Abstrict A jaw crusher having a stationary jaw and a movable jaw which define
a variable crushing gap (or closed side setting), a toggle beam,
and a toggle between the toggle beam and the movable jaw, and a
toggle seat between the toggle and each of the beam and movable
jaw for seating the toggle against the beam and movable jaw. A double-acting
hydraulic ram having a connection with the toggle beam for shifting
the toggle beam toward and away from the fixed jaw. An abutment
is supported by the housing and engageable by the toggle beam for
defining an adjustably variable limit of shifting thereof. End caps
provide a rigidly guided sliding toggle beam having a plurality
of alternatively selectable positions of adjustment. An hydraulic
circuit is connected to each end of the relief ram for extending
and retracting thereof, a relief valve is provided for the ram for
providing a quick discharge path for oil in the rams to vent the
latter to substantially lower pressure to thereby provide a rapid
overload release of the cylinder when uncrushable material is encountered
in the crusher, and a double-acting toggle tension hydraulic ram
in the circuit and pivotally connected between the toggle beam and
the movable jaw to tension the toggle and its seats together. The
jaw crusher and its hydraulic circuit enable the material between
the jaws to be cleared when the machine has encountered an unscheduled
stop due to, for example, an overload in the system, the failure
of the electrical power system, the failure of the belt driving
system, or any other unscheduled stops.
Claims What is claimed is:
1. A jaw crusher comprising a housing that supports a stationary
jaw and has a pair of opposed upright walls between which a movable
jaw is suspended, each of said walls defines a way slot that is
elongated in directions toward and from the stationary jaw, a toggle
beam extending across the housing and having opposite end portions
received in said way slots and substantially confined by them for
slidable shifting in said directions, a toggle between said toggle
beam and the movable jaw for supporting the latter, a toggle seat
between said toggle and each of said beam and movable jaw for seating
said toggle against said beam and movable jaw;
double-acting hydraulic ram means having a cylinder and a double-acting
piston extendable from one end of said cylinder, said piston having
a connection with said toggle for shifting said toggle in said directions,
said cylinder having a rigid connection with said housing and extending
between said side walls;
abutment means supported by the housing and engageable by the toggle
beam for defining an adjustably variable limit of shifting thereof
in one of said directions and thus providing a rigidly guided sliding
toggle beam having a plurality of alternatively selectable positions
of adjustment of the toggle beam;
an hydraulic circuit connected to said cylinder for extending and
retracting said piston;
a tramp iron relief valve between opposite ends of said cylinder
for providing a quick discharge path for oil in said cylinder to
vent the latter to substantially lower pressure to thereby provide
a rapid overload relief of said cylinder when tramp material is
encountered in said crusher;
a directional control valve in said circuit and connected with
said ram means for retracting or extending said pistons; and
said hydraulic circuit providing for power opening of said movable
jaw to permit clearing of said crushing chamber when an unscheduled
stop occurs due to failure of the electrical system, the drive means
or excessive material in said crushing chamber.
2. The crusher set forth in claim 1 including an adjustable fixed
stop in said abutment means for defining said limit of shifting
said beam.
3. The crusher described in claim 1 including adjustable shims
for adjusting said fixed stop.
4. The crusher as set forth in claim 1 including beam retainers
secured to the end of said beam and bearing against said housing
to ensure said beam can slide to and from the stationary jaw in
a parallel motion and remain square with the housing.
5. The crusher described in claim 1 including adjustable wedges
secured to said beam to provide a height adjustment of said beam
to ensure a good sliding fit between said beam and said abutment
means.
6. The crusher set forth in claim 1 including a double-acting toggle
tension hydraulic ram in said circuit and pivotally connected between
the toggle beam and said movable jaw to tension the toggle and its
seats together.
7. A jaw crusher comprising a housing and having a pair of opposed
upright side walls, a stationary jaw fixed between said side walls,
a movable jaw suspended between said side walls, for swingable relationship
with said movable jaw, each of said side walls having a way slot
that is elongated in directions toward and from the stationary jaw,
a toggle beam extending across the housing and having opposite end
portions received in said way slots and substantially confined and
rigidly guided by said slots for slidable shifting in said directions,
a toggle between said toggle beam and the movable jaw for engaging
and supporting the latter, a generally channel-shaped toggle seat
between said toggle and each of said beam and movable jaw for seating
said toggle firmly against said beam and movable jaw;
double-acting hydraulic ram means having a cylinder and a double-acting
piston rod extendable from one end of said cylinder, said piston
rod having a connection with said toggle for shifting said toggle
in said directions, said cylinder having a rigid connection with
said housing and extending between said side walls;
adjustable abutment means in said way slots and engageable by the
toggle beam for defining an adjustably variable limit stop of shifting
thereof in one of said directions and thus providing a rigidly guided
sliding toggle beam having a plurality of alternatively selectable
positions of adjustment of the toggle beam;
an hydraulic circuit connected to said cylinder for extending and
retracting said piston rod;
a tramp iron relief valve in said circuit and between opposite
ends of said cylinder for providing a quick discharge path for oil
in said cylinder to vent the latter to substantially lower pressure
to thereby provide a rapid overload relief of said cylinder when
tramp material is encountered in said crusher; and
a directional control valve in said circuit and connected with
said ram means for retracting or extending said piston rod.
8. The crusher set forth in claim 7 including an adjustable and
fixed stop in said way slot for defining said limit of shifting
said beam.
9. The crusher described in claim 7 including adjustable shims
for adjusting said limit stop.
10. The crusher as set forth in claim 7 including beam retainers
secured to the end of said beam and bearing against said housing
side wall to said beam can slide to and from the stationary jaw
in a parallel motion and remain square with the side walls.
11. The crusher described in claim 7 including adjustable wedges
secured to said beam to provide a height adjustment of said beam
to ensure a good sliding fit between said beam and said way slots.
12. The crusher set forth in claim 7 including a double-acting
toggle tension hydraulic ram in said circuit and pivotally connected
between the toggle beam and said movable jaw to tension the toggle
and its seats together, and an hydraulic accumulator connected with
said ram which provides an easily adjustable tension force.
13. A jaw crusher comprising a housing that has a pair of upright
walls between which a movable jaw is movable relative to a fixed
jaw, each of said walls defines a way slot that is elongated in
directions toward and from the stationary jaw, a toggle beam extending
across the housing and having opposite end portions received in
said way slots and substantially confined by them for slidable shifting
in said directions, a toggle between said toggle beam and the movable
jaw for supporting the latter, a toggle seat which is generally
C-shaped in cross section and is located between said toggle and
each of said beam and movable jaw for seating said toggle against
said beam and movable jaw;
double-acting hydraulic ram means having a connection with said
toggle for shifting said toggle in said directions,
an hydraulic circuit connected to each of said rams for extending
and retracting said rams and consequently shifting said toggle beam,
and a double-acting toggle tension hydraulic ram in said circuit
and pivotally connected between the toggle beam and said movable
jaw to tension the toggle and its seats together.
14. The crusher set forth in claim 13 including an adjustable and
fixed stop in said way slot for defining said limit of shifting
said beam.
15. The crusher described in claim 14 including adjustable shims
for adjusting said limit stop.
16. The crusher as set forth in claim 13 including beam retainers
secured to the end of said beam and bearing against said housing
side wall to said beam can slide to and from the stationary jaw
in a parallel motion and remain square with the side walls.
17. The crusher described in claim 13 including adjustable wedges
secured to said beam to provide a height adjustment of said beam
to ensure a good sliding fit between said beam and said way slots.
18. A jaw crusher comprising a housing that supports a stationary
jaw and has a pair of opposed upright walls between which a movable
jaw is suspended, each of said walls defines a way slot that is
elongated in directions toward and from the stationary jaw, a toggle
beam extending across the housing and having opposite end portions
received in said way slots and substantially confined by them for
slidable shifting in said directions, a toggle between said toggle
beam and the movable jaw for supporting the latter;
double-acting hydraulic ram having a cylinder and a double-acting
piston extendable from one end of said cylinder, said piston having
a connection with said toggle for shifting said toggle in said directions,
said cylinder having a rigid connection with said housing and extending
between said side walls;
abutment means in said way slot engageable by the toggle beam for
defining an adjustably variable limit of shifting thereof in one
of said directions;
an hydraulic circuit connected to said cylinder for extending and
retracting said piston;
a tramp iron relief valve between opposite ends of said cylinder
for providing a quick discharge path for oil in said cylinder to
vent the latter to substantially lower pressure to thereby provide
a rapid overload relief of said cylinder when tramp material is
encountered in said crusher; and
a directional control valve in said circuit and connected with
said ram means for retracting or extending said pistons.
19. The crusher described in claim 18 including adjustable shims
for adjusting said limit.
20. The crusher as set forth in claim 18 including beam retainers
secured to the end of said beam and bearing against said housing
to ensure said beam can slide to and from the stationary jaw in
a parallel motion and remain square with the housing.
21. The crusher described in claim 18 including adjustable wedges
secured to said beam to provide a height adjustment of said beam
to ensure a good sliding fit between said beam and said abutment
means.
22. The crusher set forth in claim 18 including a double-acting
toggle tension hydraulic ram in said circuit and pivotally connected
between the toggle beam and said movable jaw.
23. The crusher and hydraulic circuit of claim 18 wherein said
rams can be operated to power open said jaws in the event of an
unscheduled stoppage of said crusher to thereby clear said material
in said crusher.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to jaw crushers wherein a movable
jaw that cooperates with a stationary jaw is rockably fulcrumed
on a toggle plate which in turn is fulcrumed on a toggle beam that
is adjustable in opposite directions toward and from the stationary
jaw.
2. Description of the Related Art
A jaw crusher of the general type to which this invention relates
is disclosed in U.S. Pat. No. 4165044 issued Aug. 21 1979 to
Batch. That patent has been assigned to an assignee common with
the present invention and discloses a toggle beam and a transversely
shiftable wedge at each end of the beam whereby the toggle beam
is wedged downwardly into a position in the way slots of the crusher
side walls and locked therein.
Another prior art example of this type of jaw crusher is shown
in U.S. Pat. No. 4783013 issued Nov. 8 1988 to Polzin, and which
also has been assigned to an assignee common with the present invention.
That patent discloses shims behind a toggle beam which define various
positions of its fore and aft adjustment along the way slots and
in which the ends of the beam are guided.
Another example of the prior art is shown in the U.S. Pat. No.
4927089 issued May 22 1990 to Joseph Altmayer. That patent discloses
a pair of hydraulic cylinders or rams for controlling the movement
of the movable jaw of a rock crusher between a first set position
and a retracted position. That patent has means for simultaneously
locking hydraulic fluid in first and second supply conduits to hold
an extensible ram in a substantially rigid fixed length condition
when in the set position during normal crushing operation. The ram
50 is mounted on one end to a non-adjustable fixed point on the
main frame and the other end of the ram connects directly to the
movable jaw. The length of the ram extension directly determines
the location of the movable jaw.
U.S. Pat. No. 3976255 issued Aug. 24 1976 to Edwards discloses
a jaw crusher which utilizes a normal operating position between
the jaws. The control system used in that patent is a timed action
arrangement which utilizes an air/liquid intensifier for controlling
liquid pressure within the cylinder by a supply and exhaust of air
to and from the unit.
U.S. Pat. No. 4637562 issued Jan. 20 1987 to Hagiwara et al.,
discloses hydraulic rams connected to the outlet portion of the
breaker plate means and which operate independently of the breaker
plate drive means to increase and decrease cyclically and incrementally
the spacing between the lower ends of the breaker jaws. Still other
examples of the prior art are shown in U.S. Pat. No. 5799888
issued Sep. 1 1988; U.S. Pat. No. 5765769 issued Jun. 16 1998;
U.S. Pat. No. 5769334 issued Jun. 23 1998; and U.S. Pat. No.
5857630 issued Jan. 12 1999.
SUMMARY OF THE INVENTION
The present invention provides an eccentric jaw crusher for rock
material and the like having a rigidly guided sliding toggle beam
and a toggle for being hydraulically urged against the movable jaw
to relatively position the movable jaw with respect to a fixed jaw
to thereby vary the crusher closed side setting.
More specifically, the present invention provides a parallel hydraulic
circuit including one or more double-acting hydraulic rams which
provide a reliable overload relief system when tramp iron or other
uncrushable material is encountered in the crusher. There is also
provided a mechanical fixed stop for the movable jaw to ensure closer
control of the closed side setting. With this fixed stop, it is
possible to permit the uncrushable object to pass through the crushing
chamber, and then the movable jaw is automatically returned to the
established closed side setting. The hydraulic circuit provided
by the present invention includes direct mounted relief valves,
one for each ram, which permit a quick dumping of the oil to vent
to a lower pressure area.
The invention thus provides a hydraulically clamping of the toggle
beam forward and holding the beam rigid until the clamping force
is overcome, for instance, by uncrushable material. A relief force
is then transferred from the movable jaw to the toggle and to the
toggle beam, to the ram rod and oil in the ram, which will then
open the relief valves to dump only enough oil to drop to the preset
pressure. A pressure compensated pump supplies makeup oil to restore
the ram to its original position.
Another aspect of the invention relates to a crusher of the above
type in which the toggle beam can be powered back by hydraulic rams
to allow for quick closed side setting changes. The beam can also
be powered back to allow for quick crushing chamber clearing of
material due to unscheduled stoppage.
The toggle tensioning system provided is accomplished through a
hydraulic ram and associated accumulator which is only powered to
provide an easily adjustable constant tension force on the toggle
and toggle seats. Tension must be maintained to keep the toggle
in place between the seats due to the large amount of movement required
when the crusher clears an uncrushable object. The movement is greater
than a spring will handle effectively.
Another aspect of the invention relates to the adjustable wedges
which remove any vertical clearance from the guide slots, and shims
are provided to compensate for side-to-side clearance in the frame.
The hydraulic system provided by the present invention removes
high shock loads from the frame and reduces many attendant problems.
These and other objects and advantages of the present invention
will appear herein as this disclosure progresses.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of the jaw crusher embodying the present
invention;
FIG. 2 is a vertical, longitudinal cross-sectional view through
the jaw crusher, more or less schematic in character;
FIG. 3 is a perspective view of the crusher shown in FIG. 1 but
with parts broken away or remove or the sake of clarity;
FIG. 4 is a perspective view of the crusher, with parts broken
away or removed or shown in an exploded fashion for clarity in the
drawings;
FIG. 5 is a perspective, exploded view of portions of the parts
shown in FIG. 4 but on an enlarge scale;
FIG. 6 is a perspective, fragmentary view of the crusher shown
in the other views but taken generally from the opposite side thereof
and showing certain parts as being broken away or removed for the
sake of clarity;
FIG. 7 is an exploded perspective view of a toggle tension ram
and its mounting brackets, shown in FIG. 6 but on an enlarged scale;
and
FIG. 8 is a hydraulic, schematic drawing of the crusher iron relief
rams which are shown in FIGS. 1 2 3 and 4 and also showing the
counterbalanced valve, the directional control valve, and the toggle
tension valve.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The general organization of the crusher includes a main frame parallel
vertical sides 1 and 2 secured rigidly together by the cross brace
3 construction and which is welded to the side frames, and the members
4 5 and 24 which are welded between the side walls and which form
a frame for mounting two hydraulic rams 6 and 7. Positioned across
the rear edges of frame members 4 and 5 is a mounting plate 24 which
is welded to the side walls and members 4 and 5 to form a rigid
unitary structure in which is mounted the large double-acting hydraulic
rams 6 and 7 now to be described. A large cast steel housing 10
which is rigidly mounted in the saddles 11 and 12 which in turn
are welded to the side walls 1 and 2 respectively. This housing
10 encloses the jaw crusher overhead eccentric shaft 14 in anti-friction
bearings in the well known and conventional manner.
The main frame also includes suitable reinforcing steel members
20 21 which are welded to the side walls (FIGS. 1 and 4).
The hydraulic relief rams 6 and 7 are themselves conventional in
nature and have cylinder rods 6' and 7', respectively, extending
therefrom. The rod end of the rams have the conventional heads 26
and 27 by means of which they are bolted to the mounting plate 24.
The mounting plate 24 has suitable apertures 30 through which the
piston rods extend.
As shown in FIG. 4 cylinder rod retaining clamps 31 and 32 mount
to the toggle beam 40 as being bolted thereto in conventional manner
by means of bolts.
The toggle beam 40 is generally elongated and extends between the
side walls 1 and 2 and is furthermore generally rectangular in cross
section and slides in the guides 44. The guides 44 have elongated
openings and are welded to the side walls. The toggle beam is rigidly
guided and slides in the guide 44 by the hydraulic relief rams 6
and 7 to thereby allow placing of shims 85 to adjust the closed
side setting 60 between the fixed jaw 50 and the movable jaw 52
at the lower edges thereof (FIG. 2). The rams are used to move the
toggle beam when setting closed side setting with shims 85. The
upper end of the movable jaw 52 is mounted by its eccentric shaft
14 to cause the movable jaw to oscillate back and forth to effect
the crushing action of the material between the jaws in the known
manner.
A large V-belt pulley 70 is provided at one end of the shaft 14
and through which power is furnished (from a source not shown) to
cause the movable jaw 52 to be moved, as indicated.
The connection between the toggle beam 40 and the lower end of
the swing jaws is provided by an elongated toggle 72 (FIGS. 2 3
5 and 6).
As shown in FIGS. 2 3 and 5 one end of the toggle 72 is seated
in a correspondingly shaped channel member or seat 76 located in
the front face of the toggle beam 40. The other end of the toggle
is firmly seated in channel member or seat 74 located on the lower
end of the movable jaw.
The two large double-acting hydraulic rams 6 and 7 act to move
the toggle beam 40 in the side frames in any adjusted position as
determined by the crusher closed side setting 60 desired between
the lower end of the jaws. In this manner, the sliding toggle beam
is rigidly guided to allow a parallel hydraulic circuit to function
and provide a more reliable overload relief system, as will appear.
As shown in FIGS. 4 and 5 beam shims 80 and beam retainer 81 are
secured to the ends of the beam 40. By use of these beam retainers,
the beam position cannot become skewed with the main frame and instead
with the beam retainers located on the ends of the toggle beam,
the beam can only slide to and from the stationary jaw in a parallel
motion. The retainers bear against the outside of the main frame
to ensure the beam will stay square with the frame. Wedges are used
which allow for the height adjustment of the toggle beam to ensure
a better sliding fit between the beam and the slots in the main
frame, for example. A toggle beam wedge 82 is secured in the lower
side ends of the beam 40 to provide a height adjustment for the
beam. FIG. 4 also shows shims 85 (which are insertable in guides
44) for setting the crusher closed side setting, as shown in FIG.
5 curved end plate 83 is provided for securing the shims 85 in
position in the crusher to form a fixed top. The curved end plate
84 acts as a return stop for the beam when it is retracted, as will
appear.
Thus, the toggle beam 40 is rigidly and accurately secured in the
elongated slot 44 in each of the side walls of the crusher. In the
above manner, the toggle and toggle beam are held in any desired
position by the hydraulic relief rams, rather than being mechanically
locked to the side frame.
More hydraulic relief rams may be provided for additional holding
power. In the event a smaller crusher is used, a single relief ram
may be sufficient.
With the above described structure it is possible to maintain a
mechanical fixed stop to ensure more control of the closed side
setting as determined by shims 85. With the above described structure,
the toggle beam 40 is allowed to slide away from the fixed stop,
permitting uncrushable objects to pass through the crushing chamber.
The toggle beam 40 will then return to the established closed side
setting against the fixed stop.
As shown in FIGS. 6 and 7 a double-acting toggle tension hydraulic
ram 90 is provided between the toggle beam 40 and the lower end
of the swing jaw. The toggle tension ram 90 is pivotally connected
to a mounting bracket 91 (FIGS. 6 and 7) on the lower side of the
toggle beam and to the mounting bracket 92 which is welded to the
lower end of the movable jaw. The toggle tensioning ram 90 eliminates
the need for springs to tension the toggle and its seats 74 76.
This tension is now provided with the hydraulic ram 90 and its accumulator
99 (FIG. 7) which is powered to provide an easily adjustable tension
force.
With the hydraulic circuit is shown in FIG. 8 the invention provides
for hydraulically clamping the beam 40 forward and holding the beam
rigid against the shims 85 until the clamping force of the rams
is overcome (by uncrushable material) which will then open the relief
valves 96 97 to dump only enough oil to drop to the preset pressure.
The present hydraulic circuit provides a relief and automatically
returns the jaw to the original adjustable fixed stop. In other
words, the hydraulic circuit allows oil from the cylinder to vent
to a lower pressure by means of a relief valve and, by connection,
move the movable jaw away from the stationary jaw until the uncrushable
material passes between the jaws. Once the uncrushable material
passes, the pressure in the cylinder will drop below the preset
relief pressure, the pump will replace the oil vented, and the beam
will return to its adjustable fixed stop. The opening between the
jaws can be easily adjusted by shifting the directional control
valve to retract the beam to allow for insertion of shims to vary
the fixed stop for the beam. The pressure compensated pump P will
supply the makeup oil to restore the rams to their original set
positions. The direct mounted relief valves allow for a quick path
for the oil to vent to a lower psi area.
The adjustable wedges 82 remove any vertical clearance from the
guide slots on the sides of the crusher. Furthermore, shims 80 are
provided to compensate for side-to-side clearance in the frame.
All the sliding surfaces have replaceable linear bearing material
on them.
This hydraulic system will prevent high shock loads from being
transferred to the frame and replaces the need of a mechanical fuse
as when the toggle is used as a conventional machine.
FIG. 8 shows the hydraulic circuitry for the two relief/one tension
ram configuration and includes the crusher tramp iron relief rams
6 and 7 the dual counterbalance valve 100 which is a combination
of a two valves and two pilot operated check valves. The directional
control valve 101 provides for retraction or extension of the relief
rams 6 7 in the known manner. A system relief valve 102 is also
provided in the circuit. In regard to the double-acting toggle tension
ram 90 a toggle tension relief valve 103 a directional control
valve 104 and a pilot operated check valve 105 are provided. A
pressure reducing valve 106 is provided and may provide a lower
pressure than system pressure. In regard to powering the hydraulic
circuit, an electric motor 110 drives the pump P which provides
the necessary oil flow and pressure for the circuit. Suitable check
valves 111 low pressure switch 112 and oil cooler 113 are provided
as conventional.
The present invention which can retain the toggle beam eliminates
the potential or the beam's position to become skewed with the main
frame. With the beam retainers located on the ends of the toggle
beam, the beam can only slide to and from the stationary jaw in
a parallel motion. The retainers bear against the outside of the
main frame to ensure the beam will stay square with the frame. The
present invention also utilizes wedges that allow for height adjustment
of the toggle beam to ensure a better sliding fit between the beam
and slots or ways of the main frame.
The hydraulic tension ram 90 that connects on one end to the movable
jaw and on the other end to the bottom of the toggle beam acts as
a clamp-like retention device for the toggle. Due to the range of
motion that the present design must cover, prior art devices for
maintaining clamping pressure throughout the bearing length, such
as springs, were unsatisfactory. The present invention utilizes
a hydraulic ram to give an adjustably constant clamp pressure. The
ram applies the predetermined set pressure to clamp the toggle between
its seats. Thus, the pressure applied by the ram will be constant.
Furthermore, the hydraulic ram tension can be varied by adjusting
the pressure reducing valve.
The present invention allows the operator to clear the machine
of excess material when the machine has stopped due to an overload
of material in the machine, the electricity powering the machine
goes out for some reason or another, the belt mechanism may break
or other unscheduled stops occur. In these cases, the jaws can be
powered open to clear the machine from material that has accumulated
in the crushing chamber. In other words, the chamber is opened to
permit the accumulated material to fall out from between the jaws.
Recapitulation
With this arrangement, a rigidly guided sliding toggle beam allows
a parallel hydraulic circuit to function and provide for a reliable
overload relief system. The relief valves 96 and 97 in the relief
rams 6 and 7 allow for a quick path for oil to vent to a lower psi
area, as mentioned. The present arrangement provides for hydraulically
clamping the beam in the forward (crushing) position, holding the
beam rigid until the clamping force is overcome (by uncrushable
material) which will open the relief valves (96 97) and then release
only enough oil to drop the preset pressure. When the uncrushable
material passes, the pressure in the ram will drop below the preset
relief pressure, and the compensated pump P will supply the makeup
oil to restore the rams to their original fixed stop position.
The present hydraulic system prevents high shock loads on the crusher
frame and replaces the need for a mechanical fuse link when the
toggle is used in a conventional manner. The present arrangement
maintains a mechanical fixed stop for the toggle beam to ensure
more control of the closed side setting as determined by the shims
85 as mentioned This allows for an uncrushable object in the jaws
to pass between the jaws and the jaw 52 is automatically returned
to the established closed setting. A toggle tensioning system is
provided by an hydraulic ram and an accumulator which provides an
easily adjustable tension force.
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