Ten facts about longwalls:
1. Geology is not the cause of roof falls.
2. 100% of roof falls are caused by people.
3. 95% of roof falls are avoidable.
4. Poor roof conditions are frequently caused by faulty roof supports.
5. Roof falls statistically occur after a shutdown.
6. A 950 ton roof support will hold the weight of two fully loaded Boeing 747-400 passenger jets … with ease.
7. Set load is more important than yield load.
8. Longwall roof falls cost the coal industry millions of dollars every year.
9. The powered roof support system on a modern longwall is the most physically abused, grossly neglected and totally misunderstood integration of leading edge technology that exists today … and you can’t buy one for less than $15 million.
10. YOU can make a difference.
Today’s modern longwall is a highly sophisticated technological marvel when compared to the “simple” equipment used 30 years ago. Equipment has got bigger, heavier and smarter, with computers that can do almost anything.
Unfortunately, roof falls seem to have also got bigger, the size of falling rocks heavier, and the people needed to fix the equipment need to be much smarter.
So why is it we still get bad roof conditions and cavities?
The answer lies in our approach to keeping our longwall healthy, and knowing the important things to look for. The 10-point Longwall Health Checklist is a back to basics approach which can be applied to any longwall new or old, simple or complex.
Answer the following questions about your longwall, take note of your score and the health of your longwall will be revealed. When selecting your answers, ensure you are completely honest, and avoid self-delusion!
The 10-point Longwall Health Checklist
1.What is the system pressure being supplied to your longwall supports?
a. More than 4600psi.
b. 2500-4500psi.
c. Less than 2500psi.
d. Don’t know.
2.What is the designed set pressure for your supports?
a. More than 4600psi.
b. 2500-4500psi.
c. Less than 2500psi.
d. Don’t know.
3.Is your longwall straight?
a. Always.
b. Most of the time.
c. Almost straight sometimes.
d. Never.
4.Where is support advance relative to the shearer?
a. Just behind the lead drum.
b. Just behind the trailing drum.
c. 10 supports behind the trailing drum.
d. Depends upon the driver.
5.Is positive or guaranteed set used on your longwall?
a. Yes, all the time.
b. Some are ON and some are OFF.
c. I haven’t looked recently.
d. What is guaranteed set?
6.How would you rate your hydraulic maintenance?
a. Immaculate. There are no leaks or bypasses.
b. Good. Leaks and bypasses are fixed within 48 hours.
c. Okay. There are up to 200 leaks and bypasses at any time.
d. What maintenance? There are leaks and bypasses everywhere!
7.How would you rate your horizon control?
a. Brilliant. Auto steering works perfectly.
b. Good. Our shearer drivers all work together.
c. It depends upon which crew is on the longwall.
d. Ask the shearer driver, it’s his job.
8.Do you have an AFC Creep Management Plan?
a. Yes.
b. No, the face crews take care of that.
c. No, that’s the longwall coordinators job.
d. Don’t know.
9.What is the actual canopy tip to face distance on your longwall?
a. Less than 16 in.
b. 16-30in.
c. More than 30in.
d. Don’t know.
10.Where does the roof break line appear?
a. At the back edge of the shield canopy.
b. Over the shield canopy.
c. Behind the shield canopy.
d. In front of the shield canopy.
For every answer marked (a), you score five points; (b) three points; (c) one point;
and (d) nil.
How did I do?
Score 50: You have a perfectly healthy longwall and you are probably in the wrong job. Or perhaps you are prone to self-delusion and don’t go underground too often?
Score 40-49: Excellent. Your longwall is in good shape and is well managed. Roof falls are not common and the roof is generally good.
Score 30-39: This longwall needs some attention, and there is the potential for some problems. The roof is probably in reasonable shape, but breaks in the roof are not uncommon and falls do happen. Face spall is probably very common.
Score 20-29: This longwall is sick. There is potential for some serious roof problems. Consult your Longwall Doctor immediately.
Less than 20: Surely not?
Recommendations
These very basic checks can reveal a great deal about the state of equipment and the way in which your longwall is managed. Next time you visit your longwall run through the checklist and identify the areas where some therapy may help.
* Nick Wills is a longwall consultant.
