CA1107539A - Granulation method and apparatus - Google Patents

Abstract

Abstract of the Disclosure According to the invention, a rod billet is melted by using a low-temperature plasma jet generator built into a lid of a melting chamber. The plasma jet generator can be oriented at different angles from 0° to 70°. The plasma jet's axis can be displaced, parallel to its original posi-tion at the center of the end face of the billet being mel-ted, towards the periphery of that end face along its radius.
These features account for an increased output and a better uniformity of granules.

Description

~l~C~G~OUND OF ~ INVæN'llION
1. Fiald of th~ appliGation ~ he present inventioll relates to powder metallur~y and, more particularly, to methods and apparatus for producing ~lobular powders or ~ranules from meltable materials which may be both metallic and nonmetallic.
~: 2. Description oY the prior art ~ here are ~now~ methods anà apparatus for producing gra~ules of metals and alloys by mel~ing the end of a fast-rotati~g rod-type billet with the use of an electric heat source, f`or exa~ple, an electron beam. '~he centrifugal forces spray the molten metal inside a sealed chamber so that the ~olten metal solidifies into spherical particles whose size is determined by the densit~ of the metal, the diameter and the rotation speed of the billet (cf. Italian Patent ~o 712,814, Cl. B22 d, of 1966 a~d ~XG Pa~ent ~ .
i ~o. ~,291~842, Cl. 21h 16/60, of 1966).
: In the United States, a common type of an apparatus for producing metal granules is the one tha~ comprises a collet means for clamping a cylinder-shaped billet to be --melted, a mechanism ~or rotating the billet and moving it ~ in the longitudinal direction, and a melting chamber filled :
; with an inert gas and accommodating a nonconsumable electro- -de; finally, the apparatus comprises wiring and busbar means to connect the collet means and the nonconsumable electrode to a power source (cf. US Patent ~o 3,099,041, Cl. 425-8 3~ of 1963). An electric arc is produced between the nonconsu-; ~ ' , , ~ , .

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~ 75''9 ma~le eiectrode and the end of the rotating billet. The arc melts the billet's end; the molten metal is spra~ed by `le c~trifuJal f`orces and particles o~ metal solidif7 in the i~ert gas inside the melting chamber.
lhe foregoing devices and apparatus all have a limited output~ the main reason for this being that it is extre-mely di~`~icult to introduce a ~ew billet into the ~elting chamber without unseali~g ~hat chamber. In addition, the billet diameter is limited, being determlned by vhe relati-vely ~mall area of the heat-a~fected zone. With a cross-sec-tional area of the billet several times greater than the area oY the heat-a~fected zone, the end of the billet cannot be heated uniforml~. As a result, o~ly the center ol the bil-let is melted a~d sprayed, whereas at the peripheIy the me-tal only reaches the plastic state to be tor~ by the centri-fugal forces into large shapeless lumps. ~'he output of good granules is thus sha~ply reduced~
The closest prototype of the present inve~tion, with regard to its technical features and positive e~ect, is the granulation device developed i~ the Soviet Union and paten-ted in a number of countries (cf. US Patent ~o 3,752,610, Cl. 425-6, of 1973).
The latter device comprises a sealed round chamber, its -axis extending horizo~tally. On one side, the chamber is provided with a round ope~ing ~or a billet, which ope~i~g is coa~-ial with the chamber. On the other side, the chamber is provided with a lid into which there is built a heat source.
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' 75''9 q'he la~ter is a nonconsu~able tungsten elec-trode arranged coaxially wi~h the cn~lber. '~he device further inclu~es a billet rotating mechanism, composed of two sync~ronously rGtating hori~ontal rolls and arran~ed outside the chamber.
'l~he axes oi' the rolls are parallel to the axis of the cham~er. ~rranged above the rolls is a screw-type mechanism intended to drive a billet betwee~ the rolls and through the round hole into the chamber. mhe apparatus further includes a charging means composed of a tray and a revolvin6 drum, a brush-type lead to the rotating billet, a power source to pro~uce an electric arc between the rotating billet and the nonco~sumable electrode, a~d other mecha~isms and com-ponents.
;~ A batch o~ billets is loaded in the charging means. ~he chamber is evacuated asd ~illed with an inert gas. ~lhe bil-lets are fed one by one to the melting ~one o~ the chamber to be melted b~ the electric arc produced between the noncon-s~able electrode and the rotatlng billet. ~he centri~ugal forces break the molten metal into small particles which ; crystallize as they fly from the billet to the lateral walls o~ the chamber. The granules thus produced accumulate at the bottom o~ the chamber; the u~melted part of the billet is also dropped to the bottom. Unlike the American apparatus ; described above (c~. US Pa~ent ~o. 3,099,041, Cl. 425-8), the apparatus under review is quite economical because the entire contents of the charging means can be processed without u~sealing the chamber. Ilhat notwithstanding, this ;

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75 ~9 ~his advanced ap-v,aratus (cf. US ~;atent llo 3,752,610, Cl.
~25-6) is not ~ree from some o~ the disadvantages typical o~ all convel;~ional devices, such as a relatively limited output or limitations imposed on billet diameters.
Fur~hermore, the coa~ial arrangement of the nonconsu-mable electrode and the rotating billet makes maintenance di~icult. For example, in order to push the unmelted part of a billet through the round opening into the chamber, one must first use a special mecha~ism to move aside the heat source. It is difficult to observe the granulation process because the sight glasses are arranged at an angle to the axis o~ the rotating billet.
~ esides, some of the brush material, which is normall~
a ra~idly wearing material, such as graphite or copper, is caught by the granules, which af~ects the purity o~ the product.
~ inally, none of the above apparatus, wherein an elec-tric arc or electronic beam ~re used to melt a rotating bi-lleG, can be used to granulate non-conducting materials.
Summary ol` the Invention lt is an object o~ the present invention to increase the ou~put o~ granulation devices by increasing the ma~imum permissible diameter o~ billets, as well as increasin~ the yield o~ good granules through a more uniform heat distribu- -tion over the billet's end being melted.
It is another object o~ the inven~ion to improve the purity o~ granules and m~ke granulation devices ca~able o~

.-,. ",.~, 1~¢D75~9 processing nonconducting materials through making it unnec-cassary ~o supply current to rotating billats.
It is still anothex object of the invention to provide a granula~ion method which would make it possible to increa-se the output, quali~y and u~iformity of granules, as ~vell as raise the perce~tage o~ good granules.
It is yet a~ot~er object of the invention to provide an apparatus for effecting the foregoing method of granula-tion, which would make it possible to increase the maximum permissible diameter of billets.
It is a further object of the inve~tion to provide a granulation apparatus which would be easier to operate and serYice tha~ conventional devices.
It is a further obaect of the inventio~ to modify the ., .-, above-mentioned advanced granulation apparatus in such a ~` -way aq to improve its reliability without resorting to costly alterations in the design of that device.
`! ~he ~oregoing and other objects of the present inven-tion are attained by providing a method for producing gra~ules from a rod billet, comprising melting the end fa-ce of the free end of the billet by using a concentrated heat source, rotatin~ the rod billet about its longitudinal axis and moving the billet along that axis as the billet's free end melts, so that molten particles o~ the billet are sprayed and solidi~y in the form o~ granules; the method according to the inve~tion i8 characterized in that the di--~ rectio~ of the concentrated heat flux is ~aried with respect :~ .

-1~¢3 75~9 -~o ~he lon~itudinal axis of th~ billet from 0 to 70, ard in -~hat the axis of the concentrated heat flux is si~ulta-neously displ~ced parallel to its original position at the center of the billet's end face as far as the periphery of ~l-,at end face along its radius.
When compared to conventional methods, the method of this invention makes it possible to increase the output of good-quality spherical granules to as high as 97 percent.
The method further makes it possible to increase the e~ficiency oI the granul;dtion process bWO- or three-fold by increasing the billet diameter.
'~he method makes it possible to improve the granulome-tric unif`ormity by reducing variations in the granule sizes.
ally, the method makes it possible to improve tha purity of ~he end product by dispensing with rapidly wearing brush-type means for supplying current to the rotating billet.
~ he present invention further consists in provi~i~g a granulation apparatus comprising a sealed chamber witn a .
lid on one side of said chamber, which lid has a built-in concentrated heat source, whereas on the opposite side said chambar has an opening for feedin~ the free end of a billet into that chamber, the apparatus further including mechanisms ror rotating the billet around its longitudinal axis mat-ched with the axis of the chamber, as well as for feeding the billet into the chamber along that axis, the a~paratus being characterized by that the lid of the chamber is shaped as a conical funnel arran6ed coaxially with the opening for ~ee-.; .
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ding the billet into the cham~er and expanding towards thatopening, the concentrated heat source being built into the inclined lateral surface of the conical funnel, whereas arranged at the apex of the conical funnel is a sight glass located opposite to the end face of the billet being melted, the lid being arranged so that the concentrated heat source is displaceable parallel with the axis of that source.
The apparatus of this invention features an increased efficiency because it can handle billets of greater diameters that conventional apparatus, The apparatus of this invention is easier to service that conventional devices, - According to a preferred embodiment of the present invention, the concentrated heat source is a low-temperature plasma jet generator The above feature makes it possible to granulate not only metallic, but also nonmetallic meltable materlals, such ~ as oxides and carbides.
-1 The apparatus o~ this invention features a simpler design and an improved reliability because, first, it ~- dispenses with the complicated brush-type means for supplying current to the rotating billet and, second, it makes it possible to reduce the rotation speed of the billet, while additionally accelerating particles of molten metal by the velocity head of the plasma jet According to another preferred embodiment of the invention, the granulation apparatus is characterized by that `~
; 8 il~75qg the ca~mber's lid is shaped as a conical fu,lnel arranged coa~;ially ~itll the openin& for ~eeding the bill~t into said chamber a~d expandin~ towards that opening, the sight glass being arlanged at the apex of the conical ~unnel~ whereas the concentr~ted heat source is built into the inclined lateral sur~ce o~ the lid. l'his is one of the o~timum em-bodiments o~ the device.
~rief Description of the Attached Dra~ings Other objects and advantages of the present invention will become more apparent f`rom the ~ollowing detailed des-cription o~ preferred embodi~ents thereof to be read in conjunction with the accompa~ing drawings, wherein:
FlG. 1 is an elevation view o~ a granulation apparatus with a flat lid;
~ IG. 2 is a view o~ the lid with a heat source, taken in the direction o~ arrow A;
FIG. 3 is an elevation view of a granulation apparatus with a cone-shaped lid;
~- C ~IG. 4 is a section taken on line IV-IV~a~d showlng the mutual arrangement o~ the heat source and the opening for feedi~g the billet into the melting chamber.
~etailed Description o~ the Invention Referring to the attached drawings, the gra~ulation arjparatus of th~ present inve~tio~ comprises a cylindrical chamber 1 with a horizontally extending a~is. ~he chamber 1 includes a charging compartment 2 which accommodates a ma-: _ g _ -... . .

75~9 gazine 3, for example! of the c~ssette type, intended to hold a batch of billets and feed them one by one into the chamber l for processing, ~rranged below the magazine 3 is a billet rotating mechanism 4 composed of two rolls 5 are arranged horizontally and parallel to each other and secured in supports 6, The clearance between the rolls 5 is less than the billet diameter.
The rolls 5 are coupled to a drive 7 which rotates both rolls 5 at equal speeds and in the same direction. Arranged in the vertical plane extending between the rolls 5 (in the plane of FIG. 1) are a roller 8 intended to press a billet against the rolls 5, and a mechanism 9 for moving a billet in the longitudinal direction~ The mechanism 9 includes a drive screw 11, a pusher 12 and a drive 13, Arranged in the ~, , same plane and mounted on an axle 14 located below the rolls ' 5 and extending at a perpendicular to them is a pusher 15 intended to remove the unmelted part of a billet. The charaing compartment 2 further includes a vacuum line 16 with a check valve 17, intended to evacuate air from the chamber l, as well 20 as an opening 18 for introducing gas into the chamber 1, a hatch 19 for placing billets in the magazine 3 and other auxiliary systems (not sho~n) necessary for proper functioning of the mechanisms inside the chamber 1.
A melting compartment 20 of the sealed chamber 1 has water-cooled walls and is separated from the c,harging compartment 2 by a water-cooled diaphragm 21 provided with an : ;
- opening 22 for the billet, .~
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., 1~7539 The di~eter o~ the opening 22 is 1.02 to 1.0~ of ~rle billet diame~er. rlo process billets o~ different diameters, it is necessary to have a set o~ intercha~Oe~'Dle diaphragms 21 with the diameters ol~ the openings 22 corresponding to those o~ the billets. Provided in a front wall 23 of the melting compartment 20 is a hatch 24 covered by a detachable lid 25. ~'he hatch 24 is used to clea~ the inside of the chamber 1 and replace the diaphragms 21. Mounted on the lid 25 is a plasma generator 26 which is an indirect-action cy-lindrical arc plasmatron introduced into the ch~mber 1 through a seal 27. Preferably, the seal 27 should be of the ball type ~or a possible deviation o~ the a~is of the plasma generator 26 ~rom that of the opening 22 by an angle of ~20. The plasma generator 26 is arranged horizo~tally and coupled to a mecha~ism 28 mounted on the lid 2~ and intended to move the plasma ge~erator 26 along the axis of the cham~er 1.
Mounted on the front wall 23 of the chamber 1 at an angle o~ 70 to 110 to its axis (in ~IGS 1 and 2 the angle is 90) is a guide rod 29 pivotably co~nected to hinges 30 mou~ted on the chamber 1. ~he rod 29 is coupled to the lid 25 by means of two hing~es 31 and 32, ~orming a pivotable pair with the lower hinge 31 and a scre~ pair with the upper hinge 32. Thus as the rod 29 rotates, the lid 25 moves along the axis of` the rod 29; according to ~IGS 1 and 2, the lid 25 moves at a perpendicular to the rotatio~ axis of the bi-llet. ~t the same time the rod 29 serves as an axle about , ~ :

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75''9 which the lid 25 swivels when the hatch 24 is opened.
loc~ nut 33 limits the displacement of the lid 25 with respect to the rod 29 and, co~sequently, with respect to the a~is of the chamber 1. The lid 25 of the cham~er 1 is water-cooled and provided with inspection windo~s 34. A
seal ~5 and a clamping means 36 provide for a~ airtight joint betwee~ the hatch 24 and the detachable lid 25. In the direction parallel to the rod 29, the size of the lid 25 must be greater than the cross-sectional size of the ha-tch 24 by the length of displacement of the lid 25 along the rod 29.
In its upper part, the melting compartment 20 has an opening 37 for the removal of excess gas ~rom the chamber 1;
i~ its power part the melting compartment 20 is provided with an opening 38 communicating with a detachable container 39 which serves to accumulate granules.
Apart from the foregoing units and mechanisms, the apparatus according to the invention is provided with power sources, vacuum pumps, a system for the supply, purification and circulation of inert gas, automatic control means and other means necessary ~or ~ormal operation o~ the device, but not sho~J~ in ~IG~ 1 and 2.
~ he granulation apparatus of the present invention opera-tes as ~ollows.
Cylinder-~haped billets 40 are placed through the hatch 19 in the magazine 3. One o~ the billets 40 is placed on the . n rolls 5. ~he roller 8 presses this billet 40 agaist the rolls _ 12 -~ 75~,~

5 from above, while ~he pusher 12 exerts pressure on it fro~ the rear. '~he chamber 1 is sealed and ev~cuated through the li~e 16. mhe valve 17 is ~hen closed and the chamber 1 is filled with an inert gas through the openi~g 18. The drives 7 a~d '13 are brou~ht i~to play, a,~d the billet 40 is i~troduced through the opening 22 into the melting compart-ment 20 so that an end 41 to be melted is spaced f'rom ~he wall of the diaphragm 21 at a distance equal to 0.5 ~o 1.5 ol the àiameter o~ the billet 40. The plasma jet ge~erator ; 26 is ~witched on, and its plasma jet 42 is directed at the end face o~ the end 41 of the billet 40 to heat it to the melting point of the material o~ the billet 40. The peripheral speed of the rotating billet 40 is 10 to 35 me-ters per second; the greater the rotation speed of the billet 40, the lesser the diameter of` the granules produced.
~ The centrif'ugal f'orces resulting from the rotation of the billet 40 about its longitudinal axis tear the molten metal from the end 41 of' the billet 40; the molten metal is thus uni~ormly spra~ed in the radial direction i~side the . . .
.' melting compartment 20. ~he inert gas pressure in the chamber 1 is maintained at a level sufficie~t f'or cooling and comple- .
~" te solidif'ication of particles o~ molten metal in the course : o~ their flight from the end 41 of the billet 40 to the lateral wall of the chamber 1. It is best to maintain an e~cess pressu~e in the cha~ber 1 so as to avoid penetration : of air into the chamber 1 through possible leaks and movable aoints. In such a case, the gas, which is continuously sup-, - 13 _ . ;- ' - . .
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~ ~ 7 5 q9 plicd to the ch~mber 1 with the plasma jet 42, is let out throu~h the opening ~7. It is advisable that the outlet ~as should be directed from the openin~ 37 to a special comEre-ssor a~d fed again to the low-temperature plasma generator 26. ~he speed of the driving mechanism 9 is selected so as to ensure uniform heating o~ the end 41 of the billet 40, i.e. so as to main~ain a constant spacing between the end 41 and the plasma generator 26. Solidified particles fall to the botto~ o~ the compartment 20 and proceed thIough the opening ~8 to the co~tainer 39.
~ he opposite end o~ the billet 40, which cannot be mel-ted, is pushed by the pusher 15 through the opening 22 into ~he compartment 20. I~ this operation is hindered by the plasma generator 26, the latter is withdrawn by the mechanism 28.
The pressure roller is then li~ted, and the pusher 15 is withdrawn to its rearmost position. A~other billet 40 from --the`magazine 3 is placed on the rolls 5, and the above se-quence of events is repeated. Durin~ a change of billets the plasma generator 26 is switched of~ to avoid heating of the mechanisms in the compartment 2 bytthe plasma jet 42 coming A;, .
-` through the opening 22.
~ he apparatus described above is characterized by that the ge~erator 26 and lid 2~ are displaced with respect to the billet 40 at an an~le of 70 to 110 to the axis of the billet 40. As a result, the heat-affected zo~e moves away from the axis of the billet 40, which provides ~or a more :
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11f~D75''9 uni~`ol~m dis~ribution of the ther~al flux of the ~lasma jet 42 over the e~d 1~ace o~ the e~d 41 of the billet 40.
When the plasma jet 42 is directed straight at the center of the end face of the billet 40, the central part o~ the billet 40 is melted away, whereas the peripheral part o~ the billet 40 remains 1-nmelted and disintegrates into large-size lumps. ~owe~er, when the plasma jet 42 is moved towards the periphery of the rotatin~ billet 40, its end 41 becomes tapered; as a result, the peripheral speed of molten metal is reduced with a reduction in the billet's radius, which accounts for the formatio~ of' granu-les of different sizes; large drops of` molten metal ma~
even ~all from the end of` the tapered bille~. On the other hand, in the case of a relatively unif'o~m distribution of the heat flux~ the end face of' the billet 40 is either flat or slightly concave. ~he molten metal at the end 41 of the billet 40 is then accelerated by the centrifugal forces to a speed equal to the peripberal speed of the bl~nk 40; as a result, all the granules are formed under e~ual conditions~
which accounts ~or the formation of 95 to 98 percent of gra-nules of the same size. If the diameter of the billet is 2 to 5 times greater than that of` the heat-affected zone, the latter must f'irst be displaced with respect to the axis of the billet by 1/8 to 3/8 of the billet's diameter; the gene-rator ~6 remains stationary in the course of mel~ing the billet. lf the billet diameter is much greater ~more than 4 or 5 times greater) tha~ that of the heat-affected zone, it ; - 15 -,.
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it is advisable that the ~enerator 26 should De continuousl~if displaced while the free end of the billet is being ~elted;
for this purpose, the generat~r 26 may be swiveled in the ball joint 27 through an angle of +20P with respect to that position of said generator 26 at which it is coaxial with the billet.
In the case of the apparatus of FIGS. l and 2, it is only prior to operation that the generator 26 and lid 25 should be displaced along the rod 29 as may be required by changes in the diameter or chemical composition of the billet, which may call for a different distribution of the thermal flux over the end face of the billet 40. The apparatus of FIGS. 1 and 2 is easy in maintenance and is advantageous for processing large batches of identical billets.
In the proposed apparatus, the electric heat source is a low-temperature plasma generator which can form a jet of gas of practically any chemical composition, which jet can ~, practically be heated to any deslred temperature. Apart ~`- from maintaining the oriyinal chemical composition of the material, this feature also makes it possible to further act upon the material in a desired way; for example, one can combine the melting of materials with refining, reduction,-alloying and other chemometallurgical operations. The low-temperature plasma generator is fit to melt any material no matter if it conducts electricity or not. Besides, the generator can operate at high pressures of 1 to 50 atm. This is a valuable feature, keeping in mind that an increa~

c ` 30 ~16-:

~75q9 sed pressure in the meltin~ cha~ber ~ccounts for a high ra-te o~ cr~rstallization, which improves the ~uali~y of ~ra~lules and ma~es it possible to reduce the cross-sectio-nal dimensions OL' the meltin~ chamber. Of all low-tempera-ture plasma generators, the indirect-action arc plas~a ~e-nerator is preferable, being the simples~ a~d readily avai-lable. IIowever, i~ some cases other types o~ low-temperature generators are pre~erable, ~or example, high-frequency gene-rators ~hich ca~ operate in oxidi~ing media and can produce a plasma jet of a large cross-sectional area. 'I~here may be ot~er embodimants of the proposed apparatus, apart from the one sho~n in FIGS 1 and 2~
The guide rod 29 and lid 25 ma~ be secured to the cham-ber 1 at an an~le of 70 to the axis of said chamber 1. This arrangement accounts for a better ~iew of the end 41 of the billet 40 ~rom the inspection window 34 (FIG. 1~, as ~ell as ; for further scattering of the thermal flu~ of the plasma ~ aet 42.
-~ When the plasma jet is at a~ a~gle to the billet 40, the resultant velocity co~ponent of the plasma jet is condu-cive to the transfer of heat from the heat-affected zone in the radial direction over the end ~ace of the billet 40.
~ he granulation apparatus according to the invention can also operate in a sem~continuous mode. ~or this purpose, - the apparatus is provided with airlock chambers mounted o~
the rlatch 19 and over the opening 38 for the dischar~e of granules. In such cases it is advisable that the functio~n _ 17 --:' .
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, 75~9 oi` th~ ma~azine 3 should be performed by a set OL interchan~e-able c~ssettes with billets installed thare in advance.
According to t~sts, the apparatus in accordance with ~he invention ca~ process billets with a diameter o~ 55 to ~100 mm~ ~uch diameters are 2 or 3 times greater than the diameters of Dillets processed in conventional apparatus, ~herein the heater is stationary and coaxial with the ro-tating billet. A provision of a charging magazine helps to increase productivity several times. q~he apparatus of the present invention accounts for a better size and shape uni-formity of granules; this, in turn, accounts for a higher percenta~e of good-~ualicy gra~ules~ which may be as high as 95 to 98 percent of the total mass o~ molten material. The use of a plasmatron as a heat source helps to improve the puri~y of granul~s~ ~vhich is in contrast with apparatus employing electric arc heating, where granules are contami-nated with tungsten and graphite admi~tures. The apparatus of- the present invention makes it possible to produce powders of metals and alloys, as well as of nonmetallic materials, such as tungste~ carbide; such powders consists o~ pure, sphere-sha~ed particles.
According to another preferred embodiment, the proposed apparatus comprises a sealed cylindrical cham~er 43 (~IGS 3 and 4). ~he axis of th~ chamber 43 extends horizo~tally. l'he chamber 43 has a charging compartment 4~ accommodating a magazine 45 which may be a cassette to hold a batch of billets and ~eed them one by one to the chamber 43,for processing.

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Arranged under the magazine 45 is a billet rotatin~ mec~a~ism 46 composed of two rolls 47. The rolls 47 extend hori~ontally a~d parallel to eac~l other a~d are installed in supports 48.
'~'ne clearance between the rolls 47 is less than the billet diameter.
The rolls 47 are coupled to the drive 49 which rotates both rolls 47 at equal speeds and in the same direction.
Arranged in the vertical pla~e between the rolls 4'~ (in the plane o~ ~IG. 3~ are a roller 50 intended to press the bil-let against the rolls 47, and a mechani~m 51 for mo~ing the billet in the longitudinal direction. ~he mechanism 51 comprises a drive screw 52 extending parallel with the rolls 47, as well as bearings 53, a pusher 54 and a drive 55. ~JioU~-ted i~ the same plane on an a~le 56, which is arra~ged below and at a perpendicular to the rolls 47, is a pusher 57 inten-ded to remove the unmelted part o~ the billet. The charging compartment 44 also includes a vacuum line 58 with a check ~alve 59 intended to ev~cuate air from the chamber 43; the charging compartment 44 further includes an opening 60 ~or ~illing the chamber 43 with gas, a hatch 61 for placing bi-llets in the magazine and other auxaliary s~stems (not shown) ~ecessary for proper ~u~ctioning o~ the mechanisms in the chamber 43.
A melting compartment 62 of the chamber 43 has water--cooled walls and is separated ~rom the charging compartment 44 by a water-cooled diaphragm 63 having an opening 64 for introducing a billet into the chamber 43. ~he diameter of -. .
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~7sq9 ~e opening 64 is norrnally 1.02 to 1.08 of the billet diame-~er. A ~xont wall 65 of the meltirl~ compar~ment 62 is provi-ded WitQ a hatch ~6 covered with a detachable lid 67. The - hatch ~6 is used to clean ~he inside of the chamber 43 and replace the diaphragm 63. Mounted on the lid 67 is a heat source ~hich is an indirect-action cylindrical arc plasma generator 68. The generator 68 is introduced into the cham-ber 43 through a seal 69. ~he plasma generator 68 is coupled to a mechanism 70 intended to set it in motion in the longi-tudinal direction.
In the upper part of the melting compartment 62 there is an ope~ingr 71 for the removal of excess gas from the chamber 43; irl the lower part of the melting compartment 62 t~ere is an opening 72 commu~icating with a detachable container 73 in~ended Yor accumulation of granules~
The plasma generator 68 is built into the conical wall 65 of the lid b7 at an an~le of 20 to 70 to the axis of the opening 64, i.e. to the axi~ of the chamber 4~. ~ccording to ~IG. 3, the heat soulce 68 is an arc plasmatron construc-ted as a tube extending throuLrh the seal ~9 ~ arl angle of 45 to the axis of the operling 64. Provided in the ~arrowing portion of the conical wall 74, coaxially with the opening 64, is an inspection window 75. ~he ~ront wall 65 has a concave cone-shaped surface so as to reduce the ~olume of the sealed chamber 43.
- ~he lid 67 is provided with a drive mechanism comprising a drive screw 8~ mounted on the wall 65 and secuIed in sup-' ~''- . :` ' ' ' ' ', ' ' :' ~ ~
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75~9 ports 82, and a nut 8~ seculed to said lid 67. 'l~he drive screw 81 also acts as an a~le arounà which the lid 67 pivots when the hatch 66 i~ opened.
'~he plasma generator 68 is displaced from the axis of the opening 64 by no more than 1/3 of the diam~ter of said opening 64 (according to FIG. 4, the displacement is equal to ~/~ of the diameter of the opening 64).
The a-oparatus according~ to the invention is further equipped with power sources, vacuum pumps, a system for the supply, purification and circulation of inert gas, automa-tic control units and other means which are necessary for no~mal ~unctioning o~ the device, but not sho~ in FIGS
and 4.
'i'he granulatio~ apparatus described above operates as follows.
C~lindrical billets 76 are placed through the hatch 61 i~ the magazine 3; one of the billets 76 is placed on the rolls 47; it is pressed by the roller from above, whereas the pusher 54 pushes it ~rom the rear.
B~ turning the screw 81, the generator 68 is displaced as desired with respect to the center of the opening~ 64, the value of that displacement being proportio~al to the diameter of the billet 76; the displacement is also depen-dent upon the crosq-sectional area of the plasma jet 77, tne p~ysical properties of the billet material and some other parameters. ~he lid 67 is closed and the chamber 43 is evacuated through the line 58. The valve 59 is then clo-:

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~ed anù the chamber 4~ is filled with an inert gas throughthe opening 60. The drives 49 and 55 are brought into pla~, and the billet 76 is introduced through the opening 64 into the melting compartment 62. Ylhe plasma generator 68 is suA/itched on and its plasma jet 77 is directed at the end ~ace 78 o~ the billet 76 to heat it to the melting point of the billet material.
~ he centrifugal ~orces resulting from the rotation of the billet 76 about its longitudinal axis tear the mol-ten metal fxom the end ~ace 78 of the billet 76, which molten metal is uniformly sprayed inside the melting com-partment 62. ~he inert gas pressure in the chamber 43 is maintained at a level su~ficient to ensure cooling a~d com-plete solidification o~ particles o~ molten metal in the course of their flight from the end face 78 of the billet 76 to the cylindrical wall of the chamber 43. ~he gas, which is continuously supplied to the chamber 43 with the plasma jet 77, is released through the opening 7~. ~he speed of the mechanism 51 is selected so as to e~sure unif`orm heating of the end face 78 of the billet 76, i.e. a constant spacing between sai~ end face 78 and the generator 68. Solidi~ied particles 79 fall to the bottom of the compartment 62 and th~ough the opening 72 proceed to the container 73. The unmelted part of the billet 76 is pushed by the pusher 57 through the opening into the compartment 62. The pressure roller 50 is then lifted, the pusher 54 is brought to its rearmost position, another billet ?6 from the magazine 45 " .
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is placed on the rolls 47, a~d the above se~uence of events is repeated.
The aoparatus under review features a more uniform distribution of ~he ther~al flux pro~uced by ~he heat source 68 68 over the end face 7~ of the billet 76. This is due to the fact ~hat the plasma jet 77 is directed at an angle of 20 to 70 to said end ~ace 78 and b~ that said plasma jet 77 is displaced with respect to the axis of the rotatin~
billet 76. As a result, it is possible to significantly increase the billet diameter and thus raise the output of the apparatus. lt is advisable that the billet 76 should be rotated in the dire~tio~ opposite to that of the plasma jet 77, as shown i~ FIG. 4. As a result, particles of mol-ten ma~erial tor~ from the e~d ~ace 78 are acted upon ~ot only by the centrifugal forces, but also b~ the velocity head oX the plasma jet '77. I'his makes it possible ~o produce smaller granules 79 or reduce the speed of rotation o~ the billet 76, which, in turn, makes it possible to simplify the billet rotating mecha~ism 46. For example, in conventio-~al apparatus a billet with a diameter o~ 50 mm must be rota-ted at a speed of 12,000 to 18,000 rpm to produce gra~ules with a diameter of 100 to 200 mu. ~he apparatus of this in-vention makes it possible to reduce the speed of rota-tion o~ the billet at least two-fold, while producing ~ra~ules oI the same size.
~ Ln important feature about the ploposed apparatus is that it makes it possible to remove the u~melted part of -Y -,.-.,: , - .

:
,, ;75~9 the billet from the compar~ment 44 to the compartment 62 .~.ithou~ interferin~ with the generator 63, and that it provides a ~ood view of ~he end face '~8 of the ~illet ~6 ~rom tha inspection ~vindow 75. Apart from facilitating maintenance of the apparatus, this fea~ure provides for a be~ter control oY some process parameters. It is possible, for e~ampLe, to measure the temperature o~ the end face eYl~osed to th~ plasma jet by using a pyrometer; it is pos-sible to control the size, shape and location o~ the heat-affected zone, etc.
It is best to arrange the ge~erator 68 at an angle of 20 to 70 to the axis of the opening 64. With an angle of less than 20, no positive e~ect is produced, i.e. it is impossible to ~acilitate maintena~ce and increase output.
With an angle o~ more than 70, particles of ~olten mate-rial may reach the generator 68, which may interfere with operation of the apparatus.
'~he embodiment of ~I~S 3 a~d 4 iS not the last embodi-men~ of an apparatus in accorda~ce with the invention, whereo~ various modifications will be apparent to those skilled in the art within the spirit and scope of the inven-tion.
~ or example, when processing billet~ o~ very large diameters (200 to 400 mm and more), use should be made of a ~umber of heat sources. One may use, for example, three di-rect-action arc plasma ge~erators powered by three-phase alternating current so that the billet is a common zero .

.
, ' . -7 5~9 p~irlt o~ three star-con~ected plasma arcs. ~lach of the three ~e~erators should be displaced to a diff`erent degree from the axis o~ the opening for introducin~ the billet into t:1e mel-tlng chamber. ~eeping in mind the ~reat mass of each billet, it may be practicable to dispense with the char~ing magazirle and process billets one by one. In such a case it is prefe-rable that the billet rotating mechanism should be construc- -ted as a vertical spindle with a billet.clamping chuck.
The apparatus in accol;dance with th~ invention makes it possible to handle billets with diametars that are ~ to 4 times greater than the diameters of` billets processed in co~ventio~al apparatus; this accounts for a two- to three--~old increase in the outputS while maintaining the same dimensions, uniformi~ and chemical composition of the gra-nules. I~ addition, the proposed apparatus is much simpler to maintain than conventional apparatus, and provides for a be~ter control of process parameters.
While ~articular embodimen~s oY the pxes~nt inverltion have been shown and described, various modiYications ther~of . will be apparent to those skilled i~ the art and therefore it is not intended that the in~ention should be limited to the disclosed embodimen~s or to the details thereoY and the departures ma~ be made therefrom within the spirit and scope ~ :
of the invention as defined in the claims.

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Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for producing granules from a rod billet comprising melting an end face of a free end of the billet by means of a concentrated heat source, rotating the rod billet about its longitudinal axis, and, as the free end of the billet melts, moving the billet along its longitudinal axis towards the concentrated heat source so that molten particles of the billet are sprayed and solidify in the form of granules, the direction of flux from the concentrated heat source being varied with respect to the longitudinal axis of the billet within a range of 0° to 70°, and the axis of the flux being displaced at the same time parallel to its original position at the center of the molten end face of the billet, along the radius of that end face and as far as its periphery.

2. An apparatus for producing granules, comprising a sealed chamber having a lid and a concentrated heat source in said lid on one side of the chamber, and an opening on an opposite side of the chamber, for feeding a free end of a billet into the chamber; means for rotating the billet about its longitudinal axis matched with the axis of the chamber, and for moving the billet along said axis; a sight glass for observing an end face of the billet as it is being melted; the lid being so arranged that the concentrated heat source is displaceable parallel with the axis of said source.

3. An apparatus as claimed in claim 2, wherein the concentrated heat source is a low-temperature plasma jet generator.

4. An apparatus as claimed in claim 2, wherein the chamber lid is in the shape of a conical funnel coaxial with the opening for feeding the billet and expanding towards said opening, the sight glass being at the apex of the conical lid, and the concentrated heat source being in an inclined lateral wall of the lid.