GB2102154A

GB2102154A - Device for regulating the superficial weight of a produced fiber mat

Info

Publication number: GB2102154A
Application number: GB08215127A
Authority: GB
Inventors: Sten Eriksson; Bengt Sinner; Nils Eric Andersson
Original assignee: ASEA AB
Current assignee: ABB Norden Holding AB
Priority date: 1981-05-25
Filing date: 1982-05-24
Publication date: 1983-01-26
Also published as: FR2506357A1; SE8103266L; DE3217838A1; GB2102154B; FI821844A0

Abstract

In a device for regulating the superficial weight of a fiber mat (31) produced in a paper-making machine (30), for example, comprising a pump (2) for delivery of a fiber suspension to a conduit (26) leading to a head box included in the machine, the flow rate of the suspension is set to a value appropriate for the desired production rate and that the fiber concentration is measured, for example via the power fed to the pump motor or by a fiber concentration meter, the signal (Q) thus obtained being supplied to a device (28) for regulating the speed of the paper machine (30) for the purpose of obtaining a substantially constant superficial weight. <IMAGE>

Description

SPECIFICATION Device for regulating the superficial weight of a produced fiber mat Technical field The pFesent invention relates to a device for regulating the superficial weight of a produced fiber mat in a machine, comprising, for example, a pump for delivery of a fiber suspension to a head box of the machine.

The need for such a device arises in various industries. For example, in the paper-making industry it is desired to regulate the fiber concentration in the fiber stock supplied via a conduit to a paper-making machine for the purpose of controlling the weight per unit area (hereinafter called the "superficial weight") of the paper produced.

Discussion of prior art Currently available systems for regulating the superficial weight of a mat of fibers often comprise an expensive superficial weight meter positioned at the point of rolling-up of the paper web formed from the mat, a volumetric flow meter and a computer system for computing a suitable control signal for a superficial weight valve, by means of which the superficial weight can be controlled. The disadvantage of this known system, besides the price, is that in the event of an error in the superficial weight, it is not possible to make the necessary corrections until a substantial continuous length of faulty paper has been produced.

From our U.K. Patent Application 2073454 (published 14 October 1981) which is incorporated herein by reference, it is known to use a device for regulating the fiber concentration of a fiber suspension flowing in a conduit, comprising a variable-speed controlled pump, such as a centrifugal pump for impelling the fiber suspension through the conduit. The power (P) supplied to the driving motor of the pump is arranged to be measured by a measuring device, for example by measuring the armature current (I) and the speed (n) of the pump motor. Signals representative of I and n are supplied to a multiplying device, the output signal (Ixn) of which gives a measure of the power (P) fed to the pump.This power signal is arranged to be supplied to a dividing device together with the output signal (q) from a flow meter in the conduit from the pump, possibly after due correction for the static loss height, in order to obtain a signal related to the dynamic loss height sK-P/q, which is also a measure of the fiber concentration (Q), which is fed as an input signal to a regulating system.

Brief statement of invention The invention is a further development of the above-mentioned prior art systems and is characterised in that the flow of the fiber suspension in the conduit is adjusted to a value proportional to the production rate of the fiber mat and that the fiber concentration is arranged to be measured, for example, via the power fed to the pump motor or by a concentration meter the measuring signal thus obtained being arranged to be supplied to a device for regulating the speed of the mat-making machine with a view to obtaining a substantially constant superficial weight of the produced fiber mat. It is thus fairly easy to obtain a control signal, corresponding to the fiber concentration, for example via the pump motor power, and via the said power assessment to control the speed of the machine and thus the superficial weight of the mat produced.Any change in the fiber concentration will result in a rapid control measure so that no significant quantity of sub-standard mat (e.g. paper web) will be produced.

Brief description of drawing The invention will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 shows a device according to the above-mentioned publication, and Figure 2 shows a device according to the present invention.

Description of prior art arrangement Referring first to Figure 1, stock material is fed from a machine chest 1 via a fiber suspension pump 2 by a variable-speed controlled drive motor 3 into a conduit 4 to an inlet 12 for the stock and pulp water drawn from a wire pit 5 and thence to a mixing pump 6. The mixing pump 6 feeds the stock/water mixture via a vortex cleaner 7, a deaeration tank 8 and a shive screen 9 to a head box pump 10 to be forwarded to a head box 11. In the conduit 4, between the machine chest pump 2 and the mixing pump 6, and upstream of the inlet 12, a stock flow meter 13 is provided which generates an output signal q,.A meter is located in the inlet 1 2 for sensing the static pressure p at the inlet 12 and a volumetric flow meter 1 5 in the inlet 12 senses the flow into the mixing pump 6 and generates an output signal q2. The numeral 16 designates a tachometer generator G sensing speed (n) of the motor 3. The current (I) fed to the motor 3 is arranged to be measured at 1 7.

The output signals I and n are supplied to a multiplying device 18, the output signal of which is proportional to the power supplied to the machine chest pump 2. The product P=nxl is obtained from the multiplying device 18, and from a subsequently positioned dividing circuit 19, the quotient P/q, is obtained, which is a measure of the pressure drop prevailing in the pump 2 and in the conduit 4. In a summator 25 the static pressure p is compensated for, whereafter the output signal from this summator is proportional to the dynamic pressure drop at the flow rate q,.

The output signal from a dividing device 20 is a measure of the pressure drop per unit flow and corresponds to the fiber concentration. This signal can possibly be corrected for the flow ratio q,/q2 in a multiplying device 24 to obtain the fiber concentration fed to the wire pit 5.

The present invention is a further development of this known system or of the other currently available system discussed earlier.

Description of embodiment according to the invention Referring now to Figure 2, the numeral 2 again designates a superficial weight control pump. The fiber concentration is measured at 25 in a pump conduit 26 (but this measurement can be made upstream or downstream of the pump 2), and the volumetric flow is measured in a unit 27. The volumetric flow can also be measured upstream or downstream of the pump 2. It is also possible to measure the fiber concentration via the power fed to the pump 2 in the manner shown in Figure 1. The pump 2 is set to provide a constant flow rate corresponding to a certain superficial weight required for the production from a paper-making machine 30 and an output signal corresponding to the fiber concentration Q is fed to a control device 28 responsible for setting a reference voltage 29 for the machine 30.The machine 30 would include a head box, a wire, a press, a drying portion, etc., but these have not been shown in Figure 2. The end product 31 from the machine 30 is required to have a constant superficial weight, and this is obtained by measuring the fiber concentration in the pump and in the pump conduit 26. Any deviation in the fiber concentration results in an adjustment of the reference voltage 29 and an appropriate compensating change of the machine speed. If, for example, the fiber concentration in the pump 2 is increased, the machine speed is also increased, and a constant superficial weight of the outgoing paper 31 is thereby obtained.Thus, the variations in, for example, the power fed to the motor driving the pump 2 or in the output signal from some other fiber concentration measuring means are made use of to control the machine speed in such a way that the superficial weight is substantially constant. This results in a higher control accuracy and a lower price with a device according to the invention. The flow of the pump motor 2 is regulated by variable-speed control. Also a certain reference voltage 32 is fed to the control device 27. The superficial weight of the product 31 is determined by the fiber quantity flowing per unit of time to the machine 30. Thus, the fiber concentration is measured, and on the basis of this measured value, the speed of the machine 30 is controlled via the reference voltage 29 (the supply voltage) fed to the paper machine. The different parts of the paper machine are easily arranged to mutually operate synchronously, so that any change in the reference voltage 29, involves a corresponding change in the synchronous speed for the different component parts of the machine 30.

The invention according to Figure 2 can be varied in many ways within the scope of the following claims.

Claims

1. A device for regulating the superficial weight of a produced fiber mat issuing from a machine which comprises a pump for impelling a fiber suspension along a conduit of the machine, wherein first means is provided to set the flow rate of the fiber suspension in the said conduit to a value appropriate for the desired production rate of fiber mat in the machine, second means is provided to measure the fiber concentration in the suspension flowing at the said rate in the conduit and generate a signal related thereto, and a control means for the speed of the machine is provided, which control means is arranged to be fed with the signal derived from said second means, whereby the speed of the machine is varied to obtain a fiber mat therefrom which is of substantially constant superficial weight irrespective of changes in said measured fiber concentration.

2. A device according to claim 1, in which the fiber concentration is measured in the conduit.

3. A device according to claim 2, in which the fiber concentration is measured upstream of the pump.

4. A device according to claim 2, in which the fiber concentration is measured downstream of the pump.

5. A device according to claim 1 or claim 2, in which said control means controls the supply voltage fed to the machine.

6. A device for regulating the superficial weight of a produced fiber mat issuing from a machine substantially as hereinbefore described with reference to Figure 2 of the accompanying drawing.

7. A method of regulating the superficial weight of a produced fiber mat issuing from a machine which comprises impelling a fiber suspension along a conduit of the machine, setting the flow rate of the fiber suspension in the said conduit to a value appropriate for the desired production rate of fiber mat in the machine, measuring the fiber concentration in the suspension flowing at the said rate in the conduit and generating a signal related thereto, and controlling the speed of the machine to obtain a fiber mat therefrom which is of substantially constant superficial weight irrespective of changes in said measured fiber concentration.