JPS6354839B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steam-heated drying cylinder having a cylindrical jacket and a flange formed at its end.

Particularly in high speed paper machines where the paper web is dried on rotating steam-heated drying cylinders, an undesirable effect occurs where the paper web dries faster at the edges than in the center. Therefore, the edges may shrink faster than other portions of the web, causing wrinkles and web tearing. Additionally, edges that are overstretched and overdried are of poorer quality than other parts of the web.
It also becomes an obstacle during smoothing and other processing, resulting in defective products. Attempts have been made to eliminate this effect by spraying water onto the drying web, but the technical success has been minimal and this has increased the amount of energy required for drying.

It has been established that excessive drying of the edges is caused by strong air circulation in the edge area.

The invention is based on the problem of avoiding excessive drying of the web edges by simple measures, thus improving the paper quality, reducing the reject rate and saving drying energy. In this case, the cylinder should be as narrow as possible in order to dry a web of a given width. Besides reducing the cost of the drying cylinder, this also has the advantage that the guiding rope can be arranged closer to the paper web edge and the guiding of the paper web after interruptions in operation is easier, faster and more reliable. ing.

This object is achieved by applying an adhesive layer of insulating material to the inner surface of the transition region from the cylindrical part of the jacket to the cylindrical part of the flange. The inventor discovered the following. That is,
Although the known effect of air circulation in the edge region is effective, it produces two other effects. For one thing,
In the jacket of the thermal cylinder, the temperature in the axial direction is higher and can flow from the edge, which does not give off heat, to the edge of the paper web, where the heat of vaporization is consumed. Secondly, the condensate ring of the cylindrical part of the drying cylinder has an important insulating effect, since the transition area to the conical or rounded flange projects from it. , not in this area. Particularly in this part of the jacket which protrudes from the condensate membrane but does not reach the full thickness of the flange, on the one hand there is no insulation of the condensate membrane, and on the other hand the thickness of this wall is greater than in the outer flange area. Since it is small, its insulation properties are low. This effect was previously unknown. In any case, very little heat flows through the thicker part of the jacket in the flange area. However, due to the insulating effect of the condensate film increasing with speed, the relationship is reversed for low speed applications. This reversal has long been recognized but misinterpreted. This was interpreted as the above-mentioned effect of supplying stronger drying air from the sides to the edge region of the web.

The path to the above technical improvements was opened only by this new and surprising knowledge disproving the prevailing view.

It is not necessary to install an insulating layer in the conical or rounded transition area from the jacket to the flange of all dry cylinders. A definite improvement is achieved by applying an insulating adhesive layer to the transition area of only some of the cylinders. In particular, when the insulation layer is made thick enough, it is sufficient to insulate one-third or less of the cylinder edge area in order to compensate for the effects of excessive edge drying.

As the web shrinks in width as it dries, the position of the web edge changes with respect to the width of the cylinder. To take this effect into account, it may be appropriate in some cases to extend the insulating coating to the cylindrical part of the flange (beginning of the drying section) or to the cylindrical part of the jacket (end of the drying section). . Once a suitable material is chosen for the insulation, it will also provide a good insulation inside the condensate film, since the thermal conductivity of this material is only a fraction of that of the condensate film. It has an effect.

By choosing an insulating adhesive layer with very low thermal conductivity, an insulating effect can be achieved with a layer thickness of 0.5 mm;
This is greater than the insulating effect of a 2 mm thick condensate film.

However, since it is cheap to fit an insulating layer only on some cylinders, it is necessary to apply a considerable thickness to these few cylinders, for example up to 5 mm, to compensate for excessive drying of the edges of other cylinders. An adhesive layer may be selected. For this thickness,
The insulation effect is so great that it is hardly appropriate to associate it with thicker layers.

If a large layer thickness is selected, it is appropriate to construct it as a "cover" or "mat" and to apply or vulcanize it onto the cylinder area to be insulated.

A particularly advantageous embodiment provides for applying the insulating adhesive layer of curable material in paste form. In this case, it is possible to use self-curing multicomponent synthetic resin mixtures, or else to use solid materials which are softened by the solvent and harden by evaporation of the solvent. The technique of applying a pasty adhesive layer is useful when smaller layers to be applied are in question or which not only cover the transition area between the jacket and the flange but also extend to the cylindrical jacket area and/or the flange area. Particularly suitable when the layer to be maintained is in question.

The invention will be explained in more detail on the basis of FIGS. 1 to 3. In this case, all figures show partial longitudinal sections of the ends of cylinder jackets with different paper web widths. The cylinder cover following the right side of the flange is not shown as it is not a requirement of the invention.

In the three figures, a cylindrical part of the jacket 1 with a transition region 2 to the flange and a cylindrical flange 3 is shown. The insulating adhesive layer 4 and the paper web 5 running through the cylinder and the condensate ring 7 are visible. Curve 6 shows the humidity distribution of the web at the end of the paper machine when no adhesive layer according to the invention is used.

In all three cases, the curve 6 can clearly indicate excessive dryness in the edge region (a low height of the curve 8 means a low final humidity).

In FIG. 1, the paper web 5 fully extends to the outer surface 17 of the cylindrical flange portion 3 of the jacket. Especially cylinder jacket 1 and flange part 3.
Excessive dryness occurs on the outer surface 19 of the transition region 2 between. At the edges, the web humidity can possibly increase slightly again depending on the flange height and the axial heat radiation to the right (see curve 6).

The humidity distribution can in this case be made straight 9 by the insulating layer 4 of the cylinder inner wall 18 in the transition region 2.

In Figure 2, the jacket 1 and flange 3 are
A web of medium width is shown extending only as far as the outer surface 19 of the transition region 2 between. Curve 6 shows a very high degree of dryness in the edge region of web 5. This excessive dryness can be compensated for by the insulating adhesive layer 4, which extends beyond the region 2 to a part of the inner surface 16 of the flange region 3.

1 to 3 can also be seen as three successive stages in the drying process of one paper web during drying in a multi-cylinder dryer. In this case, FIG. 1 shows the unshrinked web width at the beginning of drying, FIG. 2 shows the partially shrunken web width in the central region of the drying section, and FIG. 3 shows the partially shrunken web width near the end of the drying section. The contracted web width is shown.

In order to achieve a complete compensation of excessive drying effects, according to the proposal in FIGS. 1 to 3, the width of the insulating layer can be varied from the beginning to the end of the drying section according to the shrinkage of the web width. can. However, it is substantially sufficient to fit all cylinders with an insulating layer of medium width, ie an insulating layer according to the proposal of FIG. The curve 6 then becomes - by application of the invention - a straight line (horizontal line) 9.

Note that the jacket 1 constitutes the central region.

[Brief explanation of drawings]

1 is a partial longitudinal sectional view of the end of an embodiment of the invention showing the wide web extending into the cylindrical portion of the flange; FIG. 2 shows the transition between the cylinder jacket and the flange; FIG. 3 is a partial longitudinal sectional view of the end of another embodiment showing a medium width web extending into the region; FIG. FIG. 3 is a partial vertical cross-sectional view of an example end; 1...Cylinder jacket, 2...Transition area,
3... Flange portion, 4... Insulating layer, 5... Paper web, 6... Curve, 7... Condensate ring, 8...
Low curved part, 9... straight line, 16, 18... inner surface,
17, 19...external surface.

Claims (1)

Claims: 1. A central region of substantially uniform thickness having an inner surface, an end flange having an inner surface extending abruptly inwardly of the central region, and said central region and end portions. a cylindrical outer frame having an inner surface including a transition region disposed between the flanges and having an inner surface sloping sharply in an outward direction from the end flanges to the central region; a thermally insulating layer on an inner surface of the transition region for substantially uniform drying along the width of the paper machine. 2. Drying cylinder according to claim 1, characterized in that the insulating layer also extends to the inner surface of the end flanges and/or the central region. 3. Drying cylinder according to claim 1 or 2, characterized in that the insulating layer has a thickness of 0.5 to 5 mm. 4. The drying cylinder according to any one of claims 1 to 3, characterized in that it is composed of a mat made of an insulating material to which an insulating layer is adhered or vulcanized to make it adhere. 5. The drying cylinder according to any one of claims 1 to 3, characterized in that the insulating layer is made of a material that is applied in the form of a paste and hardens.