Continuous press with low-friction sliding device

Abstract: A continuous press device comprises metal belts (14, 15) shaped into a ring which slide with their sections facing each other and each close to a plate (12, 13) of a press. Disposed between each plate (12, 13) of the press and the respective section of belt (14, 15) are supporting devices (17, 18) to enable it to slide with a minimum of friction. Each sliding device (17, 18) comprises a plurality of parallel pins (21, 21') each being provided with a row of roller bearings (22, 22'). Rollers (25, 25') are freely supported to rest on each adjacent row of bearings (22, 22') and on the relative section of the belt (14, 15) facing the plate of the press.Moreover, in axial passages in the rollers (25, 25') heat is generated in material (16) which is subjected to pressure between the belts (14, 15) by means of heating elements (16, 26') or by the direct flow of heated fluid.

Description: There are known presses of the continuous type, in which there are usually two metal belts joined to form a ring in order to slide overlapped between the press plates, thus transporting the material to be pressed, generally in the form of a continuous strip, such as for example multi-layer laminated plastic, particle board, fibreboard, plywood, strips of rubber, PVC or the like. One problem in such presses is ensuring that the metal belts and the press plates to slide together with as little friction as possible despite the considerable pressure exerted by the latter. One solution proposed, for example, consists of continuous presses in which a film of oil or pressurized air is disposed between the press plates and the belts in order to keep the plates and the belts apart and thus ensure their reciprocal sliding. Unfortunately, such presses present numerous drawbacks. For example, in the case of oil film separation, the oil tends to seep out of the sides of the press, soiling the material being pressed, and making it necessary to top it up. In the case of air separation, it is not possible to obtain high pressing forces and it is therefore necessary to make do with pressures which are insufficient for various high-quality productions. Moreover, in both types of presses, if the material to be pressed is not even, the consequent overpressures in circumscribed areas of the belts cause local voids in the separating fluid resulting in momentary contact and consequent seizure between the belts and the press plates. Continuous presses have also been proposed in which the belts slide over the press plates by means of rollers which run freely along the press plates transported by the movement of the belts. It is not possible to support the rollers only at the ends because the forces generated by the press would tend to curve them due also to their necessarily limited diameter. These presses consequently require a complex and costly mechanism which collects the rollers once they have reached one end of the press and transfers them to the opposite end. In addition to the complexity of the mechanism, this type of press has the disadvantage that the idle rollers can easily become disaligned, resulting in their dragging or seizure, which also causes the belt to side skid. Disalignment can be caused for example by inserting the rollers slightly out-of-plumb with respect to the direction of movement of the belts, tapering of the rollers due to wear, tolerances, uneven temperatures along the axis of the rollers, dirt which has worked its way into the press, unevenness of the material being pressed which generates irregular pressure on the moving rollers, etc. Moreover, continuous presses usually have to simultaneously subject the pressed material to heat and this is done in roller-type presses by heating the press plates on which the rollers rest so as to transmit the heat through the rollers themselves to the metal belts and from the latter to the material. Unfortunately, the heat transmission efficiency is low, since the heat is transmitted by the rollers only through two generating lines. Moreover, continually removing the rollers from one end of the press and reinserting them at the other causes them to cool down, resulting in a further deterioration of their function of heating the material. DE-A-2 853 285 discloses a continuous press device as claimed in the preamble of claim 1 The general scope of this invention is to obviate the aforementioned problems by proving a continuous press with sliding belts in which the friction between the belts and the press plates is reduced to a minimum, without the need for complicated mechanisms, and in which the heat required for heating the material being pressed is transmitted more efficiently. This scope is achieved, according to the invention, by providing a continuous press device of the type comprising metal belts shaped into a ring which slide with their sections facing each other and each close to a plate of a press, a device being disposed between each press plate and the respective section of belt to enable it to slide with a minimum of friction, each sliding device comprises a supporting element fitted on the plate of the press to support in a plurality of longitudinally spaced apart areas a plurality of parallel pins each being fitted with a row of roller bearings, characterized by the fact that rollers are freely supported to each rest on each pair of adjacent rows of bearings and on the relative section of belt facing the plate of the press. Moreover, said continuous press device is further characterized by the fact that the freely supported rollers are hollow cylinders with axial passages traversed by heating elements. The innovatory principles of this invention and its advantages compared to the known technique will be more clearly evident from the following description of a possible exemplificative embodiment applying such principles, with reference to the accompanying drawings, in which: figure 1 shows a schematic side view of a continuous press made according to the invention; figure 2 shows a partial plan view of a detail of the press of figure 1; figure 3 shows a cross-sectional view along the line III-III of figure 2; figure 4 shows a cross-sectional view along the line IV-IV of figure 2. With reference to the figures, figure 1 shows a schematic side view of a continuous press device, generically indicated by reference 10, made according to this invention. The device 10 comprises a press 11, between the head 12 and the base 13 of which slide two metal belts wound into a ring 14 and 15, respectively. The belts 14, 15 are powered to move forward in synchronism so as to transport between the press plates 12 and 13 a continuous strip 16 of material to be pressed, for example laminated plastic sections or the like. Between each press plate 12, 13 and the respective belt 14, 15 is disposed a rolling device 17 and 18, respectively, which transmits the pressure of the press and at the same time allows the belt to slide without excessive friction. Figures 2, 3 and 4 show enlarged views of the aforementioned rolling devices. Since they are substantially identical the following description refers explicitly to only one of them and, wherever necessary, the corresponding elements of which the other device is composed are indicated with the same reference number preceded by the suffix "prime". As can be clearly seen in figures 2 and 3, each device is composed of a plate 19 carrying supports 20 for parallel pins 21 provided with rolling elements comprising rolling bearings 22, for example roller bearings, disposed in groups between the supports 20. Antifriction washers 23 are disposed between each support and the respective group of bearings. Stop collars 24 are disposed at the ends of the pins. Between each row of bearings placed side by side on adjacent pins rests a hollow cylinder 25 which rotates freely on the bearings 22. In figure 2, said cylinders are been partially removed to display the bearings underneath. As can be more clearly seen in figure 3, each hollow cylinder 25 is axially traversed by a heating element 26 placed between shoulders holding the cylinders in place. The heating element can, for example, either be made in the form of an electric resistor or in the form of a duct with heated fluid flowing through it. The partial cross-section of figure 4 shows a schematic assembly of the two rolling devices 17 and 18 secured to the plates of the press. The supporting plates 19, 19' have ducts 28, 28', respectively, to enable a coolant to circulate through them if necessary, so as not to transmit excessive quantities of heat to the press. It will be clear at this point that the intended scopes have been achieved. When the press is in operation each cylinder 25 is made to rotate on its axis by the sliding movement of the belt which is supported in a substantially uniform fashion by the large number of cylinders placed closely together side by side. The cylinders 25 are in turn supported by the bearings 22 which enable them to roll with a minimum amount of friction and at the same time prevent them from flexing, while enabling very small diameters to be used so as to distribute the pressing pressure extremely evenly. The pins supporting the bearings do not flex inasmuch as they are supported at regular intervals by the supports 20. The material subjected to pressing is heated extremely efficiently since the heating elements are directly inside the cylinders and the heat is consequently transmitted to the belts without the need for large thermal resistances, also due to the presence of only one contact generator. At the same time, the rest of the press can be kept substantially cool by means of the cooling circuit provided in the plates 19, 19'. This makes it possible to obtain a very sturdy and relatively inexpensive continuous press, without the need to provide complicated devices for moving the idle rollers of the belts or to create fluid sliding layers. Moreover, the cylinders 25, 25' can be quickly and easily replaced whenever they wear out. The foregoing description of an embodiment applying the innovatory principles of this invention is obviously given by way of example in order to illustrate such innovatory principles and should not therefore be understood as a limitation to the sphere of the invention claimed herein. For example, the number of supports and bearings provided in conjunction with the pins 21 can differ from the number shown in order to adapt to particular load conditions envisaged while the press is in operation and to the size of the latter. Moreover, the rollers 25 can be heated by circulating hot fluid directly through their axial cavities, by providing airtight feed ducts, as will be obvious to any technician.

Claims: Continuous press device of the type comprising metal belts (14, 15) shaped into a ring which slide with their sections facing each other and each close to a plate (12, 13) of a press, a device (17, 18) being disposed between each press plate (12, 13) and the respective section of the belt to enable it to slide with a minimum of friction, each sliding device (17, 18) comprises a supporting element (19, 20, 19', 20') fitted on the plate of the press to support in a plurality of longitudinally spaced apart areas a plurality of parallel pins (21, 21') each being fitted with a row of roller bearings (22, 22'), characterized by the fact that rollers (25, 25') are freely supported to rest on each pair of adjacent rows of bearings (22, 22') and on the relative section of the belt (14, 15) facing the plate of the press. Continuous press device as claimed in claim 1, characterized by the fact that the freely supported rollers (25, 25') are hollow cylinders with axial passages traversed by heating means. Continuous press device as claimed in claim 1, characterized by the fact that disposed between each sliding device (17, 18) and the corresponding press plate (12, 13) is a supporting plate comprising ducts (28) traversed by a cooling fluid. Continuous press device as claimed in claim 2, characterized by the fact that the heating means comprise heating elements with electrical resistances. Continuous press device as claimed in claim 2, characterized by the fact that the heating means comprise ducts for conveying hot fluid. Continuous press device as claimed in claim 1, characterized by the fact that disposed close to the ends of the rollers (25, 25') are shoulders (27) for holding the rollers in place.

Inventors: PAGNONI GIORGIO, PAGNONI, GIORGIO
Applicants: PAGNONI IMPIANTI S P A, PAGNONI IMPIANTI S.P.A.
Application year: 1991
Main classification: B30B5
IPC codes: B30B5