ELECTRODEPOSITION PAINTING METHOD AND THROUGHFLOW SYSTEM FOR CARRYING OUT SAID METHOD

PROCEDE DE PEINTURE ELECTROPHORETIQUE PAR IMMERSION ET DISPOSITIF DE PASSAGE DESTINE A LA MISE EN OEUVRE DE CE PROCEDE

English Abstract

A method for the electrodeposition painting of substrates (2) in a thoughflow
system (1) according to figure (1), comprising an electrodeposition paint
basin (1.1) and overflow basin (1.2), circulating pumps (1.3) and (1.5), flow
pipes (1.8), a directed basin flow (1.9) flowing in the region of the basin
bottom (1.6) in the transport device and counter to the direction of transport
of the substrates (2) in the region of the surface of the bath (1.10), in
addition to a conveyor device (1.11) provided with devices for transporting,
rotating, immersing and removing the substates (2), wherein the substrates(2)
are disposed in the form of a cathode or anode and are supplied to the
immersion area (1.12) of the electrodeposition paint bath (1.11) via the
overflow basin (1.2) with the aid of the conveyor device (1.11), whereupon
they are rotated at an angle of > 100~ in relation to the original position
thereof during immersion in the electrodeposition paint basin (1.1), whereupon
they are transported through the electrodeposition paint basin (1.1) and are
coated, whereupon they are rotated back into the original position when they
are removed therefrom and are subsequently subjected to further machining.

French Abstract

L'invention concerne un procédé de peinture électrophorétique par immersion de substrats (2) dans un dispositif de passage (1) (fig. 1) composé d'un bac de peinture électrophorétique par immersion (1.1), d'un bac de trop-plein (1.2), de pompes de recirculation (1.3, 1.5), de tuyaux de flux (1.8), d'un système de courant ciblé (1.9) se déplaçant dans le sens de transport des substrats (2) dans le fond du bac (1.6) et contre le sens de transport à la surface du bain (1.10), et d'un système de transport (1.11) comportant des éléments de transport, de rotation, d'immersion, et d'émersion des substrats (2). Selon l'invention, les substrats (2) sont montés en tant qu'anode ou cathode et amenés au-delà du bac de trop-plein (1.2), vers le zone d'immersion (1.12) du bac de peinture électrophorétique par immersion (1.1), au moyen du système de transport (1.11), tournés d'un angle supérieur à 100· par rapport à la position initiale lors de l'immersion dans le bac de peinture électrophorétique par immersion (1.1), transportés au travers dudit bac (1.1) et revêtus, puis ramenés en position initiale lors de l'émersion et amenés vers un traitement ultérieur.

Claims

-19-
What is claimed is:
1. A method of electrocoating electrically conductive
three-dimensional substrates (2) in a continuous
installation (1) comprising
- an electrocoating tank (1.1) containing the
electrocoat material,
- an overflow tank (1.2) containing the electrocoat
material,
- at least one circulating pump (1.3) for drawing
off the electrocoat material on the base (1.4) of
the overflow tank (1.2),
- at least one circulating pump (1.5) for drawing
off the electrocoat material on the tank base
(1.6) at the end (1.7) of the electrocoating tank
(1.1) that is opposite the overflow tank (1.2),
- at least two flood pipes (1.8) for returning the
electrocoat material drawn off by way of the
circulating pumps (1.3) and (1.5) to the
electrocoating tank (1.1) at its base (1.6) in
such a way that in the electrocoating tank (1.1)
in the longitudinal direction a directed tank flow
(1.9) is produced and maintained,
- the tank flow (1.9) in the area of the tank base
(1.6) being opposite to the tank flow (1.9) in the
area of the bath surface (1.10), and

-20-
- at least one conveying device (1.11) with means of
transporting the substrates (2) to the
electrocoating tank (1.1), rotating and immersing
the substrates (2) in the electrocoating tank
(1.1) at one end thereof in the immersing area
(1.12), transporting the substrates (2) through
the electrocoating tank (1.1) in the longitudinal
direction, and rotating and emersing the
substrates from the electrocoating tank (1.1) at
its other end, as viewed in the transport
direction, in the emersing area (1.13),
wherein the substrates (2)
I. are connected as cathode or anode and
II. with the aid of the conveying device or devices
(1.11)
II.1 are supplied over the overflow tank (1.2) to
the immersing area (1.12) of the
electrocoating tank (1.1),
II.2 on immersion in the electrocoating tank (1.1)
are rotated about a horizontal axis
perpendicular to the transport direction at
an angle of > 100° to the original position,

-21-
II.3 are passed in the new orientation through the
electrocoating tank (1.1) and coated,
II.4 on emersion from the electrocoating tank
(1.1) are rotated in the emersing area (1.13)
about a horizontal axis perpendicular to the
transport direction back into the original
position, and
II.5 following emersion are passed on for further
processing,
which comprises the electrocoat material drawn off by
way of the circulating pumps (1.3) and (1.5) being
returned by way of the flood pipes (1.8) to the base
(1.6) of the electrocoating tank (1.1) in such a way as
to produce and maintain a directed tank flow (1.9)
which flows in the transport direction of the
substrates (2) in the area of the tank base (1.6) and
opposite to the transport direction of the substrates
(2) in the area of the bath surface (1.10).
2. The method as claimed in claim 1, wherein the
substrates (2) have cavities.
3. The method as claimed in claim 1 or 2, wherein the
substrates (2) are rotated in the transport direction.

-22-
4. The method as claimed in any of claims 1 to 3,
wherein the substrates (2) are vehicle bodies,
radiators or casings of washing machines, dishwashers
or ovens.
5. The method as claimed in any of claims 1 to 4,
wherein the substrates (2) are oriented transverse to
the axis of rotation or longitudinally to the axis of
rotation.
6. The method as claimed in any of claims 1 to 5,
wherein on immersion in the electrocoating tank (1.1)
the substrates (2) are rotated in the transport
direction at an angle of about 180° or 180° to the
original position.
7. The method as claimed in any of claims 1 to 6,
wherein on transport through the electrocoating tank
the substrates (2) are moved.
8. The method as claimed in any of claims 1 to 7,
wherein the substrates (2) are connected as cathode.
9. The method as claimed in claim 8, wherein the
electrocoat material is a cathodically depositable
electrocoat material.
10. The method as claimed in any of claims 1 to 9,
wherein the electrocoat material drawn off by means of

-23-
the circulating pumps (1.3) and (1.5) is filtered (1.14)
before being returned to the electrocoating tank (1.1).
11. The method as claimed in claim 10, wherein the
electrocoat material drawn off is subjected to
ultrafiltration.
12. The method as claimed in any of claims 1 to 11,
wherein the continuous installation (1) comprises at
least one power supply, electronic, mechanical, and
pneumatic measurement and control devices, electric
motors, overflow devices, heat exchangers, devices for
the supply of electrocoat material, electrocoat
material components, and neutralizing agents,
ultrafiltration units, filters, anolyte circuits for
the cathodically depositable electrocoat material, and
rinsing zones.
13. A continuous installation (1) for implementing the
method as claimed in any of claims 1 to 12, comprising
- an electrocoating tank (1.1) containing the
electrocoat material,
- an overflow tank (1.2) containing the electrocoat
material,
- at least one circulating pump (1.3) for drawing
off the electrocoat material on the base (1.4) of
the overflow tank (1.2),

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at least one circulating pump (1.5) for drawing
off the electrocoat material on the tank base
(1.6) at the end (1.7) of the electrocoating tank
(1.1) that is opposite the overflow tank (1.2),
- at least two flood pipes (1.8) for returning the
electrocoat material drawn off by way of the
circulating pumps (1.3) and (1.5) to the
electrocoating tank (1.1) at its base (1.6) in
such a way that in the electrocoating tank (1.1)
in the longitudinal direction a directed tank flow
(1.9) is produced,
- the tank flow (1.9) in the area of the tank base
(1.6) being opposite to the tank flow (1.9) in the
area of the bath surface (1.10),
- at least one conveying device (1.11) with means of
transporting the substrates (2) to the
electrocoating tank (1.1), rotating and immersing
the substrates (2) in the electrocoating tank
(1.1) at one end thereof in the immersing area
(1.12), transporting the substrates (2) through
the electrocoating tank (1.1) in the longitudinal
direction, and rotating and emersing the
substrates from the electrocoating tank (1.1) at
its other end in the emersing area (1.13),
- an immersing area (1.12) at the end of the
electrocoating tank (1.1), to which the overflow
tank (1.2) connects, and

-25-
- an emersing area (1.13) at the other end of the
electrocoating tank (1.1) as viewed in the
transport direction of the substrates,
wherein the directed tank flow (1.9) in the area of the
bath surface (1.10) is opposite to the transport
direction of the substrates (2).
14. The continuous installation (1) as claimed in
claim 13, which comprises at least one power supply,
electronic, mechanical, and pneumatic measurement and
control devices, electric motors, pumps, overflow
devices, heat exchangers, devices for the supply of
electrocoat material, electrocoat material components,
and neutralizing agents, ultrafiltration units,
filters, anolyte circuits for the cathodically
depositable electrocoat material, and rinsing zones.

Description

CA 02523210 2005-10-21
1
ELECTRODEPOSITION PAINTING METHOD AND THROUGHFLOW
SYSTEM FOR CARRYING OUT SAID METHOD
The present invention relates to a new method of
electrocoating electrically conductive three-
dimensional substrates in a continuous installation.
The present invention also relates to a new continuous
installation for implementing the new method of
electrocoating electrically conductive three
dimensional substrates.
Methods of immersing and emersing electrically
conductive three-dimensional substrates, especially
vehicle bodies, in and from the electrocoating bath of
a continuous installation are known from patent
applications DE 196 41 048 Al, EP 1 170 063 Al, WO
98/15359 A1, WO 0111'7691 A1 and European patent EP 0
929 365 Bl and from publications, such as 'Status of
RoDip Experience: RoDip-3 - New Rotational System for
High Capacity Automotive Paint Finishing", DLJRR,
Schorbacherstrasse 9, 35510 Butzbach, Federal Republic
of Germany; Anonymous, "New technology for high
capacity pretreatment and electrocoating of motor
vehicle bodies", Surface World 2002, Volume 9, No. 3,
page 44, or K. Werner, "Improvement in surface quality
by continuous rotational dipping", Besser Lackieren,
2000, Volume 2, No. 13, page 4. In these known methods
the vehicle bodies are immersed in the electrocoating

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tank with rotation about a horizontal axis
perpendicular to the transport direction at an angle >
100° to their original position. On emersion from the
electrocoating tank they are then again rotated about
the horizontal axis perpendicular to the transport
direction into their original position. In total the
substrates execute a rotation of 360°.
These known continuous installations are shorter than
the known continuous installations in which the vehicle
bodies are not rotated during immersion and emersion.
In the methods in which the vehicle bodies are rotated
during immersion and emersion, moreover, there are
fewer sediments, if indeed any at a11, on the areas of
the vehicles bodies which will become visible later,
such as the outside of the roof, of the hood, and of
the trunk lid, so that there is no need for labor-
intensive work subsequently, such as sanding, polishing
or buffing, on the resulting electrocoat. The other
side of the coin is that these sediments accumulate to
a greater extent in the area of the insides of the
roof, of the hood, and of the trunk lid; however, since
these areas do not become visible later on, this causes
no further disruption to the overall appearance of the
finished vehicle.
Rotation of the vehicle bodies does, however, introduce
the drawback that the foam that is formed when the
vehicle bodies are immersed is caught by the cavities

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and the underbody, which can lead to coating defects
and considerable detractions from quality in terms of
corrosion control, which is especially critical in the
area of the underbody and of the cavities. These
coating defects may also arise as a result of the
hydrogen which is formed during electrolysis and
caught.
It is an object of the present invention to find a new
method of electrocoating electrically conductive three-
dimensional substrates in a continuous installation in
the course of which the substrates are rotated on
immersion and emersion so that on their outsides of
particularly high subsequent visibility there is less
sedimentation or none at all and where the foam formed
during immersion of the substrates and/or the hydrogen
formed during electrolysis in critical areas of the
substrates no longer lead/leads to coating defects and
considerable detractions from quality in terms of
corrosion control.
It was a further object of the present invention to
provide a new continuous installation permitting the
implementation of a method of electrocoating
electrically conductive three-dimensional substrates in
a continuous installation in the course of which the
substrates are rotated on immersion and emersion so
that on their outsides of particularly high subsequent
visibility there is less sedimentation or none at all

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and where the foam formed during immersion of the
substrates and/or the hydrogen formed during
electrolysis in critical areas of the substrates no
longer lead/leads to coating defects and considerable
detractions from quality in terms of corrosion control.
The invention accordingly provides the new method of
electrocoating electrically conductive three
dimensional substrates in a continuous installation
comprising
- an electrocoating tank containing the electrocoat
material,
- an overflow tank containing the electrocoat
material,
- at least one circulating pump for drawing off the
electrocoat material on the base of the overflow
tank,
- at least one circulating pump for drawing off the
electrocoat material on the tank base at the end
of the electrocoating tank that is opposite the
overflow tank,
- at least two flood pipes for returning the
electrocoat material drawn off by way of the
circulating pumps to the electrocoating tank at
its base in such a way that in the electrocoating
tank in the longitudinal direction a directed tank
flow is produced and maintained,

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- the tank flow in the area of the tank base being
opposite to the tank flow in the area of the bath
surface, and
at least one conveying device with means of
transporting the substrates to the electrocoating
tank, rotating and immersing the substrates in the
electrocoating tank at one end thereof in the
immersing area, transporting the substrates
through the electrocoating tank in the
longitudinal direction, and rotating and emersing
the substrates from the electrocoating tank at its
other end in the emersing area,
wherein the substrates
I. are connected as cathode or anode and
II. with the aid of the conveying device or devices
II.1 are supplied over the overflow tank to the
immersing area of the electrocoating tank,
II.2 on immersion in the electrocoating tank are
rotated about a horizontal axis perpendicular
to the transport direction at an angle of
> 100° to the original position,
II.3 are passed in the new orientation through the
electrocoating tank and coated,

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II.4 on emersion from the electrocoating tank are
rotated in the emersing area about a
horizontal axis perpendicular to the
transport direction back into the original
position, and
II.S following emersion are passed on for further
processing,
which involves the electrocoat material drawn off by
way of the circulating pumps being returned by way of
the flood pipes to the base of the electrocoating tank
in such a way as to produce and maintain a directed
tank flow which flows in the transport direction of the
substrates in the area of the tank base and opposite to
the transport direction of the substrates in the area
of the bath surface.
The new method of electrocoating electrically
conductive, three-dimensional substrates in a
continuous installation is referred to below as "method
of the invention".
The invention also provides the new continuous
installation for implementing the method of the
invention, comprising
- an electrocoating tank containing the electrocoat
material,

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_ 7 _
- an overflow tank containing the electrocoat
material,
- at least one circulating pump for drawing off the
electrocoat material on the base of the overflow
tank,
- at least one circulating pump for drawing off the
electrocoat material on the tank base at the end
of the electrocoating tank that is opposite the
overflow tank,
- at least two flood pipes for returning the
electrocoat material drawn off by way of the
circulating pumps to the electrocoating tank at
its base in such a way that in the electrocoating
tank in the longitudinal direction a directed tank
flow is produced,
- the tank flow in the area of the tank base being
opposite to the tank flow in the area of the bath
surface,
- at least one conveying device with means of
transporting the substrates to the electrocoating
tank, rotating and immersing the substrates in the
electrocoating tank at one end thereof in the
immersing area, transporting the substrates
through the electrocoating tank in the
longitudinal direction, and rotating and emersing
the substrates from the electrocoating tank at its
other end in the emersing area,
- an immersing area at the end of the electrocoating
tank, to which the overflow tank connects, and

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- an emersing area at the other end of the
electrocoating tank as viewed in the transport
direction of the substrates,
wherein the directed tank flow in the area of the bath
surface is opposite to the transport direction of the
substrates.
The new continuous installation for implementing the
method of the invention is referred to below as
'installation of the invention".
In the light of the prior art it was surprising and
unforeseeable for the skilled worker that the objects
on which the present invention was based could be
achieved by means of the method of the invention and
the installation of the invention.
In particular it was surprising that the substrates
coated by means of the method of the invention
exhibited very few if any of the sedimentation-induced
coating defects on the outsides which were subsequently
of high visibility. In addition they no longer
exhibited any foam-induced coating defects in critical
areas, such as cavities. A particular surprise was that
these advantages were achievable with comparative
simplicity by modifying existing continuous
installations.

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_ g _
Accordingly the substrates coated by means of the
method of the invention were clearly superior to the
conventionally coated substrates in terms of overall
appearance and corrosion control. These particular
advantages of the method of the invention appeared with
particular advantage in the case of vehicle bodies,
especially motor vehicle bodies, since it is
particularly in the case of motor vehicles, especially
automobiles, that especially stringent requirements are
imposed on the appearance of the visible outsides and
on corrosion control in the area of the cavities and of
the underbody.
A further surprise was that the installations of the
invention could be provided with comparative simplicity
without great financial, technical, and workplace
safety expenditure, by modification of existing
continuous installations, so that there was no need for
investment in new plant.
The installation of the invention and the method of the
invention serve to coat electrically conductive three-
dimensional substrates, especially vehicle bodies,
radiators, and casings of washing machines,
dishwashers, and cookers, with a conventional
electrocoat material. The electrocoat material may
familiarly be depositable either anodically or
cathodically, especially cathodically. This coating
method is, as is known, termed electrocoating and the

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installation termed an electrocoating installation (cf.
Rompp Online, 2002, "Electrocoating installation",
"Electrocoat materials", and "Electrocoating", and also
the BASF Lackiertechnik handbook, BASF Coatings AG,
2002, Vincentz Verlag, Hannover, pages 497 to 520).
The installation of the invention is a continuous
installation, i.e., it is used to coat substrates which
are supplied continuously to the installation of the
invention and taken off continuously from it again.
The installation of the invention comprises the
following essential elements:
- an electrocoating tank containing the electrocoat
material,
- an overflow tank containing the electrocoat
material,
- at least one, especially one, circulating pump for
drawing off the electrocoat material on the base
of the overflow tank,
- at least one, especially one, circulating pump for
drawing off the electrocoat material on the tank
base at the end of the electrocoating tank that is
opposite the overflow tank,
- at least two, preferably at least three, very
preferably at least four, with particular
preference at least five, and in particular at
least six flood pipes for returning the

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electrocoat material drawn off by way of the
circulating pumps to the electrocoating tank at
its base in such a way that in the electrocoating
tank in the longitudinal direction a directed tank
flow is produced,
- the tank flow in the area of the tank base being
opposite to the tank flow in the area of the bath
surface, i.e., so that the tank flow is made
circulating;
- at least one, especially one, conveying device
with means of transporting the substrate to the
electrocoating tank, rotating and immersing the
substrates in the electrocoating tank at one end
thereof in the immersing area, transporting the
substrates through the electrocoating tank in the
longitudinal direction, and rotating and emersing
the substrates from the electrocoating tank at its
other end in the emersing area, as known for
example from patent applications DE 196 41 048 Al,
EP 1 170 063 A1, WO 98/15359 A1, WO 01/17691 Al
and European patent EP 0 929 365 B1 and from
publications, such as "Status of RoDip Experience:
RoDip-3 - New Rotational System for High Capacity
Automotive Paint Finishing", D(JRR,
Schorbacherstrasse 9, 35510 Butzbach, Federal
Republic of Germany; Anonymous, "New technology
for high capacity pretreatment and electrocoating
of motor vehicle bodies", Surface World 2002,
Volume 9, No. 3, page 44, or K. Werner,

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'Improvement in surface quality by continuous
rotational dipping", Besser Lackieren, 2000,
Volume 2, No. 13, page 4, in detail,
- an immersing area at the end of the electrocoating
tank, to which the overflow tank connects, and
- an emersing area at the other end of the
electrocoating tank as viewed in the transport
direction of the substrates.
The installation of the invention may further comprise
conventional, additional elements necessary for its
operation, such as at least one power supply,
electronic, mechanical, and pneumatic measurement and
control devices, electric motors, pumps, overflow
devices, heat exchangers, devices for supplying
electrocoat material, electrocoat material components,
and neutralizing agents, ultrafiltration units,
filters, anolyte circuits for the cathodically
depositable electrocoat, and rinsing zones. These
elements are known for example from Rompp Online, 2002,
"Electrocoating installation", ~~Electrocoat materials",
and ~~Electrocoating", and also the BASF Lackiertechnik
handbook, BASF Coatings AG, 2002, Vincentz Verlag,
Hannover, pages 497 to 520.
For the installation of the invention it is essential
that the directed tank flow in the electrocoating tank
is made circulating such that it is opposite to the
transport direction of the substrates in the area of

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the bath surface. A preferred means of accomplishing
this is to return the electrocoat material drawn off by
way of the circulating pumps to the electrocoating bath
at the tank base by way of the flood pipes opposite to
the transport direction of the substrates.
The installation of the invention serves to implement
the method of the invention.
In the method of the invention the substrates are
connected as cathode or anode, in particular as
cathode, and with the aid of the conveying device or
devices are supplied over the overflow tank to the
immersing area of the electrocoating tank, on immersion
in the electrocoating tank are rotated about a
horizontal axis perpendicular to the transport
direction at an angle of > 100°, in particular at an
angle of about 180° or 180°, to the original position,
transported in the new orientation through the
electrocoating tank and coated, on emersion from the
electrocoating tank rotated back into the original
position about a horizontal axis perpendicular to the
transport direction in the emersing area, and following
emersion are passed on for further processing.
For the method of the invention it is essential that
the electrocoat material drawn off by way of the
circulating pumps is returned by way of the flood pipes
to the base of the electrocoating tank in such a way as

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to produce and maintain a directed tank flow which
flows in the transport direction of the substrates in
the area of the tank base and opposite the transport
direction of the substrates in the area of the bath
surface.
Before being returned to the electrocoating tank the
electrocoat material drawn off is preferably filtered,
in particular by ultrafiltration.
For the method of the invention it is advantageous if
the substrates are rotated in transport direction. In
the course of such rotation they may be oriented
transverse to the axis of rotation or longitudinally to
the axis of rotation.
It is also of advantage for the method of the invention
if during their transport through the electrocoating
tank the substrates are moved, in particular are
seesawed in the transport direction or transverse
thereto and/or lowered down and up perpendicularly to
the transport direction.
The installation and method of the invention are
illustrated with reference to Figure 1.
In Figure 1 the reference numerals have the following
meanings:

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(1) continuous installation,
(l. l) electrocoating tank,
(1.2) overflow tank,
(1.3) circulating pump for drawing off the
electrocoat material at the base (1.4) of the
overflow tank (1.2),
(1.4) base of the overflow tank (1.2),
(1.5) circulating pump for drawing off the
electrocoat material at the tank base (1.6),
(1.6) tank base at the end (1.7) of the
electrocoating tank (1.1) opposite the overflow
tank (1.2),
(1.7) end of the electrocoating tank (l. l) opposite
the overflow tank (1.2),
(1.8) flood pipes,
(1.9) tank flow,
(1.10) bath surface,
(1.11) conveying device,

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(1.12) immersing area,
(1.13) emersing area,
(1.14) filter, and
(2) substrates, especially vehicle bodies.
Uncoated vehicle bodies (2) were joined redetachably to
the conveying device (1.11) in conventional fashion
(cf. for example German patent application DE 196 41
048 A1). The conveying device (1.11) contained
conventional means of transporting the vehicle bodies
(2) over the overflow tank (1.2) to the electrocoating
tank (1.1), means of rotating and immersing the
substrates (2) in the electrocoating tank (1.1) in the
immersing area (1.12), means of transporting the
vehicle bodies (2) through the electrocoating tank
(1.1) in the longitudinal direction, and means of
rotating and emersing the vehicles bodies (2) at the
end of the electrocoating tank (l.l) opposite the
overflow tank (1.2), in the emersing area (1.13).
The vehicle bodies (2) were connected as cathodes and
with the aid of the conveying means (1.11) were
immersed and rotated on immersion about a horizontal
axis perpendicular to the transport direction at an
angle of 180°, transported through the electrocoating
tank (1.1), in which they were coated with a

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conventional cathodic electrocoat material, and in
coated condition were emersed, in the course of which
they were rotated back into the original position about
a horizontal axis perpendicular to the transport
direction. Following emersion they were passed on by
means of the conveying device (l.ll) for further
processing, in particular for the drying and thermal
curing of the cathodically deposited electrocoat film,
thereby resulting in the electrocoated vehicle bodies
(2) .
In the course of electrocoating the electrocoat
material was drawn off with a circulating pump (1.3) at
the base (1.4) of the overflow tank (1.2) and drawn off
with a circulating pump (1.5) at the tank base (1.6) at
the end (1.7) of the electrocoating tank (1.1) opposite
the overflow tank (1.2), and filtered (1.14). The
filtered electrocoat material was returned by way of
flood pipes (1.8) to the electrocoating tank (1.1) at
its base (1.6) so that in the longitudinal direction a
directed tank flow (1.9) was produced and maintained.
The tank flow (1.9) in the area of the tank base (1.6)
was opposite to the tank flow (1.9) in the area of the
bath surface (1.10). The exit apertures of the flood
pipes (1.8) were oriented in such a way that the
directed tank flow (1.9) flowed in the transport
direction of the vehicle bodies (2) in the area of the
tank base (1.6) and opposite to the transport direction

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of the vehicle bodies (2) in the area of the bath
surface (1.10).
The electrocoated vehicle bodies (2) no longer
exhibited any paint defects induced by foam and/or
hydrogen caught in the underbody area and in the
cavities. The corrosion protection effect of the
electrocoats was therefore outstanding. In those areas
of the vehicle bodies which would later be outwardly
visible, such as the outsides of the roof and the
outsides of the hoods and trunk lids, there were no
paint defects induced by sedimentation, so that prior
to overcoating there was no need for any
aftertreatment, such as sanding, polishing or buffing.