Paper making and fiber liberation – Processes and products – Running or indefinite length work forming and/or treating...
Patent
1981-11-03
1983-09-27
Fisher, Richard V.
Paper making and fiber liberation
Processes and products
Running or indefinite length work forming and/or treating...
162300, 162301, 162306, 162363, 162374, D21F 100, D21F 140, D21F 150, D21F 1102
Patent
active
044067399
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a procedure in the wire section of a paper machine, wherein the web formation at least partially takes place between two wires, for dewatering the web and for detaching the web from one of the two wires.
The present invention moreover concerns a twin-wire former comprising a loop of the carrying wire, in the initial part of the run of which the web is formed with dewatering taking place in one direction therethrough, and a loop of a covering wire, which is at a suitable web forming stage conducted to cover the web and the carrying wire loop, in such manner that dewatering of the web is achieved through the covering wire loop as well, and in support of which after the twin-wire section the web is transferred for further conduction to the press section of the paper machine.
The present invention concerns twin-wire formers which are generally of the type disclosed in applicant's Finnish Pat. No. 50648, which corresponds to U.S. Pat. No. 3,846,233. Such former comprises a lower wire loop, the web being in actual fact formed on the substantially horizontal run or on a run thereof deviating from horizontal to some degree, after the headbox, with dewatering taking place in one direction downwardly through this wire, and an upper wire loop, which at a given web forming stage is conducted to cover the lower wire loop and the wet web being supported by the lower wire loop, in such manner that the dewatering takes place also through the upper wire. In this former the web being produced rests on termination of the forming and dewatering process supported on the lower wire, from which the web is thereafter detached for further conduction to the press section of the paper machine.
In a modification of the known former, the upper wire loop, i.e. the covering wire, also operates as a web forming wire, but that modification is concerned with the production of a two-ply or multi-ply web. The present invention may in certain substantial parts be applied in such formers as well in which a two-ply or multi-ply web is produced.
In said Finnish Pat. No. 50648 corresponding to U.S. Pat. No. 3,846,233, a special stationary forming shoe is used after a single-wire forming part, this forming shoe being provided with a suction zone and/or a blowing zone, but in the use of the stationary forming shoe a problem has been encountered that as it is operating against the carrying wire it often causes excessive attrition of the wire. Similarly, the surface of the forming shoe facing the wire is subject to wear at the same time. A problem additional to the wear problem just mentioned is the fact that the friction arising from the stationary shoe gives rise to extra energy consumption. In the said Finnish Patent has been disclosed, as an alternative, the use of a rotating dewatering roll, but this affords only a partial solution to the problems.
Regardless of whether formers of the described above are used to produce a single-ply or two-ply web, a problem frequently encountered is that after the dewatering stage between two wires the web fails to follow reliably along with the lower, carrying wire, but tends instead, from time to time at least, to follow along with the upper, covering wire. This may result in a web break and shutdown of the machine. In addition, even if no actual break should occur, the web may partially adhere to the upper wire, which may have the consequence for instance of poor upper surface finish of a single-ply web or of a splitting tendency of the web in the case where a two-ply web is being produced.
The object of the twin-wire former of the invention, considered as a whole, is to provide a construction which causes only a minimum of wire attrition and which reduces the drive energy consumption of the wire section, while at the same time the consumption of suction energy required for the actual dewatering is reduced. In general, structural components causing wear of the wire are naturally all those stationary members which guide the run of the wire and exert an influence on the dewaterin
REFERENCES:
patent: 3649449 (1972-03-01), Nykopp
patent: 3726758 (1973-04-01), Parker et al.
patent: 3846233 (1974-11-01), Kankaanpaa162312
Fisher Richard V.
Valmet Oy
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