A DEVICE FOR GUIDING A PLUNGER OF A JACK

Abstract: A device for guiding a plunger (3) of a jack (2), comprising at least one hinged mechanism having an overall parallelogram arrangement in turn comprising members as follows: two con rods (4) having first ends thereof hinged to the plunger by means of pivots (14); two squared elements (5, 6) hinged on two shafts (15, 16) which have axes that are parallel to axes of the pivots (14) and to which second ends of the con rods are hinged at predetermined distances from the two shafts; a connecting element functioning as a con rod (7) and having ends hinged to the squared elements.

Description: Description A Device for Guiding a Plunger of a Jack. Technical Field The invention relates to a device for guiding a plunger of a jack. Specifically, though not exclusively, the invention is usefully applied in the field of hydraulic jacks in presses, having large non-circular plungers (elliptic, oval, rectangular etc.) Background Art At present one of the factors limiting the force which a hydraulic press is able to develop is the small active area of the piston itself. The active area of the piston is in fact directly proportional to the force the press can exert. For this reason, if an increase in force is desired, it is necessary either to increase the active area of the piston, or to increase the pressure with which the oil is pumped internally of the cylinder. The technology presently used makes use of large hydraulic jacks where raising oil pressure above 400 bars is either unreliable or uneconomical. Therefore, if an increase of pressing surface (up to above three metres by one metre) is required, needing a like increase in the force of the press, the only method available is that of increasing the active area of the piston. In the ceramic field in particular the surfaces to be pressed are always rectangular, and for a perfect pressing operation it is necessary to use pistons which are of as close a shape as possible to the shape of the objects to be pressed (i.e. rectangular pistons with bevelled edges, or at least oval). By using normal circular pistons a large part of the active area is lost, which means that in order not to lose a part of the pressing force an excessive increase in hydraulic oil pressure is required. On the other hand, the use of oval or rectangular pistons is at present prevented or gravely limited by the difficulty of uniformly raising and lowering the piston itself (i.e. with the piston pressing surface constantly parallel to the plane to be pressed). This is because of the small differences in the reaction springs located in the corners, or perhaps merely the differences in friction of the elastic strips in the liner; in an elongate hydraulic piston these factors can cause small rolling or jolting movements as the arm rises or lowers. The above situation can at present be obviated only by applying small balancing pistons to the corners of the main piston, which small pistons are individually controlled and fed through very fϊnely-tuned electronically-regulated valves. With these devices, controlled through a PLC thanks to precise sensors located on the piston corners, an oval or rectangular piston can be made to rise and lower correctly and precisely. These are, however, sophisticated applications which make the whole apparatus functionally rather complex and very expensive. The present invention offers a valid and viable alternative to the above-described hydraulic-electronic systems, and is characterised by a completely mechanical operation and structure. The advantages of the invention are mainly connected with its substantial simplicity, making it extremely reliable. These aims and advantages and more besides are all attained by the object of the invention, as it is characterised in the appended claims. Further characteristics and advantages of the present invention will better emerge from the detailed description that follows of a preferred but non-exclusive embodiment of the invention, illustrated purely by way of a non-limiting example in the accompanying figures of the drawings, in which: figure 1 shows part of a schematic and partly-sectioned vertical elevation of a press equipped with the device of the invention; figure 2 is a perspective schematic view of the invention. Disclosure of Invention With reference to the figures of the drawings, 1 denotes in its entirety a press having a jack 2 with a non-circular section, in particular elliptical. The press 1 is used to compact ceramic powders 8 to obtain generally rectangular products. In the described case, the rectangular pressing surface is very large and the elliptical plunger 3 of the jack 2 is also of a considerable size. The problem of raising and lowering the plunger 3 uniformly, i.e. with the mobile pressing surface constantly parallel to the fixed pressing plane, is solved by using at least one hinged mechanism, basically a parallel-bar link comprising the following members: two con rods 4 having their first ends hinged to the plunger 3 by means of pivots 14; two squared elements 5, 6 hinged on two shafts 15, 16 having axes which are parallel to those of the pivots 14 and to which the second ends of the con rods 4 are hinged at predetermined distances from the shafts 15, 16; a connecting element, i.e. a connection element functioning as a con rod 7 and having ends hinged to the squared elements 5, 6. This hinged mechanism has the special characteristic that at least one of its members is elastically deformable to a predetermined degree. In particular, in the preferred embodiment illustrated in the figures, two hinged mechanisms are present, having as mentioned an overall parallelogram shape, being identical and arranged symmetrically with respect to a halfway median plane parallel to the direction of the plunger 3 stroke. The symmetrically arranged and aligned squared elements 5, 6 of the two hinged mechanisms are both solidly constrained to ends of the two shafts 15, 16. The shafts 15 and 16 are coupled in seatings which are made solid to the jack 2, and are freely rotatable about their own axes. The elastically deformable members are mainly the con rods 4 which are so conformed and structured as to exhibit a flexional elastic deformability, enabling their length to vary. For this aim the con rods 4 exhibit a non-straight natural configuration even in the absence of flexional solicitation. The action of the described two hinged mechanisms maintains the plunger 3 constantly parallel to the fixed pressing plane. When the plunger reaches the end of its upper stroke, with the con rods 4 in their most vertical position, and begins to compact the ceramic material, any lack of uniformity in the ceramic material induces the plunger to follow the non-uniform arrangement of the material and to be arranged not-exactly parallel to the fixed pressing plane. This tendency of the plunger is opposed by the two hinged mechanisms, but the elastic deformability of the con rods 4 enables the plunger to adapt and assume a not-perfectly-parallel position with regard to the fixed pressing plane. This elastic deformability is calculated in such a way as to enter into play during the pressing phase when the forces reach certain predetermined levels. Advantages of the present invention are its simplicity and reliability. Furthermore, the invention guarantees optimum pressing of the ceramic powders (in terms of umformity) even where the material to be pressed has been loaded unevenly. Also, thanks to its elastic deformability, the invention protects the mechanism against any eventual overloads.

Claims: Claims. 1). A device for guiding a plunger of a jack, comprising at least one hinged mechanism having an overall parallelogram arrangement, which at least one hinged mechanism comprises members as follows: two con rods having first ends thereof hinged to the plunger by means of pivots; two squared elements hinged on two shafts, which two shafts have axes which are parallel to axes of the pivots and to which second ends of the two con rods are hinged at predetermined distances from the two shafts; a connection element functioning as a con rod and having ends hinged to the squared elements. 2). The device of claim 1, wherein at least one of the members of the hinged mechanism is predisposed to deform elastically to a predetermined degree. 3). The device of claim 1 or 2, comprising two hinged mechanisms having overall parallelogram arrangements, being identical one to another and arranged symmetrically with respect to a median plane which is parallel to a direction of a piston stroke. 4). The device of claim 3, wherein the symmetrically arranged and aligned squared elements of the two hinged mechanisms are solidly constrained to ends of the two shafts. 5). The device of claim 4, wherein the two shafts are torque shafts. 6). The device of claim 4 or 5, wherein the con rods are structured and conformed in order to be elastically deformable up to a predetermined degree. 7). The device of claim 6, wherein the elastic deformability of the con rods is flexional; the con rods having a configuration which is not straight when not solicited. 8). The device of any one of the preceding claims, wherein the shafts are freely rotatably coupled about axes thereof, and pivoted at seatings which are solidly connected to the jack.

Inventors: STEFANI FRANCO, STEFANI, FRANCO
Applicants: RONFLETTE S A, STEFANI FRANCO, RONFLETTE S.A., STEFANI, FRANCO
Application year: 2001
Main classification: F15B15
IPC codes: B30B15, F15B15