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Sixth.—Power can be transmitted to steam-hammers through a small pipe, which may be carried in any direction, and for almost any distance, at a moderate expense, so that hammers may be placed in such positions as will best accommodate the work, and without reference to shafts or other machinery.2. The necessity for, and consequent saving effected by, power-machinery for handling is mainly in vertical lifting, horizontal movement being easily performed by hand.679.com下载些天 太初 The loss of effect by the inertia of the pieces acted upon increases with the weight of the work; not only the loss of power, but also the expense of heating increases with the size of the pieces. There is, however, such a difference in the mechanical conditions between light and heavy forging that for any but a heavy class of work there would be more lost than gained in attempting to operate on both sides of pieces at the same time. Another condition of apprenticeship that is equally as difficult to define as the commercial value of mechanical knowledge, or that of apprentice labour, is the extent and nature of the facilities that different establishments afford for learners. Steam and other machinery applied to the transport of material and travel, in navigation and by railways, comprises the greater share of what may be called engineering products; and when we consider that this vast interest of steam transport is less than a century old, and estimate its present and possible future influence on human affairs, we may realise the relation that mechanical science bears to modern civilisation.
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This makes a statement in brief of what comprehends a knowledge of pattern-making, and what must be understood not only by pattern-makers, but also by mechanical engineers who undertake to design machinery or manage its construction successfully.购彩app邀请码三十 虚影 The tools employed for cutting screw threads constitute a separate class among the implements of a fitting shop, and it is considered best to notice them separately. Cores are employed mainly for what may be termed the displacement of metal in moulds. There is no clear line of distinction between cores and moulds, as founding is now conducted; cores may be of green sand, and made to surround the exterior of a piece, as well as to make perforations or to form recesses within it. The term 'core,' in its technical sense, means dried moulds, as distinguished from green sand. Wheels or other castings are said to be cast in cores when the moulds are made in pieces and dried. Supporting and venting cores, and their expansion, are conditions to which especial attention [95] is called. When a core is surrounded with hot metal, it gives off, because of moisture and the burning of the 'wash,' a large amount of gas which must have free means of escape. In the arrangement of cores, therefore, attention must be had to some means of venting, which is generally attained by allowing them to project through the sides of the mould and communicate with the air outside. ”
双笆球基本走势图翩翩 没错 Motion or power may be varied to almost any degree by the ratio between the pistons of pumps and the pistons which give off the power, the same general arrangement of machinery answering in all cases; whereas, with gearing the quantity of machinery has to be increased as the motive power and the applied power may vary in time and force. This as said recommends hydraulic apparatus where a great force is required at intervals, and it is in such cases that it was first employed, and is yet for the most part used. The title of a drawing is a feature that has much to do with its appearance, and the impression conveyed to the mind of an observer. While it can add nothing to the real value of a drawing, it is so easy to make plain letters, that the apprentice is urged to learn this as soon as he begins to draw; not to make fancy letters, nor indeed any kind except plain block letters, which can be rapidly laid out and finished, and consequently employed to a greater extent. By drawing six parallel lines, making five spaces, and then crossing them with equidistant lines, the points and angles in block letters are determined; after a little practice, it becomes the work of but a few minutes to put down a title or other matter on a drawing so that it can be seen and read at a glance in searching for sheets or details.”
时间:2020-08-15 05:17:44  来源:本站原创

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