and for attachment to end plates. The flue length is chucked with its axis vertically, the chuck, Fig. 242, being of the jaw type, having simultaneous movements. The work table is rotated by gearing, and the tool is held in a box having radial and vertical adjustments. The speed of rotation may be uniform, or a speed cone may be fitted.

Boiler Flue Flanging Machine. This machine arose out of the necessity of substituting flanged ends for furnace flues in place of the old angle iron joints. The flue lengths being first bent and welded have their flanges produced by a rolling process, which though gradual is rapid, and is easily done at one heat. In a few machines of this class the flue is held with its axis vertically on a chuck, but in the majority it is held at an angle. The operation is as follows: The flue is pinched in a chuck, Fig. 243, rotated by power through bevel gears, and while supported thus at the bottom end, and resting by its periphery on friction rollers near the other, its upper end is subject to a turningover process by a roller carried in a sliding head, the resistance to which is supplied by another roller behind the flange.

In the earlier machines the bracket which carries the flanging rollers is pivoted on a pin, and is actuated by a quadrant worm rack, the idea being to facilitate the gradual turning over of the flange, the curvature being regulated by

of steam users was in many cases simply amazing. Hundreds of lives have been sacrificed that would have been preserved under the present system of inspection. Hundreds of wretched follies in practice would never have been perpetrated if an average knowledge of the principles of boiler construction had been brought to bear upon it.

When too we compare the pressures of from 10 to 20 lb. in land and marine boilers of sixty years ago with the pressures ranging from 100 to 200 of to-day we begin to realise the magnitude of the accompanying changes in the constructive details of boilers. The developments of the modern steam engine, though spoken of as marvellous, are no more so than those of steam boilers. Imagine the total pressure on the shell or ends or furnace tubes of a highclass modern boiler, and then try to conceive the enormous strength requisite to withstand those pressures. As the strength of a chain is measured by that of its weakest link, so the strength of the minutest detail of a boiler must be estimated by the maximum pressure the boiler has to carry. Plates, seams, rivets, stays, flanges, bursting and collapsing strengths should each be strong enough for that pressure. Then besides the structural proportions of boilers, the changes of their life history must be under stood. Some boilers grow prematurely old, others last longer than the average term of human life. It is largely a question of original construction, but it is also one of the wear and tear of service. Boilers are subject to many accidents and diseases, due to bad management, bad feed water, deposit and incrustation, corrosion and grooving, overheating and local stress. The diagnosis of these evils gives work to the boiler inspector, and the warding off or cure of these troubles demands continual watchfulness.

The employment of high pressures has led to greater care being exercised over the fittings and mountings of boilers, and steam users are practically compelled to take all reasonable care to prevent the risk of explosion. Faulty and unsafe fittings and mountings have therefore mostly given place to those of better construction. The lessons of many hundreds of explosions have been utilised in the direction of safer practice, and out of evil there has been

evolved much good. A modern boiler manufactured according to the most approved methods of design, tested and inspected during manufacture and periodically inspected afterwards, is almost perfectly safe.

With

The story of boiler inspection during the last fifty years runs side by side with that of the development in boiler practice due to the introduction of mild steel in place of wrought iron, to the employment of very much higher pressures, and the developments of new types, and modifications in types. It has also been extended to include economisers, superheaters, steam-pipes, water-tube boilers, and mill engines, and also the designing of new boilers. regard to the work of the Manchester Steam Users' Association just now referred to, and the parent of all others in existence, this Association was mainly responsible for the passing of the Boiler Explosion Acts, and for the conduct of a number of classical experiments, some of which were very costly. The Association takes a very lofty view of its own responsibilities. They have a guarantee fund, but with an income of about £17,000 a year they distribute no dividends, nor do they seek any, all surplus being utilised for advancing the knowledge of boilers and related subjects. Associations similar to the Manchester have been formed now in most civilised countries, and there is an international union, comprising fifty boiler inspection associations, who have 149,000 boilers under their inspection. The Manchester Association accept no boiler for insurance which is not first of all thoroughly inspected and found safe, or which is so constructed that it cannot in future be efficiently inspected. None is accepted if constructed entirely or partly of cast iron or similar unreliable material, among which are included some so-called cast steels and steel alloys.

The duties of boiler inspectors involve much more than can be stated in this article. They include a knowledge of the strength and behaviour of wrought iron, mild steel, and copper, the strength of riveted joints, the appearances and causes of deterioration of the various kinds noted in the article Boiler Explosions, the making of tests, to ascertain Boiler Efficiency, and they make external and internal

examinations, in brick-work flues, shells, and furnace flues; scaling, drilling, and close ocular examinations under very trying conditions of temperature. Practically the work of the boiler inspector will be found covered in the

various articles in these volumes under which steam boilers and the matters relating thereto are described.

Boilermaker.-In its most comprehensive sense, as understood a few years ago, it meant a man who was capable of carrying through the construction of a boiler from beginning to completion; that is, he would be able to line off plates, punch, drill, rivet, caulk, do the angle iron work or hand flanging at the forge, put the boiler together, and execute all kinds of repairs that might be required on boilers. Boilermakers were also expected to be able to turn their hand to a job of ordinary plating. Gradually subdivision of tasks has been having the same results here as in many other trades. First of all there was the separation of the templet-maker from the actual work of the shops; flanging done by machines has to a great extent displaced the work of the angle iron smith, in the attachments of furnaces to end plates and crowns, and of barrels to end plates. Drilling to templet has taken the place of punching, reamering, and drifting, or the plates of a boiler are drilled through one another; so here another great branch of the boilermaker's work has been relegated to the driller. The men who operate hydraulic and pneumatic riveting machines have taken away another important section of the old work. The result is that except in the smaller shops, and for repairs, the occupation of the all-round boilermaker is nearly gone, replaced by the work of sectional departments.

Boilermaker's Dolly. A flat-ended bar held up under the heads of rivets, similarly to the holding-up hammer, and for the same purpose, to offer a dead resistance to the riveting

hammer.

Boiler Mountings. These include safety valves, stop valves, back pressure valve, steam

and water gauges, try cocks, blow-off cock, and fusible plugs.

Boiler Patching.-When a minute crack is discovered in the plate of a boiler, it is not always necessary to cut out the cracked portion and put on a patch. When the crack is only in an incipient stage the practice of studding is frequently adopted. That is, a hole is drilled and tapped at each end of the crack, and a screwed stud inserted. This localises the fracture, and so prevents its extension.

When putting patches on old boilers it often occurs that by the careless removal of rivets the plates become cracked, or otherwise damaged between the rivet holes. Or the seams may show grooving, or corrosion. In such cases the old rivet holes should not be utilised again, but the entire seam should be cut away, and new rivet holes made for the attachment of the patch piece.

When fitting a patch to a boiler care must be taken to make it of the correct shape, curvature, or otherwise necessary to ensure a perfect fit. If this is neglected, especially in thick plates, the riveting up strains the parts, and more caulking is necessary than when they are properly fitted before riveting. Small patches should never be put into boiler furnaces as they tend to cause overheating.

Boilers patched with pieces of plate bolted on, and cocks and mountings bolted direct to the boiler shell are seldom seen now. But such things were common in the experience of the older boiler inspectors. The practice was very bad, and has been the occasion of wasting and failure of plates. The bolts permit of leakage, which corrodes the portions of the plate adjacent thereto. Always patches should be riveted on, and mountings be bolted to seatings riveted to the boiler.

Sometimes in the case of an iron boiler which has exploded, it has been found that patches which have been put on had been laid with the grain running longitudinally, or with the axis of the boiler instead of circumferentially, which would be the direction of greatest strength.