SPRING DOCTOR

DOCTEUR A RESSORT

English Abstract

A spring doctor, particularly for use for cleaning the surface of rolls (2),
used in the paper industry, during operation and including a blade (8) that is
essentially the width of the roll (2) being cleaned, and which is attached to
a blade holder (1). In the device, there are operating means (for example, 6,
7) for creating the desired pressure of the doctor blade against the roll.
Longitudinally, the blade (8) is curved for at least part of its length.

French Abstract

Cette invention concerne un docteur élastique, destiné en particulier au nettoyage de rouleaux (2) dans l'industrie papetière, comprenant un balai (8) essentiellement de la largeur du rouleau (2) à nettoyer, et qui est fixé à un porte-balai (1). Ce dispositif comporte des moyens (tels que 6, 7) qui plaquent le balai de docteur contre le rouleau. Le balai (8) est incurvé sur au moins une partie de sa longueur.

Claims

6
WHAT IS CLAIMED IS:
1. A spring doctor for use for cleaning the rolls (2) of a paper machine
during operation and including a blade (8) that is essentially the width of
the roll
(2) being cleaned, and which is attached to a blade holder (1), and operating
means (6, 7) for creating the desired pressure of the blade against the roll,
the
blade (8) being manufactured from a composite material formed of a matrix and
a fibrous reinforcement wherein the blade (8) is of essentially non-deflecting
construction and wherein, in the operating situation, the blade is curved on
at
least part of its length and has, in the immediate vicinity of the attachment
location of the blade holder, a bend (12), or curve.
2. A spring doctor according to claim 1, characterized in that the blade
holder (1) is pivoted around a shaft pin (4), to be able to be rotated to at
least a
limited extent.
3. A spring doctor according to claim 1, characterized in that the blade (8)
has, at a distance from its point, particularly a plate-like dirt protector
(13).
4. A spring doctor according to any one of claims 1 to 3, characterized in
that the blade (8) is a combination of a curved portion and essentially
straight
portion.
5. A spring doctor according to any one of claims 1 to 4, characterized in
that the thickness of the blade (8) varies over its length.
6. A spring doctor according to claim 5, characterized in that the blade (8)
thins towards its point.
7. A spring doctor according to claim 1, characterized in that the number or
orientation of the reinforcing fibres of the composite material of the blade
(8)
vary in different parts of the blade.

Description

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1
Spring Doctor
The present invention relates to a spring doctor, and more specifically to a
doctor, which is used to scrape clean the various rolls of a machine used in
the
manufacture of paper.
The usual construction and positioning of doctors are such that the doctor
blade, which is usually in the order of 75 - 85 mm-long and of the desired
width,
i.e. essentially the same width as the roll being doctored, rests with a
specific
force against the surface of the roll and cleans the surface of fibres and
other
materials adhering to it. Though the angle of contact of the blade relative to
the
surface of the roll is often in the order of 25 degrees when the blade is new,
the
angle of contact changes as the blade wears, so that the angle can be in the
order of 35 degrees before the blade is replaced with a new one.
Before replacement, the length of present doctor blades is about 60 mm. Wear
causes the surface pressure of the blade to change according to it. In
practice, it
has also been noted that when using existing types of blade construction there
is very little possibility to increase the wear margin/length of the blade, as
this
will lead to problems arising from the deflection of the blade. Similar
problems
also arise if the pressure of the blade is increased, when the point of the
blade
will open and will no longer closely follow the surface of the roll. This
results in a
poorer doctoring result.
The deficiencies of blades according to the prior art also lead to various
compromises being made in the manufacture of blades, the avoidance of which
would improve the quality of the blades being manufactured.
Doctor blades are changed in paper machines at approximately weekly
intervals. The change as such is not a difficult operation, but it is
expensive, as it
takes about one hour and costs can easily rise to about à 20 000. Thus, a
lengthening of the interval between changes would easily have even
considerable financial effects in the manufacture of paper.

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2
The present invention is intended to create a new, improved doctor-blade
construction, with the aid of which the drawbacks besetting the prior art can
be
avoided and savings will become possible in the manufacture of paper.
These and other benefits and advantages of the invention are achieved in the
manner stated to be characteristic in the accompanying Claims.
In the following, the invention is examined in greater detail with reference
to the
accompanying schematic drawings, which show one embodiment according to
the invention. Thus
Figure 1 shows one blade carrier, blade holder, and blade according to the
invention, when the blade is at its full size, and
Figure 2 shows the same construction in a situation, in which the blade has
worn more or less to a state in which it must be replaced.
The roll, the surface of which is cleaned by the doctor blade, in marked in
the
figures with the reference number 2. As can be seen, the present case concerns
a roll 2 with a relatively large diameter, the surface of which is only
slightly
curved in the figures.
The blade holder 1 has a more or less conventional construction. It is formed
of
a frame structure, which is permanently attached, for example, to the frame
structure of the paper machine. The frame 5 of the blade holder 1 has a lug 3
for a shaft 4. The blade holder 1 is pivoted around the shaft 4, allowing the
blade holder to be rotated to a limited extent around the shaft 4 according to
the
control. The control is, in turn, provided by using hose-like components 6 and
7,
filled with a pressure medium, which act on the blade holder to rotate it in
different directions, as they are located on different sides of the pivot. The
hoses
6 and 7 are supported between the body 5 and a suitable surface of the blade
holder.

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3
It should be noted that there are numerous different models of known blade
holders on the market. The invention is thus not limited to the blade holder
shown by way of example.
The actual doctor blade 8 is attached and suitable supported on the side of
the
blade holder 1 facing the roll. The attachment is made in a conventional
manner, with the aid of a loading plate 9 and a counter-plate 10.
The blade construction 11 according to the prior art is shown by a broken line
in
Figure 1. In practice, this means that the doctor blade 11 is shorter than the
blade according to the invention. The blade according to the prior art is also
of a
straight construction.
Instead of using a straight construction, the blade construction 8 according
to
the invention is made to be curved, which also means that the construction is
made sturdy, compared to the doctor blade according to the prior art. Thanks
to
the non-buckling and essentially non-deflecting construction achieved, the
doctor blade can be made clearly longer than a blade according to the prior
art,
which in turn means that replacement will be needed much less frequently than
when using a traditional doctor blade. The savings will be considerable.
The construction according to the invention also achieves another advantage,
which is that, by curving the doctor blade 8 as shown, and bending it slightly
upwards, as shown by the reference number 12, the angle of the blade relative
to the surface 2 of the roll can be made to remain nearly constant over the
entire operating life of the blade. This also brings savings, as separate
measures are not required to adjust the angle. Similarly, the doctoring
situation
remains constant for the entire operating life of the doctor, because the
angle,
the contact surface, and the pressure will not change.
A protector plate suitable for the purpose can be attached behind the blade
and
will prevent dirt that may accumulate on the back of the blade from entering
the
blade holder. Figure 1 shows an example of such a protector plate, marked with

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the reference number 13. In particular, cleanliness is an extremely important
factor in the inside of a hose-loaded holder. If solid dirt gets between the
loading
hose and the loading plate, it will cause a deviation in the loading profile
of the
blade. This will lead to uneven blade wear, a reduction in doctoring effect,
possible entry of dirt into the paper, a deterioration in the moisture profile
of the
paper and, at the very least, a reduction in the production efficiency of the
paper
machine, due to web breaks.
As stated above, the improvements in the doctor blade according to the
invention bring considerable savings, because the use of this construction
minimizes the operations that cause detriments to production. The increases in
the manufacture of the actual blade, and in the subsequent costs are only very
small.
The invention is described above with reference to only one well regarded
embodiment, which must be considered as in no way restricting the invention.
Thus, the blade according to the invention shown in the figures can be adapted
in many ways. For example, instead of the blade being curved over its entire
length, it can also be made as a combination with a curved portion and also a
straight portion. A blade curved in two directions is also possible. The
radius of
the curve can also be changed as desired over the length of the blade. It may
also be sensible to make the blade with a varying thickness. Such an
alternative, in which the blade thins towards its point may be particularly
suitable.
Blades like that shown are usually manufactured from a composite material,
which, in other words, is usually formed of a plastic-based matrix, to which
reinforcement is added. The reinforcement is normally of a fibrous material;
aramid fibres, carbon fibres, kevlarTM, or similar. The invention also permits
the
desired elasticity properties and stiffness to be achieved by altering the
amount
and orientation of the reinforcement. In other words, if desired, the
properties
can be altered by arranging more fibres in one part of the blade than in
another,

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while similarly the fibres can be oriented in one direction or another in
specific
parts of the blade.
The shape and construction of the blade holder shown in the figures by way of
example can differ even greatly from the model shown. The invention is in no
way restricted to the solution shown. It is also self-evident that the
pressure,
exerted by the blade on the roll being doctored, can by created in any way at
all.
The means for creating the pressure need be in no way connected to the blade
holder. For example, the pressure can be regulated by a microprocessor and be
variable for the entire duration of the operation.

Representative Drawing