GOVERNMENT APPRECIATION 145 forgings which were admittedly altogether beyond the scope of firms whose speciality was none other than that of drop-forging, and of which the Directors of Army Ordnance were well-nigh at their wits' end to secure an adequate, if indeed any, supply at all. Significant, and sufficiently expressive of appreciation, if not of actual open-mouthed astonishment, is the following letter received by Mr. Cooke from a well-known Government Department: "I have to thank you and your staff on behalf of the Ministry of Munitions for the excellent work you have done in producing stampings of trunnion brackets. The part in question has hitherto been considered almost impossible to produce as a stamping, and the work you have now produced will add materially to the efficiency of this important equipment. I should be glad if this letter could be brought to the notice of your subordinate staff who carried out the work." From the same source, but at a later date, came this further little note of esteem: "Your previous production of the trunnion bracket has been the means of great saving to the State, and it is with great satisfaction that I am able to again congratulate your operating staff on a renewed success in your stamping department." For the benefit of those uninitiated in the fascinating art of drop-stamping or forging, it may not be considered superfluous if a brief explanation is given of the principles embodied in the system, and for this purpose one cannot do better than read and inwardly digest the opinion which has been advanced by Mr. Brett, founder of the Brett Patent Lifter Company of Coventry and inventor and patentee of the hammer in question. "Having in mind," he says, "that the plastic or forgeable condition of wroughtiron or steel, when obtained, cannot be retained beyond limited periods, especially in the case of articles having thin or light parts, when its duration is very brief," it rests with the engineer "to provide for the forger a suitable form of power for actuating the dies or tools by means of which properly-formed forgings may be obtained." Further, "this power must be capable of instantaneous application," similar in all essentials to that produced by the smith "with hand hammer or sledge; that is to say, a perfectly elastic blow of sufficient force to produce an immediate and substantial effect upon the material." The secret of providing this particular form of power lies obviously in the Brett drop-hammer, and in it alone, and the method evolved consists in the raising of the hammer-head or "tup" between a pair of parallel and vertical guides to a certain height by pressure of steam exerted within an overhead cylinder; no sooner is this pressure shut off than the "tup" automatically descends by force of gravity, delivering the hammer-blow simply with the weight of its falling mass, and rebounding, is lifted once again 1 [Extract from Paper read by Mr. Brett before the Engineering Conference of the Institution of Civil Engineers, June, 1899, and published in Engineering, June 30th, 1899.] THE DROP-HAMMER DESCRIBED 147 by re-admission of the steam into the cylinder, preparatory to the next descent and the delivery of a further succession of blows. It is largely thanks to a flexible cord and strap connection between the "tup" and the piston and pistonarm working in the overhead cylinder that the blow delivered is not only "smashing" in effect, but altogether resilient, in direct contrast to that of a steam-hammer, the blow of which is more in the nature of a dull thud or a rigid push. It is obvious, as Mr. Brett goes on to point out, that "the vibrations from blows of sufficient power and elasticity (or sharpness) to cause metal at a moderate heat to flow completely into the impressions of the dies," i.e. the blocks in which are cut the impression of the required forging, "and to make clean work, are calculated to destroy any rigidly built machine." Hence the fact, which a cursory glance at the hammers cannot fail to establish, that nothing has been overlooked or omitted in regard to detail in design, "not any of the parts affected by the work are bolted together or in any wise rigidly fixed; the guides are held and the dies set in position by flexible means, i.e. the lower end of each guide fits into a recess into the base block, the top end passes up into a socket having sufficient clearance for wood packing, the wood is intended to absorb the vibrations which pass up the guide-rod." The plant at Crewe as originally installed in 1899, by the late Mr. F. W. Webb, of "compound" fame, consisted merely of one "battery" of hammers, comprising two 7-cwt. stamping hammers, and one 5-cwt. "dummying" or roughing-out hammer, and although the production of small stampings for signal apparatus etc., was all that was attempted in those early days, little by little the variety of work became extended, embracing, ere long, locomotive parts of small dimensions such as brake-rod ends, joints, levers, handles, etc., with the result that as time went on and as ever-increasing experience with confidence proportionate accrued to the staff employed, jobs of still greater variety were successfully tackled. There are at the present time no fewer than eight "batteries" of hammers "in action" at Crewe, the actual number of hammers being twenty-two, and some idea of the extent of the progress made may be gauged by the fact that the yearly tonnage output of stampings rose from 400 tons in 1902 to 1450 tons in 1917, a time when the plant was largely devoted to the manufacture of a regular pot-pourri" of essential munitions of war. 66 It was primarily due to the urgent demands of the Ministry of Munitions for a supply of trunnion brackets, which, cast in steel, were proving defective, and which had "been considered almost impossible to produce as stampings," that Mr. Cooke determined on the course of laying down an additional hammer, having a "tup" weighing no less than four solid tons. Complete with gas-producers, stationary |