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Post by John on Dec 26, 2008 9:08:03 GMT -5
It's thought that Longwall mining started in Shropshire, UK, sometime in the late 17th century. Dating was done from opencast workings, where long wall workings were discovered and dated from records in that county of mine workings. It spread throughout the Midlands by the early 19th century.
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Post by John on Dec 27, 2008 9:04:11 GMT -5
Evidence of coal use goes back to the Roman's settlement of Britain, possibly even further back. The Romans coal was probably mined from outcrops, or "sea coles" gathered from beaches and transported to where it was needed. Next stage was sinking shallow shafts down to shallow coal seams and working outwards in all directions until the roof became unstable. These were commonly known as bell pits because of the cross sectional shape of the pits. Evidence of these pits have been found all over Britain. It's thought the next step was accidental, when one bell pit operator broke through into an old bell pit and discovered ventilation! From there all they had to do was support the roof with timber and start learning by mistakes.
Forms of Bord and Pillar mining have been discovered in open cast mines when the overburden was removed from shallow coal seams.
It was during the late 17th century that long wall mining started in Shropshire and spread across the Midlands.
A miner would have a section of a face, it was called a "stint", he'd have an assistant, probably a trainee to "bar" the coal down after he'd undercut the seam with a small pick. The coal would then be loaded into "corves", large baskets that children would drag off the face to pit bottom. Faces would have several roads through the goaf area, these roads were more often only the height of the working seam!
As the age limits for working underground were raised during the 19th century, mechanisation started to creep into mining with rail mounted tubs to replace the corves, then as electricity was introduced, crude undercutting machines started to take over from the hewers.
From early undercutting machines, came the "push" for full mechanisation, the first of the "powered" cutting machines, the Meco Moore slicer cutter evolved, it was a cyclic machine, in that it only cut the coal, and the coal still had to be loaded by shovel. It eventually evolved into a cutter loader and was a success, with many being used before and after WW2. The next machine to appear was a drum cutting machine, it eventually went through many modifications to become the Anderton Shearer Loader we know today. Patents were owned by the UK National Coal Board and licenses were issued to three companies to manufacture it, namely Anderson Boyes of Motherwell, British Jeffery Diamond of Wakefield, and Eichoff of Germany. Other machines were trepanners, variations trepanner shearer. German invented Ploughs which sheared a couple of inches of the face as it was hauled at high speed by chain haulage through the length of the face. Huwood slicer loader, a powered plough that either hauled itself via its own power pack, or was hauled in the same way as the plough.
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Post by John on Dec 30, 2008 11:19:05 GMT -5
As stated, early longwalls were totally handgot and coal transported by children.
Conveyors and explosives appeared on the scene and faces became more mechanised, with the invention of the undercutting machines modern coal production had arrived, this was around the turn of the 20th century. A face was operated on a three shift system, day shift would undercut the coal, it would be drilled for shotfiring, then fired down. Then the coal would be shovelled on to the face conveyor, props set, conveyor advanced on another shift, then the whole face timbered up on another shift. This was called a conventional longwall face. Sometimes two faces sharing the common main gate were operated, these were called "double units", main problem was both had to keep up with each other, or ventilation problems could occur.
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Mick
Shotfirer.
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Post by Mick on Dec 30, 2008 15:58:38 GMT -5
Hi John The way longwall hand got was worked at Gomersal was day shift filled face off then afternoons came on and broke belt ripped gates and started to cut face. Also on afternoons gob drawers cut props out of old belt track and drew steel bars out of gob,at the same time borers bored face. Night shift came on and built conveyor up on face and cut wot was left of the face,the next day it all started again. happy days Mick.
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Post by John on Dec 30, 2008 16:37:02 GMT -5
Thanks Mick, I had to think back to mining technology lessons we had at Tech years ago, never worked on hand got faces. Just missed one by a year or so.
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Post by John on Dec 30, 2008 16:51:23 GMT -5
Next came the fully mechanised faces, well as far as cutting and loading goes. During the 1950's and 60's, the UK National Coal Board who ran the UK coal industry went all out to mechanise the industry. First came the Meco-Moore Slicer Loader which took a web of coal loaded it on an AFC, then "ploughed back" to the main gate cleaning any coal left from the cutting process. The AFC would then be pushed over by either air rams or hydraulic rams. Support would either be steel friction props on link bars or hydraulic, (Dowty) props.
Powered roof supports came along in the mid to late 1950's. As the shearer evolved from early under cutting machines and became proven, then it replace the Meco-Moores.
Together with powered supports and AFC's, the Anderton Power Loader became the machine of choice. It soon developed into double ended shearer loaders capable of high outputs and is the machine commonly used today throught the world. In it's early years it was manufactured by Anderson Boyes, as the AB16/125 and 200 hp machines, smaller ones were made, BJD Magnamatic shearers, and a German Eichoff. Other machines around in the 50's and 60's were made by Anderson Boyes and BJD of Wakefield, they were trepanners and trepan shearers, usually used to produce "large coal" for household and industrial uses.
There were some other makes of shearers, the Japanese have pioneered a range which are still made, there was a French shearer, I believe a Polish and a Russian unit. I know the Chinese are now in the business with face packages, Joy Manufacturing of the USA produce face packages.
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Mick
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Post by Mick on Dec 30, 2008 16:55:18 GMT -5
Glad to help John,When i started at Gomersal in 66 all the faces were hand filled and apart from a couple of time ware we tryed machines it closed in 73 still hand filling. Mick
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Post by John on Dec 30, 2008 17:04:10 GMT -5
I started my apprenticeship around March of 64, I know there was a hand got face at Bestwood, our area HQ, but don't know of any others in the South Notts Area Mick. Trev who I know from way back knew of them and worked on some, but he's about 5 years older than me.
Just for the readers, those faces were from around 42 inches high to 60 inches high that I worked on.
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Mick
Shotfirer.
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Post by Mick on Dec 30, 2008 18:35:02 GMT -5
Them faces i worked on were 22in to 30in,and there was about 4 to 6ins of water. We used to fill 15 yards with a 6ft cut.some of the faces were as you said double units,but on the hole they were single units about 100 to 150 yards long. Mick.
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Post by John on Dec 31, 2008 8:34:18 GMT -5
All the mechanised faces I've worked on have been 260 yards and upwards in length Mick. I was looking at Cliftons abandonment plans yesterday and measured 12's face, it was around 280 yards long, pretty long for a 1960's face! That was the highest face I worked on in England too, at 60 inch cutting height. Right at the far western edge of the pit and pretty close to the Bunter Sandstone!
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Post by welderpaul on Jul 13, 2013 14:23:54 GMT -5
What determined the length of a face? Was it just laid out to a standard (most efficient?) length? or did geology/mine layout determine the lengths? Ta
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Post by Wheldale on Jul 13, 2013 15:39:55 GMT -5
I'm not sure about face width, I always thought 200m was the average width for a retreating panel in the UK. I've just been looking at some info about Kellingley and it says the face width is 350m, panel length is 2700m. Maybe with bigger capacity shields face width can be increased? www.ukcoal.com/businesses/deep-mining/our-deep-mines/kellingley-deep-mine#!prettyPhoto I would have thought ventilation would have played a part in the width of a face from the point of view of emissions of gas and quantity of air passing through. It would be interesting to find out what pillar of coal is left between faces at Kellingley.
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Post by John on Jul 13, 2013 15:46:31 GMT -5
What determined the length of a face? Was it just laid out to a standard (most efficient?) length? or did geology/mine layout determine the lengths? Ta Today costs, years back lack of high horsepower motors. The longer the face, the more horsepower required to haul the AFC chain full of coal. On 200 yard faces we used three 60 hp motors, then came the 125hp motors, two of them at the M/G drive and one at the T/G drive, then you have other problems, back then we were only allowed 550 volts on the face, this went up to 1100volts late 60's early 70's with exemptions granted due to sensitive earth leakage in the GEB's..
Now faces are reaching 1000ft in length, same problems, cost, horsepower and power availability. Joy faces now used DC variable speed motors as well as variable frequency drives, these run on 3000 plus volts. One Australian company has a drive motor run on 11Kv!!
Fluid coupling drives are at last on their way out and direct drive variable drive motors are replacing them. These are speed controlled via sophisticated electronics, which monitor speed, load and other factors.
I think the longest face I worked on in the 60's was around 200 yards, I'd have to get a ruler out and measure one on the abandonment plans. We used to move the transformer up every couple of days to keep the face voltage up to scratch.
Costs involved, trailing cables large enough to prevent power losses, high horsepower drive motors, heavy duty chains for the AFC, large transformers to supply the high power for the large motors.
1960's 150Kva transformers, one in each gate road, late 60's 70's 200Kva transformers, late 70's early 80's 600Kva transformers, now rated at 1100 volts on the secondary.... Today 1.5 to 2 Mva transformers, 11Kv to 3.3Kv or higher.... I believe theres a couple of companies now making 5Mva gas filled transformers for modern faces, that's a hell of a lot of power!!
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Post by Wheldale on Jul 13, 2013 15:48:18 GMT -5
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Post by John on Jul 13, 2013 15:50:15 GMT -5
Joy now have shields that yield at over 1000 tonnes, ventilation is no problem with longwall faces, it's far easier to ventilate a longwall than bord and pillar faces.
The block of coal between panels is worked out by the Manager, in conjunction with geologists and rock mechanics, like all the support rules.
The retreat faces I worked on in Oz had two entry chain pillars between each longwall panel and a large safety barrier between the main road and where the face line finished, I'll see if I have a plan of Angus Place to show how it worked.
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History.
Jul 13, 2013 15:54:59 GMT -5
via mobile
Post by Wheldale on Jul 13, 2013 15:54:59 GMT -5
I was just wondering John with ventilation if when a seam is very gassey if there was a maximum length depending on the velocity of ventilation current?
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Post by welderpaul on Jul 13, 2013 16:16:21 GMT -5
Was Kellingley mining the coal that was once part of the Selby coalfield?
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History.
Jul 13, 2013 16:24:27 GMT -5
via mobile
Post by Wheldale on Jul 13, 2013 16:24:27 GMT -5
Selby worked the Barnsley seam and a small area of the Stanley main seam. Kellingley works the beeston and silkstone seams.
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Post by welderpaul on Jul 13, 2013 16:28:31 GMT -5
John - when you say the shields yield at 1000 tonnes, what's that? Do they start to close up at that weight rather than damage themselves? 1000T is some massive load. What would happen on a face if the shields started to yield? Could that spell the end of a face? Did shields/chocks ever get permanently stuck and left behind?
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Post by John on Jul 13, 2013 17:46:52 GMT -5
John - when you say the shields yield at 1000 tonnes, what's that? Do they start to close up at that weight rather than damage themselves? 1000T is some massive load. What would happen on a face if the shields started to yield? Could that spell the end of a face? Did shields/chocks ever get permanently stuck and left behind? OK, one thing you must realize is you don't "hold the roof up" That's going against nature, you control the roof to how you want it to lower..(convergence)...That's the theory anyway.....Sometimes nature won't co-operate... On longwall faces you have forces you want to control to take weight off the face to allow the machine to cut easily,(Pressure arc) so the hydraulic supports are so designed to "cantilever" those forces into the goaf...Hope I've explained that clear enough... Now, there is no way we can "hold" weight, (convergence) from coming on a face, all we can do is control it as much as engineering allows. So each support has relief valves, that when the weight reaches a certain point, lets say we have 100 ton relief valves on our powered supports, when 100 tons is reached, the relief valve will open and close when that weight is released. On the old chocks years back we could hear the supports "clicking" as they relieved, never heard the big shields make any noise though!! Now Joy has a range of supports that yield when they have loaded to 1000 plus tonnes, it's only a millimetre or so, once relieved the valve closes, much like a 5 ton car jack, once you reach 5 tons you cannot exceed it, the safety relief valve opens each action you put on it.... Again, any hydraulically operated machine once it reaches it's limit, has an overload relief valve to protect it. In powered supports, the relief valve does perform two functions, first it controls the convergence and second if that weight starts to come on "heavy", it will relieve at a steady pace to prevent the legs on the support from "binding". Normal convergence is at a steady pace, so many mm a day, sometimes it will be feet in minutes!! Scary!! These large heavy duty shields are designed to control that convergence to a better degree than the old Dowty Roofmasters and Gullick chocks did.
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Post by dazbt on Jul 14, 2013 13:40:36 GMT -5
"On longwall faces you have forces you want to control to take weight off the face to allow the machine to cut easily"
Can you explain that in a bit more detail J? ............ just enough to make it clear to a thick pit fitter
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Post by John on Jul 14, 2013 14:59:04 GMT -5
"On longwall faces you have forces you want to control to take weight off the face to allow the machine to cut easily"
Can you explain that in a bit more detail J? ............ just enough to make it clear to a thick pit fitter Think "cantilever" Daz, it's even more important on a retreat face so as not to cause roof failure on the gate roads... I think there's a good section on roof control on longwall faces at the Wollongong University website. It practice, you need to cause the roof to fracture at the back of the supports. I take it you have never come across a weighted face?? I recall one in the Piper seam, not only was the face converging heavily, but the shearer was struggling to cut the coal, one problem led to another, slow shearing to the tailgate, roof supports having to be chopped out to flit the shearer back to the maingate. Thinking back, I wonder if heavy duty supports had been available, would it have eased the problem??? Who knows?? But the brand spanking new ABDECMT saved our day, well for a few more months that is... Thinner machine, cutting both directions, and cutting 24 hours a day with a few cuts over the weekend..
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Post by dazbt on Jul 14, 2013 15:37:31 GMT -5
"On longwall faces you have forces you want to control to take weight off the face to allow the machine to cut easily"
Can you explain that in a bit more detail J? ............ just enough to make it clear to a thick pit fitter Think "cantilever" Daz, it's even more important on a retreat face so as not to cause roof failure on the gate roads... I think there's a good section on roof control on longwall faces at the Wollongong University website. It practice, you need to cause the roof to fracture at the back of the supports. I take it you have never come across a weighted face?? I recall one in the Piper seam, not only was the face converging heavily, but the shearer was struggling to cut the coal, one problem led to another, slow shearing to the tailgate, roof supports having to be chopped out to flit the shearer back to the maingate. Thinking back, I wonder if heavy duty supports had been available, would it have eased the problem??? Who knows?? But the brand spanking new ABDECMT saved our day, well for a few more months that is... Thinner machine, cutting both directions, and cutting 24 hours a day with a few cuts over the weekend.. Thanks for that j, but, are you saying that the convergence should be prevented from acting on the coal and directed totally above and beyond the rear of the roof support to create the gob breakline, [/I] "not only was the face converging heavily, but the shearer was struggling to cut the coal,"[/i] do I take it that what you're saying is that it was as a result of the weight acting on the face that made it difficult for the shearer to cut the coal ........... or, did you really mean that the convergence reduced the shearer body clearance and trapped the machine, which is a bit different to 'struggling to cut the coal'?
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Post by John on Jul 14, 2013 16:42:00 GMT -5
Think "cantilever" Daz, it's even more important on a retreat face so as not to cause roof failure on the gate roads... I think there's a good section on roof control on longwall faces at the Wollongong University website. It practice, you need to cause the roof to fracture at the back of the supports. I take it you have never come across a weighted face?? I recall one in the Piper seam, not only was the face converging heavily, but the shearer was struggling to cut the coal, one problem led to another, slow shearing to the tailgate, roof supports having to be chopped out to flit the shearer back to the maingate. Thinking back, I wonder if heavy duty supports had been available, would it have eased the problem??? Who knows?? But the brand spanking new ABDECMT saved our day, well for a few more months that is... Thinner machine, cutting both directions, and cutting 24 hours a day with a few cuts over the weekend.. Thanks for that j, but, are you saying that the convergence should be prevented from acting on the coal and directed totally above and beyond the rear of the roof support to create the gob breakline, [/I] "not only was the face converging heavily, but the shearer was struggling to cut the coal,"[/i] do I take it that what you're saying is that it was as a result of the weight acting on the face that made it difficult for the shearer to cut the coal ........... or, did you really mean that the convergence reduced the shearer body clearance and trapped the machine, which is a bit different to 'struggling to cut the coal'? [/quote] The way I understood it Daz, was convergence puts pressure on the coal in the faceline, to counteract that pressure, ie relieve it, roof supports are designed to "slope" from front to back to act like a cantilever, causing the stresses to form a natural breakline at the rear of the roof canopy, there by relieving direct stresses on the coalface itself. Yes, on the shearer in the Piper seam, the coal was under heavy stress, so the shearer was finding cutting very heavy and at the same time with convergence was being "pinned" It was so serious, management ordered coal cut 24 hours a day, the face was a contract face, the face crew were working virtually for nothing, and working very hard. The shearer cut out, then each chock had to be lowered and the roof chopped out to get the shearer under it. Hence the reason Area diverted the first conveyor mounted trepanner, which was supposed to go to another pit for field trials , to try and save the face...Either that or we were down to two faces for a couple of months..
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Post by tygwyn on Jul 14, 2013 18:56:58 GMT -5
Looks like a case of to big a machine in the said seam,to allow for clearance when weighting comes on.
I would have said the coal should have been easier to cut in them circumstances,when weighting is on,the coal pounces off the face,a sure sign of weighting,if one had`nt noticed earlier.
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Post by dazbt on Jul 28, 2013 15:43:30 GMT -5
"I take it you have never come across a weighted face??"
I left replying to this topic and particularly your question above J just in case anyone else might have posted their thoughts on this topic of roof control and particularly their opinions about your personal experiences of a coal face being made more difficult to cut as a direct result of roof convergence forces acting upon it, (not to be confused with the actual reduction of machine clearance and physical restrictions of reduced height and machine clearance as you made clear). In answer to your question or presumption that I have never come across a weighted face, what I can say is that I haven't come across a face that has been made more difficult to cut in terms of 'pick force' particularly, but I have certainly worked on one or two that have had weighting problems that have affected directly machine clearance and therefore performance, not to mention weighted faces that have been under compressive forces to the extent of being categorically dangerous, faces where normally hard standing coal has literally in part exploded, faces where coal has been pressurised into spalling, sometimes literally two metres in depth from what should have been the definitive face line, but, in honesty I can't recall having worked on a single face where the direct effect of weighting has prevented the machine from actually cutting the coal in terms of increasing coal hardness, reducing 'cuttability' or generally producing compressive forces that reduced a shearer's performance other than by a reduction in clearance, I'm not saying that it couldn't have happened or doesn't still happen, I'm simply answering your question as to whether I have experienced a face weighting. Having worked on at least 200 longwalls around the world, (200 being a conservative estimate by the way) the chances that I've worked on a 'weighted face' somewhere or other are fairly good, even if I haven't had the mentality to recognise that fact. What I do know for definite, is that I have, along with others, have on occasions, prayed to Saint Barbara to grant us the benefit of putting weight forward onto a coal face probably more times than I've prayed for her to take it off.
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Post by erichall on Oct 3, 2013 6:59:02 GMT -5
One of the most frightening shifts I ever worked was in the Blackshale Seam at Markham Colliery. The new face had been developed and had started advancing. Unfortunately, the roof of the Blackshale tended to be rather 'strong' in that the Goaf/Gob (call it what you like) had not broken down and the face had advanced a good number of yards. During the shift the first 'weight' came onto the face and props started to really take up the load. The goaf started to descend at what seemed an alarming rate, until finally it broke along the line of the rear chock legs, at which point the 'weight' started to lift off the chocks. The theory behind this is that, whenever a portion of seam is removed, the immediate roof forms a pressure arch, with one side on the coal in front and the other on the goaf behind. Once the goaf has broken 'normal service is resumed' and the pressures of the immediate roof then settle with one point in the coal in front of the face, and the other on the rear line of supports. It was always a point on a Blackshale face which was greeted with a relieving sigh, but care always had to be taken since the first flush of the goaf breaking would also release a flush of methane which had been stored in the inbroken goaf. Engineers used this 'pressure arch theory' to help determine face lenghts, types of support used and also in some cases the actual method of goal getting. The pressure arch could be used to aid the cutter loader, in that coal with some pressure on it made for easier cutting than 'solid' coal. This 'weighting' was closely observed by all concerned, with the comment being passed from the off-going to the on-coming shift 'watch it. Gob's not broken for a day or two'.
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Post by John on Oct 3, 2013 9:32:30 GMT -5
What you mention Eric happened on all our faces at Angus Place, some would "hang up" for many yards because of the thick sandstone roof, many hundreds of feet thick! Fortunately the faces never weighted through it. I was swing shift electrician on the longwall there for a long time and saw several new faces start off cutting, all retreat and between 10 and 14 feet cuts. Methane was no problem, what methane was released was diluted in the Bleeder heading behind the initial face line, thereafter never saw any readings either on a D6 or oil lamp, in fact methane was a question posed by someone in the mines monthly magazine.
Being the third shift on, we stopped cutting many times at the initial startup of a new face, I mentioned this before in a post, the goaf was holding up for many yards, almost two days of cutting!! Imagine the huge expanse of unsupported roof behind the chocks!!
We came on shift and the Manager was at work, he'd come in late to make a decision whether or not to use a few well positioned shots to help the goaf collapse. Before we started cutting, the Deputy and the Manager went into the returns to examine the goaf, the whole face was eerily quiet, no excess weight causing the supports to yield..I never asked the question, but guessed the Manager was worried that if we had too much goaf exposed, eventually when it fell, it would cause severe damage to the chock shields. The decision was made to cut another shear and assess the situation after that....Didn't have to, it dropped. We had a couple that were as bad as that, most just hung up for about 50 to 60 yards..
Sounds a lot, but remember we had thick sandstone layers above us, not shales..
I wonder what stress a hung up goaf would put on gate roads in an advancing longwall face??
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Post by pitsparky on Nov 17, 2013 10:56:39 GMT -5
I can remember working on a new face at Burradon Colliery in Northumberland and it was decending downhill with the goaf behind us and it took about a week or more before the roof broke and the goaf fell !!, it was a weird feeling to look behind you and see this huge " Dance Hall " about 110 yards wide.
Everybody on the face was terrified that it would break and slide down and crush everything and everybody on the face, and the first question you asked the shift you were relieving was has it broken yet?, but when it did come it just dropped and stayed put.
I was on another face in the Bensham seam ( later called " The Maudlin " ) and I was about to step onto the face from the tailgate end and the under manager George Lavender grabbed my arm and said " Don't go on there Malcolm the chocks have bottomed out!"
They were 50 ton Desford chocks set about every couple of yards apart and there was so much weight coming down that over the course of the next few hours they were all pushed into the ground and the face and everything on it was lost.
A very sobering thought!.
Malcolm.
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Post by John on Nov 17, 2013 12:49:47 GMT -5
I can remember working on a new face at Burradon Colliery in Northumberland and it was decending downhill with the goaf behind us and it took about a week or more before the roof broke and the goaf fell !!, it was a weird feeling to look behind you and see this huge " Dance Hall " about 110 yards wide. Everybody on the face was terrified that it would break and slide down and crush everything and everybody on the face, and the first question you asked the shift you were relieving was has it broken yet?, but when it did come it just dropped and stayed put. I was on another face in the Bensham seam ( later called " The Maudlin " ) and I was about to step onto the face from the tailgate end and the under manager George Lavender grabbed my arm and said " Don't go on there Malcolm the chocks have bottomed out!" They were 50 ton Desford chocks set about every couple of yards apart and there was so much weight coming down that over the course of the next few hours they were all pushed into the ground and the face and everything on it was lost. A very sobering thought!. Malcolm. I started U/G after a face called 10's had converged rapidly...I worked with the same face team on another face and asked them what happens when it starts converging....."Crawl like effing 'ell" they said. The Deputy told me after it had settled down, he asked for a volunteer to go through the face with him.........He and the volunteer got through, most of the way flat on their bellies...From 5ft down to almost closed up chocks...Eventually it closed up solid, the only equipment they recovered was scrap iron, but it was recovered.
That's one of the things that did scare me on faces, rapid convergence, I'm thankful I never experienced it.
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