Scientific American Supplement, No. 717, September 28, 1889 | Page 4

is now fast disappearing. In large engines
the only metals used are cast iron and white brass, an advantage also in
reducing the amount of wear on the recess by corrosion and grinding
where sea water was used often to a considerable extent.
[Illustration: Fig. 1 Fig. 2]
Figs. No. 1 and No. 2 show the design of the old and new main
bearings, and, I think, require but little explanation. Most of you
present will remember your feelings when, after a hot bearing, the
brasses were found to be cracked at top and bottom, and the trouble you
had afterward to keep these brasses in position. When a smoking hot
bearing occurred, say in the heating of a crank pin, it had the effect of
damaging the material of the shaft more or less, according to its
original soundness, generally at the fillets in the angles of the cranks.
For when the outer surface of the iron got hot, cold water, often of a
low temperature, was suddenly poured on, and the hot iron, previously
expanded, was suddenly contracted, setting up strains which in my
opinion made a small tear transversely where the metal was solid; and
where what is termed lamination flaws, due to construction, existed,
these were extended in their natural direction, and by a repetition of this
treatment these flaws became of such a serious character that the shafts
had to be condemned, or actually gave way at sea. The introduction of

the triple expansion engine, with the three cranks, gave better balance
to the shaft, and the forces acting in the path of the crank pin, being
better divided, caused more regular motion on the shaft, and so to the
propeller. This is specially noticeable in screw steamers, and is taken
advantage of by placing the cabins further aft, nearer the propeller, the
stern having but little vibration; the dull and heavy surging sound, due
to unequal motions of the shaft in the two-crank engines, is exchanged
for a more regular sound of less extent, and the power formerly wasted
in vibrating the stern is utilized in propelling the vessel. In spite of all
these improvements I have mentioned, there remains the serious
question of defects in the material, due to variety of quality and the
extreme care that has to be exercised in all the stages during
construction of crank or other shafts built of iron. Many shafts have
given out at sea and been condemned, through no other cause than
original defects in their construction and material.
The process of welding and forging a crank shaft of large diameter now
is to make it up of so many small pieces, the best shafts being made of
what is termed scrap, representing thousands of small pieces of selected
iron, such as cuttings of old iron boiler plates, cuttings off forgings, old
bolts, horseshoes, angle iron, etc., all welded together, forged into
billets, reheated, and rolled into bars. It is then cut into lengths, piled,
and formed into slabs of suitable size for welding up into the shafts. No
doubt this method is preferable to the old method of "fagoting," so
called, as the iron bars were placed side by side, resembling a bundle of
fagots of about 18 or 20 inches square.
The result was that while the outside bars would be welded, the inside
would be improperly welded, or, the hammer being weak, the blow
would be insufficient to secure the proper weld, and it was no
uncommon thing for a shaft to break and expose the internal bars,
showing them to be quite separate, or only partially united. This danger
has been much lessened in late years by careful selection of the
materials, improved methods of cleaning the scrap, better furnaces, the
use of the most suitable fuels, and more powerful steam hammers. Still,
with all this care, I think I may say there is not a shaft without flaws or
defects, more or less, and when these flaws are situated in line of the

greatest strains, and though you may not have a hot bearing, they often
extend until the shaft becomes unseaworthy.
[Diagrams shown illustrated the various forms of flaws.] These flaws
were not observable when the shafts were new, although carefully
inspected. They gradually increased under strain, came to the outside,
and were detected. Considerable loss fell upon the owners of these
vessels, who were in no way to blame; nor could they recover any
money from the makers of the shafts, who were alone to blame. I am
pleased to state, and some of the members here present know, that
considerable improvement has been effected in the use of better
material than iron for crank shafts, by the introduction of a special mild
steel, by Messrs. Vickers, Sons & Co.,