing this longwall to a screaming halt without breaking anything or switching anything off?

The answer: cut a large step in the floor and ignore it.

The result: a perfectly good longwall that within a few shears will stop because either the shearer cannot get through the face or worse, the supports are at full extension and that perfectly good roof is about to fall in.

Fact: longwalls can be incredibly productive units but they are extremely unforgiving of operational and engineering errors or human errors for that matter.

Fact: whatever profile the shearer cuts, everything else must follow.

Fact: it will take eight to 12 shears to fully recover from an ignored “bad cut”

The key word in the question above was “ignore”. Cutting a large step in the floor can happen to the best of shearer drivers (even with automation) but ignoring a bad cut will lead to dire consequences.

The first indication of a bad cut in the floor is when the armoured face conveyor is pushed over and the pans either rise or fall on the face side. Remember, the next time the shearer comes through it will be cutting at that new angle.

Tip: if the angle of the AFC looks abnormal then it probably is!

Tip: if the pans start to rise, pull the AFC back and trim the floor.

Tip: if the pans start to fall, pull the AFC back and fill the hole.

Failure to fix the problem immediately can result in the following:

• Rapid loss of extracted height;
• No clearance for the shearer under the support canopies;
• Inability of the shearer to undercut the panline;
• Total loss of the coal seam;
• Subsequent manual excavation under the panline to regain height;
• Increase in height of the supports so they are fully extended; and
• Strata failure and roof falls.

In order to prevent such consequences, follow these simple rules:

Dos

• Do a visual recce of the humps and swilleys and angle of the pans before you start the cutting with the shearer;
• Everyone on the longwall should monitor horizon;
• Make small changes in floor horizon in small steps and never on the subsequent cut;
• Take immediate action if a mistake is made, do not carry on and hope someone else will fix it;
• Maintain shearer picks in good order. Blunt or missing picks will cause bad horizon control;
• Ensure a good clean up. AFC pans can ride up on fines. Poor clean-up can also stop full push and the relay bars can “tip the pans” on the goaf side;
• If in doubt pull the pans back and look at the new floor you have cut;
• If auto steering is available, use it; and
• Note the distance from the bottom of the ranging arm to the top of the AFC as a guide to the amount of undercut.

Don’ts

• Don’t cut big steps in the floor – ever;
• Don’t cut up or down on successive shears as you will create a rapidly increasing angle of the AFC;
• Don’t ignore a sudden change in the angle of the AFC. If it looks wrong it probably is;
• Don’t cut with blunt, damaged or missing picks. This will adversely affect horizon control;
• Don’t cut with the AFC stopped; and
• Don’t cut without hydraulic pressure on the rams.

Tricks

• None.

This article first appeared in the September edition of Australian Longwall magazine.