Heating – Advancing structure flexing – looping or coiling sheet – web...
Patent
1989-08-22
1991-02-05
Bennet, Henry A.
Heating
Advancing structure flexing, looping or coiling sheet, web...
34155, 34156, F27B 928, F26B 1300
Patent
active
049900854
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an arrangement for an exhaust in a plant arranged for the heat-treatment of products in the form of a continuous strip, which includes means for influencing the continuous strip in question with air or some other heat-treatment medium, which is supplied to the continuous strip in such a way as to flow essentially parallel along same in a common direction, and an opening, which permits the air, etc., with which the continuous strip is treated, to pass outwards from one surface of the continuous strip in question.
In conjunction with the drying or other heat-treatment of products in the form of a continuous strip, such as paper and plastic webs, use is frequently made of heat-treatment plants, such as driers, in which air or some other heat-treatment medium is intended to transfer heat, absorb gases or water vapour released from the continuous strip by evaporation, and stabilize the continuous strip on its way through the plant. The air is sometimes also used to transport or carry the continuous strip through the plant. Heat-treatment plants other than those which operate with a supply of air can be found, for example those which operate on the basis of IR radiation or direct heat.
The design of the outlet openings of the plant and the exhaust air openings influence the above-mentioned factors, especially in connection with the processing of thin products, such as paper. The design of such openings is also critical when broad and/or fast-moving continuous strips are used, since this has an effect on the result of heat-treatment, the performance and the ease of operation of the plant.
A previously disclosed drier plant is illustrated in the drawings in FIGS. 2 and 3, and the problems associated with this plant include the following:
1. The quantity of supply air and exhaust air must be precisely balanced in order to prevent heat from leaking out into the surroundings and reducing the quality of the environment around the drier.
2. The quantity of supply air and exhaust air must be precisely balanced in order that the distance between the drier and the continuous strip shall be neither too short (thereby reducing efficiency) nor too long (thereby giving rise to the risk of scoring of the continuous strip). This is in spite of the fact that the stretching and tensioning of the continuous strip often varies for different reasons.
3. Any variation in the distance will result in a variation in drying, which will affect the drying process adversely, resulting in varying moisture profiles.
Certain solutions are associated with a considerable risk, if the quantity of exhaust air is too great, of the continuous strip simply being sucked fast against the exhaust air gap. The quantity of exhaust air must be reduced in such cases, leading to a change in drying, in the distance of the continuous strip, and in the amount of air which leaks into the premises.
4. The driers are often large (1-20 m in length, and 1-10 m in width), since the drying times for the majority of drying processes require this. The immediate problem which arises is one of maintaining the pressure distribution inside the drier completely even across the continuous strip. Uneven pressure distribution leads to uneven pressure on the continuous strip, and thus to differences in heat transfer and the risk of creasing, fluttering or similar problems which can cause serious operational breakdowns.
The previously disclosed arrangement used in the plant referred to in SE patent application (as published for opposition) No. 7513864-4 (Publication No. 397 547) includes blower boxes, from which air is intended to be blown out onto a continuous strip of product in such a way as to lift the strip for the purpose of transporting same. Arranged between said blower boxes are openings which are in communication with a surrounding space, or separately with a space in which ambient pressure is present. What is not present in this case, however, is an exhaust channel which operates by negative pressure in said previously disclosed plant,
REFERENCES:
patent: 4475294 (1984-10-01), Hendricks
patent: 4589843 (1986-05-01), Smith
Bennet Henry A.
Impact Systems Inc.
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