SCREW MACHINE AND METHOD FOR THE PROCESSING OF MATERIAL TO BE PROCESSED

Abstract

A screw machine includes an inductive heating device for processing of material to be processed. The inductive heating device is used to heat the material in a heating zone. In the heating zone, at least one housing portion is made of an electromagnetically transparent material at least partly, the material being non-magnetic and electrically non-conductive, whereas at least one treatment element shaft is made of an electrically conductive material at least partly. The inductive heating device includes at least one coil formed integrally with a component of the at least one housing portion, in particular in such a way as to form a hybrid component. During the processing of the material, the inductive heating device generates an alternating magnetic field that produces eddy current losses in the at least one treatment element shaft, the eddy current losses leading to a temperature increase of the at least one treatment element shaft.

Claims

1. A screw machine, comprising: a housing comprising a plurality of interconnected housing portions arranged in succession in a conveying direction, at least one housing bore formed in the housing, a feed opening leading into the at least one housing bore; at least one treatment element shaft arranged in the at least one housing bore such that the at least one treatment element shaft is drivable for rotation about at least one rotational axis; an inductive heating device configured to form a heating zone with at least one coil, wherein the at least one coil surrounds the at least one treatment element shaft, at least one housing portion in the heating zone comprising a component made of a non-magnetic and electrically non-conductive material, the at least one treatment element shaft comprising an electrically conductive material at least in the heating zone, the at least one coil being integrated in the component, and at least one cooling duct being integrated in the component.

2. A screw machine according to claim 1, wherein the at least one coil forms in each case a plurality of windings, the windings being surrounded by the component.

3. A screw machine according to claim 1, wherein the at least one coil forms in each case at least two terminals, the terminals being accessible from an outside of the component.

4. A screw machine according to claim 1, wherein the at least one cooling duct is formed at a side of the at least one coil facing away from the at least one housing bore.

5. A screw machine according to claim 1, wherein the at least one coil and the component are configured to form a hybrid component.

6. A screw machine according to claim 1, wherein the component forms an inner sleeve, which defines at least a portion of the at least one housing bore in the heating zone.

7. A screw machine according to claim 1, wherein the at least one coil comprises an associated conductor, the component having a material thickness in a region of the conductor perpendicular to the at least one rotational axis, the material thickness being greater than or equal to five millimeters and the material thickness being less than or equal to fifty millimeters.

8. A screw machine according to claim 1, wherein the at least one coil comprises an associated conductor, the conductor having a cross-section free of hollow spaces.

9. A screw machine according to claim 1, wherein the at least one coil defines an inner space and the at least one housing portion is made exclusively of the non-magnetic and electrically non-conductive material in the inner space.

10. A screw machine according to claim 1, wherein the at least one housing portion comprises at least one outer part, and the component is supported against the at least one outer part.

11. A screw machine according to claim 1, wherein a flow line and a return flow line of a cooling device are connected to the cooling duct, and at least one of a flow temperature in the flow line and a return flow temperature in the return flow line is measurable by at least one temperature measuring sensor.

12. A screw machine according to claim 1, wherein the inductive heating device comprises an energy supply device to operate the at least one coil, the energy supply device providing at least one of an alternating voltage and an alternating current.

13. A screw machine according to claim 1, further comprising: a temperature measuring sensor configured to measure a measured temperature of the material to be processed; and a control device configured to control the inductive heating device in response to the measured temperature of the material to be processed.

14. A screw machine according to claim 1, wherein the at least one coil comprises a conductor, the conductor forming a plurality of windings and terminals arranged at ends thereof, the windings having a shape of a horizontal figure eight and the windings being adapted to two housing bores.

15. A screw machine according to claim 1, wherein the at least one cooling duct has a shape of a horizontal figure eight and the at least one cooling duct is adapted to one or more of two housing bores and windings of the at least one coil.

16. A method for processing of material to be processed, the method comprising the following steps: providing a screw machine comprising a housing including a plurality of interconnected housing portions arranged in succession in a conveying direction, at least one housing bore formed in the housing, a feed opening leading into the at least one housing bore, at least one treatment element shaft arranged in the at least one housing bore such that the at least one treatment element shaft is drivable for rotation about at least one rotational axis and an inductive heating device configured to form a heating zone with at least one coil, wherein the at least one coil surrounds the at least one treatment element shaft, at least one housing portion in the heating zone comprising a component made of a non-magnetic and electrically non-conductive material, the at least one treatment element shaft comprising an electrically conductive material at least in the heating zone, the at least one coil being integrated in the component, at least one cooling duct being integrated in the component; feeding a material to be processed into the at least one housing bore; heating the at least one treatment element shaft via the inductive heating device; heating the material to be processed on the at least one heated treatment element shaft.

17. A method according to claim 16, wherein the inductive heating device is operated such that a temperature of the at least one coil is above a melting temperature of the material to be processed.

18. A screw machine according to claim 8, wherein at least a portion of the cross-section free of hollow spaces is formed linearly.

19. A screw machine according to claim 12, wherein the at least one of the alternating voltage and the alternating current is provided with an adjustable frequency.

20. A screw machine according to claim 12, wherein the at least one of the alternating voltage and the alternating current is provided with an adjustable amplitude.

21. A method according to claim 16, wherein the at least one treatment element shaft is heated via the inductive heating device until the material has molten at least partly in the heating zone.

22. A method according to claim 17, wherein the temperature of the at least one coil is above 100 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In the drawings:

[0035] FIG. 1 is a partly sectional view of a multi-shaft screw machine for the processing of material to be processed;

[0036] FIG. 2 is an enlarged view of the multi-shaft screw machine in FIG. 1 in a region of an inductive heating device;

[0037] FIG. 3 is a partly sectional plan view of the multi-shaft screw machine in FIG. 1; and

[0038] FIG. 4 is a cross-sectional view of the multi-shaft screw machine along section line IV-IV in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] A multi-shaft screw machine is used for the processing of a material 2 to be processed. The material 2 to be processed is a plastic material, for example.

[0040] The screw machine 1 has a housing 3 made of a plurality of housing portions 5 to 9, also referred to as housing units, arranged in succession in a conveying direction 4 of the plastic material 2. The housing portions 5 to 9 are connected to each other via flanges 10 arranged at the ends thereof in such a way as to form the housing 3.

[0041] In the housing 3, two housing bores 11, 12 are formed, which are parallel to one another and penetrate one another in such a way as to have the shape of a horizontal figure eight when seen in cross-section. In the housing bores 11, 12, two treatment element shafts 13, 14 are arranged concentrically, which are drivable for rotation about associated rotational axes 16, 17 by means of a drive motor 15. The treatment element shafts 13, 14 are driven about the rotational axes 16, 17 in the same direction, i.e. in the same rotational directions 18, 19. A coupling 20 and branching gear unit 21 are arranged between the drive motor 15 and the treatment element shafts 13, 14.

[0042] In the first housing portion 5 adjacent to the branching gear unit 21, a feed opening 22 is formed through which the plastic material is feedable into the housing bores 11, 12. For the feeding through the feed opening 22, a material feeder 23 configured as a hopper is arranged on the first housing portion 5.

[0043] The screw machine 1 has an inlet zone 24, a heating zone 25, a homogenizing zone 26 and a pressure build-up zone 27, which are arranged in succession in the conveying direction 4. At the last housing portion 9, the housing 3 is closed by a nozzle plate 28 provided with a discharge opening 29.

[0044] The treatment element shafts 13, 14 are formed by shafts 30, 31 and treatment elements 32 to 37 or 32 to 37, respectively, arranged thereon. The treatment elements 32 to 37 arranged on the first shaft 30 and the treatment elements 32 to 37 arranged on the second shaft 31 correspond to each other, with the reference numerals of the treatment elements 32 to 37 arranged on the second shaft 31 having an additional , allowing them to be differentiated from the treatment elements 32 to 37 arranged on the first shaft 30.

[0045] The treatment elements 32 to 37 and 32 to 37 are configured as closely intermeshing pairs, in other words the engage one another. The treatment elements are configured as screw elements 32, 32 and 33, 33 in the inlet zone 24 and in the heating zone 25. In the homogenizing zone 26 arranged downstream thereof, the treatment elements are configured as screw elements 34, 34 and kneading elements 35, 36 as well as 35, 36. Each of the kneading elements 35, 36 and 35, 36 is configured as a kneading block, in other words they are configured in one piece. The kneading elements 35, 36 and 35, 36 each have a plurality of kneading disks 38, 38, which are arranged at an angular offset to each other and are connected to each other. In the pressure build-up zone 27, the treatment elements are again configured as screw elements 37, 37.

[0046] The treatment elements 32 to 37 and 32 to 37 are arranged on the associated shafts 31, 31 in non-rotational manner. To this end, the shafts 30, 31 have an outer profile A that engages a corresponding inner profile I of the treatment elements 32 to 37 and 32 to 37.

[0047] In order to melt the plastic material 2 in the heating zone 25, the screw machine 1 has an inductive heating device 39. The inductive heating device 39 comprises a coil 40, an associated energy supply device 41 and a cooling device 42.

[0048] The housing portion 6 located in the heating zone 25 will hereinafter also be referred to as heating zone housing portion. The heating zone housing portion 6 comprises a component 45 configured as an inner sleeve and an outer part 44 in which the component is arranged by clamping. Said clamping arrangement can be achieved by means of an interference fit, for example. The outer part 44 is in particular configured as an outer jacket. Alternatively, a plurality of outer parts 44 may be provided, which are interconnected to form a multi-part outer jacket. At the ends of the housing portion 6, the flanges are formed on the outer part 44. The housing bores 11, 12 are defined by the component 45.

[0049] The coil 40 and the component 45 are designed as an integral unit so as to form a hybrid component 43. The hybrid component 43 is produced in layers, for example, by means of an additive manufacturing process.

[0050] The coil 40 has a longitudinal center axis 49 and defines an inner space 50. The longitudinal center axis 49 extends essentially parallel to the rotational axes 16, 17 such that the treatment element shafts 13, 14 run through the inner space 50 of the coil 40. The coil 40 therefore surrounds the treatment element shafts 13, 14 in the heating zone 25. The coil 40 comprises a conductor 51, which forms a plurality of windings W and terminals 46 arranged at the ends thereof. The terminals 46 are guided from each winding W formed at a respective end to an outside of the component 45 so as to be accessible there. The integral design of the coil 40 and the component 45 ensures that the windings W are fully surrounded by the component 45. In particular, the conductor 51 forming the windings W bears against the component 45 when seen in a radial direction relative to the respective rotational axis 16, 17. Seen in the rotational axes 16, 17, the windings W have the shape of a horizontal figure eight and are therefore adapted to the housing bores 11, 12, in other words to the shape thereof.

[0051] A cooling duct 52, which is part of the cooling device 42, is integrated in the component 45. The cooling duct 52 is formed at a side of the coil 40, in particular of the windings W, that faces away from the housing bores 11, 12. The cooling duct 52 has a helical shape to match the shape of the coil 40 and is connected to a flow line 47 and a return flow line 48 on the outside of the component 45. During additive manufacturing of the hybrid component 43, for example, the cooling duct 52 is automatically produced as well. Seen in the direction of the rotational axes 16, 17, the cooling duct 52 has the shape of a horizontal figure eight and is therefore adapted to the housing bores 11, 12 and/or to the windings W of the coil 40.

[0052] The outer part 44 is provided with a respective through hole at each end through which the electrical connection lines 54 to the terminals 46 and the flow line 47 and the return flow line 48 to the cooling duct 52 are guided. Outside the heating zone housing portion 6, the cooling duct 52 is connected, via the flow line 47 and the return flow line 48, to a coolant pump 56, which allows a coolant to be pumped through the cooling duct 52. The coolant pump 56 is part of the cooling device 42. A preferred coolant is water or oil.

[0053] The coil 40 is connected to the energy supply device 41, which supplies the coil 40 with an alternating voltage U.sub.S and/or an alternating current I.sub.S with an adjustable frequency f and/or an adjustable amplitude A. The energy supply device 41 is in particular a frequency converter. The energy supply device 41 is connected, via terminals 55, to a mains power supply that provides a mains voltage U.sub.N.

[0054] Heating the plastic material 2 is carried out by means of the treatment elements 33 and 33. For simple and efficient heating, the treatment elements 33, 33 have a three-layer design. An inner torque transmitting layer 57 is surrounded by an insulating layer 58, which in turn is surrounded by an outer heating layer 59. The insulating layer 58 of the respective treatment element 33, 33 thermally insulates the associated heating layer 59 from the associated torque transmitting layer 57 and the associated shaft 30 or 31, respectively. To this end, the respective insulating layer 58 is provided over the entire circumference and the entire length of the torque transmitting layer 57. The respective insulating layer 58 therefore surrounds the associated rotational axis 16 or 17, respectively. The respective heating layer 59 forms a surface of the treatment element 33 or 33.

[0055] In order to form the layers 57 to 59, the treatment elements 33, 33 are made of a metal ceramics composite material. The respective torque transmitting layer 57 is made of a first metal M.sub.1 while the respective heating layer 59 is made of a second metal material M.sub.3, whereas the respective insulating layer 58 arranged therebetween is made of a ceramic material M.sub.2. Material M.sub.1 is a steel, for example, as steel possesses a suitable mechanical strength. Contrary thereto, material M.sub.2 is thermally and electrically non-conductive and non-magnetic, in other words it is electromagnetically transparent. Material M.sub.3 is ferrous, i.e. a steel, for example, so eddy currents induced by means of the inductive heating device 39 may produce eddy current losses by means of which the heating layers 59 can be heated to a desired heating temperature T.sub.H. Furthermore, the alternating magnetic field of the inductive heating device 39 causes hysteresis losses to develop in the ferrous material M.sub.3, resulting in an additional temperature increase of the heating layers 59.

[0056] The component 45 is made of an electromagnetically transparent material M.sub.4. The electromagnetically transparent material M.sub.4 is non-magnetic and electrically non-conductive. This prevents a temperature increase of the component 45 caused by the alternating magnetic field of the inductive heating device 39. Material M.sub.4 is preferably a ceramic material. Material K is an oxide ceramic fiber-reinforced composite, for example. An oxide ceramic fiber-reinforced composite combines properties of a metal with those of a ceramics, such as electromagnetic transparency, electric and thermal insulating ability, ductile and non-brittle breaking behavior, high tensile and bending stiffness, thermal shock resistance and high temperature stability up to temperatures above 1300 C.

[0057] The conductor 51 is made of an electrically conductive material M.sub.5. Preferably, the material M.sub.5 is a good conductor of electricity. The material M.sub.5 is copper or aluminum, for example.

[0058] The hybrid component 43 is produced in layers of the electromagnetically transparent material M.sub.4, which forms the component 45, and of the electrically conductive material M.sub.5, which forms the conductor 51, in particular in an additive manufacturing process so as to obtain a composite component made of at least two different materials M.sub.4 and M.sub.5. The conductor 51 has a cross-sectional shape free of hollow spaces and joints. Preferably, the conductor 51 has a non-round cross-sectional shape, which is linear at least partly. The conductor 51 has a rectangular cross-sectional shape, for example. Preferably, the conductor 51 is arranged in such a way that a linear long side of the cross-sectional shape faces the housing bores 11, 12. In regions B between the conductor 51 and the housing bores 11, 12 seen in a direction perpendicular to the rotational axes 16, 17, the component 45 has a material thickness D, with 5 mmD50 mm, in particular 10 mmD40 mm, and in particular 15 mmD30 mm. As the windings W formed by the conductor 51 are in a full surface-to-surface contact with the component 45 and a composite component is formed from the coil 40 and the component 45, the component 45 is not weakened by the arrangement of the coil 40 and has a high mechanical stability. Furthermore, the component is in a full surface-to-surface contact with the outer part 44 except in the region of the through holes 53. This enables the component 45 to reliably absorb forces acting in the radial direction when processing the material 2 to be processed and to dissipate these forces to the outer part 44.

[0059] In the inner space 50, the heating zone housing portion 6 is made preferably exclusively of the non-magnetic and electrically non-conductive material M.sub.4. The portion of the component 54 located in the inner space 50 is made preferably exclusively of the non-magnetic and electrically non-conductive material M.sub.4.

[0060] As the outer part 44 is arranged outside the coil 40, only low eddy currents are induced in the outer part 44 by the alternating magnetic field. The outer part 44 is therefore made of a metal material M.sub.6. Preferably, the other housing portions 5 and 7 to 9 are made of the metal material M.sub.6 as well. The metal material M.sub.6 is in particular a steel. Alternatively, the outer part 44 may be made of the material M.sub.4 as well. This prevents a temperature increase of the outer part 44 substantially completely.

[0061] In order to measure a temperature T.sub.K of the plastic material 2, the screw machine 1 has a first temperature measuring sensor 60. The temperature measuring sensor 60 is arranged on the housing portion 7 at the beginning of the homogenizing zone 26, for example. The screw machine is further provided with a second temperature measuring sensor 62 to measure a flow temperature T.sub.V in the flow line 47 and with a third temperature measuring sensor 63 to measure a return flow temperature T.sub.R in the return flow line 48. The temperature measuring sensors 60, 62, 63 are in signal communication with a control device 61 used to control the screw machine 1 and in particular the inductive heating device 39. To this end, the control device 61 is in particular in signal communication with the energy supply device 41 and the cooling device 42. The control device 61 is in particular used to control the inductive heating device 39 in response to the measured temperature T.sub.K, T.sub.V and/or T.sub.R.

[0062] The screw machine 1 further has a cooling device, which comprises cooling ducts 64 formed in the housing portions 7 and 8. The cooling ducts 64 allow delivery, by means of a coolant pump not shown in more detail, of a coolant in the usual manner. The coolant is in particular water.

[0063] The functioning of the screw machine 1 is as follows:

[0064] Via the feed opening 22, powdery or pelletized plastic material 2 is fed into the inlet zone 24 of the screw machine 1. In the inlet zone 24, the plastic material 2 is conveyed in the conveying direction 4 up to the heating zone 25.

[0065] In the heating zone 25, the plastic material 2 is heated by means of the inductive heating device 39. To this end, the inductive heating device 39 generates an alternating magnetic field by means of the energy supply device 41 and the coil 40. The inductive heating device 39 is in particular operated at a frequency f, the frequency fin a first frequency range being such that 1 kHz<f50 kHz, in particular 5 kHzf45 kHz, and in particular 10 kHzf40 kHz. Furthermore, the frequency fin a second frequency range is such that 140 kHzf360 kHz, in particular 150 kHzf350 kHz, and in particular 160 kHzf340 kHz. Preferably, the inductive heating device 39 is operated in both frequency ranges alternately, with the result that various penetration depths of the alternating magnetic field are achieved. Field lines F of the alternating magnetic field are illustrated in FIG. 2. The concentration of the field lines F is high in the inner space 50 of the coil 40 so the magnetic field strength is high there. The heating layers 59 of the treatment elements 33, 33 further act in the manner of a core. The alternating magnetic field causes eddy currents to be induced in the heating layers 59, the eddy currents producing ohmic eddy current losses. Furthermore, the alternating magnetic field causes hysteresis losses to develop in the heating layers 59. The ohmic eddy current losses and the hysteresis losses lead to a temperature increase of the heating layers 59 to the heating temperature T.sub.H. The heating temperature T.sub.H can be changed via the frequency f and/or the amplitude A. Due to the close contact of the plastic material 2 with the treatment element shafts 13, 14, the plastic material 2 is heated by the heating layers 59. The heat generated in the heating layers 59 is therefore transferred to the plastic material 2, causing the temperature thereof to increase in the heating zone 25 up to the temperature T.sub.K. The temperature T.sub.K is in particular above a melting temperature T.sub.M of the plastic material 2, causing the solid plastic material 2 to melt at least partly in the heating zone 25.

[0066] As the component 45 is made of the electromagnetically transparent material M.sub.4, which is non-magnetic and electrically non-conductive, the alternating magnetic field does not produce a temperature increase of the component 45. The energy provided by the inductive heating device 39 is therefore introduced into the plastic material 2 in a simple and efficient manner via the heating layers 59 of the treatment elements 33, 33. Furthermore, the insulating layers 58 prevent the heat generated in the heating layers 59 from being transferred in the direction of the shafts 30, 31.

[0067] As the conductor 51 is free of joints and in particular free of soldering material, this allows the inductive heating device 39 to be operated at a high power as a maximum permissible temperature of the conductor 51 is only limited by a melting temperature of the material M.sub.5 and not by a maximum permissible temperature of the soldering material. During the operation of the inductive heating device 39, the temperature of the conductor 51 increases due to ohmic losses and has a temperature T.sub.L. The heat loss generated in the conductor 51 is dissipated to the component 45. The inductive heating device 39 is preferably operated such that the temperature T.sub.L of the conductor 51 or of the coil 40 is above the melting temperature T.sub.M of the material 2 to be processed. Preferably, the temperature T.sub.L is above 100 C., in particular above 160 C., and in particular above 230 C. In this manner, the heat loss is transferred, via the component 45, to the material 2 to be processed, causing the material 2 to be processed to be heated from inside via the treatment element shafts 13, 14 on the one hand and from the outside via the component 45 on the other. In this manner, the heat loss of the coil 40 is used for heating the material 2 to be processed as well, with the result that the efficiency of the inductive heating device 39 is improved.

[0068] The temperature T.sub.K of the plastic material 2 is measured by means of the temperature measuring sensor 60 and transmitted to the control device 61. The control device 61 compares the temperature T.sub.K with a predefined nominal temperature T.sub.S, which is preferably above the melting temperature T.sub.M of the plastic material 2. If the temperature T.sub.K is below the nominal temperature T.sub.S, then the control device 61 actuates the energy supply device 41 to increase the amplitude A and/or the frequency f. Conversely, if the temperature T.sub.K is too high, then the amplitude A and/or the frequency is reduced. If necessary, the conductor 51 is cooled. For this purpose, the cooling device 42 pumps a coolant, in particular water or oil, through the cooling duct 52 by means of the coolant pump 56. Measuring the flow temperature T.sub.V and the return flow temperature T.sub.R and measuring the temperature T.sub.K of the material 2 allows one to determine the amount of energy introduced into the material 2 to be processed via the heated treatment element shafts 13, 14 and, potentially, via the heat loss transferred by the component 45. This allows the processing method to be optimized thermally.

[0069] In the homogenizing zone 26, the plastic material 2 is homogenized and molten completely in case there is still any solid plastic material 2. If necessary, the plastic material 2 is cooled by means of a coolant, in particular water, which is pumped through the coolant ducts 64.

[0070] In the pressure-build up zone 27, the pressure of the completely molten and homogenized plastic material 2 is increased. The plastic material 2 is then discharged via the discharge opening 29.

[0071] The screw machine 1 according to the invention allows energy to be introduced into the material 2 to be processed in a simple and efficient manner by induction or heat, thus allowing a mechanical energy input to be reduced significantly, with the result that the mechanical load and the wear of the screw machine 1 are reduced significantly. The efficient energy input further allows an energy-saving operation of the screw machine 1. In relation to a total power of the screw machine 1, the inductive heating device 39 in particular has a heating power of 10% to 90%, in particular of 20% to 80%, and in particular of 30% of 70%. If necessary, the inductive heating device 39 can also be operated at a plurality of different frequencies fat the same time. This allows regions to be heated, which that are disposed at various distances, such as the circumferential heating layers 59.

[0072] The composite material of the treatment elements 33, 33 is produced in a 3D printing process followed by subsequent sintering, for example. Methods for producing composite materials or composite bodies of this type are known.

[0073] For example, the hybrid component 43 can be produced in layers in an additive manufacturing process, in other words by means of a 3D printing process followed by subsequent sintering. The electromagnetically trans-parent material M.sub.4 of the component 45 is a ceramic material, for example. If necessary, the material M.sub.4 can be provided with reinforcing particles, in particular reinforcing fibers, and/or with ferrites to increase and direct the alternating magnetic field. The electrically conductive material M.sub.5 is, for example, a metal material, a metal material composition and/or an electrically conductive ceramic material. Preferably, the hybrid component 43 is a metal ceramic hybrid component. The hybrid component 43 is in particular designed as a composite component formed of the magnetically transparent material M.sub.4 and the electrically conductive material M.sub.5.

[0074] While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.