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Piston Ring Manufacture.

28th September 1916
Page 16
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Page 16, 28th September 1916 — Piston Ring Manufacture.
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A Few Notes and Reflections Suggested by a Visit to the Works of the British Chuck and Piston Ring Co., Ltd.

The method of specialized manufacturing of one or two details, as opposed to that of producing a varied assortment of parts or accessories, has made great headway in connection with such components as carburetters, lubricators, and— this brings us to the subject of our article—piston rings. We have known the products of the British Chuck and Piston Ring Co., Ltd., of Holbrook. Lane, Coventry, for several years Until quite recently the company made piston rings, and piston, rings only. Of late it has gravitated. by degrees from piston rings to pistons, made by special request for a few makers who appreciated the .rings, from pistons to gudgeon pins, from gudgeon pins the transition to shackle pins was easy and rapid, and since nowadays shackle pins by being screwed on their ends and bored become at one and the same. time shackle pins and grease cups, it is only to be expected that the company would complete the fitting by making the screwed nuts to retain the grease.

We think, however, that we have now defined the limits of its activities, but the main output is still piston rings. The piston rings, as It were, form the means of obtaining the bread and butter for the company ; the other items enable an occasional supply of jam to be added. Of piston rings for internal-combustion engines the company has probably a store of experience equal to any. From the foundry, where only one grade of metal is melted, the ingredients and east metal being carefully scrutinized and analysed, to the machine shop, where at every stage special and novel machinery designed by the company for its own particular purpose is evident at every stage of the manufacture, to the viewing room, and finally to the packing and despatch department, the concentration of the firm's ener gies on this speciality for a number of years is evident; furthermore, the same keen attention is being given in the newer department— that of producing high-grade gud-. geon and shackle pins. B.ere, again, we observe the careful choice of machinery, the extremely accurate measuring appliances used for checking the parts in various stages of their manufacture, and the very

complete and compact department where the steel receives its heat treatment.

The policy in the piston-ring department has been to stick to one

grade of metal, one which has been found from experience to give the best results. On the new side of the works,. so far as it is possible, operations are confined to Uhas steel, which is renowned through the indhstry for its uniformity in structure and performance.

The piston rings made vary in size from those for the small motor bicycle engine to 30 in. rings for

Diesel oil engines and small gas engines. Our attention may properly

be confined to those sizes custom arily employed on petrol engines. An examination of the progress of a casting from the foundry to the despatch department is replete with interest. The casting for the rings is in the form of a long cylinder flanged at one end ; the shape of this flange is peculiar, and enables the casting to be gripped in the lathe chuck or loosened again in the minimum of time and with the least amount of trouble. For obvious reasons, particulars of this cannot be divulged. The outside and inside of the rough casting are then machined and the rings parted off to a thickness slightly greliter than that required in the finished product. All these operations are performed on the one machine. Thence the rings go to the grinding machines by which this minute excess is removed.

For rings where the greatest accuracy is required, a special machine is used ; this, again, has been designed by the company. In the ordinary way, piston rings of this type are ground by being laid on the top-of a table which is ,„in point of fact, a large magnet. 'The table is revolved while the upper surface of the ring is ground ; the ring is then turned over and ground on the other side. The difficulty with a magnetic chuck of this description when extreme accuracy is required is that it is almost impossible to ensure against small specks of dust intervening between chuck and ring. In such cases as rings for aircraft engines, and for highclass touring.and racing-car engines where a degree of accuracy within three quarters of -one-thousandth part of an inch of the accurate size is insisted upon, the intervention of dust in the manner stated would be fatal. On the special machines designed by the company, each ring is held by an internal-expanding chuck and ground between two revolving emery wheels. It is claimed that the finest needful degree of curacy-is obtainable by this method.

From the grinding machines the rings go to be cut. If they are of the eccentric variety, each is marked so that the slot comes precisely at the thinnest part of the ring. After being cut, the portions of the ring near the slot are hammered on the outside, again by a special machine. It is claimed that the advantage of hammering them on the outside is that the natural spring of the ring is maintained. The dents made by the hammer which cannot be removed when on the inside of the ring, and which in some cases serve as starting points for cracks or breakages, are taken out in the grinding process.

A point worthy of note in regard to the actual cutting of the ring is that the company considers the plain slot at an acute angle to the edge of the ring as being equally efficient as any other, but it repudiates the suggestion that the lapjointed ring gives any better results. On the other hand the former type can be cut several at a time, the latter type must be done one by one and each slot necessitates two operations.

Incidentally, in passing through the works we were shown one or two special types of ring brought into being by the newest branch of

petrol-motor engineering, that of aircraft. A novel form of ring which is much favoured by this section of the industry is a very narrow one, and, in some cases, in order to obtain the necessary strength while at the same time reducing the width to less than an "eighth of an inch, the more usual metal, cast-iron, has been discarded in favour of high tensile steel. That the latter is not likely to become a popular metal for piston rings may be gathered from the fact that each ring costs half a guinea.

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Locations: Coventry

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