Modern Machine-Shop Practice Part 194

The lap of the two pieces, when scarfed in this manner, is shown in Fig.

2884.

[Ill.u.s.tration: Fig. 2884.]

To take the welding heat the fire should be cleaned out and clear c.o.ked coal, and not gaseous coal, used. The main points in a welding heat are, to heat the iron equally all through, to obtain the proper degree of heat, and to keep the scarfed surfaces as free from oxidation, and at the same time as clean, as possible.

To accomplish these ends the iron must not be heated too quickly after it is at a good red heat, and the fire must be so made that the blast cannot meet it at any point until it has pa.s.sed through the bed of the fire.

When the iron is getting near the welding heat it may be sprinkled with white sand, which will melt over it and form a flux that will prevent oxidation and cool the exterior, giving time to the interior to become equally heated. The sand should be thrown on the work while in the fire, as removing the work from the fire causes it to oxidize or scale rapidly. The work should be turned over and over in the fire, the scarf face being kept uppermost until the very last part of the heating, when the blast must be put on full, the bed of the fire kept full and clear so that there shall be sufficient bed to prevent the blast from meeting the heat until it has pa.s.sed through the glowing coals.

When the heat is taken from the fire it should meet the anvil with a blow, the scarfed face being downwards, to jar off any dirt, cinder, &c., and the scarf should be cleaned by a stroke or two of a wire brush.

But as every instant the iron is in the air it is both cooling and oxidizing, these operations must be performed as quickly as possible.

The two scarfs being laid together as shown in Fig. 2884, the first blows must be delivered lightly, so as not to cause the upper piece to move, and as quickly as possible, the force of the blows being increased regularly and gradually until the weld is sufficiently firm to hold well together, when it may be turned on edge and the edges of the scarf hammered to close and weld the seam. If this turning is done too soon, however, it may cause the two halves to separate. When the weld is firmly and completely made the enlarged diameter due to the scarfing may be forged down, working the iron as thoroughly as possible.

[Ill.u.s.tration: Fig. 2885.]

[Ill.u.s.tration: Fig. 2886.]

To form the scarf of a ring or collar, one end is bevelled, as at B in Fig. 2885 and after the piece is bent to a circle it is cut off and bevelled as at A. When a slight band is to be welded, and it is difficult to steady the ends to bring them together, a clamp may be used to hold them as in Fig. 2886.

[Ill.u.s.tration: Fig. 2887.]

Fig. 2887 represents a tongue weld, and it is obvious that to insure soundness the wedge piece should fit in the bottom of the split, which may be well closed upon it by the hammer blows.

[Ill.u.s.tration: Fig. 2888.]

Fig. 2888 represents an example of a [V]-weld applied to welding up a band that is to be square when finished, and as the lengths of the sides must be equal when finished, the side on which the weld is made should be made shorter, so that in stretching under the welding blows it will be brought to its proper length. The [V] form of weld is employed because it stretches less in welding than the lap weld. The [V]-piece to be welded in should bear at the bottom of the [V], and the weld made by fullering.

[Ill.u.s.tration: Fig. 2889.]

[Ill.u.s.tration: Fig. 2890.]

Welds of this kind are obviously most suitable for cases in which the weld is required to influence the shape of the piece as little as possible. The figures above, which are taken from _Mechanics_, ill.u.s.trate as an example the repairing of a broken strap for the beam of a river steamboat. The crack is at A, Fig. 2889, and is held together by a clamp as shown; a [V]-recess is cut out as in Fig. 2890, and this recess is fullered larger, as in Fig. 2891. A [V]-block is then welded in. The strap is then turned over a second [V]-groove, cut out and fullered out, and a second [V]-piece welded in. By thus welding one side at a time the welding is taken in detail as it were, and the blows can be less heavy than if a larger weld were made at one heat, as would be the case if but one [V] block were used. A similar form of weld may be employed to form a square corner, as is shown in Fig. 2892, which is taken from "The Blacksmith and Wheelwright." In this example the inside corner is shown to have a fillet, which greatly increases the difficulty of the job. The weld is made by first fullering the [V]-piece on the sides and on the rounded corner and then laying the piece on the anvil to forge down, the fullering leaving the finished job as in Fig. 2893.

[Ill.u.s.tration: Fig. 2891.]

[Ill.u.s.tration: Fig. 2892.]

[Ill.u.s.tration: Fig. 2893.]

[Ill.u.s.tration: Fig. 2894.]

[Ill.u.s.tration: Fig. 2895.]

When one piece has to be driven on to the other, the weld is called a pump-weld, for which the ends should be rounded as in Fig. 2894, so that they will meet at their centres, and will, when struck endways to make the weld, come to the shape shown in Fig. 2895.

[Ill.u.s.tration: Fig. 2896.]

It is obvious that in this case the interior of the iron comes together and is welded, and that dirt, &c., is effectually excluded; hence if the iron is properly heated the weld may be as sound as a lap weld, and is preferred by many as the sounder weld of the two. When a stem requires to be welded to a large flat surface, the pump weld is the only one possible, being formed as in Fig. 2896, in which the stem is supposed to be welded to a frame. The plate is cupped as shown, and the metal being driven up on the sides as much as possible, the stem overlaps well at C B, so that it may be fullered there. The stem should first meet its seat at A, so that dirt, &c., may squeeze out as the welding proceeds.

[Ill.u.s.tration: Fig. 2897.]

[Ill.u.s.tration: Fig. 2898.]

Figs. 2897 and 2898 represent an example of welding a collar on round iron. The bar is upset so as to enlarge it at A, where the collar is to be. The collar is left open at the joint, and while it is cold it is placed on the red-hot bar and swaged until the ends are closed. The welding of the whole may then be done at one heat, swaging the outside of the collar first. Unless the bar is upset there would be a crack in the neck B of the collar on both sides.

WELDING ANGLE IRON.--Let it be required to form a piece of straight angle iron to a right angle.

[Ill.u.s.tration: Fig. 2899.]

The first operation is to cut out the frog, leaving the piece as shown in Fig. 2899; the width at the mouth A of the frog being 3/4 inch to every inch of breadth measured inside the f.l.a.n.g.e as at B.

The edges of the frog are then scarfed and the piece bent to an acute angle; but in this operation it is necessary to keep the scarfs quite clean and not to bend them into position to weld until they are ready for the welding heat; otherwise scale will form where the scarfs overlap and the weld will not be sound.

The heat should be confined as closely as possible to the parts to be welded; otherwise the iron will scale and become reduced below its proper thickness.

The iron is then bent to the shape shown in Fig. 2900; and the angle to which it is bent is an important consideration. The object is to leave the overlapping scarf thicker than the rest of the metal, and then the stretching which accompanies the welding will bring the two arms or wings to a right angle.

[Ill.u.s.tration: Fig. 2900.]

It is obvious, then, that the thickness of the metal at the weld determines the angle to which the arms must be bent before welding. The thicker the iron the more acute the angle. If the angle be made too acute for the thickness of the iron at the weld there is no alternative but to swage the f.l.a.n.g.e down and thin it enough to bring the arms to a right angle. Hence it is advisable to leave the scarf too thick rather than too thin, because while it is easy to cut away the extra metal, if necessary, it is not so easy to weld a piece in to give more metal. In very thin angle irons, in which the wastage in the heating is greater in proportion to the whole body of metal, the width of the frog at A in Fig. 2901 may be less, as, say, 9/16 inch for every inch of angle-iron width measured as at B in the figure. For angles other than a right angle the process is the same, allowance being made in the scarf-joint and bend before welding for the stretching that will accompany the welding operation.

The welding blows should be light and quick, while during the scarfing the scale should be cleaned off as soon as the heat leaves the fire, so that it will not drive into the metal and prevent proper welding. The outside corner should not receive any blows at its apex; and as it will stretch on the outside and compress on the inside, the forging to bring the corner up square should be done after the welding.

[Ill.u.s.tration: Fig. 2901.]

The welding is done on the corner of an angle block, as in Fig. 2901, in which A is the angle iron and B the angle block.

[Ill.u.s.tration: Fig. 2902.]

To bend an angle iron into a circle, with the f.l.a.n.g.e at the extreme diameter, the block and pins shown in Fig. 2902 are employed. The block is provided with the numerous holes shown for the reception of the pins.

The pins marked 1 and 2 are first inserted and the iron bent by placing it between them and placed under strain in the necessary direction. Pins 3 and 4 are then added and the iron again bent, and so on; but when the holes do not fall in the right position, the length of the pin-heads vary in length to suit various curves.

To straighten the iron it is flattened on the surface A and swaged on the edge of the f.l.a.n.g.e B, the bending and straightening being performed alternately.

[Ill.u.s.tration: Fig. 2903.]

When the f.l.a.n.g.e of the angle iron is to be inside the circle, as in Fig.

2903, a special iron made thicker on the f.l.a.n.g.e A is employed. The bending is accomplished, partly by the pins as before, and partly by forging thinner, and thus stretching the f.l.a.n.g.e A while reducing it to its proper thickness.

TO FORGE A BOLT BY HAND.--The blanks for bolts must be cut off sufficiently long to admit of one end being upset to form the head, the amount of this allowance, obviously, being determined by the size of the head.

[Ill.u.s.tration: Fig. 2904.]

[Ill.u.s.tration: Fig. 2905.]

Fig. 2904 is a side view, partly in section, and Fig. 2905 a top view of an anvil block for upsetting the ends of blanks to form the heads of bolts. The stem fits into the square hole of the anvil. The tongue is pivoted as shown in the top view to two lugs provided on the block; upon the tongue rests a steel pin whose length determines the height to which the blank will project above the top of the block, and, therefore, the amount or length of blank that will be upset to form the head, this amount being three times the diameter of the bolt for _black heads_.