article

Lacquering brake discs
Eye-catching discs
They look their best when they are at rest. It is particularly when the vehicle
to which they are fitted is at a standstill that lacquered brake discs attract the
eyes of car fans. At Audi, sophisticated technology from Sprimag and Festo is
generating some striking impressions in the automotive“underworld”.
he cheapest versions are cast, but
those for well-heeled customers
are cold-forged and precision-machined using CAD
modelling and water-jet cutting machines.
Aluminium wheels are the pride and joy
of prestige-conscious drivers. Their
unquestionably good looks also have a
small disadvantage: more and more of
the wheel interior is exposed to the
critical gaze. This means that the hubs, in
particular the brake discs, are exposed to
the ravages of time. Even with the most
exquisite alloy wheels, rusty steel will
spoil the picture.
T
It is therefore fortunate that dedicated
developers from Kirchheim in Southern
Germany have found an elegant solution
to the problem. The injection machinery
manufacturer Sprimag
Spritzmaschinenbau GmbH & Co. KG
protects brake discs with lacquer
technology to prevent corrosion,
transforming them into a feast for the eye
of motorists – including those driving the
premium brand Audi. The clever feature
of this process: proportional pressure
control valves type VPPM controlled via
Profibus by a valve terminal MPA are used
to regulate the spray pressure so finely
during the lacquering process that there
is no need to mask the friction surface of
the discs to protect them against lacquer
mist. This innovative solution reduces the
consumption of lacquer with semi- and
fully-coated brake discs and makes the
finishing process quick and cost-effective.
Powerful valves: A dozen proportional valves VPPM regulate the
spray pressure precisely.
Minimised overspray
At the heart of the lacquering process is
the perfect implementation of computer
programs by pneumatic components.
Within the brake disc feed system, a laser
probe identifies the type of brake disc
and sends this information to the PLC.
The system controller sends the
appropriate data packet with the
necessary parameters for the product
specific spray pressure to the
proportional valves VPPM. The cascade
control system for these valves, with
integrated multi-sensor control, adjusts
the atomiser air, the spray jet and the
pilot air to optimum settings and reduces
overspray. This is the amount of lacquer
which escapes during spraying
applications into the environment in
Fine nozzle: No need for protective masking of brake discs which are
to be only partly lacquered.
trends in automation
Synergies 30 31
–
Eye catcher: Brake discs on the Audi R8 GT.
the form of spray mist. Minimising
overspray not only improves the quality of
the lacquer finish but also saves wear and
tear on moving machine parts and
reduces the consumption of lacquer.
“Without Festo’s
reliable technology
and great capacity
for innovation, we
could not have
realised the project
in this form.”
Georg J. Langer, Mechanical Design, Sprimag
However, the Sprimag developers were
not satisfied merely with precision. They
also succeeded in making the throughput
times extremely short. The lacquer
coating is made especially weather
resistant, shock and impact resistant by
subsequent baking in a hot air oven.
A round dozen
A unique feature of this solution, not
found anywhere else in the world, is the
interaction of twelve Festo proportional
valves VPPM. Each of the four painting
robots has three valves, each of which
provides a spray function. The first
provides for perfectly metered atomising
air, the second controls the spray jet and
the third precisely regulates the amount
of lacquer material. In comparison with a
single regulator, the Festo proportional
valves VPPM allow considerably higher
control accuracy and more dynamic
operation. The overall controlled section
is subdivided into smaller subsections
which can be controlled more accurately
in accordance with task specific
requirements; thus, not only the output
pressure but also the diaphragm pressure
is monitored in the valve. The two values
can be evaluated together, leading to
highly stable and precise control
behaviour.
The Sprimag system delivers lacquer
finishes of consistently high quality. It
requires no set up for changeovers from
one product type to another and reduces
the tubing and wiring in the two identical
lacquering systems at Audi. The twin
systems increase process reliability and
ensure that the manufacturing process is
not interrupted by malfunctions, failures
or maintenance work. At times when
demand is particularly high, both units
are operated together for a higher
production rate. ¢
www.festo.co.uk/proportional
is infoservice 21-04
Proportional pneumatics brochure
The Sprimag lacquering station
at Audi finishes a brake disc.
Sprimag
Spritzmaschinenbau
GmbH & Co. KG
Henriettenstraße 90
D-73230 Kirchheim-Teck
www.sprimag.com
Area of activity: Manufacture of
automated painting and lacquering
machines for the external coating
of series-produced workpieces
and the internal coating of metal
packaging