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Mechanics magazine
- Bandzählung
- N.S. 16=85.1866
- Erscheinungsdatum
- 1866
- Sprache
- Englisch
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- A146
- Vorlage
- Universitätsbibliothek Chemnitz
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- Universitätsbibliothek Chemnitz
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- urn:nbn:de:bsz:14-db-id507363582-186600025
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- http://digital.slub-dresden.de/id507363582-18660002
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- oai:de:slub-dresden:db:id-507363582-18660002
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- Projekt: Bestände der Universitätsbibliothek Chemnitz
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Zeitschrift
Mechanics magazine
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Band N.S. 16=85.1866
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- Titelblatt Titelblatt -
- Register Illustrations to vol. XVI -
- Register Index to vol. XVI I
- Ausgabe July 6, 1866 1
- Ausgabe July 13, 1866 17
- Ausgabe July 20, 1866 33
- Ausgabe July 27, 1866 49
- Ausgabe August 3, 1866 65
- Ausgabe August 10, 1866 77
- Ausgabe August 17, 1866 93
- Ausgabe August 24, 1866 109
- Ausgabe August 31, 1866 125
- Ausgabe September 7, 1866 141
- Ausgabe September 14, 1866 157
- Ausgabe September 21, 1866 173
- Ausgabe September 28, 1866 189
- Ausgabe October 5, 1866 205
- Ausgabe October 12, 1866 221
- Ausgabe October 19, 1866 237
- Ausgabe October 26, 1866 253
- Ausgabe November 2, 1866 269
- Ausgabe November 9, 1866 285
- Ausgabe November 16, 1866 301
- Ausgabe November 23, 1866 317
- Ausgabe November 30, 1866 333
- Ausgabe December 7, 1866 349
- Ausgabe December 14, 1866 365
- Ausgabe December 21, 1866 381
- Ausgabe December 28, 1866 397
- Ausgabe No. 2179 I
- Ausgabe No. 2180 I
- Ausgabe No. 2181 I
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- Ausgabe No. 2204 I
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Band N.S. 16=85.1866
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THE MECHANICS’ MAGAZINE. LONDON: FRIDAY, OCTOBER 19, 1866. WELDED JOINTS IN LOCOMOTIVE BOILERS. A MONGST the numerous causes which lead to the explosion of locomotive boilers con structed in the ordinary way with lap joints, none contribute more largely to swell the cate gory of accidents than corrosion of the plates. This corrosion is usually confined to particular localities, being found principally round the smoke-box end of the boiler barrel, in the inte rior, opposite to the edge of the outside angle- iron, when an annular groove is found to be eaten out of the plates by corrosion. A simi lar grooving also takes place along the edge of the inside lap at the longitudinal joints, and likewise at the transverse circular joints. This grooving, however, only occurs below the water-line, thus showing it to be the result of a chemical action. But the peculiar direction of the grooving, which invariably chooses for its locality the line of a seam of rivets, is not to be accounted for upon chemical principles ; we must look for a mechanical cause. It can only be attributed to the springing of the plates of boilers when under pressure, whereby the metal at the joints becomes bent in conse quence of the plates not being originally in the line of strain. As expansion and con traction are continually succeeding each other in the boiler, the scaly deposit is constantly being broken off at the edges of the joints. The plates are thus laid bare by this mechanical action at the lines of the joints, and thw the metal is kept con tinually exposed to the corroding action of the water instead of being protected by the scale. Corrosion is, of course, to be found in other parts of the same boiler, but then it is very limited in extent as compared with the groov ing at the seams. In the former case, the sur faces of the plates are only irregularly over pitted; in the latter, deep channels are eaten into the metal, sometimes leaving it on the outside as thin as a sixpence. This corrosion sometimes goes on so rapidly that plates will require renewal after only a few years’ work, whilst pitting may continue for a number of years before it becomes dangerous. The de tails of construction of a locomotive, too, exert an influence upon it with regard to grooving. Rigid attachments are found to offer special oints of resistance to the expansion of the oiler when under pressure, and so to increase the loeal action to a serious extent. The defects arising from riveted lap joints are, however, capable of remedy, by construct ing the boiler on different principles. On the London and North-Western Railway each length of the barrel ot the locomotive boilers is formed out of a single plate bent round into a complete circle, so as to have only one longi tudinal joint instead of two. This joint is turned to the upper side of the barrel, so as to be in the steam space above the water-line, and thus the difficulty of corrosion along the longitudinal joint is to a great extent over come. But a still better method of construc tion is adopted on the Midland Railway. This consists in having the plates rolled with thickened edges. This plan, which is found to obviate the injury previously experienced from corrosion, was recently described by Mr. W. Kirtley before the Institution of Mechani cal Engineers. The ordinary thickness of 7-16in. is preserved in the body of the plate, the edges being thickened to fin., with a long gradual taper in the thickness about din. long. When the plate is flanged, in order to do away with the angle-iron, this taper ensures a gradual springing of the plate distributed over all that length instead of the sudden bending concentrated at one point. The trans verse circular joints are also formed with a similar section of thick-edge plate. By this mode of construction additional strength is gained, as the increased thickness of the plates between the rivet holes compensates for the loss of section by the holes. An ex ample of the practical working of this system is afforded by one of the Midland Company’s engines, which had originally an ordinary boiler. After working eleven years and a half this boiler was removed, the plates having become much grooved and pitted, and a new boiler, constructed with thick-edge plates, was substituted. The engine has con tinued to work with the new boiler for six years and a half, to the beginning of the present year, when an examination showed that the plates were free from grooving, although they were badly pitted. Although this is evidently a step in the right direction, and is clearly the means of preventing the evil of grooving, it does not, however, remove the injurious strains which must result wherever a lap joint is employed. This can only be done by making th8 barrel truly cylindrical and circular throughout; then the strains would be removed, and an impor tant improvement effected. And this has been done on the Midland Railway, where they now weld the longitudinal joints of the three rings forming the boiler barrel, making them ail exactly the same diameter, and uniting them to each other with flush butt joints. The meeting ends of each ring are turned in a lathe, and united by covering strips formed of welded flush rings, shrunk on over the joints and double riveted. On each of the eentre plates strengthening hoops are also shrunk, which cross the longitudinal welded joints, and are secured by a few rivets. Thus the boilers are truly cylindrical at every point, and their circular form is in no way changed by any strain to which they are subjected. The soundness of this principle has been cor roborated in a very remarkable manner by a Midland engine, the boiler of which was con structed with butt joints, all flush throughout, the transverse joints being covered by exter nal hoops and the longitudinal by internal slips. This boiler was started in 1847, and has consequently been at work about nineteen years. The original boiler plates still stand, never having been repaired, and grooving has not taken place at the butt joints; a little irregular pitting on the inside of the plates being the only visible sign of deterioration. This remarkable freedom from the grooving so prevalent in ordinary boilers with lap joints, can only be attributed to the circumstance of different construction. In another engine, the boiler plates were found badly grooved at an angle-iron joint constructed in the ordinary way at the smoke box end, whilst the rest of the joints, which were butt joints, were free from grooving. The thick-edge plates are flanged, bent, and welded by means of special machines, particulars of which we purpose lav ing before our readers next week. Various experiments have been made to test the tensile strength of the welded joints, the results of which will compare well with those of riveted joints. Strips of plate were cut out across the weld from pieces taken from several boilers to form the opening for the steam dome. Three sets of strips were tested of lin., If in., and ljin. respectively, each piece being 7*in. in length, and cut transversely to the weld, which was in the middle of each piece. In all twenty-three strips were tested, eleven of which broke in the weld, and twelve broke in the solid; the average breaking strength per square inch was 20'6 tons, a very fair average. There were also eleven strips of the same plates unv, elded tested, and the result was an average breaking strain of 23'6 tons. It will thus be seen that more than half of the welded strips broke in the solid and not in the weld, and that the average breaking strength of the twenty-three welded plates was within one- eighth of the full strength of the eleven un welded plates. It wa$ also found by these trials that the worst pieces, including some cases of defective weld, had more than two-thirds of the full strength of the unwelded plates. Welded boilers are a little heavier and some what more expensive than the ordinary class of lap-jointed, single-riveted boilers with angle- iron ends. In the new boiler the increase of weight is about 1J tons, which arises from the thick-edge plates, and from the hoops and joint strips. As regards cost of labour and material, the new boiler shows an increase of about £50 over the old one. The extra weight and cost, however, form no serious bar to the use of the system, which, when its advantages are taken into consideration, comes out much cheaper than the old system. The Midland Railway Company were not slow to recognise this fact, for they have had nineteen of these welded boilers in constant use for the last six years and ahalf. The result has proved so satis factory that this system of construction has been permanently adopted for the engines on this line. The fact of the safety of welded boilers ought to tell with other railway companies, some of whom, if not all, we hope to find imitating so good an example as that set by the Midland. We shall then hear of.far fewer locomotive boiler explosions, whilst, at the same time, the irrepressible item of repairs will figure much smaller in railway accounts than heretofore. THE SMOKE NUISANCE. HEN the discussion of the smoke nui sance was at its height some years since, a deputation waited on Lord Palmerston and stated that it was impossible to stop the smoke. His lordship told them he would show them how to do it, and the result was a great abatement of the nuisance complained of, as far as the metropolis was concerned. But the provinces were practically unaffected by the steps then taken, and so remain to the present day; the majority of our manufacturing towns being enveloped from Monday morning to Saturday night in an atmosphere of the mur kiest and most objectionable kind. That such an atmosphere darkens, dirts, and depresses, needs no demonstration at our hands; it is only too well known. That it has a delete rious effect upon health is also a fact about which no two opinions can exist; and the greater the preponderance of factory furnaces over domestic fireplaces the worse the results, in a sanatory point of view. In fact, the smoke from dwelling-houses is comparatively harm less, while that from factories is highly dele terious. This was recently very forcibly pointed out to the members of the Social Science Congress by Dr. Crace Calvert, who bases his conclusions upon thefollowing data:— First, with reference to the smoke from pri vate dwellings, he states, in effect, that solely at the time, and shortly after fresh coals are added, the smoke from the domestic fire carries with it only carbonic acid, carbonic oxide, and sulphuric acid gases. There is also a small quantity of the most volatile hydro carbons, the less volatile products forming soot, which remains in the chimney. In this case the gases continue to escape but for a few minutes after firing, and have little or no action of an unhealthy character either on vegetation or on man. A very different case, however, is presented by the steam boiler. Here the fuel is not perfectly consumed, as in private dwellings, but there is a continuous distillation of deleterious tarry products. By the draught of the tall factory chimney these products, with many others of a noxious charac ter, are carried into the cold atmosphere at the top of the stack, where they quickly condense and fall, exercising a deadly influence on all within their reach. We need not enter further into details respecting the difference of action which the smoke issuing from our factories has on health and vegetation as compared with that given off from those of private dwellings, as a full abstract of Dr. Calvert’s interesting paper will be found on a subsequent page. We have said that the atmosphere of some of our manufacturing towns dirts, darkens, and
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