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ENGINEERING MAGAZINE, ,

COMMENCED JANUARY, 1869,

Published on the 15th of the month at $5.00 per year.

ot

The January number

this MAGAZINE, for the year 1881, begins the Twenty-fourth Volume. Beginning as an Eclectic Journal, and presenting almost exclusively matter selected from current literature, it has gradually become the chief medium through which the leading writers on engineering subjects can best present their original essays to American readers.

The attitude of the MAGAZINE has been, and will continue to be, that of a journal of original and selected papers upon subjects relating to modern advanced Engineering. Theoretical and Practical Essays are alike presented in its pages, although the latter largely out-number the former, as best suited to the tastes and demands of the American Engineers. Some of the most valuable contributions to the literature of technical science within the last few years have been first presented in these pages.

Among the more extended original contributions to the later volumes may be cited new contributions to Graphical Statics— Transmission of Power by Wire Ropes— Maximum Stresses in Framed Bridges-Momentum and Vis Viva-Rapid Methods of Laying out Gearing–Transmission of Power by Compressed Air-Geographica. SurveyingMathematical Theory of Fluid Motion - Thermodynamics — Practical Theory of Voussoir Arches—Cable Making for Suspension Bridges, &c., &c.

To the above may be added the following valuable essays, translated from foreign sources, which have first appeared in these pages: Linkages and their Applications, The Origin of Metallurgy-and The Theory of Ice Machines.

The plans for future volumes comprehend many improvements in the same direction. The wants of the educated practical engineer, who desires to keep in the foremost rank of his profession will be steadily kept in view, and our constantly increasing resources for supplying the best of scientific information will be employed to secure such result.

18 Cloth covers for Volumes I. to XXIII. inclusive, elegantly stamped in gilt, will be furnished by the publisher, for fifty cents each.

If the back numbers be sent, the volumes will be bound neatly in black cloth and lettered, for seventy-five cents each. The expense of carriage must be borne by the subscriber.

Notice to New Subscribers.—Persons commencing their subscriptions with the Twenty-fourth Volume (January, 1881), and who are desirous of possessing the work from its com. mencement, will be supplied with Volumes I. to XXIII. inclusive, neatly bound in cloth, for $60.00 in half morocco, $90.00.

Notice to Clubs.-An extra copy will be supplied gratis 10 every Club of Five subscriber, at $5.00 each, sent in one remittance.

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PAGE.

A RATIONAL SYSTEM OF PISTON PACKING. By Prof. S. W.
Robinson, C. E. (Illustrated)..

Contrıb. Van Nostrand's Magazine., 441 THE METRIC SYSTEM....

.Proceedings Boston Society Ciol Eng... 450 SUGGESTIONS FOR PREVENTING LONDON SMOKE. By W. D. Scott-Moncrieff, C.E., F.R.S.S.A.....

Journal of the Society of Arts.... 458 ROMAN BUILDING IN ENGLAND AND IN ITALY.

...Builder.....

465 THE MANUFACTURE AND USES OF CAST STEEL,..

English Mechanic.

469 EXPERIMENTS ON THE STRENGTH AND STIFFNESS OF SMALL SPRUCE BEAMS. By F. E. Kidder.....

.Proc. Amer. Acad. Arts and Sciences.. 473 GAS AND ELECTRICITY AS HEATING AGENTS. By Dr. C. William Siemens, F.R.S.....

.Iron..... THE EFFECT OF PUNCHING ON STEEL AND IRON PLATES... Engineer .

497 THE OPTICAL DYNAMOMETER. (Illustrated)...

Trans. from l'Electricien...

490 CAPABILITIES OF STANDING HEAT OF VARIOUS BUILDING STONES. By Hiram A. Cutting, Ph. D.

491 OUR CENTER OF POPULATION. By Frank D. Y. Carpenter, C.E...

Written for Van Nostrand's Magazine, 496 NEw MODE OF COMPENSATING BALANCES. (Illustrated). By Charles V. Woerd......

502 RECENT ADVANCES IN ELECTRIC LIGHTING. By W. H. Preece ...

...Journal of Society of Arts... ILLUSORY SANITATION.

.Building Neros.

512 ADDITIONAL WIDTH OF GAUGE ON RAILWAY CURVES. By Thomas Doane..

Paper read before Boston Soc. Civil Eng. 517

PARAGRAPHS.—The Tunis side of the St. Gothard Tunnel, 449; Arrival of Clyde laborers, 457 ; Persons who can

not recover for injury on R. R. cars, 501. REPORTS OF ENGINEERING SOCIETIES.-American Society of Civil Engineers, 518; Engineer's Club of Phila

delphia, 519,

ENGINEERING NOTES.-Railway boring near Abbott's Cliff, England, 519,
RAILWAY NOTES.-Mountain Railways, 519; Observations on fractures of steel rails, 520,
IRON AND STEEL NOTES.–Stock of the North British Railway Co.; Dividend of the North British Railway Co.

Concrete slag a substitute for stone, 520,
ORDNANCE AND NAVAL.-Macbine Guns at Shoeburyness, 520; The Russian Navy, 521.
BOOK NOTICES.–Publications Received; Graphical Determination of Forces in Engineering Structures, by Jam

B. Chalmers, C.E.; Practical Organ-Building, by W. E. Dickson, M.A.; Induction Coils, How Made and How tsed The Plumber and Sanitary Houses (second edition), by S. Stevens Hellyer; The Wool Carder's Vade Mecum, to William Calvert Bramwell; Lathe Work, by Paul N. Hasluck; Steam Boilers, by William H. Shock, Engineer-id

Chief, U. S. N.; The Telescope, by Thomas Nolan, B. S., 522, MISCELLANEOUS.—The Corrosion of Iron in Boilers ; The Great Brush Light ; Experiments on the Electric Currens,

Boudet's Microphone, 524.

VAN NOSTRAND'S

ENGINEERING MAGAZINE. .

NO. CXLX.-JUNE, 1881.-VOL. XXIV.

A RATIONAL SYSTEM OF PISTON PACKING. By S. W. ROBINSON, C. E., Professor Mechanical Engineering, Ohio State University, Columbus. Read before the American Society of Mechanical Engineers, May Meeting, Hartford, Conn.

Contributed to VAN NOSTRAND'S ENGINEERING MAGAZINE. The primary object of a good piston against its packing glands; and that in packing is evidently to prevent the work- view of these facts it may be desirable ing fluid from escaping past the piston. to introduce a groove containing a solid, The sole object of the present paper is stout half ring about at the middle of to investigate how this can be done most the face of piston to serve as a carriage, efficiently ; leaving out of the question with the piston properly jacked upon it: all such uses of packing as making it and, finally, that all these devices may serve the purpose of a carriage for sup. be replaced by a considerable breadth of port of the piston, &c.; except, perhaps, piston rims for support of piston, and å reference to this matter of carriage narrow packing rings under outward support—in that it seems desirable to pressure to prevent escape of working have a carriage for the piston, especially fluid. This is all the more evident when in horizontal engines, and where the we reflect that the piston may be made cylinder has been bored out larger than light-hollow, if necessary, for this end, the piston to correct irregular wear after and the weight added to the cross head

But a glance at the matter or the connecting rod—in which event will show that for the packing to serve the piston and cylinder will be subjected as carriage, it must be very wide in order to the least possible wear, and thus to present the necessary wearing surface scarcely need re-boring within the life of for durability, and that where the pack- the engine. It is evident that this result ing is wide, the rims of the piston must is preferable to that where the cylinder be correspondingly narrow, and be ac- frequently gets out of form to the extent cordingly unfitted for bearing the weight necessitating repeated re-boring, when of the piston ; and that the flexibility of the lifetime of the engine will be more or the packing rings will allow them to less afflicted with “piston blowing.” take a somewhat irregular form, thus Hence, it is proposed, here, to adopt tending to wear the cylinder out of as light a piston as possible, to use very round, and that the devices for setting narrow packing rings, and wide rims on out the rings may change in intensity the piston, especially for horizontal enof action so as to cause the piston to ride gines. The simplest possible packing upon the cylinder at some side, causing consists of a single ring split upon one relatively rapid wear of the narrow rims side. The simplest piston is one in a of piston; and that the piston rod will single piece, possibly cast hollow for thus be brought into wearing contact securing desirable form. Hence, a sin

VOL. XXIV.-No. 6–31.

some use.

FORM OF PACKING RING.

gle ring, sprung into a groove turned on the radius of the ring. To define it clearly, the face of such a piston, combines the draw a line parallel to BO and very near elements of simplicity. Two or more to B as at C. Suppose these lines fixed rings may, however, be used on a single to the ring, and parallel before flexure. piston, each sprung into its own groove. After flexure these lines will intersect at

We will now investigate the single some point more or less remote from B, ring packing. It will appear afterwards according to the amount of bending, that, to set the ring out by pressure of The distance from B to the point of inthe working fluid transmitted to the un- tersection is p. It is evident that if the derside of the ring through holes, causes ring is of circular form before flexure, and excessive frictional contact of the ring also after, p will be of constant length upon the surface of cylinder. It would for all parts of the ring. As the ring is seem desirable, therefore, to give the most conveniently made of circular form, ring its pressure of contact by means of and as it will be used in a circular cylin. the inherent stiffness of the ring itself, der, it is desirable that the thickness by turning it larger than the cylinder shall so vary as to realize this and make bore.

p constant. A ring, split upon one side and press According to the theory of flexure, the ing outward with a constant pressure, as flexural moment must equal the moment it evidently should for greatest efficiency, of the applied forces. This latter will, will necessarily be thicker at points op in the present case, be the resultant mo. posite the split, as shown in Fig. 2. ment of all the normal pressures on AB.

Let P represent the normal pressure per

unit of surface of the ring against the To find the law of varying thickness, cylinder, and if i be the breadth of ring, let AB, Fig. 1, represent a piece of such the pressure per unit of length of ring a packing ring, the end or split being at will be Pb, and for a length rdh, the

pressure will be Pb.rde.

The moment
of this element will be Pbrdo.; sin
\

with reference to an origin of moments
at B, where the origin is taken for eq.
(1). The integral of this, for varied
between the limits x and 0, will give the
total moment of the forces acting on the
part AB, or
EI
= SPbr" sin 6 db=Pbro(1–cos x)
=2Pbro sin?

(2)

2 Fig.1

P being regarded as constant.

Let z be the thickness of the ring at B. Then

I=1, bz

EI
A. Then the normal pressure of the and

Ez
=2Pr* sin

sin ring against the cylinder along the out

p
12p

2 side of AB will be due to a flexural mo- At the middle of ring, or where AB= ment, or resistance to bending, of the 180°, we have section of ring at B. This, according to

Ez the theory of flexure, will be

=2Popa

12p,
EI
Flexural moment at B=

(1)
whence

sin

(3)

P where E is the coefficient of elasticity of

Pi

2 the material of the ring, I the moment of an equation for the whole ring, and givinertia of the section of ring at B, and p ing the relation between 2, p and x; upon the radius of curvature due to the bending any one of which we may impose arbitrary This radius is not to be confounded with conditions, the other two remaining mu

A

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