DRY PAPER MACHINE
Dry' paper machine The present invention concerns a dry paper machine wherein in the step after the forming section the fibre web has been conducted with the aid of topside and/or underside wires .through the machine to the purpose of adding, drying and polymerizing the bonding agent. When the uncured web is being handled and transported, care must be exercised because of its low strength. This is particularly im¬ portant in paper machines, where shut-downs are costly. In modern dry paper machines, the path of the web has so-called open draws where the web is not supported at all. At these points tensions build up in the web, and it breaks unless the web is run at low speed. As a consequence, present-day dry paper machines have poor efficiency because one has been forced to strike a compromise between the breaking tendency of the web and the throughput rate of the machine. The object of the present invention is to eliminate the drawbacks mentioned above. In order to achieve this effect, the Invention is characterized In that the topside and underside wires are disposed to overlap so that the web runs In a state of rest and without open draws causing tensions, through the entire process. The invention is further characterized in that the fully bonded web is subjected to hot calendering after the drying process. Moreover, the invention is characterized in that the partly bonded web is subjected to hot calendering after the drying process. By this arrangement the advantage is gained that tha absorption of the bonding agent in the second step takes place efficiently, owing to the pressing preceding the spraying. The invention is described in the following with the aid of an
example with reference made to the attached drawing, wherein Fig. 1 presents a paper machine according to the invention. Fig. 2 presents another embodiment of the invention. In the paper machine of Fig. 1, the web 1 is transferred from the formiαg wire 2 to the underside of the first drying wire 3 with the aid of the suction box 4. The bonding agent 5 is therafter sprayed on the web from below. It is possible, instead of bonding agent spraying, also to use compounds added at the web-forming step (hot-bonding resins or equivalent). The web Is further carried, supported by a topside vacuum (suction box 7) through the first drying section S. The web is picked up into the embossing calender 14 with the aid of a smooth roll, possibly making use of water or steam, from the underside of the drying wire 3 and carried through the embossing calender nip. The web is thereafter transferred from the embossing calender 14 to the next wire 9 with the aid of the suction box 10. Finally, the web is carried in support of the wire 9 through the second bonding agent spraying 12, the drying section 3 and the polymerizing section 13. In the arrangement depicted in Fig. 2, calendering is not carried out until after polymerizing, when the web is strong and durable. It is obvious to a person skilled in the art that the invention is not confined to the example presented above and may instead be applied within the scope of the claims following below.
In a dry paper machine, in the step following the forming section, the fiber web has been conducted with the aid of topside and/or underside wires through the machine to the purpose of adding, drying and polymerizing the bonding agent.
The unbonded fiber web has low strength and requires careful handling so that it might not break and cause process shut-downs. This circumstance has in modern paper machines resulted in a running speed which is low compared with the theoretical
capacity of the machines. It has been found that web breaks tend to occur at the so-called open draws of its carry-through path, where the fiber web is not supported and is allowed to hang free in the air or carried by a wire (2, 3, 9). The object
of the invention is to avoid open draws and to convey the web (1) in supported fashion through the entire process. The reliability of the procedure is improved by placing the mechanically drying calendering to be the last treatment step before
polymerizing. Claims 1. Dry paper machine wherein in the step afcer the forming section the fibre web has been conducted with the aid of topside and un¬ derside wires through the machine for adding, drying and polymer¬ izing the bonding agent, characterized in that the topside and underside wires (3,9) are disposed to overlap so that the web-(L) runs in a state of rest without open draws causing tensions, through the entire process. 2. Procedure according to claim 1, characterized in that the fully bonded web-(l)* is subjected to hot calendering after the drying process. 3. Procedure according to claim 1, characterized in that the partly bonded web is subjected to hot calendering after the drying process. U KE>