Method and apparatus for producing powder coating melts

Abstract

To provide a method and a device for producing a powder coating melt which, in a simple, flexible and efficient manner, allows recycling of powder coating particles.SOLUTION: In a method and a device (1) for producing a powder coating melt (2, 3), firstly a first powder coating melt (2) is produced from a powder coating premix (31) by means of a screw machine (4). Powder coating particles (39) are supplied to the first powder coating melt (2). Then a second powder coating melt (3) is produced by mixing the first powder coating melt (2) and the powder coating particles (39) by means of the screw machine (4). This allows a simple, gentle and efficient recycling of powder coating particles (39), in particular of so-called off-spec powder coating particles.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for producing a powder coating melt. [Background technology]

[0002] To produce powder coating powder, a powder coating premix is prepared using a screw machine (screw injection molding machine) and the prepared powder coating melt is extruded. The extruded powder coating melt is then cooled and crushed into powder coating powder. The powder coating powder is then separated into a useful fraction and a fine fraction. The useful fraction, which has powder coating particles with the desired particle size, is used for powder coating, while the fine fraction, which has smaller powder coating particles, is not suitable for powder coating. Furthermore, during powder coating, the powder coating particles that are not suitable for powder coating are deposited, for example, in a particle filter in the spray booth. Such powder coating particles or fine powder coating particles are known as fine particles or ultrafine particles. Summary of the Invention [Problem to be solved by the invention]

[0003] The present invention is based on the object of creating a method for producing a powder coating melt that allows for the simple, flexible, and efficient recycling of powder coating particles. In particular, so-called non-standard powder coating particles must be recycled. Non-standard powder coating particles are powder coating particles that are outside the desired specifications or do not comply with the desired specifications with respect to at least one characteristic, such as color and / or particle size. [Means for solving the problem]

[0004] This object is achieved by a method having the features of claim 1. According to the present invention, it has been found that powder coating particles to be recycled are produced from a homogenized powder coating melt or powder coating powder, and therefore do not need to be subjected to intensive homogenization for recycling. Thus, in the method according to the present invention, a first powder coating melt is first produced from a powder coating premix by a screw machine. The powder coating particles to be recycled are then fed into this first powder coating melt and then simply mixed with the first powder coating melt by the screw machine, thereby producing a second powder coating melt containing the powder coating particles to be recycled. The second powder coating melt is then discharged or extruded from the screw machine and further processed into powder coating powder in the usual way. The powder coating particles to be recycled are particularly fine powder coating particles.

[0005] The first powder coating melt is preferably fully prepared and suitable for further processing into powder coating powder. The first powder coating melt is particularly plasticized and homogenized. The powder coating particles are particularly homogeneously mixed and / or melted, preferably completely melted, after being fed into the first powder coating melt and before being discharged. Due to the complete melting of the powder coating particles, in particular so-called off-spec powder coating particles can be recycled.

[0006] The powder coating particles are simply mixed into the first powder coating melt, and therefore the production or preparation of the first powder coating melt from the powder coating premix is not carried out in reverse. The first powder coating melt may be produced at a normal quality and / or at a normal speed, allowing the powder coating particles to be mixed into the first powder coating melt simply and flexibly. The feed rate of the powder coating particles may vary over a wide range, in particular between 0 and the intake limit. No intensive homogenization of the mixed, in particular dissolved or melted, powder coating particles is required by the screw machine.

[0007] The screw machine is in particular configured as a multi-screw machine, preferably as a twin-screw machine. The multi-screw machine in particular has at least two processing element shafts that can be driven in rotation in the same direction. The at least two processing element shafts are preferably configured to be tightly intermeshed.

[0008] The method according to claim 2 ensures a simple, flexible and efficient recycling of powder coating particles. 最大 Because of this, the powder coating particles are not suitable for use as powder coating powder but must be recycled. The powder coating particles as supplied are easily mixed into the first powder coating melt. The percentage numbers indicate the number or weight fraction of particles. Maximum particle size A 最大 indicates the maximum particle size in particular. In particular, at least 70%, in particular at least 90%, in particular A 最大 ≦90 μm, especially A 最大 ≦80 μm, especially A 最大 ≦60 μm applies.

[0009] The method according to claim 3 ensures a simple, flexible and efficient recycling of powder coating particles. 最大 Because of this, the powder coating particles are easily fed and mixed into the first powder coating melt. The percentage numbers indicate the number or weight fraction of particles. Maximum particle size A 最大 indicates the maximum particle size in particular. In particular, at least 70%, in particular at least 90%, in particular A 最大 ≧5 μm, especially A 最大 ≧10 μm applies.

[0010] The method according to claim 4 ensures simple, flexible and efficient recycling of powder coating particles. The powder coating particles are particularly completely melted after being fed into the first powder coating melt and before being discharged through the discharge opening. Because the powder coating particles are melted before being discharged through the discharge opening of the screw machine, they are optimally adhered to and bonded to the powder coating melt, thereby resulting in a homogeneous second powder coating melt. The feeding of powder coating particles reduces the outlet temperature of the second powder coating melt, which is advantageous for the cooling and hardening of the second powder coating melt after discharge.

[0011] The method according to claim 5 ensures simple, flexible, and efficient recycling of powder coating particles. The screw machine has, successively in the conveying direction, an intake zone, a plasticization zone, and a homogenization zone. In the intake zone, the powder coating premix is fed to the screw machine and conveyed to the plasticization zone. In the plasticization zone, the powder coating premix is melted and then homogenized in the homogenization zone. The powder coating particles are fed downstream of the plasticization zone, so that the plasticization of the powder coating premix is only slightly or adversely affected. Preferably, the powder coating particles are fed downstream of the homogenization zone, so that the powder coating premix is plasticized and the first powder coating melt is optimally homogenized before the powder coating particles are fed. Thus, the preparation of the powder coating premix into the first powder coating melt is substantially unaffected, so that the first powder coating melt can be prepared with high quality and at a high throughput rate. In the plasticization zone, the screw machine preferably has kneading elements, in particular kneading disks, which ensure a fast and efficient plasticization of the powder coating premix. In the homogenization zone, the screw machine preferably has kneading elements, in particular kneading disks, which ensure an efficient homogenization of the polymer melt.

[0012] The method according to claim 6 ensures simple, flexible, and efficient recycling of powder coating particles. In the feeding zone, powder coating particles are fed to a screw machine. A feeding device, particularly one connected to the screw machine, is preferably used. The feeding zone is arranged downstream of the plasticization zone in the conveying direction, so that the powder coating particles are fed to the plasticized powder coating premix or powder coating melt. Preferably, the powder coating particles are fed downstream of the homogenization zone, so that the powder coating particles are fed to a fully prepared polymer melt, with substantially no adverse effect on the plasticization and homogenization of the powder coating premix. A mixing zone is provided downstream of the feeding zone, in which the fed powder coating particles are mixed with the first powder coating melt, so that there are no free powder coating particles, i.e., no powder coating particles not adhering to the powder coating melt, before discharge. The mixing zone is preferably configured and / or arranged to first ensure mixing of the fed powder coating particles before discharge and second ensure as low a shear force as possible acting on the powder coating particles before discharge. The mixing zone has at least one conveying element, in particular at least one screw element and / or at least one kneading element, in particular at least one kneading disk. The mixing zone may, for example, have several conveying elements arranged in series, so that the first powder coating melt and the supplied powder coating particles are conveyed together long enough for the powder coating particles to be mixed and / or melted, preferably completely melted. The mixing zone may, for example, have several kneading elements arranged in series, in particular several kneading disks. This improves mixing. Preferably, at least one conveying element and at least one kneading element are arranged one after the other in the mixing zone. The at least one conveying element initially conveys the first powder coating melt with the supplied powder coating particles away from the supply zone, so that no buildup occurs in the supply zone. By the at least one kneading element, the supplied powder coating particles are mixed with the first powder coating melt over a short length.

[0013] Claim 1,The method according to claim 7 ensures a simple, flexible and efficient recycling of powder coating particles. The feeding device allows for automatic feeding of the powder coating particles. The feeding device in particular has a weight dosing unit and / or a volume dosing unit and / or a feeding screw machine. The feeding screw machine is in particular configured as a side feed device. The feeding screw machine in particular has two screw shafts that can be driven in rotation in particular in the same direction. The feeding screw machine is connected to the screw machine. For this purpose, the screw machine has a housing with a feed opening, via which the feeding screw machine feeds the powder coating particles to the screw machine. The feeding device is in particular coolable. Preferably, the dosing unit and / or the feeding screw machine are coolable. The feeding device preferably has a cooling device for cooling.

[0014] The method according to claim 8 ensures simple, flexible, and efficient recycling of powder coating particles. During the production of powder coating particles, the hardened powder coating melt is ground into powder coating powder, which is then separated into at least two particle size fractions. Separation is performed by a separator, e.g., a screen or a cyclone. Powder coating particles separated by the separator and unsuitable for powder coating are returned to the screw machine, where they are fed, e.g., by a feeder, to the first powder coating melt. The powder coating particles unsuitable for powder coating are thus directly fed for recycling.

[0015] The method according to claim 9 ensures a simple, flexible and efficient recycling of the powder coating particles. The feeding screw machine ensures a simple and uniform feeding of the powder coating particles into the powder coating melt exiting the screw machine. The powder coating particles are fed by means of a feed screw machine which is in particular cooled. The feed screw machine has at least one screw shaft, preferably at least two screw shafts, and is preferably connected to the side of the screw machine, so that the powder coating particles are fed to the screw machine through a side feed opening.

[0016] The method according to claim 10 ensures simple, flexible, and efficient recycling of powder coating particles. The feed insert is connected to the housing of the feed screw machine and opens into a housing opening of the screw machine housing, forming a feed opening for feeding powder coating powder. The feed insert is removably connected to the housing of the feed screw machine and / or the screw machine housing. The feed insert can be replaced or removed for cleaning. Preferably, the feed insert has a flange and a feed channel part attached thereto. The feed insert preferably has at least one cooling element. The at least one cooling element is preferably configured as a cooling channel. Preferably, the flange and / or the feed channel part can be cooled by a cooling fluid. For this purpose, the flange and / or the feed channel part have at least one cooling element, in particular at least one cooling channel. The at least one cooling channel is formed in the flange and / or the feed channel part. The cooling reduces, in particular largely prevents, adhesion of the powder coating powder to the feed insert and / or the feed screw machine due to melting. For example, respective cooling channels may be formed in the flange and in the feed channel part, so that the flange and the feed channel part can be cooled separately and / or together. By a controller, the corresponding cooling circuits may be controlled and operated separately from each other and / or together. For example, the cooling circuit for the flange may be operated continuously, and the cooling circuit for the feed channel part may be operated in response to certain operating conditions, such as during a shutdown of the screw machine or when the temperature exceeds a predetermined level in the area of the feed channel part.

[0017] The method according to claim 11 ensures simple, flexible, and efficient recycling of powder coating particles. By cooling the injection hopper and / or the housing and / or at least one screw shaft, adhesion of powder coating particles due to melting on the injection hopper and / or on the inner wall of the housing and / or on at least one screw shaft is reduced or substantially prevented. At least one cooling device, for example configured as a compressed air cooler and / or a water cooler, serves for cooling. Preferably, at least one cooling channel is formed in the injection hopper and / or in the housing of the feed screw machine and / or in at least one screw shaft. A cooling fluid flows through the cooling channel for cooling.

[0018] The method according to claim 12 ensures simple, flexible, and efficient recycling of powder coating particles. The dosing unit allows for precise dosing of the powder coating particles, whereby the dosed powder coating particles are melted and homogeneously mixed into the powder coating melt. The dosing unit is designed as a weight or volume dosing unit. Due to the cooling of the dosing unit, adhesion of the powder coating particles due to melting is reduced or essentially prevented. In particular, the container and / or the discharge pipe of the dosing unit are cooled. At least one cooling device, for example configured as a compressed air cooling device and / or a water cooling device, serves for the cooling. Preferably, the dosing unit and the feed screw machine have a common cooling, or rather a cooling device.

[0019] The invention is further based on the object of providing an apparatus for producing a powder coating melt which allows for a simple, flexible and efficient recycling of powder coating particles.

[0020] This object is achieved by an apparatus with the features of claim 13. The advantages of the apparatus according to the invention correspond to the advantages of the method according to the invention. The apparatus is in particular also refined by at least one of the features of claims 1 to 12.

[0021] The screw machine is particularly configured as a multi-screw machine, preferably as a twin-screw machine. The screw machine has a housing, at least one housing bore formed in the housing, and at least one processing element shaft rotatably mounted in the at least one housing bore. When configured as a multi-screw machine, at least two interpenetrating housing bores are formed in the housing, and at least two processing element shafts are arranged therein. The at least two processing element shafts are preferably rotatably drivable in the same direction. The at least two processing element shafts are configured to be particularly tightly intermeshed.

[0022] The device preferably comprises a control device for controlling the screw machine and / or the feeding device. The feeding device in particular comprises a cooling device. The cooling device serves to cool the dosing unit and / or the feeding screw machine. In particular, the cooling device cooling the feeding device can be controlled by the control device.

[0023] The device according to claim 14 ensures simple, flexible, and efficient recycling of powder coating particles. The screw machine has, successively in the conveying direction, an intake zone, a plasticization zone, and a homogenization zone. The second feed opening is located between the plasticization zone and the discharge opening, so that the powder coating particles are easily mixed into the plasticized powder coating premix or powder coating melt. Preferably, the second feed opening is located between the homogenization zone and the discharge opening. This allows the powder coating particles to be fed into the fully prepared powder coating melt, so that the preparation of the powder coating melt from the powder coating premix is not substantially affected or adversely affected. Preferably, downstream of the second feed opening, the screw machine has a mixing zone located upstream of the discharge opening. The second feed opening is particularly arranged between the homogenization zone and the mixing zone. The screw machine has at least one conveying element and / or at least one kneading element in the mixing zone. Preferably, the screw machine has at least one conveying element and at least one kneading element in succession in the mixing zone.

[0024] Claim 13,The device according to claim 15 ensures simple, flexible, and efficient recycling of powder coating particles. The feed screw machine has a housing in which at least one housing bore is formed. The housing has a feed opening, in particular an injection hopper. At least one screw shaft is rotatably arranged in the at least one housing bore. Preferably, at least two interpenetrating housing bores are formed in the housing. At least two screw shafts are rotatably arranged in the two housing bores. The feed screw machine is particularly configured as a side feed device. The feed screw machine is connected to a side of the screw machine housing. The feed screw machine and / or the dosing unit may preferably be cooled by at least one cooling device, such as a compressed air cooling device and / or a water cooling device. The at least one cooling device functions to cool the injection hopper and / or housing of the feed screw machine and / or at least one screw shaft and / or the container and / or discharge pipe of the dosing unit. Preferably, the feed device has a gravimetric or volumetric dosing unit that feeds the powder coating particles into the feed screw machine. The powder coating particles are preferably provided by a separator. The injection hopper preferably has a double wall. Due to the double wall design, the injection hopper particularly has cooling channels. The cooling channels are particularly part of at least one cooling device. A cooling fluid, such as compressed air or water, flows through the cooling channels. The cooled injection hopper prevents adhesion of the powder coating particles.

[0025] Claim 13The device according to the invention ensures a simple, flexible and efficient recycling of powder coating particles. The feeding device preferably comprises a feeding screw machine connected to the screw machine by a feeding insert. The feeding insert in particular comprises a flange and a feeding channel part attached thereto. The feeding insert comprises at least one cooling element, in particular at least one cooling channel, which serves to cool the flange and / or the feeding channel part. The flange in particular is attached to a housing of the feeding screw machine, so that the feeding channel part extends to a housing opening of the screw machine housing.

[0026] Further advantages, features and details of the invention emerge from the following description of several exemplary embodiments. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a partial cross-sectional view of an apparatus for producing a powder coating melt according to a first exemplary embodiment, having a multi-screw machine for preparing a powder coating premix and a feeding device connected thereto by a feeding screw machine for feeding powder coating particles; FIG. [Figure 2] FIG. 2 is a plan view, partially in section, of the device in FIG. 1. [Figure 3] FIG. 1 is a perspective view of a coolable feed insert for connecting the feed screw machine to a multiple screw machine. [Figure 4] 10 is a partial cross-sectional view of an apparatus for producing a powder coating melt according to a second exemplary embodiment. [Figure 5] FIG. 5 is a plan view, partially in section, of the device in FIG. 4. DETAILED DESCRIPTION OF THE INVENTION

[0028] A first exemplary embodiment of the invention will now be described with reference to figures 1 to 3. The apparatus 1 shown in the figures serves to produce powder coating melts 2,3.

[0029] The apparatus 1 comprises a multi-screw machine 4 having a housing 5 made up of a plurality of successively arranged housing sections 6-14. The housing sections 6-14 are connected together to form the housing 5. Two mutually parallel, interpenetrating housing bores 15, 16, which have the shape of a horizontal figure eight in cross section, are formed in the housing 5. Two processing element shafts 17, 18 are coaxially arranged in the housing bores 15, 16 and can be driven in rotation about respective rotation axes 20, 21 by a drive motor 19. A bifurcated gear mechanism 22 is arranged between the processing element shafts 17, 18 and the drive motor 19. A coupling 23 is in turn arranged between the drive motor 19 and the bifurcated gear mechanism 22. The processing element shafts 17, 18 are driven by the drive motor 19 about the rotation axes 20, 21 in the same direction, i.e., in the same rotational direction.

[0030] The multi-screw machine 4 comprises, successively in the conveying direction 24 , an intake zone 25 , a plasticizing zone 26 , a homogenizing zone 27 , a feeding zone 28 , a mixing zone 29 and a discharge zone 30 .

[0031] A powder coating premix 31 is fed to the multi-screw machine 4 in the intake region 25. For this purpose, a first feed opening 32 is formed in the first housing part 6, via which the powder coating premix 31 is introduced into the housing bores 15, 16. For feeding the powder coating premix 31, the apparatus 1 has a first feed device 33 connected to the first feed opening 32. The first feed device 33 comprises, for example, a gravimetric dosing unit.

[0032] In the intake zone 25, the supplied powder coating premix 31 is conveyed to the plasticization zone 26. In the intake zone 25, the processing element shafts 17, 18 have screw elements 34, 34' arranged rotatably fixed on assigned shafts 35, 36 and serving to convey the powder coating premix 31.

[0033] The supplied powder coating premix 31 is melted in the plasticizing zone 26. In the plasticizing zone 26, kneading elements 37, 37' are rotatably fixedly arranged on shafts 35, 36 for melting and dispersing. The kneading elements 37, 37' are configured as kneading disks. Preferably, in the plasticizing zone 26, a kneading block having a plurality of integrally formed kneading disks is arranged on the shafts 35, 36.

[0034] The powder coating premix 31 plasticized or melted in the plasticization zone 26 is conveyed to the homogenization zone 27. In the homogenization zone 27, the plasticized powder coating premix 31 is homogenized into the first powder coating melt 2. In the homogenization zone 27, the plasticized powder coating premix 31 is intensively mixed so that the first powder coating melt 2 is completely prepared at the downstream end of the homogenization zone 27. In the homogenization zone 27, kneading elements 38, 38' are rotatably fixedly arranged on the shafts 35, 36. The kneading elements 38, 38' are in particular configured as kneading disks. Preferably, a kneading block formed from a plurality of integrally formed kneading disks is arranged in the homogenization zone 27.

[0035] In the feed area 28, powder coating particles 39 are fed to the fully prepared powder coating melt 2. The powder coating particles 39 are not suitable for powder coating and must be recycled. The feeding of the powder coating particles 39 to the first powder coating melt 2 reduces its temperature, which is advantageous for further processing of the powder coating melt 2.

[0036] To supply the powder coating particles 39, the apparatus 1 has a second supply device 40. The second supply device 40 has a weight dosing unit 41, an injection hopper 80, a feed screw mechanism 42 and a feed insert 43. The feed screw mechanism 42 is connected to the side of the housing 5 by the feed insert 43, so that a second supply opening 44 is formed in the housing 5 in the supply area 28. The second supply opening 44 opens up to the housing bores 15, 16 or to the housing bore 16. The metering unit 41 is connected to the feed screw mechanism 42 by the injection hopper 80.

[0037] In the feeding region 28, screw elements 45, 45' are rotatably fixedly arranged on the shafts 35, 36. The screw elements 45, 45' convey the first powder coating melt 2 with the supplied powder coating particles 39 to the mixing region 29.

[0038] In the mixing zone 29, the supplied powder coating particles 39 are mixed into the first powder coating melt 2 and melted therein. For this purpose, screw elements 46, 46' and kneading elements 47, 47' are arranged in the mixing zone 29, fixedly arranged so as to be continuously rotatable on the shafts 35, 36. The screw elements 46, 46' serve to convey the first powder coating melt 2 with the supplied powder coating particles 39 away from the second feed opening 44, so that pile-up does not occur in the feed zone 28. By means of the kneading elements 47, 47', the powder coating particles 39 are mixed into the first powder coating melt 2 as gently as possible and without intensive shear, thereby producing the second powder coating melt 3. The kneading elements 47, 47' are preferably configured as kneading disks. For example, a kneading block formed of integrally interconnected kneading disks is arranged in the mixing zone 29.

[0039] After the powder coating particles 39 are mixed in the mixing zone 29, the second powder coating melt 3 is discharged in the discharge zone 30. In the discharge zone 30, screw elements 48, 48' are rotatably fixed to the shafts 35, 36 for discharging the second powder coating melt 3. A nozzle plate 49 is located in the final housing section 14, terminating the housing 5 and forming a discharge opening 50. Depending on the design of the nozzle plate 49, the discharge opening 50 may be vertically disposed so that the discharge occurs horizontally, or horizontally disposed so that the discharge occurs vertically. Vertical discharge does not require special pressure. Figures 1 and 2 show horizontal discharge. The second powder coating melt 3 is discharged through the discharge opening 50. The second powder coating melt 3 is fully prepared; it no longer contains free (loose) powder coating particles 39. The powder coating particles 39 are mixed and dissolved by the time of discharge.

[0040] After the second powder coating melt 3 is discharged, it is cooled in a conventional manner. The cooled and hardened powder coating melt 3 is then ground into powder coating powder 51.

[0041] To separate the powder coating powder 51, the apparatus 1 has a separator 52. The separator 52 separates the supplied powder coating powder 51 into usable fragments F1 and recycled fragments F2. The usable fragments F1 are suitable for powder coating. In contrast, the recycled fragments F2 contain powder coating particles 39 that are not suitable for powder coating. The powder coating particles 39 are supplied from the separator 52 to a second supply device 40.

[0042] Each powder coating particle 39 has a maximum particle size A 最大 and for at least 50%, in particular for at least 70%, in particular for at least 90%, A 最大 ≦100 μm, especially A 最大 ≦90 μm, especially A 最大 ≦80 μm, especially A 最大 ≦60 μm. Furthermore, for at least 50%, in particular for at least 70%, in particular for at least 90% of the powder coating particles 39, A 最大 ≧1 μm, especially A 最大 ≧5 μm, especially A 最大 ≧10 μm applies.

[0043] First, the powder coating particles 39 reach a weighing unit 41. The weighing unit 41 is connected to a feed screw machine 42, to which the powder coating particles 39 are fed.

[0044] The feed screw machine 42 is configured as a twin-shaft feed machine. It has a housing 53 with two interpenetrating housing bores 54, 55, which have the shape of a horizontal figure eight in cross section. Two screw shafts 56, 57 are coaxially arranged in the housing bores 54, 55 and can be driven to rotate in the same direction around associated rotation axes 60, 61 by a drive motor 59 via a bifurcated gear mechanism 58. A feed opening 62, into which the metering unit 41 opens above the dosing hopper 80, is formed in the housing 53.

[0045] The feed screw machine 42 is connected to the multi-screw machine 4 by a feed insert 43. The feed insert 43 has a feed channel part 63 and a flange 64 attached thereto. The feed insert 43 is attached to the end of the housing 53 by the flange 64 so that the holes 65, 66 formed in the feed channel part 63 are aligned with the housing holes 54, 55. The holes 65, 66 formed in the feed channel part 63 are interpenetrating (overlapping) and have the shape of a horizontal figure eight in cross section. The feed channel part 63 is positioned in an associated housing opening 67 of the housing 5 so that the holes 65, 66 open into the housing holes 15, 16 or the housing hole 16 to form the second feed opening 44.

[0046] The feed insert 43 has a cooling passage 75. The cooling passage 75 has an inlet opening 76 and an outlet opening 77 for a cooling fluid 78. The cooling passage 75 extends through the flange 64 and through the feed passage fitting 63.

[0047] To cool the second supply device 40, the apparatus 1 has a cooling device 68. The cooling device 68 has a compressed air supply unit 69 with a valve 70. A compressed air pipe 71 runs from the compressed air supply unit 69 via the valve 70 to the supply opening 62. Compressed air is supplied to the supply opening 62 via the compressed air pipe 71, creating a compressed air flow from the supply opening 62 through the housing bores 54, 55 to the second supply opening 44, which firstly prevents the escape of waste heat from the multi-screw machine 4, for example when the multi-screw machine 4 is stopped, and secondly creates a slight positive pressure which allows cooling of the housing 53 and the screw shafts 56, 57.

[0048] The cooling device 68 further includes a cooling pipe 72, a heat exchanger 73, and a pump 74. The cooling pipe 72 is connected to the heat exchanger 73 and the pump 74 and is attached to an inlet opening 76 and an outlet opening 77 of a cooling passage 75. The pump 74 pumps a cooling fluid 78, such as water, through the cooling pipe 72 into the cooling passage 75 and from there to the heat exchanger 73, whereby heat is extracted from the feed insert 43 and the feed insert 43 is cooled. The heated cooling fluid 78 is cooled again in the heat exchanger 73.

[0049] The inlet hopper 80 is formed by a double wall, which allows the inlet hopper 80 to form a cooling channel, which is part of the cooling system 68 and is cooled by, for example, compressed air or water.

[0050] The cooling device 68 reduces, and preferably prevents, the powder coating particles 39 from melting and adhering to the injection hopper 80 , the inner walls of the housing 53 , the screw shafts 56 , 57 and / or the feed insert 43 .

[0051] The device 1 includes a control device 79. The control device 79 includes a drive motor 19, supply devices 33, 40, and a cooling device 68.

[0052] Because the powder coating particles 39 are provided to the fully prepared first powder coating melt 2, the preparation of the first powder coating melt 2 is not affected or adversely affected. Because the powder coating particles 39 are already prepared, they simply need to be mixed into the first powder coating melt 2. The mixing is performed gently. Because the preparation of the first powder coating melt 2 is not substantially adversely affected, the amount of powder coating particles 39 may be varied within wide limits. Thus, the powder coating particles 39 can be recycled flexibly depending on the amount produced. Because there is no second intensive mixing and homogenization, the powder coating particles 39 are recycled gently. This is advantageous because the powder coating particles 39 are more reactive than the powder coating premix 31, and therefore a deterioration in the quality of the second powder coating melt 3 is avoided. The powder coating particles 39 are therefore recycled simply, flexibly, and efficiently.

[0053] A second exemplary embodiment of the invention is described below in conjunction with Figures 4 and 5. Unlike the above-described exemplary embodiment, the device 1 has a first feed device 33 with a gravimetric dosing unit 81 and a feed screw machine 82. The gravimetric dosing unit 81 opens into the feed screw machine 82. The feed screw machine 82 is connected directly, i.e. without a feed insert, to the intake area 25 of the housing 5, so that the first feed opening 32 opens into the housing bore 15, 16 or into the housing bore 16 at the side of the intake area 25. The dosing unit 81 and the feed screw machine 82 are formed similarly to the dosing unit 41 and the feed screw machine 42.

[0054] The supply device 33 functions to supply powder coating particles 84 that are not suitable for powder coating. The powder coating particles 84 are supplied to the intake zone 25 together with the powder coating premix 31, melted together with the powder coating premix 31 in the plasticization zone 26, and then homogenized into the first powder coating melt 2 in the homogenization zone 27. The amount of powder coating particles 84 supplied to the powder coating premix 31 is determined by the subsequent plasticization and homogenization. Thus, the powder coating particles 84 may be supplied in an amount that does not adversely affect the preparation of the powder coating premix 31, e.g., does not result in a decrease in quality and / or throughput rate. The supply and recycling of the powder coating particles 39 is performed in the same manner as in the first exemplary embodiment. For further configurations and functions of the device 1, please refer to the previous exemplary embodiment.

[0055] In general, the following applies: The mixing zone 29 may be exclusively provided with screw elements 46, 46'. In this case, the mixing zone 29 must be long enough to mix and, in particular, melt the supplied powder coating particles 39. The length of the mixing zone 29 may be shortened by providing kneading elements 47, 47' in the mixing zone 29.

[0056] Powder coating particles 39 of any particle size or grain size may be fed downstream of the plasticization zone 26, in particular the homogenization zone 27. Preferably, fine powder coating particles are fed. The required length of the mixing zone 29 depends on the viscosity of the powder coating melt 2, the melt temperature, the rotation speed of the processing element shafts 17, 18 and the feed rate of the powder coating particles 39. The powder coating particles 39 may also be fed into the center of the homogenization zone 27, as long as this does not adversely affect the preparation of the powder coating melt 2.

[0057] A relatively small amount of powder coating particles 84 may be provided to intake area 25 as long as it does not adversely affect the preparation of powder coating premix 31 .

[0058] Since the amount of powder coating particles 39 supplied may vary within wide limits, it is possible to supply the powder coating particles 39 just produced in the separating device 52 directly to the feeding screw machine 42, i.e. without the intervention of a dosing unit, for example by means of a pneumatic conveyor.

[0059] The powder coating particles 39 may also be fed to the second feeder 40 via a so-called big bag.

[0060] Cooling with compressed air may be carried out in particular during shutdown of the multi-screw machine 4. The shutdown is detected, for example, from the rotational speed of the drive motor 19 or from a control signal present in the control device 79. [Explanation of symbols]

[0061] 2. First Powder Coating Melt 3. Second powder coating melt 4 screw machine 31 Powder Coating Premix 39 Powder coating particles

Claims

1. 1. A method of producing a powder coating melt, comprising: - equipped with a screw machine (4), - producing a first powder coating melt (2) from the powder coating premix (31) by means of said screw machine (4), - feeding powder coating particles (39) into said first powder coating melt (2) present in said screw machine (4), --the powder coating particles (39) are fed to the screw machine (4) by a feeding device (40); - said feeding device (40) comprising at least one of a feeding screw machine (42) and a feeding insert (43) for connection to said screw machine (4); - at least one of said feed screw machine (42) and said feed insert (43) is cooled by a cooling device (68); and - mixing said first powder coating melt (2) and said powder coating particles (39) by means of said screw machine (4) to produce a second powder coating melt (3).

2. The powder coating particles (39) supplied each have a maximum particle size A 最大 and for at least 50% of the powder coating particles (39) provided, A 最大 2. The method of claim 1, wherein ≦100 μm applies.

3. The powder coating particles (39) supplied each have a maximum particle size A 最大 and for at least 50% of the powder coating particles (39) provided, A 最大 3. The method according to claim 1, wherein ≧1 μm applies.

4. 4. The method according to claim 1, wherein the powder coating particles (39) are melted before the second powder coating melt (3) is discharged from the screw machine (4).

5. 5. The method according to claim 1, wherein the powder coating particles (39) are fed downstream of the plasticization zone (26) of the screw machine (4).

6. 6. The method according to claim 1, wherein the powder coating particles (39) are fed to a feed zone (28) of a screw machine (4) arranged downstream of a plasticization zone (26) and upstream of a mixing zone (29).

7. A method according to any one of claims 1 to 6, characterized in that the supply device (40) has a dosing unit (41).

8. 8. The method according to any one of claims 1 to 7, characterized in that the powder coating particles (39) are provided by a separating device (51).

9. 9. The method according to any one of claims 1 to 8, characterized in that the powder coating particles (39) are fed by the feed screw machine (42).

10. 10. The method according to claim 9, characterized in that the feed screw machine (42) is connected to the screw machine (4) by means of the feed insert (43), and the feed insert (43) is cooled.

11. 11. The method according to claim 9 or 10, characterized in that the housing (53) and / or at least one screw shaft (56, 57) and / or the injection hopper (80) of the feed screw machine (42) are cooled.

12. 12. The method according to any one of claims 1 to 11, characterized in that the powder coating particles (39) are supplied by a dosing unit (41), and the dosing unit (41) is cooled.

13. 1. An apparatus for producing a powder coating melt, comprising: a first supply opening (32) for supplying a powder coating premix (31), and a screw machine (4) with a second feed opening (44) arranged downstream for feeding powder coating particles (39); a feeding device (40) for feeding the powder coating particles (39) to the screw machine (4) through the second feeding opening (44); The supply device (40) has a cooling device (68), The feeding device (40) comprises at least one of a feeding screw machine (42) and a feeding insert (43) for connection to the screw machine (4); and 10. The apparatus according to claim 9, wherein at least one of the feed screw machine (42) and the feed insert (43) is coolable by the cooling device (68).

14. 14. The device according to claim 13, characterized in that the second feed opening (44) is arranged between the plasticization zone (26) and the discharge opening (50) of the screw machine (4).

15. 15. Apparatus according to claim 13 or 14, characterized in that the supply device (40) comprises a dosing unit (41), which can be cooled by the cooling device (68).

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