Working thin coal - the coal plow and Hydrominer

In the last couple of years there has been a growing concern about the amount of coal that remains in the productive reserve for the world. At the same time the incoming British Government, which had been somewhat antagonistic to coal while in opposition, may be giving large coal-fired power plants a reprieve. Questions might therefore arise as to how long this fuel source is going to last, if use increases more than projected. While I am not going to answer that specific question today, I will address a part of the issue. Namely what do you use to mine coal when the seams get too thin for modern equipment?

The lowest coal which I personally have mined was about 1 ft 8 inches high. The low coal was caused by a roll in the middle of the face (the floor got closer to the roof) which was normally about 3 ft high (The Beaumont seam at Seghill Colliery in the spring of 1962). In that height you lie on your back, put a pit prop under your shoulder to give you some leverage, and shovel across your chest. In more advanced mining countries it is unlikely that we will return to such manual labor, which is not very productive. So what do you use?

The most productive machine in most longwall operations is the shearer, which I described in the last tech post. The problem is that it most effectively runs on top of the armored face conveyor (AFC) and the power pack that drives the cutting head and haulage unit takes up quite a bit of space. One idea was to take the shearer off the conveyor and have it slide along the ground on special shoes, with the cutting head mounted ahead of it on the longwall. My father had rather strong opinions on this, since two of the mines he worked with had such machines. Remember that the coal conveyor must snake over behind the machine in order to allow the supports to also advance.

To hold the machine together, the gear boxes at each end and the power pack in the middle, there are through-bolts down the machine. Now it breaks down in low coal. The roof is say 2 ft 6 inches above the floor, the machine is 22 ft long, and the conveyor is 7 inches high. How are you going to take the machine apart to fix it? (The answer involves explosives, and is not a “quick fix.”)*

So if the shearer is not an ideal machine, what is? The answer is known as a coal plow (or Hobel in Germany where they were developed by a company then called Westfalia Lunen.) Very simply in some coal types, particularly those that are brittle, the coal at the front of the face is weakened and cracked by the pressure of the overlying ground. Thus if you take a narrow pick and drag it across the coal it will peel off some coal. Put a number of these picks together and the coal between them will also chip off – perhaps to a depth of a couple of inches. Make the machine move down the face rapidly, with the rams pushing through the AFC to keep the plow pressed against the coal, and you have a simple but effective mining machine.

Plow on face – note the picks in the different elements that can be removed to adjust for varying seam heights. (Shield parts removed to show the plow)

The coal in which this is most effective does not necessarily have to be mined over its full height, since often, when undercut, it will fall under its own weight. Depending on the coal strength, the depth of cut of the machine can be adjusted. As a result the coal produced can be quite large, sometimes bigger than the average size of the fragment coming from a longwall shearer face. It is, however, an "interesting" experience, to see one working under a sandstone roof, where the face rolls a bit.

There were a variety of plows built, depending on coal height, coal type, and the speed at which the plow could be moved down the face. It is a fast moving operation, but one that is not that popular at the moment, since, in most higher coal a shearer may be more effective and produce more coal. However in the years to come the plow may make a comeback.

By then, however, it is possible that the picks on the machine, that generate dust, will be replaced by high pressure (10,000 psi) water jets which cut into the coal perhaps a foot ahead of the machine, and allow mining without the generation of the dust and sparks that make current operations so dangerous. It has been done before, and is a relatively simple technology to adapt to future conditions.

Waterjet plow operating underground in Germany (from Gluckauf)

We called it the Hydrominer, and as I learn how, I’ll put up some video on Youtube of it operating. There are better ways of using the jets than those shown, so that the plow can actually mine coal to a web depth of over 3 ft 9 inches (we have) at shearer speeds.

Incidentally longwall mining was not a part of the Modern Marvels review of Coal Mining, though in Part 3 they do show the development of the continuous miner, and shuttle car. (H/t to Pasttense who gives a list of some Youtube films), though there are a number more than I had thought there would be.

* At least in those days they excavated a chamber ahead of the machine by blasting it out with explosive and removing the coal by hand. This allowed them space to pull off the head, remove the bolts, fix the machine, and put it back together again.

Coal mining - the transition to pit ponies

One of the problems that has consistently plagued underground coal mining lies in the height of the coal seam that is being mined. This was the portal (i.e. entrance) to a coal mine that we once ran a research project in, near Summersville, W Va.

Dr. Rupert and I in May 1975 at the portal of a W Va mine. (Note the kneepads).

The mine was extracting only the coal, and you can see that the entry height comes to just below our shoulder blades, which made walking into the mine (about half-a-mile or more) very tiring, since you have to walk in quite bent over. As a result, the machines that work in these low conditions, have the operators lying almost recumbent as they steer and operate them. Back in earlier times, however, before there was much machinery underground, conditions were much different. And so today I thought I would talk a little more about those early conditions and how changes began to evolve.


I’m motivated a bit in this by finding (on a market stall in Lancaster) an illustrated autobiography by James Dunn called “From Coal Mine Upwards,” that was written in 1910 by a 70-year old who began his life in a mine. As the prologue noted (abbreviated):

Over sixty years ago in a small village on the border of the Leicestershire coalfields a company of men met to discuss what was to be done with a poor lad eight years old. The richest farmer in the neighborhood said” “I should like to ask two questions before you decide. The first is, how much learning does it want to drive the plough?” and “How much learning does it need for a lad to work in the coal-pit?” The answer was very little, and to the coal pit at eight years of age I was sent to work. It was in those dismal mines, four hundred yards deep and about a mile underground from the bottom of the shaft, that I commenced to earn my daily bread.”

He was fitted with a flannel shirt, wide trousers, a cap, a smock-frock, and heavy nailed boots. He walked the two miles to the mine to be there at 6 am and he earned tenpence a day, except that the mine rarely worked more than half days, so that he made around 30 pence (when 240 pence made a pound which was worth about $4 at the time I believe) a week. After a ten to twelve hour day underground he then had to walk home.

He was lowered into the mine on a chain fitted with loops, and then walked to the working face, having been given a candle to light the way. His job was to haul at the front of a tub, so that he took off all, but his trousers, socks and boots and his flannel cap.

The man I had to work with showed me how to place a leathern belt around my loins, with a light chain attached about a yard long, which was hooked to the front of the small wagon of coal thus pulling from the front while the man pushed behind.

From James Dunn “From Coal Mine Upwards”, W. Green London, 1910. 227 pages

The mine was worked by subletting different jobs, thus a miner would work in measures of a“stint” which was two yards wide, by a yard deep to mine the coal. He loaded the tub from the face of a tunnel that he was driving into the coal, and then swopped out a full and an empty tub to continue.

Loading the coal. A sculpture in the archive at Missouri S&T

The initial rails were wooden, and the tubs were turned on steel plates at the end of the tunnel (the “flat”). Once the tubs were started back to the mine shaft, they passed through a series of folk:

this process was worked in what they called “stages”, or lengths, a man having one stage, and then two boys the next, then another miner, and then two boys, and this was continued throughout the whole length. Now it will be seen that every pair of boys were running between two men – one at each end of their stage, and the great concern of the boys was to meet the man at either end, so as not to keep them waiting. . . .(if late) The man at the other end would be waiting with his empty truck (tub) and the probability was that the boys would be beaten with his strap.

The men were paid by the ton delivered to the shaft top (a token in the tub marked who had loaded it) but the boys were paid by the day, and thus not nearly as well rewarded.

Rails were the first major improvement, transitioning from just dragging the corves on one’s back, which had been the earlier method. But the tubs had still to be moved manually. It was pictures such as this, that had led to the legislation that got women and young children out of the mines in 1842.

Woman hauling a corf, Royal Commission Report, UK, 1842.

Hauling the flat (on which a corf or two would be mounted. Note the chain) MO S&T archive

They were replaced, in large part by ponies, but there was an immediate consequence. It had been possible to use people to drag tubs along in low coal, but that doesn’t work with ponies. (And in some seams they still remained impractical).

Putting in a 2 ft 10 inch coal seam, 1929 (A Bevin Boy Remembers, Ted Holloway, Henge Publications, 1993)

The tubs were also of wood at this time, since it allowed the front planks to be removed to fill the tub, where the roof was too low to easily fill it over the walls. But the ponies had to have more height, and so the height of the roadways had to be increased. (Which also made it easier to walk down them). This was done by blasting a small amount of rock from the roof of the tunnel, giving the extra height. As James Dunn noted “My lot was never as hard again.”

From "The Miners," Anthony Burton, Andre Deutsch Ltd 1976

The ponies had the advantage that they could pull more than one tub at once, and with the restriction on height gone, they were more frequently made of metal. You may notice the lad riding on “the limmers.” That was, strictly speaking, forbidden, though I think we all did it.

As mines became more productive, so the ponies could not keep up with the number of tubs that had to be hauled down the access roads, and they were, in turn, replaced by long “endless” ropes of wire, to which we attached the tubs, and which then hauled them from around the face area down the mile or more to the shaft, where they were disconnected, loaded onto the skip and hauled to the surface. But I’ll talk about the first steps in mechanization next time.