GB2032056A

GB2032056A - Drying cylinders for paper machines

Info

Publication number: GB2032056A
Application number: GB7930853A
Authority: GB
Original assignee: Escher Wyss GmbH
Current assignee: Sulzer Escher Wyss GmbH
Priority date: 1978-09-05
Filing date: 1979-09-05
Publication date: 1980-04-30
Also published as: AT363319B; DE2844273C2; DE2844273B1; SE7907060L; GB2032056B; IT1122824B; IT7925287A0; ATA653278A

Abstract

A paper machine drying cylinder having a smooth inner surface 13 to which bars 22 are secured. The bars 22 along at least half their length, are spaced from the inner surface 13 by a distance S of not less than 0.5 mm and not more than 3 mm so that steam condensate can flow between the bars and the cylinder surface as well as swashing over the bars. The bars 22 may be secured either to the cylinder wall 11 directly, or to a support structure 17 mounted upon members 2 and 3 in the central region of the cylinder 1. <IMAGE>

Description

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

A drying cylinder which, in operation, is steam and which has a smooth cylindrical inner surface along which extend elongated bars to improve the heat transfer has been proposed in Austrian Patent Specification No. 299 123. In this drying cylinder, bars parallel to the cylinder axis are secured to the smooth inner surface of the cylinder. The bars are adapted to move or "swash" the layer of condensate backwards and forwards in the cylinder during the rotation thereof, thus improving the heat transfer between the condensate layer and the cylinder wall.

According to the present invention a paper machine drying cylinder which, in operation is heated by condensing steam has a smooth cylindrical inner surface along which extend elongated bars to improve the heat transfer, the bars, along at least half their length in the longitudinal direction, being at a distance of at least 0.5 and not more than 3 mm from the inner surface of the cylinder. The distance between the bars and the inner wail of the cylinder in a drying cylinder constructed in accordance with the invention is such that a flow can occur under the bars and this, together with the flow of condensate over the bars, results in particularly high turbulence of the flow of condensate which improves heat transfer. The temperature of the cylinder wall is also made more uniform since the condensate can flow under the bars across the inner surface of the cylinder.

The distance between the bars and the inner surface, namely at least 0.5 and not more than 3 mm, is determined by the thickness of the unavoidable layer of condensate, and should be less than or at most equal to the layer thickness.

The improvement in heat transfer obtained arises because soine of the condensate flows under the bars whereas the rest swashes over them. If the distance is made great enough for the condensate to flow between the bars and the inner surface of the cylinder without swashing over, there will be a considerable reduction in the heat transfer.

The bars can be secured to the cylinder wall, which results in a very simple cylinder construction.

Alternatively, the bars can be secured to a support structure mounted in the central region of the cylinder. The resulting cylinder is somewhat more complicated but the bars can be disposed so that they do not anywhere touch the inner surface of the cylinder and are at the desired distance therefrom. In any case, the bars can have a rectangular or a round cross-section.

The invention may be carried into practice in various ways but one drying cylinder embodying the invention and a number of modifications of the drying cylinder will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is an axial section through the drying cylinder; Figure 2 is a cross section on the plane Il-I I in Figure 1; Figure 3 shows to a larger scale a section through a bar of the cylinder shown in Figures 1 and 2; Figure 4 is a section, similar to Figure 3, through a rectangular bar which may be substituted for the cylindrical bar shown in Figure 3; Figure 5 is a fragmentary section through a drying cylinder with bars secured to the cylinder wall along section V-V in Figure 6; Figure 6 is a section VI--VI through Figure 5; and Figure 7 is a view corresponding to Figure 6 of another possible form of bar.

Figure 1 is a view in axial section of a drying cylinder 1 which comprises a hollow core comprising two parts 2, 3 held together with bolts and having journals 4, 5 by means of which the cylinder is rotatably mounted. Journal 4 is connected to a steam supply pipe 6 and journal 5 is connected to a pipe 7 for discharging condensate. Parts 2 and 3 of the core are separated by a wall 8 having outlet pipe 10 for the steam which flows from the pipes i 0 into the space between the core and a cylindrical casing 11 secured to the core by annular end covers 12.

A condensate suction pipe 14 is located adjacent the inner surface 13 of the cylinder wall 11 and has a slot 1 5 facing the inner surface 13.

The pipe 1 4 is connected to the interior of the core part 3 by a pipe 16. The suction pipe 14 is also secured to the core parts 2, 3 by struts (not shown) which have been omitted for simplicity.

The drying cylinder shown in Figures 1 and 2 has near each end radial support arms 1 7 which are secured to the core parts 2 and 3 and carry rings 1 8. As shown in Figure 2, each ring 1 8 is divided into four portions pivotally interconnected by fish plates 20. There is also a gap 21 in the ring 18 in the neighbourhood of the pipe 14. This allows the rings 1 8 to expand when heated.

Bars 22 are secured to the rings 1 8 and extend parallel to the cylinder axis A and are interconnected by rings 23 intermediate the rings 18.

Figure 3, which shows a pdrtion of Figure 2 to a larger scale, shpws bars 22 having a round crosssection, a diameter D, and at a distance S from the inner surface 13 of the cylinder wall 11. As already mentioned, the distance S is at least 0.5 and at most 3mm, in view of the fact that the layer of condensate present during operation normally has a thickness of 1 to 3 mm. The diameter D is chosen so that the condensate, besides flowing between the inner surface 1 3 and the bars 22, can also swash over the bars 22 when the condensate moves back and forth during rotation of the cylinder. Usually the size H of each bar 22 at right angles to the inner surface 13 (equal to the diameter D in the present case) should not be greater than about 1 5 mm.

Figure 4 is a view corresponding to Figure 3 of an alternative form of bar 22 having a rectangular cross-section, its second measurement E being smaller than H. Its height is determined as already described in connection with Figure 3.

Figures 5 and 6 show an alternative arrangement in which the bars 22 having a rectangular cross-section are directly secured to the cylinder wall 11. In this case, the bars 22 are secured by screws 30, and a spacer washer 31 surrounding each screw 30 is disposed between each bar 22 and the inner surface 13 of cylinder wall 1 The thickness of washer 31 is chosen so as to obtain the desired distance S.

Figure 7 shows another alternative in which the spacers 31 are integral with each bar 22, so that the bar has projections which bear on the surface 13 of cylinder wall 1 The spacers or projections 31 are dimensioned so that the length M of the gap 32 having the width S between bar 22 and inner surface 13 is at least half the distance L between two projections 31. This is because it is believed that, in order to obtain the effects described, it is necessary for the sum of the lengths N of the spacers 31 in the longitudinal direction of the bar 22 to be not more than half the total length of the bar 22.

Claims

1. A paper machine drying cylinder which, in operation, is heated by condensing steam and has a smooth cylindrical inner surface along which extend elongated bars to improve the heat transfer, the bars, along at least half their length in the longitudinal direction, being at a distance of at least 0.5 and not more than 3 mm from the inner surface of the cylinder.

2. A cylinder as claimed in Claim 1 in which the bars are secured to the wall of the cylinder.

3. A cylinder as claimed in Claim 1 in which the bars are secured to a support structure mounted in the central region of the cylinder.

4. A cylinder as claimed in Claim 1 or Claim 2 or Claim 3 in which at least some of the bars have a rectangular cross-section.

5. A cylinder as claimed in Claim 1 or Claim 2 or Claim 3 in which at least some of the bars have a round cross-section.

6. A paper machine drying cylinder constructed and arranged to operate substantially as described herein with reference to Figures 1 to 3 of the accompanying drawings.

7. A drying cylinder as claimed in Claim 6 modified substantially as described herein in Figure 4 or Figures 5 and 6 or Figure 7 of the accompanying drawings.