During the late 80s to mid 90s, longwall consultant Nick Wills* helped many longwall operations recover from massive falls of roof and helped pioneer some of the techniques now common in the industry. In recent years, however, he has concentrated on preventative techniques through education and training and correct specification of equipment. Here Wills challenges operators to test their knowledge of longwalls.
The scientific theory behind, and engineering solutions to, longwall strata control are intricate and complex, and to this day there are many unanswered questions. However, the basic rules of longwall management are not complex, but they do require strong discipline, high standards, engineering excellence and continuity of both men and machines.
Like many other aspects of industry, results achieved are based on the quality of resources applied. Apply substandard resources and you will get substandard results. Apply the best resources available and you will have the best prospects of achieving the best results.
To the questionnaire. An acceptable pass rate is 75%. Anything less and you really should be looking at development work. Before we continue, please read the warning below. You must accept the conditions of this questionnaire, or else proceed to the next article.
WARNING: Completion of this questionnaire is entirely at your own risk. The author hereby absolves himself and his family (and friends) of any subsequent psychological, financial or emotional problems that may ensue, and for any loss of earnings, feelings of guilt, or indeed sudden euphoria that may or may not occur.
Questionnaire
1. Which company manufactured the first ever 4-leg powered support in 1946?
a) Westfalia
b) Joy
c) Dowty
d) Gullick Dobson
e) Huwood
2. Which of the following is the most important for effective roof support?
a) Setting load, ie the load which is initially put into the roof.
b) Yield load, ie the pressure that is built up in the legs through weighting of the roof strata.
c) The width of the support: the bigger the better.
3. Statistically, longwall roof falls usually occur after a period of downtime. True or false?
4. During longwall operations, the hydraulics pumps are temporarily shut down. Do you:
a) Continue to cut until the shearer reaches the maingate leaving all the supports back and catch up later.
b) Cut to the maingate but only if the roof looks competent
c) Stop the shearer until chock pressure is restored?
5. On a typical 200m longwall using 800 tonne yield roof supports, approximately how much load would be lost if the system pressure drops from 320 bar down to 240 bar?
a) None at all because the supports still yield at 800 tonnes.
b) About 17,000 tonnes.
c) Quite a bit actually.
6. How many shears can be cut using less than designed system pressure before damage to the roof could occur ahead of the coal face?
a) None.
b) A maximum of three in weak roof (shale) and five in strong competent roof (sandstone).
c) No limit. Our roof conditions are always bad and it makes no difference.
7. What does a yield valve do on a powered support leg cylinder?
a) Protect the operator.
b) It gets rid of excess emulsion when the pumps are set too high.
c) Protects the roof from getting crushed.
d) Protects the powered support.
8. Positive Set should be turned ON in cavities. True or false?
9. AFC creep* has been responsible for the following events on longwalls in Australia:
a) Loss of roof control.
b) Destruction of the maingate drive frame.
c) Toppling of roof supports.
d) Failure to cut out at face ends.
e) Iron bound supports.
f) All of the above.
* In this context AFC creep refers to lateral migration of the face conveyor, not a disreputable salesperson.
10. According to the JCB statistics, which Australian longwall mine produced in excess of 6 million tonnes for the year ended 2001?
a) Crinum
b) Oaky North
c) Moranbah North
d) Kestrel
e) South Bulga
11. If a support leg is setting on the minor stage because the major stage is already fully extended, this could result in:
a) Up to 50% less set load and 50% less yield load.
b) Up to 50% more set load and the same yield load.
c) Loss of emulsion.
d) No appreciable difference.
12. Spalling coal is a direct consequence of:
a) Inadequate roof support.
b) Weak coal.
c) Horizontal stresses.
d) Earth tremors.
13. What is the theoretical setting load of the supports on your longwall?
a) 75% or more of yield load.
b) An awful lot.
c) 1000 tonnes.
d) Ask a friend?
14. In a cavity situation, support canopies should be set:
a) As high as possible to catch the roof.
b) One web back from the AFC.
c) At the same level as those under good roof.
15. Congratulations! You have a brand new longwall! Your manager says: “Look chaps we want to make this one last a bit longer than the last one, so we only want to set alternate supports to the roof. We’ll halve the maintenance bill, and use less spares and we will still be putting the same load into the roof as our old clapped out supports.” Do you:
a) Apply for long service leave?
b) Tell him to go forth and multiply?
c) Smile and nod, then have him certified?
d) All of the above?
16. The roof on your longwall is fractured, and some minor cavities are present. There is coal spalling on the AFC ahead of the shearer. The first thing you do is:
a) Keep cutting and leave it to the next shift to fix?
b) Call the geotech and tell him to put weak roof on his hazard plan?
c) Immediately check the support setting pressures and tighten up support advance behind the shearer?
17. At the start of your shift you notice that the middle of the face is hanging back in a large bend. Do you:
a) Leave it until the next shift as you did a straightening cut yesterday?
b) Leave it for dogwatch as they are assigned to do the straightening cuts?
c) Look the other way and hope someone else takes responsibility?
d) Do a straightening cut and fix it?
18. You are working on the supports at the maingate and you notice the AFC is climbing very steeply from 20 to 50 chock. The shearer is already at the tailgate. Do you:
a) Keep quiet, the shearer driver always knows what he is doing?
b) Call the shearer driver on the DAC and politely suggest he might take a look?
c) Pull the AFC back and ask the shearer driver to trim the floor?
19. On your way in to the longwall, as you pass the hydraulic pump station, you notice that the pressure being developed by the pumps is only 230 bar. Do you:
a) Report it to the longwall coordinator at the end of your shift?
b) Report it immediately to the longwall deputy and fitter?
c) I never look at the pump pressures so I’ll just go to question 20?
d) Carry on regardless and say she’ll be right?
20. In 1984, which legendary (Pommie) coal miner broke the “world weekly production record for an advancing longwall in the infamous Barnsley Seam of Yorkshire” and what was the tonnage?
a) Nick Wills: 17,100 tonnes (in a 5 day week)
b) Brian Nicholls: 35,670 tonnes (in a 7 day week)
c) Chris Taylor: 72, 000 tonnes (with one hand tied behind his back)
For answers and scoring see attached.
