The present invention relates to conversion presses.
Particularly the invention concerns an adjustment
device of the stroke pressure in conversion presses for
converting stock shells into easy-open covers used as
closing ends for drink and food cans and the like, although
it is understood that the invention is also applicable to
presses for working stocks of different kinds.
Conversion presses for semi-raw shells are known,
comprising fixtures designed for converting such shells in
easy-open covers, by virtue of a tab application that
allows the opening of the cover.
Known presses generally include a bed that supports
lateral uprights on which is fastened, by means of tie rods
extending through the uprights, a crown that generally
supports the main drive of the press motion members.
Sliding support guides for a ram, which supports the
tools of the press upper die shoe, are connected to the
These tools are fit to co-operate with correspondent
tools of a lower die shoe, supported by the bed, so forming
a series of work stations for the shells.
These latter are for instance placed in succession in
housings of a conveyor belt that carries the shells through
the press dies, moving them station by station, so allowing
the progressive shell conversion into covers by means of
cyclical stroke of the upper die shoe onto the lower.
The main disadvantage of known presses is that the
elevated stroke rate and the elevated work effort connected
to the press operating cause member elastic deformations of
the presses, principally the movement deformation. Moreover
there are elongation effects by thermal expansion for such
In fact, during the press running, a part of energy
needed for member motion has an heat dissipation inevitably
transmitted to the members causing a dimensional variation
thereof, particularly a longitudinal elongation.
Such variations are also found during the press stop
required periodically for cleaning or maintenance because
of jams, such as for instance feeding the press with the
Particularly the uprights, the crown, the ram and
besides the main component of the driving members like for
instance the connecting rods and the crankshaft are
influenced differently by thermal effect variations: mostly
these elements contribute to the distance variation between
the upper and lower die shoe tools.
The above said effects can reduce the precision and the
dimensional stability of the press during the whole
productive cycle, and therefore must be reduced or even
For instance, the press stroke pressure varies during
the productive cycle in consequence of the working space
variation between the upper and the lower die shoe tools:
this fact influences the shell working, particularly on
scoring depth of their output or opening inlet and
therefore on the qualitative level of formed covers.
Besides the different stroke pressure supply involves
an increasing of noisiness and vibrations of the press.
This problem is commonly resolved heating the
connecting rods causing their elongation so balancing the
upright elongation happening progressively during the press
Other known technique, complementary to the preceding
one for resolving this drawback, is to check the press
circulation oil temperature by heating or cooling it as
Nevertheless, the drawback is not yet resolved since it
is difficult to check the elongation of the moving members
through a thermal balancing (inducing their heat decrease
or increase), and therefore the stroke pressure of the
upper die shoe onto the seats of the lower one is different
during the press working cycle.
Besides, since the required time for inducing
temperature variations are rather long, only partially is
possible to compensate the drawbacks made for formed cover.
The main object of the present invention is therefore
to propose a device for conversion presses fit to check and
regulate the press stroke pressure compensating thermal
expansion and elastic deformation effects to which the main
press components are submitted during its running.
Other object of the present invention is to propose a
device able to check and correct continuously the press
stroke pressure with quick response times.
Further object of the present invention is to propose a
device of easy realization and reliable running and
The above mentioned objects are reached according to
The features of the present invention are underlined in
the follow with reference to attach drawing tables, where:
- figure 1 shows a frontal view of a conversion press
having the device object of the present invention;
- figure 2 shows a side view of the press in figure 1;
- figure 3 shows a plan view of the adjustment stroke
device of the press in figure 1;
- figure 4 shows a partially sectioned side view of
device in figure 3, in which some portions has been removed
for better showing others;
- figure 5 shows a block diagram relative to the
driving of the device in figure 3.
With reference to figures from 1 to 4, numeral 40
refers to a stroke pressure adjustment device in a
conversion press 100 of shells into easy-open covers for
drink or in general food cans.
The press 100 includes a bed 26, a crown 1, and
The bed 26, put on the ground by means of supports 20,
supports a bolster 10, on which are fixed a lower die shoe
5 and four uprights 4, not interacting with the bolster 10,
placed at the bolster 10 sides and provided with
longitudinal guides 21 turned toward the inside of the
The crown 1 is supported by the uprights 4 and is
provided with motion members 60 of a ram 3, sliding by
means of the longitudinal guides 21 and supporting an upper
die shoe 6.
Lower 5 and upper 6 die shoes normally support dies or
tooling destined to progressive conversion of the shells
into covers provided with tear tab.
Between the two die shoes, lower 5 and upper 6, a
conveyor belt of the shells slides longitudinally, that are
progressively converted into formed covers by means of the
cyclical stroke of the upper die on the lower one.
Inside each upright 4 is housed a connecting rod that
maintains mutually constrained the crown 1 and the bed 26.
The rectangular shaped bolster 10 includes an upper
plate 10a, supporting the lower die shoe 5, and a lower
plate 10b, fixed to the bed 26.
The plates, upper 10a and lower 10b, are mutually
connected by means of guides 11, placed near the plate
edges. Each guide is essentially constituted by a
cylindrical pivot, connected with the upper plate 10a by
means of a spherical cage 31 and a bush 32 and with the
lower plate 10b by means of an housing hole made in this
Between the upper plate 10a and lower plate 10b, spacer
members 70 are interposed, that include two couples of
opposed movable wedge elements 71 co-operating with
correspondent fixed wedge elements 72 locked to the upper
plate 10b inside surface.
Such couples of movable wedge elements 71 are driven by
motion means 80 that include, for each couple, a threaded
rod 82 supported by a bracket 83 fixed to the lower plate
10b and rotating by operating a motor member 17.
The ends of each threaded rod 82 are engaged in
correspondent threaded nuts 81, each fixed to the side wall
of every movable wedge element 71.
The threaded rod 82 has opposed threads in such a way
that the rotation of said rod causes the mutual distance
variation between the movable wedges 41.
Between the contact surfaces of the wedge elements 71
with the lower plate 10b and the correspondent wedge
elements 72 of the upper plate 10a hydrostatic sumps are
carried out delimited by an hydrostatic sump boundary
The bolster 10 comprises moreover reaction members 90
put between the upper 10a and lower 10b plates.
Such reaction members 90 include four pistons 91,
placed near the edges of plates forming the bolster 10,
each having an end locked at the upper plate 10a and the
other end widened and housed within a seal box 92 made in
the lower plate 10b and containing a pressure fluid.
The stoke adjustment device 40 includes moreover sensor
members 7 placed on the uprights 4 and fit to detect their
longitudinal dimensional variations.
The sensor members 7 are constituted by electric
elongation sensors joined to the uprights 4, for instance
they are particular resistances called "strain gauge".
With particular reference to figure 5, the device 40
includes also control and command means 50 that receive in
input the signals of the sensor members 7 and send a
control signal, through an estensimetric device 8, to a
comparator 16 between this last signal and a reference
signal 19 pre-established in the device, fit to provide a
operating signal to the motor member 17 that therefore
starts the spacer members 70.
The running of the device 40 is simple because, once
the press 100 is opereated, the sensor members 7 send a
signal proportional to the elongation (or shrinkage) of the
uprights 4 to the estensimetric device 8 that sends a
control signal to a comparator 16 that compares between
this last signal with a reference signal 19 pre-established
in the device.
This comparator 16 sends a signal to the motor member
17 that drives the threaded rods 82 rotating them inside
the threaded nuts 81 of each movable wedge 71.
The axial shifting of these nuts 81 change in turn the
longitudinal position of the movable wedges 71 bound
thereto. Particularly the moving away of the movable wedges
71 causes a push on the upper plate 10a, that determines
its vertical shifting.
The mutual movements between the movable wedges 71 and
the fixed wedges 72 and between the movable wedges 71 and
the lower plate 10b are facilitated by an hydrostatic
support system, obtained by means of the insertion of
pressure oil inside the hydrostatic sumps.
The reaction members 90, opposing to the upper plate
10a vertical shifting, guarantee a correct positioning
within the normal running limits.
Such opposition is got by means of the action made on
the piston 91 heads by the pressure fluid contained in the
seal box 92, that pushes down these heads, in contrast with
the raising of the upper plate through the spacer means 70.
In such a way the stroke or closing pressure of the
press 100 is dynamically regulated.
In a variant of the device 40 the sensor members 7 are
constituted besides by load cells 23 placed under the
bolster 10 and are fit to send a signal proportional to the
stroke pressure of the press 100 to the control and command
means 50 so as to regulate the stroke pressure, in
feedback, by means of the activation of the spacer means
It is besides advantageous to point out that the
conveyer belt 95, returning from the working area between
the upper die shoe and the lower die shoe, longitudinally
slides between the couples of movable guides 71.
It is also useful to point out that the two threaded
rods 82 are connected by a mechanism, for instance through
a chain, and connected to the motor member 17 that can be,
for instance, a step by step motor.
The main advantage of the present invention is
therefore to provide a device for conversion presses fit to
check and regulate the press stroke pressure compensating
thermal expansion and elastic deformation effects to which
the main press moving component are submitted during the
Other advantage of the present invention is to provide
a device fit to check and correct continuously the press
stroke pressure, varying the upper plate position, with
rapid response times.
Ulterior advantage of the present invention is to
provide a device of easy realization and reliable operation
The present invention has been described, with
reference to attached drawings, only as an example, not
limitative, and it is evident that all modification or
variation suggested by the experience as well as its
realization and use, however included within the following