. October 11, 1918. THE COLLIERY GUARDIAN. 757 far as cleanliness was concerned, the innovation might be called an ideal one. In this country, however, we seemed to prefer a great blazing fire, even although we well knew one-half of the heat went up the chimney. He thought the coal owners in Scotland ought to know that under normal conditions, and all things being suitable, it was possible to clear the whole cost of a briquetting plant, out of profits alone, in a period of two years at the outside. It was even possible to clear the whole of the initial cost of the plant from the profits to be made in the course of a single year. Care, however, ought to be taken to go about the business in a proper and right way. The best arrangement was to instal a distinct plant for briquetting right from the very beginning. The inno- vation had proved distinctly successful in different parts of the country. The President, in calling for a vote of thanks to the author, remarked that the paper was a suggestive and informative one. It was quite true that Mr. Yeadon did not deal with the methods of briquetting but only with the general policy and principle of adopting such a plant. The meeting afterwards terminated. HADFIELDS LIMITED. Messrs. Hadfields Limited, on Thursday, October 3, had the pleasure of a visit to their East Hecla Works from his Excellency M. Miehalocopoulos, Minister of Agriculture, and the Greek commercial delegates. This visit was one of a series arranged by the Federa- tion of British Industries with the object of proving to the commercial representatives of Greece the pre- eminent position occupied by Great Britain for meet- ing the extraordinary trade demands that are likely to arise at the conclusion of the war. The delegates in attendance were Messrs. L. Em- biricos, ex-Minister of Supply; A. Skintzopoulos, official representative of the Greek Ministry of National Economy: B. Zamanos, Member of Parlia- ’■ I I 11 Zf.. Greek Commercial Delegates at Hadfields Ltd. ment and founder of the Vodena Cement Works; L. CEconomides, chemical manufacturer; J. Damala, finance and banking; A. Tsitis, cotton spinner; C. Malikopoulos, importer of textiles; E. Caralo- poulos, iron, steel, machinery and development schemes; and M. Kazazes, importer of agricutural machinery. Monseiur K. Venizelos, the son of the Greek Prime Minister, who has so consistently championed the cause of the Entente Allies from the first outbreak of hostilities, accompanied the party, and was accorded a true Yorkshire reception. Other guests included Mr. A. T. Waugh; his Britannic Majesty’s Commer- cial Attache at Athens; Mr. E. C. D. Rawlins, De- partment of Overseas Trade (lately H.M. Consul for Crete); Lieut. Lambros, R.N.V.R., attached to the Department of Overseas Trade; also the following officials of the Federation of British Industries: Vice-Admiral Sir Charles Dundas of Dundas, K.C.M.G., Mr. Edmund L. Hill, M.I.Mech.E., M. I.E.E., Mr. H. W. Babington-Browne, Mr. W. Hill. In the absence of the chairman, Sir Robert Had- field, Bart., F.R.S., the visitors were received by Mr. A. M. Jack (deputy chairman), Mr. P. B. Brown, M.Inst.C.E., and Major Clerke, late R.A., managing directors) and other directors of the company. Follow- ing the extension of a hearty welcome by Mr. Jack, the members of the party proceeded to a tour round the works, in the course of which the delegates saw much that was impressive, the comprehensive scope of the firm’s capabilities being fully demonstrated. As was to be expected, in the present abnormal times, the arrangements made for coping with the Govern- ment war requirements .perhaps attracted chief atten- tion. Naturally, information with regard to the firm’s products in war material cannot be stated pub- licly. Visitors, from what they say, do not fail to appreciate that in times of peace Hadfields Limited are equally well equipped for meeting the needs of many branches of industry. Complete crushing machinery of various classes was on view, including the firm’s patent jaw breaker, which has a solid cast steel frame and patent “ Era ” manganese steel wear- ing parts, the “ Heclon ” gyratory rock and ore crusher, the “Hecla” disc crusher (Symons patent), together with many types of renewal parts in the patent “ Era ” manganese steel and other special steels the company has put on the market from time to time. In their famous steel foundry, the largest in the world, moulding and casting were to be seen in all stages. There were large and small castings, some destined for immediate war purposes, and others for more congenial industrial occupations, all of great importance to the Allies. A portion of the works is set apart for such items as wheels and axles for colliery use, mining tubs, wagons, etc., for railways, mines, quarries, etc. In normal times Hadfields make a speciality of cast steel cylinders and rams for the olive presses connected with one of the staple trades of Greece. They also produce castings and forgings in wear-resisting materials for dredging machinery, etc., and are specialists in the manufacture and con- struction of points, crossings, as well as complete junc- tions for railways and electric tramways which are usually supplied in Hadfields’ patent “Era” man- ganese steel. Quite a number of the shops now wholly engaged on turning out shell for the British and Allied Govern- ments have been entirely built since war broke out, a remark applying also to the National Ordnance Factory, which, under the management of Hadfields Limited, is now engaged on the construction and repair of heavy field guns. Shell were seen in various stages of manufacture, from the casting of ingots by Hadfields’ patent “sound steel” system to the forg- ing, machining and finishing of the shell, including capping and banding. The shell were in large and small calibres, from 3 in. to 15 in., embracing anti- aircraft, small naval gun ammunition, howitzer, H.E. and A.P., the firm’s “ Heclon ” and “ Eron ” shells making what will probably be a very lasting impres- sion on all those who were privileged to see them. Intense interest was taken in an exhibition of all sizes of projectiles that, whilst themselves remaining unbroken, have pierced the latest type of hard faced plates of varying thicknesses up to 15 in. The Re- search Department had more to show than could really be satisfactorily covered in the relatively short time at the disposal of the visitors, who saw, amongst other tangible results of the care and experiments associated with the department, firing tests carried out on the firm’s “ Resista ” steel helmets, of which millions have been used at the front, also body shield plates which have been such a wonderfully life-saving boon to our own and Allied armies. The enormous extension and growth of Hadfields Limited during the war is shown by the fact that, whereas in pre-war days their employees numbered about 7,000, they now employ something like 15,000 workpeople, and their works cover an area of over 200 acres. Lens Coal Field.—M. Reumaux, director-general of the Lens mines, expresses himself hopefully regarding the early working of the Lens mines. He says that, although the mines of Lens itself can only be worked after the Germans have been driven about twelve miles from the -town, there are certain mines in the vicinity which could immediately be made to produce about 10,000 or 15,000 tons for this winter. M. Basly, the deputy mayor of the reconquered town, is, on the other hand, by no means so optimistic. According to him the mines have sustained immense damage, and will require an entirely new plant. Before the war the Lens region yielded some 3,000,000 tons of coal a year. At the most during the coming months the three great companies of Lens, Courrieres, and Lievin, will be able, with the aid from the Govern- ment of £80,000, to begin the task of plant renewal. Wages in the Iron Trade.—The average net selling price (including subsidy) of No. 3 Cleveland pig iron for July, August and September has been certified at 118s. 10-86d. per ton, as compared with 1.07s. 10-68d. per ton for the second quarter of the year. There has thus been ■ an ad- vance in price of Ils. 0-18d. per ton in the third quarter of the year. This means an advance in blastfurnacemen’s wages of 13-75 per cent., which raises wages from 94-75 per cent, above the standard to 108-50 per cent, above the standard. The advance takes effect from the 6th inst. The accountants to the Board of Conciliation and Arbi- tration for the manufactured iron and steel trade of the North of England have certified the average net selling price of iron bars and angles for the two months ending August 31 last at £14 Ils. 9-96d. per ton, as compared with £14 2s. 8-62d. per ton for the previous two months. This carries an advance of 6d. per ton on puddling, and 5 per cent, on all other forge and mill wages, to take effect from the 30th ult. In accordance with the Ministry of Munitions lines of settlements of January 3 and Feb- ruary 20 last, this advance will merge into the 12^ per cent, bonus and the 7| per cent, bonus granted under those settlements. RUNNING AND MAINTENANCE OF INDUCTION MOTORS AT COLLIERIES. By L. Fokes. (Continued from page 702.) Cleaning and Varnishing. When a motor is dismantled for 'cleaning, its wind- ings should always be varnished. It is of vital importance, however, that before varnishing the stator—and in this respect these remarks can also apply to the rotor—all dirt and oil should be removed. To varnish over corners filled with oily matter is merely to seek trouble. Blowing or wiping is not sufficient. Some kind of scraping tool is necessary to enable the slots to be thoroughly cleaned out and all dirt removed from between the tubes where they project from the stator iron. If oil is present it is advisable to wash the windings with petrol and an ordinary paint brush, but when doing so, care should be taken to keep all naked lights away, and no smoking should be allowed in the vicinity. This also applies to varnishing, as varnish is usually of an inflammable nature, and the real danger is not of the can of petrol or varnish igniting, but the possibility of a freshly treated winding bursting into flames and being destroyed. If possible, varnish should be applied with a com- pressed air spray. The best work which can be done with a brush is very poor in comparison with this method of varnishing. The varnish spray easily pene- trates to those positions reached by oil spray when a motor is running, and it is in such places that the varnish is most needed. Also, a spray leaves the surface of the windings with a glossy surface to which dust does not readily adhere, and from which it is easily removed. Given systematic treatment with varnish of the proper quality, there is no definite limit to the probable life of any form of winding, providing that the electrical conditions under which it works are normal. As a result of the treatment described, the writer knows of a large colliery installation well over ten years old where the breakdown of a stator winding either on high or low tension machines has never been experienced. Slip-Ring Rotors. Windings.—With regard to the rotor windings of slip-ring rotors, these may take either of the forms used for the stator—i.e., lap or wave windings. When lap winding is used, the coils are wound with wire, but although it forms a very efficient winding electrically, it is one which does not lend itself to ideal construction from a dust-resisting standpoint, owing to the difficulty of taping the closely wound coils. The “wave” winding of copper bars is much more satisfactory, and forms a good mechanical job, pro- viding ample ventilation to the windings, whilst the comparatively low voltages encountered during start- ing do not introduce the same objections as have been mentioned in connection with the “wave” winding for stators. The windings may be either two or three phase, and be provided with three or four slip-rings. General Treatment of Rotors. As regards the rotor windings, the treatment neces- sary is simply a repetition of that suggested for the stator. The principal point, however, is the care of the slip-ring gear, as neglect in this direction often causes difficulties in starting. When the rotor is standing on open circuit and the stator is switched on to the line, the slip is equal to 100 per cent., and consequently the voltage induced in the rotor, and existing between the slip-rings, is a maximum. To allow dirt and oil to collect between the slip-ring is likely to cause a flash over when the stator circuit is closed for starting. This dirt may consist of a variety of matter. In the case of motors not fitted with short-circuiting gear, such as those used for haulage work, the brushes, which are usually of carbon, are always in contact with the rings. When the brushes are continually working on the rings, one finds that a mixture of carbon and metal becomes deposited over the insu- lating bushes, and to this may often be added coal dust, to say nothing of oil. That such matter forms a good conducting path is obvious, and it should there- fore be prevented from collecting in quantities likely to cause flashing over. When slip-riri^s are cleaned, the operation should be immediately followed by brushing away all carbon and metal dust. In order to avoid the necessity of cleaning slip- rings, the brushes should be of copper morganite. The high conductivity of this class of brush is such as to secure the rings from pitting, and experience shows that such rings may run for years without resorting to cleaning, as the metal and metal contact keeps both ring and brush surfaces clean and bright. Starting. In order to keep the voltage between the slip-rings at a minimum, the circuit should never be entirely broken. For instance,- in the case of a motor for haulage work, the controller should be so arranged that the rotor circuit is closed through all of the resistance when the controller is in the “ off ” position. In this way a current circulates in the rotor imme- diately the stator switch is closed and the E.M.F. between the rings never rises to the value which is possible with the rotor on open circuit. In the case of motors started by liquid starters, a permanent metallic resistance connected across the rotor circuit, as shown in fig. 5, guards against the possibility of the rotor being left on open circuit due to the plates of the starter being but of the liquid. To allow a machine to stand with its stator con- nected to the line and the rotor on open circuit should be avoided.