Varnished paper and cardboard dryer - has hollow conductors to deliver microwave energy to moving material across its line of travel

To dry paper or cardboard webs or sheets, coated with a water soluble dispersion varnish, microwave energy is applied to the moving material through hollow conductors across its line of travel. The residual energy is measured at the end of each hollow conductor for comparison with a nominal value to adjust the oscillator which generates the microwave, on a deviation. The drying capacity is altered by a change of nominal value. The hollow conductors can be aligned at an angle to the direction of material travel so that, on max. wetness of the varnish and max. power of each oscillator, the water is evaporated on a single pass to leave only a small remainder. Each hollow conductor is heated to prevent condensn. build-up, and at least one hollow conductor is flushed with air to clear it of water vapour. At least one hollow conductor is shrouded by a wave inert film above and/or below the material, and air is blown between the paper/cardboard and the film shrouding, or all the hollow conductors are shrouded above or below the material, and air is blown between the unshrouded conductors and the paper/cardboard. USE/ADVANTAGE -Used for drying constantly moving paper/cardboard materials which have been coated in a varnishing machine, or through the final rollers of a printing press. it gives a consistent drying action, irrespective of ambient conditions, and does not need an application of non-stick powder to prevent adhesion between adjacent sheets after drying.