Device for the gravitational self-voiding of liquid-state alloys or metals under their own weight.
Marta, Constantin ; Midan, Aurel ; Suciu, Lenuta 等
1. INTRODUCTION
The metallic alloys must comply with increasingly rigorous quality
norms, and the level of inclusions and gases should be minimum (Hance,
2001). The degassing or voiding installations used are made of pieces of
equipment that must be insulated from the external environment, require
voiding whenever one introduces another quantity of alloy, and sometimes
it is necessary to assure the existence of a reheating system, which
implies high costs, as well as a long liquid treatment time. The
literature has a rich supply when it comes to the presentation of
voiding systems, but all the systems presented are very complicated and
require high costs of maintenance and operation. We conceived a simple
voiding system, which uses the vacuumetric effect created by the
controlled flow of a liquid from a closed space into a collecting ladle.
The system is in the stage of model, and it was tested in the laboratory
of mechanics of fluids. After the model shape became definitive we
effected calculations of the filling time (Procast, 2008) of the device,
and calculations on the emptying time, and also on the filling of a
collecting ladle. We continued by performing simulations on the filling
and flowing of alloys in the modular voiding system. The system was
conceived for a quantity of 12 t liquid steel. The system can be applied
also to other types of alloys.
2. INFORMATION
The principle of the method is based on the casting through siphon devices of a liquid into a space which, at the moment of filling, is
sealed. The vacuumetric effect is created by the controlled flow of the
liquid from this space into a collecting ladle. The components and
construction of the modular self-voiding system are shown in figure 1.
The upper part of the device contains a separating wall of the passage
diaphragm type, for liquid. The liquid filling rate is higher than the
rate of emptying into the ladle. At the upper part the device contains
" vent " type sealing elements.
[FIGURE 1 OMITTED]
These vents function as valves for the elimination of the air
during filling and are blocked the moment the designated liquid level is
reached.
The components of the system are the following :
1. Gas evacuation valve
2. Alloy jet
3. The space destined to self-voiding
4. Diaphragm
5. The siphon-type space for feeding with liquid alloy. The liquid
column in this space will decrease in height during evacuation, down to
the level of the passage gallery.
6. Liquid alloy passage gallery
7. Evacuation orifice
8. Drawer-type closing-opening device
9. Collecting ladle
The vents or valves (1) allow the evacuation of air during the
space filling (3) and they are blocked when the level designed in this
space is reached. The blocking is done either through the solidification
of the alloy inside them (the vents are made of 6 orifices with the
diameter of 30 mm each), or by means of mechanic valves. Through the
lower side, which contains the evacuation orifice, one can control the
emptying rate or time, with << drawer >>-type mechanism (8),
or the dimensioning through calculus of the orifice (7), for assuring
the proposed level of the alloy in space (3).
[FIGURE 2 OMITTED]
3. DESCRIPTION OF THE SYSTEM FUNCTIONING
The self-voiding effect will manifest itself when the valves are
blocked and the liquid column in feeding space (5) reaches the level of
the liquid in space (3). After the filling of the system, figure 3.a, at
the moment of the drawer opening, the liquid column in the feeding space
(5) drops the first, and the collecting ladle begins to be fed, whereas
the liquid level goes under the level of the entry into gallery (6). At
that moment we witness the feeding of an air quantity under diaphragm
(4). The air absorbed produces the lowering of the liquid level from
space (3), figure. 3.b., as through heating it increases its volume,
triggering the increase of the pressure under the diaphragm. Thus part
of the liquid will flow into the collecting ladle, and another volume
will rebalance the liquid volume in the feeding network (5), based on
the principle of communicating vessels, (Campean, 2006) the process of
liquid lowering-rising being much more complex and cyclic. The new gas
volume penetrating into (3) through expansion cools off and diminishes
in volume, which produces a shock (impulse) effect for the new voiding
cycle. Under the impulses the liquid bubbling occurs, the voiding being
much more efficient. The collecting ladle can be a classical ladle or a
casting mould. The physical realisation of the device allows
technological adaptations, depending on the calculations related to the
diameters of the feeding and evacuation orifices, the volume of the
space destined to self-voiding, the debit of fed liquid metal, the debit
of metal liquid for the feeding of the collecting ladle, the total
height of the voiding space. We calculated the filling time of the
self-voiding device and the emptying time of this device, as well as the
filling time of the collecting ladle (www.ceet.niu.edu) These values are
very important as one avoids the use of supplemental systems for alloy
reheating over-heating during elaboration).
3.1 Calculus of the alloy filling time of the self-voiding system
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (1)
[C.sub.1] = [Q.sub.i]/[rho][A.sub.m] = 0,062 (2)
[C.sub.2] = [A.sub.i]/[A.sub.m] [square root of] 2g = 0,02 (3)
where: [T.sub.u]--filling time (m); [Q.sub.i]--liquid debit at the
entry into gallery (6) ; Z--height of space (3) (m) ; [Z.sub.max]--total
height of the system (m); [rho]--steel specific weight (kg/[m.sup.3]) ;
[A.sub.m]-- interior surface of space (3) less the orifice surface (7);
gallery surface (6)
3.2. Calculus of the emptying time of the self-voiding system, and
the filling time of the collecting ladle respectively
[t.sub.g] = [A.sub.o]/[A.sub.oe] 1/[micro]g ([square root of
2g[h.sub.o] - [square root of 2g[h.sub.e]) = 202,26s (4)
where: [t.sub.g]--emptying time of the self-voiding system, and
emptying of the collecting ladle; [A.sub.o]--surface of the ladle;
[A.sub.oe]-- surface of the evacuation orifice (7) ; [mu]--friction
coefficient of the liquid with the refractory part of the self-voiding
system, having the value 0.8; g--gravitational acceleration; [d.sub.e]
diameter of the evacuation orifice. The calculations were done for a
ladle with a 12000 kg capacity, figure 4.
[FIGURE 3 OMITTED]
The parameters of this ladle are : diameter 1.177 m, ladle height
1.413 m, ladle volume 1.53 [m.sup.3], diameter of the evacuation orifice
0.150 m. One chose 30 iterations i = [0..i.sub.max], [i.sub.max] =30
(Mathcad 11).
[t.sub.i] = i[t.sub.max]/[i.sub.max] (5)
One can calculate in the same manner the height of liquid depending
on time :
[h.sub.i] = ([square root of [h.sub.o] - [A.sub.oe]/Ao [mu][[square
root of g/2 [t.sub.i]).sup.2] (6)
Depending on the height hi one can calculate the debit:
[Q.sub.i] = [A.sub.oe] [mu][square root of 2 g[h.sub.i]] (7)
[Q.sub.min] = 3,34x[10.sup.3] [cm.sup.3]/s (8)
[Q.sub.max] = 1,026x[10.sup.4] [cm.sup.3] (9)
4. CONCLUSIONS
Through the rising and lowering movement between the voiding space
and feeding space a homogenisation occurs of temperature and chemical
composition of the alloy. The liquid flow into the collecting ladle
along with the intermittent penetration of air into the voiding space,
due to the vacuum created in the upper part, a strong bubbling of steel
is produced, with favourable effects on the reduction of the gas content
and inclusions. The laboratory tests encourage the practical realisation
of the model. The calculations were effected for a ladle with a capacity
of 12,000 kg. The theoretical total voiding time is 270 seconds, i.e.
4.5 minutes. This voiding time requires neither a high over-heating of
the steel, nor an installations for the alloy reheating. The maintenance
and operation costs are reduced.
5. REFERENCES
Campean, V. (2006). Mechanics of fluid, ISBN 973-30-1522-9, Resita
Hance, B and N-C. Lee, 2001 "Voiding in BGA", in Proc. of
ISHM, Los Angeles, CA, pp 535
*** Mathcad engineering calculation software 11
*** Procast 2008.1., software casting
*** (2001)www.ceet.niu.edu - Kostic N.;Northen Illionois
University, Accesed on 2009-02-03
