CHAPTER II
BOILER SHOP
Boiler Plates and Making the Boiler Barrel. The steel plates are delivered into the boiler shop after they have been sheared to sizes about ½ in. larger all round than the finished sizes to which they are put together in the boiler. They must be of the very finest quality, since they have to undergo processes, such as flanging, punching, etc., which would inevitably crack or otherwise injure inferior material.
After their arrival, the plates are first straightened to remove any slight waviness, by passing them through a machine, sometimes known as a “mangle,” which has a number of hard steel rollers, usually four above and three below. By passing the plate through between the upper and lower rollers two or three times the irregularities are removed.
The length of the barrel of the boiler may vary from about 10 ft. to 16½ ft. in British engines. In boiler barrels up to about 12 ft. long, two plates are generally used instead of three plates as in former practice. For longer barrels three plates are usual, though two are sometimes used. Engines have recently been built for the Great Northern Railway, in which the barrel 11 ft. 5½ ins. long is made of a single plate. Such plates have
