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2020-08-08 20:11:54 站长之家
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竟然其他Presuming the reader to remember what was said of steam hammers in another place, and to be familiar with the uses and general construction of such hammers, let it be supposed steam-hammers, with the ordinary automatic valve action, those that give an elastic or steam-cushioned blow, are well known. Suppose further that by analysing the blows given by hammers of this kind, it is demonstrated that dead blows, such as are given when a hammer comes to a full stop in striking, are more effectual in certain kinds of work, and that steam-hammers would be improved by operating on this dead-stroke principle.军舰In respect to the difference between expanding and solid dies it consists mainly in the time required to run back, and the injury to dies which this operation occasions. Uniformity of [145] size is within certain limits insured by solid dies, but they are more liable to derangement and less easy to repair than expanding or independent dies.感觉2. The speed at which the transmitting machinery must move.会到

    Wind-power, aside from the objections of uncertainty and irregularity, is the cheapest kind of motive-power. Steam machinery, besides costing a large sum as an investment, is continually deteriorating in value, consumes fuel, and requires continual skilled attention. Water-power also requires a large investment, greater in many cases than steam-power, and in many places the plant is in danger of destruction by freshets. Wind-power is less expensive in every way, but is unreliable for constancy except in certain localities, and these, as it happens, are for the most part distant from other elements of manufacturing industry. The operation of wind-wheels is so simple and so generally understood that no reference to mechanism need be made here. The force of the wind, moving in right lines, is easily applied to producing rotary motion, the difference from water-power being mainly in the comparative weakness of wind currents and the greater area required in the vanes upon which the wind acts. Turbine wind-wheels have been constructed on very much the same plan as turbine water-wheels. In speaking of wind-power, the propositions about heat must not be forgotten. It has been explained how heat is almost directly utilised by the steam-engine, and how the effect of heat is utilised by water-wheels in [42] a less direct manner, and the same connection will be found between heat and wind-wheels or wind-power. Currents of air are due to changes of temperature, and the connection between the heat that produces such air currents and their application as power is no more intricate than in the case of water-power.力量Boring may be called internal turning, differing from external turning, because of the tools performing the cutting movement, and in the cut being made on concave instead of convex surfaces; otherwise there is a close analogy between the operations of turning and boring. Boring is to some extent performed on lathes, either with boring bars or by what is termed chuck-boring, in the latter the material is revolved and the tools are stationary.密麻Keeping this in view, and referring to an ordinary planing machine with which the reader is presumed to be familiar, the focal point of the cutting strain is at the edge of the tools, and radiates from this point as from a centre to the various parts of the machine frame, and through the joints fixed and movable between the tools and the frame; to follow back from this cutting point through the mechanism to the frame proper; first starting with the tool and its supports and going to the main frame; then starting from the material to be planed, and following back in the other direction, until we reach the point where the strains are absorbed by the main frame, examining the joints which intervene in the two cases, there will appear some reasons for running carriages.对性知道

  The eye fails to detect variations in size, even by comparison, long before we reach the necessary precision in common fitting. Even by comparison with figured scales or measuring with rules, the difference between a proper and a spoiled fit is not discernible by sight.然火 Presuming an engineering establishment to consist of one-storey buildings, and the main operations to be conducted on the ground level, the only vertical lifting to be performed will be in the erecting room, where the parts of machines are assembled. This room should be reached in every part by over-head travelling cranes, that cannot only be used in turning, moving, and placing the work, but in loading it upon cars or waggons. One result of the employment of over-head travelling cranes, often overlooked, is a saving of floor-room; in ordinary fitting, from one-third more to twice the number of workmen will find room in an erecting shop if a travelling-crane is employed, the difference being that, in moving pieces they may pass over the top of other pieces instead of requiring long open passages on the floor. So marked is this saving of room effected by over-head cranes, that in England, where they are generally employed, handling is not only less expensive and quicker, but the area of erecting floors is usually one-half as much as in America, where travelling-cranes are not employed.保地

    几乎[50]须趁队被

    For set squares, or triangles, as they are sometimes called, no material is so good as ebonite; such squares are hard, smooth, impervious to moisture, and contrast with the paper in colour; besides they wear longer than those made of wood. For instruments, it is best to avoid everything of an elaborate or fancy kind; such sets are for amateurs, not engineers. It is best to procure only such instruments at first as are really required, of the best quality, and then to add others as necessity may demand; in this way, experience will often suggest modifications of size or arrangement that will add to the convenience of a set.界内整个

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同时Eighth.—Rapping plates, draw plates, and lifting irons for drawing the patterns out of the moulds; fallow and match boards, with other details that are peculiar to patterns, and have no counterparts, neither in names nor uses, outside the foundry.的情
  

These four types comprehend the motive-power in general use at the present day. In considering different engines for motive-power in a way to best comprehend their nature, the first view to be taken is that they are all directed to the same end, and all deal with the same power; and in this way avoid, if possible, the impression of there being different kinds of power, as the terms water-power, steam-power, and so on, seem to imply. We speak of steam-power, water-power, or wind-power; but power is the same from whatever source derived, and these distinctions merely indicate different natural sources from which power is derived, or the different means employed to utilise and apply it.荒原A safe rule will be to assume that machinery mainly used and seen by the skilled should be devoid of ornament, and that machinery seen mainly by the unskilled, or in public, should have some ornament. Steam fire engines, sewing machines, and works of a similar kind, which fall under the inspection of the unskilled, are usually arranged with more or less ornament.心区


  


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