Mechanical low-noise press, particularly of the screw type

Abstract: The present invention concerns a mechanical, low-noise press, particularly of the screw type, comprising a tup-bearing ram (12, 28) connected with a driving screw (13, 24), rotatingly connected with a lead nut (14, 21-23), which is integrally fixed on the frame supporting the press (10). The press also comprises sealing means (18, 19, 30) which define, together with the mating surfaces of the screw and of the lead nut, at least one chamber (16, 31), having a pre-determined volume, adapted to collect an incompressible medium, such as lubricating oil, and circulation means (16, 17, 19, 20) in order to maintain within said chamber a controlled delivery of the medium. Such delivery insures the presence of a constant spacing film of medium between the mating surfaces during the operation phases of the press, so as to prevent, during such phases, the direct contact between the screw and the lead nut, thereby absorbing the vibrations and the collisions generated by their interaction.

Description: The present invention concerns a mechanical, low-noise press, particularly but not exclusively a screw press of the fly or friction type. Such known types of press comprise a ram bearing a striking mass or tup, driven by a sturdy screw with a practically vertical axis, which engages a fixed nut thread which is integrally mounted on the machine vertical posts. The displacements of the tup are obtained by rotating the screw, generally by means of a central wheel keyed on its axis, such wheel being alternatively brought into contact with two lateral wheels, which are driven in opposite directions by a motor, so that one of the wheels controls the upward movement, the other one the downward movement of the tup. These presses, as well as others, are usually rather noisy, not so much because of the impact of the tup on the piece being formed or on the die, but rather because of the impacts and the collisions between the screw and the nut thread during the recovery of their mating backlash, following the action of the tup during the working phase. In fact, during the collision of the tup against the piece to be formed, its kinetic energy is transformed, in part, into deformation and heat transferred to the piece and, in part, it is transmitted to the screw and the nut thread, threby generating very high friction and overheating between the contact surfaces, with subsequent mechanical and acustic vibrations of very remarkable intensity. The noise level is further enhanced by the fact that, in general, the screw is made of high-resistance steel and the nut-thread is made of bronze, which materials give rise to different resonance phenomena induced by collisions and vibrations. Heretofore, many attempts have been made to reduce the noise level of such presses, mostly striving to acoustically insulating the structure of the machines from the rooms containing them, with rather unsatisfying results and at fairly high expense. As known, in all the machines of this type, a centralized, automatic, normal lubrication system is provided which obviously involves also the screw and nut-tread coupling. However, said lubrication pratically has no influence on the noise and the acoustic behavior of the assembly. In the German patent application DE-A-2 851 551, in the name of Reikle, a screw press is described which comprises a lubrication and cooling device for the screw/nut thread assembly, having the purpose of solving the problem of the high overheating of the two components during the working phase of the press. Such problem is solved by means of ducts arranged near the meshing threads, wherein a cooling medium, in the liquid or gas form, is forced. Said medium is collected into a supply tank and is brought into circulation by means of a pump or by gravity, after it has been cooled in a suitable external heat-exchanger. In a particular embodiment, the liquid medium is oil, collected in a chamber obtained between the bottom walls of the screw and of the nut thread, which thus form together a piston/cylinder assembly. Although this device improves the working conditions of the press and permits a reduction of the clearances between the screw and the nut thread, it is not without inconveniences since it leaves practically unchanged the contact conditions between these two components and it does not help, therefore, to decrease the noise level of the assembly. Although this device improves the working conditions of the press and permits a reduction of the clearances between the screw and the nut thread, it is not without inconveniences since it leaves practically unchanged the contact conditions between these two components and it does not help, therefore, to decrease the noise level of the assembly. Also the patent document GE-A-1.108.542 discloses a press of the screw type wherein the nut presents of each and of its threaded bore scaling means limiting a chamber trough which passes on incompressible medium moved by circulation means suited to maintain in such a chamber a controlled delivery medium. But not low-noise problems seem to have been afforded. The main object of the present invention is to eliminate the above-mentioned inconveniences, by providing a low-noise press of the screw type which affords actual and drastic reduction of the loudness of such machine, bringing about at the same time a further improvement in its working conditions. Another object of the invention is that of providing a low-noise press of such a simple structure as to make it possible to apply this arrangement even on already existing machines, without substantially modifying their original structure. Not the least object is that of creating a low-noise press which is technically reliable and easy to build by using components and materials which are present on the market, so as to be competitive from a purely economic point of view. The above mentioned objects and others, which will be better described hereafter, are reached by a mechanical press, in particular of the screw type, the main feature of which are according to claim 1. Such a device presents the advantages of: considerably reducing the overall noise of the machine; improving the mating between the screw and the nut thread, thereby reducing its wear; improving the lubrication system of the two mating elements and of the accessory elements; increasing the performance and the life-span of the machine; improving the working environment of the machine operators, also reducing environmentalpollution. Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter and from the enclosed drawings. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description and from the drawings, wherein: Fig. 1 represents a schematic front view of a screw press, which is partially sectioned, in order to show a first embodiment of the device according to the invention; Fig. 2 represents a perspective view of a detail of Fig. 1; Fig. 3 represents a schematic view of a detail of a press with a second embodiment of the device according to the invention. Fig. 4 represents a sectional view in an enlarged scale of the detail "A" of fig. 3. With reference to the mentioned Figs. 1 and 2, a screw press comprises essentially a supporting frame 10 with two posts 11 between which a ram 12, bearing a striking mass or tup, is vertically driven. Ram 12 is connected with the lower end of a driving screw 13, which engages a nut thread 14, which is integrally fixed on bed 10 and driven by a motor assembly for instance of the fly-type. According to the invention, sealing means are present, which delimit at least one chamber 16, presenting a pre-determined volume, which has the task of collecting an incompressible medium, preferably lubricating oil, and of keeping it between the mating surfaces of the screw and the nut thread. These sealing means may consist of a flexible sleeve 18, having the shape of a bellows, which can expand and contract depending on the strokes of the tup-bearing ram 12. The flexible sleeve 18 surrounds the driving screw 13, so that the medium contained therein is sent to at least one part of the mating surfaces of the screw and of the nut thread. The ends of the sleeve are sealed by means of a lower metal ring to the nut thread 14 and by means of an upper metal ring to ram 12. As an alternative, chamber 16 can be delimited by stiff sleeve elements - not represented in the drawings - which are arranged around screw 13 and are telescopically joined together, some of them being fixed on the ram, others on the nut-thread. Similary it will also be possible to provide such a chamber in the upper part of the screw and of the nut thread, or on both positions of said elements, so as to include the entire area of the mating surfaces. The medium is introduced into chamber 16 through the ducts 17. The circulation of the medium within the chamber or chambers can be realized in a forced way, starting from a reserve tank 19, by means of a pump 20. As an alternative, it can also be realized by cascade, starting from a tank placed at a suitable height. The discharge of the medium from chamber 16 can be realized by means of independent ducts - not shown in the drawings - and it can eventually be controlled by valve means, also not represented in the drawings. In any case, in chamber 16 there is constantly some medium, although in varying quantities, mutually spacing the mating surfaces of the screw and the nut thread. More precisely, between the mating threads, or at least a part thereof, there is a spacing film which prevents, or at leasts limits, the direct contact between the mating elements, so as to prevent them from colliding and to dampen the vibrations. Surprisingly, this solution permits to decrease the causes of the loud noise which characterizes the previous technique, so that the assembly has a considerably reduced loudness and permits to reach the objects of the invention. A second embodiment of the invention will now be described in detail with special reference to Fig. 3, wherein for clarity's sake some of the previously described elements constituting the machine have not been represented. In detail, the nut thread, indicated as a whole with reference number 21, comprises a fixed frame 22, presenting a toroidal shape, which encloses and supports a lead nut 23. A screw 24 is connected with a pre-determined tolerance with the lead nut 23 and bears on its upper end a flywheel 25 and on its lower end a ram or tup 26. At the ends of the lead nut 24 there are two fixed pilot sleeves indicated with 27 and 28 respectively. The upper face of the pilot boss 28 forms an abutting element for the upward movement of tup 26. Attached to the pilot sleeves 27 and 28 there are ring-shaped seals 29 and 30, made of metal or synthetic antifriction materials. Said ring-shaped seals delimit, together with the threaded surfaces of the lead nut and of the screw, chamber 31, adapted to collect the lubricating medium, as better shown in figure 4. At the end portions of chamber 31 there are the ducts 32 and 33, for the inlet and outlet of the medium, respectively. The oil can be forced through chamber 31 and the ducts 32 and 33 by means of a hydraulic pumping unit, comprising a pump P, a supply tank S and filter elements F. As an alternative, the circulation of the medium can be accomplished by gravity, starting from a supply tank - not represented - placed at a suitable height, supplied in turn by the central lubrication circuit of the press. In both cases, the medium delivery is so abundant and, at any rate, sufficient to insure the constant presence of oil in chamber 31 while the machine is on operation. Advantageously, at the top of the delivery duct 32, there is a venting orifice 34, opening to the atmosphere, so as to allow the chamber 31 to be purged of air and to be completely filled-up. The excess oil, overflowing from the venting orifice 34 and possibly also from the ring-shaped seal 29, will be collected in a first anular 35, which is partially enclosed by an elastic, deformable bellows 36, following the displacement of the screw. Similarly, the oil overflowing from the lower ring-shaped seal 30 will be collected in the second anular seat 37, which is also partially enclosed by an elastic bellows 38 or by a similar protecting element. In order to complete the description, it will be added that the pilot sleeve 28, which forms the abutting ledge for the tup 26, presents a height which is lower than the walls of the ring-anular 37, in order to prevent any deformation of the latter at the moment of the impact of the tup with the piece being formed. Moreover, the annular seats 35 and 37 are provided with the drainage 39, 40 which are connected with the outlet duct 33 and the collecting tank through a backflow duct 50. Similarly to what has been previously described concerning the first embodiment of the invention, also in this case, the medium is caused to circulate through chamber 31, where it creates a spacing film or liquid buffer between the threaded surfaces of the screw and of the lead nut, thereby preventing their contact during the active phases of the screw, particularly at the moment of the impact of the tup on the piece to be formed. In this connection, it can be observed that in the movement of the threaded surfaces relative to the interposed medium, a boundary layer is created, whose lift effect is similar to that of the plain bearings, said lift effect attaining its maximum thickness in the final part of the ram stroke. Finally it will be remarked that the above-described arrangementfor reducing loudness can be applied with the appropriate modifications even to presses with different driving systems, such as toggle presses or eccentric-shaft presses. The present press may set forth various changes and modifications which will, however, not exceed the scope of the invention, as defined in the appended claims.

Claims: A mechanical, low-noise press, particularly of the screw type, comprising a tup-bearing ram (12, 28) connected with a driving screw (13, 24) said screw meshing with a lead nut (14, 21, 22, 23) said nut being integrally mounted on the supporting frame of the press, comprising sealing means (18, 29, 30) adapted to limit together with the mating surfaces of said screw and of said lead nut at least one chamber (16, 31) having a pre-determined volume, said chamber being adapted to collect an incompressible medium, such as lubricating oil, and further comprising means for the circulation of said medium (16, 17, 19, 20, 33, 34), such as to maintain through said chamber a controlled delivery of medium and to insure the presence of a constant spacing film of medium, between the mating surfaces during the operation phases of the press, to thereby prevent, during such phases, the direct contact between the screw and the lead nut, and to dampen the vibrations and the collisions generated during their inter-action, characterized in that said at least one chamber (26,31) presents at its upper end a venting orifice (35) connected with the atmosphere. A low-noise press according to claim (1), characterized in that the means for the circulation of the medium comprise a delivery duct (32) supplied by gravity from a supply tank arranged at on appropriate height. A low-noise press according to one or more of the preceding claims, characterized in that proximately to each ring-shaped seal (29, 30) there is a flexible protecting sleeve (36, 38) for the collection of the excess medium overflowing from said sealing elements. A low-noise press according to one or more of the preceding claims, characterized in that it further comprises drainage ducts (39, 40) connecting said collecting sleeves with a supply tank (S). A low-noise press according to claim 1, characterized in that said at least one chamber (31) extends along the entire length of said lead nut and including an anular zoen above the upper end of said lead nut. A low-noise press according to claim 1, characterized in that said sealing means comprise an extensible wall (18) which surrounds at least one end of said screw, one end of said wall being attached to said ram or tup (12), the other end thereof being fixed to a portion of said lead nut (14), so that said chamber (16) has a variable volume, ducts (17) for the circulation of the medium and for the discharge of air being connected with said chamber. A low-noise press according to claims 6, characterized in that said wall (18) consists of a flexible or bellows-shaped sleeve. A low-noise press according to claims 6, characterized in that said wall consists of a plurality of telescopic sleeves elements, some of which are sealed to the lead nut (14), others are sealed to said screw (13) or to said tup-bearing ram (12). A low-noise press according to either claim 7 or 8, characterized in that said chamber (16) is formed in the upper section of said lead nut (14) near the upper support of said screw (13). A low-noise press according to either claim 7 or 8, characterized in that said chamber (16) is formed in the lower section of said lead nut (14) near said tup-bearing ram (12). A low-noise press according to either claim 7 or 8, characterized in that said chamber (16) comprises on upper section, near the upper end of said lead nut, and a lower section, near the lower end of said lead nut.

Inventors: CAMOSSI ROBERTO, CAMOSSI, ROBERTO
Applicants: VACCARI SPA, VACCARI S.P.A.
Application year: 1989
Main classification: B30B1
IPC codes: B30B15, B30B1