Patent Application
20080096037
In the following, preferred embodiments are described with reference to the drawings. It shows:
In the following, preferred embodiments of the present invention are described.
As mentioned above, the invention relates to the use of a particular steel alloy with a particular composition for the production of blades (coater blades and doctor blades, scrapers, creping blades, blades, doctor knives, wipers) in the form of cold rolled, hardened and tempered bands.
As shown in
The content of the different alloy elements and their significance for the steel for this particular field of use is explained in detail in the following.
According to a first embodiment of the invention, carbon should exist in sufficient amounts in the steel to give it a basic hardness, sufficient to endure being pressed against the paper web or ink application roll, respectively, without suffering permanent deformation, and to form MC carbides during tempering. The MC carbides provide precipitation hardening and thus improved abrasion resistance. The carbon content should therefore be at least 1.0%, preferably 1.5%. The maximum carbon content is 3%.
Vanadium should exist in the steel to form very small MC carbides during tempering, through precipitation. These MC carbides are thought to be the major reason for the surprisingly good abrasion resistance of the doctor blades according to the invention. The carbides are of a submicroscopic scale, which means a maximum size of the order of magnitude between 1-3 μm. To provide a sufficiently high volume fraction of MC carbides, the vanadium content should be at least 4% V. The vanadium content should not exceed 10% V.
The Chromium content should be at least 6% Cr, preferably at least 6.5% Cr, to give the steel sufficient hardenability, i.e., transform it into martensite during air quenching or after austenitizing. However, chromium is also carbide forming, which makes it compete with vanadium for the carbon in the steel matrix. The higher the chromium content, the less stable are the vanadium carbides. The chromium carbides, however, do not provide the precipitation hardening that is desirable and which can be formed by the vanadium in the above mentioned amounts. Chromium in higher amounts also generates an increased risk for retained austenite. Thus, the chromium content in the steel is limited to 10%, preferably at most 8.5.
The Molybdenum content should be at least 1%, so that it jointly with vanadium can be a part of the MC carbides and in a positive way contribute to the formation of these carbides. Since there is molybdenum in the MC carbides, these dissolve more easily during austenitizing when hardening occurs and are then a part of the MC carbides formed during the tempering. Molybdenum content may, however, be not so high as to form detrimental amounts of molybdenum carbides, which are instable, just like chromium carbides, and grow at high temperatures. The molybdenum content should therefore be limited to 2%, preferably about 1.5%.
Molybdenum can, in the usual fashion, be replaced, completely or partially, by the double amount of tungsten. In the preferred embodiment the alloy composition should therefore not contain tungsten, more than contaminant levels.
The Manganese content in the steel is limited to 1% and contributes, just like chromium, to give the steel the desired hardenability. Preferably the content of manganese is 0.4-0.5% Mn.
The Silicon content should be at least 0.8% to increase the carbon activity in steel and speed up the precipitation of the small vanadium carbides during tempering. The increased carbon activity can, however, also lead to a faster coarsening of the carbides, resulting in a quicker softening of the steel. In other words, the tempering curve is moved to the left and the hardness maximum is moved upwards, when silicon content is high. The steel should, however, not contain more than at most 1.1% silicon and preferably at most 1.0% silicon.
Nickel does not provide any positive contributions to the steel in the intended application area. Possibly, nickel can complicate the heat treatment of the steel. Therefore, it is best if the steel does not contain more nickel than contaminant levels.
Otherwise, the steel contains essentially nothing but iron. Other elements, including for example aluminum, nitrogen, copper, cobalt, titanium, niobium, sulphur and phosphorus, only exist in contaminant levels or as unavoidable accessory elements in the steel.
In this first embodiment of the invention, three different steel alloys have been powder metallurgically produced, cold rolled and tested with good results. These three alloys have been cold rolled to form thin strips, with a thickness of 0.05-1.2 mm and a width between 10-250 mm and can be used for the manufacturing of coater blades, doctor blades and creping blades. The nominal compositions of these steel alloys were as follows:
1.5% C, 1% Si, 0.4% Mn, 8% Cr, 1.5% Mo, 4% V and the remainder iron and unavoidable contaminants,
2.1% C, 1% Si, 0.4% Mn, 6.8% Cr, 1.5% Mo, 5.4% V and the remainder iron and unavoidable contaminants.
2.9% C, 1% Si, 0.5% Mn, 8% Cr, 1.5% Mo, 9.8% V and the remainder iron and unavoidable contaminants.
According to a second embodiment of the invention, carbon should exist in sufficient amounts in the steel to give it a basic hardness, sufficient to endure being pressed against the paper web or ink application roll, respectively, without suffering permanent deformation, and to form MC carbides during tempering. The MC carbides provide precipitation hardening and thus improved abrasion resistance. The carbon content should therefore be at least 1.0% C, preferably 1.2% C. The maximum carbon content is 2.5% C, preferably at most 2.3% C.
Vanadium should exist in the steel to form very small MC carbides during tempering, through precipitation. These MC carbides are thought to be the major reason for the surprisingly good abrasion resistance of the doctor blades. The carbides are of a submicroscopic scale, which means a maximum size of the order of magnitude of 1-3 μm. To provide a sufficiently high volume fraction of MC carbides, the vanadium content should be at least 2.5% V, preferably at least 3.0% V. The vanadium content should not exceed 7% V, and preferably the steel contains at most 6.5% vanadium.
In this embodiment the amount of chromium is delimited. In order to give the steel sufficient hardenability, i.e., transform it into martensite during air quenching or after austenitizing, the chromium content should be at least 4% Cr. However, chromium is also carbide forming, which makes it compete with vanadium for the carbon in the steel matrix. The higher the chromium content, the less stable are the vanadium carbides. The chromium content in the steel can amount to 5%. The nominal content is about 4.2%.
The molybdenum content should be at least 4%, so that it jointly with vanadium can form the MC carbides and in a positive way contribute to the formation of these carbides. Since there is molybdenum in the MC carbides, these dissolve more easily during austenitizing when hardening occurs and are then a part of the MC carbides formed during the tempering. The Molybdenum content may, however, not be so high as to form detrimental amounts of molybdenum carbides, which are instable, just like chromium carbides, and grow at high temperatures. According to this second embodiment of the invention, the molybdenum content should be limited to 8% Mo, and preferably between 5-7% Mo.
Molybdenum can, in the usual fashion, be replaced, completely or partially, by the double amount of tungsten. Tungsten improves the wear resistance, raise the hardening temperature and improves the heat resistance. According to this second embodiment of the invention, the steel contains 6-7% W, suitably about 6.4-6.5% tungsten.
The manganese content in the steel is limited to 1% and contributes, just like chromium, to give the steel the desired hardenability. Preferably the content of manganese is 0.3% Mn.
The silicon content should be at least 0.8% to increase the carbon activity in steel and speed up the precipitation of the small vanadium carbides during tempering. The increased carbon activity can, however, also lead to a faster coarsening of the carbides, resulting in a quicker softening of the steel. In other words, the tempering curve is moved to the left and the hardness maximum is moved upwards, when silicon content is high. The steel should, however, not contain more than at most 0.8% silicon and preferably at most 0.5% silicon.
Nickel does not provide any positive contributions to the steel in the intended application area. Possibly, nickel can complicate the heat treatment of the steel. Therefor, according to the second embodiment of the invention, it is best if the steel does not contain more nickel than contaminant levels.
According to the second embodiment of the present invention, the steel contains cobalt in an amount of at least 8%. Cobalt improves the hot workability of the steel. However, cobalt also makes the steel more brittle and raises the deformation hardening in cold work operations. Thus, the steel should not contain more than 12% cobalt, preferably not more than 11%. An improved hot workability is no critical property of the steel, and therefore the steel according to this second embodiment essentially does not contain any cobalt.
Otherwise, the steel contains essentially nothing but iron. Other elements, including for example aluminum, nitrogen, copper, cobalt, titanium, niobium, sulphur and phosphorus, only exist in contaminant levels or as unavoidable accessory elements in the steel.
In this second embodiment of the invention, three different steel alloys have been made with a powder-metallurgical method, cold rolled and tested with good results. The three alloys have been cold rolled to form thin strips, with a thickness of 0.05-1.2 mm and a width between 10-250 mm and can be used for the manufacturing of blades. The nominal compositions of these steel alloys were as follows:
1.28% C, 0.5% Si, 0.3% Mn, 4.2% Cr, 5% Mo, 6.4% W, 3.1% V and the remainder iron and unavoidable contaminants.
1.28% C, 0.5% Si, 0.3% Mn, 4.2% Cr, 5% Mo, 6.4% W, 5.4% V, 8.5% Co and the remainder iron and unavoidable contaminants.
2.3% C, 0.5% Si, 0.3% Mn, 4.2% Cr, 7% Mo, 6.5% W, 6.5% V, 10.5% Co and the remainder iron and unavoidable contaminants.
The manufacturing of coater blades, doctor blades or creping blades, according to the present invention, will be done as follows. An alloy containing the desired composition, described above and in the patent claims, is produced using powder metallurgical processing. Thereby, the powder is mixed to the desired composition and is compacted to solid blanks or blocks by means of hot isostatic pressing. The blanks (respectively blocks) are hot-rolled into strips of an approximate thickness of 3-3.5 mm. Then, these strips are cold-rolled to a desired thickness of less than 1.2 mm, alternating with reheating operations. In order to avoid edge cracks in the strips 1, the cold rolling operation takes place with the use of edge supports at the thickness reduction from approximately 3.5 mm down to 1 mm. The cold rolled strip 1 is then hardened and tempered in a continuous process, when the strip has reached its final thickness T in the cold rolling.
The cold-rolled strips 1 of the first embodiment will be hardened using austenitizing at a temperature between 950° C.-1050° C., followed by quenching between cooling plates down to a temperature between 150° C.-250° C., and tempering at 550° C.-650° C.
The cold-rolled strips 1 of the second embodiment will be hardened using austenitizing at a temperature between 1000° C.-1050° C., followed by quenching between cooling plates down to a temperature between 150° C.-250° C., and tempering at 550° C.-650° C.
This is followed by brushing of the surfaces of the strips 1. If desired, the strips 1 can be colored by tempering in an oxidizing atmosphere. The strips 1 are cut to correct length and width B, and the edge 10, 20 is machined through planing and/or grinding to obtain the desired edge profile.
Thanks to the method according the invention, cold rolled strips with widths up to 250 mm can be manufactured without waive to, primarily, sufficient straightness of the working edge. But the flatness of the strip is of significant importance as well. The working edge should have a straightness of 0.3 mm/3000 mm length of the band. The flatness should be at least 0.3% of nominal strip width, according to the standard Pilhöjd.
Furthermore, the strips are characterized in that the working edges 10, 20 show improved properties, especially improved wear resistance, in comparison to other strips available for these applications today.
According to an alterative embodiment the working edge 10, 20 may be hardened using local heating of the edge section, for example by induction heating. Preferably, high energy beam hardening is used, for example laser, plasma or electron beam hardening, which gives the working edge 10, 20 a distinct hardened section that doesn't impair the straightness of the strip. To this end, preferably, a laser beam is used. The working edge 10, 20, hardened in this manner, will obtain an improved hardness of up to 630 HV, preferably 620 HV.
Further, the working edge 10, 20 of a steel band according to the invention due to the powder metallurgical production process comprises a particularly fine microstructure. In
At the right side of
The method according to the invention which allows to successfully produce cold rolled bands with width up to 250 mm makes it possible that a plurality of small stripes are made simultaneously. In this case, a wide stripe 1 is cut into small stripes, prior to a working of the edges 10, 20. In that way, for example, two narrow bands can be obtained by means of a single cold rolling process from one wide band.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102004034905.3 | Jul 2004 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP05/07356 | 7/7/2005 | WO | 00 | 1/19/2007 |
