US20200023420A1

US20200023420A1 - Method for producing a strip steel knife, and strip steel knife for tools

Info

Publication number: US20200023420A1
Application number: US16/447,503
Authority: US
Inventors: Anton Haas; Andreas Kastner
Original assignee: Voestalpine Precision Strip GmbH
Current assignee: Voestalpine Precision Strip GmbH
Priority date: 2018-06-29
Filing date: 2019-06-20
Publication date: 2020-01-23
Also published as: TWI753257B; JP2020001164A; KR20200002635A; KR102571038B1; CN110653581A; AT520930A4; EP3586991B1; AT520930B1; JP7068235B2; TW202000332A; EP3586991A1; CN110653581B

Abstract

Method and strip steel knife from a steel strip having a bainite and decarburized surface. The steel strip has a generally rectangular cross-section, and the method includes machining a plurality of beveled surfaces in a region of a longitudinal edge of the steel strip to create at least a cutting surface defining a longitudinal cutting edge; first hardening at least a part of the cutting surface to form a first cutting edge region of the longitudinal cutting edge; smoothing the cutting surface of at least the first cutting edge region toward the longitudinal cutting edge; and at least one further hardening in the first cutting edge region to form a distal cutting edge region of the longitudinal cutting edge within the first cutting edge region having an increased material hardness with respect to the first cutting edge region located outside the distal cutting edge region.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119(a) of Austrian Patent Application No. A 50538/2018 filed Jun. 29, 2018, the disclosure of which is expressly incorporated by reference herein in its entirety.

BACKGROUND

1. Field of the Invention

Embodiments relate to a method for producing a strip steel knife having a hardened cutting edge. A hardenable steel strip that proximally comprises a bainite and at the surface comprises a decarburization and that is essentially rectangular in cross section is subjected to a machining process with the formation of a longitudinal cutting edge and subsequently to a hardening of the material in the cutting edge region.
Furthermore, embodiments relate to a strip steel knife for producing a tool for a processing of planar materials.

2. Discussion of Background Information

The aforementioned strip steel knives are used for a fabrication of tools for a cutting and/or scoring of planar material.
A tool production essentially takes place by a bending of the strip steel knife into a desired shape and the fixing of the same in a knife holder.
When a strip steel knife is bent transversely to the longitudinal extension thereof, tensile stresses naturally occur in the material on the outer side of the knife up to the neutral axis, which stresses can lead to cracks during a material separation.
For this reason, as a starting material for a production of strip steel knives, an essentially rectangular spring steel strip with a surface decarburization is used to increase the deformability of this layer and is used with a proximal bainite in view of a hardening of the material in the cutting edge region.
A starting material of the aforementioned type is subsequently subjected to a machining process with the formation of a longitudinal cutting edge, which process normally takes place by means of shaving.
To improve the edge-holding ability of the strip steel knife or to increase to service life of the tool fabricated therefrom for a processing of planar material, the cutting edge or the cutting edge region can be subjected to a thermal hardening and tempering of the material or to a hardening of the same.
A thermal treatment by hardening and tempering or by hardening thereby takes place by heating the material with a creation of an austenitic or partially austenitic crystalline structure, followed by a rapid cooling.
Normally used production technologies can cause an unfavorable distribution of the material hardness in the cutting edge region, a reduced flexural capacity, an undesired tendency of the planar workpieces to adhere to the cutting edge bevels of the strip steel knife, and the like.

SUMMARY

Embodiments specify a method for producing a strip steel knife of the type named at the outset, which overcomes the disadvantages of the previous fabrication and yields advantageous product quality in an economical manner in one sequence of production steps.
Other embodiments demonstrate an improvement in the quality of the strip steel knives and an increase in the service life of the same with use-related advantages in tools.
According to embodiments, in terms of production, a machining formation of cutting edge bevels with a cutting edge takes place longitudinally in a first step, whereupon, in a second step, a hardening of the cutting edge region is carried out. This cutting edge is further beveled in a third step and subsequently undergoes a machining process via precision processing by smoothing in order to shape the surface towards the cutting edge. After this machining process, in a fourth step, at least one subsequent hardening is carried out and a hardness increase of the material in the distal cutting edge region takes place towards the cutting edge.
The advantages obtained with the embodiments are essentially a coordinated sequence of steps.
A machining formation of the cutting edge bevels from the spring steel strip exposes the proximally positioned bainite, which leads to an advantageous hardenability of the material in the cutting edge region during a thermal hardening and tempering.
A bainite is to a great extent acicular and comprises small, possibly sub-microscopic, carbides that are rapidly dissolved during an austenitization and which generate a fine hardened structure after a rapid cooling.
Particularly, in the cutting edge region, the cutting edge bevels consistently have a disadvantageous roughness measure of the surface from the production of the bevels, which roughness results in an unfavorable adhesion of the planar material during a processing or a creation of a cut. To eliminate this disadvantage, it is provided according to embodiments that a shaping is performed after a hardening in a third step via precision processing by a smoothing of the surface of the cutting edge region towards the cutting edge and that a roughness measure is set, which measure causes a minimal tendency of the cuttings or of the planar material to adhere to the strip steel knife.
A precision processing of the surface of the cutting edge bevels with corresponding efficiency can, due to a resulting heat, lead to a tempering of the hardened structure with an unfavorable decrease in the material hardness towards the cutting edge. According to the invention, in a subsequent fourth step, at least one subsequent hardening is carried out which causes a hardness increase in the material towards the cutting edge.
Preferred regions of a respective material hardness that are to be set, the geometric shape of the cutting edge, and the roughness of the surface are recited in other embodiments according to the invention.
Other embodiments include that the strip steel knife has proximally in cross section a bainite; that the cutting edge bevels comprise surfaces smoothed by precision processing towards the cutting edge with a radius of max. 2.5 μm; and that the hardness of the material in the distal cutting edge region up to a depth of 0.05 to 0.15 mm into the bevel region is at least 650 HV and is reduced in a proximal direction.
As was discovered, particularly for a processing of planar plastic materials, tool blades with small edge radii are advantageous.
A high hardness of the tool material in the edge region beneficially extends the edge-holding ability in heavy-duty use and can yield advantages if the strip steel knives are leveled in the tool (see Austria Patent AT 508 551 B1).
A strip steel knife for producing a tool according to embodiments are described.
Embodiments are explained in greater detail with the aid of the example illustrated in the drawing and materials testing for a strip steel knife.
Embodiments are directed to a method for producing a strip steel knife with a hardened cutting edge from a steel strip that includes bainite and has a decarburized surface. The steel strip has a generally rectangular cross-section, and the method includes machining a plurality of beveled surfaces in a region of a longitudinal edge of the steel strip to create at least a cutting surface defining a longitudinal cutting edge, first hardening at least a part of the cutting surface to form a first cutting edge region of the longitudinal cutting edge, smoothing the cutting surface of at least the first cutting edge region toward the longitudinal cutting edge, and at least one further hardening in the first cutting edge region to form a distal cutting edge region of the longitudinal cutting edge within the first cutting edge region haying an increased material hardness with respect to the first cutting edge region located outside the distal cutting edge region.
According to embodiments, the machining of the plurality of beveled surfaces can include shaving, and the first hardening may include inductive hardening of at least the first cutting edge region to a value of 550 to 700 HV.
In accordance with other embodiments, after the first hardening, the cutting surfaces layers of at least the first cutting edge region are smoothed with roughness values Ra of 0.005 to 0.12 μm and Rz of 0.05 to 1.2 μm, and an edge radius of the longitudinal cutting edge is ≤2.5 μm. Ra and Rz are in accordance with ÖNORM EN ISO 4287 or ASME B46.1.
According to other embodiments, parameters of the at least one further hardening may be determined based on a geometric embodiment of the first cutting edge region and a local energy input into the smoothed cutting surface layers. Further, the at least one further hardening can produce a material hardness of over 650 HV in the distal cutting edge region proximally from the longitudinal cutting edge to a depth of up to 0.05 to 0.15 mm into the first cutting edge region.
In accordance with still other embodiments, the at least one further hardening can produce a material hardness of over 650 HV in the distal cutting edge region proximally from the longitudinal cutting edge to a depth of up to 0.05 to 0.15 mm into the first cutting edge region.
Embodiments are directed to a strip steel knife that includes a strip steel body having, in cross section, at least partially bainitic microstructure and at least one cutting edge bevel forming a longitudinal cutting edge having a maximum radius of 2.5 μm, a first cutting edge region of the longitudinal cutting edge includes a smoothed surface layer of the at least one longitudinal cutting edge bevel, and a distal cutting edge region, which is formed in the first cutting edge region and includes the longitudinal cutting edge, has a material hardness of at least 650 HV up to a depth of 0.05 to 0.15 mm from the longitudinal cutting edge. A material hardness outside of the distal cutting region decreases in a direction away from the longitudinal cutting edge.
According to embodiments, the at least one cutting edge can include a plurality of cutting edge bevels having smoothed surface layers exhibiting roughness values Ra of 0.005 to 0.12 μm and Rz of 0.05 to 1.2 μm. Ra and Rz are in accordance with ÖNORM EN ISO 4287 or ASME B46.1.
In accordance with still other embodiments, a surface layer may include at least one of an oxide layer, a sliding layer or a hard material layer is formed in the distal cutting edge region.
According to other embodiments, the first cutting edge region can be hardened from the distal cutting edge region to a depth of 300 μm from the longitudinal cutting edge to a hardness greater than a hardness of the strip steel body outside of the first cutting edge region.
In accordance with still yet other embodiments, a tool can include the strip steel knife, as described above. The strip steel knife can be configured for processing planar materials. Further, the planar materials to be processed may include at least one of cardboard, corrugated cardboard or plastic films.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein:

FIG. 1 shows in cross section a theoretical construction and an arrangement of regions of a strip steel knife according to the invention;

FIG. 2 shows a metallographic structural depiction of a strip steel knife according to the invention; and

FIG. 3 shows a detailed illustration of FIG. 2 in the bevel region.

DETAILED DESCRIPTION

The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.
FIG. 1 schematically shows a strip steel knife in cross section, formed from a steel strip 1 with a skin decarburization 4; 4′ and cutting edge bevels 3; 3′ towards the cutting edge 2 that are positioned on the narrow side of the steel strip and each have an additional bevel 5; 5′.
Even though such a cross-section shape of a strip steel knife with a cutting edge 2 and at least one bevel 3; 3′ can be produced using various machining processes, a shaping is in many cases carried out by a shaving of a steel strip 1 and a hardening with an induction heating of the region of the cutting edge 2.
However, a material removal at least involves the creation of process score marks in the workpiece and/or a roughness of a surface layer 8, 8′ in the surface of cutting edge bevels 3; 3′ on the strip steel knife, which cause consistently unfavorable adhesive tendencies between the tool and workpiece when a planar material is being cut. it has already been attempted to smooth the surface of the cutting edge bevels 3; 3′ by polishing or fine-grinding in order to overcome this disadvantage.
In contrast to expert opinion, however, it was discovered that, for an advantageous release of the planar material from at least the surface layer 8 of cutting edge bevels 3, 3′ on the strip steel knife, both a maximum value and a minimum measure of roughness preferably constitute limit values. Accordingly, values for Ra are to be set between 0.005 to 0.12 μm and the values for Rz are between 0.05 to 1.2 μm via precision processing by smoothing. These roughness values Ra and Rz are in accordance with the standards described in ÖNORM EN ISO 4287 or ASME B46.1.
However, a targeted high-performance precision processing on the cutting edge bevels 3; 3′ in the region towards the cutting edge 2 may be accompanied by a decrease in the material hardness in this region, i.e., in a direction away from the cutting edge 2. According to embodiments, the material hardness in a distal (second) cutting edge region 7 is to be set to over 650 HV proximally on the cutting edge 2 up to a depth of 0.15 mm by a subsequent hardening or by subsequent hardenings, whereby a high edge-holding ability of the strip steel knife is achieved. Further, surface layer 8, 8′ in the smoothed first cutting edge region 6 after the first hardening, and/or at least, in the distal cutting edge region 7 after the at least one subsequent hardening, comprise at least an oxide layer and/or a sliding layer and/or a hard material layer.
FIG. 2 shows in cross section a strip steel knife according to embodiments following an etching treatment for the purpose of illustrating the structure. A steel strip 1 with a bainite and a skin decarburization at the surface (brightly etched) respectively comprises multi-section bevels with a cutting edge. A (first) cutting edge region 6 shows a hardened and tempered structure that extends from the cutting edge 2 through approximately 300 μm into the cutting edge bevel 3, 3′. From the cutting edge 2 through approximately 145 μm into the cutting edge region, the hardened and tempered structure of the distal (second) cutting edge region 7 is formed by a subsequent hardening as a finely structured hardened structure, which is brightly etched.
FIG. 3 shows the cutting edge bevel 3, 3′ from. FIG. 2 in an enlarged view.
It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to an exemplary embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.
The following list of reference numerals is intended to provide easier association of the regions of a strip steel knife according to the invention:

1 Steel strip
2 Longitudinal cutting edge
3; 3′ Cutting edge bevels
4; 4′ Skin decarburization
5; 5′ Additional bevel section(s)
6 First cutting edge region, hardened
7 Distal cutting edge region with subsequent hardening(s)
8 Surface layer

Claims

1. A method for producing a strip steel knife with a hardened cutting edge from a steel strip comprising bainite and having a decarburized surface, the steel strip having a generally rectangular cross-section the method comprising:

machining a plurality of beveled surfaces in a region of a longitudinal edge of the steel strip to create at least a cutting surface defining a longitudinal cutting edge;

first hardening at least a part of the cutting surface to form a first cutting edge region of the longitudinal cutting edge;

smoothing the cutting surface of at least the first cutting edge region toward the longitudinal cutting edge; and

at least one further hardening in the first cutting edge region to form a distal cutting edge region of the longitudinal cutting edge within the first cutting edge region having an increased material hardness with respect to the first cutting edge region located outside the distal cutting edge region.

2. The method according to claim 1, wherein the machining of the plurality of beveled surfaces comprises shaving, and

wherein the first hardening comprises inductive hardening, of at least the first cutting edge region to a value of 550 to 700 HV.

3. The method according to claim 1, wherein, after the first hardening, the cutting surfaces layers of at least the first cutting edge region are smoothed with roughness values Ra of 0.005 to 0.12 μm and Rz of 0.05 to 1.2 μm, and an edge radius of the longitudinal cutting edge is ≤2.5 μm, and

wherein Ra and Rz are in accordance with ÖNORM EN ISO 4287 or ASME B46.1.

4. The method according to claim 1, wherein parameters of the at least one further hardening are determined based on a geometric embodiment of the first cutting edge region and a local energy input into the smoothed cutting surface layers.

5. The method according to claim 4, wherein the at least one further hardening produces a material hardness of over 650 HV in the distal cutting edge region proximally from the longitudinal cutting edge to a depth of up to 0.05 to 0.15 mm into the first cutting edge region.

6. The method according to claim 1, wherein the at least one further hardening produces a material hardness of over 650 HV in the distal cutting edge region proximally from the longitudinal cutting edge to a depth of up to 0.05 to 0.15 mm into the first cutting edge region.

7. A strip steel knife comprising:

a strip steel body having, in cross section, at least partial bainitic microstructure and at least one cutting edge bevel forming a longitudinal cutting edge having a maximum radius of 2.5 μm;

a first cutting edge region of the longitudinal cutting edge includes a smoothed surface layer of the at least one longitudinal cutting edge bevel;

a distal cutting edge region, which is formed in the first cutting edge region and includes the longitudinal cutting edge, has a material hardness of at least 650 HV up to a depth of 0.05 to 0.15 mm from the longitudinal cutting edge,

wherein a material hardness outside of the distal cutting region decreases in a direction away from the longitudinal cutting edge.

8. The strip steel knife according to claim 7, wherein the at least one cutting edge bevel comprises a plurality of cutting edge bevels having smoothed surface layers exhibiting roughness values Ra of 0.005 to 0.12 μm and Rz of 0.05 to 1.2 μm,

wherein Ra and Rz are in accordance with ÖNORM EN ISO 4287 or ASME B46.1.

9. The strip steel knife according to claim 7, wherein a surface layer comprising at least one of an oxide layer, a sliding layer or a hard material layer is formed in the distal cutting edge region.

10. The strip steel knife according to claim 7, wherein the first cutting edge region is hardened from the distal cutting edge region to a depth of 300 μm from the longitudinal cutting edge to a hardness greater than a hardness of the strip steel body outside of the first cutting edge region.

11. A tool comprising the strip steel knife according to claim 7, wherein the strip steel knife is configured for processing planar materials.

12. The tool according to claim 11, wherein the planar materials to be processed comprise at least one of cardboard, corrugated cardboard or plastic films.