DE102020120576A1 - Carbide knife for strand cutting and knife holder - Google Patents

Abstract

A cutting knife (1) for a cutting device in a strand unit for cutting a strand into rod-shaped products, in which the material of the knife has a hardness of 1,400 to 2,200 HV30 and a transverse rupture strength of 3,600 to 4,400 MPa and the grain size of the material from 0.2 to 1.3 µm, does not require the knife to be ground during the cutting process and still ensures a sufficiently long service life for the strand unit. A knife holder (2) for such a cutting knife has a planar clamping jaw (22) and a planar counter support (21), the clamping jaw (22) is adjustable about a clamping jaw joint (222), the clamping jaw (22) being operatively connected to a lever with mass (23) in such a way that a force generated by the lever with mass (23) causes the clamping jaw (22) presses against the counter-surface (21), as a result of which the cutting blade (1) is clamped flat between the clamping jaw (22) and the counter-surface (21).

Description

The present invention relates to a cutting knife for a cutting device in a rod unit for cutting a rod into rod-shaped products, a knife holder designed and set up to hold a cutting knife for such a cutting device, a knife carrier comprising at least one such knife holder and a rod machine in the tobacco processing industry and a drinking straw manufacturing machine , each comprising a cutting device.

Rod-shaped products are known from various areas of everyday life. According to the invention, these are rod-shaped products with a diameter of 1 mm to 20 mm. In particular, they include drinking straws and products from the tobacco processing industry such as cigarettes, cigarillos or filters for cigarettes or cigarillos. Modern packaging machines are used to produce the rod-shaped products, which include, among other things, a working step with a cutting device in which the rod-shaped product is cut off from a continuously fed strand.

The cutting device is essentially formed from a rotating knife carrier with one or more cutting knives and at least one tube with a guide for the strand. Due to the high cutting frequency, the cutting knife is subject to natural wear, which can lead to an unclean cutting edge on the cut surface of the strand. To compensate for the wear, the cutting blades in the packaging machine are ground during operation in the machine by means of one or more grinding wheels and are pushed in the direction of the cutting edge by a feed device. After a certain amount of wear, the cutting knives have to be replaced, for which purpose the operation of the packaging machine has to be interrupted.

Currently, steel knives (e.g. steel X65) are used to cut the rod (e.g. filter, cigarette and drinking straw) on the rod unit. These steel knives become blunt after about 300 to 2,000 cuts (depending on the product to be cut) and must be reground in the cutting unit during production. In order to obtain an optimal cutting quality, the grinding device and the knife feed must be optimally adjusted to the product to be cut. During production, the grinding wheels must be cleaned and replaced regularly.

This conventional cutting device is disadvantageous because the resulting grinding dust pollutes the strand unit, so that it has to be cleaned regularly in order to have a clean production environment. Furthermore, the grinding dust mixes with the glue in the product and soils the knife. The dirt partially dissolves and contaminates some products with so-called "black particles". These are particularly undesirable in filter and drinking straw production.

Another disadvantage is that sparks can occur during grinding. The flying sparks can damage parts of the machine or the strand. In extreme cases, fires can even break out. This is to be avoided.

From the EP 2 338 358 A1 It is known to provide at least one of the side faces of a cutting blade with a coating that increases the surface hardness. Due to the higher surface hardness of the side surface, self-sharpening of the cutting blade is to be achieved by the side surfaces of the cutting blade being worn differently during the cutting process. The side surface with the higher surface hardness should wear less than the one with the lower surface hardness, which should lead to a cutting edge that keeps sharpening itself again and again. Although fewer grinding processes are required in this way, abrasion and the undesirable particles associated with it cannot be avoided.

The object of the invention was therefore to provide a cutting device which does not require the knives to be ground during the cutting process and which nevertheless ensures a sufficiently long service life for the strand unit.

According to the invention, this object is achieved with a cutting blade of the type mentioned at the outset in that the material of the blade has a hardness of 1,400 to 2,200 HV30, preferably 1,500 to 2,100 HV30, in particular 1,600 to 2,000 HV30 and particularly preferably 1,800 to 1,950 HV30 and a Flexural strength of 3,600 to 4,400 MPa, preferably 3,700 to 4,200 MPa, in particular 3,800 to 4,100 MPa and particularly preferably 3,900 to 4,000 MPa, and the grain size of the material from 0.2 to 1.3 μm, preferably 0.2 to 0.8 µm and more preferably from 0.2 to 0.4 µm.

Such a knife according to the invention has a high wear resistance. Such a knife has a service life of more than 500,000 Cuts for non-abrasive products are achieved so that, depending on the product to be cut, a service life improved by a factor of 250 to 1600 compared to knives conventionally used in strand units. Since grinding is avoided during operation, grinding particles cannot contaminate or damage products and machines, and there is no risk of sparking. This makes the cutting process safer and the manufactured products are of higher quality.

The properties of the knife according to the invention can be further improved if the initial cutting edge radius of the cutting knife is from 1 to 25 μm, preferably from 1 to 15 μm, and particularly preferably from 1 to 3 μm. The cutting edge radius describes the radius of the circle at the tip of the blade. The cutting edge radius has a great influence on the cutting quality. The smaller the cutting edge radius, the better the cut quality. In the present invention, “initial cutting edge radius” refers to the cutting edge radius that the knife has in the delivery state. In the course of use, the cutting edge radius increases, which, above a certain size, is accompanied by a deterioration in the quality of the cut. The smaller the initial cutting edge radius, the greater the difference to the cutting edge radius at which the knife must be renewed or sharpened, and the longer the service life of the strand unit.

It is particularly favorable if the cutting edge radius is larger than the grain size by a factor of 4 to 6.

A possible material for the cutting blade according to the invention is ceramic. Ceramics are characterized by great hardness. A particularly preferred material for the cutting blade according to the invention is a hard metal with a hard material phase selected from at least one compound from the group consisting of tungsten carbide, titanium carbide, titanium nitride, niobium carbide, tantalum carbide or vanadium carbide, with tungsten carbide being particularly preferred, and a binder phase of cobalt , nickel or a mixture of the two, with cobalt being particularly preferred. The proportion of binder is preferably from 4 to 15% by weight, particularly preferably from 6 to 10% by weight. A cutting blade with a particularly good service life can be obtained with such a material.

Furthermore, it has been found that with regard to the quality of the cut and the service life of the cutting blade, it is particularly advantageous if the cutting edge angle (β) is from 15° to 45°, preferably from 25° to 40°. In addition, the cutting edge angle (β) can have at least one leading angle (β _n ), the leading angle being smaller than the cutting edge angle and each further leading angle (β _n+1 ) in turn being smaller than the preceding leading angle (β _n ). Alternatively, the cutting edge can be designed in the shape of a pointed arch, in particular in the form of an elevated pointed arch. Such a cutting edge shape leads to a particularly long service life. In addition, it is particularly advantageous if the blade tip is arranged in the middle, that is to say the cutting blade has a mirror-symmetrical cross-section.

In addition, it is particularly favorable if the cutting surface has a roughness of 1 to 6 μm, preferably 1 to 3 μm and particularly preferably 1 to 2 μm.

With these geometry and material values in combination, a cutting blade is produced that has such a well-closed contour that no gaps or breakouts in the cutting edge can be seen with the light-optical microscope. On the one hand, such a cutting knife delivers cuts of outstanding quality, on the other hand, the wear is extremely low.

In view of the fact that the cutting blades according to the invention do not have to be ground during operation, it is possible to adapt the geometry of the cutting contour to the requirements of the product to be cut, such as different product lengths with different properties, or other requirements. Various geometries are possible for the cutting contour. The cutting contour can be straight or curved. A straight cutting contour is particularly cost-effective and is therefore used in particular when costs are of particular relevance. In contrast to conventional cutting edge contours, which only allow a circular geometry, with the knife according to the invention it is also possible to use any curved shape as the contour. Alternatively or additionally, the cutting edge can have a serrated edge in some areas. The cutting edge preferably has a serrated edge in the first cut. This can reduce the compression phase when cutting. The shape of the contour also influences the cutting length of the cutting knife used. A curved contour can adapt particularly well to the course of the cut and make particularly good use of the length of the cutting edge. Compared to a straight cutting contour, longer service lives of the cutting blade can be achieved in this way.

In addition, it is particularly advantageous if the cutting surfaces and/or the side surfaces of the cutting blade have a laser structure. With such a structure in the nano range applied with a laser, adhesion of glue from the strand on the cutting surfaces or the side surfaces can be reduced or even avoided. As far as the side surfaces are concerned, a coating, which can consist of cerite, for example, can alternatively be applied to these to avoid adhesion of glue. The coating can be applied either after the cutting blade has been sharpened or before the sharpening. In the latter case the coating is applied and oven cured. The coating on the cutting edges is removed again in the course of grinding the cutting knife.

It is particularly advantageous for the cutting edges to be ground not parallel to the cutting edge but at an angle of at least 20° to the cutting edge, preferably at an angle of 45° to 90°, in particular at an angle of 80° to 90° and most preferably at right angles to the cutting edge. When grinding at an angle of less than 90° to the cutting edge, the grind on one side should be offset by 90° or approximately 90°, i.e. 90° +/- 5°, to the grind on the other side.

• • Messerstärke (t) von 0,2 bis 0,4 mm, vorzugsweise von 0,25 bis 0,3 mm
• • Schneidenhöhe von 4 bis 11 mm, vorzugsweise von 8 bis 11 mm, insbesondere 11 mm
• • Messerlänge von 40 und 70 mm, vorzugsweise von 50 bis 60 mm, insbesondere 60 mm

Particularly preferred dimensions of the cutting blade are as follows, it being possible for some or all of the preferred dimensions to be realized, the latter in any combination:

• • Knife thickness (t) from 0.2 to 0.4 mm, preferably from 0.25 to 0.3 mm
• • Cutting edge height from 4 to 11 mm, preferably from 8 to 11 mm, in particular 11 mm
• • Knife length of 40 and 70 mm, preferably 50 to 60 mm, in particular 60 mm

In order to make the cutting blade counterfeit-proof, it is advantageous if the cutting blade has a forgery-proof marking or inscription. Such a marking can e.g. B. be introduced with a laser such as a short-pulse laser or with an acid stamp. In particular, holographic security features such as holograms or forgery-proof diffractive writing come into consideration as counterfeit-proof markings.

The present invention also relates to a knife holder for a cutting device in a strand unit for cutting a strand into stick-shaped products.

Current knife holders in the strand unit's knife carrier are optimized for a steel knife (X65) that is reground during operation. The cutting knife is held between two pairs of rollers and advanced over this holding device for grinding. However, this holding device is not suitable for holding any type of cutting knife, in particular not for a cutting knife according to the invention which is sensitive to breakage. In addition, for a cutting blade according to the invention, the function of advancing for grinding is not required.

The object of the present invention was therefore also to provide a knife holder for fragile cutting knives, in particular cutting knives according to the invention, which prevent the cutting knife from breaking and ensure that the service life of the knife is limited solely by the wear of the blade and not through other signs of fatigue of the knife.

This object is achieved by a knife holder of the type mentioned at the outset, which has a planar clamping jaw and a planar counter-surface, the clamping jaw being adjustable about a clamping jaw joint, the clamping jaw being operatively connected to a lever with mass in such a way that a lever with The force generated by the mass presses the clamping jaw against the counter-surface, whereby the cutting blade is clamped flat between the clamping jaw and the counter-surface.

"Planar clamping jaw" means that the side of the clamping jaw facing the cutting blade is designed as a flat surface. Correspondingly, “planar counter-surface” means that the side of the counter-surface facing the cutting blade is designed as a flat surface.

With such a knife holder, the knife is clamped in a non-positive manner and with low surface pressure until it is close to the point of action via the holding device. The movable clamping jaw avoids bending stress on the cutting knife when clamping. Since the clamping takes place over surfaces, the surface pressure is reduced. There is no line or even point contact, but instead a surface contact, through which the resulting forces are distributed as best as possible. A force generated by the lever with mass presses the clamping jaw against the counter-position. The cutting blade is located between the two and is thus firmly clamped between the clamping jaw and the counter-surface.

In order to avoid bending stresses, the clamping jaw is designed with a clamping jaw joint with at least one degree of freedom, so that the clamping jaw can be aligned parallel to the cutting blade in a plane, regardless of any angle that the clamping jaw may have cke to the opposite position, in that the mass acts on the lever and thus on the clamping jaw. The jaw joint can be designed as a rotary joint with one degree of freedom. In this case, the adjustment in the second level is ensured by precisely manufactured components. Particularly preferably, the jaw joint is a ball and socket joint with three degrees of freedom, the axis being restricted in such a way that the top edge of the jaw cannot rotate relative to the counter-layer edge, but is always arranged parallel to it. This ensures that the clamping jaw is aligned in two planes parallel to the cutting knife during clamping, but that there is no undesired change in alignment in the third degree of freedom.

Advantageously, the force generated by the lever with mass is a centrifugal force. The centrifugal force acting on the blade increases as the blade carrier speed increases. This also increases the holding force required for the knife to prevent it from being detached from the knife holder. The centrifugal force that drives the knife out of the knife holder is compensated by a holding force that is also formed by the centrifugal force. The centrifugal force depends on the speed of the knife carrier. Due to this dependency, the holding power of the knife increases with increasing speed and the knife is held with the same level of security. The size of the centrifugal force can be optimally adapted to the knife and the properties of the other components of the knife holder by the weight of the mass. The weight of the lever with mass can be adjusted in particular by the choice of the material for the lever with mass as well as its size. Preferably the mass is integral with the lever.

Alternatively or in particular additionally, the holding force is generated via spring force, in that the lever with mass continues to be operatively connected to at least one spring, so that a force generated by the at least one spring presses the clamping jaw against the counter-position. Unlike the centrifugal force, the spring force is constant and independent of the speed. It is also possible to generate the holding force only via spring force. In this case, the spring tension must be selected sufficiently high to ensure security against the knife becoming detached, even with increasing speed.

The holding force is particularly preferably generated by a spring force component and a centrifugal force component which act on the clamping jaw via the lever with mass. The spring force is constant and is present regardless of whether the knife holder is rotating or at rest. In particular when the cutting device is at rest and when it is starting up, the spring force component ensures that there is sufficient holding force to secure the knife in the knife holder and in particular to prevent it from slipping. The spring force component is generated by at least one spring. The spring force can be transferred from the spring to the lever, for example via a pressure pin or a pressure piece. The knife holder particularly preferably has at least two springs.

The centrifugal force depends on the speed of the knife carrier. With a corresponding adjustment of the lever with mass, this dependency can be used to ensure that the holding force increases to the same extent as the centrifugal force acting on the knife and this from the knife holder, so that the knife can be used with the same level of safety in every state of the cutting device is held.

Another way to increase the holding force is to increase the coefficient of friction (or coefficients of friction) of the clamping jaw and/or counter-surface. Since the holding force results from the product of the coefficient of friction and the normal force, an increase in the coefficient of friction leads to an increase in the holding force. To increase the coefficient of friction, the clamping jaw and/or the counter-surface can preferably be coated with a coating that has a greater roughness than the material of the clamping jaw or counter-surface. Nickel in particular is used as such a material, but rubber would also be conceivable.

Preferably, the jaw and the backing have a width substantially equal to the length l of the cutting blade. “Essentially the same” means either equal to the length of the cutting blade or at most 10 mm, in particular at most 5 mm less or more than the length of the cutting blade. The more the length of the cutting blade corresponds to that of the clamping jaw and counter support, the lower the risk of bending stress occurring, which would result in damage to the cutting blade.

Furthermore, it is particularly favorable if the bending stress in the cutting blade only occurs in one plane during cutting, since the clamping jaw and the counter support on the blade are straight and have curves when the blade exits, i.e. the upper edge of the clamping jaw and/or the counter support is straight and/or are rounded. Preferably, the upper edges of both the jaw and the anvil are straight and rounded.

Since the weight of the jaw counteracts the mass lever and the force generated by it, it is advantageous if the jaw is made of a material with as low a density as possible. Aluminum is therefore particularly preferred as the material for the clamping jaw. For the lever and the mass it is the other way around. For these, a high-density material is particularly preferred. Brass has proven to be a particularly suitable material for the lever and mass.

In a further preferred embodiment, the knife holder has lateral guides and/or a lower stop for the cutting knife. In this way, a very simple, very quick and very precise positioning of the cutting blade is possible. The bottom stop ensures that when inserting the cutting blade, the protruding blade length does not have to be adjusted. It results from the attack. In this way it is possible to ensure that the blade is positioned precisely in such a way that the product is cut in the desired way. It is then not necessary to first determine the correct positioning of the knife in a start-up phase. It is preset. The lateral guides position the knife in the cutting direction. The lower stop can be designed in the form of one or more, in particular two, pins against which the knife strikes. It is not a problem that the stop is not formed over the entire length of the knife, since the contact pressure of the clamping jaw against the counter-surface is so great that it is superimposed on the cutting force and thus there are no bending stress and damage problems on the knife due to the not over the entire Length occurring load is to be feared.

Advantageously, the knife holder also has an unlocking mechanism which causes the clamping jaw to be spaced apart from the counter-surface. The unlocking mechanism is in operative connection with the lever. The unlocking mechanism counteracts the force (e.g. the spring force) acting on the jaw and ensures that the jaw is released from the knife. It can then be opened manually. It is favorable if the clamping jaw is about 1 to 2 mm open in the unlocked position in order to be able to insert the knife easily.

Furthermore, the present invention relates to a knife carrier for a cutting device in a strand unit for cutting a strand into rod-shaped products. The knife carrier has at least one knife holder according to the invention with a cutting knife according to the invention. The at least one knife holder is arranged on the knife carrier. The knife carrier has an axis of rotation R, about which the knife holder is rotatably arranged. Knife carriers according to the prior art also have at least one grinding wheel in order to regrind the cutting knife or knives during operation. Such a grinding wheel or another grinding device is not required for the present invention, so that the knife carrier can be made much simpler. It is not necessary to coordinate with a grinding device.

The knife holder is preferably attached to the knife carrier in such a way that the knife is arranged at an angle to the axis of rotation of the knife carrier. In this way, a particularly straight cut of the strand can be ensured.

The knife carrier preferably has one or two knife holders according to the invention, with two knife holders being particularly preferred. The cutting quality achieved in this way over the entirety of the cuts has thus turned out to be particularly good.

It is particularly favorable if the knife holder is a preassembled assembly that can be easily removed from the knife carrier for maintenance and then reinserted.

Finally, the present invention relates to a rod machine in the tobacco processing industry, comprising a cutting device with at least one blade carrier according to the invention and at least one cutting blade according to the invention, and a drinking straw manufacturing machine, comprising a cutting device with at least one blade carrier according to the invention and at least one cutting blade according to the invention.

All the preferred configurations described above can each be implemented individually or in any combination with one another.

Subclaims are directed to the above-mentioned and other expedient and advantageous embodiments of the invention. Only particularly expedient and advantageous forms and options are described in more detail with reference to the following description of the exemplary embodiments illustrated in the schematic drawing. Each described individual or detailed design within an exemplary embodiment is to be understood as a structurally independent detailed example for other designs and designs that fall under the invention and are not described or not fully described.

• 1 eine Ausführungsform eines erfindungsgemäßen Schneidmessers in Seitenansicht,
• 2 das Schneidmesser im Querschnitt, in Schnittrichtung A-A der 1,
• 3 einen Ausschnitt des Schneidmessers aus 1 zur Darstellung der Schneidfläche,
• 4a-c drei verschiedene Ausführungsformen von Schneiden des erfindungsgemäßen Schneidmessers im Querschnitt,
• 5.1 bis 5.4 eine schematische Darstellung des Schneidvorgangs mit einem erfindungsgemäßen Schneidmesser mit kurvenförmiger Schneide in Seitenansicht, wobei vier Phasen eines Schneidevorgangs schematisch illustriert sind,
• 6.1 bis 6.4 eine schematische Darstellung des Schneidvorgangs mit einem erfindungsgemäßen Schneidmesser mit gerader Schneide in Seitenansicht, wobei vier Phasen eines Schneidevorgangs schematisch illustriert sind,
• 7 eine Ausführungsform eines erfindungsgemäßen Messerhalters mit eingeklemmtem Schneidmesser in perspektivischer Darstellung,
• 8 einen Schnitt durch den erfindungsgemäßen Messerhalter aus 7, geschnitten durch die Mitte des Messerhalters, wobei sich der Messerhalter in seinem geöffneten Zustand mit betätigter Entriegelung befindet,
• 9 einen Schnitt durch den erfindungsgemäßen Messerhalter aus 7 wie in 8, nur im gespannten Zustand, bei dem die Klemmbacke gegen die Gegenlage gepresst ist,
• 10 einen Messerträger mit zwei erfindungsgemäßen Messerhaltern in perspektivischer Darstellung.

Show it

• 1 an embodiment of a cutting blade according to the invention in a side view,
• 2 the cutting blade in cross section, in the cutting direction AA of 1 ,
• 3 a section of the cutting blade 1 to represent the cutting surface,
• 4a-c three different embodiments of cutting of the cutting blade according to the invention in cross section,
• 5 .1 to 5.4 a schematic representation of the cutting process with a cutting blade according to the invention with a curved cutting edge in a side view, with four phases of a cutting process being illustrated schematically,
• 6 .1 to 6.4 a schematic representation of the cutting process with a cutting knife according to the invention with a straight cutting edge in a side view, with four phases of a cutting process being illustrated schematically,
• 7 an embodiment of a knife holder according to the invention with a clamped cutting knife in a perspective view,
• 8th a section through the knife holder according to the invention 7 , sectioned through the center of the knife holder, with the knife holder in its open condition with the latch actuated,
• 9 a section through the knife holder according to the invention 7 as in 8th , only in the clamped state, in which the clamping jaw is pressed against the counter surface,
• 10 a knife carrier with two knife holders according to the invention in a perspective view.

A first embodiment of a cutting blade 1 according to the invention is shown in FIGS 1 until 3 shown. 1 is a side view looking at the side surface 11 of the cutting blade 1, 2 a cross-section in the direction of section AA 1 and 3 a section of the cutting blade 1 1 .

At the top of the side surface 11 of the cutting blade is the cutting edge 12 which, in the embodiment shown, is straight and rises from the front end to the rear end of the cutting edge 12 over the length l of the blade. The difference between the height at the beginning and at the end of the blade 12 is the blade height h, which is 11 mm in the embodiment shown. The knife length I is 60 mm. The blade width or thickness b of the cutting blade 1 is 0.3 mm. The blade tip 14 of the cutting blade 1 is defined by the cutting edge radius r. In the embodiment shown, this is 2 μm. The knife tip 14 is arranged centrally, i.e. the knife is mirror-symmetrical in cross-section. The roughness of the cutting surface is 1.5 µm.

The side surfaces 11 are coated with Cerit to prevent glue from sticking to the side surfaces, which would impair the cutting quality. A counterfeit-proof marking in the form of a hologram is also applied to the side surface 11, with which it can be traced whether the cutting blade is an original product or a counterfeit. The hologram can be supplemented or replaced by diffractive writing.

The cutout in 3 shows the cutting edge enlarged and illustrates the cut. In the embodiment shown, this is approximately perpendicular to the cutting edge, ie has an angle of approximately 90° to the cutting edge. Other angles (> 20°) to the cutting edge are also possible. It is important that, in the event that the angle differs from 90°, the angle from the grinding direction to the cutting surface 13a on one side of the cutting blade 1 is offset by 90° to the angle from the grinding direction to the cutting surface 13b on the other Side of the cutting blade 1.

The cutting blade 1 consists of a hard metal with a hard material phase made of tungsten carbide and a binder phase made of cobalt. The hard material phase has a grain size of 0.5 to 0.8 µm. The cutting edge radius r is therefore larger than the grain size by a factor of 4, which is a particularly favorable ratio of cutting edge radius r to grain size. The binder content of the hard metal is 6 to 10% by weight. The cutting blade according to the invention has a hardness of 1930 HV30 and a bending strength of 3800 MPa. The cutting blade 1 has, as in 2 can be seen, a single cutting edge angle β. This is 40°.

With these geometry and material values, a cutting edge 12 is produced in combination, which has a perfectly closed contour (no gaps or breakouts in the cutting edge that can be seen with the light-optical microscope). This cutting edge achieves optimal cutting quality and a service life of more than 500,000 cuts for non-abrasive products, which, depending on the product to be cut, corresponds to an improvement by a factor of at least 250 to 1600 compared to current state-of-the-art cutting knives in a strand unit.

4a-c show three different embodiments of cutting 12 of erfindungsge measured cutting blade 1 in cross section. In 4a a cutting edge 12 with a single cutting edge angle β is shown. Such a design of the cutting edge is particularly cost-effective. 4b shows another embodiment of the cutting edge 12, in which the cutting edge has a cutting edge angle β and a pre-angle _β1 . The cutting edge 12 can also have a plurality of leading angles β _n , each leading angle β _n+1 being smaller than the preceding leading angle β _n . As a limit variant with an infinite number of advance angles, the in 4c cutting edge shape shown, which has the shape of a pointed arch. Such a cutting edge shape results in a particularly long service life of the cutting blade, since wear is low.

This in 1 The cutting knife 1 shown has a straight cutting contour. In contrast to the prior art, which only allows arcuate contours, the cutting blades 1 according to the invention can have any cutting edge contours because the cutting blade 1 does not have to be reground in the blade holder 2 on the blade carrier 3 during operation.

5 .1 to 5.4 are a schematic representation of the cutting process with a cutting blade according to the invention with a curved cutting edge in a side view, with four phases of a cutting process being illustrated schematically. The path of the cutting blade is illustrated by the two circular arcs 4 and 5. Reference number 4 indicates the path of the beginning of the knife 122 (in the example of 5 curved), reference number 5 the path of the knife end 123 again. The arrow indicates the direction of movement of the cutting blade 1.

At cutting blade 1 of 5 the cutting edge 12 is curved. This is particularly advantageous because the contour of the cutting blade 1 is matched to the various phases of the cut through the product 6 to be cut.

5 .1 shows the state at the moment when the cutting edge 12 touches the product 6. 5 .2 illustrates the compression and gating phase where the cut begins. The product 6 is slightly dented. It is advantageous for this if the cutting edge 12 rises steeply in a curve. Likewise, in the initial area 122 of the cutting edge 12, the cutting knife 1 can have a serrated edge, which particularly supports the compression and cutting phase. 5 .3 shows the knife during the cut through the product 6. Cutting edge 12 is essentially straight in the corresponding area. This allows for a slow cut that takes advantage of the blade length. At the in 5 .4 the state shown, the product 6 has already been completely cut through. The remaining piece of cutting edge 12 serves as security, so that the product 6 is then completely cut off.

6 .1 to 6.4 are a schematic representation of the cutting process with a cutting knife according to the invention with a straight cutting edge 12 in side view, again four phases of the cutting process corresponding to the 5 .1 to 5.4 are illustrated schematically, the course of the cutting blade 1 is again illustrated by the two circular arcs 4 and 5. Reference number 4 indicates the path of the beginning of the knife 122 (in the example of 6 straight), reference number 5 the path of the knife end 123 again. The arrow indicates the direction of movement of the cutting blade 1.

As in 6 .1 can be seen, the cutting blade 1 has already passed under the product 6 to a large extent before the cutting blade 1 even touches it. Correspondingly later along the cutting edge 12, it meets the product 6 in the compression and cutting phase. 6 .3 shows the knife during the cut through the product 6. At the in 6 .4 the state shown, the product 6 has already been completely cut through.

A comparison of 5 .1 to 5.4 with 6.1 to 6.4 shows the difference in the cutting edge length used for the cut, which is due to the contour of the cutting blade 1. While in the curved cutting blade of 5 About 80% of the cutting edge length is used for the cut, this is the case with the cutting knife with the straight contour from the 6 only about 30%. In the case of a straight cutting contour, only a fraction of the cutting length of the cutting blade 1 is used for the cut in comparison to a curved cutting contour. As a result, the service life of the cutting knife 1 with a curved cutting edge can be approximately doubled compared to a cutting knife with a straight cutting edge.

Next, an embodiment of the knife holder 2 according to the invention with reference to FIG 7 until 9 described. A knife holder 2 is attached to a knife carrier 3, as in 8th and 9 is shown. The knife holder 2 has a planar clamping jaw 22 and a planar counter-surface 21 . Due to the planar design of the clamping jaw 22 and counter support 21, the cutting blade 1 rests completely flat on both the clamping jaw 22 and the counter support 21, so that any bending stresses are minimized or even avoided. The holding force F _H , which is required to press the clamping jaw 22 against the cutting blade 1 and the counter-surface 21 , is increased by spring force F _F and centrifugal force F _M brought. Both forces F _F and F _M act on the lever with mass 23 which rotates about the lever axis 222 and presses against the clamping jaw 22 . Lever with mass 23 is made of brass, clamping jaw 22 is made of aluminum. Clamping jaw 22 is designed with a clamping jaw joint 231, a rotary joint with one degree of freedom, so that the clamping jaw 22 can be aligned parallel to the cutting knife 1 clamped between the clamping jaw 22 and the counter-surface 21 in a plane. Alignment in the second plane is ensured by the precisely manufactured components, in particular by the lateral guides 212 which position the cutting blade 1 in the cutting direction. The clamping jaw 22 has a nickel coating to increase the coefficient of friction and thus to increase the holding force.

The spring force component F _F of the holding force F _H is generated by the two springs 25 that are arranged in the spring holder 24 . The pen holder is closed with a pen holder cover 241 . The spring force component F _F generated by the two springs 25 is transmitted via pin-shaped spring pieces 26 to the lever with mass 23, which in turn presses the clamping jaw 22 against the counter-surface 21, whereby the cutting blade 1 is clamped between the two. The spring force component F _F is constant.

The centrifugal force component F _M of the holding force F _H is generated by the lever with mass 23 when the knife holder rotates. Due to the centrifugal force, the lever with mass 23 is pushed outwards. This in turn presses on the clamping jaw 22, whereby the cutting blade 1 is also clamped between the clamping jaw 22 and the counter-surface 21. The centrifugal force depends on the speed of the knife carrier 3. Due to this dependency, the holding force F _H of the cutting knife increases with increasing speed. This compensates for the fact that the centrifugal force on the other side causes the cutting blade 1 to be driven out of the blade holder 2 . Appropriate choice of the lever with mass 23 can ensure that the holding force F _H acting on the cutting blade 1 is always greater than the force that drives the blade out of the blade holder 2 . In this way, the cutting blade 1 is held with constant security.

The cutting blade 1 is thus clamped in a non-positive manner and with low surface pressure up to the point of action via the blade holder 2 .

If the cutting blade 1 is to be changed, the blade holder 2 can be unlocked via the unlocking mechanism 28, which is accessible via a recess in the cover 29, by pressing it down. 9 shows the knife holder 2 in the clamped state, 8th shows him without knife in the unlocked state with open jaw 22, which is spaced from the counter-surface 21 about 1 to 2 mm. In the unlocked state, the cutting blade 1 is released and can be removed. Unlocking will only occur when the device is stopped. At the time of unlocking, the holding force F _H consists only of the spring force component F _F . The unlocking mechanism 28 thus only has to counteract and compensate for the spring force component F _F . The clamping jaw 22 can then simply be moved manually away from the counter-surface 21 in order to remove the cutting knife 1.

As already mentioned above, the knife holder 2 has lateral guides 212 in order to simplify the positioning of the cutting knife 1. In order to be able to use the cutting blade 1 at the correct height without any problems and without separate adjustment, the blade holder also has two stop pins 27 .

Both counter-surface 21 and clamping jaw 22 have curves on their upper edges 211, 221. This reduces the notch effect caused by the bending of the knife when cutting.

10 finally shows a perspective view of a knife carrier 3 with two knife holders 2 according to the invention. One of the two knife holders 2 is in 10 not visible as it lies under the cover 29 with which it is covered. Knife carrier 3 rotates about a knife carrier axis (not shown) which runs through centering 32 . The blade carrier 3 is attached to a strand machine with the flange surface 31 . Two knife holders 2 are fastened to knife carrier 3, in each of which a cutting knife 1 is clamped.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• EP 2338358 A1 [0007]

Claims (19)

Cutting knife (1) for a cutting device in a strand unit for cutting a strand into rod-shaped products, characterized in that the material of the knife has a hardness of 1,400 to 2,200 HV30, preferably 1,500 to 2,100 HV30, in particular 1,600 to 2,000 HV30 and particularly preferred from 1800 to 1950 HV30 and a transverse rupture strength from 3600 to 4400 MPa, preferably from 3700 to 4200 MPa, in particular from 3800 to 4100 MPa and particularly preferably from 3900 to 4000 MPa, and the grain size of the material from 0.2 to 1.3 µm, preferably from 0.2 to 0.8 µm and more preferably from 0.2 to 0.4 µm. Cutting knife (1) after claim 1 , characterized in that the initial cutting edge radius (r) is from 1 to 25 µm, preferably from 1 to 15 µm, in particular less than 5 µm and particularly preferably from 1 to 3 µm. Cutting knife (1) after claim 1 or 2 , characterized in that the material is a hard metal with a hard material phase selected from at least one compound from the group consisting of tungsten carbide, titanium carbide, titanium nitride, niobium carbide, tantalum carbide or vanadium carbide, with tungsten carbide being particularly preferred, and a binder phase of cobalt, nickel or a mixture of the two, with cobalt being particularly preferred. Cutting knife (1) after claim 3 , characterized in that the proportion of binder is from 4 to 15% by weight, preferably from 6 to 10% by weight Cutting blade (1) according to one of Claims 1 until 4 , characterized in that the cutting edge angle (β) is from 15° to 45°, preferably from 25° to 40°. Cutting blade (1) according to one of Claims 1 until 5 , characterized in that the cutting edge angle (β) has at least one pre-angle (β _n ), the pre-angle (β _n ) being smaller than the cutting edge angle (β), or in that the cutting edge (12) is ogive-shaped. Cutting blade (1) according to one of Claims 1 until 6 , characterized in that the cutting edge contour is straight or curved and/or has a serrated edge in some areas. Cutting blade (1) according to one of Claims 1 until 7 , characterized in that the cutting surfaces (13) have a laser structure. Cutting blade (1) according to one of Claims 1 until 8th , characterized in that the side surfaces (11, 11a, 11b) of the cutting blade (1) have a coating and/or a laser structure. Knife holder (2), designed and set up for holding a cutting knife (1) for a cutting device in a strand unit for cutting a strand into rod-shaped products, in particular a cutting knife (1) according to one of Claims 1 until 9 , characterized in that the knife holder (2) has a planar clamping jaw (22) and a planar counter-surface (21), the clamping jaw (22) being adjustable about a clamping jaw joint (222), the clamping jaw (22) having a lever with Mass (23) is operatively connected in such a way that a force generated by the lever with mass (23) presses the clamping jaw (22) against the counter-surface (21), whereby the cutting blade (1) between the clamping jaw (22) and counter-surface (21) is flattened. Knife holder (2) after claim 10 , characterized in that the force generated by the lever with mass (23) is a centrifugal force. Knife holder (2) after claim 10 or 11 , characterized in that the lever with mass (23) is also operatively connected to at least one spring (25), so that a force generated by the at least one spring (25) presses the clamping jaw (22) against the counter-surface (21). Knife holder (2) according to one of Claims 10 until 12 , characterized in that the clamping jaw (22) and the counter-surface (21) have a width which is at least substantially equal to the length I of the cutting knife (1). Knife holder (2) according to one of Claims 10 until 13 , characterized in that it has lateral guides (212) and/or a lower stop (27) for the cutting knife (1). Knife holder according to one of the Claims 10 until 14 , characterized in that it comprises an unlocking mechanism (28) for spacing the clamping jaw (22) from the counter-surface (21), the unlocking mechanism (28) being operatively connected to the lever with mass (23). Knife holder (2) according to one of Claims 10 until 15 , characterized in that the upper edge (211, 221) of the clamping jaw (22) and/or the counter-surface (21) is rounded. Knife carrier (3) for a cutting device in a strand unit for cutting a strand into rod-shaped products, characterized in that the knife carrier (3) has at least one knife holder (2) arranged on the knife holder (3) and rotatable about an axis of rotation R of the knife holder (3). after one of Claims 10 until 16 having. Rod machine of the tobacco processing industry, comprising a cutting device with at least one knife carrier according to one of Claims 10 until 16 and at least one cutting blade according to one of Claims 1 until 9 . Drinking straw manufacturing machine, comprising a cutting device with at least one knife carrier according to one of Claims 10 until 16 and at least one cutting blade according to one of Claims 1 until 9 .

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