Important Piston-ring Development
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PIIORMICAST is the name bestowed by Hepworth and Grandage,. Ltd., St. John's Works, Bradford, _upon its latest piston rings, for which it. makes :the proud claim that " they have a permanence exceeding any other known method." Convincing, explanation is put forward in sidistantiation, and this can be studied in full in a leaflet recently issued by the company.
Briefly, the main points are these. It has been found that for maximum ring efficiency, particularly at high speeds, it is desirable for a ring to be designed so that the pressures at which it bears on. the cylinder bore, at all points on its circumference, should be graduated in a specific manner and of considerable magnitude. Roughly, they should be highest near the gap and opposite it, and, if the gap be at 12 o'clock, should have a minimum value at 1.30 and 10.30. And a mean value at 3.0 and 9.0. These conditions are ,satisfactorily fulfilled by adopting , a manufacturing process based on the following prin
ciple. An ordinary circular ring is expanded to the theoretical ahape by inserting a distance-piece in the gap. This is used as a pattern from which a new ring is cast. (These rings are, of course, cast singly.) Then the equivalent of the spaces is cut out and when the ring is closed into a circular jig the presures are to requirelents.
By the concern's " cast-out-ofround" method, which is a process of this nature, the " pressure pattern " is permanent and cast into the ring. The graduation and arrangement of the pressures,-also their magnitude which is high • (20-30 lb. per sq. 'in.) minimize blow-by of gas and ." flutter." It is essential, however, because of the high wall pressure, that the supply of lubricant should be really copious.