Trade fairs - Lenze

Zinc, not rust
Lenze technology gets things moving in a hot dip simulator
Steelworks and research institutions are
constantly exploring more effective
processes and new alloys in order to galvanise
steel more effectively. For this
purpose many of them use hot dip simulators
made by the Japanese company
Iwatani. These systems, which incorporate
Lenze servo technology, allow production
processes to be simulated with
high precision. This helps prevent nasty
surprises when moving from the laboratory
to full-scale production.
The Iwatani hot dip process simulator
reproduces the entire sheet galvanising
process in a small space. This includes
cleaning the metal by heating it in a
hydrogen-nitrogen atmosphere before
dipping. Lenze servo technology takes
care of the movement processes within
the system, which was supplied by the
engineering specialists at Falk Steuerungssysteme
GmbH, Stadthagen.
The hot dip simulator makes use of a
9300 Servo PLC series user-programmable
servo inverter. This inverter controls an
MCS series synchronous servo motor, a
little powerhouse which in turn drives a
recirculating ball screw via a toothed
belt. This ball screw takes the metal
sample vertically through the various
zones of the machine. The processes
performed in these zones include heating
the metal by infrared or induction,
and cooling it down after galvanisation.
The 12 x 20 cm metal sample is
dipped at high speed into the zinc bath,
and remains there for only a short time.
It is then removed again in only 120 milliseconds.
“This involves an acceleration
The hot dip process simulator reproduces
large-scale production processes
with great precision.
of 25 m/s2 , which would not be possible
without tough, powerful servo motors.
They’re extremely quick,”explains Martin
Falk, proprietor of the engineering company.
The process makes use of the
entire overload capacity of the motor.
This high speed is necessary in order
to avoid what is known as the “fir-tree
effect” during hot dip galvanising, since
this would distort the laboratory results
enormously. The longer the metal plate
remains in the molten zinc, the thicker
the coating becomes. So if the sample
was dipped slowly into the liquid metal,
it would end up with a much thicker
coating of zinc at the bottom than at
the top. This effect does not actually
occur in practice during sheet metal galvanisation,
since the sheet steel passes
In action
through the zinc bath continuously, and
any given point remains immersed for
the same amount of time.
The way in which the metal sample
touches down onto the surface of the
liquid zinc is crucial to prevent the 460
degrees Celsius molten metal from
splashing. The touch-down position can
be measured using a current sensor. The
measured data is collected via the
inverter and via external subassemblies.
The 9300 Servo PLC is part of a control
assembly consisting of an industrial PC
with a bus connection, and non-central
components. The industrial PC can be
used to precisely define all of the parameters
of the machine such as gas
mixture, temperature zones and times.
This enables product and process
improvements to be simulated at a lost
cost, since very little material is used
and valuable test production capacities
are preserved.
Hard alloys
Steel is everywhere, be it in the form of
cars, bridges or high-rise buildings.
This universal material does, however,
have one great weakness: it rusts. Hot
dip galvanising offers the best protection
against rust. It involves immersing
the steel in zinc heated to more than
450 degrees Celsius. Whilst in this
zinc bath, a metallurgical reaction
takes place, and the resulting iron-zinc
alloy layers are highly durable. Treated
this way, steel is protected against corrosion
for decades, and the protective
coating can resist even severe physical
wear.
15