Casting of Granulated Magnesium and Magnesium Alloys by Centrifugal by qnq11541

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									CASTTNG 01 GItZNULAT1:D MA(rNES1UM AND MAGNESIUM ALLOYS
        BY C l N SRElJGAL SPKAYTNC;0 LIQUID METAL
                                    1
                ADVAN SAGF,SANT) LIMITATIONS



                         Tltaniurn Inst~tute
                        180 prospekt I xnina
                        Zaporozhyc. liliraine


Abstract

                                        Magnesium, the most efficient and environrnci!tai!\ 11 l.:~i'.il; . ~ - a ! :
                                        tbr hot metal desulfurizatmn is used ~noi-e      ;ind riiolc ~ . \ I i ~ ! i i l \ i . l \
                                        11 ,21.
                                        'lhe most economical process fbr ~lesulfiirl/;iuori I > tlic ~ I : ) L C Y ~
                                        based on injecting pure granulated ixigncsluni 111to I I I C i,dI;
                                        i \vithout such diluents as llmc or culcluin car-txiie i j i.4 j
                                        111 Lkalne; an industrial process CIS castliig g r a m ~ l c ~ l                    il

                                        ~nagnesium and inagnesiurn-based d l o \ s 1i;is h e w (It.\ clopcd
                                        ~ p x i a l l > ~ out-of-funlace iron desulfurl~atio~r c e i ~ t r ~ i ~ i g ~ i l
                                                      for                                          13)
                                        spraying of liquid metal in a ~nlxture i ~ t h add~tivesi 5-'1
                                                                                \     salt
                                                                       at
                                        Kesultq of testwork a i ~ n c d the improvement of' the prow.;> ii11
                                        the production of salt-coated magnesiuru gramilcs ;u-c picsc~~tcii
                                        below

                                                 of
                                       Ilescr~pt~on the Process
                                       --

                                       'I'ests were performed in laboraton and m d ~ i a t i ~ ~ ~ l
                                                                                                 ~oridi!ri~i.\ i t       ;<

                                       existing updated industrial !'~cllities).
                                       In the course of testn-ork, p r i r n q attentloll \\:ih pait1 1;. ihe
                                       selection of additive coniposition to ohtam a Iilgh-cjualit? j l r i ~ l i i ~ t .
                                       i.c. spherical magnesium granules 1~1th the ~n,~\iln~li:i r c               .ICII
                                       magnesium (MgaCt)content and the inlimnulii colite~it ot' wit
                                                                                                     ic
                                       additive in the product (product analysis for ~ l i l o r ~1011
                                       hi laboratory conditions. the salt melt ~r-as    ;~dil~:~oii,ill\      c\:ili~citc~l
                                       for the rate of nmisturc absorption t q wlts lt;clu~lcii 111 tile
                                       addit~ve.
                                       Basic process flov diagram of granules produc[i,!li I S sIiti\\!i I N
                                       Fig. I
                                          -
                                        Molten magnesium (see Fig.1) cooled do\\ri rr! it sail-lieaitc~l
                                       filniace (1) is transferred hy a siphon (2) 111 rr i.ollt:~~i~(>~is to  >tc';in:
                                       thc mixing unit (3), to nhich a lnoltcri salt d d ~ t ~ \I S                         c
                                       simultaneously fed in a p e s e t proportion from ;I I ' L I I I I ~ I ~ C I wit
                                                                                                                   81



                                       additive (4) Magnesium IS maintai~ledat a ten~lmarirrcc l t 71111-
                                       720•‹C.salt additive temperature is 720-770•‹C'




                         htagnei~umTrchnoiogy 2000
               E d ~ t r d H.I. Kaplan, J . Hryn, m d R. Clo\v
                         by
                                                    Society, 2000
             I'he M i n ~ r a l s Metals & Clntrric~ls
                                  ,
Sti-em1 of molten magnesium in a mixture lvith the salt melt is                Tables 1 and 2 show that a lugh-quality product (Mg,,, > 0 3 ~ .
coiitiliuously fed to a steel vessel with a perforated side wall (5)           C1'1 3%; sphericity - 9 5 4 9 % ) can be obtained using d t
rotating at high frequency, and, under the action of centrifugal               additives in wluch hygroscopic salts (MgCl:, CaCl?) are preseiit 111
l'orcc. ~t is atoini~cd in the cooling and granules collection                 minimum quantities with increased content of sodlum chlorldc: ( up
~ I l i i i ~ i t 6 ji
                  w                                                            to 4045D/o).
hl~igiiesiurndrops coated 1vit11 thin salt film (E 50-100pm), during           The expediency of fluorine ion introduction (as calcium fluoride)
tIl~'i1- jl~ght 111 the chamber: are cooled by air sucked from the             into salt additives has been confinned as mentioned by us earlier
iliainkw with a t r i i ( 7 ) Solidified granules accumulate in the            PI.
hottom plvt of the cooling chamber and are transferred via an                  The range of perforated vessel rotation frequencies has been
                                     rm
ilitennediate bin (8) into a d u screen (9). After the drum screen.            determined. By varying the granulator perforated vessel rotatloll
the pnin+ product is separated into recycled rejects [particle                 frequency one can, mithin a certain range. regulate the aberage
sizes - 0 5 mi11 and + 1.4 inrn or + 1.6 mm) and a marketable                  diameter of formed granules. Additional dniin scrcriiing enables
p~oduct        \vl?ich is packed ill drums, barrels (10) or 500 kg big bags.   the product separation into narrower Gact~ons (for e ~ a ~ r i p l r .
1.01- many >ears; ",+,ovstal" Plant delivers granulated magnesium              0.4(0.5)- 1.0 I ~ and 1. O - 2 mm, etc.). With tlus. the Iliain nus.;
                                                                                                     I
111 railroad hopper cars 181.                                                  of the salt additive used in the process is separated on the XI-ec.11.
                                                                               Screenings (size fraction 4 . 5 nun and +1.6 mrn) art: recycled
                                                                                                                                         the
                                                                               The granulator production rate is regulated by chang~ng siphoii
                                                                               pipe diameter (2).
I'lic.rcsults of industrial testing are shoun beloa- in Tables 1. 2.
l'liese data u.ere obtained at t\vo commercial units in parallel.




                                                                                        lo   *-                 eranulated
                                                                                                                Gagnesiurn




                                         Fig. 1. Process flow diagram of granulated magnesium production
                     1 - furnace for manesium, 2 - siphon, 3 -mixing unit, 4 - furnace for salt melt, 5 - perforated vessel,
                           6 - cooling chamber, 7 - fan, 8 -intermediate bin, 9 - screen, 10 - barrels, 11 - bag filter.
                                       TABLE 1. Techrucal indices of granulation plant No1 operation




                                       TABLE 2. Technical indices of granulation plant No2 operation




Notes 1 The folloulng abbreviations are used in the tables: t, - salt additive temperature, t,, magnesium temperature, Q - consumption ol'
itiagrleslurn fed to the granulator; Kf - content of spherical magnesium granules.
         2 Fluorine ion (F') concentration in the salt additives ~ v a s
                                                                       0.1-0.2%.

Splierical gra~iulescan be obtained a i t h magnesium chloride           samples of remelted salt mixtures of the following composit~o~~
concentration in the salt additive within a range from 2 to 10%          (see Table 3) ground to powder (size fraction O 2543.6 Inn1
and a 4 0 4 5 % sodium chloride content (Tables 1 and 2).                As seen from Tables 3 and 4, magnesium chloride (see No2 and
"\l'eighting" salts (BaCl*,NaBr) are added to the salt additive in       5, 6) and sodium chloride (see No3 and 3) influence the
ca.stnlg the granules of Mg-Al-Zn type alloys. So far, their direct      hygroscopicity of the salt additive more ~iotlceably Sodium
~ntluence on the shape of particles has not been revealed.               bromide,      obviously,      influences    the    hygroscopicity
l'robably. this influence is camouflaged by a stronger negative          insignificantly, or, possibly, somehow lowers it (compare Nol
elkct exerted b aluminium. Its increased concentration in
                   !                                                     and 3). But the last statement needs additional check.
nlagnrsium miikcs the process of spheroidization less stable: as a       Thus, regarding the results of commercial testing, it is possible
      the            ty
1x1~. q ~ ~ n t l of spherical particles is reduced to 90-92%.           to recommend to use; as optimal, the follo\ving salt addit~ves
That 1s x h ) . in the practice of the manufacture of granules of        compositions: 3-8% of MgC12; 40-45% of NaC1: KC1 - the rest
rec!clzd materials (scrap and rejects of magnesium alloys of             0.5-1.O% of ground sodium Aoride should be added into the salt
hlg-A1 and Mg-A1-Zn systems), primary magnesium is added to              additive.
:i lnolten secondary alloy to ensure a stable quality of the             While casting granules of zink and alununiu~n   containing alloh s.
marketable product.                                                      it is necessary to inject 5-10% of "weighting" salts, prefzrably.
                                                                         sodium bromide or barium chloride, into the salt additive to
Sele~t~ori Salt Add~tlve
        of                                                               increase its density.
                                                                         To reduce the salt mixture hygroscopicity, it 1s adv~sableto
:Is the sdt additive composition is easily adjusted at the stage of      prepare salt additives with the ~riir~irnuln content of the most
~ t s preparation. tests were carried out in our laboratory              hygroscopic salts (2-3% MgC12, 0-2% CaC12),\vhle density can
~oc\uluate the absorption of at~nospheric moisture by salt               be regulated by the addition of less hygroscopic sodium bromide
tdtlltives depending on their chemical composition. The degree           or barium chloride. Sodium chloride concentration increase is
01' molsture absorption Lvas estimated by gain in weight of two          advisable for economical reasons: too.
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