WO1989004763A1

WO1989004763A1 - A laminated steel strip and an edge tool made of the steel strip

Info

Publication number: WO1989004763A1
Application number: PCT/SE1988/000595
Authority: WO
Inventors: Erik Von Wachenfeldt; Lars Göran THORÉN
Original assignee: Uddeholm Strip Steel Aktiebolag
Priority date: 1987-11-27
Filing date: 1988-11-04
Publication date: 1989-06-01
Also published as: SE459722B; SE8704729D0; AU2803789A; SE8704729L

Abstract

The invention relates to a laminated steel strip of the type consisting of at least two layers, namely a first layer (2) of a high alloyed steel and a second layer (3) of a low alloyed steel. The high alloyed steel in the first layer (2) contains in weight-%: 0.2-0.8 C, 0.2-2.0 Si, 0.1-2.0 Mn, 5-12 Cr, from traces to max 5 Mo, from traces to max 2 (V+Ta/Nb+Ti+N), balance substantially iron and impurities in normal amounts, while the low alloyed steel in the second layer (3) contains in weight-%: 0.5-1.5 C, 0.1-0.8 Si, 0.2-1.5 Mn, from traces to max 3 Cr, balance substantially iron and impurities in normal amounts. From this steel strip there can be made edge tools, for example doctor blades and textile cutting knife blades.

Description

A LAMINATED STEEL STRIP AND AN EDGE TOOL MADE OF THE STEEL STRIP

TECHNICAL FIELD The invention relates to a laminated steel strip of the kind consisting of at least two layers, namely a first layer of a high alloyed steel and a second layer of a low alloyed steel. The invention also relates to edge tools made from the laminated steel strip. Knives, doctor blades and other scraper tools which are subject to heavy wear are examples of such tools. Knife blades consisting of combinations of layers of carbon steels and stainless steels are known in the art. An example of a tool which is designed in this way is described in the U.S. patent No. 3,537,828. Laminated steel strips and edge tools made from such steel strips are also known through the Swedish patent No. 450495.

BRIEF DESCRIPTION OF THE INVENTION

The purpose of the invention is to bring about a laminated steel strip with features which are still more adapted to certain specific fields of use of the strip as well as to the production of the strip than what has been achieved according to the known art. Thus, it is an objective of the invention to bring about a steel strip suitable for the production of doctor blades, particularly for creping doctor blades, as well as a steel strip for the production of textile cutting knives. In order to obtain a good creping function there is i.a. a demand for a better heat resistance than what has been achieved with known materials. Creping doctor blades of today are namely subject to high temperature through the contact with the paper web and with the crape cylinder of cast iron, against which cylinder the creping operation is performed. These cylinders are often repaired through the deposition of flame sprayed covering layers. The high temperature causes the doctor blade to be fully annealed in the edge portion such that the hardness and wear resistance is reduced, which in its turn will cause that the edge is worn out very fast and has to be regrouπd or will require that the doctor blade has to be replaced. In both cases there will be a loss of efficient production time in the machine. The heating of the doctor blade also will cause a thermal expansion of the doctor blade which is difficult to control and will also cause that the blade will easily buckle, which in its turn will cause uneven creping.

The above mentioned problems per se could be solved through the selection of a material having a very high heat resistance. Such materials, however, are difficult or impossible to manufacture through conventional cold rolling technique. Particularly, it is usually very difficult and unreliable from a production point of view to coil a cold rolled, high alloyed, hardenable steel strip after hardening, as the hardness ought to be 62-64 HRC or about 750 HV, a problem which concerns not only materials intended for doctor blades but also materials intended for by way of example textile cutting knives. The risk for rupture of the strip is evident.

These problems, however, can be solved if there is used a laminated steel strip consisting of at least two layers, namely a first layer of a high alloyed steel and a second layer of a low alloyed steel, and wherein the two layers havethe compositions which are stated in the appending claims. The high alloyed steel will give a better heat resistance and more wear resistant carbides than what conventional doctor blades or textile cutting knives have, and also the low alloyed steel in the laminated steel strip has a better heat resistance and wear resistance than conventional blades of low alloyed steels, which implies that the two layers in this respect are comparatively well adapted to each other, at the same time as the layer or the layers of low alloyed steel will allow the steel strip to be coiled also in the hardened condition.

Suitably the low alloyed steel may be of the type which is referred to as hardenable spring steel in order to give the doctor blade construc¬ tion a sufficient flexibility. According to a preferred embodiment of the invention at least a surface adjacent to the edge of the edge tool made from the steel strip is provided with a coating of molybdenum or a molybdenum alloy. The molybdenum layer will reduce the friction and hence the power _ consumption. Further, as far as creping doctor blades are concerned, the wear on the expensive creping cylinder which is used during the creping operation will be reduced. Possibly also the edge wear of the doctor blade may be reduced.

The lamination may be performed by welding the layers together through hot rolling prior to cold rolling to final dimension or through cold rolling. The thickness of the final, laminated steel strip may in a manner known per se be 0.1-3 mm. After rolling to final dimension the strip is cut to desired lengths and the edges are formed to desired shape and hardened. This material then is cut to desired lengths and are in certain cases surface coated.

Further aspects, advantages and features of the invention will be apparent from the following description of some preferred embodiments of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Example 1

This example relates to a laminated steel strip for doctor blades such as doctor blades for coating purposes and particularly creping doctor blades. The drawing shows a creping doctor blade 1. According to the preferred embodiment the two outer layers 2 consist of a high alloyed steel, while the centre layer 3 consists of a low alloyed steel. The doctor blade has an overall thickness of 0.1-3 mm. In the two edges one of the layers consisting of a high alloyed steel is provided .with a bevelled surface 4, which forms an angle A against the plane side of the blade. The angle A may be between 60 and 105°, which angle A defines the edge angle in an edge 6. According to the embodiment the high alloyed layer 2 is covered with a sprayed layer 5 of molybdenum. The molybdenum layer has a maximum thickness of about 0.05-0.30 mm, which decreases in the direction towards the edge 6 and is made such that the high alloyed layer 2 is exposed in the edge 6, which constitutes a portion which will be in contact with the creping roll. The width of the layer 5 may vary. For creping doctor blades a width of 5-15 mm may be suitable and sufficient, but for other applications other widths may be more suitable.

The steels in the layers 2 and 3 have the following nominal compositions.

Composition of: Si Mn Cr Mo Ni Cu

The high alloyed steel in layer No. 2 0.50 1.0 0.5 8-.0 1.5 0.5 balance iron and impurities in normal amounts

The low alloyed max max max steel in layer No. 3 1.05 0.28 0.35 1.50 0.08 - 0.25 0.35 balance iron and impurities in normal amounts

Test creping with a doctor blade according to the drawing (without molybdenum coating on the bevelled surface 4) gave

a) a delay time interval which was at least three times as long as what is normal, b) an even creping from edge to edge of the produced paper web, c) an improved (more even) quality of the creping along the paper web, and d) a reduced power consumption, which may be taken advantage of in terms of increased production (higher rate).

By covering a zone of the doctor blade surface close to the corner of contact with molybdenum there will as a result be achieved a steel edge which will crepe, and the molybdenum layer will further reduce the friction and consequently also the power consumption. At the same time it will also reduce the wear on the expensive crape cylinder against which the creping doctor blade is pressed. Example 2

This example relates to a laminated steel strip for the production of textile cutting knives. In this case the high alloyed layer is located in the centre of the laminate, while the two outer layers are made of a low alloyed steel. The same steel grades are used in this example as in the previous example.

Claims

1. A laminated steel strip of the -type consisting of at least two layers, namely a first layer (2) of a high alloyed steel and a second layer (3) of a low alloyed steel, c h a r a c t e r i z e d therein that the high alloyed steel in the first layer (2) contains in weight-%:

0.2 - 0.8 C 0.2 - 2.0 Si 0.1 - 2.0 Mn 5 - 12 Cr from traces to max 5 Mo from traces to max 2 (V+Ta/Nb+Ti+N) balance substantially iron and impurities in normal amounts,

and that the low alloyed steel in the second layer (3) contains in weight-%:

0.5 - 1.5 C

0.1 - 0.8 Si

0.2 - 1.5 Mn from traces to max 3 Cr balance substantially iron and impurities in normal amounts.

2. A steel strip according to claim 1, c h a r a c t e r i z e d therein that the high alloyed steel contains in weight-%: 6-10 Cr, 0.5-3 Mo and totally 0.3-1.0 (V+Ta/Nb+Ti+N).

3. A steel strip according to claim 1, c h a r a c t e r i z e d therein that the high alloyed steel contains in weight-%: 0.35-070 C.

4. A steel strip according to claim 2 and 3, c h a r a c t e r i z e d therein that the high alloyed steel has the following nominal composition in weight-%: 0.50 C 1.0 Si 0.5 Mn 8.0 Cr ^' 5 _... 1.5 Mo 0.5 V balance essentially only iron and impurities in normal amounts.

0 5. A steel strip according to claim 1, c h a r a c t e r i z e d therein that the low alloyed steel contains in weight-%: 0.7-1.3 C.

6. A steel strip according to claim 1, c h a r a c t e r i z e d therein that the low alloyed steel contains in weight-%: 1-2 Cr. 5

7. A steel strip according to claim 5 and 6, c h a r a c t e r i z e d therein that the low alloyed steel contains in weight-%:

0.8 - 1.2 C

0.1 - 0.5 Si 0 0.1 - 0.8 Mn

0.2 - 1.8 Cr max 0.5 Ni max 0.5 Cu max 0.1 Mo 5

8. A steel strip according to any of claims 1-7, c h a r a c ¬ t e r i z e d therein that it has an overall thickness of 0.1-3 mm.

9. An edge tool intended for cutting purposes or which is subject to 0 wear, c h a r a c t e r i z e d therein that it is made of a laminated steel strip of the type consistingOf at least two layers, namely a first layer (2) of a high alloyed steel and a second layer (3) of a low alloyed steel, wherein the high alloyed steel in the first layer (2) contains in weight-%: 5 0.2 - 0.8 C 0.2 - 2.0 Si 0.1 - 2.0 Mn 5 - 12 Cr _ from traces to max 5 Mo from traces to max 2 (V+Ta/Nb+Ti+N) balance substantially iron and impurities in normal amounts,

and wherein the low alloyed steel in the second layer (3) contains in weight-%:

0.5 - 1.5 C

0.1 - 0.8 Si

10. A tool according to claim 9, c h a r a c t e r i z e d therein that it is a doctor blade having one up to four edges (6).

11. A tool according to claim 9, c h a r a c t e r i z e d therein that it is a knife blade, particularly a textile cutting knife blade.

12. A tool according to any of claims 9-11, c h a r a c t e r i z e d therein that a surface adjacent to the edge or the edges (6) is coated with a layer (5) of molybdenum or a molybdenum alloy.

13. A tool according to claim 12, c h a r a c t e r i z e d therein that the thickness of said layer (5) is reduced in the direction towards the edge (6).