Fig. 2456.
The fit of the flange to the boiler, however, should vary according to the kind of bolt used to hold the fitting to the boiler. If stud bolts are used they are supposed to screw into the boiler steam-tight, hence the flange may be fitted so that it has the closest contact with an annular ring extending from the outside of the bolt holes to the central hole of the flange, as shown in [Fig. 2456], in which the area within the dotted circle c encloses the area to be most closely bedded. This is a highly important consideration in flange joints of every description, for, if a joint is made there, that is all that is necessary, and the fit outside of the bolt holes—that is to say from the bolt holes to the perimeter of the flange—has nothing to do with making the joint, unless the studs or bolts leak, and in that case the leak will find egress beneath the nut, unless grummets are used. A grummet is a washer made of twisted hemp, cotton, or other material, and coated with red-lead putty, and is placed beneath the heads of bolts, or under washers placed beneath nuts to stop leaks. It is not necessary to ease the flange from the bolt holes outward much, but to merely make the flange, or fitting, bed clearly and distinctly the most around the main hole, and outwards to the inside of the bolt holes; for, if there was given too much clearance, the flange would bend from the pressure of the nuts, and would in consequence spring if made of brass, or perhaps break if made of cast iron.
To make the joint, gauze wire, pasteboard, or asbestos board may be used, or if the joint is to have ample time to set, a red-lead joint without the gauze may be used; but in this case it is an advantage to cut up into pieces about 3⁄8 inch long, and thoroughly shred some hemp, and well mix it in the lead, well beating the same with a hammer.
To preserve red-lead putty from becoming hard and dry, as it will do if exposed to the air, it should be kept covered with water.
In some cases joints of flanges to boilers are made by riveting the flanges to the boiler and caulking or closing the edge of the flanges to the boiler shell; but this possesses the disadvantage that the rivets must be cut off to remove the fitting from the boiler when necessary, and access to the interior of the boiler is necessary in order to attach the fitting again by rivets.
Fig. 2457.
[Fig. 2457] (which is taken from The American Machinist), represents a joint for boiler fittings, designed to facilitate the breaking and re-making of the joint. c represents, say, a boiler plate, b a piece having a ball joint seat in c ground steam tight, and a a flange, say, for a feed pipe; the studs d thread permanently into c, and the joint is bolted up by the stud nuts e. It is obvious that the ball joint between b and c permits the flange a to set at an angle if necessary.
Rust Joints.—These are joints made by means of filling the space between the flanges, or annular spaces, as the case may be, with cast-iron turnings, and compacting them with a caulking tool. Any interstices through which steam or water, &c., might leak become filled by the subsequent rusting of the iron cuttings, the rust occupying considerably more space than the iron from which it was formed.