The present invention relates to a method and device for guiding a paper web or the like. In general, this concerns guiding the web with the aid of air jets.
In a modern paper machine, there are numerous rolls and felts arranged as individual rolls, pairs of rolls, or series of rolls, depending on their position and purpose. In connection with many rolls, means are arranged to assist in removing water from the stock used in papermaking, thus resulting in the desired quality grade and the desired type of paper, which is finally reeled for later processing and use. The most, usual means of this kind are roll grooving, roll heating, and the introduction of a vacuum to the rolls. Also used are special highly absorbent felts, the water absorbed in which being removed during circulation for reuse.
A paper web made from stock is a very long totality, which, in the various stages of papermaking, must be transported around, or between numerous rolls. The rolls are situated over the entire length of the paper machine, at both the wet and dry ends, and are especially numerous in the paper machine's drying section, in which the rolls, around which the paper web travels, are usually in two rows.
If the paper web breaks for one reason or another, or if some other disturbance occurs, the paper web must be fed again to travel through the machine. Most of the paper web coming from the wet end is led to the pulper and a powerful, sharp water jet, for example, is used to cut and thus separate from the web a so-called web-threading tail, which is then attempted to be threaded through the machine and, if this succeeds, the tail is widened so that finally the full-width web travels through the machine, and is reeled as completed paper after the drying section.
Traditionally, a tail-threading rope, which conveys the web-threading tail forward in and through the drying section, has been used to carry the web-threading tail into the drying section, and indeed is still used in older machines. However, using a rope is very demanding and dangerous work, which will be prohibited by regulations due to be introduced.
Air jets are used for many purposes in paper machines. For example, air jets have been used to aid the separation of the paper web from a roll, while similarly air jets have also been used in many ways to guide the paper web.
Finnish patent 114491 discloses an example of a solution using an air jet to guide a paper web travelling through a drying section, and particularly to guide it from one roll to another in the drying section for the purpose of threading a web-threading tail. The said patent describes a method for carrying a paper web, usually a web-threading tail, from one roll to another, over a route in which a felt does not support the tail. In the method, four air nozzles are generally used, two of which are located on one side of the web and two on the other. On each side of the web, one air nozzle blows air in a direction nearly opposite to the direction of travel of the web while another nozzle blows air in nearly the same direction as the direction of travel of the web. This is claimed to carry the web steadily to the next roll.
While the aforementioned construction may be indeed very functional, it is, however, relatively complicated and requires accurate positioning on the opposite sides of the web. On the other hand, however, it appears that the said arrangement will not achieve very great precision in the lateral control of the web threading tail.
In addition, the use, in the drying section of a paper machine, of an air jet oriented in two different directions is known from U.S. Pat. Nos. 5,987,777 and 6,145,217. The drying section is equipped with a belt, on the surface of which the fibre web travels. In the first of the publications referred to, the air jets are intended on the one hand to detach the web from a roll in the conventional manner and on the other hand to hold the web on the conveyor belt.
In the second of the publications referred to, numerous air jets are used with the intention of guiding the free travel of the fibre web in the area between two rolls in a two-row drying section. The supposition is that, if a sufficient number of air jets are set to blow on different sides of a fibre web, the web will remain straight and travel in the direction in which the main flow of the air jets carries it.
Though certain parts of the solutions known from the two aforementioned publications function, the operation of certain other parts is highly uncertain. In neither of the publications is the intention to create a vacuum, nor is it to guide a material web accurately with the aid of the vacuum created.
The present invention is intended to create a method and device particularly for guiding the movement of a paper web simply and functionally. The intention is also particularly to position the web laterally in a sure manner.
The aforementioned and other benefits and advantages of the present invention are achieved by means of a method and device, the characteristic features of which are stated in the accompanying Claims.
In the following, one embodiment of the invention is described in great detail, with reference to the accompanying drawings, which show one well-regarded application of the invention.
Thus:
Thus,
The air jets (which are marked with arrows in the figures) from ducts 4 and 5 create a vacuum in the area between the blast points. This means in turn that the web tends to be pulled by the vacuum to move towards the surface 2 and possibly onto it thus sliding along the surface. In this way, the web also travels forward in a manner that is laterally both controllable and stable. Here the actual transportation of the web is not interfered with, but is handled using conventional technology.
The positioning of the air-jet nozzles is very important in terms of the invention. The undisturbed transportation of the web in the manner shown by the invention cannot be achieved, if the ducts are formed with the aid of pipes that clearly rise above the surface 2. In such a case, the web would probably not travel at all along the surface between the airjet nozzles. The nozzles are therefore placed directly on the surface 2, or in shoulders slightly below it, as described in the following.
Further, in the publications referred to in the review of the prior art, it is possible that some kind of zone of lower pressure will arise in the area between the air jets blowing in two directions. However, in this case the paper web is not intended, as it is in the present invention, to be substantially sucked onto a smooth and slippery surface between the nozzles, but rather to be kept floating at a distance form the nozzles.
The relative strengths of the air jets can be easily controlled by adjusting the size of the flow ducts 4 and 5. Adjustment can also take place using a suitable control element, by means of which the cross-sectional area of at least one of the ducts 4 or 5 can be altered. Such control elements are not, however, drawn in the figures.
Though in this case the surface 2 shown by
In practical tests, the principle of the invention has been shown to function well. The vacuum sucks the web into a firm grip and lateral stability is excellent.
The direction of the air jets, shown in
Though reference is made above to only a paper web, the invention is in no way restricted to that. Any web-like material whatever, which is not entirely permeable by air, can be guided using the method and basic apparatus described.
Number | Date | Country | Kind |
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20060757 | Aug 2006 | FI | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FI2007/000209 | 8/24/2007 | WO | 00 | 3/23/2009 |