Scientific American Supplement, No. 717, September 28, 1889 | Page 5

of Sheffield, and that instead of
having to record the old familiar defects found in iron shafts, I can
safely say no flaws have been observed, when new or during eight
years running, and there are now twenty-two shafts of this mild steel in
the company's service.
I may here state that steel was used for crank shafts in this service in
1863, as then manufactured in Prussia by Messrs. Krupp, and generally
known as Krupp's steel, the tensile strength of which was about 40 tons
per square inch, and though free from flaws, it was unable to stand the
fatigue, and broke, giving little warning. It was of too brittle a nature,
more resembling chisel steel. It was broken again under a falling
weight of 10 cwt. with a 10 ft. drop = 12½ tons.
The mild steel now used was first tried in 1880. It possessed tensile
strength of 24 to 25 tons per square inch. It was then considered
advisable not to exceed this, and err rather on the safe side. This shaft
has been in use eight years, and no sign of any flaw has been observed.
Since then the tensile strength of mild steel has gradually been
increased by Messrs. Vickers, the steel still retaining the elasticity and
toughness to endure fatigue. This has only been arrived at by
improvements in the manufacture and more powerful and better
adapted hammers to forge it down from the large ingots to the size
required. The amount of work they are now able to subject the steel to
renders it more fit to sustain the fatigue such as that to be endured by a

crank shaft. These ingots of steel can be cast up to 100 tons weight, and
require powerful machines to deal with them. For shafts say of 20
inches diameter, the diameter of the ingot would be about 52 inches.
This allows sufficient work to be put on the couplings, as well as the
shaft. To make solid crank shafts of this material, say of 19 inches
diameter, the ingot would weigh 42 tons, the forging, when completed,
17 tons, and the finished shaft 11¾ tons; so that you see there is 25 tons
wasted before any machining is done, and 5¼ tons between the forging
and finished shaft. This makes it very expensive for solid shafts of
large size, and it is found better to make what is termed a built shaft;
the cranks are a little heavier, and engine framings necessarily a little
wider, a matter comparatively of little moment. I give you a rough
drawing of the hydraulic hammer, or strictly speaking a press, used by
Messrs. Vickers in forging down the ingots in shafts, guns, or other
large work. This hammer can give a squeeze of 3,000 tons. The steel
seems to yield under it like tough putty, and, unlike the steam hammer,
there is no jarring on the material, and it is manipulated with the same
ease as a small hammer by hydraulics.
The tensile strength of steel used for shafts having increased from 24 to
30 tons, and in some cases 31 tons, considering that this was 2 tons
above that specified, and that we were approaching what may be
termed hard steel, I proposed to the makers to test this material beyond
the usual tests, viz., tensile, extension, and cold bending test. The latter,
I considered, was much too easy for this fine material, as a piece of fair
iron will bend cold to a radius of 1½ times its diameter or thickness,
without fracture; and I proposed a test more resembling the fatigue that
a crank shaft has sometimes to stand, and more worthy of this material;
and in the event of its standing this successfully, I would pass the
material of 30 or 31 tons tensile strength. Specimens of steel used in the
shafts were cut off different parts--crank pins and main bearings--(the
shafts being built shafts) and roughly planed to 1½ inches square, and
about 12 inches long. They were laid on the block as shown, and a cast
iron block, fitted with a hammer head ½ ton weight, let suddenly fall 12
inches, the block striking the bar with a blow of about 4 tons. The steel
bar was then turned upside down, and the blow repeated, reversing the
piece every time until fracture was observed, and the bar ultimately

broken. The results were that this steel stood 58 blows before showing
signs of fracture, and was only broken after 77 blows. It is noticeable
how many blows it stood after fracture. A bar of good wrought iron,
undressed, of same dimensions, was tried, and broke the first blow. A
bar cut from a piece of iron to form a large chain, afterward forged
down and