Influence of the natural aluminium oxide layer on ... - ALU-WEB.DE

ROLLING INDUSTRY
<strong>the</strong> essential consumers <strong>of</strong> electrical power in
a rolling mill. 60 to 80% <strong>of</strong> <strong>the</strong> electrical power
installed in a foil rolling mill are required
for <strong>the</strong> main drives, i.e. <strong>the</strong> mill motor and
<strong>the</strong> coiler drives. Accordingly, top priority to
achieve best energy efficiency is given to <strong>the</strong>
design <strong>of</strong> drives, motors and control systems
main drives <strong>of</strong> <strong>the</strong> rolling mill:
• In cold rolling mills, decoiler and recoiler
drives are connected to a common DC link,
which is fed by <strong>the</strong> rectifier unit. So <strong>the</strong> generated
power <strong>of</strong> <strong>the</strong> de-coiler, which is applying
<strong>the</strong> tension to <strong>the</strong> mill, is kept in <strong>the</strong> system
feeding <strong>the</strong> mill motor and re-coiler motor,
which are operated in motoric mode.
• Modern drive systems are additionally
equipped with an active feeder, which (contrary
to a simple rectifier) is able to feed back
electrical energy into <strong>the</strong> mains supply. Usually,
this is possible whenever <strong>the</strong> rolling mill
is stopped and <strong>the</strong> rotational energy <strong>of</strong> <strong>the</strong>
coils and rolls can be recovered by inverters
that are working in generator mode.
• Saving electrical energy is moreover possible
with efficient motors that consume fur<strong>the</strong>r
1 to 2% less electrical energy compared to
conventional motors. Considering that 99% <strong>of</strong>
<strong>the</strong> motor cost during its lifetime arises from
energy cost, also such small effects are a valuable
contribution to an efficient rolling mill.
• Besides <strong>the</strong> installation <strong>of</strong> efficient components
also an intelligent automation and control
system is a decisive factor for an efficient
rolling mill. Frequency-controlled pumps and
fans are good examples for such intelligent
and energy-saving control systems. Frequency
control allows always and continuously adjusting
<strong>the</strong> power as per <strong>the</strong> actual process
requirements. An ‘Airpure’ fan for example
can be reduced in its rotations per minute
(and accordingly power consumption) when
less air must be moved in case not all rolling
mills <strong>of</strong> a rolling mill line are in operation.
The same applies for pumps <strong>of</strong> a rolling oil
circulation system. Compared to a bypass-controlled
volume flow, <strong>the</strong> frequency-controlled
pump is able to save up to 50% <strong>of</strong> electrical
energy with a ‘Superstack’ rolling oil filtration
system.
Intelligent flow-rate control and efficient
drives for pumps and fans are good examples
for saving electrical energy with shortest return
on investment.
2.2 Rolling oil filtration
Saving electrical energy for fluid circulation is
not <strong>the</strong> only criterion for efficiency <strong>of</strong> <strong>the</strong> rolling
oil purification system. The second aspect
is maintaining <strong>the</strong> good quality <strong>of</strong> rolling oil
by perfect filtration. In that way, <strong>the</strong> lifetime
<strong>of</strong> rolling oil is maximized and fresh rolling oil
must be added to <strong>the</strong> system less frequently.
In o<strong>the</strong>r words: <strong>the</strong> SuperstackII micr<strong>of</strong>iltration
system preserves a valuable resource –
mineral-oil based rolling oil.
A third aspect <strong>of</strong> efficiency is <strong>the</strong> continuously
controlled dosage <strong>of</strong> filter aid. Depending
on <strong>the</strong> differential pressure filter aid is
added, preventing <strong>the</strong> filter cake from getting
clogged. By means <strong>of</strong> this, <strong>the</strong> filtration cycle is
extended compared to an uncontrolled forming
<strong>of</strong> <strong>the</strong> filter cake.
Final aspects <strong>of</strong> maintaining <strong>the</strong> rolling oil
quality are in-house developed Achenbach
recipes for filtration aids and additives. These
recipes are designed specifically to <strong>the</strong> customer’s
rolling processes.
The result <strong>of</strong> <strong>the</strong>se features is perfectly
clean rolling oil with extended filtration cycles,
preserving valuable resources.
2.3 Savings and recovery
For <strong>the</strong> <strong>aluminium</strong> cold rolling process a huge
amount <strong>of</strong> rolling oil is circulated for cooling
and lubricating. As this oil is applied to <strong>the</strong>
hot work rolls through sprays, a significant
amount <strong>of</strong> rolling oil is taken by <strong>the</strong> exhaust
air <strong>of</strong> <strong>the</strong> rolling mill in form <strong>of</strong> fume and mist.
Recovering that oil from <strong>the</strong> exhaust air is not
only recovering a valuable resource, but also
recovering energy in form <strong>of</strong> mineral oil. That
oil is fed back into <strong>the</strong> process without any
restrictions.
Today’s high degree <strong>of</strong> rolling oil recovery
is based on <strong>the</strong> advanced design feasible by
physical/chemical engineering. Important features
<strong>of</strong> this optimization are:
• recuperators for higher heat recovery
• improved condensers for low-temperature
distillation
• reduced pressure losses in air ducts.
Optimized fume hoods and speed-controlled
fans are fur<strong>the</strong>r criteria <strong>of</strong> <strong>the</strong> highly efficient
Airpure system. The maximized recovery <strong>of</strong>
rolling oil and <strong>the</strong> minimum energy consumption
<strong>of</strong> <strong>the</strong> Airpure exhaust air purification is
not only remarkable with respect to energy
and resources efficiency, but also for reasons
<strong>of</strong> environmental protection: A rolling mill
with an Airpure system is surpassing <strong>the</strong> strict
European restrictions for VOC emissions.
The efficiency <strong>of</strong> <strong>the</strong> Airpure system in recovering
resources becomes visible comparing
<strong>the</strong> amount <strong>of</strong> rolling oil which is recovered
from <strong>the</strong> exhaust air with <strong>the</strong> electrical energy
that is generated by a wind turbine: <strong>the</strong> typical
electrical energy generated by one state<strong>of</strong>-<strong>the</strong>-art
wind turbine for on-shore installation
is comparable to <strong>the</strong> energy (mineral oil)
recovered from one foil rolling mill.
Saving energy and resources and saving costs
here are in accordance with sustainability and
ecology <strong>of</strong> a modern <strong>aluminium</strong> cold rolling
mill. These benefits are multiplied in rolling
mill lines with three or even more rolling
mills.
3 Service and support
A crucial aspect for any pr<strong>of</strong>essional service
and support package for rolling mill machinery
is an integrative modular concept that
aims at maintaining and even increasing <strong>the</strong>
machinery performance by taking <strong>the</strong> following
measures:
• Restoring by immediate measures in <strong>the</strong>
case <strong>of</strong> breakdown
• Preserving by remote and on-site
maintenance
• Improving by optimization measures.
Optimization measures in <strong>the</strong> sense <strong>of</strong> Achenbach
Service and Support comprise:
• inspection with ‘Quick Wins’
• analysis <strong>of</strong> <strong>the</strong> process data
• options for system modernization
• sustainability measures including tele-
service.
Offering three support packages – Optiroll
check, resources and efficiency check, and
productivity check – Achenbach act as a pr<strong>of</strong>essional
partner to guarantee high efficiency
and availability <strong>of</strong> <strong>the</strong>ir rolling mills all over
<strong>the</strong> world. In order to support <strong>the</strong>ir customers
in maintaining competitive advantages in
<strong>the</strong>ir markets, Achenbach developed a concept
to ascertain fields with potential for systems’
optimization and / or conversion respectively
modernization by installing particular new
individual components. In any case, this concept
<strong>of</strong> supporting <strong>the</strong>ir customers include special
training units.
In concrete terms and in view <strong>of</strong> <strong>the</strong> important
issue <strong>of</strong> resources efficiency, this can
mean:
• new vacuum pumps for better perform-
ance <strong>of</strong> <strong>the</strong> Airpure system
• new drives for higher speed and thus
improved productivity
• new automation systems for better
product quality
• new components for continuous availabil-
ity and maintainability.
All <strong>the</strong> aforementioned facts classify Achenbach
as leaders in technology and quality
delivering everything from a single source
– mechanical engineering, machinery, and
service and support – always keeping one eye
on rolling mill efficiency in both, installation
<strong>of</strong> new machinery, modernization and supporting
high performance in <strong>the</strong> long run. �
12 ALUMINIUM · EAC CONGRESS 2011