Modern Machine-Shop Practice Part 161

No. 6 is raw limestone (not burned).

Take of No. 1, 45 lbs., and of No. 2, 12 lbs. Pulverize finely and dissolve in as much water as will dissolve it and no more--say 14 gallons of water in a tight barrel; and let it be well dissolved before using it.

Then take three bushels of No. 3, hardwood charcoal broken small and sifted through a No. 4 sieve. Put the charcoal in a wooden or iron box of suitable size made water-tight.

Next take of No. 4, 5 lbs., and of No. 5, 5 lbs., the rosin pulverized very fine. Mix thoroughly No. 4 and No. 5 with the charcoal in your box.

Then take of the liquid made by dissolving No. 1 and No. 2 in a barrel as stated, and thoroughly wet the charcoal with the whole of said liquid, and mix well.

The charcoal compound is now ready for use.

A suitable box of wrought or cast iron (wrought iron is preferable) should next be provided, large enough for the work intended to be steelified.

Now take No. 6, raw limestone broken small (about the size of peas), and put a layer of the broken limestone, about 1-1/2 inches thick, in the bottom of the box. A plate of sheet iron, one-tenth of an inch in thickness, is perforated with 1/4-inch holes one inch apart. Let this plate drop loose on the limestone inside the box. Place a layer of the charcoal compound, two inches thick, on the top of said perforated plate. Then put a layer of the work intended to be steelified on the layer of charcoal compound, and alternate layers of iron and of the compound until the box is full, taking care to finish with a thick layer of compound on the top of the box. Care should also be taken not to let the work in the box come in contact with the sides or ends of the box.

Place a suitable cover on the box and lute it with fire-clay or yellow mud. The cover should have a quarter-inch hole in it to permit the steam to escape while heating.

The box should now be put in an open fire or furnace (furnace preferred), and subjected to a strong heat for five to ten hours, according to the size of the box, and the bulk of iron to be steelified.

Remove the pieces from the box one by one and clean with a broom, taking care not to waste the residue, after which, chill in a sufficient body of clear, cold water, and there will be a uniform coat of actual steel on the entire surface of the work to the depth of 1/16 or 1/8 of an inch, according to the time it is left in the fire. The longer it is left in the fire the deeper will be the coat of steel.

Then remove the residue that remains in the box, and cool with the liquid of No. 1 and No. 2, made for the purpose with 20 gallons of water, instead of 14 gallons, as first used with the charcoal compound.

The residue must be cooled off while it is hot, on a piece of sheet iron or an iron box made for the purpose. Turn the residue into the supply box, and it will be ready for use again. The more it is used, the better and stronger it will be for future work.

There is nothing to be renewed for each batch of work but the limestone, and that, after each job, will be good burned lime.

A process used at the Elevated R.R. shops in New York city is as follows: The materials used are: leather, 1 part; bone dust, 5 parts; salt, 1 part. Heat for 48 hours to a red heat in a box sealed with fire clay, and quench in a solution of 3 pounds of potash to 30 gallons of water.

The wrought iron thus treated is impervious to a new smooth file at a depth of 1/16 of an inch.

The potash water is said to prevent both warping and the formation of blister marks on the work.

The durability of work case-hardened is greatly enhanced, but it is an expensive process; not so much by reason of the cost of it, but because it involves resetting and a refitting of the parts. The resetting is necessary because the work warps under or during the process. This warping can be prevented to some extent by placing the heaviest pieces in the bottom of the box, and so packing the same that the weight of the top pieces shall not tend to bend those beneath them when the hardening material has burned away, and so placing the upper pieces that they shall not be bent by their own weight. Thus both in packing and locating the work in the box the utmost care is necessary.

SETTING WORK AFTER HARDENING IT.--Work that has been hardened or case-hardened usually swells during the hardening process, and therefore requires refitting afterwards. This swelling usually occurs in all directions, thus holes and bores become of smaller dimensions, while the outside dimensions also increase, bolts become of larger diameter and sometimes increase in length.

In very exceptional cases, however, the dimensions of a piece of work will not alter.

This renders it usually necessary to refit the work after it has been hardened, thus holes which are ground out by laps or bolts may be ground to diameter in a grinding lathe.

In some practice, however, the work to be hardened is made a somewhat too easy fit, the holes tapped out and the bolts ground in by direct application of the bolts to their holes in connection with flour emery and oil. This latter plan is also adopted for forms not easily ground out in a machine, as, for example, a die in a link of a link motion.

[Ill.u.s.tration: Fig. 2413.]

[Ill.u.s.tration: Fig. 2414.]

To prevent surfaces or forms of this cla.s.s from altering their shape or dimensions during the hardening process, slips of iron are sometimes fitted to them before they are placed in the hardening box. Thus Fig.

2414 represents a double eye, and Fig. 2413 a link having thin pieces fitted in as shown at A in both figures.

The heating for the hardening process is also apt to impair the alignment of the work, causing it to require resetting by the aid of parallel strips and straight-edges.

[Ill.u.s.tration: Fig. 2415.]

The faces of the link having been set, the width of the link slot must be set, for it may open or close in places. If it opens it may be closed by the jaws of a powerful vice, while if it closes it may be opened by a pair of inverted keys, inserted as shown in Fig. 2415, and driven in by the hammer. At each trial, however, a mark should be made on the driven key, so that it may be known how far to drive it at the next trial.

[Ill.u.s.tration: Fig. 2416.]

[Ill.u.s.tration: Fig. 2417.]

Fig. 2416 represents a link that is supposed to have been case-hardened, and to therefore require resetting. The stem from A to B should first be straightened to a straight-edge on both its side and edge faces. It should then be tested for winding with the winding strips, C, D, placed as in Fig. 2416, and then as in Fig. 2417.

[Ill.u.s.tration: Fig. 2418.]

[Ill.u.s.tration: Fig. 2419.]

To test the alignment of end E, press a straight-edge S fair against its side face, as in Fig. 2418, and measure the distance H. Then place the straight-edge on the other side face of E and measure the distance I, Fig. 2419, and these distances both measuring alike, E will be true providing that the jaws at end F have not altered from their proper width apart.

To test the alignment of the jaws at end F, press a straightedge against the outside face of the hub and measure the distance J, Fig. 2420, then apply it on the other side and measure distance K, Fig. 2421, and when distances J and K are equal and the width L between the jaws is correct, end F is in line in one direction. To test it in the other direction, apply a pair of parallel strips, placing one on end E as in Fig. 2417, and the other across the face of the hub of end F to see if there is any twist.

[Ill.u.s.tration: Fig. 2420.]

[Ill.u.s.tration: Fig. 2421.]

Suppose, however, that distances J K are unequal, then if distance L is too narrow (when tested by the piece that fits between the jaws) then the jaw at F that gives the widest distance at E is the one that requires correction, or if distance L is too wide, the jaw that shows the least distance at end E is the one requiring correction.

The link should be warmed to about 300, or nearly _black_ hot, and pieces of sheet copper placed between the work and the anvil, and between the blacksmith's tools and the work, so that the latter may not be bruised by the blows delivered to effect the straightening.

After the process has been performed at each end individually the testing should be repeated, because setting the end F may have impaired the setting of end E, in the alignment to F.

It is obvious that the same setting or aligning process would be required in the case of a large link, where the ends were forged separately and welded to the body after the machine work and fitting had been done to them.

[Ill.u.s.tration: Fig. 2422.]

[Ill.u.s.tration: Fig. 2423.]

[Ill.u.s.tration: Fig. 2424.]

[Ill.u.s.tration: Fig. 2425.]

[Ill.u.s.tration: Fig. 2426.]

FITTING BRa.s.sES TO BOXES OR TO PILLAR BLOCKS.--In the operation of fitting bra.s.ses to their boxes or to pillar blocks there are two things to be especially guarded against: First, having the bra.s.s let down one-sided, as shown in Fig. 2422; and next, aslant, as shown in Fig.

2423. The first depends on taking the proper amount off the two side faces, and the second in cutting the inside of the f.l.a.n.g.es fair. To cut the side faces fair, grip the bra.s.s in the vice, as shown in Fig. 2424 (the bra.s.s being shown in section), in which a is A block of wood. Take the measure of the box, down where the bra.s.s will come when home, and, if there be any taper to the box, set the inside calipers to the top of the location for the bra.s.s, and after the bra.s.s is in the vice place a square under one side-face, as at B in Fig. 2426, and see how much there is to come off. This saves the use of outside calipers, and is better because, not only is the trouble of setting the latter avoided, but the inside calipers can be tried to the box and the work in an instant, and a correction can at once be made if the calipers have got shifted. The cape chisel, or cross-cut, as it is sometimes termed, should first be used, taking a cut close to the f.l.a.n.g.e, and making it half as deep as the calipers (applied as shown in Fig. 2426) show there is metal to come off. Then a similar cut should be taken close to the other f.l.a.n.g.e, especial care being taken to take both cuts equally deep, and leaving as much to come off the other side face of the bra.s.s; otherwise, the bra.s.s will come atwist. Then take a straight-edge, and, placing its edge fair with the two chisel-grooves, while holding it firmly against the joint face of the bra.s.s, mark a line running from one chisel groove to the other; this line serving as a guide for the depth of all the other cape-chisel grooves. Now cut off the intermediate s.p.a.ces with the flat chisel, using a straight-edge as a guide. If the box is taper, chip the side face to a corresponding taper, using a bevel-square, or estimating the amount by the eye if it is not too much. Now file the chipped surface flat and true, and then turn the bra.s.s upside down, gripping it with the wood as before, and dress the other side face (applying the inside calipers as in Fig. 2426), and bring that face down to within about 1/64 inch of the size to which the calipers are set. If the block of wood is made a little shorter than the length of the bra.s.s, the calipers can be applied without moving the bra.s.s from or in the vice.

The method of applying the square to these side faces is shown in Fig.

2425, in which A is the bra.s.s in section, B a straight-edge, and C a square.

[Ill.u.s.tration: Fig. 2427.]

[Ill.u.s.tration: Fig. 2428.]