Note: Descriptions are shown in the official language in which they were submitted.
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SPECIFICATION
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This invention relates to the art of driver tool
or power hammers useful for driving posts, drills, chisels
and the like of the type having a rapidly oscillating hammer
driven by pneumatic, hyaraulic, electric or gasoline motors
to deliver high velocity blows to an anvil. Specifically,
the invention deals with incr~asing the efficiency of such
driver tools and power hammers by creating and building up
vibrations from the hammer blows on the anvil in a
compression spring which stoxes energy from attempted recoil
of the anvil continually thrusting it against the workpiece
or breaker tool and releasing the energy in the direction of
the hammer blow to add to the driving force of the blow.
Conventional power hammer rock drills, demolition
tools and breaker tools operate with a rebound or pogo stick
action allowing the rock drill, chisel or the like member
driven by the tool to leave the work being acted on to pro-
duce a chopping or chipping action which was considered
desirable. These power hammer tools transmitted their
rebound or pogo stick action to the operator requiring
considerable physical effort to hold the tool in position.
This effort and vibration of the tool quickly fatigued the
operator. In the Ferwerda U. S. Patent No. 3,244,241,
issued April 5, 1966, a light recoil spring was provided on
a power hammer to cushion the recoil of the anvil after the
blow was delivered, but in common with the conventional
power hammer tools, the chisel for the breaking tool was
caused to leave the work for creating a chipping stroke and,
in so operating, the undesired recoil or pogo stick action
has to develop.
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According to this invention, the efficiency of
power hammer tools is greatly increased by thrusting the
anvil or anvil mounted drill or chisel of a power hammer
tool constantly against the workpiece, by creating and
building up vibrations from the hammer blows in a coil spring
which absorbs and stores the rebound action of the anvil
after the hammer has delivered its blow, and by delivering
the stored energy in the spring and the built-up vibrations
to add to the power impact force on the workpiece. The
spring is compressed, by the weight of the tool and by
downcrowding loads placed on the tool from the operator or
from a boom on which the tool may be mounted, sufficiently
to thrust the anvil or anvil mounted chisel or the like
; constantly against the workpiece but insufficient to inter-
fere with the free stroke of the hammer so that it may
continue to deliver effective blows to the anvil. The
vibrations delivered to the anvil cause it to "dance" on the
workpiece without losing its thrust load on the workpiece.
Then when the hammer blow is delivered, the anvil advances
and the spring lengthens to keep the anvil against the
: workpiece with any rebound force being fed back to the
spring to add to the downcrowding force.
The spring has a stiffness and travel length
selected to be compatible with the particular power hammer
tool to support the downcrowding load and absorb the rebound
or pogo stick action normally encountered in the operation
of such hammer tools while developing vibrations adding to
the driving force imparted to the anvil by the hammer. The
selected compression spring picks up and enhances vibrations
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from the hammer blow on the an~il and feeds these back
through the anvil dividing the hammer blows into increments
or pulses and adding energy in the driving direction to the
workpiece. A housing which slips over the anvil surrounds
the spring which thrusts the housing against the bottom edge
of the ha~mer tool body. The spring is compressed between
the anvil and the bottom of the tool body and one or more
vibrations absorbing slip washers are interposed between
the housing and the tool body to further absorb vibrations
back into the tool body and to accommodate rotation of the
anvil relati~e to the tool body.
This invention thus provides a power tool of the
type having a piston driven to reciprocate at high speeds,
an anvil suspended from the tool impacted by the piston to
deliver driving forces to a workpiece, and adapted to move
axially between the anvil and workpiece. A spaced coil
spring is mounted on the tool receiving vibrations from the
anvil and is compressed against the anvil without collapsing
the coils into contact with each other when the tool is
downcrowded against the workpiece to deliver driving forces.
: The spring stores downcrowding and rebounding forces from
the tool and builds up vibration from the piston blows on
the anvil to deliver the stored forces and vibrations
through the anvil to the workpiece while the anvil dances
on the workpiece and a vibration separation film is formed
between the anvil and workpiece. The dancing action
delivers energy to the workpiece in impulses on each
piston blow.
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The invention also provides an attachment fox a
power hammer having a stem projecting into the open bottom
of a power hammer body to be impacted by the piston in the
body. The stem is engageable with a retaining device to
suspend it from the body and has an anvil head. An open
coil spring surrounds the stem and thrusts at opposite ends
against the body and the anvil. Means are provided to
suspend a tool from the anvil while permitting the tool to
shift axially. The spring is effective to vibrate the anvil
head and to cause it to dance on the tool or workpiece for
breaking up the impact blows into high frequency impulses.
The invention also provides a method of increasing
the driving force of power hammers by incorporating a
compression spring between the tool body of the hammer and
the anvil of the hammer which is selected for stiffness and
length to prevent collapse under the downcrowding load
applied to the hammer and will elongate from its down-
crowded loaded position to maintain the anvil against a
workpiece. The spring will shorten from its elongated length
to absorb rebound of the anvil while continuing to hold it
into thrusting engagement against the workpiece. The spring
also builds up vibrations from the piston blows on the anvil
to cause it to dance on the workpiece.
ON THE DRAWINGS:
FIG. 1 is a side perspective view of a power
hammer according to this invention.
FIG. 2 is a fragmentary enlarged longitudinal
cross-sectional view of the power hammer of FIG. 1 taken
generally along the line II-II of FIG. 1 and with the
components in a relaxed extended position.
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FIG. 3 is a transverse sectional view taken along
the line III-III of FIG. 2.
FIG. 4 is a transverse sectional view taken along
the line IV-IV of FIG. 2.
FIG. 5 is a view similar to FIG. 2 but showing the
downcrowded positions of the components at the top of the
stroke of the hammer.
FIG. 6 is a view similar to FIG. 5 but showing the
positions of the components at the bottom of the stroke of
the hammer.
FIG. 7 is a view similar to FIG. 6 but showing the
' positions of the components immediately after impact by the
hammer to illustrate the build-up of the vibrations in the
~, spring.
FIG. 8 is a view similar to FIG. 7 but showing the
recovered position of the components after impact, with the
tool body at a lower level resulting from the penetration of
', the chisel to the level of FIGS. 6 and 7.
FIG. 9 is a fragmentary longitudinal section of
the lower end of the power hammer with the anvil receiving
a post being driven into the ground.
: FIG. lO is a view similar to FIG. 9, but showing
an adapter in the anvil to accommodate a small diameter rod '
being driven in the ground.
FIG. ll is a view similar to FIG. lO showing the
lower end of the tool according to this invention adapted
for driving nails.
FIG. 12 is an illustrative graph showing how
; tools of the prior art are limited to delivery of impact
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blows below the fatigue strength of the workpiece without
damaging the workpiece.
FIG. 13 is an illstrative graph showing how the
tools of this invention can deliver impact blows exceeding
the fatigue strength of the workpiece without damaging the
; workpiece and how these blows are pulsed or incremented to
increase the driving energy.
FIG. 14 is an illustrative graph comparing the
power output of a conventional 60-pound power hammer and the
same power hammer equipped with this invention.
In FIG. 1, the reference numeral 10 designates
; generally a power hammer having an upstanding cylindrical
body 11, a transverse top handle 12 to be grasped by an
operator, an actuating lever 13 on the handle 12 for admit-
ting power operating fluid from a supply hose 14 to drive a
hammer which is slidably mounted in the body 11. The body
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11 has a bottom end face 15. A latch 16 is pivotally
mounted on the side of the body adjacent the bottom end
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face 15.
A shock-absorbing washer 17, preferably formed of
a slippery plastics material such as a nylon bearing
material, is mounted under the bottom end 15 of the body 11,
-~ and a cylindrical housing 18 abuts against this washer 17.
An anvil head 19 projects from the open bottom end of the
cylindrical housing 18 and mounts a chisel tool 20 having
an elongated stem 20a and a chisel head 20b to be driven
into rock, concrete, or 'he like material M acted on by the
power hammer 10. The hammer is downcrowded through the
chisel 20 against the material M by loads L applied to the
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handle 12 fro~ the operator or from a power operated
downcrowding boom ~ secured to the body 11 of the tool by a
clamp C.
As shown in FIG. 2, the body 11 has a bore 21
slidably mounting a piston 22 which is rapidly reciprocated
in a conventional manner from a ~ower source such as
compressed air, hydraulic fluid, an electric motor or a
gasoline engine. The bore 21 communicates with an enlarged
counter bore or chamber 23 in the lower end of the body and
extending through the bottom end 15.
The anvil head 19 has a stem 24 extending through
the housing 18 and chamber or bore 23 into the lower end of
the bore 21. This stem 24 has a collar 25 therearound
intermediate the ends thereof which fits freely in the
chamber 23. The latch 16 has a central body portion 16a
fitting in a slot lla in the body 11 at the bottom end 15
thereof and a pin 26 carried by the housing spans the slot
to pivotally mount the latch. A first arm or finger 16b of
the latch projects from the slot lla upwardly alongside of
the housing while a second finger or arm 16c extends
` through the slot to underlie the collar 25. A spring
pressed detent 27 is slidably mounted in the housing 11 and
acts on the body portion 16a of the latch to resist un-
authorized tilting thereof. When the stem 24 is inserted
in the chamber 23, the collar 25 will engage the undersur-
face of the finger llc of the latch and as the collar is
pushed upwardly, the latch will be tilted until the collar
clears the finger whereupon the detent 27 will be effective
to rotate the latch bringing the finger 16b against the
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housing 11 and positioning the finger 16c under the collar
so that the stem will be retained in the housing 11. When
it is desired to remove the stem and anvil, the finger 16b
will be manually depressed to rotate the finger 16c out of
contact with the collar 25, whereupon the stem will drop out
of the housing.
The anvil head 19 is fixed on the lowex end of the
stem 24 in any suitable manner such as by wedging a tapered
end 26 of the stem into a tapered well 27 in the anvil head.
The anvil head has a free sliding fit in the cylindrical
housing 18 and has an open bottom cylindrical chamber 28
receiving the top end of the chisel shank or stem 20a. The
~ recess 28 is substantially greater in diameter than the
; stem 20a and an adapter sleeve 29 fitting the recess isslipped over the top end of the stem 20a above an integral
collar 30 on the stem. This sleeve 29 centers the stem in
the recess 20a and is shorter in length than the distance
between the collar 30 and the top end face 20b of the stem.
This top end face 20b confronts a bottom face l9a of the
anvil head to impact thereagainst.
` The chisel stem is held in the recess 20a by a pin
31 rotatably mounted in a transverse boss 32 adjacent the
bottom of the anvil 19 and as also shown in FIG. 3, the pin
31 has a central slot or recess 31a adapted to register with
the chamber 28 to accommodate insertion of the collar 30
into the chamber above the pin. Then, when the pin is
rotated to move the slot 31a out of registration with the
chamber 28, the body of the pin will underlie the collar 30
and be effective to hold the chisel in the anvil. A nut 33
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on the pin is effective to lock it against unauthorized
rotation.
An open coil helical spring 34 is provided in the
housing 18 with a bottom end coil 34a bottomed on the top
J. 5 of the anvil head 19 in snug engagement with a boss or
nipple 35 in which the well 27 is formed. A rib 36 on this
boss overlies the end coil 34a to maintain firm contact of
the end coil with the anvil head for transferring vibrations
and for aligning the spring and anvil.
The top end coLl 34b of the spring 34 is bottomed
against a top wall 18a of the housing. This top wall 18a
, underlies the washer 17 and has a large diameter central
'l aperture therethrough receiving a rim 17a of the washer to
, center it on top of the housing.
In the position shown in FIG. 2, the spring 34 is
in a relaxed expanded condition with the chisel 20 sus-
pended freely from the anvil l9 with its collar 30 resting
~ on the pin 31. In this relaxed condition of the spring 34,
`~ the collar 25 of the anvil stem 24 will rest on the latch
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finger 16c and the anvil head 19 will be suspended from
this latch with the spring 34 holding the upper wall 18a of
the housing loosely under the washer 17. The top end 24a
of the anvil stem 24 is then spaced below the bottom of the
stroke of the piston 22 so that, in the event the piston is
"~ 25 activated; no impact blow will be received by the anvil.
-~ However, when, as shown in FIG. 5, the weight of
the tool lO is supported by resting the chisel 20 on the
material M to be broken up for impact, the spring 34 will
be compressed by the weight of the tool body resting on the
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spring and will, of course, be further compressed upon
application of a downcrowding load L on the tool body. In
this attitude of the tool lO, the ~ollar 25 of the anvil
stem 24 will be raised above the latch finger 16a and the
top end face 24a of the stem will be brought into the range
of the stroke of the piston 22 to be impacted by the piston
for the delivery of a hammer blow through the stem 24 to
the anvil 19 and then, of c~urse, through the chisel 20 to
its cutting head 2Ob.
The initial downcrowding of the tool by its own
weight and by the applied load L thus lowers the tool moving
the housing 18 downwardly along the anvil head 19 and
exerting an initial downcrowding load on the chisel.
:~ Then, when the piston 22 impacts the top striking
end 24a of the anvil stem 24 as shown in FIG. 6, the
hammer blow on the anvil drives the head 20b of the chisel
20 into the material ~ and the spring 34 will expand to :
keep the level of the tool body ll above the spring the
same as before impact as shown in FIG. 5. The expanding
spring 34 thus delivers its energy to the anvil and adds
: to the driving force of the tool. ::
The impact blow of the hammer 20 on the top end
24a of the anvil stem 24 creates vibrations which are built
up along the length of the stem into the anvil head 19 and
transmitted to the spring 34 through the bottom end coil
34a which, as explained above, is in good contact with the
anvil head around the boss 35. The vibrations then travel
through the spring coils 34 as illustrated from a compari-
son of FIGS. 6 and 7 where the bottom end coils of the
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spring are first closer together and then as the load is
distributed along the length of the spring, the upper end
coils are closer together. The vibrations are dampened
against traveling into the tool body 11 by the washer 17
which, of course, is then pressed against the bottom end
face 15 of the tool body.
The high velocity rapidly repeated hammer blows
on the anvil stem create high frequency vibrations built up
through the stem and spring and transferred to the anvil
head 19 causing the impact surface l9a to dance on the top
end face 2Ob of the chisel stem 2Oa. A vibration separation
film is created between the surfaces l9a and 20b. Thus, the
hammer blows are divided into impulses of very high frequen-
cy and even though the anvil trAnsfers a hammer blow of
sufficient magnitude to exceed the elastic limit of the
workpiece which, in the illustrated case would be the top
end 20b of the chisel stem, the workpiece remains undamaged
because the blow is delivered in high frequency impulses
allowing the stressed workpiece to recover between impulses.
In addition, the high frequency impulses are transferred to
the workpiece causing it to vibrate with the vibration
adding to the driving force of the downcrowding spring and
the impact blow of the hammer thereby increasing the driving
capacity of the tool without damaging the work. The energy
stored in the compressed spring both from a downcrowding
-~ load thereon and the vibrations imparted thereto is thus
released in a driving direction with the impact blows from
the hammer.
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As shown in FIG. 8, after the hammer blow and the
retraction of the hammer 22 away from the top end 24a of the
anvil stem 24, there would normally be a recoil action
causing the tool body ll to bounce like a pogo stick.
However, in accordance with this invention, the spring 34
keeps the anvil 19 in thrusting engagement with the chisel
and the continued weight of the tool body ll and the down-
crowding load L causes the tool body to descend to the new
level of the chisel which has pierced the material M and in
so doing, the spring 34 is compressed back to the condition
of FIG. 5 with its stored energy ready to be delivered to
the work on the next hammer blow.
It should be appreciated that all of the operating
steps of FIGS. 5 - 8 occur on each stroke of the piston 22
and since power hammer tools generally operate in the range
of 900 to 3,000 piston strokes per minute, the operating
sequence occurs at very high frequency developing sonic
and even ultrasonic vibrations.
The stiffness or rate of the spring 34 is
selected so that the applied downcrowding loads will not
collapse the spaced coils into contact nor will the vibra-
tions or loads overheat the spring. The resistance or
classification of the material to receive the workpiece is
a factor in selecting spring rate or stiffness. If the
tool is to be used for driving a workpiece into hard
material such as concrete or rock, the spring should be
stiffer than when the tool is to be used on soil or sand.
In general, a rock tool will use a spring 30 to 50% stiffer
than a sand or soil tool. Thus, for a 60-pound hammer
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(60-foot-pounds per blow) a 90-pound spring is useful in
sand or soil while a 120-pound or stiffer spring is useful
in rock.
- The compressed or downcrowded length of the open
,.
coil spring should not permit the anvil stem to move into
the bore 21 sufficiently to receive the hammer blow before
the hammer has a sufficient free downstroke to develop
acceleration for an effective impact blow. In general, the
blow should not be delivered to the anvil stem in the upper
half of the downstroke of the piston. Thus, the lighter or
less stiff springs for soil or sand use may be longer than
, the stiffer springs for rock use to prevent the anvil stem
from riding into the upper half of the piston downstroke.
As shown in FIG. 9, in place of driving the chisel
20 shown in FIGS. 2 - 8, the anvil head 19 may directly act
on a workpiece such as post P being driven into the ground
G. The upper end of the post P fits freely in the chamber
28 of the anvil head 19 with the top end of the post
impacted by the surface l9a of the anvil head and dancing
on the post from the high frequency vibrations imparted to
the anvil head so as to prevent peening or damage of the
post.
As shown in FIG. 10, the workpiece is in the form
of a rod R being driven in the ground G. To adapt the rod
to the chamber 28 of the anvil head 19, a cap 35 is fitted
over the top end of the rod and snugly fits in the chamber
28 to be impacted by surface l9a of the anvil 19 and operate
in the same manner as described above.
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As shown in FIG. 11, the anvil head 19 takes the
form of a solid cylinder loosely fitting in the housing 18
but having a small diameter well 36 for receiving a work-
piece in the form of a metal nail N to be driven into mater-
ial M such as a pavement, a wall or the like.
From the showings in FIGS. 9 - 11, it will be
understood that adapters and anvil shapes and sizes are
widely variable for different working conditions.
FIGS. 12 - 14 attempt to illustrate graphically
the operation of the power hammers of this invention, but
it should be understood that they are not intended to
reflect actual operating data and are illustrative only.
In FIG. 12, the effect of the conventional power
, hammer impact on a workpiece is illustrated by the curve 40
' 15 plotted in terms of time in which it acts on the workpiece
and foot-pound impact load which it delivers. A single
stroke of the power hammer is illustrated. The curve 40
raises rapidly from zero to a peak 41 and then drops
abruptly back to zero after delivery of the impact blow.
Now, if the impact blow is heavy enough to exceed the
elastic limit of the workpiece, deformation of the work-
; piece will occur during that portion of the blow illustrated
by the shaded area 42 and because of the elapsed time inter-
val in which this overstressing of the workpiece occurs
: 25 above the elastic limit, permanent deformation and damage
to the workpiece will take place in the form of peening,
. . ,
feathering and even splintering of the workpiece. Thus,
the blow must not exceed the plateau 43.
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However, as shown in FIG. 13, the same stroke of
a power hammer of this invention is plotted in the same
time interval as in FIG. 12, but because of the energy
stored by the spring 34 and the vibrations imparted to the
anvil, causing it to dance on the workpiece, the load
delivered is increased from curve 40 to curve 44 and is
delivered in the form of impulses ~5 which rapidly rise and
fall so that the stressed workpiece even at stresses above
its elastic limit, will recover without deformation. Thus,
a peak 46 substantially above the peak 41 is achieved
without damage to the workpiece and with the same power
: input to the hammer.
. In FIG. 14, the output of a conventional 60-foot-
pound per blow jack hammer is plotted against the output of
. 15 the same jack hammer equipped with the vibration and down-
~ crowding spring assembly of this invention. As shown, the
:~ strokes per minute of a 60-pound hammer are plotted as
abscissa and the foot-pound deliveries for each blow of the
hammer are plotted as ordinates. As shown by the line 47,
the conventional 60-pound jack hammer because of its pogo
stick rebound action, only has a power delivery of about
40-foot pounds per blow regardless of the increase in the
strokes per minute of the hammer. By comparison, the curve
48 shows that the same hammer will have a power delivery of
about 90-foot pounds per blow and that this delivery
increases as the rate of hammer strokes increase. The
increased power delivery is brought about by the downcrowd-
ing load snd by the absorption of rebound action which
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compress the spring to store energy that is delivered with
the ham~.er blow and by the development of higher frequency
vibrations which pulse or increment each blow to render it
more effective for driving.
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