[0001] The invention concerns the construction of a hydraulic lifting device, which is particularly
suited to lift the dies placed on the die supporting tables of presses, thus allowing
their rapid and easy removal.
[0002] In the present technical situation, devices exist which lift off the die to be removed
from the working area. They consist essentially of several hydraulic cylinders, placed
close to each other and inserted into a T-shaped bar. The bars, in turn, are inserted
into the guiding slots of the die supporting table. The number of said bars and, therefore,
that of the lifting cylinders is proportional to the weight of the die to be lifted.
[0003] Inside the cylinders, which are vertically inserted into the T-shaped bars, there
is a sliding piston. Each piston is provided, on the upper surface of its head, with
a ball, which is lodged within a seat having a suitable shape, allowing it to freely
rotate within its seat.
[0004] When the cylinders are put under pressure by activating the correspondig valve, which
connects the tubes of said cylinders with the hydraulic power pack of the press, each
of the pistons moves upward and the ball it is provided with at its upper end gets
into contact with the die and lifts it, since the total strength exerted by the cylinders
with the liquid being under pressure, overcomes the contrasting action of the weight
of said die. Therefore, in order to remove the die, it suffices to make it slide along
the die-supporting table, since the cylinders support its weight and the balls allow
it to slide.
[0005] One of the main inconveniences presented by the just described devices is their considerable
cost, due to the need for several hydraulically operated cylinders. The cylinders
must necesserily be numerous, since their dimensions are rather limited, because they
must fit into the grooves of the press surface together with the bar which contains
them and which also acts as a distributor of the hydraulic liquid.
[0006] Another inconvenience presented by these devices appears when the die is removed
from the die-supporting table. In fact, when the die rests on said table, its weight
is equally distributed on the pistons supporting it, on the other hand, when the die
is made to move and it gradually exits from the table, its weight rests only on the
few pistons which still support it, thus causing dangerous unbalances and strong strains
which might lead to the breaking down of the last lifting pistons.
[0007] The main purpose of the present invention is that of overcoming the just mentioned
inconveniences, by building an extremely simple and, therefore, economical device,
not requiring the use of costly hydraulic cylinders in order to obtain the same results
of the traditional devices.
[0008] Yet another proposed goal is that of obtaining a hydraulic lifting device suited
to equally support, under any condition, the strain caused by the weight of the die.
[0009] Another set goal is that of building a lifting device which does not force to perform
any special operations on the guiding slots of the die-supporting table, so that said
device can simply and adequately be housed even on the tables of presses already being
in operation.
[0010] The just mentioned purposes are obtained by means of a lifting device for dies including
one or more T-shaped bars being inserted into the grooves of the press table and presenting
at their upper ends means allowing the sliding motion of the die, characterized by
the fact that the lifting and lowering of the T-shaped bars and, therefore, of the
die, are obtained by means of the variations caused by the elastic deformation of
pipe systems which are put under pressure and which are arranged under the bars.
[0011] Advantageously, when the die is set on the die-supporting table, the pipe system
appears to be flat, because of the action exerted by the weight of the die, while,
when the hydraulic liquid flows into the pipe, the pressure increases and creates
a force which is able to lift the die.
[0012] The main advantage presented by the device of the invention consists in the fact
that the hydraulic cylinders are replaced by a single flexible pipe system performing
an identical function, with considerable practicality and money saving. Besides, this
device is even more economical, since it does not require any additional operation
for its insertion into the table, thanks to the fact that the existing grooves can
be used.
[0013] Other advantages and constructive and operational details will be better understood
from the description of three preferred forms of execution of the invention, said
descriptions being given by way of illustration only, but not being meant to limit
the scope of the invention, such as it is illustrated in the enclosed tables of drawing,
wherein:
- Fig. 1 is a perspective view of the device of the invention being inserted in the
guiding slot of the die-supporting table;
- Fig. 2 is a cross-section view of the device when the liquid is under pressure within
the flexible pipe system;
- Fig. 3 is a cross-section view of the device of Fig. 2, when the weight of the die
causes the deformation of the flexible pipe being without pressure;
- Fig. 4 is a cross-section view of a variation of the device being the object of
the invention, using a different method for the removal of the die;
- Fig. 5 is a cross-section view of the device of Fig. 4, when the weight of the die
deforms the flexible pipe not being under pressure;
- Fig. 6 is yet another constructive variation of the device of Fig. 2, presenting
a groove system, which has been performed on the die-supporting table and which is
suited to house the flexible pipe.
- Fig. 7 is a front view of the device of Fig. 6 with the flexible pipe not being
under pressure and being deformed by the weight of the die.
[0014] With reference to the mentioned drawings, the device of Fig. 1 consists of three
T-shaped bars 1, being horizontally inserted into guide 2 of table 3 of the press;
said bars present on their upper surface the rollers 4 which allow the sliding movement
of the die on said table, when the rollers protrude from the surface of the table,
as can be seen in Fig. 2.
[0015] The T-shaped bar is inserted axially into guiding slot 2 of the die-supporting table,
with a sufficient lateral play to allow both the horizontal and the vertical sliding
of the respective contact surfaces. In the lower surface of bar 1 there is an axial
slot 5 having an almost semi-cylindrical shape with flares 6 and 7 at its ends. Within
said slot an appropriate flexible pipe 8 , made of rubber or other materials which
can stand medium-high pressures, is housed. Said pipe rests with its lower part on
the horizontal surface 9 of the guiding slot 2 and with its upper part in the cylindrical
part of slot 5.
[0016] Bar 1 presents a series of holes being arranged horizontally and transversally in
relation to the length of the bar and being equally spaced from one another. Each
of said holes contains a pivot 10 which supports roller 4 being housed within the
seat which is obtained in bar 1 itself.
[0017] When the hydraulic fluid under pressure is present within the elastic pipe 8, as
can be observed in Fig. 2, bar 1 is in its upward position, so that the series of
rollers 4 protrudes from the surface 14 of the press, thus allowing the sliding of
the die placed on top of it.
[0018] On the other hand, when the pressure is removed from pipe 8, the weight of the die
exerts itself on the bars 1, by means of the rollers 4, so that pipe 8 is deformed
and, as a consequence, it allows bar 1 and the rollers 4 to lower themselves until
they are flush with the surface of the press, as can be observed in Fig. 3.
[0019] On this subject it is important to notice that the value of the maximum theoretical
stroke imparted by pipe 8 to bar 1 must be approximately twice the actaul stroke required
for the lifting. This is due to the fact that the pressure acting within the pipe
exerts on the overlying bar and, therefore, on the die, a force which is proportional
to the surface of contact between the pipe and the surface of contact on the guiding
slot; as a consequence of this fact the highest lifting strength is impressed by the
pipe on the bar, when the deformation of the pipe is at its utmost, since in that
case the surface of contact is the largest. As the pressure within the pipe gradually
increases, the contact surface decreases, so the reaction force impressed by the pipe
on bar 1 decreases.
[0020] In actuality the force impressed decreases while the stroke increases and, therefore,
when the pressure has caused the maximum theoretical stroke, which corresponds to
the section of the pipe which has not been deformed, the pipe system can no longer
push the overlying die. So, in order to obtain a sufficient lifting of the die, it
is necessary to apply stroke values being intermediate in relation to the maximum
theoretical stroke.
[0021] Various tests performed with dies of different weights have further proved the just
expressed concept.
[0022] For instance, given a die weighing 3000 Kg, two 750 mm.-long pipes with an inner
diameter of 13 mm., a theoretical stroke of bar 1 corresponding to 3 mm. and a pressure
of 30 Atm., the actual stroke proved to be of 1,6 mm, while with 40 Atm. it was of
2 mm and with 60 Atm. it reached 2,2 mm.
[0023] On the other hand, given a die weighing 2000 Kg., with the same pipes at a 30 Atm.
pressure, the actual stroke of bar 1 proved to be 1,7 mm, with a 40 Atm pressure 1,9
mm and with a 60 Atm pressure 2,2 mm.
[0024] Thus, on the basis of what has been expressed herefore, already by the value of 30
Atm. the stroke reaches the desired value of 1,6 mm, which practically corresponds
to half of the maximum theoretical stroke of 3 mm.
[0025] Figs. 4 and 5 represent a construction variation of the device of the invention,
which adopts the same functional principle which has just been described, but differs
from it because of the different sliding element allowing the removal of the die.
In fact, instead of roller 4, a cylindrical support 11 carrying a small ball 12, which
is contained within an appropriate seat and surfaces upward, has been inserted into
bar 1. The arrangement of the elastic pipe 8 and the shape of bar 1 remain identical
to those of Fig. 1.
[0026] In Figs. 6 and 7 yet another constructive variation is represented, which is characterized
by the fact that the elastic pipe system 8 is housed within groove 13, having a practically
semi-cylindrical shape, obtained internally within guiding slot 2 of the die-supporting
table, instead of being obtained directly within bar 1.
[0027] This solution can easily be built, mainly in presses that are being manufactured,
while, if the system needs to be applied to already existing presses, the previously
described solutions are preferable.
[0028] The just described device according to the invention, especially suited to move dies
on the tables of presses, can actually prove to be very advantageous even when it
is used on surfaces or within the sliding tracks for the displacement of very heavy
materials or machinery, such as, for instance, tool machines while they are being
manufactured. In order to obtain this, it suffices to equip a work bench or a sliding
track with grooves housing the bars which are supported by elastic pipe systems under
pressure, as described herefore.
[0029] During the construction phase of the invention, construction variations can be applied,
concerning, for instance, the element allowing the displacement of the die, or the
arrangement of the grooves housing the pipe system. Each variation will still be included
within the scope of the just described inventive idea, such as it is defined in the
following claims.
1) A hydraulic lifting device especially suited to lift dies from presses, including
two or more bars (1), preferably shaped as a T, being inserted into the grooves of
the press table and supporting at their upper end sliding means (4, 12), characterized
by the fact that the lifting and lowering of the T-shaped bars and, as a consequence,
of the die, is obtained by means of the shape variation due to the elastic deformation
of pipe systems under pressure, arranged underneath the bars themselves.
2) A device according to claim 1), characterized by the fact that the elastic pipe
system (8) which is put under pressure and moves the T-shaped bar (1) is lodged within
a groove (5) obtained within the bar itself.
3) A device according to claim 1), characterized by the fact that the elastic pipe-system
(8), which is put under pressure and moves the T-shaped bar (1) is lodged within a
groove (13) being obtained within the guiding slot of the press table.
4) A device according to one of the preceding claims, characterized by the fact that
the lifting bar (1) presents elements for the sliding motion on the table, consisting
of rollers (4).
5) A device according to one of the claims from 1) to 3), characterized by the fact
that the lifting bar (1) presents elements for the sliding motion on the table, consisting
of balls (12) lodged within cylindrical supports (11).