GRANULATOR DEVICE WITH MAGNETIC COUPLING

Abstract

Apparatus for cutting off extrudate produced with an extruder having a die with at least one opening includes a knife which is mounted rotatably about an axis of rotation and which can be driven by a drive, in particular an electric motor, in that a torque is transmitted from the drive to the knife. A bearing element is provided which can be rigidly connected to the extruder and via which the knife can be rotatably connected to the extruder around the axis of rotation, whereby the drive can be placed separately from the bearing element and a magnetic coupling is provided between the bearing element and the drive in order to transmit the torque from the drive to the knife via magnetic forces.

Claims

1. An extruder for producing pet food having a die with at least one opening through which a material can be pressed in order to form an extrudate, wherein an apparatus for cutting off the extrudate is provided in material flow direction adjoining the die which apparatus has a knife which is mounted rotatably about an axis of rotation and which can be driven by a drive, in particular an electric motor, in that a torque is transmitted from the drive to the knife, wherein a bearing element is provided which can be rigidly connected to the extruder and via which the knife can be rotatably connected to the extruder around the axis of rotation, whereby the drive can be placed separately from the bearing element and a magnetic coupling is provided between the bearing element and the drive in order to transmit the torque from the drive to the knife via magnetic forces, wherein a housing is provided that is sealed to an environment, in which housing the bearing element and the knife are located, so that the extruder is suitable for a method in which the interior of the housing is subjected to a pressure 2.5 bar higher than the environment.

2. The extruder according to claim 1, wherein an air gap is between the drive and the knife and the torque can be transmitted via the air gap exclusively via magnetic forces.

3. The extruder according to claim 1, wherein a coupling element is provided which has a first element, which first element is rotatably connected to the bearing element and which coupling element is connected to the knife on the one hand and to the drive via the magnetic coupling on the other hand in order to transmit the torque from the drive to the knife.

4. The extruder according to claim 3, wherein the coupling element has a second element, which second element is movable relative to the first element in an axial direction and is connected to the first element in a rotationally fixed way around the axis of rotation.

5. The extruder according to claim 4, wherein the second element can also be tilted relative to the first element around an axis perpendicular to the axis of rotation.

6. The extruder according to claim 1, wherein the knife and/or the coupling element can be fixed in axial direction relative to the bearing element, in particular by a ball lock pin.

7. The extruder according to claim 1, wherein a spring element is provided with which a preload can be applied to the knife in an axial direction in order to press the knife against the die when the apparatus is connected to the extruder.

8.-9. (canceled)

10. The extruder according to claim 1, wherein the drive is located outside the housing and the torque is transmitted into the housing via the magnetic coupling.

11. The extruder according to claim 1, wherein a distance between the die and the knife is 0 mm to 0.5 mm, in particular 0.01 mm to 0.3 mm.

12. The extruder according to claim 1, wherein a linear system with a motor or a manually operated spindle drive is provided in order to disengage the magnetic coupling.

Description

[0024] Additional features, advantages and effects of the invention follow from the exemplary embodiment described below. The drawings which are thereby referenced show the following:

[0025] FIG. 1 and FIG. 2 a detail of an extruder according to the prior art in schematic illustration;

[0026] FIG. 3 and FIG. 4 an extruder according to the invention in sectional illustration;

[0027] FIG. 5 a detail of an extruder according to the invention in sectional illustration.

[0028] FIG. 1 shows a detail of an extruder 2 with an apparatus 1 according to the prior art. The extruder 2 is embodied as a screw extruder and comprises a die embodied as a die plate 3 with openings 4 through which fluid, semifluid or viscous material is pressed in order to build extrudate, in particular pet food. A knife head 10 with several knives 5 rotating around a axis of rotation 6 is arranged next to the die plate 3 to cut off the product pressed through the openings 4. If the openings 4 are circular and a distance between the knives 5 and the die plate 3 is small, cylindrical pieces of product 20 are cut. A distance 23 between the knives 5 and the die should be as small as possible to obtain a high quality cut product 20. Preferably the distance 23 is smaller than 0.2 mm.

[0029] As can be seen, the knife head 10 is driven by a drive which is here embodied by an electric motor 7, whereby the motor 7 and the knife head 10 have according to the prior art a common shaft 21. The motor 7 and therefore the knife head 10 and the knives 5 are mounted in a housing 22, which hermetically separates the inside of the extruder 2 and the knives 5 from an environment 19. During operation, an internal pressure inside the housing 22 can be higher than an ambient pressure in the environment 19, for example by 2.5 bar. This pressure difference can cause a deformation of the housing 22 in the area where the motor 7 is mounted in the housing 22. This may result in tilting of the motor axis and the shaft 21 as shown in FIG. 2. This tilting will result in a larger distance 23 between the die plate 3 and the knife 5, resulting in poor quality of the product 20. As the knife 5 displaces from the die, the extruder 2 starts to create fines and flakes from the product 20, which is unacceptable. The pressure in the housing 22 is according to the prior art therefore limited to the pressure where flakes start to form.

[0030] FIGS. 3 and 4 show an extruder 2 with an apparatus 1 according to the invention in sectional illustration. FIG. 4 shows a sectional illustration in which the axis of rotation 6 lies in a sectional plane. As can be seen in FIG. 4, the knife head 10 with the knives 5 is not supported via the motor 7 and the housing 22, but directly attached to the die plate 3 by means of a bearing element 8. The bearing element 8 is rigidly connected to the die plate 3 or to a component adjacent to the die plate 3, in this case a mounting plate 24. The knife head 10, which carries several knives 5, is not physically connected to the motor 7. Rather, the torque is transmitted via an air gap 11 with a magnetic coupling between a first part 25 of the magnetic coupling and a second part 26 of the magnetic coupling. The first part 25 of the magnetic coupling is rotationally fixed to the motor 7 and the second part 26 of the magnetic coupling is rotationally fixed to the knife head 10. A minor change in the position of the motor 7 for example due to a deformation of the housing 22 caused by a pressure inside the housing 22 therefore does not cause a change in the position of the knives 5 or the knife head 10, in particular no tilting of the axis of rotation 6 of the knives 5. Therefore, a small distance between the knives 5 and the die plate 3 and a high product quality are ensured regardless of any deformation of the housing 22. As shown, the motor 7 is arranged outside the housing 22 and a torque to rotate the knives 5 around the axis of rotation 6 is transmitted by the motor 7 through the housing 22 without contact by means of the magnetic coupling.

[0031] A torque is transmitted between the motor 7 and the knives 5 via a coupling element 12. The coupling element 12 has a first element 13 and a second element 14, which are coupled in an axial direction 18 by spring elements 15, which are formed here by helical springs. The first element 13 is rotatably connected to the bearing element 8 at a fixed axial position and can be moved relative to the bearing element 8 only around the axis of rotation 6. For this purpose, the first element 13 is connected to the bearing element 8 via two rolling bearings 17 and a contact element. The contact element is embodied as a sleeve 16 and releasably rigidly connected to the bearing element 8 via a ball lock pin 28.

[0032] The second element 14 is movable relative to the first element 13 in the axial direction 18 and is usually connected to the first element 13 in a rotationally fixed way around the axis of rotation 6. The first element 13 and the second element 14 are therefore rotatable relative to the sleeve 16 around the axis of rotation 6. Furthermore, the knife head 10 with the knives 5 is connected to the second element 14 by means of a form fit, so that the knives 5 can be set into a rotary motion around the axis of rotation 6 by means of the second element 14. The spring elements 15 are tensioned in the position shown when the knives 5 are positioned on the die plate 3. Each knife 5 is thus pressed against the die plate 3 in the axial direction 18 with a force generated by the spring elements 15. This ensures an optimum distance 23 between the knives 5 and the die plate 3 even in the event of shaft deformation or vibrations. Thus, a contact between the knife 5 and the die plate 3 is achieved during operation. The distance 23 between knife 5 and the die plate 3 in the shown embodiment is therefore 0 mm.

[0033] As the axis of rotation 6 of the knives 5 is installed essentially perpendicular to the die plate 3, and the knives 5 operate perpendicular to the axis of rotation 6, the knives 5 will always operate parallel to the die plate 3, and therefore eliminate the need for alignment of the knife head 10 towards the die plate 3.

[0034] The motor 7 is positioned outside the housing 22. The torque is thus transmitted through the housing 22 with the magnetic coupling. A first part 25 of the magnetic coupling is connected to the motor 7 and a second part 26 of the magnetic coupling is connected to the first element 13 of the coupling element 12. The two parts 25, 26 of the magnetic coupling are thus separated in the axial direction 18, in contrast to a claw coupling, for example. Small movements of the motor 7, for example due to a deformation of the housing 22, therefore have no effect on the alignment of the knife head 10 and the knives 5 relative to the die plate 3. The housing 22 is usually formed at least in the area of the magnetic coupling by a non-magnetic material.

[0035] Since the motor 7 is located outside the housing 22, it can be easily replaced and serviced. Thus, the motor 7 can also be replaced if the pressure in the extruder 2 and in the housing 22 deviates from an ambient pressure in an environment 19. A linear system 9 is provided to release the magnetic coupling. The linear system 9 can be operated manually or by a drive. A hand crank or a handwheel 27 is preferred to operate the linear system in order to remove the motor 7 from the housing 22.

[0036] The knife head 10 is connected to the bearing element 8 via the coupling element 12 by means of a ball lock pin 28. The ball lock pin 28 can easily be released, by a push with a finger on the pusher 29. When it is released, it is easy to mount and dismount the knife head 10 by sliding the sleeve 16 onto or away from the bearing element 8. Since the knife head 10 is not secured or fastened towards the coupling element 12, it can be removed and replaced by hand once the coupling element 12 is released. The knife head 10 including the knives 5 can therefore be replaced without any need of tools.

[0037] As regards the installation procedure, the coupling element 12 is moved onto the bearing element 8, whereby the spring elements 15 are loaded. Then, the ball lock pin 28 is used to secure the loaded coupling element 12 on the bearing element 8, whereby the ball lock pin 28 is enduring the load in the spring elements 15.

[0038] However, the apparatus 1 may be designed so that the knife head 10 can first be connected to the coupling element 12 and then the coupling element 12 and the knife head 10 are together moved on the bearing element 8 in a final axial position where they are secured by the ball lock pin 28. It is also possible to first position the knife head 10 axially against the tool and then connect the coupling element 12 to the knife head 10 and the bearing element 8. So, an operator can first put the knife head 10 on the bearing element 8, then afterwards use the coupling element 12 to pressurize the knife head 10 towards the die plate 3. The coupling element 12 is then correctly secured towards the bearing element 8 by the ball lock pin 28. When dismantling, the ball lock pin 28 can be released, and the coupling element 12 dismantled and finally the knife head 10 is removed.

[0039] FIG. 5 shows a situation where the coupling element 12 is released from the knife head 10. As can be seen, the coupling element 12 with the first element 13 and the second element 14 as well as the sleeve 16 can be moved axially relative to the bearing element 8, for example to replace the knife head 10 or the knives 5. As can be seen, the ball lock pin 28 is also removed from the bearing element 8 in this position, since the ball lock pin 28 establishes an axial connection between the coupling element 12 and the bearing element 8 during operation. Here also pins 30 arranged on the second element 14 are visible, which during operation engage in corresponding recesses 31 in the knife head 10 in order to connect the knife head 10 positively with the coupling element 12 so that a torque can be transmitted via the coupling element 12.

[0040] With an apparatus 1 according to the invention, an exact alignment of the knives 5 relative to the die plate 3 and a constant small distance between the knives 5 and the die plate 3 is possible even if the housing 22 in which the motor 7 is mounted deforms due to a high internal pressure. A high quality product 20 can therefore be formed even at high internal pressure in the extruder 2 an in the housing 22. Furthermore, the alignment and maintenance of an extruder 2 equipped with a apparatus 1 according to the invention is very simple.