EP2732056B9 - Knife and method for the production thereof - Google Patents

Description

introduction

The invention relates to a helical knife, wherein the blade is made of hardenable steel and has a cutting leg having both at a lower end a foot surface and at an upper end a cutting surface, wherein the cutting surface along a front edge having a cutting edge.

Moreover, the present invention relates to a method for producing such a helical knife.

For the purposes of the present application, "hardenable steels" are ferritic or martensitic steels, the latter being produced by means of hardening of a ferritic steel. For hardenability, it is necessary that the steel has a minimum content of alloying elements, for example, at least 0.8% of carbon in the case of unalloyed steel.

Curing in the context of the present application means an increase in the hardness of a steel by means of a heat treatment (heating with subsequent quenching and optionally subsequent tempering), the hardness of a steel being specified, for example, in the units HRC (Rockwell) or HV (Vickers) can be. Hardening therefore includes both the classic "hardening" (generating a hardness of ≥ 50 HRC or ≥ 510 HV) and the classical "tempering" (hardness is increased but 50 HRC or 510 HV are not achieved), since in both processes the Hardness of the respective treated steel is increased by means of a heat treatment. Thus, if the present application designates a knife or certain portion of it as "hardened", it merely means that the hardness of the knife has been increased. According to the aforementioned classical definition, which is based on the achieved hardness, it may be that a "hardened knife" in the sense of the present application would only be referred to as remunerated.

Specifically, not meant by the term "hardenable steel" are austenitic steels whose lattice structure undergoes no change in the course of a heat treatment (heating with subsequent quenching) and consequently does not experience any increase in hardness. An increase of the hardness, optionally achieved by means of cold deformation, is likewise not included according to the above definition, since this is not brought about by means of a heat treatment.

State of the art

Knives of the type described above are known in leather and textile processing for some time, where they are used in the field of leather processing for so-called "defilement" and / or "folding" and in textile processing for shearing the textile fibers. As a generic term for a machine that is used for processing either animal skins - especially leather - or fibrous materials - especially textile fibers - is used, the term "cutting unit" is used below. If, on the other hand, reference is made exclusively to leather processing, the terms "debossing aggregate" or "folding aggregate" are used, depending on the application in the context of leather processing. Knives of the type described above come for example in the cutting unit according to the utility model DE 74 03 463 U used, wherein it is the cutting unit disclosed therein is a shearing device for processing textiles. SU 1 152 966 A discloses a spiral knife wherein the knife is carbon loaded and then cured.

With regard to the economic efficiency of the cutting units on which the blades are mounted, it is above all the long service lives of the blades that are crucial. The use of hardenable steels or hardened knives is therefore of central importance in order to minimize abrasion in the area of the cutting edge of the knives and to delay the change of knives as long as possible. Although the goods to be cut are usually of low hardness, the permanent use and engagement of the cutting edge with the material to be cut inevitably leads to a dulling of the cutting edge. This applies in particular to the folding and fleshing out, ie processes in the course of cutting animal skins, since these typically require a relatively high cutting force and the blades are subjected to correspondingly high levels of stress. Another wear The knife or the cutting edge results from a permanent resharpening of the knife by means of a grindstone, which runs automatically.

The problem of the durability of a sharp cutting edge of the knife is also determined or reduced by an oxidation of the blade steel apart from a purely mechanical abrasion. This is particularly problematic in the field of leather processing, since aggressive chemicals are used here in advance of the use of a Entfleischaggregats to rid the dermis of the so-called epidermis. On the other hand, the removal of the subcutaneous skin, which is also connected to the dermis, must be mechanical, which is typically achieved through the use of dehiscing knives. This is called "fleshing out". The knives of the Entfleischaggregats come during this Entfleischens in particular extent with the previously used chemicals in contact. Due to the aggressiveness of the chemicals, the steel of the knives corrodes particularly quickly, especially if the destacking unit is not permanently in use. During operation of the Entfleischaggregats the knives are subject to constant abrasion, so that forming rust, which is very soft, is ground directly. The amounts of oxidized material (rust), which reach the dermis, are so small that a visual impairment of the leather is not detectable. However, once the Entfleischaggregat stands still for a long time (weekend, holidays, non-use, etc.), it comes to the formation of a pronounced rust layer on the knives, because the steel is not able to withstand the aggressive environment of the chemicals used. Once the Entfleischaggregat is put back into operation after the service life, it can be particularly easy to a process-related removal of the resulting rust, which leads to a color impairment of the dermis. Such discolorations can usually not be eliminated, so that the discolored material must be cut out, can not be recycled and thus an economic damage.

To solve the problem, the use of stainless steels for the knives has been considered. However, these have a relatively low hardness of less than 600 HV due to the type and are therefore not suitable for the folding or the Entfleischbetrieb due to the high mechanical stress of the cutting edge of the knife. Especially when folding, that is the processing of the thickness of the dermis (ie the cutting of tanned leather), the cutting edges are special strongly abrasive stressed and require for a high durability of the cutting edge sharpness necessarily a high hardness. For these reasons, stainless steels have not yet been realized for making knives for use in the leather sector.

The DE 695 10 719 T2 or EP 0 678 589 A1 describes a stainless steel with a particularly hard surface layer which has a hardness in the range of 700 HV to 1050 HV. The steel described is an austenitic steel which, as such, is not curable, as explained above. This is disadvantageous in particular with regard to a core region of the respective component made from this steel, since it can not be tempered and is therefore comparatively soft. The low rigidity of such an austenitic steel makes it seldom usable as a base material for a knife for use in textile or leather processing in such cases where the knife is subjected to greatly increased cutting forces. This is due to the fact that deformations of a knife with comparatively low rigidity under the influence of greatly increased cutting forces would be too high in order to obtain a good cutting result. Furthermore, the steel according to the DE 695 10 719 T1 insofar disadvantageous as it typically contains high amounts of nickel, which basically has harmful potential. Since in the textile and / or leather processing the knives used there must be reground relatively frequently, a steel with a high nickel content is undesirable for reasons of occupational safety alone.

task

The object of the present invention is based on the above-described prior art to produce a knife and a method for its production, which has both corrosion-resistant properties as well as a sufficient hardness and rigidity, so that it is particularly suitable for use in leather processing in high demands on the quality of cut is suitable.

This object is achieved according to the method and the knife of claim 1 and 4.

solution

The underlying object is achieved from a process engineering point of view, starting from a method of the type described above according to the invention that the hardenable steel of the knife is also a stainless steel and an edge layer of the knife is enriched with carbon and then cured. Advantageously, the remainder of the blade is hardened simultaneously with the hardening of the edge layer of the blade, that is to say its core region. Depending on the particular hardness achieved in the different areas of the knife (surface layer, core area), the core area after curing can also be referred to as "tempered" (hardness of <50 HRC). In principle, an increase in the hardness of at least the surface layer takes place through the "hardening" according to claim 1 (compare also introductory definition of "hardenable steel").

As a starting material for carbon enrichment and subsequent hardening, the group of ferritic high-alloyed stainless (chromium) steels is particularly relevant, although the present application is not limited to such steels, provided that said properties "hardenable" and "stainless" are met. After hardening, these steels are referred to as martensitic high-alloyed stainless (chromium) steels, with the martensite of the hardened steel forming during the hardening process from the ferrite of the base steel. Since the freedom from rust is typically generated by the alloying element chromium, the end product can also be appropriately called stainless martensitic chromium steel, which is curable as such in the context of this application, that is curable and / or heat-treatable.

The carbon enrichment step significantly increases the carbon content of the edge layer of the blade relative to its core region. This procedure of "carburizing" an already hardenable steel, ie a ferritic steel, which already has a minimum content of alloying elements necessary for the hardening, is atypical. The enrichment of a steel with carbon is usually only carried out if the respective steel is to be made curable, that is, a minimum content of carbon is to be produced as an alloying element. Carburizing, in contrast to the procedure proposed here, is normally applied to non-hardenable (ferritic) steels, so-called case hardening steels. The latter therefore apply without one Separate enrichment with carbon as non-curable in the context of this application, this is not due to the fact that it is an austenitic steel in a case-hardening steel - case-hardened steels are generally ferritic - but the lack of hardenability is due solely to their low carbon content.

The further enrichment of the steel with carbon, the so-called "carburizing", which is carried out according to the invention, although the steel is already curable, leads to a significantly improved hardenability of the knife with respect to said surface layer, than the achievable hardness values in the course of a subsequent Hardening of the knife considerably above the otherwise realizable values. In this way, hardness values of more than 700 HV can be achieved. Although the stainless steel properties of the steel used in the carburized edge layer of the knife are adversely affected by the enrichment with carbon, the corrosion resistance of the steel is minimally reduced, while the hardenability increases significantly. In this way, the steel can be further provided with good remaining corrosion resistance with a high hardness, so that the finished knife is ideal for the processing of leather, especially for fleshing and folding.

The method according to the invention comprises the step of hardening the edge layer of the knife. Due to the changing carbon content of the blade after its carburizing (only the surface layer is carburized), the hardness of the steel varies over the cross section of the blade, which is increased in the boundary layer against a core region. By means of a hardening of the knife produced in this way, the hardness of the surface layer can be increased considerably and particularly easily exceed the extent of at least 630 HV. Advantageously, a hardness of at least 670 HV, more preferably at least 720 HV should be exceeded. In the core region of the blade advantageously a hardness of more than 300 HV, preferably of more than 350 HV, more preferably of more than 400 HV, is achieved. Consequently, the hardened core area of the knife is classified as (highly) tempered according to the classical definition (see introductory definition). In the course of a hardness measurement, it should be noted that a known manner in the course of carburizing outer edge oxidation, which typically has a thickness of about 20 microns ± 10 microns, not for the assessment of the hardness of the invention Boundary layer is taken into account. A correct determination of hardness is particularly easy by removing the edge oxidation layer on the hardened blade by means of grinding-polishing processes and then testing the metallically bright surface of the blade with the lowest possible test load.

The method described above is particularly advantageous if the edge layer is circumferentially enriched with carbon on the knife and then cured. In this case, a "peripheral edge layer" is understood to mean that the edge layer completely encloses the respectively treated knife, that is to say not only on a specific side or flank of the knife. The advantage of a circumferentially hard edge layer is due to the stabilizing effect of that edge layer which lies opposite the cutting edge of the knife. Although this site itself does not interfere with the material to be processed and thus does not in principle make any higher demands on its hardness. However, due to the positive stabilizing effect of a hard layer stiffening the entire knife, it is particularly advantageous.

The method can be carried out in a particularly advantageous manner, when the base material is a steel having the properties of a stainless, martensitic chromium steel of the type X20Cr13. Steels of this type are curable and stainless and are particularly well available as standardized steel. As base material, such a steel is not yet available as martensitic but as ferritic steel. The formation of the martensite occurs only in the course of hardening of the steel. If a steel of the aforementioned type X20Cr13 is used as the basis for the method according to the invention, the surface layer of the blade is changed in its structure due to the carburizing process step, since carbon is incorporated. The term X20Cr13 therefore no longer applies after carburizing at least to the surface layer.

The underlying object is device-based starting from a knife of the type described above according to the invention solved in that the curable steel of the knife is a stainless steel and the knife has a carbon enriched and hardened surface layer. Advantageously, in addition to the edge layer and the rest of the knife, that is, the core portion thereof, hardened, wherein the hardness of the Core segment is typically not raised above 510 HV and is thus considered to be remunerated according to the classical definition (see introductory definition).

As described above, such a knife can be hardened particularly well, that is to a particularly high degree, and thus both achieve a high hardness in the region of the edge layer (typically of at least 630 HV) and essentially retain its stainless properties and therefore only corrode to a relatively small extent. Experiments have shown that even after considerable residence times of such a knife according to the invention in a corrosive environment only very slight signs of corrosion occur ("rust rust"), while the corrosion is already far advanced in conventional, non-corrosion-resistant knives and the shape of real "rust craters "has assumed great depth.

As already described above, such a knife is particularly advantageous in which a hardness of the surface layer is at least 630 HV, preferably at least 670 HV, more preferably at least 720 HV. Knives that have hardnesses in this area are particularly suitable for textile and leather processing in terms of their susceptibility to abrasive wear, since they are able to withstand the respective textile or leather well.

The knife according to the invention should also be designed so that the carburized edge layer has a thickness between 0.001 mm and 0.30 mm, preferably between 0.05 mm and 0.20 mm. Such a layer thickness is sufficient to guarantee a long service life of the knife, since a removal of this layer thickness in the course of the operation of the associated cutting unit takes some time. Furthermore, the small layer thickness offers the advantage that an even greater part of the knife remains in the core with a low carbon content in relation to the edge layer and the entire knife retains a high degree of toughness despite the particularly hard edge layer, which reduces the risk of breakage. In addition, the carburizing time, that is, the time that the blade steel needs to be carburized, can be kept short, resulting in greater manufacturing efficiency. When indicating the thickness of the carburized surface layer, it should be noted that the above-mentioned edge oxidation layer, which is formed in the course of the carburizing process, is not included.

In the surface layer, the knife should preferably have a carbon content of more than 0.25%, preferably more than 0.4%, more preferably at least 0.6%. In this way, the edge layer is particularly good curable, so that they can withstand the abrasive stress of the cutting operation by means of curing for a particularly long time.

The hardenable steel used for the knife should have a carbon content between 0.10% and 0.60%, preferably between 0.15% and 0.50%, before the carburizing of the surface layer. Such steels are characterized by a particularly high toughness with good hardenability, with the latter being highly dependent on the proportions of the other alloying elements. By way of example, the type X20Cr13 from the group of stainless martensitic chromium steels, which by definition has about 0.2% ± 0.05% carbon and about 13% ± 1.0% chromium and is curable, may also be mentioned here as a knife steel. The high chromium content gives this steel its corrosion resistance. At the same time, it serves as a strong carbide former, making the steel curable despite its relatively low carbon content of 0.2%.

Depending on the composition of the respective steel, a higher carbon content of 0.4% may also be expedient, whereby advantageously the steel from which the knife is made should have a chromium content of at least 12.5%. By observing this minimum in terms of chromium content, the stainless or corrosion-resistant property of the respective steel is favored or ensured. This applies in particular to the carburized edge layer of the knife, which still retains a high corrosion resistance despite such carburizing despite being carburized to, for example, 1.0% carbon.

Particularly advantageous is a knife whose steel is not alloyed with nickel, in particular a nickel content of at most 1.0%, preferably at most 0.5%, more preferably at most 0.25%. The low nickel content is particularly advantageous from the point of view of industrial safety, since no harmful nickel is released during grinding operations which have to take place at regular intervals for the purpose of sharpening the knives.

Particularly advantageous is such a knife whose inner core region is hardened. Such a hardened core region is particularly advantageous for the applicability of the knife, since the knife thereby obtains a particularly high rigidity. The hardness of the knife in the core region is then advantageously in a range of at least 300 HV, preferably at least 350 HV, more preferably at least 400 HV. An increased stiffness of the knife is particularly advantageous in terms of higher resistance under the action of shear forces, since the deformations of the blade for high-quality processing of textiles and / or leather should be kept low.

Further, such a knife is particularly preferable in which the carbon-enriched and hardened surface layer circulates around the blade. The advantages of a circumferentially hardened surface layer are already explained above.

embodiments

The knife according to the invention and the method according to the invention are explained in more detail below with reference to an exemplary embodiment which is illustrated in the figures.

Fig. 1:

Eine mikroskopische Aufnahme eines erfindungsgemäßen Messers und

Fig. 2:

Einen Entfleischzylinder mit einer Mehrzahl der erfindungsgemäßen Messer.

It shows:

Fig. 1:

A micrograph of a knife according to the invention and

Fig. 2:

A Entfleischzylinder with a plurality of the knife according to the invention.

An inventive knife 1, the in FIG. 1 is shown, has an edge layer 2 and an edge oxidation layer 3. The boundary layer 2 and the edge oxidation layer 3 merge into one another along a transition region 4. The boundary layer 2 is in FIG. 1 in particular by a bright representation and the edge oxidation layer 3 by a dark representation particularly clearly visible. The edge oxidation layer 3 is a product of carburizing the blade 1. It typically has only a very low hardness.

The knife 1 is made of a martensitic chromium steel of the type X20Cr13 and accordingly has a carbon content of about 0.2% ± 0.05% and a chromium content of about 13% ± 1.0%. This steel is hardenable and at the same time corrosion resistant. At the Example of knife 1, the specified values apply to a core region, not shown, while the edge layer 2 of the blade 1, however, is enriched with carbon and therefore has a carbon content of about 1.0%. A thickness of the edge layer 2 of the knife 1 is about 0.15 mm. The enrichment of the boundary layer 2 with carbon takes place in the course of a so-called "carburizing".

The high carbon content of the edge layer 2 of the blade 1 causes the same in this area as a result of quenching a particularly high hardness developed (the in oxidation become inactive edge oxidation layer 3 remains unconsidered), the steel inherent corrosion resistance, although reduced, but in an extensive Dimensions are retained. Due to this combination of high hardness and good corrosion resistance, the knife 1 is particularly suitable for use in leather processing.

Exemplary is in FIG. 2 a Entfleischzylinder 5, which is used in the course of leather processing, shown. This has a plurality of knives 1 according to the invention, which are arranged on a circumferential surface 6 of a cylinder body 7 of the Entfleischzylinders 5. The Entfleischzylinder 5 rotates in operation about a longitudinal axis 8, wherein a cutting edge 9 of the knife 1 is brought into engagement with a material to be machined and this cuts as a result. The knives 1 each have a cutting edge 10, which has at a lower end a foot surface 11, with which the knives 1 are respectively arranged on the lateral surface 6 of the cylinder body 7. Furthermore, the knives 1 have a cutting surface 12 at an upper end of the cutting edge 10. This comprises at a front edge 13, the cutting edge 9 of the knife 1. The blades 1 are fixed by means of caulking with copper 14 in grooves of the cylinder body 7.

LIST OF REFERENCE NUMBERS

1

knife

2

boundary layer

3

Surface oxidation layer

4

Transition area

5

Entfleischzylinder

6

lateral surface

7

cylinder body

8th

longitudinal axis

9

cutting edge

10

cut leg

11

foot surface

12

cutting surface

13

edge

14

copper

Claims (13)

1. A method for the production of a helical knife (1), wherein the knife (1) is produced from hardenable steel and comprises a cutting leg (10) which comprises both a foot face (11) at a lower end and a cutting face (12) at an upper end, wherein the cutting face (12) comprises a cutting edge (9) along a front edge (13), wherein the knife (1) is enriched with carbon, characterised in that the hardenable steel of the knife (1) is a stainless steel and the enrichment of the knife (1) with carbon takes place only on a margin layer (2) of the knife (1) and the knife (1) is then hardened, as a result of which a hardness of the margin layer (2) of at least 630 HV is produced and wherein the margin layer (2) has a thickness between 0.001 mm and 0.30 mm.
2. The method according to claim 1, characterised in that the margin layer (2) is enriched with carbon running around the knife (1) and is then hardened.
3. The method according to claim 1 or 2, characterised in that the knife (1), after the method step in which the knife (1) is hardened, is present as a stainless, martensitic chrome steel of type X20Cr13 with the case-hardened margin layer (2).
4. A helical knife (1), wherein the knife (1) is produced from hardenable steel and comprises a cutting leg (10) which comprises both a foot face (11) at a lower end and a cutting face (12) at an upper end, wherein the cutting face (12) comprises a cutting edge (9) along a front edge (13), wherein the knife (1) is enriched with carbon, characterised in that the hardenable steel of the knife (1) is a stainless steel and only a margin layer (2) of the knife (1) is enriched with carbon and the knife (1) is hardened, wherein the margin layer (2) has a thickness between 0.001 mm and 0.30 mm and hardness of at least 630 HV.
5. The knife (1) according to claim 4, characterised in that a hardness of the margin layer (2) amounts to at least 630 HV, preferably at least 670 HV, further preferably at least 720 HV.
6. The knife (1) according to claim 4 or 5, characterised in that the margin layer (2) has a thickness between 0.05 mm and 0.20 mm.
7. The knife (1) according to any one of claims 4 to 6, characterised in that the hardenable steel from which the knife (1) is produced comprises, in the margin layer (2), a carbon content of at least 0.25%, preferably of at least 0.4%, further preferably of at least 0.6%.
8. The knife (1) according to any one of claims 4 to 7, characterised in that the hardenable steel from which the knife (1) is produced comprises, in a core region, a carbon content between 0.05% and 0.60%, preferably between 0.15% and 0.50%.
9. The knife (1) according to any one of claims 4 to 8, characterised in that the hardenable steel from which the knife (1) is produced comprises a chromium content of at least 12.5%.
10. The knife (1) according to any one of claims 4 to 9, characterised in that the hardenable steel comprises a nickel content of at most 1.0%, preferably at most 0.5%, further preferably at most 0.25%.
11. The knife (1) according to any one of claims 4 to 10, characterised in that the hardened margin layer (2) enriched with carbon runs around the knife (1).
12. The knife (1) according to any one of claims 4 to 11, characterised in that the hardened steel is a stainless, martensitic steel of type X20Cr13.
13. The knife (1) according to any one of claims 4 to 12, characterised in that a core region of the knife (1) is hardened and has a hardness of at least 300 HV, preferably of at least 350 HV, further preferably of at least 400 HV.

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