Cutting knives, high-speed slicers and methods for slicing food products

Abstract

Cutting blade for machines for slicing food products, in particular for high-speed slicers, wherein the cutting blade is a sickle blade which rotates about an axis of rotation (1) during cutting operation and which has, on its radially outer circumference, a cutting edge (2) which deviates from a circular shape and encircles the axis of rotation (1) in particular in the manner of a spiral and which lies in a cutting plane (3) running perpendicular to the axis of rotation (1), wherein the cutting edge (2) forms the radially outer end of a cutting surface (4), the radially inner end of which is formed by the transition to a discharge surface (5), characterized in that the discharge surface (5) encloses discharge angles (β) with the cutting plane (3) which vary in the circumferential direction of the cutting edge (2).

Description

[0001] The invention relates to a cutting blade for machines for slicing food products, in particular for high-speed slicers, wherein the cutting blade is a sickle blade which rotates about an axis of rotation during the cutting operation and which has on its radially outer circumference a cutting edge which deviates from a circular shape and encircles the axis of rotation, in particular in the manner of a spiral, which lies in a cutting plane running perpendicular to the axis of rotation, wherein the cutting edge forms the radially outer end of a cutting surface, the radially inner end of which is formed by the transition to a discharge surface.

[0002] The invention also relates to a high-speed slicer and a method for slicing foodstuffs, in particular stick-shaped foods.

[0003] Such cutting knives are generally known, for example from EP 0 709 170 A1 or DE 10 2007 040 350 A1. The knives used for slicers, and in particular high-speed slicers, usually have a bowl-like or dish-like shape in the broadest sense, or corresponding clearances in the form of pockets, i.e. on the side facing the product during cutting operation, the knife body is set back from the cutting plane defined by the cutting edge of the knife. The surface facing the product during cutting, emanating from the cutting edge, referred to as the clearance surface, forms the clearance angle φ with the cutting plane and opens the front side of the knife conically radially inwards. This ensures that the knife does not rub against the product to be sliced during cutting and that product compression is avoided.This one-sided bowl or bowl shape of the knife has virtually no influence on the product itself during cutting; only the product slice that has just been cut has to evade the cutting knife, which is unproblematic due to its easy deformability.

[0004] In practice, the size of the so-called cutting angle is an important factor for achieving optimal cutting results. The cutting angle is the angle formed by a surface located on the radially outer circumference of the cutting blade, also referred to below as the cutting surface, whose radially outer end is formed by the cutting edge, with the cutting plane running perpendicular to the blade's axis of rotation.

[0005] Especially for high-speed slicers, which have blade speeds of up to 2400 rpm and thus make up to 40 cuts per second, it is essential that the cutting angle is adapted to the cutting properties of the product.

[0006] In practice, knives with a constant cutting angle are used, with the size of the cutting angle representing a compromise for the specific product being sliced. This compromise is primarily due to the dual function of the cutting surface: on the one hand, it is responsible for forming a stable cutting wedge together with the cutting edge; on the other hand, the cutting surface applies a shear force to the slice being cut.

[0007] This force is higher or lower depending on the cutting edge angle. A small cutting edge angle, i.e. a relatively flat cutting surface, results in gentle cuts with correspondingly low cutting forces. However, with a small cutting edge angle the severed slice is thrown off the knife over the cutting surface to a much lesser extent, so that the slice falls in an uncontrolled and therefore irregular manner. This makes it impossible or at least very difficult to form orderly portions, such as a shingle or a stack consisting of several slices. Small cutting edge angles together with the necessary clearance angles result in slender knife edges that are less stable and therefore have a shorter service life than knife edges with large cutting angles.

[0008] A large cutting edge angle leads to high cutting forces, which can sometimes destroy the product during cutting through compression. A further disadvantage of large cutting edge angles is that the ejection force between the cutting edge and a severed slice is too high when the slice is ejected. This can cause the friction force in the tangential direction between the knife and slice to increase to such an extent that the slices are thrown sideways out of the machine in an uncontrolled manner. Slices can also be thrown sideways out of the machine if the cutting edge is too wide or if the cut slice comes into contact with the rest of the knife back surface. For this reason, the cutting edge width is dimensioned in a range of up to a maximum of 3 mm, and a flat knife back surface with a knife back angle of no more than 15°.

[0009] DE 10 2007 040 350 A1 presents a cutting knife with a cutting angle that varies in the circumferential direction as a solution for minimizing product compression and optimizing product placement. The cutting angle is tailored to the behavior of the products for each circumferential area of the cutting knife. In particular, the cutting angle during which the knife is immersed in the product is different from that during, for example, the subsequent cutting through of the product. While this invention may be advantageous for some specific products, it does have significant disadvantages. Varying the cutting angle also varies the stiffness and strength of the knife edge. This has the disadvantage, particularly with hard products such as frozen products and products with a hard outer shell, that the cutting edge can break very quickly and the cutting ability of the cutting knife can be lost after just a few work cycles.

[0010] Cutting knives are often resharpened once per production shift by regrinding the cutting surface. For logistical reasons, this resharpening is performed by the operators of the high-performance slicers themselves. A variety of simple knife sharpening machines are available on the market for this purpose. The cutting angle is set in these machines, and, with a few inaccuracies, the cutting surface is reproducibly resharpened at this constant cutting angle around the entire circumference of the cutting knife. Grinding machines that can resharpen a variable cutting angle around the circumference of sickle knives are considerably more complex and costly, as they usually require computer-controlled drive and adjustment axes.

[0011] The object of the invention is to further develop a cutting knife, a high-speed slicer and a method of the type mentioned at the outset in such a way that, on the one hand, all product- and application-specific conditions can be taken into account and, on the other hand, the disadvantages of a weakened cutting edge and complex equipment for resharpening the knife can be avoided.

[0012] The solution to this problem is achieved with a cutting knife of the type mentioned above by the discharge surface includes discharge angles with the cutting plane, which vary in the circumferential direction of the cutting edge.

[0013] By assigning the cutting function to the cutting surface and the ejection function to the ejection surface according to the invention, each of the surfaces can be optimally designed to fulfill its function, whereas according to the prior art, compromises between both functions must be made by using a single surface. A blunt, i.e., large, cutting angle ensures the knife's edge retention over a significantly longer operating period. It was surprising to the person skilled in the art that the disadvantages of blunt cutting angles—so-called compression—mentioned in patent DE 10 2007 040 350 A1 could be completely compensated for by a smoother knife contour, in particular a lower spiral pitch.

[0014] The design of the discharge surface is particularly advantageous with variable discharge angles, since the tangential velocity is variable over the blade radius, which increases due to the spiral shape. For example, if the discharge angle is too large in the area of the initial cut, the upper part of the disc will rush ahead and roll upside down. Conversely, if the discharge angle is too small, the disc will fold backward.

[0015] The transition between the cutting surface and the discharge surface can be formed by a transition edge, so that the cutting surface and the discharge surface are directly adjacent to one another.

[0016] With regard to the regrinding explained above, it is advantageous if the cutting surface encloses a constant cutting angle with the cutting plane.

[0017] It is particularly advantageous if the cutting surface and the discharge surface are arranged on a back side of the knife facing away from a product to be sliced during the cutting operation.

[0018] Preferably, the width of the discharge surface is limited to approximately 5 mm and in particular is between 0.5 mm and 5 mm, since otherwise the discs could be thrown sideways out of the machine due to excessive frictional forces.

[0019] Coating the discharge surface with a non-stick or anti-friction coating made of plastic, particularly PTFE, has proven particularly advantageous. This minimizes frictional forces and thus the tangential forces exerted on the product slices in the direction of rotation of the knife. Due to the inventive design of the knife, especially during resharpening, only the cutting surface is reground, while the friction-minimized discharge surface and its coating remain unchanged.

[0020] The discharge surface can be provided with nubs and / or hollows and / or grooves. Hollows and / or nubs serve to reduce friction between the separated disc and the discharge surface. By carefully aligning the grooves at angles deviating from the respective normal of the cutting edge, significant radial forces can be achieved on the disc being discharged. These radial forces can further positively influence the discharge behavior of the discs.

[0021] The above-mentioned object is achieved in a high-speed slicer and a method of the type mentioned above in that a cutting blade with some or all of the features explained above is provided or used.

[0022] The invention is described below with reference to the drawings. They show: Fig. 1 a view of the back of the cutting knife according to the invention; Fig. 2 a cross-sectional view of the cutting blade according to the invention; Fig. 3 a partial cross-section of the cutting blade according to the invention together with the product to be cut and the cutting bar in a highly enlarged view; Fig. 4 a section of the back of the cutting knife according to the invention with grooved discharge surface.

[0023] The Fig. The cutting blade according to the invention shown in Figure 1 is designed as a sickle blade and comprises a cutting edge 2 which spirals around a rotational axis 1 and extends approximately over an angular range of 270° and lies in a cutting plane 3 running perpendicular to the rotational axis 1. The distance of the cutting edge 2 from the rotational axis 1, i.e. the radius R of the cutting blade, increases continuously with the blade angle µ, specifically counter to a direction of rotation T in which the cutting blade rotates around the rotational axis 1 during cutting operation. The cutting blade according to the invention is intended for use on a high-speed slicer, which is not specifically shown. This high-speed slicer is provided with a rotor which has a drive shaft defining the rotational axis 1 together with a bearing for the cutting blade. For the central mounting of the cutting blade on the rotor, the Fig. 1 and the blade fastening holes 9 are provided. The cutting edge of such sickle blades is formed by the cutting edge 2 and a cutting surface 4 and passes through a Fig. 1 below the knife and in doing so cuts off a slice from each product located in this cutting area S. The cutting knife rotating in the direction of rotation T initially enters the cutting area S with a cutting area A and the smallest radius R. The final cutting off takes place when the cutting knife exits the cutting area S in a section area B which is located at the largest radius R. The spiral shape of the knife is described in polar coordinates by the knife radius R in the respective angular position to the knife angle µ.

[0024] If the knife radius R increases sharply over a comparatively small angle range, the knife pitch is large and the knife "chops" the product. If, on the other hand, the gradient of the knife radius R is small over a range of the knife angle µ, the cut is smoother. Both the cutting surface 4 and a discharge surface 5 run approximately parallel to the cutting edge 2. A spiral-shaped knife back surface 6 is also delimited radially outward by a contour running parallel to the cutting edge 2.

[0025] In Fig. 2 shows a section through the sickle knife according to the invention, which rotates about the axis of rotation 1. The cutting edge 2 lies in the cutting plane 3, which is perpendicular to the axis of rotation 1. The cutting surface 4 extends from the cutting edge 2 across the width w at a cutting angle α to the cutting plane 3. The cutting surface 4, together with a clearance surface 7, which lies at a clearance angle ϕ relative to the cutting plane 3, forms the cutting wedge. In particular, the clearance surface 7 makes the knife hollow on the front side D and therefore does not rub against the product when cutting. Following the cutting surface 4, the discharge surface 5 follows radially inwards. The discharge surface 5 is arranged at an angle β, which varies over the circumference of the cutting knife, to the cutting plane 3 and extends across the width b to the knife back surface 6. The knife back surface 6 is arranged at an angle δ to the cutting plane 3 and forms the transition to the disc-shaped base body of the knife.To ensure that the knife back surface 6 never touches the cut slice, the knife back angle δ must be designed to be significantly smaller than the discharge angle β.

[0026] Fig. 3 illustrates the functions of the cutting surface 4 and the discharge surface 5 using a partial section of the cutting blade, the product 10 and a cutting bar 12. Due to the rotation around the rotation axis 1, the cutting wedge formed by the cutting surface 4 and the free surface 7 moves in the projection Fig. 3 downwards through the product 10. This creates the product slice 11 to be separated. The stationary cutting bar 12 supports the product 10 against weight and cutting forces and forms the counter-blade to the cutting blade. The product is cut by the cutting edge 2 and the cutting surface 4. The cutting surface 4 creates a displacement effect on the resulting product slice 11, which, however, flows around the cutting surface 4 due to the cutting pressure, product elasticity, and mass inertia and remains on the back of the blade C. When the separated material comes into contact with the discharge surface 5, it is accelerated axially towards the rotational axis 1 away from the blade. The acceleration forces depend primarily on the discharge angle β of the discharge surface 5 and the cutting speed of the cutting blade. Fig. Figure 3 shows a slight overshoot of the upper portion of the product slice 11. If this effect is too great, the product slice will curl up on a conveyor belt below, resulting in unusable portions. By varying the discharge angle β across the knife circumference, the acceleration forces can be optimally defined for the respective product.

[0027] In Fig.4 shows a special design of the discharge surface 5. In addition to the variable discharge angle β, other design elements of the discharge surface 5 serve to ensure optimal slice deposition and portion formation in high-speed slicers. By incorporating grooves 13 into the discharge surface 5, in addition to improved detachment and thus friction conditions, tangential forces Ft and radial forces Fr can be exerted on the product slice. The grooves are very fine, for example 0.3 mm deep, semicircular or prismatic, and are ground into the discharge surface 5. The edges of the respective grooves 13 exert normal forces Fn on the product slices 11 via friction. If the grooves 13 are arranged at a groove angle p relative to the normal N to the cutting edge, normal forces Fn with radial components Fr arise, which stabilize the deposition behavior of the product slices 11. Harmful tangential forces Ft, on the other hand, are reduced by increasing the groove angle p.The described effect is surprisingly high and depends on the friction coefficient of the product against the discharge surface of the knife.

Claims

[1] Cutting blade for machines for slicing food products, in particular for high-speed slicers, wherein the cutting blade is a sickle blade rotating about a rotational axis (1) during the cutting operation, which has on its radially outer circumference a cutting edge (2) which deviates from a circular shape, in particular in the manner of a spiral around the rotational axis (1), which cutting edge lies in a cutting plane (3) running perpendicular to the rotational axis (1), wherein the cutting edge (2) forms the radially outer end of a cutting surface (4), the radially inner end of which is formed by the transition to a discharge surface (5), characterized by that the discharge surface (5) encloses discharge angles (β) with the cutting plane (3) which vary in the circumferential direction of the cutting edge (2). [2] Cutting knife according to claim 1, characterized bythat the transition between the cutting surface (4) and the discharge surface (5) is formed by a transition edge, so that the cutting surface (4) and the discharge surface (5) are directly adjacent to one another. [3] Cutting knife according to claim 1 or 2, characterized by that the cutting surface (4) encloses a constant cutting angle (α) with the cutting plane (3). [4] Cutting knife according to one of the preceding claims, characterized by that the cutting surface (4) and the discharge surface (5) are arranged on a knife back side (C) facing away from a product (10) to be sliced during the cutting operation. [5] Cutting knife according to one of the preceding claims, characterized by that the width (w) of the cutting surface (4) is between 0.2mm and 5mm. [6] Cutting knife according to one of the preceding claims, characterized by that the cutting angle (α) is between 16 and 45 degrees. [7] Cutting knife according to one of the preceding claims, characterized by that the width (b) of the discharge surface (5) is between 0.5 mm and 5 mm. [8] Cutting knife according to one of the preceding claims, characterized by that the discharge surface (5) is provided with an anti-stick coating made of a plastic, in particular PTFE. [9] Cutting knife according to one of the preceding claims, characterized by that the discharge surface (5) is provided with knobs and / or grooves to improve the detachment of the product (10) from the knife. [10] Cutting knife according to one of the preceding claims, characterized by that the discharge surface (5) is provided with grooves (13) for better detachment of the product (10) from the knife. [11] Cutting knife according to claim 10, characterized by that the grooves (13) are arranged at a variable angle (p) relative to the normal (N) of the cutting edge (2) over the circumference. [12] Cutting knife according to one of the preceding claims, characterized by that the discharge surface (5) has alternating sectors with grooves (13), dimples, knobs or combinations thereof in the circumferential direction of the cutting edge (2). [13] High-speed slicers for slicing food products, particularly stick-shaped ones, characterized by that a cutting knife according to one of claims 1 to 12 is provided. [14] Method for slicing food products, in particular stick-shaped ones, in particular sausage, cheese or ham, characterized by that a cutting knife according to one of claims 1 to 12 is used.

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