The present application claims priority under 35 U.S.C. xc2xa7 119 of German Patent Application No. 199 02 274.7, filed on Jan. 21, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to a wire section of a machine for producing a fibrous material web, e.g., a paper or cardboard web, having a twin wire zone formed between two revolving endless wire belts, and a revolving flexible support belt located in a vicinity of the twin wire zone that supports at least one of the two wire belts. The revolving flexible support belt is positioned inside the loop of the at least one wire belt. The present invention also relates to a belt guidance device for the wire section, and a process for forming a fibrous material web in the wire section.
2. Discussion of Background Information
In a known twin-wire former, an inside surface of one of the two wire belts is, as a rule, guided over a former cylinder located in the vicinity of an inlet nip of the twin wire zone. In order to provide greater curvature radii, correspondingly dimensioned former cylinders must be used, which considerably increases the demand for space.
A wire section of the type generally discussed above is disclosed, e.g., in DE 44 20 801 A1. In such a wire section, an endless flexible support belt is provided instead of a former cylinder and is guided by three deflection rolls in a generally triangular course.
The present invention provides a wire section of the type generally discussed above that also provides that the wire belts are guided in the support region along a path with the greatest possible curvature radius, and with a minimal space requirement for wire belt guidance. Furthermore, a suitable belt guidance device and a process for forming the fibrous material web in the wire section is provided.
Accordingly, the instant invention provides a wire section in which the flexible support belt, which is generally guided in or along an at least essentially circular cylindrical path, is guided in the support region along a path which deviates from a circular cylindrical path and which has a greater average curvature radius than a radius of the circular cylindrical path. Further, the average curvature radius is greater than an average curvature radius of the entire path that the support belt passes through.
Based on the exemplary embodiment, greater curvature radii are possible in the support region of interest without having to simultaneously accept a correspondingly greater structural volume. The space requirement for the respective support belt guidance can be practically independent of a respective curvature radius in the support region and can be reduced to a minimum corresponding to the at least essentially circular cylindrical guidance.
The flexible support belt preferably has an open outer circumference surface that is used to store water. Thus, the outer circumference surface can, for example, be profiled and/or provided with blind bores. In particular, it can be grooved, bored, and/or blind bored, and/or can have a knob structure. In the latter case, the knobs can have a circular or square cross section, for example.
In an alternative exemplary embodiment of the wire section according to the invention, the flexible support belt can be guided in the support region by way of internal support elements that are spaced apart from one another in the web travel direction. The wire belt provided on the side of the twin wire zone remote from the support belt can preferably be acted on by internal pressing elements, which can be pressed against it in a flexible manner and can be located opposite from intermediary spaces between the support elements. The two wire belts, together with the fibrous material web formed between them, can then be pressed against the flexible support belt, particularly by the pressing elements.
The pressing elements can be constructed, e.g., of former strips or the like.
In certain cases, it can be advantageous for the pressing elements to be provided in combination with a forming box.
In another exemplary embodiment, the wire belt provided on the side of the twin wire zone remote from the support belt can be internally acted on by suction elements, e.g., slot suction elements, which are disposed opposite the support elements and/or opposite the intermediary spaces remaining between them.
In certain cases, it can be useful for the flexible support belt to be guided in at least one other region along a path that extends inside the circular cylindrical path, with the resulting additional space produced being at least partially taken up by another element of the machine, e.g., the headbox. The other region can be defined, e.g., by two internal support elements disposed spaced apart from one another, between which the flexible support belt travels in a straight line.
In order to guide the flexible support belt on the support elements, an inner region of the support belt loop, which is remote from the support element region and sealed off from it, can be subjected to overpressure. In another embodiment, the flexible support belt is guided around an internal tube and the annular space formed between the internal tube and a support belt is divided by sealing elements into a region that contains the support elements and a region that is subjected to overpressure. The overpressure can be, e.g., approximately 50 to 100 mbar and can be adjusted to, e.g., approximately 60 mbar. Fundamentally, however, other values are also conceivable.
The revolving flexible support belt may be laterally fixed in a suitable manner by covering disks or the like.
Internally, the flexible support belt can be lubricated in particular with fluid, e.g., with water, oil, and/or the like, and the support elements can be correspondingly designed for a lubrication of this kind. In this connection, a hydrodynamic and/or hydrostatic lubrication can be provided.
The belt guidance device according to the present invention includes a plurality of support elements located inside a loop of a flexible support belt, which are arranged so that the flexible support belt is guided in an at least essentially circular cylindrical fashion and, in a support region of at least one wire belt, felt band, and/or the like, is guided along a path that deviates from the circular cylindrical path. The flexible support belt has an average curvature radius (R) that is greater than a radius (RK) of the essentially circular cylindrical path, and that is greater than an average curvature radius of an entire path through which the support belt travels.
Accordingly, the present invention is directed to a wire section of a machine for producing a fibrous material web that includes two revolving endless wire belts, a twin wire zone formed between the two revolving endless wire belts, and a revolving flexible support belt located in a vicinity of the twin wire zone and positioned to support at least one of the two wire belts in a support region. The flexible support belt is generally guided along an at least essentially circular cylindrical path, and the support region includes a support path having an average curvature radius that is greater than a curvature radius of the essentially circular path.
In accordance with a feature of the invention, the average curvature radius of the support path can be greater than an average curvature radius of an entire path through which the support belt travels.
According to another feature of the invention, the flexible support belt may be located within a loop formed by the at least one wire belt.
The flexible support belt can include an open outer circumference surface adapted to store water. The outer circumference surface of the flexible support belt may be one of profiled and blind bored.
Further, internal support elements may be arranged spaced from each other in a web travel direction. The internal support elements can be positioned to guide the flexible support belt in the support region. Moreover, internal pressing elements may be positioned opposite intermediary spaces between the support elements. The internal pressing elements can be arranged to act on the wire belt located on a side of the twin wire zone remote from the flexible support belt by pressing against the wire belt. The internal pressing elements can be arranged to act on both of the two wire belts as well as the fibrous material web being formed between them. As an example, the internal pressing elements may be at least partially composed of former strips and/or a forming box can be provided, in which the internal pressing elements are provided in combination with the forming box. Alternatively, or additionally, suction elements may be positioned opposite at least one of the internal support elements and intermediary spaces between the support elements. The suction elements can be arranged to internally act on the wire belt located on a side of the twin wire zone remote from the flexible support belt.
According to still another feature of the instant invention, the flexible support belt may include at least one additional region that is guided along an additional path that extends inside the circular cylindrical path. The at least one additional region can create an additional space, and the additional space may be at least partially occupied by another element of the machine, e.g., a headbox. Moreover, internal supports may be located spaced from each other. The additional region can be defined by two of the internal support elements, and the additional path can include a straight path between the two internal support elements.
In accordance with a further feature of the present invention, the flexible support belt can include an inner region which is positioned remote from the support region. The inner region may be sealed off from the support region, and the inner region can be subjected to an overpressure. The overpressure can be between approximately 50 and 100 mbar, and the overpressure may be adjusted to approximately 60 mbar.
According to another feature of the invention, an internal tube may be provided. An annular space can be formed between the internal tube and the support belt, and sealing elements may be positioned to divide the annular space into the support region and a region subjected to overpressure. The support region can include a plurality of support elements, and the overpressure can be between approximately 50 and 100 mbar, and adjusted to approximately 60 mbar.
In accordance with another feature of the present invention, covering disks can be provided. The revolving flexible support belt may be laterally fixed by the covering disks.
Further still, the flexible support belt may be internally lubricated. The flexible support belt can be internally lubricated with a fluid, and the flexible support belt can be at least one of hydrodynamically and hydrostatically lubricated. Moreover, support elements may be located within the flexible support belt in the support region, and the support elements can be lubricated in a manner corresponding to the internal lubrication of the flexible support belt.
According to a still further feature of the invention, the fibrous material web can include one of a paper and a cardboard web.
The present invention is also directed to a belt guidance device for an apparatus for producing a fibrous material web. The belt guidance device includes a flexible support belt in the form of a loop, a plurality of support elements located inside the loop of the flexible support belt, which are arranged to generally guide the flexible support belt along an at least essentially circular cylindrical path. The flexible support belt includes a support region adapted to support and guide at least one of a wire belt and felt band along a support path that deviates from the circular cylindrical path and that has an average curvature radius that is greater than a radius of the circular cylindrical path.
The present invention is also directed to a process of forming a fibrous material web in a wire section that includes a twin wire zone formed between two endless wire belts, a revolving flexible support belt located in a vicinity of the twin wire zone. The process includes supporting at least one of the two endless wire belts with the flexible support belt in a support region, rotating the flexible support belt along a generally circular path, and deflecting the support belt from the generally circular path in the support region, whereby the support belt in the support regions travels along a support path. An average radius of curvature of the flexible support belt in the support path is greater than an average radius of curvature of the flexible support belt in the generally circular path.
According to a feature of the instant invention, the average radius of curvature of the flexible support belt in the support path may be greater than an average radius of curvature for an entire travel path of the flexible support belt.
In accordance with another feature of the present invention, the process can further include inserting fibrous material between the two wire belts, and pressing the two wire belts and the fibrous material therebetween against the flexible support belt. The process can further include suctioning the fibrous material through the wire belt positioned remote from the flexible support belt.
According to yet another feature of the instant invention, the process can further include deflecting another portion of the flexible support belt along a path that extends through the generally circular path.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.