Drying and gas or vapor contact with solids – Apparatus – With means to treat gas or vapor
Patent
1988-12-27
1990-09-04
Bennet, Henry A.
Drying and gas or vapor contact with solids
Apparatus
With means to treat gas or vapor
34114, 34116, 34123, F26B 500
Patent
active
049532979
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a method in multi-cylinder dryers of a paper machine, which said dryers comprise two lines of drying cylinders, in whose connection twin-wire draw is applied so that, by means of the said drying wires, a closed draw is obtained in the transfer of the paper web from one cylinder line onto the other, and in which said method, in view of providing the said closed draw, the guide rolls of the drying wires are placed at the proximity of the run of the other wire on which the drying wire runs from its drying cylinder to its guide roll, whereat air is blown through the said drying wires so as to ventilate the pockets defined by the said wires and the free faces of the drying cylinders.
The invention further concerns a device intended for carrying out said method in a multi-cylinder dryer of a paper machine, which said dryer comprises two lines of drying cylinders placed one above the other, in which said dryer twin-wire draw is applied so that the drying section comprises an upper wire, which is guided by its guide rolls, and a corresponding lower wire, which is guided by its guide rolls, and which said guide rolls are placed so that the web runs from the upper cylinders onto the lower cylinders and vice versa all the time supported by the drying wires and in which said device, in said gaps between the cylinders, the web is transferred from one drying wire onto the other at the guide roll of the latter drying wire.
In recent years the running speeds of paper machines have been increasing constantly, and now the limit of 1500 meters per minute is already approaching. Thereat, fluttering of the web becomes a serious problem deteriorating the running quality of the power machine. The passing of the web from the press section into the drying section and the supporting of the web within the area of single-wire draw can be controlled by means of the methods and devices suggested in the applicant's certain earlier Finnish patents and Finnish patent applications, but within an area of twin-wire draw, in particular in the 3rd and 4th drive groups, difficulties have been encountered at high running speeds.
In the present application, single-wire draw means such a mode of passing of the web over the heated drying cylinders in which the web passes from one cylinder line to the other supported by the drying wire so that on one cylinder line the web is between the drying wire and the cylinder face, and on the other cylinder line the web is outside and the drying wire is between the cylinder face and the web, and the web runs the passages between the cylinder lines supported by the drying wire. It is an advantage of this single-wire draw that the web is all the time supported by the drying wire and it has no open draws, or at least no substantially long open draws, whereby the risk of wrinkles and breaks of the web is lowered.
In the present application, twin-wire draw means the prior-art mode of supporting and passing the web in connection with the heated drying cylinders in which an upper wire is used on the upper cylinders and, correspondingly, a lower wire on the lower cylinders, which said wires are guided by the faces of the drying cylinders and by guide rolls placed between the drying cylinders so that, on the line of upper cylinders, the web is pressed by the upper wire into direct drying contact against the faces of the upper cylinders and, correspondingly, the web is pressed by the lower wire onto the faces of the lower cylinders.
in the case of twin-wire draw, the web has usually had substantially long free runs when running from one cylinder line onto the other. These free runs have been subject to fluttering and to resulting breaks and wrinkles of the web, which drawback has become worse with increased running speeds of paper machines, and the drawback has appeared with particular emphasis in the initial part of the drying section, where the web is still relatively moist and, therefore, weak and where its elastic properties are favourable for fluttering. Attempts have been made to eliminate t
REFERENCES:
patent: 3753298 (1973-08-01), Ely
patent: 4539762 (1985-09-01), Eskelinen et al.
patent: 4602499 (1986-07-01), Eskelinen et al.
Eskelinen Pekka
Karlsson Markku
Raatikainen Pentti
Virta Raimo
Bennet Henry A.
Sollecito John
Valmet Paper Machinery Inc.
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