To remove nuts or bolts that have become corroded in their places, we may adopt the following methods:—
Fig. 442.
If the nuts are so corroded that they will not unscrew with an ordinary wrench, we may, if the standing bolts and the wrench are strong enough to stand it, place a piece of gas or other pipe on the end of the wrench, so as to get a longer leverage; and, while applying the power to the wrench, we may strike the end face of the nut a few sharp blows with the hammer, interposing a set chisel, if the nut is a small one, so as to be sure to strike the nut in the proper place, and not rivet the screw end. If the joint is made with tap bolts we may strike the bolt heads with the hammer direct, using as before a light hammer and sharp blows, which will, in a majority of cases, start the thread, after which the wrench alone will usually suffice to unscrew it. If, however, this is not effective, we should take a thick washer, large enough in its bore to pass over the nut, and heat it to a yellow heat and place it over the nut, and the nut heating more rapidly than the stud or standing bolt, will be proportionately expanded and loosened; and, furthermore, the iron becomes stronger by being heated, providing the temperature does not exceed about 400°. If standing bolts or studs are employed on the joint, the heating is still advantageous, for the increase of strength more than compensates for the expansion. In this case the heating, however, may be performed more slowly, so that the hole may also become heated, and the bolt, therefore, not made a tighter fit by its excessive expansion. So also, in taking out the standing bolts or studs, heating them will often enable one to extract them without breaking them off in the hole, which would necessitate drilling out the broken piece or part. If, however, this should become necessary, we may drill a hole a little smaller than the diameter of the bottom of the bolt thread, and then drive into the hole a taper square reamer, as shown in [Fig. 442], in which w represents the work, r the square reamer, and s the drilled screw end, and then, with a wrench applied to the reamer, unscrew the bolt thread. If this plan fails there is no alternative, after drilling the hole, but to take a round-nosed cape or cross-cut chisel and cut out the screw as nearly as possible, then pick out the thread at the entrance of the hole, and insert a plug tap to cut out the remaining bolt thread.
To take out a standing bolt, take two nuts and screw them on the bolt end; then hold the outer one still with a wrench and unscrew the inner one tightly against it. We may then remove the wrench from the outer or top nut, and unscrew the bolt by a wrench applied to the bottom or inner one. If the thread of a standing bolt has become damaged or burred, we can easily correct the evil by screwing a solid die or die nut down it, applying a little oil to preserve the cutting edge of the nut. If it is found impossible to take off a corroded nut without twisting off the standing bolt, it is the better plan to sacrifice the nut in order to save the bolt; and we may first hold a hammer beneath the nut, and take a cold chisel, and holding it so that the cutting edge stands parallel with the chamfered edge of the nut, and slanting it at an angle obtuse to the direction in which the nut in unscrewing would travel, strike it a few sharp blows, using a light hand-hammer; and this will often start it, especially if the nut is heated as before directed. The hammer held beneath the nut should be a heavy one, and should be pressed firmly against the square or hexagon side of the nut, the object being to support it, and thus prevent the standing bolt from bending or breaking, as it would otherwise be very apt to do. If this plan succeeds, the nut may, for rough work, be used over again, the burr raised by the chisel head being hammered down to close it as much as possible before filing it off. By holding the chisel precisely as directed, the seating of the nut acts to support it, and thus aids the heavy hammer in its duty. If this procedure fails we may cut the nut off, and thus preserve the bolt.
To do this, we must use a cross-cut or cape chisel, and cut a groove from the end face to the seating of the nut—a narrow groove will do, and two may be cut if necessary; light cuts should be taken, and the chisel should be ground at a keen angle, so that it will keep to its cut when held at an angle, as nearly parallel to the centre line of the length of the bolt as possible, in which case the force of the blows delivered upon the chisel head will be in a direction not so liable to bend the bolt. The groove or grooves should be cut down nearly to the tops of the bolt threads, and then a wrench will unscrew the nut or else cause it to open if one, and break in halves, if two grooves were cut.
After the nuts are all taken off, we may take a hammer and two or three wedges, or chisels (according to the size of the joint), and drive them an equal distance into the joint, striking one chisel first, and the diametrically opposite one next, and going over all the wedges to keep an equal strain upon each. If the joint resists this method, we may take a hammer and strike blows between the standing bolts on the outside face, interposing a block of hard wood to prevent damage to the face, and holding the wood so that the hammer strikes it endwise of the grain; and this will, in most cases, loosen the material of which the joint is made, and break the joint. If, however, the joint, after repeated trials, still resists, we may employ the hammer without the interposition of the wood, using a copper or lead hammer, if one is at hand, so as not to cause damage to the face of the work. To facilitate the entrance of the wedges, grooves should be cut in the joint of one face, their widths being about an inch, and their depth 1⁄16 inch.
Washers.—Washers are placed upon bolts for the following purposes. First, to provide a smooth seating for the nut in the case of rough castings. Second, to prevent the nut corners from marking and marring the surface of finished work. Thirdly, to give a neat finish, and in some cases to increase the bearing area of the nut and provide an elastic cushion to prevent the nut from loosening. Washers are usually of wrought iron, except in the case of brass nuts, when the washers also are of brass. The standard sizes adopted by the manufacturers in the United States for wrought iron washers is given in the following table:—