Amazing Results of a test made with Liquid Nitrogen for Die Cooling with Isothermal Extrusion.

1. ICEB 2011-International Conference on Extrusion and Benchmark 3-5 October 2011, Bologna, Italy
Liquid Nitrogen for Die Cooling
A. Sala
S.A.I. srl Società Automazione Industriale, Molinetto, Brescia, Italy, sai@sai-automation.com
Keywords: Liquid Nitrogen, Die Cooling, Isothermal Extrusion, Profile Quality, Die Life.
Publication on: Industrial journal .
Paper
IES Isotermal Extrusion SAI can extrude the aluminum profile at a constant temperature,
increasing the speed (and hence productivity), while maintaining quality standards, realizing the
theorem of isothermal extrusion. The system is fully automatic and is based on reliable data from the
plant and intelligent: it continues to adjust itself in view of ongoing production and optimizing existing
resources in the plant.
The production in some cases needs to use liquid nitrogen to cool the dies. If the traditional
method involves the opening or the full closure of the valve and then a steady stream of 100% or its
absence, with the function of die cooling running in the context of isothermal extrusion made by IES,
the flow of liquid nitrogen is given considering the real needs of production, resulting in significant
reduction in the consumption of nitrogen. Nitrogen is in fact used at the beginning of extrusion, only to
inert the surface of the profile, whereas the die has not yet warmed to such an extent as to require
cooling.
As the billet is extruded and the temperature of the die grows, the flow of nitrogen is increased
gradually to cool the die and preserve its integrity and structure.
Figure 1: Usage of Liquid nitrogen managed by Isothermal Extrusion SAI (IES)
(a)

2. The cooling of the dies managed by IES, which provides the extrusion profile at a constant
temperature, can increase the extrusion rate of 30% average
Where the system is used, there was an increase of 20% of die life and no breakage of the dies.
The extruded profile, even in extreme conditions, where the plant was pushed to the limit, has
maintained the surface quality and has confirmed the validity of the treatment with nitrogen in terms
of hardness after aging treatment.
Below we are presenting a show case company. The data relate to tests carried out at Pandolfo
Aluminium s.r.l. using a 6060 alloy.
Figure 2: Liquid nitrogen constant use. Profile temperature reduced of 10°C.
Test to detect the variation of surface temperature of profile in relation to die cooling with liquid
nitrogen. The test is performed on billets 7. The first 4 were extruded with the parameters of extrusion
speed and billet temperature constant without cooling. The 5 and 6 billets were extruded with a flow of
liquid nitrogen. Note the reduction of the temperature profile of 10 ° C.
Figure 3: Liquid nitrogen constant use. Profile temperature reduced of 20°C.
(b)
(c)

3. The profile used is the same as the previous chart, but with a different die version. The test is
performed on 10 billets. Die cooling with liquid nitrogen starts from the third and stops at the ninth
billet varying from 40% to 70% of flow. Billet temperature and extrusion rate are constant. In this case
the reduction of the profile temperature in proportion to the flow of nitrogen reaches 20 °C
Figure 4: Liquid nitrogen use at constant speed and reducing billet temperature.
The figure above shows a test similar to previous, but with a different profile. The reduction of the
temperature profile is of 12 °C, while the temperature of the last billet was reduced by 10 °C. The
effect is seen in increasing the peak pressure.
Figure 5: Liquid nitrogen use with constant speed.
Another profile tested on 4 billets results in constant billet temperature and extrusion rate. The die
cooling with liquid nitrogen starts from the second billet and its flow constant for the whole test
doesn’t reach the maximum flow: the self regulation doesn’t require it.
(d)
(e)

4. Figure 6: Simulation of SAI Isothermal Extrusion
Test made using liquid nitrogen at constant profile temperature, increasing speed, reducing billet
temperature maintaing accettable the quality. The SPEED INCREASED of 30% (from 19 m/min to 30
m/min).
Figure 7: Simulation of SAI Isothermal Extrusion
Test made using liquid nitrogen at constant profile temperature, and dynamic speed and reducing billet
temperature. In this case the speed has been reduced to respect the set limit. 45% INCREASE SPEED
(From 13 m/min to 27 m/min)
(f)
(g)

5. Figure 8: Simulation of SAI Isothermal Extrusion
Test made using liquid nitrogen at constant profile temperature, and dynamic speed and reducing billet
temperature. It results in 43% INCREASE SPEED (From 26 m/min to 40 m/min).
Significant results concerning the surface quality of the profile: thanks to the die cooling, the profile is
extruded at a lower temperature significantly reducing the problem of the pick-up that occurs mainly
on the profiles of small thickness.
By analysis of the cost of choice to manage the flow of liquid in the extrusion process for die cooling,
the collected data confirm the validity, as illustrated above, in terms of increasing the extrusion speed
(up to 45 % more) and therefore productivity.
In addition, the die cooled in a controlled manner, maintaining its temperature below the threshold of
"annealing", protecting the work surface from erosion exerted by aluminum during its passage
(duration of die life augmented about 20%)
Another positive result can be seen by comparing the consumption of liquid nitrogen between the use
of traditional on-off solution and the SAI automatic solution that regulates the flow depending on the
actual cooling needs: on average, the savings is around 40% .
Bibliography:
Agostino Sala, “Pick up, ripples and micro scratches”, in AL Alluminio e Leghe, 2, 2010, 88-89
(h)