GB2032058A - Drying cylinders for paper machines - Google Patents

Abstract

A paper machine drying cylinder 1 heatable by condensing steam has a smooth cylindrical inner surface 12 provided with a network 20 for producing turbulence in the condensate. The network 20 is a wire mesh 30 or is made of bent strips 23. Each of the strands forming the network 20, 30 is, along much of its length, spaced at a distance S from the inner surface 12. <IMAGE>

Description

SPECIFICATION Drying cylinders for paper machines This invention relates to drying cylinders for paper machines.

A drying cylinder which, in operation, is heated by condensing steam is proposed in Austrian Patent Specification No. 229 123. In this drying cylinder the cylindrical inner surface is smooth and has means for increasing the turbulence of the layer of condensate in the form of bars, strips or the like pressed against the inner wall and extending parallel to the cylinder axis. A similar construction is also described in German Offenlegungschrift 22 57 799, in which the manner of operation is described in detail, i.e. "swashing" motion occurs between the bars and causes the condensate to move back and forth relative to the cylinder wall, thus improving heat transfer.

According to the present invention, there is provided a paper machine drying cylinder which, in operation, is heated by condensing steam and has a smooth cylindrical inner surface of which there is a network having arms which extend at angles which are inclined to the axis of the cylinder.

The network, which can be manufactured in a very simple manner, has the advantage of very vigorously spinning the condensate layer when the cylinder rotates during operation, and also moves the condensate transversely in the axial direction of the cylinder, so that the temperature of the cylinder wall is made uniform.

Preferably the arms of the network are at angles of between 5 and 600 to the axis.

In a specially simple construction, the network is a wire mesh. Alternatively the network can comprise strips of material each having a rectangular cross-section and a dimension at right angles to the inner surface of the cylinder cawing which is not greater than 1 5 mm. This ensures that, even if the layer of condensate is small, the condensate swashes over the material.

In a particularly advantageous arrangement, the strands of the network are, along the majority of their length, spaced from the inner surface of the cylinder casing. In this manner, the condensate can flow both over and under the network material. The flow between the arms-of the network and the inner surface of the cylinder wall results in increased turbulence and improved heat transfer, and also greatly simplifies the construction of the network.

The invention may be carried into practice in various ways but one paper machine drying cylinder embodying the invention and a modification of the drying cylinder will now be described by way of example with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a diagrammatic axiai section through the drying cylinder, showing the network; Figure 2 is a fragmentary view to a larger scale of the network shown in figure 1, viewed at right angles to a portion of the cylinder wall; Figure 3 is a sectioin on the line Ill-Ill in Figure 2; Figure 4 is a section on the line IV-IV in Figure 2; Figure 5 is a fragmentary view, similar to Figure 2, of another form of network which may be substituted for that shown in Figures 1 to 4; and Figure 6 is a section on the line Vl-VI in Figure 5.

Figure 1 shows a drying cylinder 1 having a hollow cylindrical core comprising two parts 2 and 3 having journals 4 and 5 respectively which are rotatably mounted in bearings 6 and one of which has a drive (not shown). The interior of part 2 is connected by a pipe to a steam supply pipe.

Condensate from the interior of part 3 is discharged through a pipe 8. A cylindrical casing 11 is secured by covers 10 to the core parts 2, 3 and has a smooth inner surface 12, i.e. without grooves.

Discharge pipes 14 extend radially through a partition wall 13 between the parts 2 and 3 and extend into the space between the parts 2 and 3 and the cylindrical casing 11.

The condensate produced at the inner surface 12 of the cylindrical casing 11 during operation is discharged through a pipe 1 5 which has a longitudinal slot 16, as shown in Figure 1.

The pipe 1 5 is connected to a pipe 1 7 to the interior of the part 3 and consequently to pipe 8.

Struts 1 8 are provided for securing the pipe 1 5 to the parts 2 and 3.

As Figure 1 also shows, a network 20 (only diagrammatically indicated in Figure 1) is secured to the inner surface 12 of the casing 11. As Figures 2 to 4 show, the network consists of flat strips or bars 21 which are suitably bent and interconnected, e.g. by welding or riveting, at junctions 22. Between the junctions 22, strips 21 form arms 23 which extend at an angle a to the axial direction A of the cylinder 1. The angle a is preferably in the range of from 50 to 600.

As Figure 3 shows, the network 20 is secured to the inner surface 12 of the casing 11 by saddles 24 and screws 25. It is preferably secured at junctions 22, thus each saddle gripping two bars 21 simultaneously.

Figure 4 shows a cross-section of an arm 23 between two junctions 22. The strip material has a dimension A, preferably not greater than 1 5 mm, at right angles to the inner surface 12 of the casing 11. The arm 23 does not lie directly on the surface 1 2 but co-operates therewith to form a gap S. The gap, which allows the condensate to flow between the arm 23 and the inner wall 12, is produced in the present case mainly because the arms are substantially straight and extend obliquely across a cylindrical curved surface.

Preferably the gap, at its widest place, is not much greater than the thickness of the layer of condensate, which is usually 1 to 3 mm.

Figures 5 and 6 shows an alternative network which is extremely simple and may be substituted for the network shown in Figures 1 to 4. In Figures 5 and 6 the network comprises a wire mesh 30 secured at intervals to the inner surface 12 of the wall 11 by bars 31 and screws 32. In this case, the wire mesh 30 is of round wire and the arms 33 are straight portions between curves 34 corresponding to junctions 22 in Figure 2. In this case, the distance S between the arms of the network and the inner surface 12 is maintained as follows. One arm of each wire of the network 30 extends along the inner surface 1 2 and the next arm is at a distance from the surface. This is clear from Figure 6, which shows curved bars 31 used for securing the network at a junction.

Claims (7)

1. A paper machine drying cylinder which, in operation, is heated by condensing steam and has a smooth cylindrical inner surface on which there is a network having arms which extend at angles which are inclined to the axis of the cylinder.

2. A cylinder as claimed in Claim 1 in which the arms are at angles of between 50 and 600 to the axis.

3. A cylinder as claimed in Claim 1 or Claim 2 in which the network is a wire mesh.

4. A cylinder as claimed in Claim 1 or Claim 2 in which the network comprises strips of material each having a rectangular cross-section and a dimension at right angles to the inner surface of the cylinder casing which is not greater than 1 5 mm.

5. A cylinder as claimed in any of the preceding Claims in which the strands of network are, along the majority of their length, spaced from the inner surface of the cylinder casing.

6. A paper machine drying cylinder constructed and arranged to operate substantially as described herein with reference to Figures 1 to 4 of the accompanying drawings.

7. A cylinder as claimed in Claim 7 modified substantially as described herein with reference to Figures 5 and 6 of the accompanying drawings.