SE430799B - PROCEDURE FOR SMOOTHING THE SURFACE OF A PAPER MANUFACTURE USES FILTER, WIRELY OR SIMILAR ENDLESS, THERMOPLASTIC TREATMENT COAT AND PLANT FOR APPLICATION OF THE PROCEDURE - Google Patents

Description

The felt is subjected to a stronger heating, which will operate with temperatures above the melting temperature of the fibers, which in turn leads to a reduced permeability, because the surface melts easily so that it becomes impermeable.

To provide a greater pressing force, it has previously been proposed to guide the felt first through a heat field, where the felt is subjected to a hot air blowing, and then through a pair of press rollers, which compress the preheated felt.

It has been necessary to limit the pressing force to the own weight of the upper roller, since an additional load causes bending of the rollers and thus uneven pressing at the edges of the felt and in its center. Different felt widths also cause uneven pressing, whereby the result is also unsatisfactory. Achieving a higher degree of smoothness with such a small pressing force would in this case require the heating of the felt to almost the melting temperature of the fibers with associated disadvantages.

With a smooth felt surface, one strives to reduce the amount of air transported by the felt, which causes so-called blowing, and the tendency of the blanket to be re-moistened after the press nip.

In recent times, efforts have been made to realize the surface smoothness of the press felts by means of flattened fibers by using ready-flattened fibers in needled surfaces. However, such a procedure is not satisfactory. because completely flat fibers cannot be controlled so that they would always be in the blanket with the wide surface facing the paper; and because a flat fiber on the other hand makes the blanket too dense.

In wet wires and drying wires, the required surface smoothness has been achieved by grinding the surface of the wire evenly. While removing material from the filaments in this way, this correspondingly weakens the strength of the wire.

With a smooth surface, wet wires strive to reduce the marking properties of the wire and in drying wires to achieve e.g. a smoother construction of the paper web against the drying cylinder. The object of the present invention is to provide a process which eliminates the above-mentioned disadvantages and which makes it possible to achieve a high degree of smoothing and stability without reducing the permeability and strength. This object is achieved with a method according to the invention, which is characterized in that the treatment web is subjected to a simultaneous stretching, heating and pressing action on the side facing the paper by passing the endless treatment web around a stretching roller and a heating roller, which together with a press roll forms a press nip.

The process according to the invention is based on the fact that the softening temperature of the thermoplastic fibers is lower than their melting temperature. The treatment web to be smoothed is subjected to a sufficient pressing force when the web is heated to the softening temperature, whereby a flattening of the felt fibers resp. the filaments of the wire and also the adhesion of the fibers and the filaments to each other at the intersection points. Thanks to the heating and pressing of the treatment web being carried out in a press formed by a pair of rollers, a pressing force can be directed on the treatment web when it is still under heating and thereby a sufficient flattening can be achieved without the treatment web having to be heated up to the melting temperature. Through the described method, precisely the fibers or filaments which, in view of the use, are desired to be flattened, i.e. the paper web touching the fibers.

The adhesion of the fibers and filaments to each other at the intersection points also increases the stability of the treatment path. In a needle felt, the needling can therefore be reduced, as a result of which the needle marking on the surface of the felt becomes smaller. Reduced needling also reduces production costs. The heat pressing glues the fibers better to each other than can be achieved with current technology.

In wet and drying wires, the required smoothness of the surface is achieved without reducing the strength, while the cross-section of the planed filaments remains unchanged.

The invention also comprises a plant for applying the method described above, which plant is characterized in that a heating roll forms with a press roll a press roll pair, through whose press nip the treatment path passes, and with a stretch roll a stretch roll pair around which the treatment path passes.

The invention will be described in more detail below with the aid of the accompanying drawing, which schematically shows a plant for applying the method according to the invention.

The drawing shows a needle-shaped endless felt made of thermoplastic fibers, such as polyamide, polyester or polypropylene fibers. the felt is passed around a stretching roller 2 and a lower roller Å in a roller pair 3 present at a distance from the press roller. An upper roller 5 in the roller pair together forms with the lower roller Ä a nip 6, through which the felt runs. The lower roller Q is designed as a circulating oil or electrically heated heating roller, the surface temperature of which is adjustable between 20-26D ° C. The upper roller is made. such as a Küsters-type press roll, the press pressure of which is adjustable by means of pressure oil in a manner known per se so that the press pressure is even over the entire length of the nip over the felt. The press pressure can be up to and including 200 kp / width-cm. A hot air hood 7 secures the felt.

When the felt passes over the heating roller, it is subjected to a heating action, whereby the fibers, at least in the surface facing the heating roller, reach the softening temperature. At the nip of the roller pair, the felt is subjected to a pressing action, by the action of which the fibers abutting the heating roller are flattened and form a smooth surface on the felt. The fibers also adhere at the intersection points to each other inside the blanket. The blanket is then allowed to cool and removed from the rollers.

The treatment is essentially the same as the web to be smoothed instead of a press blanket consists of a wet or dried wire woven from filaments. The filaments abutting the surface of the heating roller are also flattened in this case so that the wire has a smooth surface, and the filaments also adhere to each other at the crossing points so that a very stable wire is obtained.

Example A press felt 1 with the dimensions 7.5 x 26 m, weight 1200 g / m 2 and consistency of 5% wool and 95 2 polyamide (nylon 6,6) fibers, was passed as an endless web over the rollers 2 and 4. The blanket was first treated in four different heating phases at a speed of 5 m / min, whereby the temperature of the blanket was raised on the following sam in the first stage: up: in 100 ° C, in the second weak: up cm 160%, in the third step up to ZODOC and in the fourth stage up to 23006. The temperature V in the first stage up to 100 ° C and in the circulating air of the second a hood was raised in the first stage up to 160 ° C to effect a felt fixation. In the third and fourth steps, the temperature of the circulating air was not raised, as the aim was to smooth the surface. An increase in temperature carried out in different steps is suitable for producing a measured blanket. An excessive increase in temperature per step, wrinkles the blanket or wire. Thereafter, the felt was subjected for two turns on the press roll 5 to a 150 kp / cm large pressing action while the temperature was still 23008. The felt treated in this way obtained a very smooth, against the paper, due to the flattening of the surface fibers. facing surface and due to the adhesion of the fibers to each other for stability. However, the permeability of the blanket was satisfactory due to the fact that no melting took place on the surface of the blanket.

The drawing and the accompanying description are only intended to illustrate the idea of the invention. The details of the known method and the plant according to the invention also vary considerably within the scope of the claims.

Claims (3)

avs13as9 + a P a t e n t k r a v A method of smoothing the surface of a felt, wire or similar endless thermoplastic treatment web used in papermaking (1) by subjecting the web to a heating and pressing action to soften and compress it against the paper. facing the surface of the web, characterized in that the treatment web (1) is subjected to a simultaneous stretching, heating and pressing action on the side facing the paper by passing the endless treatment web (1) around a stretching roller (2) and a heating roller (4), which together with a press roller (5) forms a press nip (6). Plant for applying the method according to claim 1, wherein the device comprises rollers (2, 4) for controlling an endless treatment path (1) and heating devices and press devices for heating resp. compression of the treatment web, characterized in that a heating roller (4) forms with a press roller (5) a pair of press rollers (3), through whose press nip (6) the treatment web (1) passes, and with a stretching roller (2) a stretch roller pair (2, 4) around which the treatment path passes. Plant according to Claim 2, characterized in that the press roll (5) consists of a Küsters-type roll.