CA2007716A1

CA2007716A1 - Control method for a chip refiner

Info

Publication number: CA2007716A1
Application number: CA 2007716
Authority: CA
Inventors: Aslak Savonjousi
Original assignee: ABB Stromberg Teollisuus Oy
Current assignee: ABB Stromberg Teollisuus Oy
Priority date: 1990-01-12
Filing date: 1990-01-12
Publication date: 1991-07-12

Abstract

(57) ABSTRACT OF THE DISCLOSURE

This publication discloses a method for controlling a chip refiner. According to the method, chips are metered into a chip refiner with the help of metering means (10, 9), feeder means (3, 7) adapted to the chip refiner are used for feeding chips between refiner disks (5) for refining, and water is added to the chips prior to feeding them between the refiner disks (5). In accordance with the invention, temperature of the axial bearing is measured, and using conventional methods, the volume of chip stock metered to the feeder means (3, 7) is controlled with the help of metering means (10, 9) so as to regulate the temperature of the axial bearing to constant level.

(Figure 1)

Description

Control method for a chip refiner The present invention relates to a control method for a chip refiner in accordance with the preamble of claim 1.

In prior-art implementations, chip stock has been fed into the chip refiner at a constant rate. Because of the variations in the chip stock consistency and chip size, this method is incapable of producing refined stock at a constant quality.

Known in the art are also controlled systems in which chip stock is fed using a variable-speed motor~ In one of these methods, feed rate is controlled by regulating the input power to the chip refiner from the power source to a constant level. Even if a constant load by the refiner on the power source is maintained, uneven quality of the refined stock will result, due to variations in chip stock consistency and moisture content. In another method using control means, chip stock is fed into the chip refiner at controllable set rate by measuring the output rate and refined stock consistency from the chip refiner, computing the product of these measure-ment variables which is relative to mass flow rate, and the obtained mass flow rate is used as the input variable for the control loop of the input feed rate. ~ecause of the technical difficulties in deriving the value of the mass flow rate, the control response of the method is rather slow. Consequently, an unsatisfactory quality of refined stock results therefrom.

The aim of this invention is to overcome the disadvantages of prior-art methods described above and to achieve a novel control method for a chip refiner.

While searching the ways to eliminate the disadvantages caused by the variations of the input density of the chip stock, a surprising observation was made on the basis of the measu-rements: -the temperature of the axial bearing gives the information, which can be used while controlling a chip refiner.

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Hence, the invention is based on measuring the temperature signal of the axial bearing of the refiner and controlling this temperature to a constant level by regulating the chip stock feed rate to the chip refiner.

More specifically, the system in accordance with the invention is characterized by what is stated in the c:haracteriziny part of claim 1.

The invention provides outstanding benefits.

By way of measuring the temperature of the of the axial bearing of the refiner in order to obtain a measurement value for the density of the chip stock to be refined, 2 control method for the regulation of chip stock consistency in the refiner gap to a constant value is achieved that is superior to those used in prior-art methods, because the control variable is immediately available.

The invention is next examined in detail with the help of an exemplifying embodiment illustrated in the attached drawings.

Figure 1 shows in a diagrammatic form a control system in accordance with the invention.

Figure Z shows in a diagrammatic form another control system in accordance with the invention.

According to Fig. 1, the chip stock to be refined is brought to the refining plant with the help of a conveyor 1. The chips are fed and metered by means of a metering feeder 9 driven by a metering motor 10 into a feeder bin 2 of the refiner, from where they are further fed by means of a feeder auger 3 driven by a feeder motor 7 into the gap between the refiner disks 5. Either in the feeder bin 2, in the feeder auger 3 or between the gap of the disks 5, water is added to the chips by a volume controlled by a controller ~. Between the disks 5 the chips are ground into refined stock and the developed steam propels the refined stock forward via a control "

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valve 6 of the refined stock flow. Because density variations in fed chip stock tend to cause changes in produced refined stock quality, the temperature of the axial bearing is measured in a conventional manner by means of a measurement equipment 12, which is connected to the chip refiner and whose measure-ment signal is entered to a control unit ].1 of the metering motor 10. The control unit 11 controls the speed of the metering motor 10 so that a decrease in the temperature of the axial bearing produces an increase in the speed of the metering motor 10, and vice versa. By term axial bearing is here meant the bearing, which receives the axial load component of the refiner disc 5.

The following example clarifies a typical case of control performance.

In the performed experiments the signal level which is propor-tional to the temperature of the axial bearing, was 1.31 V, at the same moment the signal proportional to the input density was 5.40 V and the freeness value 115 CSF. When the signal proportional to the input density had attained a level of 8.6 V, the temperature signal exceeded to value 1.41 v and the freeness to value 208 CSF. When the controller decreased the input, the signal corresponding to the temperature of the axial bearing lowered to a value 1.36 V, whereby the signal cor-responding to the density was 6.30 V and the freeness 152 CSF.
The controller continued to decrease the feeding, until the temperature signal lowered down to value 1.30 V and the signal corresponding to the density to value 5.20 v while as a freeness value was measured 121 CSF. By the experiment it was proved that the temperature signal of the axial bearing can be used for controlling the input density of the chip stock and correcting the disturbances in the refining process caused by the variations in input density.

AS shown in Fig. 2, two or more refiners can be connected in tandem.

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Claims

1. A control method for a chip refiner, in which method - chip stock is metered by chip stock metering means (9, 10) for refining in a refiner, - chip feeder means (3, 7) arranged to the refiner (5) are used for feeding chips for refining between the refiner disks (5), and - water is added to the chips prior to feeding between the refiner disks (5), c h a r a c t e r i z e d in that - the temperature of the axial bearing of the refiner is measured and - on the basis of the measured temperature, the quantity of chip stock to be metered to the feeder means (3, 7) is controlled with the help of metering means (10, 9) in a conventional manner so that the temperature of the axial bearing is regulated to a constant level.

2. A method in accordance with claim 1, c h a r a c t e r-i z e d in that at a decreasing tendency of the temperature of the axial bearing is compensated by increasing the metered chip stock volume with the help of the metering means (10, 9).

3. A method in accordance with claim 1, c h a r a c t e r-i z e d in that the metering of chip stock feed is continu-ously controlled with the help of a continuous temperature measurement.

4. A method in accordance with claim 1, c h a r a c t e r-i z e d in that the metering of chip stock feed is controlled in a short-term cyclic manner with the help of repetitive temperature measurement performed at short intervals.