Volume Magnesium The Melting and Refining of Magnesium

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					                   The Melting and Refining of Magnesium
                             BY C. E. NELSON,*   A.I.M.E.
                                            MEMBER
                                (New York Meeting. February 1944)

   THE purpose of this discussion is to out-      during melting and a molten pool of flux
line briefly the practices commonly followed      into which the solid magnesium melts. I t
in this country for the melting and refining      is stirred through the molten metal bath
of magnesium and its alloys. The processes        and agglomerates oxide or similar foreign
used for the various forms of primary mag-         bodies; then on quiet standing separates
nesium, as far as there are differences in        away, leaving the refined metal ball float-
the physical shape or behavior, will be           ing in an encircling layer of molten flux.
discussed. The refining of general fine scrap     I t forms only a thin fluid iilm over the
or secondary magnesium was presented in           surface of the molten metal, which may be
an earlier paper.'                                parted for hand-ladling processes and tends
   Inasmuch as the use of fluxes is an essen-     to cover the metal again after the ladle is
tial part of all the melting and refining         removed. A very light dusting of the pot
processes, the principal aim of this paper        surface with fresh flux immediately after
will be to deal with these in sufficient detail   the ladle is removed is usually desirable.
to point out their unique characteristics,           The open-pot method is used generally
in order to make their use more effective.        in the following processes: (I) alloying and
                                                  secondary smelting in the production of
                                                  ingot, (2) in sand foundries for premelting
   All melting and refining processes for         and to a smaller extent for the production
magnesium and its alloys require the use          of small castings requiring hand ladling,
of fluxes. These fluxes have a magnesium          (3) in permanent-mold founding for pre-
chloride base and other halide salts or           melting and also direct ladling to castings,
oxides are added to give a density or be-         (4) for continuous methods of preparing
havior exactly suited to the particular           metal in the productionof billets or ingots
melting practice. The successful handling         from which wrought products are fabri-
of magnesium depends upon the proper use          cated, ( 5 ) in general scrap recovery.
of the correct fluxes.
                   -
   There are four general methods of melt-
                                                                Crucible Process
ing, summarized in the following paragraphs
and treated in more detail in the section            The crucible process makes use of No.
on Melting and Refining.                                                               f
                                                  310 flux, which has the property b being
              Open-pot Method                     thinly fluid at the start, to provide protec-
 The open-pot method makes use of                 tion and refining qualities, and then drying
No. 230 flux.2 The flux provides protection       out or thickening after a time, leaving a
                                                  protecting crust on the pot surface until
   Manuscript received a t the office of the
Institute Oct. 22, 1943. Issued as T.P.1708 in    the time of casting. At that time it can be
METALSTECHNBLOGY.       August 1944.              readily skimmed off or held back, thus
   * Metallurgical Department, The Dow
Chemical Co.. Midland. Michigan.                  allowing the contents of the crucible to be
    References are at the end of the paper.       poured out directly into castings without
     All flux numbers refer to the designations
of the Dow Chemical Co. See Table I, page 395.    fear of flux contamination. This flux is not
                                      6. E. NELSON                                   393

self-healing in its film protection, hence is silicon carbide refractory having a carbon
not suitable for hand-ladling operations.     facing next to the metal bath. The walls
  This method is used principally in the      and roof are of high-grade firebrick.
following processes: (I) sand and per-           In operation, the solid charge is fed me-
manent-mold founding as a single-step         chanically into one end of the furnace onto
melting, rehing and pouring operation,        a preheating shelf, from which it is pushed
or more commonly as a second step follow-     into the bath by the introduction of the
ing the transfer to a casting crucible of     next charge. Metal is dipped or pumped
molten metal from premelting units such       out of a well at the opposite end of the
as large open pots or tilting crucibles; (2)  furnace.
crucible processes in the batch method of        The consumption of flux for melting
melting, alloying, and pouring billets or     magnesium in these units has been the
ingots from which wrought products are        same as previously was required for stand-
fabricated; (3) the refining of die-casting   ard open-pot operation. Similarly, the
scrap.                                        melting loss closely parallels that obtained
                                              in the more conventional methods of melt-
            Reverberatory Process             ing. Fuel efficiency is much better and
    The reverberatory process is a new would amount to about two thirds of that
 development for melting magnesium. I t used in open-pot melting. Undoubtedly,
 has been stated by Beckz° that hearth the outstanding feature of the open-hearth
furnaces, whether gas or electrically heated, operation is the very high melting capacity.
 are unsuitable for the melting of magnesium The units in operation are capable of
 alloys, owing to the large surface of the melting continuously at the rate of 4000 lb.
 melt as well as to the contact between the of metal per hour.
 gases and the metal or flux. Some confi- .      Safety of operation is another notable
 dence was obtained in the possibility of feature, since the charging and preheating
 melting magnesium by direct radiation as is all automatic and spatterings cannot
a result of the successful experiments by reach the operators. Furthermore, the
the Dow company in melting magnesium likelihood of a runout is remote, because
in the resistor-heated type of Detroit the refractory construction is cold on the
electric rocking furnace. With this as a outside.
background, a reverberatory hearth fur-          The field of use of the reverberatory is
nace having a capacity of 1500 Ib. of mag- in large-scale continuous melting of mag-
nesium was built for experimental work. nesium or alloy ingot or heavy scrap. In
This unit was operated successfully using such a process, it operates as a premelter
oil and gas as fuels.                         for alloying or foundry operations. I t is
   Based on these preliminary experiments, not considered suitable for the melting of
a furnace with a capacity of approximately fine magnesium or light scrap, because of
 12,000 to 20,000 lb. of magnesium was put    the difficulty of applying adequate me-
into use. This furnace has operated for chanical puddling and the development
about two years and during that time six of the large amounts of sludge or dross
more similar furnaces have been placed in that accompany the processing of these
service.                                      materials. Protection during melting and
   Below the metal line these furnaces are holding is provided by 230 or similar types
lined with a refractory that is relatively of open-pot fluxes. In this method, the
nonreactive with the fluxes and the mag- ultimate refining of the metal is largely
nesium. The linings with the longest service obtained in the open-pot or crucible process
record are of Tercod, a carbon-bonded that follows.
394                 THE MELTING AND REFINING OF MAGNESIUM

            Die-casting Process                  sing of this material that are different from
                                                 the standard practices discussed later.
   The die-casting process makes use of
                                                     Crystalline magnesium is finely divided
No. zzo flux, which gives no surface pro-
tection but is used only for refining the        and hence oxidizes readily. Furthermore,
metal. Surface protection in this method         a variable and sometimes appreciable
comes from the use of a sulphur dioxide          amount of oxide, nitrides, and other impuri-
atmosphere, which is maintained in a             ties are occluded with the crystals. Because
closed dome over the pot. Only a very little     of these, more care must be exercised dur-
flux is used as protection during melting        ing the melting of the crystals to use a
down, and this is stirred through the            fluxing technique that will not permit
metal thoroughly for refining. After a fcw       oxidation. Normally this is accomplished
moments of quiet standing, this flux,            by charging the crystals into a "heel" of
together with agglomerated oxides and            molten metal purposely left over from a
dross, sinks to the bottom of the pot and        previous batch, or into a bath of melted flux
is removed with the sludge.                       in the bottom of the pot. Liberal quantities
                                                  of the same flux are dusted over the solid
                                                  charge and as often as required to prevent
          TYPESOF MAGNESIUM                       the start of oxidation. The crystals are
                                                  puddled into the metal or flux bath as
   The two general types of primary mag-          rapidly as possible. After the chargc has
nesium that will be considered here are the       all melted down, more flux is added and
well-known ingot made by electrolytic             stirred thoroughly through the bath, in
reduction processes and the crystalline           order to separate out the oxide and dross
condensed product from the newly intro-                        f
                                                  inclusions. I the crystals are particularly
duced reduction processes such as the ferro-    . clean and free from oxide and other un-
silicon-dolomite reaction.                        desirable materials, it may be sufficient to
                                                  proceed with the normal alloying processes,
                   Ingots                         followed by stirring of the fluxes through
                                                  the bath and finally settling out of the dross
  Little special description need be given        and sludge and pouring of the refined alloy
to the magnesium ingot, since this product        into ingots or castings.
is a solid ingot that is already in a well-          If the crystals contain a large amount of
refined state through having been dipped          oxide, or appreciable oxidation takes place
from a fused salt or flux bath. The only           during the melting, it is desirable to allow
significant impurity in this metal is iron,        a few minutes quiet settling and then dip
which normally is present to saturation           from the bottom of the pot as much of the
(0.030 per cent iron) a t the temperature of       dross and oxide as possible before proceed-
the electrolytic cell. The melting, alloying,      ing to the alloying and refining steps. The
and reiining of this ingot presents no more        decision as to whether the sludging out
difficulty than the routine melting of             should be done before alloying, refining,
magnesium-alloy ingot.                             and pouring would be made by the skilled
                                                   operator, who can feel how much sludge is
          Cvysia22ine Magnesium                    in the pot and knows from experience how
                                                   much may be present and still permit
   The melting and refining of the crystal-        proper refining and production of clean
line magnesium is somewhat difficult, and          ingot. I t has been noted that, for certain
for this reason the following discussion will      grades of crystals and scrap, refining may
attempt to point out features in the proces-       be facilitated by the addition to the 230
                                               C.;:F.   NELSON                                             395

flux of certain agents such as fluorspar, or              later stage wherever the production of
salts such as sodium or potassium chloride.               high-purity alloys is warranted. For exam-
   The magnesium crystals usually are                     ple, almost all the wrought magnesium
relatively low in iron content but may                    alloys, except the Mg-Mn type, now in
contain sodium, potassium, calcium, and                   use in the United States are of high purity
sometimes silicon as impurities. For all                  made possible by precipitation of the iron,
practical purposes, all except the silicon are            which will be described later.

    I.-Com#osition
TABLE                           and Characterristics of Fluxes joy Me1tirt.g and Re$ning Magnesium,
                                        Dow Chamical Comfialty
                                                        Approxi-
                                              of Flux

EX     Composition              Use                                       Characteristics and Remarks

                                             Pet Cent
                                             -        -
 220   57.0    KC1     Die casting               o         1-3     A heavy bottom flux used for refining metal
       28. o   CaClz                                                in a covered pot provided with SOa surface
       12.5    BaClz                                                  rotection. P1u.x I? removcd after relining.
        2.5    CaFl                                                 bsed where dipping i s so frequent that
                                                                    open-pot operatlon is impractical
 230   5 5 . 0 KC1 Sand and permanent          10-20       4-6     Characterized by high fluidity of surface film
       34. o MgCll mold casting                                     protection, allowing parting and recovering
        9.0 BaClz      Premeltin                5-10                for ladling operations. High refining quall-
        2 . o CaFz     Alloy profucttion
                       Scrap recovery
                                               10-20
                                               10-20
                                                            I
                                                           :$
                                                           4-15
                                                                    ties. General open-pol flux
                       Flux pots                100       <0.5
 250   23.0    KC1     Alloying                  o      Variable   Used for introducing manganese into alloys
       72.o    MnClz                                                made by open-pot process with 230 flux.
        a.5    BaC12                                                Reaction products approximate 230 flux
        a .5   Cap?                                                 behavior. Flux contains 31.7 per cenl
                                                                    manganese by weight
 310   20 . O KC1    Sand and permanent-        1-3         3      Crucible-type flux characterized by being
       g o . o MgClz mold foundry                                   fluid at start for melting and refimng.
       I S . o CaFz  Crucible alloying          2-5        2-5      then drying out t o crust that ca? be re-
       I S . 0 MgO   Die-cast scrap refin-      2-5        2-5                                       t
                                                                    moved or held back for d ~ r e c pouring
                        ing
 320   7 6 . 0 MnClz Crucible alloying           o      Variable Used for introducing manganese into ~ U O Y S
       1 3 . o CaFr                                               firoduced by the crucible process with 310
       11 o MgO                                                     ux. Reaction products approximate 310
                                                                  flux behavior. Flux contains 33.5 per cent
                                                                  manganese by weight.

                              Based on weight of metal poured from a given operation.

removed by reaction with the flux in the                    The methods of handling distilled
melting and refining process. The iron                    magnesium crystals are the same as those
content, on the other hand, will tend to                  outlined briefly in the prcceding para-
increase up to the saturation value if this               graphs, except that normally it is not
metal is melted,as is the common practice,                necessary to remove sludge before alloying
in steel pots. The alloying metals normally               and refining.
added to commercial magnesium contain
many times more impurities, such as iron,
than are, foui~deven in the electrolytic
magnesium, so that the natural purity of                     In order to give a clearer understanding
the crystals produced by the ferrosilicon                 of the types and uses of fluxes commonly
process is lost unless special 'high-purity               employed for the 'melting and refining of
metals are used and the whole process is                  magnesium, a list of compositions is
carried out in iron-free fluxes and melting               included in Table I.
equipment. In practice, therefore, it is more                The compositions and designations
feasible to remove the impurities a t the                 shown in this paper are those of The Dow
396                  THE NELTING AND REPINING OF MAGNESIUM

Chemical Co., but it should be pointed out       nary boiler-plate construction, madc up in
that within the last year or two other           convenient sizes and shapes to permit easy
suppliers have put fluxes on the market.         removal of the frozen cake.
Among these new suppliers are Basic                 7. Thermocouples may             be    either
Magnesium, Inc., and Permanente Metals           Chromel-Alumel or iron-constantan and
Corporation.                                     should be protected in the pots by a steel
                                                 pipe or sheath.
                                                    8. Separate flzlx pots are essential to the
                                                 production of high-quality magnesium-
                                                 alloy ingots or castings using the open-pot
   No detailed information on equipment          ladling process. These pots usually are
will be attempted here. The equipment            of the round-bottom cast-steel type having
most used may be indicated in the follow-        capacities of 400 to 600 Ib. of magnesium.
ing outline:                                     No. 2 3 0 flux is used to fill the pots, and all
   I. Open pots may vary in capacity from        ladles, tools, and other utensils are washed
 IOO to 4000 Ib. of magnesium. They are          periodically in this flux. This prevents
made of heavy cast steel. Particular care is     undue splashing and agitation in the regu-
taken to avoid the use of steels containing      lar casting pot and prevents the carry-over
more than several tenths of a per cent of        of excessive oxide or other impurities into
nickel, in order to prevent contamination        that pot, and thus into castings. Ladles
of magnesium alloys melted therein. Cast-        should be kept smooth and clean at all
iron pots are brittle and often are too          times, as dirty ladles cause flux and oxide
porous to hold the flux. They tend to grow       inclusions in the castings.
in use, thus becoming still more porous;
hence are not recommended.                              PREPARATION TKE METAL
                                                                  OF
   2 . Crucibles may vary in capacity from                   FOR MELTING
zo to aooo lb. of magnesium. The smaller
sizes usually are madc of welded steel and          Preparation of the metal is a very irn-
the very large sizes of cast steel. Ordinarily   portant part of any melting practice, since
these are made with extra thick bottom           failure to clean the solid metal properly
sections to resist corrosion, and con-           may lead to excessive gas or dirt in the
structed so that this part can be readily        melt and introduce harmful metallic
replaced by cutting off the old section and      impurities.
welding on a new one. As with open pots,            Aside from the regular precaution of pre-
contamination by nickel in the steel must        heating all metal that is to be charged
be avoided. Metallizing of these pots and        directly into molten metal or flux, no
crucibles with aluminum significantly in-        particular precautions in preparation are
creases their service life.                      necessary for virgin magnesium ingot or
   3. Pouring ladles should be constructed       crystals.
with a skimmer on the backside, for parting         Since heavy foundry scrap constitutes
the flux, and a special bottom-pouring spout.    one of the largest sources of metal being
   4. Sludge ladles are simply small hemi-       melted, the following points will be of
spherical scoops ranging in size from 6 to       interest:
9 in. in diameter, depending on pot sizes.          Oil or excessive moisture on the surface
   5. A skimmer is a handy tool. I t may be      of the scrap is almost certain to lead to
a flat, perforated plate about 6 to 9 in. in     gas in the metal and excessive porosity
diameter, attached to a long handle.             in the product. These hazards are avoided
   6. Sludge and flux pans may be of ordi-       usually by care in preventing oily materials
                                      C. E. NELSON                                     397

from coming into contact with the scrap            4. The pot may be entirely filled with
and either predrying of the scrap in an         solid ingot, providing care is taken to
oven, or sandblasting it just before melting.   dust thoroughly with the flux all parts of
   Scrap should be remelted as soon as          the charge. Any part of the charge that is
possible after the castings are sawed out,      added' directly into molten metal or flux
in order to prevent undue formation of          must be carefully preheated, in order to
hydroxide films on the surface.                                  f
                                                avoid danger o a blow and spattering
   ~rjdesirableamounts of silicon may be        when such material is added to the pot.
introduced into the molten metal by im-            5. The pot should be watched diligently
properly cleaned foundry scrap.                 to make certain that no oxidation or burn-
   It is important that all material to be      ing takes place. Whenever required, a light
returned to the melting pot be thoroughly       dusting with flux will prevent oxidation.
blasted and handled in such a way that no          6. While the charge is melting down,
residual sand can be carried back to the        the required amount of alloying materials,
melting operation.                              such as aluminum, manganese or zinc,
   f
   I the metal becomes gassed, the remedy       should be weighed out and placed on top
consists in long holding, with stirring, a t    of the solid charge, so that it will be pre-
low temperatures or, preferably, direct         heated and gradually dropped into the
chlorine treatment.                             pot as the supporting charge melts down.
                                                   7. As soon as all the materials arc
                                                melted, additional quantitie of fresh flux
                                                should be spread on the pot surface. I     f
  The various types of melting practice
                                                the manganese is added as KO. 2 5 0 flux, it
are: open-pot melting and alloying, open-
                                                should be spread on the pot surface at this
pot refining and pouring, crucible melting
                                                time and stirred into the melt. A vigorous
and pouring, two-step premelting and
                                                stirring with a sludge ladle should be given
crucible melting, and die-cast melting.
                                                from the bottom to the top of the pot, so
                                                as to produce a rolling action of the con-
  Open-pot Melting and Alloying Practice        tents and to give uniform mixing of the
   Ingot.-The                         f
                largest proportion o all        batch. This stirring time would normally
magnesium-alloy ingot used in the United        be from 5 to 10 min. This stirring also
States is produced by open-pot melting.         serves as a refining treatment to remove
The steps involved in converting mag-           all oxides and dross from the metal and
nesium into alloy ingot may be enumerated       put them into the sludge.
as follows:                                         8. At this point, a sample from the
   I. A clean cast-steel open pot (usually      pot is taken for control analysis.
between 600 and 4000-lb. capacity) is               9. The batch is allowed to stand quietly
heated and a quantity o No. 230 flux
                            f                   for a t least 10 min., or preferably longer,
approgmately equivalent to 10 per cent          in order to give the flux and sludge a
of the weight of metal to be charged is         chance to separate completely from the
melted therein.                                 ball of molten metal.
   2. Primary magnesium or heavy scrap             10. The metal is now in a refined state;
of known composition, after thorough pre-       and if the analysis is found to be satis-
heating on the edge of the pot, may be          factory, the batch is ready for pouring.
charged directly into this flux bath.              11. Clean preheated ladles of the re-
   3. Additional No. 230 flux should be         quired sizes are used to dip the metal from
lightly dusted over the charge and pot          the pot and pour into ingots. Since the
surface.                                        ladle presumably has been cleaned in the
3g8                  THE MELTING AND REFINING OF MAGNESIUM

 flux pot, it will be necessary to rinse off     metal be ladled out into ingots, because
 the excess flux by filling the ladle with       of the likelihood of mixing the metal and
 metal several times and carefully pouring       sludge near the bottom of the pot. Usually
 the metal back into the pot. After this         it is more convenient to leave a certain
 procedure, theladle may be usedrepeatedly       small heel of metal in the pot (10per cent),
 to dip metal from the pot, until it shows       thus providing a pool of metal into which
 oxidation or graininess, indicating that it     the next batch may be. charged.
 is dirty and must be cleaned again in the          15. At this point, the thick sludge, com-
 flux pot.                                       posed principally of oxide, dross and flux,
    I t is very important that the operator      may be dipped from the bottom of the pot
 carefully push back the flux film from a        and the thinly 5uid flux and metal propor-
 section of the pot surface before introduc-     tion of the sludge be allowed to drain back
 ing the ladle. The ladle should be allowed      from the dipper. The solid residue is placed
 to fill slowly over the back side. When full,   in sludge pans. After this sludge is removed,
 it should be lifted through the parted sec-     the pot is ready for the next batch.
 tion of the flux and a small amount of the         Scrap or Crystalline Magnesium.-As has
 metal poured back into the pot through the      been said before, the main deviations from
spout, so as to discharge any small amount       the foregoing process in charging scrap
of flux that may havc been present in the        metal or crystalline magnesium would be
spout. The ladle should then be raised           in the need for more careful protection
from the pot and rested momentarily on           against oxidation, more mechanical stirring
the side of the pot, while the operator          to immerse the charge in the molten bath,
flicks a fine dust of flux over the surface,     and the possible addition of a sludging
so as to prevent oxidation. This is a very       operation prior to the alloying and refining
important point from the standpoint of           steps if it appeared advisable.
quality of the metal, and one most often
neglected. Flux should ,$ever be placed on          Ofen-pot               POurifig
the pot just before the operator dips but           Open-pot refining and pouring finds most
should be applied immediately after the          use in the open-pot production of perma-
ladle is removed. I n all dipping operations,    nent-mold and sand castings. The steps
care should be taken to avoid sudden and         involved for the two processes are so similar
unnecessary motions in the pot, since these      that they may be discussed together. The
lead to mixing of the flux and metal.            steps involved are as follows:
    12. Care must be taken in the pouring           I. Cast-steel pots having capacities of
of the ingot to avoid turbulence of metal        from 600 to 1000 lb. magnesium are used.
flow into the mold, as this leads to oxida-      I n starting a batch, the pot is first heated
tion and poor quality of the ingot. The          and a quantity of 230 flux, equivalent to
size of the ladle should be chosen to permit     about 10 per cent of the desired metal
a small amount of metal to be left in the        charge, is added.
ladle after the ingot is full.                      2. When this 5ux is molten, preheated
    13. Protection for the ingot during          alloy ingot of the desired composition
pouring and solidification is provided by        should be charged into the pot.
hoods over the molds and a n atmosphere             3. A fine dusting with 230 flux should
of SO2 gas.                                      be made over the charge and repeated as
    14. With reasonable care almost all of       often as required during the meltdown, to
the metal in a given batch may be poured         prevent oxidation.
into ingots without risk of flux inclusions.        4. When the charge is entirely melted,
In no case, however, should all of the           a quantity of fresh flux should be added
                                                  NELSON                                    399

 to the pot. After this flux has melted, the       and permanent-mold castings. The steps
 entire contents of the pot should be stirred      in the process are as follows:
 thoroughly to bring the flux into intimate           I. Steel cruciblks in the size range of 60
 contact with the molten metal. The metal          to 550 lb. of magnesium are commonly
 temperature at this time should be pref-          used.
                       f
 erably in the range o 1300' to 1350°F.               2. The crucible is placed in the setting,
    5. After this stirring and refining, the       heated, and dusted with 310 flux.
 pot should stand quietly for a t least 10 min.       3. Solid ingot of the correct composition
before any metal is dipped out.                    and a portion of casting scrap are charged
    6. The pot and contents should next be         into the crucible.
                         to
 heated to about 1450~ 1500°F. and held               4. No. 310 flux is carefully sprinkled
 at this temperature during the pouring            over the entire charge.
cycle. Since the metal normally stands a t            5. After the charge is melted down and
 this temperature for an appreciable length        raised to a temperature of approximately
  f
 o time, a considerable grain-refining action      1350°F., a quantity of fresh 310 flux
is thus obtained.                                  (approximately 1.5 per cent) is added and
    7. Small sand castings may then be             allowed to melt, after which it is vigorously
poured by ladling directly from this pot           stirred through the metal. This refining
at about 145oOF In permanent-mold cast-            operation should take about one minute
ing, it is often necessary to pour at con-         and serves to agglomerate the dross so that
siderably lower temperatures; and for such         part of it rises to the surface of the metal
cases the pot temperature would be                 and the remainder goes to the bottom intb
dropped down to the appropriate 1eQel              the sludge.
before pouring. The details of the ladling            6. The clinker-like dross that rises to the
process would be the same as previously            surface should be carefully skimmed off
given.                                             and fresh 310 flux immediately dusted
    In both sand and permanent-mold cast-          behind the skimmer, to prevent reoxida-
ing from an open pot, it is common practice               f
                                                   tion. I there is any question as to the
to maintain a constant level in the pouring        quality of the refining treatment, a little
pot through the continuous addition, as            more flux should be added, the stirring
required, of alloy ingot of the same batch         operation repeated and the melt again
or of hot casting scrap that came from the         skimmed. The absence of substantial
same melt. The large quantity of residual          quantities of dross on the second skimming
flux present in this type of operation seems       indicates that the refining treatment was
to be adequate to refine this added metal          adequate.
separately. I t should be pointed out that            7. A moderate quantity (0.5 to I per
while there is about 10 per cent flux in the       cent) of 310 flux should then be spread
pot a t any one time, sufficient flux is con-      over the surface of the crucible, the tem-
tinuously carried along to reduce the over-        perature raised to 1650' to 17oo0F. and
all flux consumption in the open-pot               held for about, 15 min. This treatment
process to around 4 to 5 per cent. Tt will         refnes the grain in the alloy and causes
be necessary to dip the sludge from the            the flux to "cure" or dry out, so that when
bottom of the pot every 4 to 12 hr., depend-       the metal cools to the required casting
ing on the rate of metal turnover.                 temperature the flux either can be pushed
                                                   back away from the lip or entirely skimmed
   Crucible Meltiltg and Pouring Practice          off before pouring. Again sulphur, or a
  Crucible melting is one of the methods           mixture of sulphur and boric acid, is used
commonly used for the production of sand                                            f
                                                   for protection during pouring. I the proper
4OO                 THE MELTING AND REFINING OF MAGNESIUM

refining and fluxing technique is not           analysis. After this batch of metal has
followed, the flu^ occasionally may dry out     completely melted, it is refined and made
or crumble after superheating, thus allow-      of uniform composition by thorough stirring
ing oxidation. I t is a dangerous practice,     with No. 230 flux. Sludge must be removed
as regards fluxing the castings, to add fresh   from this crucible from time to time. Since
flux a t this stage. A very light dusting a t   the primary purpose of this unit is to melt
the exact point of oxidation is permissible,    the magnesium and provide some refining
but the general remedy is better refining       treatment, ordinarily the metal is not
and the use of more flux a t the refining       heated above about 1400°F. at this stage.
stage. It is quite important that no pro-          As often as metal is required for super-
longed delay be allowed between the time        heating and pouring, it is transferred
the metal is a t the superheating tempera-      from the premelters to smaller crucibles,
ture-that is, 1600°F. or above-and the          usually of capacities between 60 and 550 lb.
time of pouroff. The superheating treat-        of magnesium, by tilting the large units.
ment causes a desirable grain refinement,       The metal in the latter crucibles is pro-
which is lost rapidly on standing at lower      tected with No. 310 flux, which usually
temperatures.                                   is dusted lightly into the hot crucible
   8. The crucible size should be selected      before the metal is transferred. These
for a given casting job, so that a small heel   crucibles are then placed in settings and
of metal will always be left in the crucible.   the metal temperature is raised to about
After the pouroff is finished, the crucible     r350°F. At this point additional 310
is returned to the melting room and the         flux (approximately 1.5 per cent) is
sides spudded down, fresh flux being added      added. As soon as this fresh flux is melted,
when required to inhibit oxidation, and         it is stirred vigorously through the metal
the dross and sludge skimmed out of the         bath for a period of about one minute.
bottom of the crucible. The heel of flux        This refining treatment brings a clinker-
and metal then remaining may be used            like dross to the surface and drops the
as a starter for the next charge.               rest of the impurities to the sludge. From
   The normal consumption of 310 flux                                               f
                                                this point forward, the process o super-
for this type of operation would be about       heating, pouring, etc., is the same as
3 per cent.                                     that previously discussed for the crucible
                                                melting and pouring practice.
Two-step Premelting and Crucible Practice          In this type of operation, about 2 to
   Two-step premelting and crucible melt-       4 per cent of No. 230 flux would be used
ing is the most widely used method for the      in the premelting and approximately 3 per
production of sand castings and is used to      cent of No. 310 flux in the crucible. This
some extent for permanent-mold castings.        process offers many advantages, such as a
In this type of operation, all of the ingot     double refining treatment and high-speed
metal and foundry scrap is melted in large      method of melting.
tilting crucibles, usually around 2000 lb.
magnesium capacity. No. 230 flux is used                 Die-cast Melting Practice
for protection on this premelting crucible         The die-cast melting method is used
and the melting down operations are             almost universally in this country for
exactly the same as those described under       providing metal for die-casting operation.
open-pot melting practice. Ordinarily, the      I t is considerably different from any o  f
large premelting crucibles are operated on      the other practices in that it uses No. 220
a batch basis, so as to provide a single                                            f
                                                flux, which has the characteristic o being
large source of metal having the same           able to refine the metal in the same way
                                           NELSON                                  401

  as previously described fluxes but does The foregoing procedure is followed in
  not have the property of giving surface starting up a new pot, but in normal
  protection. Since the die-casting process operation it is preferable practice to keep
  requires the introduction of a ladle into the die-casting pot relatively full of metal.
  the pot many times per minute, the use of a This may be accomplished by adding fresh
  flux that gives surface protection would ingot at a rate sufficient to maintain a
  lead invariably to the inclusion of flux constant metal level; or, still better,
  in the metal, because of the continued to do all of the melting in a separate
  agitation. For this reason, this flux has premelting unit, using No. 230 flux and
  been definitely designed to do the refining then transferring molten, refined metal
  and then settle to the bottom, so that it directly to the casting pot by tilting or
 may be completely removed from the pot ladling from the premelter as convenient.
 with the sludge. Surface protection in this      The usual range of pouring temperature
 case is provided by an atmosphere of SOz, for die casting is from 1175' to IZ~OOF.,
 which usually is generated by burning so the oxidation tendency for the metal is
 sulphur in a hollow dome that operates relatively low. I n this operation, the
 as a cover for the melting pot. The ladle metal usually is protected by a thin film,
 is introduced into the pot through a small which must be parted when the ladle is
 opening through the cover. The SOt introduced. I there is evidence of undue
                                                            f
 generated within the hollow dome is oxidation on the metal surface after
 allowed to enter the space just above ladling, it means that the sulphur dome
 the metal in such a way as to blanket the is not working properly. Sometimes a
 molten metal surface and to retard the very slight dusting of sulphur or other
 entry of air through the ladle opening. similar agent may be required to control
 The primary meltdown in this case is oxidation. I n no case would fresh flux
 done by dusting the surface of the pot with be added to the pot unless the entire
 No. 220 flux and charging the solid metal rehing and sludge-removal processes were
 into the pot. with careful attention and to be repeated. I n continuous operation,
 fluxing to prevent oxidation. When the particularly if ingot is added directly to
 batch is all molten, it is stirred thoroughly the pot, i t may be necessary to re-flux
 with the flux to agglomerate the oxide. the pot every 4 to 8 hr. Ordinarily from
I t is next allowed to stand for about IQ I to 3 per cent of No. zzo flux is used in
min. to permit settling of the sludge and the process.
flux. The melt is then ready for sludging,       Sc~ap.-The melting and refiningv of
which consists of removing the sludge with die-casting scrap presents a special problem
a skimmer perforated with %-in. holes. different from that for the bulk of mag-
The skimmer is preheated and put into nesium scrap, in that a certain proportion
the metal, scraping the bottom and sides of carbonaceous materials, lubricants,
of the pot.                                    etc., are present on the scrap, so that
    When the skimmer is brought up with melting and refining in No. 230 flux as in
the metal and sludge, the molten metal ordinary practice is not satisfactory. A
runs out through the perforations, leaving reddish scum, or film, of the carbonaceous
only the sludge, which is dumped into a material seems to stay suspended through-
preheated pan. This process removes all 'out the metal. This behavior is eliminated
of the flux and dross and the metal should through the melting of such scrap in open
now appear clean and shiny. It is advisable pots or crucibles, using No. 310flux instead
to allow about 10 min. quiet standing of the usual 230. The No. 310 flux has the
before beginning to dip metal from the pot. characteristics necessary to agglomerate
 ‘
4'   2              THE MELTING AND REPINING OF MAGNESIUM

the carbonaceous film and refine this          The No. 230 flux has these characteristics
material. Melting procedures are similar       as well as less tendency than other fluxcs
to the open-pot operation with No. 230         to dry out or thicken during use, thereby
flux for scrap recovery, except for the        providing a cleaner pot, better metal
substitution of 310 flux.                      protection and better separation of flux
                                               from the metal. Another advantage has
                                               been that the amount of flux consumed
   The development of fluxes and the           for open-pot alloying operations has
 technique for their use in this country       dropped from about 8 per cent down to
 has gone a long way toward simplifying        4 per cent.
 and improving the methods originally             What is probably a still more significant
 used in Germany and practiced abroad          development is the No. 310 flux, which
even a t the present time. The original        embodies in one agent all of the behavior
 German practice made use of the naturally     and characteristics that are obtained by
occurring double salt of magnesium and         the multistep fluxing practice used abroad.
potassium chloride (carnallite). That this     More specifically, this flux a t first is thinly
material is not exactly suited to flux         fluid, so as to provide adequate protection
practices was early recognized by the          during meltdown, and gradually thickens
Germans and attempts were made to              during the refining stages. While the metal
correct its behavior through the addition      is being superheated for grain rehement,
of other materials and more practically        the flux still provides protection and is
through the use of multistep flux opera-       converted during this high-temperature
tions." I n those processes, the molten        process to a surface crust, which may be
metal is first washed with a thinly fluid      skimmed off or parted for the pouring
flux, a second flux containing thickening      operation. Flux inclusions are never ob-
agents is then added for the refining          tained in castings produced when this type
stages and finally a third flux containing     of crucible flux is used correctly. I t simpli-
thickening agents may be added, in             fies the foundry practice by requiring only
order to absorb all the fluid flux and         one main flux and eliminates the guesswork
develop a crusting protection on the           of operators in using the correct propor-
surface, which can be skimmed off or           tions of the various fluxes required in the
pushed back before pouring.3                   multistep operation. Similarly, it may be
   Those who have been long associated         said that while better fluxes undoubtedly
with the development of magnesium in           will still be discovered, the No. 230 and
the United States will well remember the       310 fluxes provide a range of protection
widespread difficulties with fluxed mag-       adequate to meet most melting problems.
nesium castings in the early days. These          I t is also of possible interest to point out
were caused primarily by the use of the        that the widespread use of premelting units
carnallite fluxes. A definite development in   in this country is a new and significant
this country has been in the evolution of a    development in handling magnesium. The
single flux such as No. 230, which, with       process is of interest primarily from the
reasonable use and appropriate technique,      standpoint of facilitating production, in
permits single-stage alloying or open-pot      that a double refining treatment is not
melting and pouring operations by provid-      needed, as either 230 or 310 flux alone gives
ing a surface protection for the metal and     a sufficient refining action. More specifi-
permitting the flux film to be parted for      cally, this permits an increase in melting
ladling and then tending to re-cover this      rates and provides a large batch of metal
surface after the ladle has been removed.      of uniform and single analysis.
                                             NELSON                                      4O.3

                                                 points in the behavior of magnesium and
    Iron is precipitated in the production of its alloys is the characteristic of a very
 essentially all the wrought magnesium marked grain-refining action obtained by
 alloys except the Mg-Mn type used in this means ol a superheating treatment some
 country. AS previously stated, iron may 2ooa to 4o0°F. above its melting point.
  occur in the original magnesium and is I n this behavior, it is considered to be
 added in larger amounts in the aluminum much like cast iron, and the theories and
 and other alloying constituents, and may hypotheses used for the explanation of the
 be picked up from the flux and from the behavior of the cast iron may be applied
 pot itself. The iron is precipitated after to magnesium with the substitution only
 the principal alloying materials have been of the alloy and the types of impurities.
 added, usually by addition of manganese            Perhaps the most widely supported
 to a saturation value for a temperature theory a t the moment is that some material
 above that a t which the metal is to be that a t normal temperatures is too large
 poured. When manganese is present up to in particle size to be effective is taken into
 its solubility value, particularly in the solution a t the high temperatures, and
 presence of aluminum, iron is greatly reprecipitates to form fine nuclei during
 reduced in solubility or tendency to stay the cooling process. The fact that after
 in suspension, and is rapidly precipitated superheating the grain-refining effect de-
 to the bottom of the pot. This concept is teriorates upon long standing a t tempera-
 somewhat different from that pointed out tures below the superheating range would
 by Beck2cand others? in that they visual- lend credence to the idea that these nuclei
 ized an entrapment of the iron in primary are again coalescing and growing to their
 crystals of manganese or silicon that could original form and relative ineffectiveness.
 be used as the precipitation agents. I n           I n any case, the superheating practice
 any case, the process operates consistently is very important in most casting opera-
 to produce iron contents on a commercial tions, in that it provides h e r grain size
scale a t an average of,o.oo~ cent or less. and a finer and more uniform distribution
                                per
  In       actual practice, the manganese of the magnesium-aluminum compound,
 usually is introduced as manganese chlo- which further leads to more homogeneous
 ride, or, preferably, as No. 250 or No. 3 2 0 heat-treated structures and high properties.
 manganese flux. The former is used'if the The method by which the superheating
 process is to be carried out in a n open pot effect is obtained has been discussed to
in the presence of 230 flux and the latter some extent, and only a few more details
if i t is to be carried out in a crucible in the will be mentioned here. Superheating
presence of 310 flux. The manganese-flux effects may be obtained as low as r5oo0F.
compositions are balanced so that the. but the time required a t this temperature
reaction products are compatible with the is rather long (several hours). As the tem-
respective fluxes.                               perature of superheating is raised to about
    While the iron-precipitation processes 1700' to 1750°F., the time required to get
can be carried out successfulIy in steel the effect gradually drops of! to approach
pots or crucibles, any attempt to remelt or zero.
reheat high-purity alloys appreciably above        I t has been stated in the literature that
 r300° to r350aF. in contact with steel the effect of superheating carries over
pots will lead to contamination by iron.                                           was
                                                 through remelting steps .2d.6Thi~ found
                                                 to be true to a limited extent, in that part
                 SUPERHEATING                    of the time metal so treated might show
   Perhaps one of the 'most interesting the full benefits of superheating but more
 404                   THE MELTING AND REFINING OF MAGNESIUM

   often the effect would be only partially        be sufficient to permit the elimination of a
   realized. I n view of this action and the       full superheating treatment just before
   need for a good job of superheating prior       pouring. Since 60 to 80 per cent of the
   to the actual pouring of the casting in         charge being melted in foundry crucibles
  production, in order to ensure uniformity        consists of foundry scrap that already has
   of behavior, the advantage of using pre-        been repeatedly superheated, any benefits
. superheated metal is considered question-        of such carry-over are already enjoyed. If
   able. T o this point may be added the fact      the final superheating is proper, no addi-
   that in most casting operations the bulk        tive effects are gained from previous
  of the material going back into the melting      superheating.
  pots is foundry scrap; which already has
  gone through from one to five superheating
                                                                        REFERENCES
                                                   I.   C.   E. Nelson: Secondary Magnesium.
  operations in connection with previous                  Secondary Metals Symposium. Metals
  castings and therefore would have whatever              Tech., Oct. 1943. A.I.M.E.
                                                   2.   Beck: The Technology of Magnesium and
  advantages are to be obtained through                   Its Alloys. (a) 319; ( b ) 313-318; ( c )
  carry-over of superheating effects. A point             318-319; ( d ) 321-322.
                                                   3.   British Patent 469347.
  on which we can fully rely is that if the        4.   Schmidt and Beck: U. S. Patent zozg8q8.
  finalsuperheating before casting is properly     5.   K. Achenback, H. A. Nippur and E. Piwo-
                                                          warsky: Contribution to the Question of
  done no additional benefits are realized                Melting Practice for Cast Magnesium
  from previous superheating.                             Alloys. D e Giesserei (1939) 26, 597-604.
                                                                   i
                                                             621-628.

                                                                    DISCUSSION
                                                      F. A. Fox.*-It is hardly possible in a
    An attempt has been made in the fore-          limited space to' comment adequately on this
  going pages to bring out the following           interesting paper by Mr. Nelson. The mcthods
 significant points:                               he describes difier considerably from standard
    I. The use of the correct fluxes and the       practicc in this country. I n our opinion the
 proper technique is fundamental in the            fluxing methods used by M.E.L. and the Elek-
  melting and refining of magnesium.               tron group possess important advantages over
    2 . Fluxes and techniques have been            the methods described in this paper, in par-
  developed and are available for use in this      ticular as regards simplicity of procedure,
                                                   reduction in quantity of flux required, negligi-
  country that are suited to the various types
                                                   ble risk of flux inclusions even with somewhal
 of melting and refining operations.
                                                   careless operation, and reduced metal losses.
    3. The use of a direct-flame reverbera-        These methods are briefly outlined later.
  tory type of furnace is a new and demon-            Mr. Nelson's references to the original
 strated development for large-scale melting.      German practice and to "methods practiced
    4. Magnesium alloys of controlled high         abroad even at thc present time" do not appear
 purity are already being produced on a            to be always correct and seem to us to be mis-
 large commercial scale for wrought mag-           leading. For instance, the impression might be
 nesium products and to a limited extent           gained, on reading Mr. Nelson's paper, that
 for castings. The use of magnesium of initial     American melting and fluxing practice was
 high purity is not a significant factor in this   ahead of that in the United Kingdom and that
                                                   the developmcnt of fluxes Nos. 230 and 310
 production, since impurities are added dur-
                                                   represented, in particular, an advancement
 ing alloying and melting. A precipitation         over existing fluxes used elsewhere. Neither
 method for lowering the iron after these          our own experience with No. 2 3 0 and No. 310
 operations appears most promising.                fluxes, nor the statements made by Mr. Nclson
    5. Superheating is very important in the       in his paper, appear to us to justify such a view.
 production of high-quality castings. I n          In iact, evidence pointing rather to the con-
 actual practice carry-over effects of pre-        -
                                                      * Chief Metallurgist, Magnesium Elektron
 superheating metal are not considered to          Limited. Clifton Works, Manchester, England.
                                                     JSSION                                        4O5

 trary might be presented; for example, from          about 750°C and a fresh layer is applied to
 the historical point of view, a flux essentially     the clean metal surface. Before pouring, the
 similar in behavior and purpose to No. 310 has       flux cover is gently drawn away from the lip
 been in use by one of our associates for'about       of the pot and the metal is then cast.
 nine years. Further, the No. 310 flux itself            An all-purpose flux, termed Melrasal UE,
 is not unlike one of the German Elrasal fluxes       which is intended for melting, refining, and as
 in both behavior and composition.                    a cover during superheating and casting, is
    The total consumption of fluxes in our own        suitable for ingot melts up to about 1000 lb. of
 foundries in one complete operation involving        metal.
 melting, alloying, refining, superheating and           No bath of fluid flux is used in melting, and
 casting of metal on the same scale as that of the    a t no time is i t necessary either to scrape flux
 Dow "open-pot alloying process" has for some         up through the metal from the bottom of the
 years been 2.5 to 3 per cent of the weight of        pot or to remove i t from the metal surface.
 metal melted, whereas the Dow flux consump-          The total consumption of flux in a single
 tion in the "open-pot alloying process" alone        operation involving melting, alloying, refining,
is now 4 per cent.                                    superheating and pouring has already been
    The trouble with flux-contaminated mag-           quotedas 2.5 to 3 per cent of the weight of
 nesium castings in the early days of develop-        metal melted, and the gross metal loss is 2 to
 ment of maghesium in America, mentioned by           3 per cent, of which a high percentage is re-
 Mr. Nelson, and which appears to have con-           coverable by suitable treatment of the flux
tinued long beyond I'the early days," could           residue. Ladling processes for the transfer-
hardly have been due primarily to the use of          ence of metal from one pot to another are
carnallite itself, because satisfactory castings      avoided and die casting by ladles is considered
were being prepared with similar flux materials       undesirable.
in England, France and Germany a t that time*
when, incidentally, the tonnage of magnesium
made and processed in Europe exceeded that in            The use of highly fluid noninspissated fluxes
the U.S.A. by a ratio of about ten to one.            in flux baths and for covering the metal seems
   The "original German process" described by         to us most undesirable from the point of view
Mr. Nelson was probably never in use in three         of complete freedom of the castings from flux.
stages as standard melting practice. Even in          The ladle casting process involving the use of a
1936, a single, all-purpose, inspissated flux         flux pot for washing the ladle, etc., appears to
essentially similar to Dow.310, was supplied by       be a complicated, and, from the metal effi-
I. G. Farbenindustrie A.G. to its casting             ciency point of view, an uneconomic way of
licensees.                                            casting ingot. Ingot produced in this country is
   A detailed account of our fluxing process was      cast continuously from automatic, tilting 2-ton
recently published in Magnesium Review and            crucibles, into molds arranged on a continuous
Abstracts (Vol. 4, No. I, Jan. 1944). For con-        conveyor belt. An inspissated flux cover is used
venience, a brief outline of the methods used         on the metal.
follows.                                                 Melting in a flux bath is used by us only in
                                                      the treatment of material obtained in the
                                                      course of metal-recovery operations; this metal
   Melting is carried out with a fluid flux           is cast into ingot and subsequently remelted.
Mclrasal 2, corresponding roughly in be-              CRUCIBLEMELTINGA N D POURINGPRACTICE
havior to Dow 230, which is sprinkled lightly
over the ingots after the latter have been               The reason for some "clinker-like dross"
charged into the melting crucible, and subse-         rising to the metal surface and requiring
quently applied as required to prevent burning.       removal is not clear.
When the metal is molten, an inspissated flux,           I n contrast with Mr. Nelson's warning
Melrasal E, which Dow 310 somewhat resem-             against addition of fresh Dow 310 flux im-
bles, is used. This is stirred into the metal a t     mediately before casting, the use of Melrasal E
                                                      flux a t this stage is perfectly permissible. Ii
   'See, for example, French Air Ministry             desired, the vvhole of the old superheated flux
Report: Le fusion industrielle des MagnCsiuin
et ses moulages en sable. by A. Caillon (1938).       cover can be removed and a layer of fresh
4 0 ~                 THE MELTING AND REFINING OF MAGNESIUM

Melrasal E applied in its place; as soon as        author expects from the exposure of metal for
melting of the flux layer is complete it may be    appreciable periods to temperatures between
drawn back from the lip of the pot and pouring     1 5 ' and 1 5 c o O F (750' to 815~C.),we would
                                                    40
beeun.                                             not consider this an effective superheating or
                                                   grain-refining temperature range, irrespective
                                                   of the length of time involved.
                                                      For a few thin-section jobs i t may be neces-
  Apart from the additional stirring with          sary to cast a t temperatures as high as 1470°F.
No. 230 flux, the desirability of which is not     (doo°C.): a t these temperatures the unpro-
appreciated, this process appears essentially      tected metal bums vigorously, and sulphur is
to correspond with our standard practice.          an inadequate protection. How would the
                                                   author avoid in such a case contamination of
                                                                                       f
                                                   the casting with oxide inclusions i the flux is
   In our opinion die casting should be done       "entirely skimmed off before pouring" (cruci-
wherever possible from smoothly operating          ble melting and pouring practice)?
tilting pots using an inspissated flux cover.
Where ladle casting is used we consider i t            C. E. NELSON (author's reply).-As         an
preferable to cover the metal surface with         opening statement pertinent to this discussion,
Melrasal E, or, better still, with Melrasal UE,    the author would like to say that M.E.L. and
part the flux cover with a flux spoon or skimmer   Elektron fluxes and methods have been tested
and then 611 the ladle. A light dusting of         and compared with American fluxes and prac-
Melrasal E is applied to the exposed metal         tices by the author and by other reliable
surface in the pot when visible oxidation be-      foundry establishments in this country. This
gins. Such a process may be conveniently           has been done recently as well as over a good
combined with the dome hlled with SO2 de-          many years. The conclusion has been that
scribed by Mr. Nelson, when it will be found       while in many cases the M.E.L. fluxes are the
that as development of thin oxide skin pro-        equivalent of those used in this country, there
gresses, i t is quite unnecessary to refine with   is no indication that they are superior in any
Melrasal E, much less to sludge the pot; mere      respect.
application of a fairly thick layer of Melrasal       There is no intention, either in this discus-
E to the metal surface followed by parting of      sion or in the paper, to indicate that any
the flux cover after melting is complete will      classes of fluxes are not suitable for the pur-
enable casting to be resumed. This treatment       pose for which they were intended; rather,
of the metal surface with Melrasal E may be        the theme is to point out that suitable fluxes
repeated a t fairly frequent intervals, as re-     are available, which, if applied and used cor-
quired to maintain a clean metal surface in the    rectly as indicated, will allow the production of
pot.                                               castings that will meet the very high inspection
                 MISCELLANEOUS                      standards in force in this country.
   The comment that "flux inclusions are               The terms "similar flux materials," "essen-
never obtained in castings produced when this       tially similar," or "corresponding roughly to,"
type of crucible flux is used correctly" is no      used by Mr. Fox are not enlightening, since
doubt justified, but it appears to imply that       almost all the fluxes under consideration are
flux-contaminated castings may sometimes be         made up from the same group of chemical
produced when other types of flux or process        compounds and differ only in respect to rela-
are employed also "rorrectly." I so, what
                                     f              tive amounts present, depending on the in-
justification can there be for using such fluxes    tended use of the product. We know that small
or processes a t all?                               amounts of some of these elements markedly
   The use of chlorine treatment mentioned         affect the behavior of the flux. We are very
by the author to degas melts of magnesium-          certain that castings made with carnallite
base material is unknown in this country, as it     would not regularly meet the inspection stand-
is never necessary: a contributing factor here      ards set up for castings in this country with
is probably the highly anhydrous character of       respect to freedom from flux inclusions.
our fluxes.                                            Melrasal Z, which is said to "correspond
   As for the grain-reKing effect which the         roughly in behavior to" Dow No. 230 flux, is
widely different in composition in that, for        paper describes two workable methods to cover
example, i t contains a large proportion of CaClr   this type of operation; namely, the open pot
not found in the 230 flux and a very leu. rela-     with No. 230 flux or the SO2 protected pot
tive proportion of potassium chloride. Actual       along with refining flux No. 220.
measurements of the surface tension on these           On the point of degassing and chlorine treat-
two fluxes show 230 to have a lower surface         ment of magnesium alloys, we would say that
                                                    this is not common practice in this country and
tension (go compared to 104 dynes per cm.),
                                                    is considered only when scrap and ingot are not
which may account for the ease of repeated
                                                    properly dried or handled or where there is abuse
ladling from pots protected with 230 flux.          in the handling or exposureof the flux. The fluxes
Ladling from pot to pot is not practiced in this    are all produced from anhydrous materials but
country.                                            take on water rapidly upon undue exposure in
   The values given in the paper for flux con-      the melting rooms. This is equally true of the
sumption are for individual and single types of     British fluxes. A few years ago we thought,
operation and the ranges, particularly on           like Mr. Fox, that there was no gas in magne-
alloying, are made broad to cover all classes of    sium alloys but experience in recent years has
magnesium melting such as crystals and a            shown that it may be present and the resultant
proportion of scrap. Wherever alloying, casting,    porosity takes the same form as the micro-
superheating and pouring are carried out within     shrinkage, and hence is difficult to distinguish
one plant, or particularly in one continuous        from it. It is still true that if great vigilance is
operation, figures on flux consumption agree        used, gas is not a serious problemon magnesium
with those quoted by Mr. Fox. Melting losses        alloys.
are also of the same order.                            No prolonged discussion will be given to the
   Regarding the removal of dross and sludge,       matter of low-temperature grain refinement.
it should be pointed out that most of the melt-     While, as stated in the paper, temperatures as
ing processes in this country are continuous or     high as 1650" to r7oo0F. are neccssary to get
semicontinuous rather than batchwise. The           dependable grain refinement in a short time,
"clinkerlike dross'' is the same as referred to     we know from long production experience that
by E. F. Emley, in Magnesium Review and             metal held for 2 hr. or more a t temperatures of
Abstracts (vol. IV, No. I, p. 11) as I'the thick     1450°F. or above will give dependable and
layer of pasty metal oxide and flux," which he      effective grain refinement of the same order as
also states must be removed with the ladle          obtained a t the higher temperatures for short
before refining. This is not too common, especi-    times.
ally in the Cwo-stage crucible operation in            I n this country the inspissated flux cover
connection with premelters. It may be due to        may or may not be removed before pouring
the melting of dirty scrap direct in the casting    from crucibles. In either case adequate protec-
crucible. This does not, however, offer any         tion is provided by Dow No. 181 agent, which
difficulty in production.                           is much more effective than sulphur. Castings
   The Melrasal E flux is almost identical in       so produced are extremely clean and free from
both composition and behavior with Dow No.          oxide.
310 but the author would definitely recommend          One h a 1 point concerns Mr. FOX'S     comment
that neither be used on the crucible just prior     that the three-stage fluxing system has never
to pouring. These fluxes require time and tem-      been used even in Germany. Within the last
perature to inspissate and failure to allow for     two or three years, M.E.L. interests in this
this is precarious.                                 country have advocated the use of a three-flux
   We believe there may, be confusion on the        system consisting of Melrasal Z, E and FSF, to
term "die casting," since the author refers to      be used concurrently in that order. Our point
pressure die cmting whereas Mr. Fox evidently       has been that the use of too many different
refers to permanent mold casting. We would          fluxes leads to mixed fluxes in the melting
not favor either Dow 310 or Melrasal E fluxes       rooms and leaves too much to the judgment of
for pot protection where a ladle must be intro-     nontechnical operators who must make the
duced repeatedly a t intervals of a minute or       additions in such a way that one flux chem-
less and final castings are being poured. The       ically balances or inspissates the other.

				
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posted:3/27/2011
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