STEEL + TECHNOLOGY 01/2020 EXTRACT

44 | STEEL TECHNOLOGY
Strip processing lines
Wiping systems for hot-dip galvanizing lines
Danieli Kohler provides wiping systems around the world to produce high-quality coated products. The ability to
supply high-technology, customized solutions is the key to its success, with 200 installations in molten metalcoating
lines of all types. This experience allows Danieli Kohler to push the technology to new heights in terms
of performance, productivity, zinc-saving and surface-quality improvement.
A
typical air wiping equipment layout
is illustrated in figure 2. The sink/rear
stabilizing roll rig (4) and front stabilizing
roll rig (8) receive the strip from the
furnace snout, hold it in the pot, establish
entering and exiting pass-lines and work
together to flatten and stabilize the strip
between the air knives (3). As the strip rises
from the pot of molten metal, the
X-JETs meter the coating.
The precisely shaped and directed jet of
pressurized air leaves a uniform coating of
the correct thickness. Non-contact edge
baffles (5) reduce the noise and provide
consistent coating at the strip edges. The
rolls and air knives are precisely and
repeatably positioned by motorized
mounts and fixed supports.
Highly efficient blowers provide air at
the required pressure and flow rate. PLCbased
automation and an advanced HMI
make the operator’s job simple and easy.
An electromagnetic strip stabilizer can be
installed to improve strip stability and
shape.
Danieli Kohler product line
Danieli Kohler provides different product
solutions to match customer requirements.
The X-JET and Compact X-JET
(CXJ) products cover all potential customers’
requirements for new lines and the
modular design, especially of the CXJ,
allows revamping of existing systems with
minor modifications and investments.
Figure 1. Danieli Kohler air knife technology installed at a continuous galvanizing line
(Picture: Danieli)
Andrea Alessandrini, Danieli SpA, Buttrio (UD), Italy
Contact: a.alessandrini@danieli.it
These new technologies, applied for
pot equipment revamping, already have
demonstrated a payback time between
0.5 to 1 year (depending upon product
mix and metal cost). This is possible
thanks to reduction of zinc consumption
(even and more precise zinc distribution
of the coating layer cuts down overcoating);
fewer product rejects due to surface
defects (better surface appearance and
effectiveness of the wiping action are
given by sharper air jet); and average production
increase (light coating weight
production is possible at higher line
speeds).
Danieli Innov-Action
In galvanizing lines, the zinc pot offers the
most effective way to reduce costs in
operation and consumables, and at the
same time to improve product quality.
Insufficient wiping capacity often results
in a bottleneck for line productivity and
coating uniformity of the final products.
For this reason Danieli concentrates its
efforts in continuously innovating the wiping
process.
Since 2003 Danieli Kohler has carried
out an intensive R&D program on the
entire wiping process, resulting in the
development of fluid-dynamic models for
simulating air flow within the air knives and
the prediction of the final coating thickness.
Danieli Research made a significant
development of KOHLERJET air knives
design using fluid dynamics modeling.
Since the core of the wiping process is
defined by the delicate and complex fluid-dynamics
phenomena that occur when
the jet impinges on the coating surface,
the study of a numerical modeling of airknife
wiping was carried out.
After extensive tuning on a full range of
products and process parameters, these
models led to a completely new design for
the air-wiping system. The study clearly
STEEL + TECHNOLOGY 2 (2020) No. 1