Continuously Operating Press

The present invention relates to an improved press for producing boards such as chipboards, fiberboards, and the like. My recently issued U.S. Pat. No. 4,004,873 discloses the general type of press which the present invention also relates to. To the extent necessary for an understanding of the present invention, the subject matter of this patent is incorporated herein by reference thereto.

The above-noted patent relates to a continuously operating press, especially a prepress, for a mat for manufacturing board, such as chipboard, fiberboard, or the like, with two endless-plate conveyors or belts, consisting of plates articulated together, said conveyors being mounted one above the other and traveling about axes located horizontally and parallel to one another, the sections of said conveyor facing one another being drivable in the same direction by pressure rollers. Each of the endless-plate belts are surrounded by an endless steel belt or pressing band which is pressed against the material being pressed by way of the belt plates. In each of the chambers surrounded by the endless pressing band (viewed in the direction of motion of the adjacent sections of the endless-plate belt) at least one high pressure roller is disposed beyond the endless-plate belts, the diameter of said high pressure rollers being greater than the diameter of each pressure roller. The high pressure rollers which produce a high-pressure zone and are surrounded by the respective two endless pressing bands are mounted in the same vertical plane. At least one of the high pressure rollers is drivable, and at least one of these high pressure rollers is movable in the direction of the other with an adjustable pressure force, and the pressure between the high pressure rollers is much higher than the pressure between the pressure rollers acting on the plate belt (low-pressure zone).

Although presses of the type referred to above have operated satisfactorily, especially when used as prepresses, they suffer from the disadvantage that the sliding elements disposed between the outlet of the endless-plate belts and the high pressure rollers forming the high-pressure zone, said sliding elements being designed to prevent the prepressed mat from springing off, are subject to relatively rapid wear. This can be eliminated by providing the surfaces of the sliding elements which face the endless steel belt (pressing band) with a coating which reduces the frictional forces which develop, for example, a coating of Teflon. Such a solution has certain advantages, but is not an optimum solution for all cases.

Therefore, an object of the invention is to improve the above-mentioned presses in such manner that there is practically no further wear of the parts which are designed to prevent the mat from springing off at least beyond the endless-plate conveyors. Moreover, the present invention is designed to prevent springing off of the material beyond the high pressure rollers that form the high-pressure zone. These and other objects are achieved according to the invention by surrounding each of the high pressure rollers forming the high-pressure zone with a high pressure endless belt disposed between the roller and the endless steel belt (pressing band). In particularly preferred embodiments, the high pressure belt is formed of polyamide material with said high pressure belt being guided over a reversing roller, said reversing roller being designed as a pressure means for the high pressure belt, being provided against and next to the endless steel belt (pressing band) surrounding the corresponding endless-plate belt. Particularly preferred embodiments also include the provision that the endless polyamide belts are of a thickness such that springing off of the mat pressed in the low-pressure zone is prevented. This is accomplished by converting the previous sliding friction into rolling friction, with much less resistance. Tests have shown that endless polyamide belts should have a thickness of about 4 mm. Although such an endless polyamide belt 4 mm thick is relatively stiff, long-term tests have shown that this belt is not damaged, although it is deformed around radii of curvature between 225 mm and 750 mm. Thus, for example, the rollers acting as the pressure means against the polyamide belt on the endless steel belt have a diameter of 450 mm, the high pressure rollers forming the high-pressure zone have a diameter of 1500 mm, and the reversing rollers provided with control means have a diameter of 660 mm; in other words the radius of curvature of the endless polyamide belt is constantly undergoing change.

Furthermore, it is provided in preferred embodiments that a second reversing roller is present for each endless polyamide (high pressure) belt, said second reversing roller being provided with control means to prevent the endless polyamide belt from shifting sidewise.

According to other preferred embodiments, three reversing rollers are provided for each high pressure endless polyamide belt, wherein the third reversing roller as viewed from the direction of movement of the corresponding endless polyamide belt is disposed beyond the high pressure roller forming the high-pressure zone and the spacing of the rotational axes of this third reversing roller must be set such that the space between the outer endless belts (pressing bands), which preferably consists of steel or plastic, is precisely the same size in the vicinity of the third reversing roller as in the vicinity of the high pressure rollers that form the high-pressure zone. This arrangements provides that the mat, compressed by the high pressure rollers forming the high-pressure zone, is able to spring back only on a delayed basis, which is particularly important in the manufacture of thick boards to avoid cracks. If the continuously operating press is stopped for some reason, the part of the mat which is influenced by the high-pressure rollers forming the high-pressure zone is subject to practically linear influence and this differential thickness of the mat would lead to crack formation when the press was started again. These cracks are advantageously avoided by providing the third reversing roller beyond the rollers forming the high-pressure zone.

It is also contemplated according to other preferred embodiments of the invention, to go one step further to improve the long-term resistance of the endless polyamide belts (high pressure belts) by providing more than three rollers for each endless polyamide belt and ensuring that the length of each endless polyamide belt is greater than the circumferential length of each of the endless-plate belts and smaller than the length of the corresponding outer endless belt. This reduces the number of changes caused by the variations in the radius of curvature of the reversing rollers and also results in a more uniform mat or a more uniform board path, because the polyamide belts which surround the endless-plate belt distribute over their outer surfaces the pressure exerted by the endless-plate conveyors and the pressure rollers. Moreover, the mat is prevented from springing back in the area between the endless-plate conveyors and the following rollers by this arrangement.

These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.

FIG. 1 is a partial schematic side view showing the outlet section of a continuously operating press with endless-plate conveyors, the rollers forming the high-pressure zone, and endless polyamide belts which are each guided over two reversing rollers, constructed in accordance with a first preferred embodiment of the invention;

FIG. 2 is a view similar to FIG. 1, which shows a second preferred embodiment of the invention, with three reversing rollers; and

FIG. 3 is a view similar to FIG. 1, which shows a further preferred embodiment of the invention, modified in such fashion that the endless polyamide belts which surround the rollers forming the high-pressure zone are also guided around the endless-plate belts.

In view of the state of the art, as exemplified by my above-noted U.S. Pat. No. 4,004,873, and in order not to obscure the present invention, the drawing figures and this description do not include certain details of the press such as the pressing means acting on the plates of the plate belts, and the driving means for the various belts. However, one skilled in the art should be readily able to practice the invention disclosed herein, especially in view of the incorporation by reference of my U.S. Pat. No. 4,004,873.

Throughout the various Figures, like reference numerals are used for like or similar structural features.

FIG. 1 shows only portions of the low-pressure zone of a continuously operating press, with the endless-plate conveyors or belts 3 and 4 mounted one above the other, each of which is surrounded by an endless belt or pressing band 48 or 47, whereby in the outlet area of the press two high pressure rollers 36 and 37 which form the high-pressure zone are disposed in the space surrounded by endless belts 48 and 47. In all embodiments illustrated, schematically depicted pressure applying means P, such as piston-cylinder mounted rollers, force the plate sections against the pressing band 48 in a manner disclosed in more detail in my above-mentioned U.S. Pat. No. 4,004,873. The upper pressure rollers 36 are preferably movably mounted with adjustably movable bearing supports M, such as piston-cylinder supports, in a manner also disclosed in more detail in my U.S. Pat. No. 4,004,873.

According to one aspect of the invention, each of the high-pressure rollers 36 and 37 forming the high-pressure zone is surrounded by an endless polyamide belt 73 or 74 disposed between it and the corresponding endless belt 48 and 47. The endless polyamide belts are guided over at least one reversing roller (75, 77), said reversing roller (75, 77) being designed to serve as a pressure means for pressing the endless polyamide belts against endless belts 48 and 47. In addition, an additional reversing roller 76 and/or 78 is provided. Rollers 76 and 78 are provided with a control means 79 and 80 to prevent the endless polyamide belts from shifting sidewise. Rollers 75 and 77, designed as the pressure means and influenceable by pressure cylinders 81 and 82, are disposed one above the other exactly like the high pressure rollers 36 and 37 forming the high-pressure zone, so that in the area in which polyamide belts 73 and 74 are in contact with endless belts 48 and 47, pressure forces can be exerted which are higher than the pressure forces exerted by the low-pressure rollers (not shown here) on endless-plate conveyors 3 and 4.

Essentially, it would suffice to guide endless polyamide belts 73 and 74 only around rollers 75 and 36 and 77 and 37, but this would pose certain difficulties, as far as preventing the two endless polyamide belts from shifting sidewise is concerned. It is more advantageous to achieve a solution using reversing rollers 76 and 78, because the sidewise slippage of the endless polyamide belts can then be controlled more precisely.

Likewise, in FIGS. 2 and 3, only the low-pressure zone of a continuously operating press is shown by the endless-plate conveyors 3 and 4 mounted one above the other, each of which is surrounded by an endless belt 48 or 47, whereby in the outlet area of the press the two high-pressure rollers 36 and 37 forming the high-pressure zone are disposed in the areas surrounded by endless belts 48 and 47.

Each of the high-pressure rollers 36 and 37 forming a high-pressure zone is surrounded by an endless polyamide belts 73 and 74 disposed between it and the corresponding outer endless belt 48 or 47, said endless polyamide belt being guided over three reversing rollers 75, 76 and 83 and 77, 78 and 84, with reversing rollers 75, 83, and 77, 84 being designed to serve as pressure means to press endless polyamide belts against the outer endless belts 48 and 47, while reversing rollers 78 and 78 are provided with control means 79 and 80 to prevent these endless polyamide belts from shifting sidewise. Rollers 75, 83 and 77, 84 designed as pressure means are disposed one opposite the other in exactly the same manner as rollers 36 and 37 which form the high-pressure zone. The compressive forces exerted by rollers 75 and 77 via endless polyamide belts 73 and 74 and endless belts 48 and 47 are dimensioned such that the mat compressed by the endless-plate conveyors 3 and 4 via endless belts 48 and 47 cannot spring back. The same is true of rollers 83 and 84 with respect to the compressive forces which are exerted by high-pressure rollers 36 and 37. Therefore, one must ensure that the space between rotational axes 85 and 86 of reversing rollers 83 and 84 are spaced such that the space between the outer endless belts 47 and 48 in the area of the third reversing rollers 83 and 84 is exactly the same size as in the vicinity of rollers 36 and 37 forming the high-pressure zone.

To adjust the pressure or vary the spacing of reversing rollers 75 and 77 and 83, adjustable pressure cylinders (fluid operated piston-cylinder devices) 81, 82 and 87 are mounted on the corresponding reversing rollers.

Reversing rollers 83 and 84 can also be provided on continuously operating presses which do not have endless-plate conveyors, but only a plurality of rollers around which the endless polyamide belts are guided, because then the compressed mat could be prevented from springing back and crack formation could be prevented.

The embodiment shown in FIG. 3 differs from the embodiment in FIG. 2 essentially only in that endless belts 73' and 74' are brought around between the outer endless belts 48 and 47 and endless-plate conveyors 3 and 4, so that the change in the radius of curvature during each cycle of an endless polyamide belt is reduced and the expansion of the precompressed mat leaving the low-pressure zone is avoided up to rollers 75 and 77. Also, the belts 73' and 74' are necessarily longer than the respective plate belts and shorter than the pressing bands 47, 48.

While I have shown and described various embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to those skilled in the art and I therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.