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1 all abrupt changes in section of the pattern should

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1.All Abrupt changes in section of the pattern should be avoided as far as possible.2.Parting line should be selected carefully, so as to allow as small portion of thepattern as far as possible in the cope area3.The thickness and section of the pattern should be kept as uniform as possible.4.Sharp corners and edges should be supported by suitable fillets or otherwise roundedof. It will facilitate easy withdrawal of pattern, smooth flow of molten metal andensure a sound casting.5.Surfaces of the casting which are specifically required to be perfectly sound andclean should be so designed that they will be molded in the drag because thepossible defects due to loose sand and inclusions will occur in the cope.6.As far as possible, full cores should be used instead of cemented half cores forreducing cost and for accuracy.7.For mass production, the use of several patterns in a mould with common riser isto be preferred.8.The pattern should have very good surface finish as it directly affects the correspondingfinish of the casting.9.Shape and size of the casting and that of the core should be carefully considered todecide the size and location of the core prints.10.Proper material should always be selected for the pattern after carefully analyzingthe factors responsible for their selection.11.Try to employ full cores always instead of jointed half cores as far as possible. Thiswill reduce cost and ensure greater dimensional accuracy.12.The use of offset parting, instead of cores as for as possible should be encouragedto the great extent.13.For large scale production of small castings, the use of gated or match- platepatterns should be preferred wherever the existing facilities permit.14.If gates, runners and risers are required to be attached with the pattern, they shouldbe properly located and their sudden variation in dimensions should be avoided.15.Wherever there is a sharp corner, a fillet should be provided, and the corners maybe rounded up for easy withdrawal of patterns as well as easy flow of molten metalin the mould.
Pattern and Core Making 19516.Proper allowances should be provided, wherever necessary.17.As for as possible, the pattern should have a good surface finish because the surfacefinish of the casting depends totally on the surface finish of the pattern and the kindof facing of the mold cavity.10.13 PATTERN LAYOUTAfter deciding the molding method and form of pattern, planning for the development ofcomplete pattern is made which may be in two different stages. The first stage is to preparea layout of the different parts of the pattern. The next stage is to shape them. The layoutpreparation consists of measuring, marking, and setting out the dimensions on a layout boardincluding needed allowances. The first step in laying out is to study the working drawingcarefully and select a suitable board of wood that can accommodate at least two views of thesame on full size scale. The next step is to decide a working face of the board and plane anadjacent edge smooth and square with the said face. Select a proper contraction scale for

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