EP3047914B1 - Installation and method for coating a workpiece with metallic material - Google Patents

Description

The invention relates to a plant for the metallic coating of a workpiece with a coating apparatus having a movable coating lance, through which a metal plasma jet for forming a coating of metal particles can be generated, and a nozzle device for generating a jet of a cooling gas, according to the preamble of Claim 1.

The invention further relates to a method for the metallic coating of a workpiece, wherein a metal plasma jet is produced by a movable coating lance of a coating apparatus, by means of which a coating of metal particles is formed on a workpiece, according to the preamble of claim 14.

In particular, in engine construction, it is necessary to provide the running surfaces of cylinder bores with a special metallic coating, so that adequate friction and lubrication conditions between a cylinder surface and a cylinder piston are ensured. This is especially true when both the engine housing and the cylinder piston are made of the same material, such as aluminum.

From the EP 1 980 328 A2 or the WO 2004/005575 A2 Systems and methods are known with which directly on an inner wall, a metal coating is applied by a coating lance. The coating lance creates a metal plasma jet. In this way, very thin-walled and very stable metal coatings can be formed.

The WO 2004/005575 A2 describes a generic device and a generic method in which a nozzle device for generating a jet of a cooling gas is additionally arranged on the movable coating lance.

The EP 282 93 27 A1 discloses a method for cleaning a burner of a plasma coating installation, in which the burner is subjected to a cleaning agent emerging from a cleaning nozzle during a coating interruption, and so that sprayed-particle particles adhering to the burner are removed.

Due to a certain scattering of the metal plasma jet, not all metal particles reach the bore wall and remain there. These non-deposited metal particles are referred to as overspray. This overspray can also lead to undesirable coatings on the coating lance itself, which over time adversely affects the function of the coating lance.

It is known to provide a suction device to remove the excess metal particles from the process space. However, this can only reduce the problem of overspray, so that, over time, unwanted deposits form on the coating lance.

The invention has for its object to provide a system and a method for the metallic coating of a workpiece, with which impairments of the coating lance can be counteracted by the overspray particularly reliable.

The object is achieved according to the invention by a system having the features of claim 1 and a method having the features of claim 13. Preferred embodiments are given in the respective dependent claims.

A basic idea of the system according to the invention is to provide a cleaning station with which unwanted false coatings on the coating lance are removed. According to the invention, this takes place at certain times. These can be times at fixed cleaning intervals or Timings, which are determined depending on the degree of contamination by an operator or a control device.

According to a further aspect of the invention, the cleaning station is provided with a nozzle device, through which a nozzle jet is directed onto the coating lance. In this case, a jet of a cleaning medium is generated, which removes the deposited on the top of the coating lance metal particles.

A preferred embodiment of the invention is that the nozzle device has at least one outlet nozzle, which is connected to a compressed gas container. This compressed gas container is in particular filled with the cleaning medium.

In principle, various cleaning media can be used to remove the deposits. According to a development of the invention, it is particularly advantageous that the jet of CO _{2 is} formed, which emerges as CO ₂ snow from the nozzle device. This cleaning medium acts in two ways, namely on the one hand mechanically by the impact of the frozen ice particles on the surface of the coating lance and on the other hand by thermal stress. Because of the CO ₂ snow, which strikes the surface of the coating lance with the adhering metal particles, the metal particles are strongly cooled, which promotes spalling or loosening of the metal particles from the surface of the coating lance or effect.

In principle, the outlet nozzle can be provided in any desired arrangement. In particular, a plurality of outlet nozzles can be arranged along the circumference of the rod-shaped, usually cylindrical coating lance. According to one embodiment of the invention, it is particularly advantageous that the at least one outlet nozzle has an elongate outlet slot which is directed parallel to the longitudinal axis of the coating lance. In this way, an elongated jet can be generated, which is directed approximately parallel to the coating lance. Preferably, during cleaning, the coating lance is rotated about its longitudinal axis so that the jet of the jet covers the entire surface of the coating lance can cover in a peripheral area. For a particularly thorough cleaning, a multiple circulation can take place.

According to the invention, it is provided that a control device for controlling the jet is arranged. In this case, the control device is provided with a throttle valve, through which the jet is controllable. In particular, the pressure and / or the volume flow of the jet can thus be adjusted in the desired manner.

A development of the invention consists in that the coating device has an exchangeable annular receiving unit which surrounds the coating lance in an annular manner and is designed to deposit metal particles, and in that the cleaning station is designed to change the receiving unit. The ring-shaped or drum-shaped receiving unit surrounds the coating lance in a retracted traversing position, wherein the receiving unit can be moved together with the coating lance between different processing points. By means of this receiving unit, metal particles of the metal plasma jet can be picked up during the process of the coating lance in the movement position or even during the process. The plasma jet can thus be operated in an efficient manner without interruption in the process. The receiving unit avoids excessive overspray.

The drum-shaped receiving unit can be changed at certain times in the cleaning station. Preferably, this can be done at each cleaning or only at certain cleaning times or depending on the level or weight of the receiving unit. For this purpose, a sensor may be mounted, which determines the level or the weight. By a control unit, the reaching of a threshold value can be determined, so that then a replacement is caused. When changing the receiving unit of the coating device and in particular a carriage of the coating lance is dissolved and removed. Subsequently, a new ring-shaped or drum-shaped receiving unit can be arranged in the coating device, so that then a further processing can take place.

A further preferred embodiment of the invention is that the receiving unit is held by means of a quick-release device on the coating device that the quick-release device is detachable in the cleaning station, wherein the receiving unit is removable and replaceable by a new receiving unit, and that the new receiving unit by operating the Quick clamping device can be attached to the coating device. The quick-release device may in particular be a strap closure or another locking mechanism which can be easily detached and closed again. Basically, this can be done by hand by an operator.

A preferred embodiment of the invention is that the receiving unit is at least partially replaceable by means of an automatic handling device. Preferably, the entire change process can be performed automatically. This is particularly advantageous in mass production. The quick-clamping device can be provided with motor-actuated or electromagnetically actuated locking elements. After releasing the drum-shaped receiving unit is removed approximately by a handling robot from the cleaning station, at the same time a new receiving unit is arranged and connected to the moving part of the coating device.

An advantageous embodiment of the invention is that the cleaning station has a support element for depositing the receiving unit and that below the support element, the nozzle device is provided for cleaning the coating lance. In particular, the cleaning station may have a sleeve-shaped receiving space, at the upper end of which an annular support plate is attached as a support element. In the underlying sleeve-shaped receiving space, the nozzle device is provided, so that the coating lance can be cleaned by the nozzle device, while the receiving unit rests on the annular support element and can be changed.

According to a development of the invention, it is expedient that a suction device is provided, through which removed during cleaning metal particles are sucked from the coating lance. In particular, air can be sucked out of the process chamber downwards via the suction device from the sleeve-shaped receiving space with the nozzle device. This allows the leaked CO ₂ snow or the vaporized CO ₂ gas is sucked and removed from the cleaning station together with the removed metal particles. The suction device may be coupled and connected to a central suction device, which also provides for the extraction of overspray during the coating or the process on the coating lance.

An advantageous embodiment of the invention is that the receiving unit is formed annularly with an outer base body and an inner receiving layer which is detachably attached to the base body. The outer body is formed as a simple pipe segment made of steel. This serves as a supporting body for the receiving layer provided on the inside, on which the metal particles accumulate. The receiving layer may have a thickness of between 0.1 millimeters to several millimeters. Due to the detachable mounting of the receiving layer on the base body, the receiving layer with the deposited metal particles can be easily removed, so that the thicker base body can be reused by applying a new recording layer.

A preferred embodiment of the invention consists in that the receiving layer is formed from a metal sheet or a plastic material, in particular silicone.

The receiving layer can therefore be a rigid body, which is inserted into the base body and secured therein. The fastening can take place via radial projections or fastening means, in particular screws. Alternatively, the receiving layer can also be applied directly to the inside of the base body, in particular sprayed on. For this purpose, in particular plastic material can be used, wherein silicone is preferred due to the high temperature resistance. In particular, the receiving layer can be elastic, so that it can be easily detached from the outer sleeve-shaped base body.

To facilitate release, it is advantageous according to a development of the invention that the outer base body for releasing the inner receiving layer in its shape is changeable, in particular divisible. Thus, the main body can be constructed in particular of two or more parts, which via connecting means or joints connected to each other. In a two-part body this can be constructed of two half-shells, which can swing apart. With regard to the method, the invention is characterized in that the coating lance is moved into a cleaning station for cleaning, that in the cleaning station a jet of a cooling gas is directed by means of a nozzle device on the coating lance, wherein deposited metal particles are removed from the coating lance, and that the jet is controlled by a control device by means of a throttle valve. With this method according to the invention, in particular, the system described above can be operated and the advantages achieved thereby achieved. The listed metal particles are particles from the plasma jet. These metal particles may comprise pure metals, alloys or metal oxides.

In principle, other soiling, such as oil or grease deposits, are removable in the cleaning station.

Fig. 1:

eine schematische Seitenansicht einer erfindungsgemäßen Anlage;

Fig. 2:

eine um 90° geklappte Seitenansicht der Anlage von Fig. 1 in stark schematisierter Form;

Fig. 3:

eine Draufsicht der Anlage gemäß den Figuren 1 und 2;

Fig. 4:

eine schematische perspektivische Ansicht der Anlage gemäß den Figuren 1 bis 3, jedoch ohne Gehäuse;

Fig. 5:

eine schematische perspektivische Ansicht einer Beschichtungsvorrichtung für die erfindungsgemäße Anlage;

Fig. 6:

eine schematische perspektivische Ansicht der Beschichtungsvorrichtung von Fig. 5, jedoch ohne Beschichtungslanze;

Fig. 7:

eine vergrößerte Querschnittsansicht zu einer Absaugglocke der Beschichtungsvorrichtung gemäß den Figuren 5 und 6;

Fig. 8:

eine schematische perspektivische Ansicht der Beschichtungsvorrichtung an einer Reinigungsstation gemäß der Erfindung;

Fig. 9:

eine vergrößerte schematische perspektivische Ansicht der Reinigungsstation von Fig. 8;

Fig. 10:

eine Querschnittsdarstellung der Reinigungsstation gemäß Fig. 9; und

Fig. 11:

eine Querschnittsansicht durch eine erfindungsgemäße Aufnahmeeinheit

A further development of the method according to the invention consists in that a receiving unit, which surrounds the coating lance annularly, is released and replaced in the cleaning station. Thus, in the method according to the invention not only a cleaning of the coating lance can take place, but the time for cleaning can simultaneously serve for changing a receiving unit, which serves to receive excess deposited metal particles. The invention will be further described by means of preferred embodiments, which are shown schematically in the accompanying drawings. In the drawings show:

Fig. 1:

a schematic side view of a system according to the invention;

Fig. 2:

a 90 ° folded side view of the plant of Fig. 1 in a highly schematized form;

3:

a plan view of the system according to the Figures 1 and 2 ;

4:

a schematic perspective view of the system according to Figures 1 to 3, but without housing;

Fig. 5:

a schematic perspective view of a coating device for the inventive system;

Fig. 6:

a schematic perspective view of the coating device of Fig. 5 but without coating lance;

Fig. 7:

an enlarged cross-sectional view of a suction bell of the coating apparatus according to the Figures 5 and 6 ;

Fig. 8:

a schematic perspective view of the coating device at a cleaning station according to the invention;

Fig. 9:

an enlarged schematic perspective view of the cleaning station of Fig. 8 ;

Fig. 10:

a cross-sectional view of the cleaning station according to Fig. 9 ; and

Fig. 11:

a cross-sectional view through a receiving unit according to the invention

An inventive system 10 for the metallic coating of holes 3 in a workpiece 1 is in FIGS. 1 to 4 shown. The workpiece 1 is in the illustrated embodiment, an engine block with 12 holes 3, which are arranged as cylinder bores in two rows of six in V-shape in the workpiece 1.

The system 10 has a machine bed 11 on which a housing 13 is arranged. The box-shaped housing 13 encloses a loading station 12 and a processing station 14 with a coating device 29.

On the machine bed 11 for receiving a workpiece 1, a base frame 16 of a conveyor 20 is arranged, which is formed in the illustrated embodiment as a turntable 22. The rotatable about a vertical axis of rotation driven horizontal turntable 22 has two opposite workpiece holders 23, in each of which a plate-shaped pallet module 21, each with a workpiece 1 is receivable. Via a pivoting device 26, the pallet module 21 can be pivoted with the workpiece 1 relative to the horizontal, so that the holes 3 in the workpiece 1 can be arranged vertically to carry out a metallic coating.

The workpiece 1 is received at the loading station 12 by a feed device, not shown. The housing 13 has in the region of the charging station 12 an opening, not shown, with a door. Furthermore, a measurement of the workpiece 1 can take place in the area of the paint station 12. Subsequently, the turntable 22 is rotated by 180 °, wherein the workpiece 1 is conveyed from the loading station 12 to the opposite processing station 14. The processing station 14 is separated from the charging station 12 via a partition wall 24. In Fig. 2 the partition 24 is only partially shown in the lower area. However, the partition 24 extends through the entire space of the housing 13, so that the processing station 14 is sealed off from the charging station 12. To pass the workpieces 1 from the loading station 12 to the processing station 14 and back again two passages 25 are provided. The passages 25 are each closed by a sliding closure element 27, which can be opened for the passage of the workpiece 1 and then closed again.

In the processing station 14, the workpiece 1 is pivoted with the pivoting device 26 about a horizontal pivot axis, wherein in each case a series of holes 3 is aligned vertically, as shown in FIGS FIGS. 1 to 4 is apparent.

For applying the metallic coating, a coating device 29 with a rod-shaped coating lance 30 is provided, which has at its lower end at least one outlet opening 32 for a metal plasma jet. The metal plasma jet is generated in a known manner by a plasma generator with a cathode and a metallic anode. By means of a correspondingly high electrical voltage, an arc is formed between the cathode and the anode, by means of which the metallic anode is melted. The metallic anode is designed as a feedable wire, so that there is always sufficient material to form a metal plasma jet with the molten metallic particles. As a source of the metallic particles, a supply of powder may be provided instead of a wire. Via a gas nozzle device, a gas stream is generated, which emerges at supersonic speed from the outlet opening 32 at the lower end of the coating lance 30 approximately horizontally. In this case, the coating lance 30 is retracted with the outlet opening 32 in the bore 3 to be coated in the workpiece 1. The coating device 29 further comprises a sleeve-shaped suction bell, which surrounds the coating lance 30, but in the FIGS. 1 to 4 for reasons of clarity is not shown.

To process the coating lance 30, a portal device 40 with two parallel first track axes 41 is provided. On the two first track axes 41, a frame-like first carriage 47 is mounted horizontally movable. The first traversing carriage 47 itself has two linear, horizontal second traverse axes 42, which are arranged parallel to one another and perpendicular to the first traverse axes 41.

Along the two second track axes 42, a beam-shaped second carriage 48 is arranged horizontally movable. The second carriage 48 itself has a single vertical third travel axis 43. Along this third travel axis 43, a receiving carriage 45 is mounted vertically movable. On the receiving carriage 45, the coating lance 30 is rotatably supported.

After a workpiece 1 is positioned in the processing station 14, the coating lance 30 of the coating device 29 is retracted into a first bore 3 to be coated in the workpiece 1. The continuously operated coating lance 30 generates a metal plasma jet which impinges on a bore wall of the bore 3 at supersonic speed. By rotating the coating lance 30 and the axial process in the vertical direction, a uniform defined metallic coating with a thickness of for example 10 microns on the bore wall.

After moving out of the coating lance 30 from the first coated bore 3 of the metal plasma jet is directed directly on exit from the bore 3 on an impact surface of a receiving unit in the suction bell, which is supported together with the coating lance 30 on the receiving carriage 45 and subsequently in connection with the FIGS. 5 to 7 will be described in more detail. The receiving unit receives the particles of the metal plasma jet and is moved together with the coating lance 30 to the next hole to be coated 3. Then, the metallic coating is repeated at this second bore 3, wherein a corresponding coating of the further bore 3 in a row of the workpiece 1 connects. Subsequently, the workpiece 1 can be pivoted about the pivoting device 26 about a horizontal axis, so that the second row of the engine block is arranged for processing in the vertical position. Then, a coating of these six holes 3 in the engine block-like workpiece 1 can join.

After completion of the coating, the coating lance 30 is retracted with the portal device 40 and the finished coated workpiece 1 can be fed back with the simultaneous feed of a new workpiece to be machined 1 in the charging station 12 through the right passage 25. In this case, the closure element 27 is opened at the passage 25. At the same time, a new workpiece 1 is conveyed from the loading station 12 into the processing station 14 through the opened left passage 25 with the rotary movement of the turntable 22.

About a handling robot 50 with a measuring device 52, the layer thickness and contour of the applied coating can be measured. With the measuring device 52, the still uncoated holes 3 of a newly supplied workpiece 1 can be measured in advance, so that even more accurate testing of the performed coating by comparing the measurement data is possible. The coated workpiece 1 can then be removed from the workpiece holder 23 of the turntable 22 in the loading station 12. Thereafter, a new workpiece 1 in the workpiece holder 23 of the conveyor 20 can be used. Thus, in the system 10 according to the invention, the loading and unloading can take place parallel to the machining of a workpiece 1 in the processing station 14 and thus neutral to the machine main time. This allows efficient machine use.

With the portal device 40, the coating lance 30 can be moved at certain time intervals to a test station 54 for checking the jet pattern of the metal plasma jet or to a cleaning station 60, which hereinafter with the FIGS. 8 to 10 will be described in more detail.

A coating device 29 for a metallic coating system 10 according to the invention is substantially in the FIGS. 5 to 7 shown. The coating device 29 has a rod-shaped coating lance 30, which is basically known and produces a metal plasma jet. The shaft-shaped coating lance 30 with an associated base unit 31 is mounted on a receiving carriage 45 which is movable in a vertical direction along a lance guide 34 by means of a lance linear drive 33 with respect to a base carriage 28. Furthermore, the coating lance 30 is rotatably mounted about its vertical longitudinal axis and driven to coat an inner wall of a cylinder bore with a radially directed metal plasma jet.

The coating device 29 further comprises a suction bell 80, which is movably mounted by means of a bell carriage 35 in the vertical direction and parallel to the direction of travel of the receiving carriage 45. For this purpose, two rail-like bell guides 36 are arranged on the base carriage 28, with which the bell carriage 35 is in leading connection via sliding shoes. A linear displacement is effected by means of a linear drive. The base carriage itself is movably mounted in a plurality of directions relative to the machine bed 11 of the installation 10 via the portal device 40 described above. On the frame-like bell carriage 35 of the suction bell 80, a cylindrical or drum-shaped cover 82 is attached.

With reference to Fig. 7 the structure of the suction bell 80 is explained in detail. The cover 82 is made of sheet metal and mounted in a holding frame 81 which is fixed to the bell carriage 35. The cover 82 has a cylindrical wall 83, which is closed at its top by a cover plate 84. The cover plate 84 is designed in two parts and has a central passage opening 85 for the passage of the coating lance 30. In the cylindrical wall 83, a discharge opening 96 is introduced, via which from the interior of the cover 82 in operation ambient air, which is loaded with metal particles, via a ventilation duct 98 by means of a suction device, not shown, in particular a pump, sucked off and discharged to a filter device can. The cover plate 84 is detachably mounted and can be removed to influence the flow conditions.

On its underside, the cover 82 is closed by an annular base plate 86 which removably fastened in the present embodiment three quick-release devices 90 to a lower annular strut 87 of the holding frame 81 is. For this purpose, radially projecting hook elements 91 are provided on the radial outer edge of the base plate 86, which come into contact with a clamping yoke of the quick-action clamping device 90.

For the passage of the coating lance 30 through the base plate 86, this has a central opening 88 along which an annular flange 92 is resiliently mounted on spring elements 93 and supported on the base plate 86. The resilient mounting of the annular flange 92 serves a precise, flexible placement of the suction bell 80 on a workpiece. 1

The annular flange 92 has on its radial inside a conical surface 94 with an upward helix angle of about 30 degrees. When the coating lance 30 passes from the workpiece 1 into the suction bell 80 in a continuously passing metal plasma jet, metal particles striking the cone surface 94 are deflected to a large extent and guided into a drum-shaped receiving unit 70, which is mounted on the base plate 86 in the suction bell 80 ,

The drum-shaped receiving unit 70 has a base body 72 made of sheet metal, which comprises a cylindrical peripheral wall 74 made of a bent and welded sheet metal strip. At the upper end of the peripheral wall 74, an annular upper edge member 76 is welded. In a corresponding manner, an annular lower edge element 78 is welded to the lower end of the peripheral wall 74. Both edge elements 76, 78 are directed radially inwards and enclose an annular receiving space.

The coating device 29 can be moved with the coating lance 30 during a continuous operation of the metal plasma jet between the individual bores 3 of a workpiece 1 by the receiving unit 70 held replaceably in the suction bell 80. Here, the metal particles accumulate in the receiving unit 70 so that it fills with time. At a certain level, which is determined by an operator or a sensor device, in particular by a weight-dependent measurement, the receiving unit 70 is to be detached from the suction bell 80 and replaced by a new receiving unit 70.

In the system 10 according to the invention a cleaning station 60 is arranged in the processing station 14, which closer in the FIGS. 8 to 10 is shown. The cleaning station 60 has a columnar frame 61, on which a sleeve-shaped housing body 62 is fastened with a perforated bottom 63. Arranged on the housing body 62 which is open at the top is an annular support element 68 on which the coating device 29 with the suction bell 80 can be placed, as in FIG Fig. 8 is shown.

For cleaning, the coating lance 30 is moved down from the suction bell 80 and into the receiving space of the sleeve-shaped housing body 62 of the cleaning station 60 in this position. Via a discharge nozzle 65 with an elongated discharge slot, a nozzle jet of CO ₂ snow is directed onto the peripheral region of the introduced coating lance 30 via a lateral nozzle device 64 on the housing body 62. The jet is directed with an overpressure, which may be about 10 bar or more, so on the surface of the coating lance 30, that attached thereto metal particles are dissolved and removed. The removed metal particles are discharged via a suction device, not shown, via the perforated bottom 63 down from the housing body 62. During irradiation with the nozzle jet of the nozzle device 64, the coating lance 30 is rotationally driven about its longitudinal axis and also moved in the axial direction. In this way, the nozzle jet of the nozzle device 64 can sweep and clean a desired area of the coating lance 30.

Furthermore, in the cleaning station 60, the receiving unit 70 in the suction bell 80 can be exchanged. For this purpose, the quick-release devices 90 are released on the outside of the suction bell 80. Subsequently, the coating device 29 is moved axially upwards, wherein the receiving unit 70 remains on the annular support element 68 of the cleaning station 60. The filled receiving unit 70 can then be removed by an operator or by a handling device and be discharged from the system 10 via an opening, not shown, in the housing 13. Subsequently, a new receiving unit 70 can be positioned in the cleaning station 60 on the support element 68. Finally, the coating device 29 is again moved axially downward, until the new receiving unit 70 is received in the suction bell 80. Then the quick-clamping devices 90 are closed again and the coating device 29 is again available for processing a further workpiece 1.

According to FIG. 11 a further embodiment of a receiving unit 70 according to the invention is shown. The sleeve-shaped receiving unit 70 has a two-part main body 72, which is formed from two half-shells 72a, 72b. On the inside of the main body 72, a sleeve or annular receiving layer 75 is attached, which is continuously formed as a sleeve. The receiving layer 75 may be formed in particular from silicone.

The two half-shells 72a, 72b of the outer basic body 72 are held together by a schematically indicated connecting device 77. By loosening the connecting device 77, the base body 72 is divisible, so that the sleeve-shaped receiving layer 75 is released from the inside of the base body 72. In this way, a receiving layer 75 covered with metal particles can be exchanged and replaced by a new receiving layer 75. After inserting the new receiving layer 75, the base body 72 and the connecting device 77 can be closed again. The Aufnaheeinheit 70 can then be used again in the previously described Appendix 10. The recording unit 70 according to FIG. 11 can be related as well as previously FIG. 7 described recording unit 70 may be provided with upper and / or lower edge elements.

Claims (14)

1. System for the metal coating of a workpiece (1) having

   - a coating device (29) which has a movable coating lance (30), by which a metal plasma jet can be produced to form a coating of metal particles, and

   - a nozzle means (64) for producing a nozzle jet of a cooling gas,

   ch ara cterized in that

   - a cleaning station (60) is provided, to which the coating lance (30) can be moved at certain points in time, and

   - in that in the cleaning station (60) the nozzle means (64) is arranged, through which the nozzle jet is directed onto the coating lance (30) for its cleaning,

   - in that a control means with a throttle valve (66) is provided, by which the nozzle jet can be controlled.
2. System according to claim 1,
   characterized in that
   the nozzle means (64) has at least one discharge nozzle (65) which is connected to a compressed gas container.
3. System according to claim 2,
   characterized in that
   the at least one discharge nozzle (65) has an elongate discharge slit which is directed approximately parallel to the longitudinal axis of the coating lance (30).
4. System according to any one of claims 1 to 3,
   characterized in that
   the nozzle jet is formed of CO₂ which is discharged from the nozzle means (64) as CO₂-snow.
5. System according to any one of claims 1 to 4,
   characterized in that
   the coating device (29) has an exchangeable annular receiving unit (70) which surrounds the coating lance (30) annularly and is designed for the accumulation of metal particles, and
   in that the cleaning station (60) is designed for changing the receiving unit (70).
6. System according to claim 5,
   characterized in that
   the receiving unit (70) is held on the coating device (29) by means of a quick-clamping means (90),
   in that the quick-clamping means (90) can be released in the cleaning station (60), wherein the receiving unit (70) can be removed and replaced by a new receiving unit (70), and
   in that the new receiving unit (70) can be fastened on the coating device (29) by actuating the quick-clamping means (90).
7. System according to claim 5 or 6,
   characterized in that
   the receiving unit (70) can be exchanged at least partially by means of an automatic handling means.
8. System according to any one of claims 5 to 7,
   characterized in that
   the cleaning station (60) has a support element (68) for placing the receiving unit (70) and
   in that below the support element (68) the nozzle means (64) for cleaning the coating lance (30) is arranged.
9. System according to any one of claims 1 to 8,
   characterized in that
   a suction means is provided, through which metal particles removed during cleaning can be sucked off from the coating lance (30).
10. System according to any one of claims 5 to 8,
    characterized in that
    the receiving unit (70) is of annular design with an external base body (72) and an internal receiving layer (75) which is releasably fixed on the base body (72).
11. System according to claim 10,
    characterized in that
    the receiving layer (75) is formed of a metal sheet or a plastic material, in particular silicone.
12. System according to claim 10 or claim 11,
    characterized in that
    to release the internal receiving layer (75) the external base body (72) can be altered in its shape, in particular by being separable.
13. Method for the metal coating of a workpiece (1), in particular with a system (10) according to any one of claims 1 to 12,
    wherein by means of a movable coating lance (30) of a coating device (29) a metal plasma jet is produced, through which a coating of metal particles is formed on a workpiece (1),
    characterized in that

    - for cleaning the coating lance (30) is moved into a cleaning station (60),

    - in that in the cleaning station (60) a nozzle jet of a cooling gas is directed by means of a nozzle means (64) onto the coating lance (30), wherein accumulated metal particles are removed from the coating lance (30), and

    - in that the nozzle jet is controlled by a control means by means of a throttle valve (66).
14. Method according to claim 13,
    characterized in that
    a receiving unit (70) which surrounds the coating lance (30) annularly is released and exchanged in the cleaning station (60).

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