7th. Every part accessible for cleaning and repairs.
With these points having been determined, No. 20 was designed. This boiler had all the desirable features just enumerated, together with a number of improvements as to detail of construction. The general form of No. 15 was adhered to but the bolted connections between sections and drum and sections and mud drum were discarded in favor of connections made by short lengths of boiler tubes expanded into the adjacent parts.
This boiler was suspended from girders, like No. 15, but these in turn were carried on vertical supports, leaving the pressure parts entirely free from the brickwork, the mutually deteriorating strains present where one was supported by the other being in this way overcome.
Hundreds of thousands of horse power of this design were built, giving great satisfaction. The boiler was known as the "C. I. F." (cast-iron front) style, an ornamental cast-iron front having been usually furnished.
[Ill.u.s.tration: No. 21]
The next step, and the one which connects the boilers as described above to the boiler as it is built to-day, was the design ill.u.s.trated in No.
21. These boilers were known as the "W. I. F." style, the fronts furnished as part of the equipment being constructed largely of wrought iron. The cast-iron drumheads used in No. 20 were replaced by wrought-steel f.l.a.n.g.ed and "b.u.mped" heads. The drums were made longer and the sections connected to wrought-steel cross boxes riveted to the bottom of the drums. The boilers were supported by girders and columns as in No. 20.
[Ill.u.s.tration: No. 22]
No. 22. This boiler, which is designated as the "Vertical Header" type, has the same general features of construction as No. 21, except that the tube sheet side of the headers is "stepped" to allow the headers to be placed vertically and at right angles to the drum and still maintain the tubes at the angle used in Nos. 20 and 21.
[Ill.u.s.tration: No. 23]
No. 23, or the cross drum design of boiler, is a development of the Babc.o.c.k & Wilc.o.x marine boiler, in which the cross drum is used exclusively. The experience of the Glasgow Works of The Babc.o.c.k & Wilc.o.x, Ltd., with No. 18 proved that proper attention to details of construction would make it a most desirable form of boiler where headroom was limited. A large number of this design have been successfully installed and are giving satisfactory results under widely varying conditions. The cross drum boiler is also built in a vertical header design.
Boilers Nos. 21, 22 and 23, with a few modifications, are now the standard forms. These designs are ill.u.s.trated, as they are constructed to-day, on pages 48, 52, 54, 58 and 60.
The last step in the development of the water-tube boiler, beyond which it seems almost impossible for science and skill to advance, consists in the making of all pressure parts of the boiler of wrought steel, including sinuous headers, cross boxes, nozzles, and the like. This construction was the result of the demands of certain Continental laws that are coming into general vogue in this country. The Babc.o.c.k & Wilc.o.x Co. have at the present time a plant producing steel forgings that have been p.r.o.nounced by the _London Engineer_ to be "a perfect triumph of the forgers" art".
The various designs of this all wrought-steel boiler are fully ill.u.s.trated in the following pages.
[Ill.u.s.tration: Wrought-steel Vertical Header Longitudinal Drum Babc.o.c.k & Wilc.o.x Boiler, Equipped with Babc.o.c.k & Wilc.o.x Superheater and Babc.o.c.k & Wilc.o.x Chain Grate Stoker]
THE BABc.o.c.k & WILc.o.x BOILER
The following brief description of the Babc.o.c.k & Wilc.o.x boiler will clearly indicate the manner in which it fulfills the requirements of the perfect steam boiler already enumerated.
The Babc.o.c.k & Wilc.o.x boiler is built in two general cla.s.ses, the longitudinal drum type and the cross drum type. Either of these designs may be constructed with vertical or inclined headers, and the headers in turn may be of wrought steel or cast iron dependent upon the working pressure for which the boiler is constructed. The headers may be of different lengths, that is, may connect different numbers of tubes, and it is by a change in the number of tubes in height per section and the number of sections in width that the size of the boiler is varied.
The longitudinal drum boiler is the generally accepted standard of Babc.o.c.k & Wilc.o.x construction. The cross drum boiler, though originally designed to meet certain conditions of headroom, has become popular for numerous cla.s.ses of work where low headroom is not a requirement which must be met.
LONGITUDINAL DRUM CONSTRUCTION--The heating surface of this type of boiler is made up of a drum or drums, depending upon the width of the boiler extending longitudinally over the other pressure parts. To the drum or drums there are connected through cross boxes at either end the sections, which are made up of headers and tubes. At the lower end of the sections there is a mud drum extending entirely across the setting and connected to all sections. The connections between all parts are by short lengths of tubes expanded into bored seats.
[Ill.u.s.tration: Forged-steel Drumhead with Manhole Plate in Position]
The drums are of three sheets, of such thickness as to give the required factor of safety under the maximum pressure for which the boiler is constructed. The circular seams are ordinarily single lap riveted though these may be double lap riveted to meet certain requirements of pressure or of specifications. The longitudinal seams are properly proportioned b.u.t.t and strap or lap riveted joints dependent upon the pressure for which the boilers are built. Where b.u.t.t strap joints are used the straps are bent to the proper radius in an hydraulic press. The courses are built independently to template and are a.s.sembled by an hydraulic forcing press. All riveted holes are punched one-quarter inch smaller than the size of rivets as driven and are reamed to full size after the plates are a.s.sembled. All rivets are driven by hydraulic pressure and held until black.
[Ill.u.s.tration: Forged-steel Drumhead Interior]
The drumheads are hydraulic forged at a single heat, the manhole opening and stiffening ring being forged in position. Flat raised seats for water column and feed connections are formed in the forging.
All heads are provided with manholes, the edges of which are turned true. The manhole plates are of forged steel and turned to fit manhole opening. These plates are held in position by forged-steel guards and bolts.
The drum nozzles are of forged steel, faced, and fitted with taper thread stud bolts.
[Ill.u.s.tration: Forged-steel Drum Nozzle]
Cross boxes by means of which the sections are attached to the drums, are of forged steel, made from a single sheet.
Where two or more drums are used in one boiler they are connected by a cross pipe having a f.l.a.n.g.ed outlet for the steam connection.
[Ill.u.s.tration: Forged-steel Cross Box]
The sections are built of 4-inch hot finished seamless open-hearth steel tubes of No. 10 B. W. G. where the boilers are built for working pressures up to 210 pounds. Where the working pressure is to be above this and below 260 pounds, No. 9 B. W. G. tubes are supplied.
[Ill.u.s.tration: Inside Handhole Fittings Wrought-steel Vertical Header]
The tubes are expanded into headers of serpentine or sinuous form, which dispose the tubes in a staggered position when a.s.sembled as a complete boiler. These headers are of wrought steel or of cast iron, the latter being ordinarily supplied where the working pressure is not to exceed 160 pounds. The headers may be either vertical or inclined as shown in the various ill.u.s.trations of a.s.sembled boilers.
[Ill.u.s.tration: Wrought-steel Vertical Header]
Opposite each tube end in the headers there is placed a handhole of sufficient size to permit the cleaning, removal or renewal of a tube.
These openings in the wrought steel vertical headers are elliptical in shape, machine faced, and milled to a true plane back from the edge a sufficient distance to make a seat. The openings are closed by inside fitting forged plates, shouldered to center in the opening, their f.l.a.n.g.ed seats milled to a true plane. These plates are held in position by studs and forged-steel binders and nuts. The joints between plates and headers are made with a thin gasket.
[Ill.u.s.tration: Inside Handhole Fitting Wrought-steel Inclined Header]
In the wrought-steel inclined headers the handhole openings are either circular or elliptical, the former being ordinarily supplied. The circular openings have a raised seat milled to a true plane. The openings are closed on the outside by forged-steel caps, milled and ground true, held in position by forged-steel safety clamps and secured by ball-headed bolts to a.s.sure correct alignment. With this style of fitting, joints are made tight, metal to metal, without packing of any kind.
[Ill.u.s.tration: Wrought-steel Inclined Header]
Where elliptical handholes are furnished they are faced inside, closed by inside fitting forged-steel plates, held to their seats by studs and secured by forged-steel binders and nuts.
The joints between plates and header are made with a thin gasket.
[Ill.u.s.tration: Cast-iron Vertical Header]
The vertical cast-iron headers have elliptical handholes with raised seats milled to a true plane. These are closed on the outside by cast-iron caps milled true, held in position by forged-steel safety clamps, which close the openings from the inside and which are secured by ball-headed bolts to a.s.sure proper alignment. All joints are made tight, metal to metal, without packing of any kind.
The mud drum to which the sections are attached at the lower end of the rear headers, is a forged-steel box 7 inches square, and of such length as to be connected to all headers by means of wrought nipples expanded into counterbored seats. The mud drum is furnished with handholes for cleaning, these being closed from the inside by forged-steel plates with studs, and secured on a faced seat in the mud drum by forged-steel binders and nuts. The joints between the plates and the drum are made with thin gaskets. The mud drum is tapped for blow-off connection.
All connections between drums and sections and between sections and mud drum are of hot finished seamless open-hearth steel tubes of No. 9 B. W. G.
Boilers of the longitudinal drum type are suspended front and rear from wrought-steel supporting frames entirely independent of the brickwork.
This allows for expansion and contraction of the pressure parts without straining either the boiler or the brickwork, and also allows of brickwork repair or renewal without in any way disturbing the boiler or its connections.
[Ill.u.s.tration: Babc.o.c.k & Wilc.o.x Wrought-steel Vertical Header Cross Drum Boiler]
CROSS DRUM CONSTRUCTION--The cross drum type of boilers differs from the longitudinal only in drum construction and method of support. The drum in this type is placed transversely across the rear of the boiler and is connected to the sections by means of circulating tubes expanded into bored seats.