Paper making and fiber liberation – Processes and products – Running or indefinite length work forming and/or treating...
Patent
1987-12-23
1990-04-10
Schor, Kenneth M.
Paper making and fiber liberation
Processes and products
Running or indefinite length work forming and/or treating...
34 4, 34 39, 34 41, F26B 1320
Patent
active
049151541
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a counter reflector, e.g. in a paper making machine. It is designed to reflect heat radiation, particularly infra-red (IR) radiation, which issues within a drying zone from heating elements, such as IR-elements with reflectors, penetrates a continuous running paper web, and is reflected back to the paper web. Thus, heat radiation, which penetrates the paper web, is recovered by means of the counter reflector, which is placed opposite to said heating elements with reflectors and thus, the energy supplied to the paper making machine can be highly exploited. The invention also relates to a method of drying a web with the aid of such a counter reflector.
It has further been proposed to produce a counter reflector from an IR-reflecting material, e.g. an aluminium plate. A disadvantage of these known counter reflectors is that the reflection appears to lack a continuous and uniform impact on the drying conditions of the advancing paper web. The reflected heat radiation fluctuates considerably as to direction and intensity, partly due to the fact that heat disappears as radiation from the opposite side of the counter reflector and that the latter is substantially unable to store heat.
According to the present invention, a most uniform counter reflector can be achieved, which is favourable to the overall energy economy and the drying/curing efficiency of a paper making machine, with a counter reflector having a major reflecting surface of shields with radiant heat conserving properties. The counter reflector shields are preferably glass ceramics. However other materials such as ceramic materials coated with glass, glass, glass coated with ceramic material may be used. Alternatively steel or nickel plates coated with alumina and/or magnesium oxide by flame spraying or plasma spraying can be used for the shields. Flame spraying is usually carried out at a temperature of 4000-5000 degrees Celcius and plasma spraying at 15000-30000 degrees.
The shields are preferably backed up by an insulation layer consisting of ceramic fibres, such as aluminium silicate having a high degree of purity and resistance to heat, or the like. Furthermore, the counter reflector is preferably built up by means of a surrounding frame of square steel tubes, within which extends a lattice-like support for carrying said shields and said insulating layers, which may be arranged in groups of six within tray-shaped boxes of thin metal sheet.
A preferred method of attaching the shields, layers and boxes to the lattice-like support is by means of hollow copper rivets. Slot-like openings are left between adjacent boxes. Spaced apart and behind the shields a rear wall closes the rear side of the counter reflector and forms a chamber which can be pressurized with a gas, preferably compressed air. The gas can flow through the slot-like openings towards the paper web, so that the web receives both radiation reflected from the surface of the shields and warm air heated by the radiation absorbed by the counter reflector. The issuing gas flow also serves to pressurise and thus to stabilise the space between the counter reflector and the adjacent web.
The counter reflector supplies heat radiation into its inner portion or chamber and is able to absorb large amounts of heat. However, it is also able to emit the stored heat again in the opposite direction as heat radiation. Thus, it has a pronounced capacity to give off a continuous and even heat radiation. When saturated with heat, the counter reflector will entrap all further heat which is generated in the drying/curing zone. Furthermore, the counter reflector of the present invention can withstand temperature shocks, as it has only a small linear thermal coefficient of expansion. It is stable at high temperatures, up to about 700 degrees Celcius, as well as in a mechanical sense and is not easily warped. The smooth upper surface of the shields stays substantially clean and is easily cleaned, a feature of the greatest importance in the environment of a paper making machine, i
REFERENCES:
patent: 4513516 (1985-04-01), Bjornberg
patent: 4594795 (1986-06-01), Stephansen
Dang Thi
Infrarodteknik AB
Schor Kenneth M.
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