THE COLLIERY GUARDIAN AND JOURNAL OF THE COAL AND IRON TRADES. Vol. CXIII. FRIDAY, APRIL 20,. 1917. No. 2938. Some Practical Notes on the Economical Use of Timber in Coal Mines.* By F. C. LEE, M.A. (Chin ), B.Sc. Introduction. — The relative values of labour and material/ despite the increased cost 'of the former, have changed to a great extent during the last two years, with the result that what might in pre-war days have been regarded as waste must now be viewed from the standpoint of material. With the recent restric- tions imposed on imports, the urgency for the preven- tion of wastage of material has become daily more acute, and a national obligation. Timber is one of the materials in the list of restricted imports. Although in normal times the employment of timber in mines has been regarded as indispensable, there has been always an abundant supply in the market at comparatively moderate prices, so that its real signifi- cance and importance was not fully realised or taken much notice of. Indeed, owing largely to section 52 of the Coal Mines Act of 1911, which imposes so many conditions as to the drawing of timber, in many long- wall workings the timber was practically all abandoned in the goaf. The reason was not far to seek. In order to comply with this section of the Act, if only one drawer was sent to the district, he would have to be accompanied by a qualified skilled workman, or, in order to save labour, be a qualified skilled workman himself . Since the services of a skilled workman could be more profitably employed as a coal getter than as a drawer of inferior classes of timber, it follows that the amount of the timber extracted by him would have to be very large before it could counterbalance the profit which might have been made if his services had been otherwise used. Thus preference was given to labour at the cost of material—which is timber in this case. As the price of timber is ever on the increase, the demand for its extremely careful use is quite apparent. Furthermore, as the price varies inversely as the quan- tity, the increase in price therefore indicates the decrease in quantity. At a time like this every means must therefore be 'employed to prevent the excessive consumption and unnecessary wastage of timber. Longwall Face Timber. — On account of the rapid advance of the face, which invariably means a good roof or fairly so, the class of timber employed in long- wall working is correspondingly inferior in quality, and, as previously stated, its extraction was not looked upon as profitable. The conditions at present, how- ever, are different, and special efforts ought to be made to have it all drawn. Apart from the economy in \H&iD7R££ \ GIRDER PROP Fig. 1.—Showing how Girders are set as Props. H *’•» z/.'d ■y, . a; ’ Fig. 2.— Showing Untidi- ness and Obstructions in Gateways by the Break- ing of Props left in the Pack. timber directly resulting therefrom, this step, under certain conditions, gives other important advantages, as the following example will show: — In a district in a seam with which the author is acquainted, the main rolleyway is driven on the level, so that on its right the workings are to the dip, and on its left the workings are to the rise. On the rise side, two districts oiitbye are worked by advancing conveyors, and the one inbye is worked, by longwall. On the dip side there are two districts, one of which has only just been opened out, and the other’has been worked for about 12 months. The depth of the seam is 480 ft., and its thickness is on an average about 3| ft. on this side, the dip being about 1 in 24. The system of working is longwall, and the roof, although friable, is good. At the very commencement the manager decided to have a drawer sent in, arid to have all the goaf props drawn after the pack was put in. This was not done entirely from the point of view of *From a paper read before the North of England Insti- tute of Mining and Mechanical Engineers, April 14, 1917. conservation of timber, but from the belief that, by thus evacuating the space behind the roof, pressure would then be draw'n away from the face, and thrown into the goaf, thereby giving the roof a better chance to settle, with 'a better condition of affairs in the gate- ways. Top canches of 3J ft. were taken off to make the total height in the mothergate 6Jft., and 2} ft. to make the gateways 6 ft. The stonemen were instructed to fire only one shot, and that in the middle, so that the shape of the roof would be as near to that of an arch as possible. Upright props in the mother- gate and gateways were avoided, and bars 5 in. in diameter and usually 6 ft. long, locally known as “ aerial timber,” were holed into the sides. The roof R/GNT WAY WRONG WAY. TOO LOW. Figs. 3 and 4.—Showing the Right and the Wrong Way .of Setting Bar Timber. is of the material known as “ blue metal,” or “ blue,” which forms a break at every cut along the face (which is cut by a chain cutter to a depth of 5 ft. per cut), so that the roof presents a peculiar spectacle of a series of breaks 5 ft. apart across the gateways. The floor is very good, but not so dry as on the rise side. The result obtained has perfectly justified the expec- tation of the officials. All the gateways and cross headings stand so well, that very little timber is required; in fact, no timber of any kind is to be seen in some gateways; and they all stand like arched tunnels without any artificial supports. The causes towards effecting such an ideal state of affairs may, be many in number, but the most impor- tant are the following: — (1) The props in the goaf being drawn, allowing the roof to settle quickly. (2) The seam being comparatively thin, and the descent of the roof short. (3) The workings being to the dip. (4) Owing to the roof being good, each break inter- locks the other. (5) The gateways being in the nature of arches. ** (6) The bar timber descending with the roof, unlike upright props, which tend to disturb it on its descent. Unfortunately, there is no other district onrthe dip side that is worked differently from the foregoing, and therefore it cannot be stated definitely as to which of the above causes contributes most towards the accom- plishment of such an ideal result. In the opinon of the officials, it is thought that the complete with- drawal of the props in the goaf is responsible for more than half, if not entirely, the cause of it. The success achieved in this district was so very encouraging that it was thought possible to imitate it in the longwall workings on the rise side, where no drawer had yet been sent, and where the gateways and cross headings, particularly the latter, were very dila- pidated, and constantly subject to falls and their asso- ciated troubles, By permission of the manager, the author took charge of this district, and the experiment commenced. The Experiment .—The purpose of this experiment was to ascertain—by systematically setting and draw- ing the face timber, and by using bar timber in the gateways—the amount of timber that could be saved, as compared with the previous amounts sent into that district periodically. One mothergate and. 10 gate- ways were taken altogether, five to the right and five to the left of the mothergate. H-girders, measuring in section 4 ft. by 3 in. by 3 in., were used as props on the right side, and were set with head pieces and sole pieces, as shown in fig. 1, and ordinary wooden props on the left. The latter were used so as to allow of a comparison being made between the cost of timber props and metal girders used as props. The deputy was instructed to keep an account of the total daily amount of timber sent in by him, and he in turn instructed the lads who took the timber into the different gateways to keep an account of each lot of timber that they sent into each gateway. The night shift officials were instructed to do the same. The experiment was commenced not very long ago, but owing to circumstances contingent upon the war, the pit has frequently been idle and a satisfactory figure therefore has not yet been obtained. What figures there are available at present are not sufficiently reli- able to form a basis for a fair and accurate comparison —nevertheless, they indicate clearly that the quantity of timber used has been very materially and substan- tially reduced. The figures for timber drawn also vary considerably from week to week. The following are the average figures for five weeks converted into approximate percentages: — Timber drawn. Unbroken. Broken. Percent. Per cent. Per cent. 100 ... 42 58 100 30 70 100 62 38 100 34 66 100 57 43 The foregoing figures give an average over the whole of 45 per cent, of unbroken timber drawn. From other considerations, such as the deputy’s figures, this percentage is slightly too high. If the total average were put at 35 to 40 per cent, for the unbroken, and 60 to 65 per cent, for the broken, it would probably be nearer the true, figure. The unbroken timbers are carried forward for further use at the face, and the broken are sent out to bank, where they are selected and cut by machinery into props for thinner seams. The shorter pieces are made into head trees, wedge pieces, etc. The Advantage of Using Girders as PropSi—So' far, the girders have proved to be excellent substitutes for props; they are very efficient and durable. Owing to the care taken in setting them, and the use of substan- tial sole pieces and head trees, not one of these girders has been bent; but, owing to heavy falls in the goaf, 5 per cent, of them have been lost. The following is a comparison of the relative costs between wooden props and girder props for a certain period. It must be noted, however, that the period over which the 5 per cent, girder loss was taken is twice as long as the period over which the cost of timber was taken,*”' so that the comparison is as favourable to the timber props as possible : — Percent. Cost of props ................................. 54-38 Cost'of planks and head trees ................. 16-76 Total ................................71-14 Value of broken props drawn (taken to be half their original value) ................... 21-39 Net cost of timber .................. 49-75 Cost of girder props through loss .............. 10-00 Cost of head trees used to prevent girders from bending ............................. 3-75 Cost of depreciation of girders (practically) ..... 0-00 Cost of repairs (so far) .............. ...j... . 0-00 Total cost of girder props ......... 13-75 The ratio of the cost of timber to the cost of props therefore equals 49-75 :13-75 = 3-62 -.1. If equal length of time had been taken, the ratio in that case would be 7-24:1; but this was not done, in order to allow for the depreciation of the girders. Moreover, girder props only become lost through falls in the goaf when the face advances slowly on account of the pit being idle, etc. If the face is kept advancing rapidly, very few, if any, should be lost, and in that case the use of girders as props would be still inore favourable, despite the correspondingly smaller amount of wooden props that would be required through less breakages; thus, taking everything into account, the use of girders as props is distinctly favourable, as compared with the use of wooden props. This kind of experiment can only yield beneficial results, and it will be well if it is carried out at different collieries, in order to have a comparison of the results obtained under all kinds of conditions, and thus advance one step in the right direction towards