See also:process of casting in
See also:metal, of making a
See also:reproduction of a given
See also:object by
See also:running molten metal into a
See also:mould taken in sand,
See also:loam or
See also:plaster from that object . To enable the founder to prepare a mould for the casting, he must receive a
See also:pattern similar to the casting required . Some few exceptions occur, to be noted presently, but the above statement is true of perhaps 98% of all castings produced . The construction of such patterns gives employment to a large number of highly skilled men, who can only acquire the necessary knowledge through an apprenticeship lasting from five to seven years . A knowledge of two trades at least is involved in the
See also:work of pattern construction—that of the craft itself and that of the moulder and founder . Patterns have to be constructed strongly . They are generally of
See also:wood, and they thus require skill in the use of woodworking tools and the making of
See also:joints, together with a knowledge of the behaviour of timber, &c . Some few patterns are made in iron, brass or
See also:white metal alloys . They have to be embedded in a
See also:matrix of sand by the founder, and being enclosed, they have to be withdrawn without inflicting any damage in the way of fracture in the sand . Since
See also:cast work involves shapes that are often very intricate, including projections and hollow spaces of all forms, it is obvious that the withdrawal of the patterns without entailing tearing up and fracture of the sand must involve many difficult problems that have to be as fully understood by the pattern-maker as by the moulder . It is from this point of view that the work of the pattern-maker should be approached in the first place . No closed mould can possibly be made without one or more joints, for if a pattern is wholly enclosed in a matrix of sand it cannot be withdrawn except by making a parting in the sand, and it is not difficult to conceive that the parting in the pattern might advantageously be made to coincide, either exactly or approximately, with that of the mould .
Nor must obstacles exist to the
See also:free withdrawal of patterns . They must therefore not be wider or larger in the
See also:lower than in the upper parts; actually they are made a trifle smaller or "tapered." Nor may they have any lateral extensions into the lower sand, unless these can be made to withdraw separately from the
See also:main portion of the pattern . Finally, there are many
See also:internal spaces which cannot be formed by a pattern directly in the sand, but
See also:provision for which must be made by some means extraneous to the pattern, as by cores . A single example must illustrate the main principles which have just been stated . The object selected is a
See also:bracket which involves questions of joints, of cores, of pattern construction and of moulding . The casting, the pattern, and its mould are illustrated . Fig. i illustrates in plan the casting of a
See also:double bracket, the end
See also:elevation of which is seen in fig . 2; the pattern of which presents obvious difficulties in the way of withdrawal from a mould, supposing it were made just like its casting . But if it be made as in fig . 3, with the open spaces A, B, in fig . 2, occupied with core prints, and the pieces A, A in fig . 3
See also:left loosely skewered on, everything will " de-
See also:liver " freely .
Moreover the pattern might be made solidly as shown in fig . 3, or else jointed and dowelled in the
See also:plane a-a, as in fig . 4, or along the upper faces of the prints b–b, fig . 3 . The 744 timber shadings in
See also:figs . 3 and 4 illustrate points in the tnost suitable arrangement of material . The prints are " boxed up." Fig . 4 shows a certain stage of the moulding, in which one
See also:half of the pattern has been " rammed " in sand, and turned over in the " bottom box," and the upper half is ready to be rammed in the top box," with " runner
See also:pin " or " git stick " A, set in place . The lower loose piece has had its skewer removed during the ramming . Fig . 5 illustrates the mould completed and ready for pouring . The boxes have been parted, the pattern has been withdrawn, cores inserted in the impressions left by the prints, vents taken from the central
See also:body of cinders, the pouring
See also:basin made and the boxes cottered -a together .
Every single detail now briefly noted in connexion with this bracket is applied and modified in an almostinfinite number of ways to suit the ever varying character of this process does not
See also:touch some of the
See also:great subdivisions of moulding and casting . There is a large
See also:volume of large and heavy work for which
See also:complete patterns and core boxes are never made, because of the great expense that would be involved in the pattern construction . There are also some cases in which the methods adopted would not permit of the use of patterns, as in that
See also:group of work in which the sand or loam is " swept " to the
See also:form required for the moulds and cores by means of striking boards, loam boards, core boards or strickles . In these classes of moulding the loose
See also:green sands and core sands are not much used; instead, loam—a wet and plastic sand mixture—is employed, supported against bricks (loam moulds) or against core bars and plates, and
See also:ropes (loam cores) . All heavy marine engine cylinders are thus made by sweeping, and all massive cores for engine cylinders and large pipes, besides much large circular and cylindrical work, as foundation cylinders,
See also:soap pans, lead pans,
See also:mortar pans, large propeller
See also:blades, &c . In these cases the edge of the striking
See also:board is a counterpart of the
See also:profile of the work swept up . Joints also have to be made in such moulds, not of course in
See also:order to provide for the removal of a pattern, but for the exposure of the
See also:separate parts in course of construction, and for closing them up, or putting them together in their due relations . These joints also are swept by the boards, generally cut to produce suitable " checks," or " registers " to ensure that they accurately
See also:fit together . Fig . 6, showing a portion of a swept-up mould, illustrates the general arrangement . A
See also:plate, A, carries a quantity of bricks, B, which are embedded in loam, and break joint . To a striking
See also:bar, C, sup-ported in a step, a striking board or sweeping board, D, is bolted, and is swept
See also:round against plastic loam, which is afterwards dried .
The check on the board at A corresponds with a similar check on the board which strikes the interior of the
See also:pan, and by which top and bottom portions of the mould are registered together . This is indicated in dotted outline . Its mould also is swept on bricks, and turned over into place, and the metal is poured into the space b, b, between the two moulds . There is also a large group of swept-up work which is not symmetrical about a centre of rotation . Then the movements of the sweeping boards are controlled by the edges of " core plates," or of " core irons " (fig . 7) .
See also:Bend pipes, and the Core-making is a
See also:special department of foundry work, often involving as much detail as the construction and moulding of patterns . Two perfectly plain boxes are shown in figs . 8 and 9, in both of which provision exists for removing the box parts from the core after the latter has been rammed . Core boxes are jointed and tapered, and often have loose pieces within them, and also prints, into the impressions of which other cores are inserted . Machine-moulding.—T here is a development of
See also:modern methods of founding which is effecting
See also:radical changes in some departments of foundry practice, namely, mouldingby
See also:machines . The advantages of this method are manifold, and its limitations volute casings of centrifugal pumps and pipes, afford examples of this kind .
In fig . 7, A is the core iron, held down by weights, and B the strickle," sweeping up the half bend C, two such halves pasted together completing the core . 9_.l r ^Tr~I^ M.1 Iri.ET^-W -OW Ililll- join OE MIA r Ys , -b are being lessened continually . There are. two broad departments between which machine-moulding is divided . One, of less importance, is that of toothed wheels; the other is that of general work, except of a very massive character .
See also:wheel moulding machines are essentially a special adaptation of the mechanism of the dividing engine, by means of which, instead of using a complete pattern of a toothed wheel, two or three pattern teeth are used, and the machine takes
See also:charge of the correct pitching or division of the teeth moulded therefrom, leaving to the moulder the work only of turning the handle of the division plate, and ramming the sand around the pattern teeth . The result is accurate pitching, and the use of two or three teeth instead of a full pattern, together with any core boxes and striking boards that are necessary for the arms . The other department of machine moulding includes nearly every conceivable class of work of small and
See also:medium dimensions . There are some dozens of distinct types of machines in use, for no one type is suitable for all classes of moulds, while some are designed specially for one or two kinds only . The fundamental principles of operation are briefly these: The pattern parts constitute, by their method of
See also:attachment to a plate or table A (fig . Io), an integral portion of the machine, so that they must partake of certain movements which are imparted to it . Often pat-terns mounted, as in fig. to, are moulded by
See also:hand, without any aid from a machine, by methods of plate - moulding." The de-
See also:livery of the pattern from the sand is in- variably accomplished by a perpendicular
See also:movement of a portion of the machine (fig .
II), withdrawing either the pattern from the mould or the mould from the pattern . The important point is that the perpendicular movement, being under thecoercion of the vertical guides provided in the or the
See also:hydraulic ram in fig. tt, is free from the unsteadiness which is incidental to withdrawal by the hands of the moulder; and if the machine performed nothing. more than this it would justify its existence . Little or no taper is required in the pattern, and the moulds are more nearly
See also:uniform in dimensions than hand-made moulds . But there are other advantages . In machine-moulding the joint faces for parting moulds are produced by the faces of the plates on which the pattern is mounted (figs. to and 1I), instead of by the hands and
See also:trowel of the moulder . When the joint
See also:face is of irregular outline, as it often is, this item alone saves a
See also:deal of
See also:time, which again is multiplied by the number of moulds repeated, often amounting to thousands . Further, provision is generally made on machine plates for the ingates and runners (fig. io) through which the metal enters the mould, the preparation of which in hand work occupies a considerable amount of time . Another great
See also:advantage applies especially to the case of deep moulds . These give much trouble in hand-moulding in consequence of the liability of the sand to become torn up during the withdrawal of the pattern . But in machine-moulding such patterns are encircled by a plate, termed a " stripping plate," which is pierced to allow the patterns to pass through, and which, being maintained firmly on the sand during the lifting of the pattern, prevents it from becoming torn up . This is not merely a
See also:matter of convenience, but is a
See also:necessity in numerous instances . The most
See also:familiar example is that of the teeth of gear wheels, in which even a very slight amount of taper interferes with accurate engagement, and this is representative of many other portions of mechanism .
These stripping plates are of metal, but in order tosave the cost of filing them in iron or
See also:steel, many are cheaply made by casting a white metal alloy round the actual pattern itself in the first place, the white metal being enclosed and retained in a plain iron
See also:frame which forms the body of the plate . Lastly, many machines, but not the majority, include provision for mechanically ramming the sand around the pattern by power instead of by hand . This is really the least valuable feature of a moulding machine, because it is not applicable to any but rather shallow moulds . It is commonly used for these, but the consistence and homogeneity of a mass of sand round a pattern 'having deep perpendicular sides can only be ensured by careful hand ramming . The highest economies of machine-moulding are obtained when (I) several small patterns are mounted and moulded at once on a single plate (fig. to); (2) when top and bottom parts of a mould are produced on different machines, carrying each its moiety of the pattern; (3) when the machine and pattern details are simplified so much that the labour of trained moulders is displaced by that of unskilled attendants who are taught in a
See also:month or two the few
See also:simple operations required . That is the direction in which repetitive casting is now rapidly tending . In fig . 11 A is the plate, which in its essentials corresponds with the plate A in fig. to, but which in the machine is made to swivel so as to bring each half of the pattern B, B in turn uppermost for ramming in the box parts C, C . The ramming is done by hand, the final squeeze being imparted against the presser D by the
See also:action of the hydraulic ram E pushing the plate, mould and box up against D . The plate being then lowered, and turned over, the further descent of the
See also:rain withdraws the bottom box from the pattern, which is the stage seen in the
See also:illustration . Then the half mould is run away on the
See also:carriage F, provided with wheels to run on rails .
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