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(11) | EP 0 941 833 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Control device of the stroke pressure in a conversion press |
| (57) In a press for converting shells in easy-open covers for food cans, constituted by
a bed (26), supporting a lower die shoe (5), four uprights (4) provided with longitudinal
guides (21) and a crown (1), supported by the uprights (4) and provided with motion
members (30) of a ram (3) supporting an upper die shoe (6) alternatively brought in
operative contact with the lower die shoe (5), said crown (1) and bed (26) being constrained
by means of connecting rods (9), a control device (40) of the press stroke pressure
comprises blocking members (10), placed near the ends of the connecting rods (9),
at least one of which has spacer means (30) from the crown (1), sensor members (7),
joined to the uprights (4) and fit to detect their longitudinal dimensional variations
of these last and control and command means (50) fit to elaborate the signals from
the sensor members (7) and consequently to operate the spacer means (30) in such a
way to contrast and compensate the dimensional variations of the uprights (4) allowing
a mutual die shoes stroke pressure dynamic regulation of the press (100). |
[0002] Particularly the invention concerns a control 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.
[0003] Conversion presses for semi-raw shells are known, including fixtures designed for converting such shells into easy-open covers, by virtue of a tab application that allows the opening of the same cover.
[0004] Known presses generally include a bed supporting lateral uprights on which is fastened, by means of tie rods extending through the uprights, a crown that generally supports the main drive means of the press motion members.
[0005] Sliding support guides for a ram, which supports the tooling of the press upper die shoe, are connected to the uprights.
[0006] 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.
[0007] These latter are placed for instance in succession in housings of a conveyor belt that carries the same through the press die shoes, 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.
[0008] The main disadvantage of prior presses is that the elevated stroke rate and the elevated work effort connected to the press running cause member elastic deformations, principally the movement ones, of the same presses. Moreover there are elongation effects by thermal expansion for such members.
[0009] 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.
[0010] 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 tab belt.
[0011] 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.
[0012] 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 eliminated.
[0013] 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.
[0014] Besides the different stroke pressure supply involves an increasing of noisiness and vibrations of the press.
[0015] This problem is commonly resolved heating the connecting rods causing their elongation so balancing the upright elongation happening progressively during the press running.
[0016] 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 needed.
[0017] 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.
[0018] Besides, since the required time for inducing temperature variations are rather long, only partially is possible to compensate the consequent drawbacks made on the formed cover.
[0019] 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 moving component are submitted during its running.
[0020] Other object of the present invention is to propose a device able to check and correct continuously the press stroke pressure and with quick response times.
[0021] Further object of the present invention is to propose a device of easy realization, reliable running and maintenance.
[0023] 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 an enlarged side view of the press in figure 2 where some portions have been removed for better showing others;
- figures 4a and 4b show a partially sectioned enlarged view of a detail in figure 3;
- figure 5 shows a block diagram relative to the driving device object of the present invention.
[0024] With reference to figures from 1 to 4b, with 40 is indicated a stroke pressure control device in a conversion press 100 of shells into easy-open covers for food cans, like drink or preserved food cans.
[0026] The bed 26 supports a lower die shoe 5 and four uprights 4, not interacting with the lower die shoe 5, placed to the sides of the lower die shoe and provided with longitudinal guides 21 turned toward the inside of the press 100.
[0027] The crown 1 is supported by the uprights 4 and is provided with motion members 60 of a ram 3, slidably guided by the longitudinal guides 21 and supporting an upper die shoe 6.
[0028] Lower 5 and upper 6 die shoes normally support dies or tools fit to progressive conversion of the shells into covers provided with tear tab.
[0029] Inside each upright 4 is housed a connecting rod 9 that maintains mutually constrained the crown 1 and the bed 26 through the co-operation with blocking members 10 placed near the ends of the connecting rods 9.
[0030] For each connecting rod 9, the blocking members 10 are essentially constituted by a bolt 24, screwed to the lower end of the relative connecting rod 9, and a ring nut 22 screwed to the upper ends of the connecting rod.
[0031] Spacer means 30 are seated inside the ring nut 22, that are constituted essentially by a ring piston 11 hydraulically driven by means of pressure fluid, through a duct 15, into the seat 27 made in the ring nut 22 and here placed also by virtue of seal rings 12 surrounding such seat.
[0032] The piston free end contacts the crown 1 for interposition of a spacer ring 14 fixed to the piston 11.
[0033] An external ring 13 is interposed between the ring nut 22 and the crown 1, placed externally to the spacer ring 14 and less high than this latter.
[0034] The 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, such as particular resistances.
[0035] With particular reference to figure 5, the device 40 includes also control and command means 50 receiving in input the signals of the sensor members 7 and sending a control signal, through an estensimetric device 8, to a comparator 16 between this signal and a predefined reference signal of the same device, connected to a flow regulator 17 acting on a hydraulic proportional valve 18 connected to the ring piston 11 through the duct 15.
[0036] The operation of this device 40 is simple since, once the press 100 is operated, the sensor members 7 send a signal proportional to the elongation (or shrinkage) of the uprights 4 to the estensimetric device 8 sending a control signal to a comparator 16 that compares this signal and a predefined reference signal of the device. This comparator 16 sends a signal to a flow regulator 17 that operates a hydraulic proportional valve 18 fit to check the fluid flow for putting in or pulling out from the seat 27 of the piston 11 so that respectively the ring nut 22 is moved away from the crown 1 in such a way of more stressing the connecting rod 9 or the ring nut 22 approaches the crown 1 so as to decrease the stress of the connecting rod 9.
[0037] In such way the stroke or closing pressure of the press 100 is dynamically regulated acting on the connecting rods 9 stress.
[0038] The distance between the crown 1 and the ring nut 22 is comprised between 0 and 10 millimeters, even if it is primarily comprised between 0 and 1 millimeter.
[0039] In a variant of the device 40 the sensor members 7 include also load cells 23 placed under the lower die shoe 5 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 control, in feedback way, through the activation of the spacer means 30.
[0040] Advantageously, the device 40, by means of the sensor members 7, detects any longitudinal variation of the uprights 4, particularly any elongation due to their heating and therefore control, in feedback, the starting tension of the connecting rods 9 through activation of the spacer means 30.
[0041] This device detects any upright length variation and therefore adjusts the strength applied during the press closing, by means of a rapid balancing of the thermal corrections occurring inevitably between inoperative or operative press conditions.
[0042] 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 components are submitted during the press operating.
1. Control device of the stroke pressure in a conversion press for converting shells
into easy-open covers for food cans, said press (100) including:
- a bed (26), supporting at least a lower die shoe (5) and at least two uprights (4), not interacting with said lower die shoe (5), and provided with longitudinal guides (21);
- a crown (1), supported by said uprights (4) and provided with motion members (60)
of a ram (3), slidingly driven by said longitudinal guides (21) and supporting at
least an upper die shoe (6) alternatively brought in operative contact with said lower
die shoe (5); said crown (1) and bed (26) being constrained by means of connecting
rods (9) provided with blocking members (10) placed near the end of said connecting
rods (9);
said device (40) being characterized in that comprises:
- ring nut means (22), fixed to at least one ends of each of sais connecting rods (9), provided with spacer means (30), spacing said ring nut means (22) from said crown (1);
- sensor members (7), joined to said uprights (4), and fit to detect longitudinal dimensional variations of these latter;
- control and command means (50) fit to elaborate the signals of said sensor members (7) and consequently to operate said spacer means (30) in such a way to contrast and compensate the dimensional variations of said uprights (4) allowing a mutual stroke pressure dynamic regulation of said press (100).
2. Device according to claim 1, characterized in that said spacer means (30) are seated in said ring nut means (22) and include at least
a piston (11), with operative axle parallel to the axle of said connecting rod (9),
and whose free end contacts said crown (1) and is fit to vary the distance from said
ring nut means (22).
3. Device according to claim 2, characterized in that the distance between said crown (1) and said ring nut means (22) is comprised between
0 and 10 millimeters.
4. Device according to claim 2, characterized in that said piston (11) is an hydraulically driven ring by means of a fluid forced into
the seat made in said ring nut means (22) and here contained by virtue of seal rings
(12).
5. Device according to claim 2, characterized in that between said ring nut means (22) and said crown (1) are interposed a spacer ring
(14) fixed to said piston (11).
6. Device according to claim 1, characterized in that said sensor members (7) are constituted by electric elongation sensors joined to
said uprights (4).
7. Device according to claim 1, characterized in that said sensor members (7) are constituted by load cells (23) placed under said lower
die shoe (5) and fit to send a signal proportional to the stroke pressure of said
press (100) to said control and command means (50).
8. Device according to claim 1, characterized in that said control and command means (50) receive in input the signals from said sensor
members (7) and send, by means of an estensimetric device (8), at least a control
signal to a comparator (16) between this last signal and a reference one, connected
to a flow regulator (17) driving an hydraulic proportional valve (18) for the pressure
control of a fluid in said spacer means (30).