Paper making and fiber liberation – Apparatus – Running or indefinite length product forming and/or treating...
Patent
1988-02-16
1989-10-03
Chin, Peter
Paper making and fiber liberation
Apparatus
Running or indefinite length product forming and/or treating...
34 16, 34155, 34156, F26B 1710
Patent
active
048714259
DESCRIPTION:
BRIEF SUMMARY
The present invention is related to a fixation device for felts and wires for paper machines, according to the preamble of the claims.
Felts and wires for paper machines today are produced in widths up to 10 meter and constructed to withstand large strains of different types, such as high moisture content, large temperature, large pressure, tension forces in the longitudinal direction and influence from chemicals.
The felts and the wires, shaped as endless bands, are running at very hight speeds in the paper machines, in extreme cases up to 2000 meters per minute. It therefore is substantial that they are homogeneous both in the longitudinal as well as in the thermally stable direction to ensure operation without problems.
One of the processes involved in the production of all types of felts and wires today is the heat treatment at a temperature substantially higher than the highest temperature by which the products are used in the paper maschines. This heat treatment, the fixation, provides the felts and the wires with thermical stabile properties and desired stretching properties. Additionally the felts and the wires also are treated with chemical solutions hardening at specified temperatures.
To provide the felts and the wires with the desired properties it is important that the same maximum temperatures is achieved across the whole width during the fixation process. Furthermore it is desired to achieve the same temperature throughout the thickness of the felt and the wire, in other words in the upper and lower surfaces as well as in the middle.
During fixation, the felt and the wires, as endless bands, are stretched between two parallel rolls of which at least one is driven in such a way that the felts can be moved through the fixation zone which is arranged parallel to and between the axis of the rolls.
A normal heating method in the fixation process is blowing heated air against both sides at the felt. As stated above, it is very important, and necessary, to maintain the same air temperature across the whole width of the felt or the wire. It is, however, not sufficient that only the temperature of the blown air is the same across the width as pressure differences may occur in the fixation zone due to small differences in the high air velocity which is necessary to achieve a good heat transfer to the felt. Surrounding air very easily will be drawn into the process by induction, which means that the environmental air is drawn into the fixation zone itself and here mixed with the air having controlled temperature.
The main parameters influencing the result of the fixation process are the temperature of the air penetrating the felt, the amount of air penetrating, the velocity of the air through the felt and strongly influencing the afore-mentioned, the distance between the jets and the felt is of major importance, e.g. the distance must be uniform along the entire length of the jets. Influencing the distance between the jets and the felt during operation is the behaviour of the upper structure due to the heat influence, which across a length of 10 meters or even more, can lead to a not acceptable distance difference between the middle of the structure and the ends.
Any leakage of surrounding air into the fixation zone will lead to a temperature reduction, and especially local reductions thereby increasing the danger of undesired temperature variations across the surface of the felt. Such air leakage is reduced to a certain extent by the use of sealings at apertures where the felt and the wire is transferred into or out of the heating zone, but a complete elimination so far has been difficult to achieve in practical work. By the fixation device according to the present invention, however, this problem in the fixation process is avoided in such a way that leakage air from the environment is not effecting the conditions in the fixation zone.
This advantage is achieved by the fixation device according to the invention as defined by the features stated in the characterizing clauses of the claims.
BRIEF DESC
REFERENCES:
patent: 3945881 (1976-03-01), Speidel
patent: 4085522 (1978-04-01), Stroszynski
patent: 4320587 (1982-03-01), Vits
patent: 4467537 (1984-08-01), Trotscher
patent: 4606137 (1986-08-01), Whipple
patent: 4625433 (1986-12-01), Giancola et al.
Alfsen & Gunderson A/S
Chin Peter
Dang Thi
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