Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF CONTROLLING IMPACT FORCE AND S~OCK INTERVAL IN DROP
HAMMERS
The invention relates to drop hammers for driving
piles or the like into the ground, comprising a core which forms
an impact surface at one end thereof, and casinys which are
mutually spaced substantially concentrically around the core,
the casing closest to the core being connected at one end there-
of with the core at the other end thereof while other casings are
interconnected alternatingly at one end and the other beginning
at the other end of said casing closest to the core.
In the ideal case a drop h~mmPr should be subs-tantially
of the same length as the pile to be driven down into the ground
by means of the drop hammer. However, this is impractical
and therefore the drop hAmmer is arranged as described above in
order to obtain a long path of propagation for the shock wave
while the drop hammer as suchhas a short length.
More particularly, the invention relates to the control
of impact force and shock interval in a drop h~mmer of the type
referred to above. It is desired to control impact force and
shock interval or the reason that for driving a pile into the
ground it may be necessary to have less force and longer shock
instead of greater force and shorter shock in order that the
pile will not wreck during driving.
An object of the invention is to make possible that
impact force and shock interval are adapt~d to the ground
conditions and the pile material in a favourable manner.
According to the present invention there is provided
a drop hammer for driving piles or the like into the ground,
the h~mm~r comprising an elongated core having at one end an
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impact surface, a plurality of casings, each casing having a
first end and a second end opposite the first end with each
first end being adjacent the impact surface of the core, the
innermost casing being connected adjacent its second end to
the end of the core opposite the impact surface, the innermost
and next adjacent casing being connected together adjacent their
first ends with the subsequent casings being connected together
alternating between the second and first ends thereof, whereby
each casing is attached to an adjacent casing, the drop hammer
including a shock wave transferring connection element between
the core, adjacent the impact surface thereof, and the adjacent
end of at least the innermost one of the casings.
The invention will be explained in more detail below
with reerence to the accompanying drawing, in which
FIGURE 1 is a longitudinal cross-sectional view of a
drop hammer of the type used in practising the method o the
invention, and
FIGURE 2 is a fragmentary longitudinal cross-sectional
view similar to that in FIGURE 1 of the lower end of the drop
hammer.
The drop hammer in FIGURE 1 comprises a cylindrical
core 10 which forms an impact surface 11 at one end thereof.
At the other end a first casing 12 is permanently connected to
the core 10 at 13, and this casing surrounds the core concentrical-
ly spaced therefrom. Outside the casing 12 a second casing 14 is
arranged concentrically with the core, and also the casings 12 and
14 are mutually spaced. The casing 14 is permanently connected
to the casing 12 at the lower end of the drop hammer at 15,
-- 2
and it is surrounded by a third casing 16 which is concentric
with the core and is spaced from the casing
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14. At 17 at the upper end of the drop hammer a
permanent connection is provided between the casings 1
and 16 while said latter casing 16 at the lower end of
the drop hammer is permanently connected at 18 to 'a
fourth casing 19 spaced from the casing 16 and arranged
concentrically with the core.
A shock wave generated in the core 10 when hitting
a pile at the impact surface 11, will propagate through
the core to the upper end thereof and:via the connection
1~ at 13 to the casing 12, then ~ownwards through said latter
casing and:v~ the.connection at-15.upwards through the
casing 14 from which the shock wave will pass to the
casing 16 via~the connection at 17 to propagate d~n. :
the casing 16 and then via the connection 18.upwards
through the casing 19. The shock wave then will be
reflected back along the path described to the impact
surface 11.
In order to shorten ~he propagation path of the
shock wave there is pro~ided by the method according to
the invention a shock'wave transferring connection,
"short circuiting",between the core and a voluntary
number of casings. Thus, a short rircuiting is shown
in FIG. 1 between the core 10 and the second casing 14
and it is provided by means of a ring 20 at the lower end
of the drop hammer such that the shock wave ~ill propagate
~rom the impact surface 11 via the ring 20 and the connec-
tion 15 dlrectly to the casin~ 14 so as to follow there-
after the same path as ~efore to the upper end of the cas-
ing 19, This shortening of the path of the shock wave
provides a greater impact force; however, the shock inter-
val will be shorter.
The ~mpact force can be furthe'r increased by short
circujting several casings as is sho~n in F~G~ 2 wherein
a ring 20' forms a shock wave transferring connection
from the core la directly to the outermost casing 19,
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which means that the shock interval will be still
shorter than in the arrangement shown in FIG. 1. By
using rings of different sizes in order to provide a
shock wave transferring connection between the core and
the casings at the ends where permanent connection is
not arranged, it is possible to adapt impact force and
shock interval to the prevailing conditions, i.e. to
the ground nature and the material of the pile to be
driven down into the ground.
The rings 20 and 20', respectively, can be attached
in different manners by ~eans of scre~ connections,
clamp connections or the like. It is important, however,
that the r;ng is securely attached while it is at the
same time possible to replace easily the ring.
E.g. the core 10 can form a shoulder facing downwards
at the lower end of the core, said shoulder surrounding
the impact surface 11 axially spaced therefrom. The ring
20 or 20' can be attached to the shoulder by means o~
screws which are passed through the ring to engage
threaded 6Ores in the shoulder. The ring can also be
attached to the casing 15 or the casing 19 as the case
may be, by simllar screw connections~
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