The Locomotive Of Today

10 The Boiler: Lagging, Joints, Rivets, Stays. is as far as possible done by hydraulic power. Seams and joints are caulked by having a blunt tool smartly hammered along the edges of the plates ; mechanical caulking tools are largely employed for this operation. 1 he exposed portions of the boiler are lagged or covered with a non-conducting material to prevent, as far as possible, loss of heat by radiation. Felt, preparations of asbestos, silicate cotton, but more often wood, sometimes covered with a tire-resisting compound, are used for this purpose; the whole is then covered with cleading plates of Steel, held in position by means of bands. It is also a practice on some railways for these cleading plates to be made a good fit to enclose a layer of air, which is alone relied on for non-conduction. In Fig. i sectional drawings are given of three forms of joint usually employed in connecting the various parts of locomotive boilers together. A shows the angle iron joint between the barrel, front tube plate, and smokebox. B a specimen of single plate butt jointing where the plates to be connected have their ends brought together in the same plane and a cover strip rivetted on one side only. This joint is the one often employed for securing the rings of the barrel to- gether. Longitudinal joints are also made in this manner, but with a cover plate on each side and double rivetting. C shows a lap joint where one plate overlaps the other; the outer firebox shell is usually fixed to the barrel by means of a lap joint. Best iron or mild Steel rivets are used with both Steel and iron boilers for the seams round the inner copper firebox, and the joints round the foundation ring and tirehole. Snap heads or their equivalents are employed where possible, but a close fit at places may necessitate a few “ countersinks.” As already mentioned it is necessary that all the flat surfaces in a locomotive boiler should be well stayed or supported to resist the high pressure generated within. The inner and outer fireboxes having flat sides, back and front, more or less parallel to each other, with pressure between which tends to force them apart, are tied together, as it were, by means of screwed stays or stay bolts. The holes to receive these are either punched or drilled through the wrapper plate before it is bent to shape, and are drilled through the inner box after it is built up and rivetted together, this latter being then secured in its appointed place by rivetting round the foundation ring and firehole. With the fireboxes in position the stay holes are tapped by means of a long tap having' fine threads of 11 or 12 to the inch, and the screwed stays are tlien driven in, either by means of a “stud wrench,” holding the