Patent GB-1266221-A (GB)
IPC: D21G9/00
Filed: 1969-02-17
Abstract: 1,266,221. Paper-making apparatus. INDUSTRIAL NUCLEONICS CORP. 17 Feb., 1969 [16 Feb., 1968 (2)], No. 8554/69. Heading D2A. [Also in Division G3] In a system for controlling a variable property of a product, the ratio of the amount of the product for which the property is outside a predetermined limit, to the total amount, is determined and utilized to maintain the ratio substantially constant. In Fig. 1, clear water from a source 11 is mixed with fibre from a source 12 and supplied by a pump 14 to a headbox 15 from which it emerges through a slice to form a sheet of paper on a Fourdrinier wire 17 through which excess water is removed by suction and gravity and returned as a white water supply to pump 14. The sheet is then dried by passing through water-removing press rollers 18, steam heated rollers 21 having a slow response, and a transversely sectioned electric or gas-heated roller 25 having a fast response. Finally, after calendering at 26, the paper is wound on a take-up reel (not shown). Sheet weight per unit area is measured before and after drying by scanning radiation gauges 31, 32 respectively across the width of the sheet. Moisture content after drying is measured by scanning a capacitance gauge 33 across the sheet. During scanning of the gauges, which may occur at different times under the control of a programmer 41, measuring circuits 42, 43, 44 produce signals corresponding to instantaneous and average values during the scan. The difference between average and instantaneous values during one scan may be added to the instantaneous value during the next scan to get an early estimate of the average value during the next scan. Programmer 41 controls switches 51, 52 so that instantaneous measurements by gauges 32, 33, applied to elements 47, 48 which deduce the weight per unit area of absolutely dry sheet, occur at the same lateral regions of the sheet as the instantaneous measurement of wet weight by gauge 31 signals from which are delayed at 45 so that they correspond to the same longitudinal region measured by gauges 32, 33 in order to compute the ratio between dry and wet weight. This ratio is produced at 54 and periodically stored at 56 for use in estimating, at 57, dry weight from applied wet weight measurements. Variations of these dry weight measurements are automatically corrected by applying them through regulators 82, 84 to control (a) the datum of a system stabilising rate of flow of the mixture by controlling valve 36 in dependence on a rate of flow measurement at 88 and (b) the datum of a system stabilising fibre density by controlling a water valve 35 in dependence on a fibre content measurement at 85. The ratio stored at 54 is also used for estimating, at 58, moisture content from applied wet weight measurements. Variations of this moisture content are then applied through a regulator 66 to control the datum of a system stabilising dryer temperatures by controlling a steam valve 23 for rolls 21 and heaters for roll 25 in dependence on roll temperature measurements at 68, 69 and 65 respectively. Rate of drying is thus suited to moisture content. The signal from measuring circuit 44 representing moisture content at the dry end is applied to a computer 61 which determines, by integration, the proportion of the sheet production which is outside a predetermined moisture content limit. This proportion is then compared with a desired value at 62 so that any error is effective through regulator 66 to control the heating of dryer 25 and thus restore the proportion to the desired value. A further computer 63 determines the proportion of the sheet production which is outside a predetermined fibre content limit. This proportion is then compared with a desired value at 64 so that any error is effective through regulator 82 to control the consistency and rate of flow of mixture to pump 14. Signals corresponding to moisture content at different points across the width of the sheet derived by a computer 75 from measuring circuit 44 are effective through a computer 76 to control regulators 73 which vary the heating across roller 25 so as to equalize moisture content across the width of the sheet. Signals derived by computers 79, 81 from measuring circuits 43 and 44 corresponding to fibre content control slice screws 16 so as to equalize fibre content across the width of the sheet. Digital as an alternative to analogue computation is referred to.