EP1520059A2

EP1520059A2 - Method and device for coating the interior of hollow areas by thermal injection

Info

Publication number: EP1520059A2
Application number: EP03740350A
Authority: EP
Inventors: Andreas Killinger; Rainer Gadow; Michael Buchmann; Daniel Martinez Lopez
Original assignee: Universitaet Stuttgart; Institut fuer Fertigungstechnologie Keramischer Bauteile Universitat Stuttgart
Current assignee: Universitaet Stuttgart; Institut fuer Fertigungstechnologie Keramischer Bauteile Universitat Stuttgart
Priority date: 2002-07-04
Filing date: 2003-06-26
Publication date: 2005-04-06
Also published as: WO2004005575A3; DE10230847B3; JP2005531693A; US20050170099A1; WO2004005575A2; AU2003281282A1

Abstract

The invention relates to a device and method for coating the interior of hollow areas (36) of workpieces (34) by thermal injection. The inventive device comprises a burner (24) for injecting a coating substance, said burner (24) being received by a positioning device (22) in such at way that it can be positioned in at least one direction; a rotatingly driveable rotary plate (14) on which a receiving element (40) is provided for a workpiece (34) and which can be positioned in relation to the burner (24) by means of a guide device (32). The guide device (32) comprises at least one first linear guide (42, 43) with a first drive device for positioning the element (40) receiving the workpiece, in addition to at least one second linear guide (44, 45) with a second drive device for positioning a balancing weight (46, 47). The first and second drive devices (48, 49, 50, 51) are driven in opposite directions, thereby ensuring mass balancing when a workpiece is displaced. In order to ensure continuous removal of the overspray, the rotary plate (14) is provided with an opening (17) in the region of the axis of rotation, which can be associated with a suction device (38).

Description

Process and device for the internal coating of cavities by thermal spraying

The invention relates to a device for internally coating rotationally symmetrical, in particular cylindrical cavities on workpieces by thermal spraying, with a burner for spraying a coating material, the burner being accommodated on a positioning device at least in one direction, with a rotationally drivable rotary mount, in particular a turntable on which a workpiece holder for a workpiece is provided, which can be positioned relative to the burner by means of a guide device. The invention further relates to a method for the internal coating of rotationally symmetrical, in particular cylindrical cavities on workpieces by thermal spraying with the aid of a burner, to which a spray material is fed, in which the burner is held at a positioning device and the workpiece is rotated relative to the burner, whereby the cavity to be coated is centered relative to the axis of the burner.

An apparatus and a method of this kind are known from M. Buchmann et al., "Solid lubricant Containing coatings for cylinder liners in pressure casted aluminum crankcase", Proceedings of the l ³ International Thermal Spray Conference, 8.-11. May 2000, Montreal, pp. 303-308.

The burner is then fixedly received on a positioning device, while the workpiece is clamped on a rotating drivable turntable.

This arrangement has advantages over the hitherto customary devices with a stationary workpiece and a rotating torch, which is usually clocked into the cavity of the workpiece to be coated, as a rule, for example in linearly arranged transfer lines. Overall, a greater distance can thus be worked, which results in a greater widening of the burner beam, which enables a more uniform surface of the coating. It is also possible to work with higher jet speeds, which significantly improves the quality of the coating. However, the exact structure of the device is not known from the aforementioned publication, which is necessary for a safe and trouble-free coating of larger workpieces, such as in the coating of cylinder liners and liners of crankcases for light metal engines.

The invention is therefore based on the object to improve a device and a method according to the type mentioned in such a way that a safe and trouble-free coating on inner surfaces is also possible with larger workpieces, the process also for series production with large numbers and short throughput times should be suitable.

This object is achieved in a device according to the type mentioned at the outset in that the guide device has at least one first linear guide with a first drive device for positioning the workpiece holder, and at least one second linear guide with a second drive device for positioning at least one counterweight, the first Drive device and the second drive device are driven in the opposite direction.

The object of the invention is further achieved in a method of the type mentioned at the outset in that an imbalance caused by movement of the workpiece is compensated for by movement of at least one counterweight.

The object of the invention is completely achieved in this way. According to the invention, an imbalance caused by the necessary centering of the cavity to be coated with respect to the burner is compensated for by a counterweight. In this way, even workpieces with a larger mass, which are irregularly shaped, such as the crankcase of reciprocating piston engines, can be rotated on the turntable at a sufficiently high speed without problems due to mass imbalance. The fact that an imbalance caused by the workpiece can always be automatically compensated for by the counterweight and thus the turntable can be balanced with respect to its axis of rotation ensures a high level of safety even at high rotational speeds of the turntable. Likewise, by compensating for the adverse effects of mass imbalances, vibrations and similar disadvantages are avoided, so that smooth running can be ensured even at higher rotational speeds. The consequence of this is that a particularly high uniformity of the coating can be achieved. For example, when coating the cylinder liners of light metal crankcases, only a post-treatment for smoothing, e.g. by honing, is necessary, but not a dimensional post-processing by machining or grinding in complex Au tensions or devices.

According to an alternative embodiment of the invention, the object is achieved in a device of the type mentioned at the outset in that the turntable is penetrated by an opening for the passage of overspray in the region of its axis of rotation.

In this way too, a particularly uniform and safe coating process without undesirable quality-reducing processes is achieved Inclusions of scattering particles from the high-energy coating and combustion process of powder-laden gas flows are guaranteed.

In this way it can be ensured that the cavity of the workpiece to be coated is centered with the opening in the turntable, so that overspray occurring during the coating process emerges downward through the cavity of the workpiece and through the opening of the turntable aligned therewith, and preferably via a Suction device can be suctioned off and removed quickly.

In this way, numerous cavities can be coated one after the other even in a series process, without there being any adverse effects from the overspray that occurs or undesirable deposits caused thereby.

In a corresponding manner, the object is achieved with regard to the method in that in the method according to the type mentioned at the outset, 0-spray which is formed during the spraying process is suctioned off through a central opening in the turntable.

In a preferred development of the invention, the workpiece holder is held on two mutually parallel first linear guides, two second linear guides each having a counterweight being provided, which are arranged parallel to the two outer sides of the first linear guides.

Here, the two counterweights are preferably of the same size and each at the same distance from the first linear guide stanchions arranged and can preferably be moved and positioned almost continuously.

In this way, even heavy workpieces can be safely balanced with respect to the axis of rotation of the turntable, resulting in a simple construction of the device.

According to a further embodiment of the invention, the first and second drive devices have drive spindles, preferably self-locking drive spindles, preferably self-locking trapezoidal spindles.

This measure has the advantage that the use of drive spindles, in particular self-locking trapezoidal spindles, ensures a high degree of reliability in centering the cavity to be coated with respect to the axis of rotation of the turntable. Furthermore, there is a high level of security against the workpiece or the counterweights moving independently, even at high rotational speeds.

In a further embodiment of the invention, the two drive spindles are driven by a common drive via a worm gear.

Here, the worm gear can be coupled to the first two drive spindles via at least one deflection gear.

In this way, both drive spindles can be driven in a simple manner by a common drive. In an additional further development of the invention, the first and second drive spindles are coupled to drive in opposite directions via deflection gears.

In this way, the opposite drive of the first and second drive spindles can be ensured with particularly simple means.

According to a further embodiment of the invention, a battery-powered DC drive is provided, which is coupled to the drive devices for the common drive.

This results in a particularly simple structure. Alternatively, a mains-powered drive for jointly driving the drive devices could also be provided, which is supplied with voltage via sliding contacts.

According to a further embodiment of the invention, limit switches are provided at the ends of the linear guides.

This contributes to a further increase in safety, since the device can be automatically stopped in the event of a displacement of the workpiece or the counterweights up to the limit switches.

The opening of the turntable for the passage of overspray can preferably be connected to a suction device.

In this way, an effective suction of overspray is guaranteed, so that there are no adverse effects can occur, which affects the quality of the coating process.

According to a further embodiment of the invention, the burner is an HVOF burner (burner for high-speed flame spraying with oxygen / fuel mixtures), which is held on the positioning device outside the workpiece.

In this way, particularly dense, well-adhering and high-quality coatings can be achieved. Since it is possible to work with a relatively large spraying distance and high kinetic energy of the particle jet up to the supersonic speed range, this also results in a greater widening of the spray jet and thus ultimately better uniformity, higher density and better adhesion of the coating.

Here, the torch is preferably moved by means of the positioning device on an elliptical path relative to the coating inner surface of the workpiece, the angle of incidence (φ) preferably between the axis of the torch and the inner surface between about 90 ° and about 10 °, preferably between about 90 ° and 20 °, is variable.

In this way, a particularly uniform coating over the circumference and height of the component can be achieved.

According to a further embodiment of the invention, at least one cooling lance for cooling the workpiece with compressed air or C0 _{2 is} provided in addition to the burner. Particularly when using a CO ₂ cooling, very good and homogeneous cooling can be ensured during the coating process. On the one hand, this avoids possible overheating problems with very temperature-sensitive workpieces or thin wall thicknesses of the base material or workpiece, such as LM crankcases, on the other hand, it avoids the adverse effects of thermally induced stresses in the coating or even optimizes the process management with regard to heat and mass transfer during the process Coating enables.

According to a further embodiment of the invention, the workpiece holder has a tilting device for tilting the workpiece relative to the axis of the burner and for representing a tilting movement according to the angular position of the bores in in-line, boxer, V and W motors or a preferably automatic turning device for pivoting of the workpiece by 180 °. These devices can be integrated in terms of control technology by means of NC methods and using programmable control devices which are part of the overall coating system.

In this way, crankcases for V-engines can also be coated automatically in a simple manner. On the other hand, workpieces can also be coated in which a part of the cavities is to be coated from one side and another part of the cavities is to be coated from the opposite side.

When using an HVOF burner, the angle of incidence (φ) is preferably between a maximum angle which is approximately in lies in a range of 90 °, varies in the TDC region of the respective cavity and an angle that decreases with increasing depth of the cavity.

In this way, when coating the cylinder liners of crankcases at the upper end of the respective cavity, a maximum impact angle of approximately 90 ° can be used, as a result of which the coating material hits the inner surface to be coated with maximum energy in this particularly highly stressed area and thus in this Area of later high stress an optimal quality and density of the coating can be achieved.

Here, the feed speed of the burner is preferably controlled approximately in proportion to the angle of incidence (φ).

In this way, the coating thickness reduced by a reduced impact angle is compensated for by the then reduced rotational speed, so that overall a uniform layer thickness is established over the entire depth of the cavity.

The burner is preferably operated continuously during the coating and is only moved away or pivoted away from the workpiece for the successive coating of different cavities in the workpiece.

In this way, through the continuous operation of the burner, particularly economical and time-saving process control can be achieved. When using an HVOF burner, a spraying distance of approximately 150 to 500 mm, preferably of approximately 150 to 400 mm, is preferably maintained between the surface of the workpiece to be coated.

The turntable is preferably driven at about 40 to 100 rpm.

With such spray parameters, particularly high-quality coatings can be achieved.

Alternatively, coating by means of atmospheric plasma spraying (APS) or electric arc spraying, preferably with internal torches, is preferably possible using a 90 ° angle torch.

In this case, a spraying distance of approximately 25 to 600 mm is preferably maintained between the inner surface of the cavity to be coated and the burner.

The turntable is preferably driven at about 80 to 200 rpm.

Advantageous coatings can also be achieved by atmospheric plasma spraying.

Since a fixed burner is also used in this case, in particular a burner with an angular head, which is moved into the cavity to be coated, this process control can achieve a higher jet speed than with conventional conventional coating process with rotating torch and stationary workpiece.

Particularly when using Ti0 ₂ as a spray material, there are advantageous coatings which are suitable for LM crank metal housings, since this results in Ti0 ₂ _ _x layers which, in addition to low wear rates, also have very low coefficients of friction under dry friction conditions.

When using an HVOF burner, the coating process can advantageously be carried out as an external coating process, the burner being located outside the cylindrical cavity of the respective bores to be coated, which is usually narrow in the case of car engines. In this way, a relatively large spraying distance can be used, which contributes to a more uniform coating. This also enables the coating of cavities with inner diameters of <50 mm.

It goes without saying that the features of the invention mentioned above and those yet to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own without departing from the scope of the invention. Further features and advantages of the invention result from the following description of preferred exemplary embodiments with reference to the drawing. Show it:

Figure 1 is a schematic representation of a first embodiment of a device according to the invention. 2 shows a schematic illustration to explain the variation of the spray angle during the movement of the burner on an elliptical path for coating the inner surface of a bore; and

Fig. 3 is a perspective view of the turntable of a device according to the invention, which was slightly modified compared to the embodiment of FIG. 1, in a simplified representation.

In Fig. 1, a first embodiment of a device according to the invention is shown schematically and generally designated by the number 10.

Within a spray booth 12, which is designed to be sound-absorbing, a turntable 14 is rotatably mounted on a table by means of a roller bearing on its outer circumference about an axis of rotation 16. The turntable can be driven by a drive 18 via a belt 20. On the turntable 14 there is a guide device, designated overall by the number 32, by means of which a workpiece holder 40 can be moved back and forth in the radial direction of the turntable 14. Provided on the tool holder 40 is a holder (not shown in more detail) for clamping a workpiece 34, which is indicated by a dash-dotted line in FIG. 1. This can be an LM crankshaft housing, for example, which has a plurality of cylinder liners whose inner surface is to be coated. In Fig. 1, a total of four cavities 36 of an LM crankshaft housing, the inner surface of which is to be spray-coated, are shown with a dash-dotted line.

The center of the turntable 14 is penetrated by an opening 17, which serves to extract overspray. A suction device 38, which is connected to a vacuum source 39, is indicated by dashed lines below the turntable 14.

An HVOF burner 24 is accommodated on a positioning device 22, which is designed as a multi-axis robot. The torch 24 can be positioned with respect to the workpiece 34 by means of the positioning device 22. Parallel to the axis 26 of the burner 24 along which the burner jet emerges are two cooling lances 28, 30 which are suitable for the radial exit of cooling gas. Although compressed air cooling would in principle be sufficient, the cooling lances 28, 30 in the present case are designed as CO ₂ cooling lances, which achieve a significantly better cooling effect. The high cooling effect of a CO ₂ cooling is based on the sublimation of the CO ₂ snow from the solid to the gaseous state. Another advantage is the cleaning effect of unmelted overspray particles.

The guide device 32 has two mutually parallel first linear guides 42, 43, on which the workpiece holder 40 can be moved. Furthermore, two second linear guides 44, 45 are provided, which are constructed identically to the first linear guides 42, 43 and enclose the two first linear guides 42, 43 from the outside. A counterweight 46, 47 can each be moved on the second linear guides 44, 45. To start Drive the guide device 32 is a battery-powered DC motor 52, which drives two 90 ° reversing gear 56, 57 via a worm gear 54. The deflection gear 56, 57 drive self-locking trapezoidal spindles 48, 49, of which the workpiece holder 40 is driven by means of spindle nuts (not shown). The trapezoidal spindles 48, 49 are coupled at their ends opposite the deflection gears 56, 57 via a 180 ° deflection gear 58, 59 with trapezoidal spindles 50, 51, of which the counterweights 46, 47 are in turn driven synchronously via spindle nuts (not shown).

A limit switch 60, 61, 62, 63 and 64, 65, 66, 67 is provided at the ends of each of the linear guides 42, 43 and 44, 45.

In Fig. 3, a slightly modified embodiment of the device according to the invention is designated by the number 10 '.

The structure of the device 10 "largely corresponds to the device according to FIG. 10. In addition, however, a tilting device is provided on the workpiece holder 40, which is indicated purely schematically by the number 74. The workpiece, for example an LM crankshaft, can be placed on the tilting device - Housing, be clamped and then tilted either to one side or to the other side in the direction of arrow 76. This is advantageous if crankshaft housings for V-engines or W-engines are to be coated.

In a corresponding manner, a turning device for turning a workpiece through 180 ° could be provided, for example if crankshaft housings are to be coated, some of which to be coated from one side and partially from the other side (such as for the six-cylinder engine of the Porsche Boxter).

The coating process is explained in more detail below.

The coating process can be either coating by atmospheric plasma spraying (APS) or electric arc spraying or by high-speed flame spraying (HVOF). A 90 ° angle torch of the GTV Fl type was used for APS interior coatings. This burner has a maximum output of 25 KW and a maximum spraying distance of 600 mm. The maximum coatable depth of the cavity was 500 mm. During the internal coating process, the angle burner plunges vertically into the rotating cavity. Due to the structural dimensions of the Fl-angle burner, only cylinder bores with an inner diameter of at least 80 mm can be coated. The achievable spray distance was at least 30 mm.

The layer is applied while rotating the workpiece while simultaneously moving the Fl plasma torch vertically. The speed of rotation of the cavity was varied between 80 and 200 rpm depending on the spraying distance and the layer system to be applied. A two-axis feed system is sufficient for a vertical feed movement of the plasma internal torch. In the case shown, however, the positioning device 22 in the form of the multi-axis robot was used. The vertical feed rate of the burner is between 2 and 10 mm / s depending on the layer system used. The number of burner transitions depends on the injection material and the required layer thickness and lies and 2 and 10 transitions. The smaller the spraying distance between the burner and the substrate surface, the smaller the widening of the particle beam and the coated surface area. Therefore, a high rotational speed of the workpiece is necessary, especially for short spraying distances, so that a homogeneous layer structure with an acceptable surface quality can be applied. At the same time as the coating process, the inner surface of the workpiece is cooled.

Either air jet compressed air cooling systems or CO ₂ cooling lances 28, 30, as described above, can be used for cooling.

When the burner 24 was designed as an HVOF burner, the TopGun® system from GTV-mbH was used for the inner coating. Due to the variable combustion chamber inserts, this type of burner also offers the option of using acetylene as the fuel gas, which can achieve combustion gas temperatures of up to 3,200 ° C. These temperatures are high enough to melt refractory materials such as MO and Zr0 ₂ . With the HVOF burner 24, spraying distances between approximately 150 mm and 500 mm can be set, depending on the spray material used, fuel gas mixture and mass flow. Due to these large spraying distances, the HVOF process can be operated as an external process, ie the burner is outside the cavity 36 of the workpiece 34 to be coated for the entire duration of the coating process. This external arrangement also allows bores with an inner diameter of less than 80 mm be coated. During HVOF spraying, the burner 24 describes an elliptical feed movement. The coating process is implemented in the coating of crankshaft housings in such a way that the TDC area of the cylinder bore, which is exposed to the highest thermal and mechanical operating loads, is coated almost below 90 °, while the lower-stressed lower cylinder areas are coated with a decreasing beam angle of incidence φ become.

These relationships are indicated in Fig. 2.

A cavity 36 to be coated is indicated in FIG. 2 in the form of a cylindrical bore in the workpiece 34.

At the upper end of the bore or cavity 36, the angle of incidence φ between the longitudinal axis 26 of the burner 24 and the inner surface 36 is approximately 90 °. As the depth of the hole increases, the spray angle φ decreases to about 30 ° at the bottom of the hole.

By adapting the feed speed of the burner 24 to the beam incident angle φ, a homogeneous layer structure and layer thickness can be achieved over the entire height of the inner surface 68 to be coated. For this purpose, the feed rate during the coating process is varied between approximately 15 mm / s (angle of incidence φ approximately 90 °) and 5 mm / s (angle of incidence φ approximately 30 °) in proportion to the angle of incidence.

Due to the complex movement kinematics, a fully automated, seven-axis robot system from Stäubli (positioning device 22) is used for the HVOF coating process. applies. The rotation speed of the turntable 14 (preferably approximately 30-100 rpm) as well as variable impact angles φ and spraying distances can be flexibly programmed via the robot control depending on the choice of the spraying material and the fuel gas mixture used.

The movement of the guide device 32, the drive speed of the turntable 14 and the movement of the burner 24 are all controlled in a coordinated manner via the robot controller. In the HVOF coating, cooling by means of CO ₂ cooling lances 24, 28 is preferably used to cool the workpiece, in particular when coating LM crankshaft housings, in order to avoid excessive heating of the workpiece 34.

For each coating of a cavity 36 of the workpiece 34, the workpiece 34 with its cavity 36 to be coated is centered with respect to the axis of rotation 16 of the turntable 14, which takes place via a corresponding actuation of the drive 56 and thus the trapezoidal spindles 42, 43.

When moving to another position, in which a further cavity 36 of the workpiece 34 is to be coated, the counterweights 46, 47 move in the opposite direction by the same amount as the workpiece 34. Thus, when the workpiece is balanced during the clamping , regardless of the radial position of the workpiece 34, a balanced state can always be achieved. Overall, the counterweights 46, 47 and the workpiece 34 can be arranged such that a balanced state with respect to the axis of rotation 16 results during the drive of the turntable 14, which is maintained even when the workpiece 34 is displaced by the mutual movement of the counterweights 46, 47.

As already mentioned above, in the middle area of the turntable 14 there is an opening 17 centered with the axis of rotation 16, through which overspray can exit downwards into the space below the turntable 14. During the coating process, the respective cavity 36 to be coated, which is open towards the bottom, is aligned with this opening 17, so that the overspray can escape freely downward, so that disruptive overspray does not have any adverse effects on the coating process , As already mentioned above, a suction device 38 can additionally be provided below the opening 18. It is understood that in this case the workpiece holder 40 must have at least one opening aligned with the opening 17 (see opening 78 according to FIG. 2), provided that the workpiece holder does not have a larger opening in the middle anyway.

Before the coating process, the inner surface 36 to be coated is pretreated by roughening, for which corundum, cast steel or a process with high pressure water jets can be used in principle.

Coatings with a number of different layer systems were tested on LM shaft housings. The resulting hardness values (HV 0.05 _M ) or porosity parameters (P _M ) and the modulus of elasticity (E _M ) are summarized in tables la), lb), lc) for ceramic layer systems, cermetic layer systems and metallic layer systems. As substrate materials Any common materials can be considered for LM crankshaft housings, such as AlMg3, Magnesium (AM50), Titan (Ti4), AlSi9Cu, AlSil7Cu4Mg3 (Alusil®), AlSi25 (Silitec®). In addition, gray cast iron crankcases and liners up to large diesel engines can be coated on the inside.

Coating tests with APS and HVOF were carried out on the substrate materials AlMg3, AM50, Ti4, AlSiCu9.

It can be seen that particularly dense layers can be achieved by using the HVOF coating process, which also have particularly good adhesion. The friction and wear coefficients of the sprayed layers were examined both under lubricated friction conditions and under dry friction conditions. The determined layer wear coefficients were all so low that all spraying materials examined apart from A1SÜ2 can be used as raceway materials.

Studies on the reworking of FeCrl7, Cr ₃ C ₂ / NiCr-80/20 and Ti0 ₂ coated individual liners have shown that these coating systems can be finished with conventional, resin-bonded diamond honing stones without additional time. Post-processing was not necessary due to the high uniformity of the sprayed layers of 0.1-0.2 mm thickness. The HVOF-sprayed coating systems in particular have very low roughness values of R _A between about 0.03 and 0.09 μm due to the very low layer porosity in the smoothly honed final state. Under dry friction conditions, the Ti0 _2.x layer systems are particularly interesting, which result from the atmospheric plasma spraying of titanium dioxide. For this very low friction coefficients could be measured under dry friction conditions. All examined coating systems except A1SÜ2 are suitable under lubricated conditions.

In addition to the application of thin layers in the order of magnitude of approximately 0.1-0.2 mm, as in the present case, to LM crankshaft housings, the described device and the described method (in particular HVOF) are also suitable for the application of thick layers in the order of magnitude of about 1 to 2 mm and also for a local spray coating at preferred locations, for example particularly stressed locations of the component in use.

Tab. La

Tab. Lb

Tab. Lc

Claims

claims

Device for the internal coating of rotationally symmetrical, in particular cylindrical cavities (36) on workpieces (34) by means of thermal spraying, with a burner (24) for spraying a coating material, the burner (24) being positioned at least in one direction on a positioning device (22) with a rotationally drivable rotary holder, in particular a turntable (14) on which a workpiece holder (40) for a workpiece (34) is provided, which can be positioned relative to the burner (24) by means of a guide device (32), that the guide device (32) has at least one first linear guide (42, 43) with a first drive device for positioning the workpiece holder (40), and at least one second linear guide (44, 45) with a second drive device for positioning at least one counterweight (46, 47), the first drive device (48, 49) and the second drive device (50, 51) are driven in the opposite direction.

Device according to claim 1, characterized in that the workpiece holder (40) is held on two mutually parallel first linear guides (42, 43), and in that two second linear guides (44, 45), each with a counterweight (46, 47), are provided , which are arranged parallel to the two outer sides of the first linear guides (42, 43).

3. Apparatus according to claim 2, characterized in that the two counterweights (46, 47) are of the same size and are each arranged at the same distance from the first linear guides (42, 43).

4. Device according to one of the preceding claims, characterized in that the first and second drive devices (48, 49, 50, 51) drive spindles, preferably self-locking drive spindles, preferably self-locking trapezoidal spindles.

5. Apparatus according to claim 2 and 4, characterized in that the two first drive spindles (48, 49) are driven by a common drive (52) via a worm gear (54).

6. The device according to claim 5, characterized in that the worm gear (54) with the two first two drive spindles (42, 43) via at least one deflection gear (56, 57) is coupled.

7. Device according to one of claims 4 to 6, characterized in that the first (48, 49) and second (50, 51) drive spindles via deflection gear (58, 59) are coupled to the opposite drive.

8. Device according to one of the preceding claims, characterized in that a battery-powered DC drive (56) is provided, which is coupled to drive devices (48, 49, 50, 51) for common drive.

9. Device according to one of the preceding claims, characterized in that the turntable (14) has an opening (17) for the passage of overspray.

10. Device according to one of the preceding claims, characterized in that limit switches (60, 61, 62, 63, 64, 65, 66, 67) are provided at the ends of the linear guides (42 - 45).

11. Device for the internal coating of rotationally symmetrical, in particular cylindrical cavities (36) on workpieces (34) by means of thermal spraying, with a burner (24) for spraying a coating material which is accommodated on a positioning device (22) so as to be positionable in at least one direction a rotatably drivable rotary holder, in particular a turntable (14), on which a workpiece holder (40) for a workpiece (34) is provided, which can be positioned relative to the axis (26) of the burner (24) by means of a guide device (32) characterized in that the rotary receptacle (14) in the region of its axis of rotation (16) is penetrated by an opening (17) for the passage of overspray.

12. The apparatus of claim 10 or 11, characterized in that the opening (17) can be connected to a suction device (38).

13. Device according to one of the preceding claims, characterized in that the burner (24) is an HVOF Is a burner, which is held on the positioning device (22) outside the workpiece (34).

14. The apparatus according to claim 13, characterized in that the burner (24) by means of the positioning device (22) on an elliptical path (72) can be positioned relative to the inner surface (68) of the workpiece (34) to be coated, the angle of incidence (φ ) between the axis (26) of the burner (24) and the inner surface (68) between about 90 ° and about 10 °, preferably between about 90 ° and 20 °, can be varied.

15. The device according to one of claims 1 to 13, characterized in that the torch is an APS torch or an electric arc torch with an angular head which can be moved into the cavity (36) of the workpiece (34) by means of the positioning device (22) is.

16. Device according to one of the preceding claims, characterized in that in addition to the burner (24) at least one cooling lance (28, 30) for cooling the workpiece (34) with compressed air or C0 _{2 is} provided.

17. Device according to one of the preceding claims, characterized in that the workpiece holder (40) has a tilting device (74) for tilting the workpiece (34) relative to the axis (26) of the burner (24) or a turning device for pivoting the workpiece (34 ) by 180 °.

18. Process for the internal coating of cavities (36) on workpieces (34) by thermal spraying with the aid of a burner (24) to which a spray material is supplied, in which the burner (24) is held on a positioning device (22) and the workpiece (34) is rotated relative to the torch (24), the cavity (36) to be coated being centered relative to the axis (26) of the torch (24), and an imbalance caused by movement of the workpiece (34) at least one balance weight (46, 47) is compensated.

19. The method according to claim 19, wherein the workpiece (34) has a plurality of rotationally symmetrical cavities (36) to be coated, the workpiece (34) being displaced linearly relative to the burner (24) for the successive coating of a plurality of cavities (36) and an imbalance caused by a movement of the workpiece (34) is compensated for by an opposite movement of the at least one balance weight (46, 47) in an opposite direction.

20. Process for the internal coating of rotationally symmetrical, in particular cylindrical cavities (36) on workpieces (34) by thermal spraying with the aid of a burner (24) to which a spray material is fed, in which the burner (24) is held on a positioning device and the workpiece (34) is rotated on a turntable, the cavity to be coated being centered relative to the axis (26) of the burner (24), overspray occurring during the spraying process is sucked off through a central opening (17) in the turntable (14).

21. The method according to any one of claims 19 to 21, are used in the crankcase as workpieces (14) preferably made of light metal, which have a plurality of cylindrical cavities (36), the inner surface (68) provided as cylinder liners is coated.

22. The method according to any one of claims 19 to 22, wherein the coating is carried out by high-speed spraying.

23. The method of claim 23, wherein the torch is moved on the elliptical path (72) relative to the workpiece (34) during coating.

24. The method of claim 23 or 24, wherein the angle of incidence (φ) between the axis (26) of the burner (24) and the inner surface (68) is varied between about 90 ° and about 10 °.

25. The method according to any one of claims 23 to 25, wherein the angle of incidence (φ) between a maximum angle, preferably in the range of about 90 °, in the TDC region of the respective cavity (36) and one with increasing depth of the cavity (36 ) decreasing angle is varied.

26. The method according to any one of claims 23 to 26, wherein the feed rate of the burner (24) is controlled approximately proportional to the angle of incidence (φ).

27. The method according to any one of claims 23 to 27, wherein the burner (24) is operated continuously during the coating and is moved away or pivoted away from the workpiece (34) for the successive coating of different cavities (36) of a workpiece (34).

28. The method according to any one of claims 23 to 28, in which a spraying distance of approximately 150 to 500 mm, preferably of approximately 150 to 400 mm, is maintained between the burner (24) and the surface of the workpiece (34) to be coated.

29. The method according to any one of claims 23 to 29, wherein the workpiece (34) is driven at about 40 to 100 rpm during the coating.

30. The method according to any one of claims 19 to 22, in which the coating is carried out by atmospheric plasma spraying or by electric arc spraying.

31. The method according to claim 31, in which a spraying distance of approximately 25 to 600 mm is maintained between the inner surface of the cavity to be coated and the burner.

32. The method of claim 31 or 32, wherein the workpiece is driven at about 80 to 200 rpm during the coating.