For a quarter of a century maritime nations have been continuously engaged
in improving the mechanical appliances of their large ports. The use of
tracks to bring goods to be placed on vessels as near as possible to the
shipping point, the substitution of oblique moles for perpendicular ones
in large docks, the creation of a hydraulic method of loading and
unloading through movable cranes (which will perhaps in a near future cede
to an electrical one), constitute the means most used for expediting
transshipments and reducing the expense of them to a minimum. But, at the
same time that the facilities for all kinds for handling packages have
been increased, it has also become necessary to greatly increase the power
of the machines applied to them. The construction of large packets now
requires the putting in place of boilers of great weight, and the adoption
of the huge pieces that compose the artillery of ironclads necessitates
the use of force that has been unknown up to recent times.
[Illustration: FIG. 1.--DIAGRAM OF SHEARS.]
[Illustration: FIG. 2.--ONE HUNDRED AND TWENTY TON SHEARS OF THE PORT OF
MARSEILLES.]
At present, then, we could no longer be content with manual power, acting
upon windlasses or capstans, for lifting and shifting. It has become
necessary to apply steam or hydraulic motors to these operations. Of
these, the latter are the most used, on account of their easy operation
and their submitting to the greatest stresses with a very satisfactory
proportionality of the expenditure of motive power. One of the most
remarkable of such apparatus is the one that the Compagnie de Fives-Lille
has recently set up on one of the moles of the national dock at
Marseilles, for the service of the chamber of commerce, and this merits a
description so much the more in that it is an important improvement upon
the analogous apparatus now in use in other ports.
According to the conditions of the programme, powers of 25, 75, and 120
tons had to be obtained at will, with a proportional output of water, and
the load had to be lifted 22 ft. above the quay and carried horizontally
from 28 ft. beyond the edge to 16 ft. in the rear, so that the load might
be taken from a ship and deposited upon a wagon, and _vice versa_. The
shears, then, had to be capable of performing two operations, viz., of
lifting the load and of carrying it horizontally. To facilitate the
description, we shall first make known the arrangements that assure the
second operation.
The apparatus is of the type known as oscillating tripod. The tripod
consists of two lateral iron plate uprights, A A (Fig. 1), resting upon
the wharf wall, and of a beam, B, jointed to them above and connected
below with the head of the piston of a hydraulic press. This latter rests
upon an iron plate frame, solidly bolted to masonry. The piston pulls the
beam, B, toward it when it descends, and carries along in the same motion
the shears, A, as well as the load suspended from their point of junction,
and the load is thus carried to a distance of 16 ft. from the edge of the
wharf in order to be placed upon a wagon. Conversely, if the piston rises,
it pushes before it the entire framework, as well as the lifting
apparatus, the hook of which travels 28 ft. beyond the edge of the wharf.
The lifting apparatus consists likewise of a hydraulic press suspended
from the summit of the tripod; but, in order to prevent the joints of the
cylinder from working under the action of the load, which would tend to
open them and cause leakages, it is not suspended from the very axis of
the junction of the shears. The cylinder rests directly upon a huge
stirrup 45 ft. in length, the arms alone of which are affixed to the axis,
through a Cardan joint. Under such circumstances, the stress of the load
carried by the piston rod is exerted solely upon the branches of the
stirrup, and the sides of the cylinder work only under the pressure of the
motive water. The latter is introduced at the base of the press, through a
valve that a special workman, standing upon a platform supported by the
stirrup, maneuvers at will.
It will be seen that the general principle applied for utilizing the
motive power is that of direct action. It has already been employed in a
few analogous apparatus constructed by Sir William Armstrong, especially
those of the arsenal of Spezia and of the Elswick cannon foundry, but
solely for the lifting press. This is the first time that use has been
made of it to effect the oscillating motion corresponding to the
horizontal shifting of the load. This was formerly done through the
intermedium of a mechanism that, aside from its complication and higher
cost, presented the inconvenience of absorbing a large quantity of force
in friction; besides, the direct action permits of performing the
maneuvers much more quickly by the use of the water in reserve contained
in the accumulators.
Another important improvement, likewise due to the Compagnie Fives-Lille,
consists in the addition of safety clicks, which engage with racks
parallel with the piston rod of each of the presses and movable with it.
The clicks, on the contrary, are jointed to axes fixed on the bottom of
the cylinders. This arrangement presents the following advantages: If a
leakage occurs in the joints or feed pipe of the hoisting press, the
descent of the load can be stopped instantaneously, thus preventing the
grave damage that would be done to ships and even to the shears themselves
by the descent of a 120 ton load, however slow it might be. As regards the
oscillating press, this arrangement permits of fixing the base of the
connecting beam at any point whatever of its travel, when it is desired to
dismount the piston. Further, it permits of maintaining the shears in an
invariable position in case of sudden damages to the piping.
[Illustration: FIG. 3.--AUTOMATIC MULTIPLIER.]
In order to produce the three powers of 25, 75, and 120 tons required by
the programme, and at the same time expend in each case a corresponding
quantity of water under pressure, it is of course necessary to cause the
pressure of the motive water to vary in the same proportion as the stress
to be extended. This result is reached by calculating the diameter of the
two cylinders in such a way as to obtain the mean power of 75 tons, in
making the water of the general conduit act directly under the normal
pressure of 50 atmospheres. For the powers of 25 and 120 tons, use is made
of an automatic multiplier, that consists of two cylinders arranged end to
end, in which move pistons, A and B (Fig. 3), of different diameters. When
it is a question of lifting 120 tons, the water at 50 atmospheres actuates
the piston, A, and the other forces into the lifting cylinder motive water
under a much greater pressure. If the load to be lifted is but 25 tons,
the water at 50 atmospheres actuates the piston, B, and A forces the water
into the same cylinder at a much lower pressure. The same operations are
effected in the other cylinder when the extreme loads of 25 and 120 tons
are moved.
The shears are likewise provided with a hydraulic cylinder, E (Fig. 1),
placed on the back of the beam, B, and serving, through a cable, to bring
the piston of the large cylinder to the end of its upward stroke, and for
certain accessory work.
Finally, the apparatus as a whole is completed by an accumulator
containing in reserve a large part of the water necessary for each
operation.
The apparatus is capable of lifting a maximum load of 120 tons from 22
feet beneath the wharf to 22 feet above, and of moving it from 28 feet
beyond the edge to 16 feet back of it, say a total of 44 feet. The
cylinders of the lifting and oscillating presses are 1-3/4 feet in diameter
and 4 inches in thickness. The stroke of the second is 22-1/2 feet. The
length of the uprights is 110-1/2 feet and that of the connecting beam is 109
feet. The apparatus has been tested under satisfactory conditions with a
load of 140 tons.--_La Nature._