THE COLLIERY GUARDIAN. 1283 ’ December18, 1914. ________________________________________________________________________________________________ . ____ r j — . Discussion. Substitutes for Wooden Roof Supports. • - The President enquired whether' in the making of concrete props there was not a tendency for the strands ’ square wooden mould with the edges taken off. Props 5jft. pu^ to reinforce the concrete to “ bunch ” together,, ; i or was the concrete sufficiently stiff to keep them 1 separate? \ , Mr. G. J. Binns asked whether it was possible to,, ... make big props of concrete—say 10 ft. props. 1 ’ Mr. Hepplewhite replied that the longest he had seen were 6 ft. 6 in. Since completing his paper he , had received some further information from a colliery where concrete props were being made. The mixture ‘ comprised nine parts of ordinary clean engine ash, one / part of cracker dust, and four parts of cement, and the props were being made in lengths varying from 4 ft. 6 in... . to 6 ft. 6 in., and from 3| in. to 4J in. in diameter. • They were shaped hexagonally, and the. longest props weighed about 13 lb. per ft., or 86 lb. for the 6 ft. That was the weight when dry and ready for use, and included the reinforcement, which weighed about 7 lb. 1 The strands of old wire rope were placed about ljin. . apart, and a sort of skeleton frame was made by ‘ ■ wrapping wire at the ends or middle of the strands, so ,, as ” ' At a general meeting of the Midland Counties Insti- tution of Engineers, held at the University College, Nottingham, on Saturday last, the President, Mr. G. S. Bragge (Moseley, Birmingham) being in the chair, Mr. W. Hutton Hepplewhite (H.M. inspector of mines, Tamworth) read a paper on the subject of “ Substitutes for Wooden Supports of the Roof in Longwall Working.” He began by pointing out that on account of the great European War the question of an adequate supply of pit timber was of more than ordinary interest at the present time. He continued It is ■ impossible to work our coal mines on the longwall principle without some systematic method of supporting the roof. Now that there is a shortage of pit props from the usual source, there is no other alternative, if the mines are to be kept at work, than to experiment with, and, if they be found suitable, to adopt substitutes in the form of steel, cast iron, or reinforced concrete props. The writer has computed, from reliable sources, that the cost of timber per ton of coal raised was 2’4d., which works out at ITO,000 for _______ _____________ every million tons of coal raised, or 1$,000,000 for the 300 that “ the only cost of making them to use is the labour and million tons raised in the United Kingdom. It is some- what disquieting to know that the amount of timber growing in this country (of which only a small percentage would be available for pit props) is infinitesimally small when com- pared with the quantity annually imported from abroad. When the fact is borne in mind that there are many mines which almost exclusively use steel props and steel bars, the estimate of 2‘4d. per ton of coal raised agrees practically with the figures of the report of the forestry branches. Turning to the question of substitutes for wooden supports, Mr. Hepplewhite reminded the members that in his paper on “ The Action and Control of Differently Constituted Coal Roofs,” he made mention of the Morgan, Gascoyne, Spencer, and Mannesmann props. He then went on to summarise the qualities of several of these as follow :—■ Morgan Adjustable Pit Prop.—This prop is made in two parts. The leg portion is of solid iron or steel, and the upper part consists of a cylindrical cap, which is about half-filled with fine slack coal pressed together as tightly as possible. The cap is fixed on the leg, and held in position by a chain holding the two halves together. When the roof pressure comes on, the cap is forced on to the slack, and somewhat solidifies it. Spencer Tapered Cast Steel Prop.—Although this prop is admirably adapted for floors which are moderately hard, it does not seem to have found much favour with mine managers. The point of the prop could be shaped according to the requirements of the floor. Mannesmann Weldless Steel Pit Props.—The writer gave a full description of this prop in his paper, and since then has not seen a single one in use. Steel Tubular Pit Props (figs. 1, 2, and 3).—The writer thinks that a splendid substitute exists in steel tubing, in . conjunction with a short length of tapered wood inserted at the foot. A short solid length (fig. 2).would be required inside the tube for the wood to press upon as the roof stratum sagged. The tapered portion would then “ burr,” and this would relieve the tube of the weight, and prevent consequent damage. The tube could with advantage be filled with con- crete consisting of a mixture of 3 parts of coarse material, of sand or granite chippings, and 1 of cement, before being sent below ground. A length of 9 in. of tube would have to be kept open for the insertion of the wood, and another 9 in. would be required for the length of taper outside, or a total length of wood of 18 in. (fig. 1). If a tube of 3 in. in diameter were to be employed, it would be advisable to use wood 5 in. or 6 in. in diameter. The part fitting into the tube would require to be shaped to fit, and, instead of a round taper, a wedge-shaped slice from opposite sides would act equally as well. So long as the ............................. .............................. wood received the roof depression it would matter little how it was treated, provided that the tube was saved from injury. If it were practicable for the manufacturers to make one of the ends bell-shaped (fig. 3) for the insertion of a tapered length at both ends, the floor end would act under pressure similarly to a whol6-length tapered wooden prop. Steel Girder Props. — This type of prop has only been adopted, to the writer’s knowledge, at a very limited number of mines, and its success is chiefly attributable to the method of preparing the ends in a manner suitable for the lid to fit on them, and of using specially prepared foot and lid timbers to receive the roof depression. As the props are rigid and unyielding to the roof weight, it is necessary to provide wood to meet the pressure, otherwise the prop would bend some- where near the centre. The writer would advise only the _______ head of the prop to be treated for the lid or bar to fit on. The foot should be allowed to remain in its rough state, and to rest on a square block of wood. Accidents have been known to occur when a treated foot was set on wood, one instance being where a prop (no doubt from sudden depression of the roof) sprang 12 yds. and injured a worker. Cast Iron Props (fig. 4).—This type of prop also belongs to the rigid class. The trunk is round, and is fitted with four vertical ribs and horizontal bars at intervals of about 1 ft. The ends are square for a length of 9 in., and the tops slightly rounded to assist in fixing the prop in position. The lids should be 2| ft. long, 5 in. broad, and 3 in. thick. Wedge- shaped pinners, varying in length from 9 in. to 18 in., should be supplied to the workers. The pinners are fitted between the prop and lid, and are driven tight from oppo- site directions (fig. 5). Used lids are very good for the foot, as they assist in receiving the roof depression. It is very rare that props break from vertical pressure. The writer has seen them bore through the lids and into the shale roof without being damaged. He is speaking from personal experience, as the company by which he was employed used nothing else,-wooden props not being allowed. There is this to be said in favour of rigid props. long and 5| in. square are made of the following mixture :— leu. ft. of ashes screened through a fin. mesh; 2cu. ft. of breeze dust screened through a J in. mesh; and 1 cu. ft. of Rugby cement. Mr. Howard Briggs, the manager of the Charity Colliery, has kindly supplied the writer with particulars of the method that he adopts in making props. He mixes the ingredients in two ways—(1) very wet, so that the stuff can be poured into the mould; and (2) very much drier, so that it has to be rammed in. In his opinion, the second method makes the stronger prop. Each prop is reinforced with nine unwound strands from an old | in. steel wire rope. The most satisfactory method of seasoning the props, before using them, is to lay them on th^ base board until they are strong enough to bear their own weight, and after- wards to stack them in a protected position, that is, sheltered from the sun and wind. They require an application of water daily, either through a hose or from buckets, for a month or six weeks. The writer has seen several props that- had been immersed for a few weeks in a running stream of water. One was taken out and thrown with great force across a permanent way railway rail without in any way being injured. With regard to the cost, Mr. Briggs states Figs, 1 to 3.-Steel Tubular Fig. 1 Figs. IRON PLATE, X 4; INS. X j IN. 6 to 9.-Details of Mould for making Fig. 6.—Side Elevation. Fig. 2 2i >N6. Pit props Fig. 3 to keep i 1 ins. them apart. The props remained in the,,/ Fig. 4.—Cast-iron Pit-prop. ROUND elevated crown' SOLID SQUARE Ribs every 12 inches • 2i 1 INS. • t — Concrete Props. e Fig. 7. -Plan. ins. INS- j-IN. BOLT jT 1 U ’ &.NS. IN8. * 16 INS.1 Fig. 8-Section. * i ins. Fig. 9 •5 INS." PLATE TO FIX IN SLOTS, SO THAT SMALLER PROPS CAN BE MADE Fig. 5. moulds about 48 hours, and were then placed in the. ; open air to season—a process which occupied from si? to eight weeks. Care should be taken to protect them : from frost when they were first exposed to the $ir. 7. There were about 50 concrete props set on the roads in this colliery, and though they had only been there for a few weeks, they appeared to be quite all right. They were set alternately with wood props, and though they could not be driven up like an ordinary wood prop, there J was no difficulty in setting them. They either tightened • the bar down to the prop, or drove the prop up by placing a good thick lid, and hitting the lid, instead of ' the prop, with the hammer. At present the inaking o£ these props was in an experimental Stage', and it was impossible to give any reliable information as to’, the z cost, but the opinion at the colliery was that they would compare very favourably in that respect jwitl^ ordinary pit timber. • Mr. Bingley (Bolsover) asked what was the effect of '■ h x .c x v vvz .... x .. _ ■ ’ a weight on a prop. ‘ ■ •• , • /;l’n ,J;< made in any^^hape pr sizeand requite fo fie foinforced with ‘ IiUconclusfon he^enhdned the saving of p^ Mr. TJepUlewbite said that he had seen ffie^ dfods > • the concrete, in order to secure the .maximum strength''with cement, and when we are in a position to make anything like a reasonable quantity, I anticipate they will come out from 7d. to 9d. per prop.” Another Warwickshire manager has experimented success- fully with concrete props. The mixture which he uses is sand and fine granite chippings; and, instead of laying the wire strands parallel, he crosses them. Tapered Props.—The tapering of pit props is now univer- sally adopted in all countries where coal mining is in progress. The simple operation of destroying a small portion of the prop in order to save the bulk has undoubtedly proved a great economic factor in reducing the timber expenditure in this country. It is somewhat amusing to note the numerous patents — fantastic and artistic, rather than practical — that have been granted in this and other countries for pit props. The whole question resolves itself into adapting something, consistently with safety to the The- workers, that will meet the roof depression and save the workers see that the pack walls are built as the buttock pro- prop from destruction. The writer would urge upon all greases, and: the third row of props is withdrawn and reset concerned where the conditions are favourable, to see that at the face.: - ■ -m m. every prop'is tapered before being sent below ground, and Concrete. Pit Props (figs. 6 fo $).>— These pfopS ffia# fib' • thus to husband the precious timber now jn stock. : i ’ _______...... -1 . . f. v. 1. a/ u ; 1, In conclusion he 'mentidned the saving of props that ’ n 1 l’; t s . r •, ... , .. ... .1 . ^11 •, t’Tii ■'t lla" i xt Mr. HepUlewbite said tJiat he had seen #he props > single strands of Wire haulage ropes Or Steel Of Tron tofis jn " would m all cases follow if the pack^ tVere built as the -• • • ■ - "• - ‘ ■, ’ ♦La m ‘‘loadihg.'progresses, and if the wasprops were with- stand where ;wooden ones had broken,tand-.he-adid' a mihimuffi of •Weight. - Each - *|jro^f in a'prepared: / draw’p'.spoh, ,^iter the packs 'finished^./.... think that4ihere was rhuch fonr ’of them collapsing. He’’7 [ L