The supply of compressed gas in metal cylinders has now assumed the
proportions of an important industry, more especially since it was
found possible, by the Brin process, to obtain oxygen direct from the
atmosphere. The industry is not exactly a new one, for carbon dioxide
and nitrous oxide (the latter for the use of dentists) have been
supplied in a compressed state for many years. Now, with the creation
of the modern amateur photographer, who can make lantern slides, and
the more general adoption of the optical lantern for the purposes of
demonstration and amusement, there has arisen a demand for the
limelight such as was never experienced before, and as the limelight
is dependent upon the two gases, hydrogen and oxygen, for its support,
these gases are now supplied in large quantities commercially. At
first the gas cylinders were made of wrought iron; they were cumbrous
and heavy, and the pressure of the inclosed gas was so low that a
receptacle to hold only ten feet was a most unwieldy concern. But
times have changed, and a cylinder of about the same size, but half
the weight, is now made to hold four times the quantity of gas at the
enormous initial pressure of 1,800 pounds on every square inch. This
means the pressure which an ordinary locomotive boiler has to
withstand multiplied by twelve. The change is due to improved methods
of manufacture and to the employment of mild steel of special quality
in lieu of the wrought iron previously employed. The cylinders are now
made without joint or seam, and the process of manufacture is most
interesting. A short time ago we had an opportunity of watching the
various necessary operations involved in making these cylinders at the
Birmingham works of Messrs. Taunton, Delamard & Co., by whose courtesy
we were enabled to make notes of the process.
[Illustration: FIG. 1.]
[Illustration: FIG. 2.]
Beginning with the raw material, we were shown a disk of metal like
that shown in Fig. 1, and measuring thirty inches in diameter and
three-quarters of an inch in thickness. From such a "blank" a cylinder
destined to hold 100 feet of compressed gas can be constructed, and
the first operation is to heat the "blank" in a furnace, and afterward
to stamp it into the cup-like form shown in Fig. 2. To all intents and
purposes this represents the end of a finished cylinder, but it is far
too bulky to form the end of one of the size indicated; indeed, it in
reality contains enough metal to make the entire vessel. By a series
of operations it is now heated and drawn out longer and longer, while
its thickness diminishes and its diameter grows less. These operations
are carried out by means of a number of hydraulic rams, which
regularly decrease in size. Fig. 3 roughly represents one of these
rams with the plunger ready to descend and force its way into the
partially formed red hot gas cylinder, C, and further into the well,
W. The plunger may be compared to a finger and the cylinder to a
glove, while the well may represent a hole into which both are thrust
in order to reduce the thickness of the glove. With huge tongs the
cylinder, fresh from the furnace, is placed in position, but just
before the plunger presses into the red hot cup, one of the workmen
empties into the latter a little water, so as to partially cool the
bottom and prevent its being thrust out by the powerful plunger. Oil
is also used plentifully, so that as the plunger works slowly down the
red hot mass, it is surrounded by smoky flames. It presently forces
the cylinder into the well, and when the end of the stroke is reached,
a stop piece is inserted through an opening in the upper part of the
well, so as to arrest the edge of the cylinder while the reverse
action of drawing out the plunger is proceeded with. Directly the
finger is drawn out of the glove--in other words, immediately the
plunger is raised out of the cylinder--the latter drops down below
with a heavy thud, still in a red hot condition.
[Illustration: FIG 3.]
This operation of hot drawing is repeated again and again in rams of
diminishing size until the cylinder assumes the diameter and length
required. This hot drawing leaves the surface of the metal marked with
longitudinal lines, not unlike the glacier scratches on a rock, albeit
they are straighter and more regular. But the next operation not only
obliterates these markings, and gives the metal a smooth surface like
that of polished silver, but it also confers upon the material a
homogeneity which it did not before possess, and without which it
would never bear the pressure which it is destined to withstand when
finished. This operation consists in a final application of the
hydraulic ram while the metal remains perfectly cold, instead of red
hot, as in the previous cases.
As the result of these various hydraulic operations, we have a
perfectly formed cylinder closed at one end, and we now follow it into
another department of the works, when its open end is once more
brought in a furnace to a red heat. The object of this is to make the
metal soft while the shoulder and neck of the vessel are formed. To
accomplish this, the heated open end of the cylinder is laid
horizontally upon a kind of semicircular cradle, and is held there by
tongs handled by two men. Another workman places over the open end a
die of the form shown in Fig. 4, and while the cylinder is slowly
turned round in its cradle, two sledge hammers are brought down with
frequent blows upon the die, closing in the end of the cylinder, but
leaving a central hole as shown in Fig. 5. Further operations reduce
the opening still more until it is closed altogether, and a projection
is formed as shown at Fig. 6. This projection is now bored through,
and the cylinder is ready for testing.
[Illustration: FIG. 4.]
[Illustration: FIG. 5.]
[Illustration: FIG. 6.]
The cylinder is submitted to a water test, the liquid being forced in
until the gauge shows a pressure of two tons to the square inch.
Cylinders have been known to give way under this ordeal, but without
any dangerous consequences. The metal simply rips up, making a report
at the moment of fracture as loud as a gun. The wonderful strength of
the metal employed may be gauged by the circumstance that the walls of
the cylinder designed to hold 100 feet of gas are only five-sixteenths
of an inch in thickness.
During the manufacture of the cylinder, as we have already indicated,
much oil is used, and, so far as steel can be saturated with that
fluid--in the popular sense--the metal is in that state. It is
essential that this oil should be completely got rid of, and this is
carefully done before the cylinder is charged with gas. Previous to
such charging, the vessel has to be fitted with its valve. Of these
valves there are three kinds, known respectively as the Brin, the
Birmingham, and the Manchester. Each has its admirers, but we cannot
here discuss their individual merits.
The charging of the cylinder is brought about by a powerful pump
having three cylinders so arranged that the compressed contents of the
first cylinder are still further compressed in the second, and still
more highly in the third. The filling of a 100 ft. cylinder occupies
about half an hour.--_Photographic News_.
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