Note: Descriptions are shown in the official language in which they were submitted.
CA 02550107 2006-06-16
WO 2005/059246 PCT/SE2004/001839
1
EDGE-PROVIDED TOOL AND METHOD FOR THE MANUFACTURE THEREOF
Scraper or cleaning blades denominated "doctor blades" are widely used in the
paper and pulp industry for different purposes, but in most cases they have
the function of
cleaning or scraping off material or left-overs from the surface of a rotary
roller. Such doctor
blades have, for instance, the purpose of detaching a paper web from a stiff
drying cylinder by
scraping the surface of the cylinder.
The paper pulp contains filler such as silicon dioxide, great particles and
paper
fibers that wear out the doctor blade, the wear being substantially evenly
distributed along the
1 o edge, and wherein it holds that the rate of wear is greater than the rate
of corrosion. Further-
more, the doctor blade is seen as an article of consumption having very short
service life, usu-
ally considerably smaller than one day. In many cases, it is exchanged already
after approxi-
mately 5 hours. Usually no regrinding of the doctor blade is carried out but
it is discarded
when consumed.
15 There are different principles in the paper mills for the use of doctor
blades, with
the same in general being worn-in initially for the formation of an edge. When
the same has
been formed, the wear is relatively even. The proper "in-situ"-grinding-in is
assumed to have a
quality-influencing effect on the manufactured paper. If the doctor blade is
used in a later
stage of the production process of paper, it influences the paper quality and
the surface struc-
2 o tore of the paper, and therefore it is seen as a very critical parameter.
The doctor blades may
be of different length and vary between about 1 and 10 m.
Thus, since a doctor blade is subj ected to extensive wear, different
techniques
are used in order to extend the service life thereof, such as addition of wear-
resistant material
on the part of the blade that meets the cylinder. As an example of such a
reinforcement of the
2 5 top or edge surface of the blade, ceramic hard coatings are presently used
as a practical solu-
tion to bring down the blade wear. Such ceramic coatings are usually applied
to a doctor blade
made by hardened and annealed carbon steel and may be applied by thermal
spraying, such as
plasma spraying or plasma depositing.
Examples of techniques to provide such wear-resistant coatings on cleaning or
3o scraper blades of the type doctor blades (in English "doctor blade") are
found in GB-A-
978 988, GB-A-1 289 609 and GB-A-2 130 924. The entire lcnown technique is
aimed at the
provision of a wear-resistant coating on the part of the blade that comes into
contact with the
surface of a rotary cylinder.
CA 02550107 2006-06-16
WO 2005/059246 PCT/SE2004/001839
2
According to prior art, with the purpose of improving the properties of the
edge-
provided tool, service life and thereby influence the paper quality, thermal
(warm) spraying
with HVOF ("High Velocity Oxygen Fuel") is, among other things, used. The
method gives
sintering of the additive material and so-called diffusion binding at about
1000 °C. Problems
with this coating method are cracks, pores, poor binding strength, adhesion
problems, etc.
Materials sprayed today are ceramics, such as A1203.
Against this background, it is an object of the present invention to be able
to
provide an edge-provided tool, such as a doctor blade, which tool has been
provided with a
coating having better adhesion than that of hitherto known tools.
Simultaneously, deforma-
z o tions of the tool arising otherwise should be tried to be minimized, at
the same time as desired
fineness requirements and absence of scratches on the completed paper product
should be
possible to meet. Furthermore, the supply of energy or influence of heat on
the base material
made by the surface treatment should as far as possible be minimized.
An additional object of the present invention is to produce a scraper andlor
z5 cleaning blade of primarily doctor blade type, which possesses long service
life and which in
the paper manufacture imparts the paper a smooth and fine surface, free from
scratches and
other defects.
These and additional obj ects have in a surprising way succeeded to be
attained
by providing the tool with the features defined in the independent claims.
Preferred embodi-
2 o ments of the present invention are defined in the dependent claims.
The invention will be closer described below in connection with the drawing
figures, where
Figure 1 shows a perspective view of a doctor blade applied in direct
connection
to a roller so as to wiping off the paper pulp in the production of paper;
2 5 Figure 2 shows an explanatory sketch of an edge-treated doctor blade
according
to the present invention;
Figure 3 shows an explanatory sketch of a coated doctor blade edge according
to
the invention, seen from the side;
Figure 4 shows an explanatory sketch of a laser-impregnated doctor blade edge
3 o according to the invention, seen from the side; and
Figure 5 shows an explanatory sketch showing laser coating of a doctor blade
according to the invention.
CA 02550107 2006-06-16
WO 2005/059246 PCT/SE2004/001839
3
Thus, the present invention relates to an edge-provided tool as well as a
method
for the manufacture thereof. More closely defined, the invention relates to a
type of tool that is
called "doctor blade" and that is a wiping, scraper and/or cleaning tool used
in, for instance,
the manufacture of paper, in order to get a smooth and fine paper product free
from scratches
and other defects. Also tools that usually axe called coater blades, and also
general knives, are
comprised in the present invention. However, with the purpose of facilitating
the description
of the invention, the subject of the invention will below be designated
"doctor blade", in
which concept also other denominations are intended to be comprised.
Thus, figure 1 shows a doctor blade l, which abuts against a roller 2 and, for
z o instance, scrapes away pulp from the same. As a preferred example of
materials that have
turned out to work well in order to coat the edge portion of the material by
means of laser
technique according to the invention, steel grades having a haxdness of at
least 450 HV have
been selected. An example of such a steel is a carbon steel having a
composition comprising
(in % by weight) 0,8-1,2 % of C, preferably about 1 % of C, 0,20-0,35 % of Si,
0,35-0,50
15 of Mn, maximum 0,02 % of P, maximum 0,01 % of S, with Fe as balance and the
content of
some additional element in the periodic system in contents below 0,5 %.
Figures 2 and 3 show a steel strip 3, which on the edge thereof has been
coated
with a coating 4 by laser technique in accordance with the invention. Thereby,
the resistance
to weax is increased considerably. The coating is composed of, for instance,
aluminum oxide
2 0 or stellite (for instance stellite 12). The laser technique is, er se well
known to a person
skilled in the art and is visualized in Figure 5. In the laser coating, the
atomic (also called
"metallurgical") binding to the steel substrate characteristic of the
invention is attained, which
is visualized in Figure 3.
Figure 4 shows a doctor blade in cross-section, which has been coated with,
for
2 5 instance, TiC in accordance with the present invention. The laser
impregnation technique is
described in the patent WO 99/56906. The steel strip is designated 5 and the
impregnation
applied by means of laser technique is designated 6. Also in this figure it is
visualized that the
particles/the carbides have penetrated into the steel substrate, whereby the
limit between the
two to a significant extent having been erased. The coating has been effected
with, for
3o instance, aluminum oxide or stellite, such as in the figures 2 and 3, while
the impregnation is
carried out with suitable carbides and/or nitrides.
According to Figure 5, the surface-reinforcing portion in the formed edge por-
tion of a strip-shaped doctor blade is provided in the way that, by means of
laser technique, a
CA 02550107 2006-06-16
WO 2005/059246 PCT/SE2004/001839
4
coating, supplied by means of powder material 7, is applied to the edge under
such supply of
heat that the powder is fused with the basic material in the doctor blade, so
that atomic and
metallurgical binding arise. The supply of heat takes place by means of a
laser gun 8, a coating
9 being provided on the substrate. The supplied material in the flow of powder
7 suitably con-
sists of a refractory material, such as aluminum oxide. Alternatively, a
material such as stellite
may be used. In connection with the coating 9 having been applied to the
doctor blade, it is
important that the material can undergo a quick cooling, so that a desired
fine structure is
obtained, which is characterized by both toughness and hardness, more closely
defined to a
level of hardness corresponding to 850-1300 HV. In this way, simultaneously
high bearing
2o strength in the surface layer is attained at the same time as requirements
of low friction and
desired corrosion resistance can be fulfilled.
As has been mentioned above, the coating may essentially be composed of
aluminum oxide or stellite. However, the coating may also contain or be
composed of other
refractory materials, such as metallic oxides, metallic silicates, metallic
carbides, metallic
15 borides, metallic nitrides and mixtures thereof. Especially preferred
ceramic materials are
selected among alumimun oxide, chromic oxide, zirconium oxide, wolfram
carbide, chro-
mium carbide, zirconium carbide, tantalum carbide, titanium carbide, titanium
nitride, nio-
bium carbide and borides.
As has been mentioned above, a laser impregnation may also be carried out by,
2 o for instance, carbides and nitrides such as TiC, NbC and TiN being added
to the surface of the
base material during the laser treatment. The particles are added by spraying
under high gas
pressure at the same time as the laser beam locally melts the surface layer on
the material so
that the wear-resistant particles can penetrate into the substrate.
Furthermore, the laser coating
may be effected in a plurality of rounds, so that multiple layers are
obtained. The steel strip
25 then receives a very wear-resistant surface.
The thickness of the steel strip is the normal one for doctor blades in the
paper
industry and may vary between 0,2 and 3 mm, suitably between 0,305 and 1,27
mm. The
thickness of the coating or the impregnation may suitably be between 5 and 15
% of the thick-
ness of the steel strip.
