METHODE DE COMMANDE D'UN RAFFINEUR DE COPEAUX

CONTROL METHOD FOR A CHIP REFINER

Abrégé anglais

(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)

Revendications

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
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.

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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