REFRACTORIES FOR GASWORKS PURPOSES
As yet, the casting process has not been sufficiently developed for any definite opinion to be given, as to the likelihood of its more general adoption. Very much must ■depend upon operating costs, and i t would appear that the cast retort will necessarily be more expensive than those made by more com-mon methods. It is stated that a denser retort with less tendency to crack is given by the ■casting process as com-pared with other methods, the reason for this being that the great homo-geneity of the retort lessens the tendency to set up local strains which
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are the main cause of cracking.
Jig. IH.—Mould and Core for Casting Retorts.
The Qualities of Hand-made and Machine-pressed Retorts
With regard to manufacturing costs, tliere is iittle to choose between the two types of retort, but from the point of view of working life the hand-made article is usually preferred. The faet that the machine type is made in a single operation may account for somewhat greater homo-geneity, but the gradual building up in distinet lifts ensures slower drying, which is desirable. Machine-made retorts are denser and heavier, but an excess of density can be avoided by the addition of sawdust or coarser grogram. Owing to the high working pressure of the machmes the pre-pared clay must of necessity be stiff, otherwise warping and sagging will occur atter the material has passed the die. StifE material put together by