Method for Coating a Component in a Dipping Bath

BACKGROUND

The disclosure relates to a method for coating a component in a dipping bath.

DE 102 10 942 B4 discloses a facility for treating articles, more particularly for the cataphoretic deposition coating of articles, more particularly of vehicle bodies. The facility in that case comprises at least one bath containing a treatment fluid into which the articles are to be immersed.

A reduction reaction may take place on the article, or on a component for coating, during the coating procedure. Through acceptance of electrons, hydrogen and hydroxide ions may be formed. This hydrogen is produced in small bubbles as a byproduct. These gas bubbles produced may adversely affect coating of the article or the component.

SUMMARY

It is an object of the present disclosure to provide a solution which allows particularly uniform coating of a component in a dipping bath even in the event of production of gas on the component.

This object is achieved in accordance with the disclosure by the subject of the independent claim. Further possible configurations of the disclosure are disclosed in the dependent claims, the description, and the figures.

The disclosure relates to a method for coating a component in a dipping bath, wherein a volume of gases produced during coating is ascertained by means of an electronic computing device for an arrangement of the component in the dipping bath, at respective points on a surface of the component. For this purpose, for example, a deposition rate of the coating may be ascertained for the respective points on the surface of the component. The computation is therefore of the deposition rate established at respective predetermined points on the surface of the component in the context of an arrangement of the component in the dipping bath. Dependent on the deposition rate ascertained, the volume of the gas produced during coating may be ascertained for the respective points by means of the electronic computing device. In other words, computation takes place to determine which volume flow of produced gas at the respective points results from the ascertained deposition rate for the respective points. Alternatively, the volume of gas produced during coating may be ascertained via an electrical potential of the component. Resistance of a layer thickness of the coating already deposited on the component influences the distribution of the electrical potential. Ascertained accordingly is the particular volume of gas occurring at the respective points on the surface of the component that is likely during coating of the component.

Additionally, with the method, by means of the electronic computing device and dependent on the ascertained volume of produced gas at the respective points, an action is triggered, thereby causing movement of the produced gas relative to the component. With the method, accordingly, an ascertainment is made as to whether and, if so, to what extent the gas produced adversely affects the coating of the component at the respective points on the surface of the component. Dependent on the adverse effect ascertained, the action is triggered, its objective being to keep particularly low any influence of the gas produced during coating on the coating of the component. This action may be performed in particular during the procedure of coating the component. In particular, on the basis of the action triggered, the gas produced at the respective points on the surface of the component during coating is transported from the respective points on the surface of the component, in order to trigger predetermined coating at these points on the surface of the component. As part of the method, the component is coated chemically, more particularly electrochemically, and so the gas is produced on the component during coating as a consequence of a voltage present at the component. This gas produced during coating may provide an insulating layer on the surface of the component that hinders the coating of the surface of the component. Via the action, the method provides at least substantial assurance that the gas produced will not keep respective regions of the surface of the component clear of the coating. As a result, particularly consistent coating of the surface of the component can be achieved.

In a further configuration of the disclosure, a flow movement of the produced gas is ascertained starting from the respective points, and the action is triggered or adapted dependent on the ascertained flow movement of the gas. In particular, the flow movement of the gas produced is ascertained by means of coupling with a multiphase computational fluid dynamics (CFD). Via the flow movement of the gas it is possible to ascertain where the gas is moving to after it has been produced at the respective points. In this case, the flow movement of the gas may be ascertained dependent on an orientation of the component in the dipping bath. The flow direction may be ascertained in particular via an ascertained buoyancy and/or an ascertained density difference between the gas and a dipping fluid contained in the dipping bath, and also dependent on tank turbulence of the dipping fluid in the dipping bath because of circulation of the dipping fluid. Via the ascertained flow direction of the gas it is possible to ascertain where the gas collects on the component. Dependent on the ascertained collection of gas on the component, the action may be triggered by means of the electronic computing device. Via the action, the gas may be transported from the component or more particularly from the location at which the gas has collected on the component. As a result, it is possible to ensure that surface regions of the component are not kept clear of the coating because of an insulating layer that forms due to the gas.

In a further configuration of the disclosure, as the action the component is moved in the dipping bath and/or by means of at least one nozzle the component in the dipping bath is subjected to flow in a targeted manner by a dipping fluid contained in the dipping bath. By the moving of the component in the dipping bath, a flow of the gas produced on the surface of the component during coating away from the surface of the component can be triggered. Alternatively, the gas produced may be moved away from a first surface region of the component toward a second surface region of the component, this being advantageous especially when this second surface region of the component already bears the coating. Consequently, the first surface region of the component can be coated after the gas has been moved away. For the moving of the component in the dipping bath, the component may be shaken, for example, in order to trigger parting of gas bubbles from the surface of the component. By subjecting the component to flow by means of the nozzle, it is possible to trigger a flow of the dipping fluid around the component, causing gas bubbles produced on the surface of the component by the dipping fluid to be transported away from the surface of the component. Furthermore, alternatively or additionally, the action may be an adaptation of a coating time for the component. This means that a time during which the component is located in the dipping bath is adapted dependent on the ascertained gas produced and/or dependent on a flow of the gas in the dipping bath, more particularly a flow of the gas along the surface of the component. Adapting the coating time ensures that at least substantially an entire surface of the component is provided with the coating during the coating procedure. In particular, the coating attaches to the surface of the component preferably in uncoated regions of the component, since as the coating thickness of the coating on the surface of the component grows, an electrical resistance at respective points on the surface of the component increases. Moreover, particularly in the case of cathodic deposition coating, alternatively or additionally, a voltage or a chronological profile of the voltage may be adapted as the action. Furthermore, alternatively or additionally, the action may be removal from the surface of a foam collecting on a surface of the dipping bath. The gas produced during the coating of the component may ascend in the dipping bath, more particularly in the dipping fluid, and may collect at the surface of the dipping fluid, so that foaming occurs due to the surface tension of the dipping fluid. If, after a coating procedure for the component, a further component is introduced into the dipping bath to be coated in the dipping bath, this further component may then carry parts of the foam collecting on the surface of the dipping bath into the dipping bath, and/or parts of the foam collecting on the surface of the dipping bath may attach to the further component and cause coating defects on the surface of the further component. In order to prevent this attachment of the foam to the further component, the foam may be removed from the surface of the dipping bath during the coating of the component and/or between respective coating procedures for the component and the further component. The foam may be removed continuously. Alternatively, removal of the foam from the surface of the dipping bath may take place only when at least a critical amount of foam has collected at the surface of the dipping bath. Determining whether at least a critical amount of foam has collected at the surface of the dipping bath may take place by means of the electronic computing device, dependent on the ascertained gas volume produced during the coating of the component. Furthermore, alternatively or additionally, the action envisaged may be that of adapting a geometry of the component. This means that, by means of the electronic computing device, the production of gas at the respective points on the surface of the component is ascertained and, consequently, the geometry of the component is adapted before the coating of the component, more particularly during a process of dimensioning the component. If the geometry of the component is adapted, the geometry of the component is altered in such a way as to promote a flow of gas produced during coating of the component away from the surface of the component. In this way, it is possible to keep the risk particularly low of surface regions of the component being kept clear by gas produced during the coating of the component.

In this context, in a further configuration of the disclosure, at least one venting aperture is provided in the component for the adaptation of the geometry. In the method, therefore, it is possible to ascertain respective regions of the component in which gas produced at the surface of the component will likely collect during the coating of the component. In these regions, the at least one venting aperture may be provided, in order to enable reliable flow of the gas away from the component. It is therefore possible to keep particularly low any risk of isolation of the region of the component in which the gas collects, thereby preventing coating of the region of the component. The provision of the at least one venting aperture hence enables particularly simple venting of respective regions of the component in which the gas produced during coating might collect.

In a further configuration of the disclosure, for the movement of the component, an orientation of the component in the dipping bath is adapted by means of an electric motor or a mechanically guided slide. In particular, for immersion into the dipping bath, the component may be held on a frame, which can be moved by means of the electric motor. Through the moving of the frame, therefore, the component held on the frame may either be immersed into the dipping bath or withdrawn from the dipping bath. Furthermore, by means of the electric motor or the mechanically guided slide, the component may be moved in such a way as to trigger detachment of the gas produced during coating from the surface of the component. By means of the electric motor or the mechanically guided slide, the orientation of the component in the dipping bath may be established with particularly simplicity.

In a further configuration of the disclosure, the orientation is adjusted dependent on an ascertained flow movement of the ascertained gas produced at the respective points. As the action, therefore, by means of the electric motor or the mechanically guided slide as conveying technology, it is possible to adapt the orientation of the component in order to promote the flow of the gas away from the surface of the component. In particular, by means of the conveying technology, the component is oriented in the dipping bath in such a way as to enable flow of the gas away from regions of the component in which the gas produced during the coating of the component has collected. For this purpose, during the coating procedure, the component may be tilted by means of the electric motor or of the mechanically guided slide, more particularly tilted a number of times, in order to ensure that the gas flows away from the surface of the component.

In a further configuration of the disclosure, for the removal of the foam from the surface of the dipping bath, the foam is blown away from the surface by means of nozzles. In that case, the nozzles may provide a flow of dipping fluid which is oriented onto the foam of the surface of the dipping bath. In particular, the mass or volume flow of dipping fluid provided by the at least one nozzle may flow along the surface of the dipping bath, causing foam collecting at the surface of the dipping bath to be blown away laterally from the surface of the dipping bath. The nozzles may further be set up to circulate the dipping fluid and/or to cause the dipping fluid to flow around the component. These nozzles may be provided for preventing sedimentation of paint particles in the dipping fluid, and may be installed in the tank of the dipping bath. By means of the nozzles, the foam can be removed particularly easily from the surface of the dipping bath.

In a further configuration of the disclosure, the component coated is a motor vehicle component, more particularly a bodywork component. This motor vehicle component, more particularly bodywork component, may be provided with the coating in the dipping bath in particular for corrosion control. Particularly in the case of complex geometries of the motor vehicle component, the method allows a coating, more particularly a paint, to be applied reliably over an entire surface of the motor vehicle component.

In a further configuration of the disclosure, the component is coated via electrophoretic deposition. More particularly, the component is provided with the coating in the method as part of a cathodic deposition coating process. In the case of electrophoretic deposition, the component is arranged in the dipping bath and a voltage is applied to the component. Because of the electrical voltage to which the component is subjected, coating particles, more particular paint particles, which are present in the dipping bath attach to the surface of the component, thereby coating the component. In particular, the component may serve as cathode, whereby hydroxide ions are produced on the component. In the case of cathodic deposition coating, a paint is deposited by virtue of chemical reactions, more particularly coagulations, of a binder. These reactions take place on the basis of a flow of electrical current from an external electrode via the conductive paint to the component acting as cathode. Cathodic deposition coating is very suitable for automated coating. It is a very eco-friendly technique, as it uses deionized water as solvent. Furthermore, cathodic deposition coating is suitable for complex geometries, allowing even internal regions of the component to be covered.

In a further configuration of the disclosure, the deposition rate for the coating is ascertained for the respective points on the surface of the component and the volume of gas produced during coating is ascertained dependent on the deposition rate, the deposition rate being ascertained dependent on a geometry of the component and/or dependent on a voltage applied in the dipping bath and/or dependent on an anode position and anode size and/or dependent on a process time and/or dependent on an electrical resistance of a liquid phase and/or of a solid phase of a dipping fluid contained in the dipping bath and/or dependent on a paint film resistance of a paint film already deposited on the component. In other words, by means of the electronic computing device, the deposition rate is ascertained using at least one of the aforementioned parameters for ascertaining the deposition rate. The greater the number of the aforementioned parameters that are used for ascertaining the deposition rate, the higher the accuracy with which the electronic computing device ascertains the deposition rate for the respective points on the surface of the component. The coating procedure may be computed, for example, by means of a networked geometry and the paint parameters described and also the predetermined voltage at the anode may be computed iteratively over time by means of FE, CFD or finite volume techniques. Alternatively, a particle-based solver may be used. A computational program used in then able to produce a solution for the coupled electrostatic field problem and a transient layer thickness development equation. Via the deposition rate, the electronic computing device is able in particular to ascertain how many hydroxide ions are produced in the reaction of coating elements contained in the dipping fluid on attachment thereof at the surface of the component. The volume or the mass of the resultant coating in one time step per element may be concluded from the deposition rate and from a density of the coating. Via the number ascertained of hydroxide ions produced during coating, it is possible with particular accuracy to compute the volume of gas produced at the respective points on the surface of the component. By back-computation from the gas produced, it is possible to conclude how many hydroxide ions have been utilized in the coating or the electrocoagulation in order to achieve the ascertained layer thickness growth. A correction factor may be included here, since possibly not all the hydroxide ions are employed for layer thickness formation. The more precisely it is possible to ascertain the respective deposition rate at the points on the surface of the component, the more accurately it is possible to ascertain the volume of gas produced at the respective points on the surface of the component, using the electronic computing device. Furthermore, it is possible to compute the formation of process gas via the current present temporally at the surface as well. As a result, conclusions may be drawn about the quantity of charge used for coating. As a result, in turn, through the equation for the electrolysis of water, conclusions may be drawn about the amount of hydrogen formed. This gas produced may serve, by coupling with a CFD code, as a transient or temporally changing boundary condition in order to compute the behavior and the transport of this gas as a result, for example, of impulse from externally or buoyancy effects.

Further features of the disclosure may become apparent form the claims, the figures, and the description of the figures. The features and feature combinations stated above in the description and also the features and feature combinations shown below in the description of the figures and/or in the figures below, can be used not only in the particular combination indicated, but also in other combinations, or on their own, without departing the scope of the disclosure.

In the drawings:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a method scheme for a method for coating a component in a dipping bath, more particularly a motor vehicle component within a cathodic deposition coating process; and

FIG. 2 shows a schematic view of a tilting procedure in which an orientation of the component arranged in the dipping bath is adapted in order to trigger a relative movement of gas produced during coating of the component to a surface of the component, as a consequence of which it can be ensured that a whole surface of the component is provided with the coating.

DETAILED DESCRIPTION

Shown in FIG. 2 is a component 12 arranged in a dipping bath 10. This component 12 is presently a motor vehicle component, more particularly a bodywork component. In its arrangement in the dipping bath 10, the component 12 is surrounded by a dipping fluid 14. Contained in this dipping fluid 14 are paint particles which can be deposited for coating the component 12 on a surface of the component 12. Presently, the paint particles are deposited via electrophoretic deposition as part of a cathodic deposition coating process. By way of this cathodic deposition coating, the component 12 is provided with corrosion control. Following the electrophoretic deposition of the paint on the surface of the component 12, gas, more particularly hydrogen, may be produced at respective points on the surface of the component 12. This gas produced may cover the surface of the component 12, so making it possible for deposition of the paint particles to be hindered by the gas in a covered region of the surface of the component 12.

Shown in FIG. 1 is a method scheme for a method for coating a component 12 in a dipping bath 10, which is intended to ensure that the surface of the component 12 is coated completely and without coating defect, by the influence of process gas, for example. The method may be carried out in particular by an electronic computing device, which is not shown in the figures. In a first method step V1 of the method, a deposition rate of the coating is ascertained for respective points on a surface of the component 12, for the arrangement of the component 12 in the dipping bath 10, more particularly in the dipping fluid 14. In this case, the deposition rate may be ascertained in particular dependent on a geometry of the component 12 and/or dependent on a voltage applied in the dipping bath 10 and/or dependent on a process time and/or dependent on an electrical resistance of a liquid phase and/or of a solid phase of the dipping fluid 14 contained in the dipping bath 10, and/or dependent on a paint film resistance of a paint film already deposited on the component 12.

In a second method step V2 of the method, a volume of gas produced during the coating is ascertained at the respective points on the surface of the component 12 by means of the electronic computing device, dependent on the ascertained deposition rate. Accordingly, via the deposition rate and by means of the electronic computing device, the quantity of gas produced in a certain time at the respective points on the surface of the component 12 during the coating of the component 12 is ascertained. In this case, it is possible to ascertain for the gas a volume flow or a source term for the mass or the volume of gas produced for the respective points on the surface of the component 12. Additionally to the volume of gas produced that is ascertained for the respective points on the surface of the component 12, the electronic computing device may be used to ascertain a flow movement of the produced gas starting from the respective points. For this purpose, modelling of the component 12 geometry to be coated, modelling of tank nozzles and/or of a circulation of the dipping fluid 14 in the dipping bath 10, and modelling of anodes of an electrophoretic coating apparatus may take place. Consequently, the electronic computing device is able to ascertain how the gas produced at the respective points on the surface of the component 12 moves in the dipping bath 10. As part of the calculation, therefore, a representation may be made of the locations at which, on the surface of the component 12, a particular volume of gas is produced, and of locations at which respective gas bubbles produced are transported along in the dipping bath 10. For ascertaining the gas produced, it is possible in particular to use a finite-volume technique or a finite-element technique. The flow movement of the gas produced may be calculated by the electronic computing device via fluid mechanics.

In a third method step V3 of the method, dependent on the volume ascertained for gas produced at the respective points on the surface of the component 12, and possibly also dependent on the flow movement ascertained for the gas produced, starting from the respective points, an action is triggered by means of the electronic computing device. Following the triggering of the action, a movement of the gas produced, relative to the component 12, is caused and/or established. As a result of the action, therefore, it is possible to exert targeted control over a movement of the gas produced at the respective points during the coating of the component 12, in order to ensure consistent coating of the surface of the component 12. A local insulating layer 16 provided by the gas blocks a field line occurring in the region of the surface of the component 12 and, consequently, blocks growth of the coating in that region of the surface of the component 12 that is covered by the insulating layer 16. The action is therefore intended to prevent the formation of the insulating layer 16 and/or the prevention of the coating of regions of the surface of the component 12.

As the action, it may be that the component 12, as shown in FIG. 2, is moved in the dipping bath 10. In this case, the component 12 may be jiggled to detach produced gas bubbles from the surface of the component 12. Alternatively or additionally, the component 12 may be adjusted in its orientation dependent on the ascertained flow movement of the produced gas ascertained at the respective points. In that case, the component 12 is moved more particularly in such a way as to prevent sustained coverage of a region of the surface of the component 12 by the gas produced. For the movement, the component 12 may be moved in particular by means of an electric motor or a slide, which mandates a defined conveying movement of the component 12, in the dipping bath 10. As can be seen in FIG. 2, an insulating layer 16 may attach to a surface of the component 12 by the gas produced, during the coating of the component 12 in the dipping bath 10. At the start, therefore, there is only coating of those regions of the surface of the component 12 with a paint film in a primary region 18 that are arranged free of coverage in relation to the insulating layer 16. If the component 12 is subsequently newly aligned in the dipping bath 10, then the region of the surface of the component 12 that is covered by the insulating layer 16 may change. Consequently, a paint film may be deposited in a secondary region 20, on a region of the surface of the component 12 that is arranged without coverage in relation to the insulating layer 16, owing to the reorientation of the component 12. Because of the paint film resistance provided by the paint film in the primary region 18, the coating first attaches to regions of the surface of the component 12 whose paint film resistance is lower than that of the paint film in the primary region 18. It is possible accordingly to achieve a coating of the component 12 with a particularly consistent film thickness of paint. Through choice of the respective orientation of the component 12 and/or through multiple defined reorientation of the component 12, dependent on the ascertained gas produced during coating, it is possible to ensure complete coating of the surface of the component 12. By reorienting the component 12 in analogy to the insulating layer 16 that is formed, complete or virtually complete coating of the surface of the component 12 can also be ensured in regions which were formerly covered by the insulating layer 16 of the nascent gas.

Alternatively or additionally, as an action the coating time may be adapted. This is advantageous especially when the component 12 is reoriented multiply during coating in order to enable complete coating of the surface of the component 12. Adapting the coating time ensures that sufficient time is available to allow the entire surface of the component 12 to be coated with the uniform film thickness.

In order to prevent accumulation of gas in a well of the component 12, as represented in FIG. 2, a geometry of the component 12 may be adapted as an action. More particularly, the geometry of the component 12 is adapted in such a way as to prevent accumulation of gas on the component 12. In this case, respective recesses in the component 12 may be designed in such a way as to enable particularly effective venting of the respective recess of gas produced during coating. Alternatively or additionally, at least one venting aperture may be provided in the component 12, enabling prevention of the accumulation of gas in respective recesses in the component 12 during the coating of the component 12.

Further alternatively or additionally, as an action, the component 12 may be subjected to flow in a targeted manner with the dipping fluid 14 by nozzles, in order to trigger detachment of gas bubbles, produced during coating, from the surface of the component 12. Furthermore, by means of the nozzles, a flow movement of the gas produced during coating may be adapted, in order to enable reliable flow of the gas away from the component 12 in the dipping bath 10.

Further alternatively or additionally, as an action, gas produced during the coating of the component 12 and collecting in the form of foam at a surface of the dipping fluid 14 may be transported away from the surface of the dipping bath 10. For this purpose, nozzles may be provided via which the foam which collects at the surface of the dipping fluid 14 in the dipping bath 10 can be blown away from the dipping bath 10. As a result, the risk of introduction of foam into the dipping fluid 14 through a further component 12 to be coated in a dipping bath 10 can be kept particularly low. In particular, adhesion of the foam on the surface of the further component when the further component is immersed into the dipping fluid 14 can be prevented. The nozzles may in particular be optimized for the removal of the foam from the surface of the dipping fluid 14.

Alternatively to the cathodic deposition coating, the component 12 may be coated in the dipping bath 10 via galvanization. The method is applicable in particular in all methods for coating components 12 that produce a gas as a waste product during chemical coating of the component 12.

The disclosure described is based on the idea that in order to ensure corrosion control on the vehicle, a cathodic deposition paint is applied to a vehicle surface of the vehicle. This is implemented by means of a rectifier which connects a direct voltage from dialysis cells or electrodes, located externally to the component 12, as anode, to the body shell as cathode. The bodyshell is therefore the component 12. Paint particles contained in the dipping fluid 14 are charged by the electrode and deposit on the cathode side and hence on the component 12. At the cathode and therefore at the component 12, a redox reaction takes place during the coating procedure. Through electron acceptance, hydrogen and hydroxide ions are formed. The hydrogen is produced in small bubbles as a secondary product. This gas produced may in certain circumstances have problematic consequences for the coating of the component 12.

A film thickness in the case of a coating produced on the component 12 as part of a cathodic deposition coating process may be based on an assumption of a computed electrical field and may be computed in a variety of different ways. In this case, for example, the Euler method or the Lagrange method may be employed. Further models with different discreditation variants are likewise possible. Apart from the geometric conditions of the component 12 and also of the dipping bath 10 with its electrodes, parameters needed for the computation are a density of the paint, a minimum specific electrical current, a coulombic efficiency, and resistances of a liquid phase and a solid phase of the paint. A ratio of coulombic efficiency to density corresponds to a deposition equivalent. These values stated as required parameters may be employed as input data for the calculation and may be calibrated on the basis of actual process parameters and/or via measurement values. For the anode, a time-variable value may be used for an input voltage. A fundamental transport equation for this is an electrical potential and a boundary condition of an electrical conductivity of the dipping fluid 14. In the case of cathodes already coated beforehand, a predefined resistance is specified which is a function of a thickness of the component 12 and its electrical conductivity. Additionally, a potential in a midpoint of the component 12 is employed in order to ascertain a paint film resistance. This potential is usually assumed to be zero, but may be calculated by additional boundary conditions, in which case there is no longer a constant potential over the component. The potential may be locally different. A deposition gradient may then be a function of the limit-specific electrical current at an interface between dipping fluid 14 and paint surface. By way of the deposition rate of individual subsegments of a complete coating time, the film thickness on the component 12 is obtained.

Insofar as the gas residues produced during coating adhere on the surface of the component 12 by virtue of their surface tension or density differences, they represent at the same time the insulating layer 16 and hence a barrier to deposition. For ideal coating, therefore, the removal of these gas residues is envisaged. Additionally, these gas residues may settle as foam on the surface of the dipping fluid 14. During a procedure of immersing the further component, the foam may remain adhering on a surface of the further component, in the event of foam penetration by the further component. Residues due to the immersion in foam may in turn constitute problems with regard to surface quality of the coating.

In the method, geometries may be represented by means of a surface network at whose cell hub or nodal point a solution is produced for equations that have already been computed. Depending on the computation method, this may take place for the terms of temperature, pressure, heat transfer coefficient, coating film deposition rate, coating film resistance, and for a coating film already deposited, iteratively in a selected time step width. On the basis of a selected element size or element area and also of the temporally varying deposition rate of the paint, it is possible to compute the mass per time step of gas produced for the respective element, using the density. In the case of cathodic deposition coating, back-calculation of the hydroxide ions produced to form the film may be used to deduce the hydrogen molecules produced during the electrolysis. Via the ratio of mass to density it is possible in turn to ascertain the volume of the gas produced. This volume of gas produced may reenter the computation through an additional source term at the respective elements. This may be coupled to fluid-mechanical solvers, and hence the transport of the gas bubbles may also be computed, taking account of the gas properties. These gas bubbles may ultimately settle either on the component 12 or at the surface of the dipping fluid 14. As a result, if a gas is produced during a coating procedure, its volume may be computed by means of a source term modified after reaction. By adding this source term, it is possible at an early stage, in particular virtually, to make an estimation of gas residues on the component 12, leading possibly to improved venting of the component 12 as a result of design changes in a vehicle architecture. At the same time, by the coupling of this new source term with commercial CFD solvers, the transport of the gas bubbles can be computed and therefore the transport of the gas bubbles can be influenced by structural alterations in paint tanks which provide the dipping bath 10.

In the text below, the computation of the film thickness growth in the context of cathodic deposition coating at time step t is described. In this case, the respective computation steps are numbered chronologically.

From the following relation, a calibrated data set may be ascertained:

$\begin{matrix} h = \int_{t_{0}}^{T} \frac{c_{paint}}{ρ_{paint}} (j_{n} - j_{\min}) dt & (1) \end{matrix}$

The entire shell thickness formed up to time T may be measured on the actual vehicle, and employed for validating/calibrating the computation. The parameters ascertained there then enter into equation (1) and/or into equation (2) as well.

The deposition rate may be ascertained by means of the following formula:

$\begin{matrix} \frac{\partial h}{\partial t} = \frac{c_{paint}}{ρ_{paint}} (j_{n} - j_{\min}) & (2) \end{matrix}$

It would be possible to employ the temporally nonconstant deposition

$\frac{c_{paint}}{ρ_{paint}}$

ratio. The current density j may be determined via the current conductivity or the resistance and the voltage has temporal initial boundary determination. The current density j is an indicator for the second technique for determining the current. Below the current density j_min, no coating takes place. j_minis a material-related parameter.

From the following equation for the cathodic electrodeposition mass of the film deposited in time step t, it is possible to compute back to the polymer NR₂:

$\begin{matrix} m = \int \int \frac{\partial h}{\partial t} dxdy \cdot ρ_{paint} & (3) \end{matrix}$

In this equation, m is ascertained relative to an area element in the xy plane.

In a first computation technique for hydrogen mass formation, a source term may be calculated from the following relation:

Example for electrocoagulation:

embedded image

Electrolysis: 4H₂O+4e⁻→4OH⁻+2H₂ (5)

In this case, the result for H₂may be employed for CFD or computational fluid

dynamics computation. A correction factor may be applied to this value.

In the case of a second computation technique for the quantity of hydrogen, the following source term may be calculated from the back-computation of the local current density:

- With computation back to the 4e⁻ from

$I = \frac{Δ Q}{Δ t} .$

(4, method 2)

- Electrolysis: 4H₂O+4e⁻→4OH⁻+2H₂(5, method 2)

The source term with the mass of hydrogen from equation (5) can then enter into the computational fluid dynamics. From the computational fluid dynamics, the following momentum equations may be used:

$\begin{matrix} \frac{D}{Dt} = ρ \frac{\partial}{\partial t} \vec{υ} + ρ (\vec{υ} \vec{\nabla}) \vec{υ} = - \vec{\nabla} p + μ {\vec{\nabla}}^{2} \vec{υ} + ρ \vec{f} & (6) \end{matrix}$

In addition, the mass retention and any turbulent modellings may be employed.

In this context, ρ=density [kg/m3], h=cathodic electrodeposition film thickness [m], t=time, T=end of the coating time [s], I=current strength [A], j_n=current density (interface), j_min=current density (minimum) [A/m2], c_paint=coulombic efficiency [kg/As], Q=electrical charge [As], x, y=element length in x or y coordinate, respectively [m].

Overall, the disclosure shows how a computation of the production and transport of gases during chemical coating procedures may take place, using cathodic electrodeposition coating as the example.

List of Reference Signs

10 Dipping bath

12 Component

14 Dipping fluid

16 Insulating layer

18 Primary region

20 Secondary region

V1-V3 Respective method steps

Method for Coating a Component in a Dipping Bath

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