Manufacturing container or tube from paper; or other manufacturi – Bending – Deflecting
Reexamination Certificate
2000-01-31
2003-12-23
Kim, Eugene (Department: 3721)
Manufacturing container or tube from paper; or other manufacturi
Bending
Deflecting
C493S459000, C493S957000, C493S958000
Reexamination Certificate
active
06666809
ABSTRACT:
This invention relates to paper webs and more particularly for a method and apparatus for decurling paper or paper board webs prior to the webs being utilized in some other downstream process.
BACKGROUND OF THE INVENTION
In the process of making paper (cardboard or a similar product is in this application also considered defined as “paper”) on a papermachine and/or coating paper forces and temperature gradients within the paper can cause it to curl to one side or the other of the web. Curl is normally the result of stresses unequally applied to the paper, say as by winding a web of paper into a roll, causing strains which become set into the rolled paper and when released, as when the roll is unwound, can cause a web or the subsequently cut sheet to curl. For example, running the web over dryer “cans” (rolls), causes the paper to take on the curve of the roll; wetting one side of a web as is done during applying coating to one side can also induce a curl, in a subsequently dried web. Even more frequent is the tendency to induce curl when winding a web onto a roll core when the paper is produced. Then there is a “roll set” curl when the roll is unwound and cut into sheets. While curl is less undesirable in some operations, where the web remains intact, curl is of a greater concern if the web is to be subsequently cut into sheets. Many of today's subsequent paper converting operations, such as forming sheets from a web, and the use of these sheets, as in printing presses and numerous office products, like photocopy machines, facsimile machines and office printers, are sensitive to curl. With too much curl, the cut or formed sheet of paper will have difficulty feeding properly in such uses. It is therefore desirable to limit or eliminate curl while the paper is in web form, before it is subsequently cut into sheets. Various attempts in the past have been made to limit or eliminate curl.
It is conventional to employ web decurlers in various paper converting operations, such as in a sheeter (a machine that converts a roll into cut sheets). These prior art decurlers were usually configured to provide a decurling action by running the web of paper over a small radius decurler, such as a small diameter roll or a non-rotating stationary bar with its edge machined into a small radius. The web is usually carried on the upstream and downstream side of the decurler bar or roll by rotating, cylindrical web supporting rolls. The amount of decurling affected is partly determined by the depth the web is deflected from its initial position on the web support rolls and/or wrap angle of the web around the decurling radius. In this respect the decurler bar or roll operates in a similar manner as a table edge, wherein a tensioned sheet of paper is drawn across the table edge to remove or induce curl. While it is clear why curl would be removed on a sheet, sometimes it is helpful to induce a curl to solve runability problems. The conventional, prior art decurler is effective if the web has an even “cross directional curl,” that is the curl is uniform in a direction running across the web. This type curl is referred to as an “even” cross directional curl profile. That is, the tendency of the paper to curl is uniform across the width of the web. However, some webs have curl profiles that can be asymmetrical or non-uniform. Such non-uniform curl can be caused by various factors such as web caliper differences which need not be addressed here. When the web has less than ideal cross direction curl profile, an uneven decurling effect can be created across the width of the web because of unequal tension of the web when traveling around the radius of the decurler bar or roll. An uneven cross directional curl profile can cause one side of the web, its center or combinations of both to receive more or less decurling effect than the rest of the web. This effect is dependent of course on the location of the tight and/or loose areas of the web. Typically, one side of the web may be “baggy” or the center of the web may be “baggy” with the edges tight. The net result is that the prior art, conventional decurlers could not readily evenly decurl webs which initially had uneven curl profiles.
SUMMARY OF THE INVENTION
The present invention provides a method and apparatus for decurling a web with both an even and, particularly an uneven, cross directional curl profile.
The decurling method and apparatus of the present invention comprises the steps of leading a paper web which may contain a precurl, say as due to being wound onto a roll core, onto a bowed roll (also sometimes called a “Mount Hope” roll), the web being wrapped around a portion of the periphery of the bowed roll. As is conventional, the bowed roll has a “bow” or high point on one side (the convex side) and a low point on the opposite side (the concave side). Operating the bowed roll, depending on the amount and direction of the bow, can cause a spreading or cross tensioning effect on the web to remove baggyness when decurling from the paper web. This spreading effect is determined by the bow roll setting, that is, where the high of the bow of the bowed roll is aimed in relation to the web, the degree of bow, and wrap angle of the web on that roll. With the high point of the bow set in a direction perpendicular (90°) to a line that bisects the wrap angle of the web on the bowed roll, a normal operating position is determined. With the bowed roll so set, it causes an even spreading or cross tensioning effect. If that angle is changed so that it is acute (less than 90°), the center of the web is tightened. If the angle is changed so that it is obtuse (greater than 90°), the edges of the web are tightened. The spreading effect produced by adjusting the amount of the bow of the bowed roll, alone, may cross tension the web enough so the web distortion (say baggyness) produced by a less than ideal web cross direction profile will be pulled tight for decurling. As noted, the bowed roll mounting has the ability to aim or rotate the direction of the bow so that it is more or less than 90 degrees to the line that bisects the web wrap angle around the bowed roll. When this angle is less than perpendicular, the web will be tightened up in the center. Likewise, if the angle is more than perpendicular the web will be tightened up on both edges. The amount that the bow has to be aimed or rotated is dependent on the amount of the web distortion for which to be compensated and the magnitude of the bow in the bowed roll. The degree of bow in the bowed roll can be varied and/or adjusted, this adjustment being conventional in the bowed roll's construction.
The decurling method and apparatus of the present invention includes a decurler assembly which may include either a stationary radiused bar or edge or a small diameter, rotating roll. The decurler bar or roll is located adjacent and, preferably, closely downstream of the bowed roll. The web can be displaced, with the decurler (be it a radiused bar or small diameter rotating roll) to load the web in a direction opposite of the precurl, a sufficient distance to remove most, if not all, of the precurl. In addition to their other functions, the first roll in front of (upstream) and behind (downstream) of the decurler act as support rolls to support the web for the decurling operation. In the preferred method, a lead in roll is also provided, and the web is first lead onto the lead in roll and then over the bowed roll. The lead in roll, the bowed roll, the aim of bow, and the motion of the decurler are controlled so that as the decurler is engaged further into the web, the wrap of the web around the bowed roll is kept essentially constant, both in wrap angle and relative aim of the bow to web.
The method and apparatus of the present invention also includes a lead out roll onto which the web is lead from the decurler. Unlike the prior lead out rolls, that of the present invention is not fixedly mounted, but is mounted so that its relative position with respect to the decurler can be changed. Optimally, additional decur
Harmon Christopher
Kim Eugene
Pyle & Piontek
Stora Enso North America Corp.
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