Title:
WEB DRYER
United States Patent 3753298


Abstract:
A web dryer structure for thermal removal of moisture from a traveling web such as a web of paper coming from the press section of a paper making machine including a row of upper dryer drums and a row of lower dryer drums with the drums positioned to carry the web in a sinuous path successively between the upper and lower drums and the web wrapping the upper and lower surfaces of the drums respectively with upper and lower looped felts wrapping the web on the upper and lower surfaces of the drums with the felt guided by guide rolls which are shifted laterally of the spaces between the drums a distance in the direction of web movement so that the pockets formed between the felts and the drums are pressurized due to the induced flow of air by the traveling felts and the guide rolls pumping air through the felts.



Inventors:
ELY D
Application Number:
05/209204
Publication Date:
08/21/1973
Filing Date:
12/17/1971
Assignee:
BELOIT CORP,US
Primary Class:
Other Classes:
34/117, 34/120, 34/123
International Classes:
D21F5/04; D21F1/00; D21F5/02; F26B13/08; (IPC1-7): F26B13/06; F26B13/16
Field of Search:
34/117,166,120,111,116,123
View Patent Images:



Primary Examiner:
Camby, John J.
Assistant Examiner:
Yuen, Henry C.
Claims:
I claim as my invention

1. A web dryer for the thermal removal of moisture from a traveling web comprising in combination,

2. A web dryer structure for the thermal removal of moisture from a traveling web constructed in accordance with claim 1 wherein a flow of air is induced through the belts into the pockets between the lower belt and the upper drums and between the upper belt and the lower drums for aiding in transfer of the web and drying of the belts.

3. A web dryer structure for the thermal removal of moisture from a traveling web constructed in accordance with claim 1 wherein lead guide means is provided so that the upper belt travels in an upward path to the first upper drum and the first lower guide roll carries the lower belt to position the web in engagement with the upper belt as the web travels from the first lower to the second upper drum.

4. A web dryer structure for the thermal removal of moisture from a traveling web constructed in accordance with claim 2 wherein the air flows axially outwardly from the ends of said pockets.

5. A web dryer structure for the thermal removal of moisture from a traveling web constructed in accordance with claim 1 and including a lead guide for the upper belt directing it in a path onto the first upper drum with the lower belt then passing down over the first lower drum.

6. A web processing device for contioning a traveling web constructed in accordance with claim 1 wherein the guide rolls comprise a perforate shell and a suction gland in said shell.

7. A web dryer structure for the thermal removal of moisture from a traveling web comprising in combination:

8. A web dryer structure for the thermal removal of moisture from a traveling web constructed in accordance with claim 7 wherein a flow of air is induced in the open spaces between the lower felt and upper drums and upper felt and lower drums.

9. A web dryer structure for the thermal removal of moisture from a traveling web constructed in accordance with claim 7 and including a heated dryer means positioned outside of the belt on the first upper dryer drum.

10. A web processing device for conditioning a traveling web comprising in combination,

11. A web processing device for conditioning a traveling web constructed in accordance with claim 10 wherein the guide rolls are positioned so that the web wraps a greater angle of the drum on the onrunning side than on the offrunning side.

Description:
BACKGROUND OF THE INVENTION

The invention relates to improvements in dryer drum structures for drying a traveling web and more particularly to a structure which is used for thermally drying a web such as a continuous run of paper which is received at high speed from the press section of a paper making machine.

More particularly, the invention relates to the particular arrangement and guidance of the felts for supporting the web on the drum so that the web is supported at all locations of its travel and air pressure is induced in the pockets between the web and the drum so that the paper machine can operate at very high speeds without flutter of the web.

In the dryer section of a thermal dryer, such as for a paper machine, the moisture bearing web is received from the press section of the machine and is directed along a serpentine path in wrapped relation with a plurality of steam heated dryer drums. These drums are usually arranged in upper and lower rows with the drums staggered so that the paper web can pass back and forth and wrap the upper and lower drums with the moisture evaporating from the web as it is heated while in contact with the drum. To aid in the heat transfer from the drum to the web and to support the web on the drum, upper and lower looped felts are provided which wrap over the outer surface of the web while on the drum surface. Arrangements have been made for guiding the felts in their travel between the drums and efforts have been made to utilize such guides to increase the drying action on the felts.

However, in relatively high speed paper making machines, disadvantages have been encountered in that the unsupported web in its travel between the felts will flutter. To attempt to run the dryer section of the machine at a slower speed to avoid such flutter will, of course, require slowing down the entire machine. Further disadvantage has been encountered in that with improvements in other sections of paper making machine, the effectiveness and efficiency of the dryer section has not kept up in certain instances so that additionally large or long dryer section have to be provided to accomodate increases in capacity of the other section of the machine. Speed and space limitations have made the drying section a limiting factor in the paper machine capacity and its speed in certain structural designs. In an attempt to avoid flutter at high speeds of 3,000 feet per minute and over, attempts have been made to stretch the paper web, but this does not eliminate flutter and tends to break the traveling web. Natural flutter is caused by air pressure buildup from air traveling with the web and felts at high web travel speeds and difficulty in controlling the web even when supported by the felt over felt turns has been encountered.

It is accordingly a feature of the present invention to eliminate the disadvantages of structures heretofore available by providing an arrangement wherein the web is in contact with or in close running relation to the supporting felt at all locations of its travel between upper and lower tiers of dryer drums.

Another feature of the invention is to provide felt support rolls in a positioned arrangement so that an induced buildup of air in the pockets between the felts and supporting rollers is avoided.

Other efforts to control the problems which have been encountered in structures heretofore available have been numerous and these have including positioning the drums very close together so as to shorten the sheet draw between dryers. This proves disadvantageous because of the difficulties in sheet threading and problems with the felts. Efforts to ventilate the pockets between the felts or to break up the air layers carried on the felts to prevent flutter have also been found to have difficulties at high rates of speed.

It is accordingly an object of the present invention to provide a machine which has a thermal dryer section which is capable of handling traveling webs at a high rate of speed such as from 3,000 to 4,000 feet per minute or more.

Another object is to provide a dryer wherein separate felt dryers are not needed. Further objects of the invention are to provide a thermal dryer embodying heated dryer drums wherein a web passing over the drums is supported at all locations of its travel by supporting belts and wherein an induced flow of air is created through the belts and the pockets to avoid web flutter causing air flows from the pockets.

A still further object of the invention is to provide an improved structure for a dryer section of a paper making machine utilizing upper and lower dryer drums which permits the possibility of reconstruction of existing dryer sections without extensive relocation of parts and without relocating the dryer drums and with a minimum of reconstruction.

Other objects, advantages and features will become more apparent including the equivalent structures and method from the teaching of the principles of the invention in connection with the disclosure of the preferred embodiments in the specification, claims and drawings in which:

DESCRIPTION OF THE DRAWINGS

The single drawing of the application is a somewhat schematic end view illustrating the position, structure and operation of a mechanism in accordance with the principles of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A traveling web W is received from the left end of the drawing traveling to the right and the web may be a traveling paper web received from the last press section of a paper making machine. The web is carried by looped belts 20 and 21, which are of cotton, plastic or other material sufficiently porous to permit the escape of steam and the flow of air therethrough and which will be referred to hereinafter as felts. The web is received on a traveling lower felt 21. A similar upper felt 20 is led onto the lower felt with the web therebetween. The lower felt is trained over a guide roller 23 and the upper felt over a guide roller 35.

The web is led by the felts through the dryer drums which are arranged in an upper row formed by the drums 12, 13, 14 and 15 and a lower row 16, 17 and 18 with the dryer drum being of the conventional steam heated type and being laterally offset from each other.

The upper felt wraps the web over the upper surfaces of the upper drums and the lower felt wraps the web over the lower surfaces of the lower drums.

The upper felt 20 is guided between the upper rolls by a series of felt guide rolls 26, 27 and 28. Similarly, the lower felt 21 is guided between the lower dryer drums by a series of guide rolls 24 and 25. The looped felts have adequate guiding and tensioning rolls which are omitted from the drawing for the sake of clarity. The felts also may be provided with felt cleaners and felt dryers.

As will be seen from the drawing, the guide rolls 26, 27 and 28 are positioned between respective pairs of lower dryer drums. Similarly, the felt guide rolls 24 and 25 are positioned between respective pairs of upper dryer drums.

The felt guide rolls are also arranged so that the guide rolls for the lower felts are positioned higher than the guide rolls for the upper felts. In the arrangement shown, considering the drum 12 to be the first upper drum and 13 the second upper drum, the first guide roll 26 is positioned below the second upper drum 13. Considering 16 to be the first lower dryer drum and 17 to be the second lower dryer drum, the first guide roll 24 is positioned above the second dryer drum 17.

As shown in the drawing, the web W travels over the first upper dryer drum 12 supported on the lower felt 21 and is guided to wrap the first lower dryer drum 16. A heated dryer means 34 is positioned outside of the belt above the upper drum 12. The web then travels upwardly in a run 21a of the lower felt to where it is transferred to the upper felt 20 at the location of the felt guide roll 26. Air moving with the web W on the felt run portion 21a is forced into the triangular space indicated at A and builds up between the felt and web as they wrap the felt roll 26. The geometrical relationship between the felt and felt roll 26 indicated at B combined with the direction of travel and rotation of the felt and roll 26, respectively, is such that a subatmospheric condition will be created at B which will draw the air trapped between the felt and web through the felt into the space B thus avoiding any tendency of the web to flutter in its travel along the span indicated at 20a. Similarly, air moving with the web W on the felt run portion 20b is forced into the triangular space C and builds up between the felt and web as they wrap the felt roll 24. The subatmospheric condition created at D will draw the air trapped between the felt and web through the felt into the space D thus avoiding web flutter. This process is repeated at felt rolls 27, 25 and 28 thus providing for a stable and controlled web run through the dryer section.

Additionally, air flowing with the lower surface of the lower felt in its run 21a will induce an upward flow of air to pressurize the space 36 thereby causing a flow of air through the felt into the pocket 30 as indicated by the arrows. This flow of air aids in the transfer of the web from the lower felt run 21a to the upper felt 20a at the guide roll 26 so that the web will travel upwardly following the upper felt in its run 20a. The pressure in the pocket 30 will support the web on the felt run 20a and the flow of air thorugh the felt in the upper portion of the felt run 21a tends to dry the felts. Moisture laden air is removed from the pockets 30, 31, 32 and 33 at the front and rear end portions thereof. The airflow pattern through the felt into the pockets is repeated at 32, 31 and 33 and through successive pockets not shown.

To further aid in the removal of air from the critical areas A,B,C and D the felt rolls 26, 27, 28, 24 and 25, as shown at 25, may be in the form of suction felt rolls comprising a perforate shell and an interior suction gland positionable for optimum air removal. Another solution to the problem of web flutter at high papermaking speeds has been presented in the co-pending application for patent Ser. No. 209205 of Elmer C. Crist filed concurrently herewith and the present invention is a specific improved form of the structure disclosed therein.

As will be observed with reference to FIG. 3 of the aforementioned application for patent by Elmer E. Crist, Ser. No. 209,205, the air carried on the felt run 10c is forced into the triangular space defined by the felt run portion 10c and feltroll 19a. The air is forced through the felt and is trapped by the web W causing it to bulge and form a bubble causing causing a potentially unstable condition.

In the arrangement of the present invention air carried on the web span 21a is forced into the triangular space defined by the web run portion 21a and roll 26. On the off-running side of the roll 26 a vacuum is created which sucks the air through the felt from the underside of the web. No air bubbles are formed around the roll 26 and the web remains in a stable condition.

Similarily air carried on the feltrum portion 21a is carried into the pocket 36 and forced into the pocket 30 through the felt as indicated by the arrows thus preventing air buildup around the roll 24.

As will be observed, the web has been supported at all locations of its travel and there are no unsupported draws where flutter or uncontrollability can occur.

Also, the guide rolls are so positioned so that the induced flow of air not only aids in transferring of the web, but aids in drying of the felts. At high speeds, this induced flow of air is significant, and the conduits at the ends of the pockets can control the flow of air so that the pockets are slightly pressurized to aid in supporting the web on the felt after it has been transferred or they may induce an increased flow of air through the felt.