Note: Descriptions are shown in the official language in which they were submitted.
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A method of detecting surface damages in the stone roll
of the press section of a paper machine or the like
The invention relates to a method of detecting
surface damages in a stone roll of a press section in
a paper machine or the like, said stone roll being
provided with a doctor blade arranged in a pivotable
holder so as to extend over the whole length of the
roll for scraping the sur~ace of the roll.
At present, stone rolls are used e.g. in the
press sections o paper machines. In a modern paper
machine the proper press of the press section can be
formed e.g. by four rolls which are so positioned with
respect to each other that they form three press nips.
One of these four rolls is made of stone, gen-
erally granite. The granite shell of ~he stone roll is
made in one piece by quarrying, machining and finally
grinding. A stone roll so obtained is an expensive
component, which is used for its good properties. Good
practical properties include the micro structure and
the anti-static quality of the surface.
However, cracks may be formed in stone rolls in
use which damage the roll when expanding. At worst
such cracks may result in total breakage of the roll
during the run. Such a roll explosion has extramely
serious consequences. In practice, the stone mass of
the roll, e.g. about 70 tons, breaks the entire press
section when it is thrown into the surrounding space,
thus causing a long and expensive break in the produc-
tion. In addition to material damages, stone roll
breakages have also caused personal injuries.
For these reasons, it is of grea-t importance
~hat a damage in the stone roll is detected before the
roll breaks up totally. By means of methods presently
in use it is possible to monitor the shape of the
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stone roll and vibrations caused by the stone roll in
the other rolls and the frame structures of the press
section. In paper industries, however, there is no
prior method by means of which cracks in the roll sur-
face could be localized during the run.
The object of the invention is to provide a
method by means o~ which the condition of the roll can
be monitored during the operation of the paper
machine. This is achieved by means of a method accord-
ing to the invention, which is characterized in that
shocks exerted on the doctor blade due to surface dam-
ages in the stone roll are recorded by acceleration
transducers positioned in the holder and that the sig-
nal obtained from each acceleration transducer is
summed in a synchronized manner with the rotation of
the roll.
A major advantage o~ the invention is its
flexibility as it is possible to accurately localize
cracks in the roll surface during the run, whereby the
hazardous roll breakages can be avoided. A further ad-
vantage is that the method is simple so that the in-
vention can be applied advantageously. The invention
can also be applied to existing press sections since
it is not necessary to make any substantial changes in
the press section.
~ he invention will be described in the follow-
ing in more detail by means of an embodiment shown in
the attached drawing, wherein
Figure 1 is a general side view of a press sec-
tion in a modern paper machine;
Figure 2 illustrates an arrangement utilizing
the invention in a view seen in the axial direction of
the stone roll;
Figure 3 is a top view of the arrangement of
Figure 2; and
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Figure ~ illustrates generally the output of
one transducer.
Figure 1 shows generally the press section of a
modern paper machine. The reference numeral 1 indi-
cates a suction roll in the proper press; the refer-
ence numeral 2 a variable crown roll; the reference
numeral 3 a stone roll; and the reference numeral 4
another variable crown roll. The reference numeral 5
indicates a doctor blade means which trails along the
surface of the stone roll, thus scraping impurities
from the surface. In the case of Figure 1, a web 6 to
be dried passes from the left to the righ-t.
The structure and operation of the press sec-
tion belong ~o the prior art, so these matters are not
discusses more closely herein.
Figures 2 and 3 show generally the doctor blade
means indicated with the reference numeral 5 in Figure
1. The same reference numerals as in Figure 1 are used
in Figures 2 and 3 for corresponding parts.
The doctor blade means 5 is formed by a holder
7 and a doctor blade 8 attached thereto. The holder 7
is mounted in bearing in the body of the press sec-tion
so that it is pivotable around the longitudinal axis
thereof. The holder 7 and the doctor blade 8 attached
thereto extend over the whole length of the stone roll
3, as appears from Figure 3. The holder 7 with the
doc~or blade 8 is pivoted so that the doctor blade 8
trails along the surface of the roll 3 during the
rotation of the roll, thus scraping it clean.
In the method according to the invention, ac-
celeration transducers 9 provided in the holder record
shocks exerted on the doctor blade 8 due to surfaces
damages in the stone roll 3. The shocks exerted on the
doctor blade 8 also affect the holder 7, so the ac-
celerat:ion transducers can be positioned in the
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holder so that they are well protecked in view of the
operation of the apparatus.
In order that surface damages in the roll, such
as cracks, could be locali~ed in the direction of the
length of the roll, a plurality of accelaration trans-
ducers 9 are positioned with a mutual spacing over the
whole length of the stonle roll 3. The positioning of
the acceleration transducers in the direction of the
length of the roll is shown generally in Figure 3, in
which the acceleration transducers 9 are indicated by
means of arrows.
According to the invention the signal obtained
from the acceleration transducers 9 is further summed
in a synchroni~ed manner with the rotation of the roll
3. In this way incidental disturbances will not inter-
fere with the measuring process. As a result of this
summing, the output obtained from each transducer 9 is
such as shown in Figure 4. It appears from the output
of Figure 4 that the sliding of the doctor blade is
clearly disturbed at points A and B. The circle shown
in Figure 4 represents the roll 3, so the disturbance,
that is, the location of the damaged point on the pe-
ripheral surface of the stone roll, can be determined.
The reference numeral 10 indicates the synchronization
point used in the summing of the signal. The wa~eli~e
line 11 in Figure 4 illustrates shocks exerted on the
doctor blade 8 by the surface of the stone roll at
each particular transducer 9. As stated above, the
roll surface is clearly damaged at the points A and B,
while the rest of the roll surface is intact.
The above embodiment is by no means intended to
restrict the invention, but the invention can be mod-
ified within the scope of the claims as desired. Ac-
cordingly, it i.s obvious that the number of the ac-
celerat:ion transducers, for instance, is by no means
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restricted but can be chosen according to the require-
ments in each particular case.
