Apparatus and method for measuring flow rate of molten aluminum through a trough

The flow rate of molten aluminum through a trough is measured by damming off the trough and diverting the flow through the measuring tube of a magnetic flow meter having a diameter, and located at a level in the trough to create a head of molten aluminum sufficient to produce a flow through the tube which is within the operating range of the meter. The apparatus includes a pair of spaced apart dam members forming a cavity therebetween which is transversed by the measuring tube. The magnet of the flow meter is located in the cavity preferably in a housing through which cooling air is circulated. The electrodes are made of an electrically conductive material which is resistant to corrosion by the molten aluminum, preferably, titanium diboride. Spring biased tapered connections seal the measuring tube with the dam members which have peripheral seals to keep molten aluminum out of the cavity.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the measurement of the flow of molten aluminum, 
and in particular, the flow of molten aluminum through a trough using a 
magnetic flow meter. 
2. Background Information 
Magnetic flow meters for measuring the flow rate of electrically conductive 
liquids are well known. They operate on the principle that a conductive 
liquid flowing through a magnetic field applied at right angles to the 
direction of flow generates an electromotive force or voltage. This 
voltage is proportional to the velocity of the conductive liquid. By 
knowing the cross-sectional area of the flow, the volumetric flow rate is 
easily calculated. 
Magnetic flow meters have some very desirable characteristics. First, the 
design is very simple; there are no moving parts. There also are no 
internal impediments to flow, they can operate in high temperature 
environments, they are versatile in that they can be installed in any 
desired location or position, they have a broad measurement span, they can 
measure bidirectional flow, they are unaffected by variations in 
viscosity, pressure, temperature and density of the media, and they have 
an accuracy of at least better than plus or minus 2%. 
Magnetic flow meters have been successfully employed in industry for over 
two decades for monitoring flow control of molten sodium in nuclear 
reactors and for the measurement of the flow rates of molten brass, lead 
and a variety of other fluids with the only criteria for implementation 
being that the media be electrically conductive. 
However, applicants are aware of no successful application of a magnetic 
flow meter to measuring the flow of molten aluminum, which presents 
special problems. First, the temperature of the molten aluminum is high, 
typically about 1350.degree. F. Also, molten aluminum is highly reactive. 
Not only must the components which contain the molten aluminum be 
resistant to corrosion, but even more importantly, the electrodes of the 
magnetic flow meter must be capable of operating with hot molten aluminum 
for prolonged periods of time without eroding, fouling or changing their 
electrical characteristics. 
U.S. Pat. No. 4,741,216 proposes either lining or constructing the 
measuring tube of a magnetic flow meter through which molten aluminum 
passes with silica carbide to resist corrosion. However, this patent also 
suggests using wire electrodes without specifying any particular material. 
Common high temperature electrode materials like steel wire are rapidly 
dissolved by molten aluminum. But even slow erosion causes drifting of the 
meter as the voltage generated by the meter is directly proportional to 
the distance between the electrodes. Erosion or fouling changes this 
critical distance. 
U.S. Pat. Nos. 4,507,975 and 4,716,649 disclose a magnetic flow meter for 
measuring the flow rate of the liquid sodium, for instance, in a nuclear 
reactor, and uses platinum or platinum alloys for the electrodes. Such 
materials are dissolved by molten aluminum. 
Molten aluminum is also very difficult to contain. It can leak through any 
crack or crevice through which water can pass. This property of molten 
aluminum, considered in addition to its high temperature and reactivity, 
make it very difficult to select materials and effect seals. 
Because of the difficulty in containing molten aluminum, it is usually 
conveyed in open troughs rather than enclosed pipes. In the typical 
production process, flow rates of a molten aluminum are not measured, but 
obtained indirectly by some other measurable quantity or variable of the 
process such as pumping speed, changes in metal height, mass flow by 
temperature balance calculation and casting rates. None of these 
approaches provide an accurate, real time indication of flow rates of the 
molten metal. In addition, the accuracy of each measurement is restricted 
to the techniques used to obtain the values of the described process 
parameters. At present, no direct reading operational flow meter system 
exists for molten aluminum flow measurement. 
Accordingly, it is a primary object of the invention to provide on-line, 
real time magnetic flow meter measurement of molten aluminum flow rates 
and in particular, measurement of molten aluminum flow rates through a 
trough. 
SUMMARY OF THE INVENTION 
This object, and others which will become evident through a reading of the 
following description, are realized by the invention which includes as one 
aspect a magnetic flow meter for measuring the flow rate of molten 
aluminum in a trough which includes a pair of spaced apart dam members 
which block off flow in the trough and create a cavity free of molten 
aluminum between them. A non-magnetic measuring tube having a bore with a 
non-conductive, non-reactive surface extends through the two dam members 
for establishing a flow of molten aluminum of known cross-sectional area. 
The magnet of the flow meter, which must be protected from the high 
temperature of the molten aluminum, is mounted in the cavity adjacent the 
measuring tube. A pair of spaced apart electrodes extend through the 
measuring tube and contact the molten aluminum. These electrodes are made 
of a material which is electrically conductive and resists corrosion by 
the molten aluminum. It is another aspect of the invention that these 
electrodes are both made of titanium diboride (TiB.sub.2). Other suitable 
electrode materials include zirconium diboride (ZrB.sub.2) and hafnium 
diboride (HfB.sub.2I). 
In a preferred form of the flow meter as adapted for measuring flow in a 
trough, the ends of the measuring tubes are tapered axially and the dam 
members have mating tapered apertures in which the tube ends seat. Spring 
biasing means urge the tapered ends of the measuring tube and apertures in 
the dam members into leak proof mating relation. 
The dam members have peripheral seals which bear against the walls of the 
trough to keep molten aluminum out of the cavity. 
As a further aspect of the invention, the magnet is mounted to provide a 
flux flowing vertically through the molten aluminum in the measuring tube 
to accommodate the generally narrow width of the trough. At the same time, 
it is important to position the measuring tube as low as possible in the 
trough to increase the head of molten aluminum to establish the required 
velocity through the measuring tube for proper operation of the flow 
meter. This is achieved by making the magnet larger above the tube and 
smaller under the tube. 
In addition, a housing is preferably provided around the magnets. Cooling 
fluid, preferably air, is circulated through the housing to maintain the 
appropriate operating temperature for the magnet. 
Another aspect of the invention is directed to the method of measuring the 
flow rate of molten aluminum in a trough by damming off the flow and 
diverting all of the flow through the measuring tube of a magnetic flow 
meter. The measuring tube is located at a level in the trough and has a 
diameter, which taken together with a range of the flow rates of the 
molten aluminum in the trough, creates a head of dammed up molten aluminum 
at the measuring tube which produces the flow rate required by the process 
and within the operating range of the flow meter. Preferably, two spaced 
apart dams are formed in the trough with a cavity between which is 
traversed by the measuring tube, and the magnet of the flow meter is 
located in the cavity adjacent the measuring tube where it is at least 
partially protected from the heat of the molten aluminum. Preferably, 
cooling air is circulated through the cavity and over the magnet. 
Furthermore, flow meters in accordance with the invention having a 
non-reactive measuring tube and non-reactive electrodes which maintain 
stable electrical and physical parameters despite prolonged contact with 
molten aluminum can also be used for measuring the flow of molten aluminum 
out of a furnace or other vessel or even through a pipe.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 illustrates a trough 1 containing a flow of molten aluminum 3. The 
trough 1 which is made of a refractory material resistant to corrosion by 
the molten aluminum, is trapezoidal in cross-section with inclined side 
walls 5 and a bottom wall 7. A magnetic flow meter 9, in accordance with 
the invention, is inserted in the trough 1 to measure the flow rate of the 
molten aluminum 3. 
The magnetic flow meter 9 comprises two spaced apart dam members 11 and 13. 
As shown in FIGS. 2 and 3, each of the dam members 11 and 13 comprises 
trapezoidal inner and outer panel members 15 and 17, respectively, clamped 
together by four bolts 19. A support plate 21 clamped between the panel 
members 15 and 17 has an upward extension 23. A rod 25 secured in holes 27 
in the extensions 23 serves as a handle for the flow meter 9. A refractory 
board which is resistant to corrosion by the molten aluminum and has low 
thermal conductivity is used for the panel members 15 and 17. A suitable 
refractory board is A1300, HT available from Gerg Industrial Products 
International, Inc. The support plate 21 is slightly smaller than the 
panel member 15 and 17 thereby forming a peripheral groove 29 on the sides 
and bottom of the dam members 11 and 13. Refractory blanket material 31 is 
folded over a refractory cord 33 and clamped in the peripheral groove 29 
to form a peripheral seal 35 for each of the dam members 11 and 13. The 
seals 35 prevent molten aluminum from entering a cavity 37 formed between 
the spaced apart dam members. 
A measuring tube 39 traverses the cavity 37 and extends through the dam 
members 11 and 13. The ends of the measuring tube 39 have an axial taper 
41 which seats in tapered apertures 43 in the dam members 11 and 13. 
Furnace tapping hole seals 45 serve as packing between the tapered ends 41 
of the tube 39 and the tapered apertures 43 to provide a leak proof 
connection between the tube and the dam members. The measuring tube 39 is 
made from a material which is resistant to corrosion by the molten 
aluminum. Boron nitride was used in the exemplary flow meter. Another 
suitable material is silicon carbide, although this material is less 
resistant to thermal shock than boron nitride. 
The tapered connections between the measuring tube 39 and the dam members 
11 and 13 are biased into leak proof engagement by spring mechanisms 47. 
In the exemplary embodiment of the invention shown, the spring mechanisms 
47 include additional bolts 49 threaded into tapped bores in the ends of 
the bolts 19. The heads of the bolts 49 bear against a series of 
Belleville springs 51 seated against bosses 53 welded to the end walls 55 
of a housing 57. The Belleville springs 51 draw the dam members 11 and 13 
against the tapered ends of the measuring tube 39 to effect a leak proof 
seal which accommodates for variations in the coefficients of thermal 
expansion of the measuring tube and the dam members. 
The housing 57, which may be fabricated from sheet metal, is suspended in 
the cavity 37 from the handle 25 by the end walls 55 with a bottom wall 59 
spaced from the bottom wall 7 of the trough. The housing 57 is enclosed by 
side walls 61 and has a lid 63 with an opening 65. Two pins 66 project 
outwardly from each side wall 55 adjacent an opening for the measuring 
tube 39. 
The housing 57 forms an enclosure for the magnet 67 of the flow meter. The 
magnet 67 includes a C shaped low reluctance yoke 68, an upper pole piece 
69 and a lower piece 71, as best seen in FIG. 4. The magnet 67 straddles 
the measuring tube 39 which extends through the end wall 55 of the 
enclosure 57. The lower pole piece 71 is smaller in height than the upper 
pole piece 69 so that the measuring tube 39 may be located as low as 
possible in the trough 1, for reasons to be explained later. The magnet 67 
generates a flux oriented vertically through the measuring tube 39. 
Compensation pole pieces 73 modify the flux through the measuring tube 39 
to make it more uniformly vertical. The exemplary pole pieces 69-73 are 
crumax 55 ceramic magnets produced by Crucible magnet Company. 
Alternatively, an electro-magnet can be used in place of a the permanent 
magnets. 
Two pair of diametrically opposite electrode assemblies 77 are provided in 
measuring tube 39. The electrode assemblies 77 include an electrode 79, 
having a shoulder 81 which seats in a counter bored aperture 83 through 
the measuring tube with the end face 85 of the electrode flush with the 
inner wall 87 of the measuring tube 39 so that it contacts molten metal 
flowing through the measuring tube without causing a turbulent flow. The 
electrode 79 is made from an electrically conductive material which is 
resistant to corrosion by the molten aluminum. In the preferred embodiment 
of the invention, the electrode 79 is made of titanium diboride. An 
electrical lead 89 is connected to the electrode 79. This electrical lead 
89 must be resistant to the high operating temperatures of the device. In 
the exemplary flow meter, the electrical lead 89 is made of stainless 
steel. It is very difficult to secure such a lead to the titanium diboride 
electrode. We have vacuum brazed the electrical lead in a bore 91 in the 
electrode using a palladium flux. Other suitable materials for the 
electrodes 79 include zirconium diboride and hafnium diboride. 
The electrode assembly 77 further includes a packing 93 of refractory 
material and a plug 95 which threads into the counterbored aperture 83 in 
the measuring tube 39. Thus, the electrode is firmly secured in the 
measuring tube 39, but can easily be replaced as required. 
The diametrically opposite electrodes 79 of each of the electrode pairs 75 
form separate panels for measuring the flow of molten aluminum through the 
tube 39. To the this end, the leads 89 are connected to conventional 
signal processing equipment shown schematically at 97 which measures the 
voltage generated across each electrode pair 75 and produces a reading of 
molten aluminum flow rate. As mentioned previously, the voltage produced 
across each electrode pair is a measure of the velocity of the molten 
aluminum. As the cross-section of the measuring tube 39 is known, the flow 
rate is easily calculated. The two separate channels formed by the 
electrode pairs 75 provide redundancy for reliability, increased signal 
strength and calibration checking. 
As discussed above, the temperature of the molten aluminum can reach for 
instance, 1350.degree. F. On the other hand, excessive temperature can 
demagnetize the magnet 67. It is desirable in the exemplary flow meter 
that the temperature of the magnet not reach more than about 150.degree. 
F. In order to protect the magnets from the very high temperature of the 
molten aluminum, the measuring tube 39 is wrapped with an insulating 
sleeve 99. In the exemplary flow meter Pyrolite Q-3083, a trademarked 
product provided by Rex Roto Corporation was used. This sleeve had a wall 
thickness of 0.5 inches (1.27 cm). The insulating sleeve 99 extends along 
the full length of the tube 39 between the dam members 11 and 13. In order 
to reduce the gap between the pole piece 69 and 71, the center section of 
the measuring tube 39 in grooved as seen in FIG. 4. The insulating sleeve 
99 has three sections. The center section 99A, which is split 
longitudinally for placement around the grooved section of the measuring 
tube 39 is rabbeted at each end. The end sections 99B and 99C of the 
insulating sleeve 99 slide over the rabbeted ends of the section 99A to 
form lap joints. 
Insulation retainers 101 having cylindrical collars 103 and radial flanges 
105 which are bolted to the dam members 11 and 13 by the bolts 19 secure 
the insulating sleeve 99 to the outside of the measuring tube 39. The pins 
66 projecting from the end wall 55 of the enclosure 57 extend into the 
collars 103 to support and align the housing. 
The magnet 67 is further protected from the high temperature of the molten 
aluminum by the circulation of cooling air which is introduced into the 
bottom of the housing 57 through apertured conduits 107 and flows upward 
and out through the opening 65 in lid 63. 
In use, the magnetic flow meter 9 is carried by the handle 25 and placed 
into the trough 1. The peripheral seals 35 around the dam members 11 and 
13 seal the dam members against the side walls and bottom wall of trough 1 
so that all flow of molten aluminum is diverted through the measuring tube 
39. The inner diameter of the measuring tube 39 is selected in conjunction 
with the head of molten metal on the upstream side of the flow meter to 
provide a velocity of the molten aluminum through the measuring tube 39 
which is within the operating range of the flow meter. Generally a 
velocity of at least about 1.5 feet per second is desirable to provide 
reliable readings, and it is recommended that preferably the velocity be 
between about 6 to 9 feet per second. As mentioned above, the lower pole 
piece 71 of the magnet 67 is made smaller than the upper pole piece 69. 
This is done so that the measuring tube may be moved as low as possible to 
increase the head of molten metal on the upstream side of the meter to 
obtain the desired flow rate. 
The magnet flow meter of the invention is not limited to measuring the flow 
of molten aluminum in a trough, but can also be used for measurement of 
molten aluminum flowing from a furnace outlet or through a closed conduit. 
While specific embodiments of the invention have been described in detail, 
it will be appreciated by those skilled in the art that various 
modifications and alternatives to those details could be developed in 
light of the overall teachings of the disclosure Accordingly, the 
particular arrangements disclosed are meant to be illustrative only and 
not limiting as to the scope of the invention which is to be given the 
full breadth of the appended claims and any and all equivalents thereof.