GB1192231A - Improved Fibrous Sheet Manufacturing Method and Apparatus. - Google Patents

Abstract

1,192,231. Papermaking. INDUSTRIAL NUCLEONICS CORP. 1 May, 1967 [29 April, 1966], No. 20071/67. Heading D2A. [Also in Division G3] A characteristic of a fibrous sheet formed from a layer of fibrous slurry emerging from a headbox is maintained at a predetermined value by automatically controlling, in dependence on a measurement of the characteristic, the flow of liquid adjacent to one horizontal surface of the slurry layer as it emerges from the headbox. In Fig. 4, a mixture of wood pulp fibrous slurry and white water is supplied to a headbox 18 containing an agitator 40. A slice 90 associated with an opening 20 causes the mixture to emerge as a layer 92 on a paper forming wire conveyor (not shown) from which the paper sheet formed passes to a dryer 24. To ensure a desired moisture content of the sheet 'before it enters the dryer, a moisture detector 100, 102, responsive to any error, controls a hydraulically operated valve 96 so that the flow of white water supplied to form a layer 98 on the upper surface of layer 92 is varied to correct the moisture content. The moisture detector may be scanned across the sheet, signals from it being stored and utilised to control a number of valves such as 96 across the width of the sheet so that a greater moisture content is maintained near the edges to compensate for subsequent greater drying at the edges. To maintain a constant weight of paper, a gauge 104, e.g. of the radiation absorption type, scanned across the sheet leaving the dryer, automatically controls at 108 the flows of white water to a number of sections across the width of the headbox at which the weight may be maintained at different values if a particular cross section of the sheet is desired. If the weight is outside the range of flow control 108, the switch shown may be operated to transfer control to a motor 112, which makes a coarse adjustment by moving slice 90. The flow of white water controlled at 108 may be confined to the lower side of layer 92 by a baffle in the headbox 18 which flexes to vary the relative thickness of the white water layer with variations in the rate of flow of white water. Such an arrangement, without the moisture control but with weight detection, preferably before the dryer, compensated for moisture content variation, is also described. Moisture control as described above with weight control by varying a slice or mixing valve, and weight control as described above with moisture control by varying a water spray or the environment are referred to.