GB1587895A

GB1587895A - Metal powder production metallurgy

Info

Publication number: GB1587895A
Application number: GB1107278A
Authority: GB
Original assignee: Karinsky V N Musienko V T
Current assignee: Karinsky V N Musienko V T
Priority date: 1978-03-21
Filing date: 1978-03-21
Publication date: 1981-04-15

Description

(54) IMPROVEMENTS IN OR RELATING TO METAL POWDERY PRODUCTION METALLURGY (71) We, VICTOR NIKOLAEVICH KARINSKY, of Moskovskoi oblasti, bulvar Novoselovoi, 10, kv. 43, Odintsovo, Viktor Tarasovich Musienko, of ulitsa Molodezhnaya, 4, kv. 286, Moscow, and Sergei Georgievich Glazunov, of ulitsa Bakinskaya, 29, kv. 90, Moscow, all of the U.S.S.R., all citizens of the Union of Soviet Socialist Republics, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to powder metallurgy and, more particularly to methods and apparatus for producing globular powders or granules from meltable materials which may be both metallic and nonmetallic.

In accordance with a first aspect of the invention, there is provided a method for producing granules from a rod-shaped billet, comprising melting the end face of a free end of the billet with the use of a concentrated heat source, rotating the rod-shaped billet about the longitudinal axis thereof during melting and, as the free end of the billet melts, moving the billet along the longitudinal axis thereof towards the concentrated heat source so that molten particles of the billet are sprayed and solidify in the form of granules, the direction of the concentrated heat source being along an axis which subtends an angle with respect to the longitudinal axis of the billet within a range of 0 to 70 , and the axis of the concentrated heat source being displaced during melting, from a starting position in which the concentrated heat source is directed at the center of the molten end face of the billet, to positions parallel to said starting position and in which the concentrated heat source is directed at the billet along a radius of the end face and as far as the periphery of the billet.

According to a second aspect of the invention there is provided an apparatus for producing granules from a rod-shaped billet, comprising: a sealed chamber with a lid and a concentrated heat source built into that lid on one side of the chamber, and an opening on the opposite side of the chamber, for feeding a free end of a billet into the chamber towards the concentrated heat source; a mechanism for rotating the billet about the longitudinal axis thereof which is arranged co-axially with the axis of the chamber, and for moving the billet along that axis; said concentrated heat source being built into said lid for providing a source of concentrated heat along an axis which subtends an angle within a range of O" to 700 with respect to the longitudinal axis of the billet; a sight glass for observing the end face of the billet as it is being melted; the lid being arranged so that the concentrated heat source is displaceable from a starting position in which the concentrated heat source is in use, directed at the centre of the billet to positions parallel to said starting position and in which the concentrated heat source is directed at the billet along a radius of the end face and as far as the periphery of the billet.

According to a preferred embodiment of the present invention, the concentrated heat source is a low-temperature plasma jet generator.

According to another preferred embodiment of the invention, the granulation apparatus is characterized in that the chamber's lid is shaped as a conical funnel arranged coaxially with the opening for feeding the billet into said chamber and expanding towards that opening, the sight glass being arranged at the apex of the conical funnel, and the concentrated heat source being built into the inclined lateral surface of the lid.

This is one of the optimum embodiments of the device.

A better understanding of the present invention will be had from a consideration of the following detailed description of preferred embodiments thereof, taken in conjunction with the accompanying drawings, wherein: Figure 1 is an elevation view of a granulation apparatus with a flat lid; Figure 2 is a view of the lid with a heat source, taken in the direction of arrow A; Figure 3 is an elevation view of a granulation apparatus with a cone-shaped lid; Figure 4 is a section taken on line IV-IV and showing the mutual arrangement of the heat source and that opening for feeding the billet into the melting chamber.

Referring to the attached drawings, the granulation apparatus of the present invention comprises a cylindrical chamber 1 with a horizontally extending axis. The chamber 1 includes a charging compartment 2 which accommodates a magazine 3, for example, of the cassette type, intended to hold a batch of billets and feed them one by one into the chamber 1 for processing. Arranged below the magazine 3 is a billet rotating mechanism 4 composed of two rolls 5. The 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 Figure 1) are a roller 8 intended to press 9 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 charging compartment 2 further includes a vacuum line 16 with a check valve 17, intended to evacuate air from the chamber 1, as well 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 shown) necessary for proper functioning of the mechanism inside the chamber 1.

A melting compartment 20 of the sealed chamber 1 has water-cooled walls and is separated from the charging compartment 2 by a water-cooled diaphragm 21 provided with an opening 22 for the billet.

The diameter of the opening 22 is 1.02 to 1.08 of the billet diameter. To process billets of different diameters, it is necessary to have a set of interchangeable diaphragms 21 with the diameters of the openings 22 corresponding to those of the billets. Provided in a front wall 23 of the melting compartment 20 is a hatch 24 covered by a detachable lid 25. The hatch 24 is used to clean 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 cylindrical arc plasmatron introduced into the chamber 1 through a seal 27.Preferably, the seal 27 should be of the ball type for possible deviation of the axis of the plasma generator 26 from that of the opening 22 by an angle of +20 . The plasma generator 26 is arranged horizontally and coupled to a mechanism 28 mounted on the lid 25 and intended to move the plasma generator 26 along the axis of the chamber 1.

Mounted on the front wall 23 of the chamber 1 at an angle of 70" to 1 10o to its axis (in Figures 1 and 2 the angle is 90 ) is a guide rod 29 pivotably connected to hinges 30 mounted on the chamber 1. The rod 29 is coupled to the lid 25 by means of two hinges 31 and 32, forming a pivotable pair with the lower hinge 31 and a screw 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 Figures 1 and 2, the lid 25 moves at a perpendicular to the roation axis of the billet. At the same time the rod 29 serves as an axle about which the lid 25 swivels when the hatch 24 is opened.

A lock nut 33 limits the displacement of the lid 25 with respect to the rod 29 and, consequently, with respect to the axis of the chamber 1. The lid 25 of the chamber 1 is water-cooled and provided with inspection windows 34. A seal 35 and a clamping means 36 provided for an airtight joint between 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 crosssectional size of the hatch 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 from the chamber 1; in its lower 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 mechan isms, the apperatus 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 for normal operation of the device, but not shown in Figures 1 and 2.

The granulation apparatus of the present invention operates as follows.

Cylinder-shaped billets 40 are placed through the hatch 19 in the magazine 3. One of the billets 40 is placed on the rolls 5. The roller 8 presses this billet 40 against the rolls 5 from above, while the pusher 12 exerts pressure on it from the rear. The chamber 1 is sealed and evacuated through the line 16. The valve 17 is then closed and the chamber 1 is filled with an inert gas through the opening 18. The drives 7 and 13 are brought into play, and the billet 40 is introduced through the opening 22 into the melting compartment 20 so that an end 41 to be melted is spaced from the wall of the diaphragm 21 at a distance equal to 0.5 to 1.5 of the diameter of the billet 40. The plasma jet generator 26 is switched on, and its plasma jet generator 26 is switched on, and its plasma jet 42 is directed at the end face of the end 41 of the billet 40 to heat it to the melting point of the material of the billet 40.

The peripheral speed of the rotating billet 40 is 10 to 35 meters per second; the greater the rotation speed of the billet 40, the lesser the diameter of the granules produced.

The centrifugal forces 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 uniformly sprayed in the radial direction inside the melting compartment 20. The inert gas pressure in the chamber 1 is maintained at a level sufficient for cooling and complete solidification of particles of molten metal in the course of their flight from the end 41 of the billet 40 to the lateral wall of the chamber 1. It is best to maintain an excess pressure in the chamber 1 so as to avoid penetration of air into the chamber 1 through possible leaks and movable joints. In such a case, the gas, which is continuously supplied to the chamber 1 with the plasma jet 42, is let out through the opening 37.It is advisable that the outlet gas should be directed from the opening 37 to a special compressor and fed again to the low-temperature plasma generator 26. The speed of the driving mechanism 9 is selected so as to ensure uniform heating of the end 41 of the billet 40, i.e. so as to maintain a constant spacing between the end 41 and the plasma generator 26. Solidified particles fall to the bottom of the compartment 20 and proceed through the opening 38 to the container 39.

The opposite end of the billet 40, which cannot be melted, is pushed by the pusher 15 through the opening 22 into the compartment 20. If this operation is hindered by the plasma generator 26, the latter is withdrawn by the mechanism 28.

The pressure roller is then lifted, and the pusher 15 is withdrawn to its rearmost position.

Another billet 40 from the magazine 3 is placed on the rolls 5, and the above sequence of events is repeated. During a change of billets the plasma generator 26 is switched off to avoid heating of the mechanisms in the compartment 2 by the plasma jet 42 coming through the opening 22.

The apparatus described above is characterized by that the generator 26 and lid 25 are displaced with respect to the billet 40 at an angle of 700 to 1100 to the axis of the billet 40. As a result, the heat-affected zone moves away from the axis of the billet 40, which provides for a more uniform distribution of the thermal flux of the plasma jet 42 over the end face of the end 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 of the billet 40 is melted away, whereas the peripheral part of the billet 40 remains unmelted and disintegrates into largesize lumps. However, when the plasma jet 42 is moved towards the periphery of the rotating 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 formation of granules of different sizes; large drops of molten metal may even fall from the end of the tapered billet. On the other hand, in the case of a relatively uniform distribution of the heat flux, the end face of the billet 40 is either flat or slightly concave.The molten metal at the end 41 of the billet 40 is then accelerated by the centrifugal forces to a speed equal to the peripheral speed of the blank 40; as a result, all the granules are formed under equal conditions, which accounts for the formation of 95 to 98 percent of granules 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 first be displaced with respect to the axis of the billet by 1/8 to 3/8 of the billet's diameter; the generator 26 remains stationary in the course of melting the billet.

If the billet diameter is much greater (more than 4 or 5 times greater) than that of the heat-affected zone, it is advisable that the generator 26 should be continuously displaced while the free end of the billet is being melted; for this purpose, the generator 26 may be swiveled in the ball jolt 27 through an angle of i20 with respect to that position of said generator 26 at which it is coaxial with the billet.

In the case of the apparatus of Figures 1 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 Figures 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 desired temperature. Apart from maintaining the original 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 increased pressure in the melting chamber accounts for a high rate of crystallization, which improves the quality of granuals and makes it possible to reduce the cross-sectional dimensions of the melting chamber. Of all low-temperature plasma generators, the indirect action arc plasma generator is preferable, being the simplest and readily available. However, in some cases other types of low-temperature generators are preferable, for example, highfrequency generators which can operate in oxidizing media and can produce a plasma jet of a large cross-sectional area. There may be other embodiments of the proposed apparatus, apart from the one shown in Figures 1 and 2.

The guide rod 29 and lid 25 mat be secured to the chamber 1 at an angle of 70 to the axis of said chamber 1. This arrangement accounts for a better view of the end 41 of the billet 40 from the inspection window 34 (Figure 1), as well as for further scattering of the thermal flux of the plasma jet 42: When the plasma jet is at an angle to the billet 40, the resultant velocity component of the plasma jet is conducive to the transfer of heat from the heat-affected zone in the radial direction over the end face of the billet 40.

The granulation apperatus according to the invention can also operate in a semicontinuous mode. For this purpose, the apparatus is provided with airlock chambers mounted on the hatch 19 and over the opening 38 for the discharge of granules Irl such cases, it is advisable that the function of the magazine 3 should be performed by a set of interchangeable cassettes with billets installed there in advance.

According to tests, the apparatus in accordance with the invention can process billets with a diameter of 55 to 100 mm. Such diameters are 2 or 3 times greater than the diameters of billets processed in conventional apparatus, wherein the heater is stationary and coaxial with the rotating billet. A provision of a charging magazine helps to increase productivity several times. The apparatus of the present invention accounts for a better size and shape uniformity of granules; this, in turn, accounts for a higher percentage of good-quality granules, which may be as high as 95 to 98 percent of the total mass of molten material. The use of a plasmatron as a heat source helps to improve the purity of granules, which is in contrast with apparatus employing electric arc heating, where granules are contaminated with tungsten and graphite admixtures.The apparatus of the present invention makes it possible to produce powders of metals and alloys, as well as of nonmetallic materials, such as tungsten carbide; such powders consists of pure sphereshaped particles.

According to another preferred embodiment, the proposed apparatus comprises a sealed cylindrical chamber 43 (Figures 3 and 4). The axis of the chamber 43 extends horizontally.

The chamber 43 has a charging compartment 44 accommodating a magazine 45 which may be a cassette to hold a batch of billets and feed them one by one to the chamber 43 for processing. Arranged under the magazine 45 is a billet rotating mechanism 46 composed of two rolls 47. The rolls 47 extend horizontally and parallel to each other and are installed in supports 48. The 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 plane between the rolls 47 (in the plane of Figure 3) are a roller 50 intended to press the billet against the rolls 47, and a mechanism 51 for moving the billet in the longitudinal direction. The 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. Mounted in the same plane on an axle 56, which is arranged below and at a perpendicular to the rolls 47, is a pusher 57 intended to remove the unmelted part of the billet.

The charging compartment 44 also includes a vacuum line 58 with a check valve 59 intended to evacuate air from the chamber 43; the charging compartment 44 further includes an opening 60 for filling the chamber 43 with gas, a hatch 61 for placing billets in the magazine and other auxiliary systems (not shown) necessary for proper functioning of the mechanisms in the chamber 43.

A melting compartment 62 of the chamber 43 has water-cooled walls and is separated from the charging compartment 44 by a watercooled diaphragm 63 having an opening 64 for introducing a billet into the chamber 43.

The diameter of the opening 64 is normally 1.02 to 1.08 of the billet diameter. A front wall 65 of the melting compartment 62 is provided with a hatch 66 covered with a detachable lid 67. The hatch 66 is used to clean the inside of the chamber 43 and replace the diaphragm 63. Mounted on the lid 67 is a heat source which is an indirect-action cylindrical arc plasma generator 68. The generator 68 is introduced into the chamber 43 through a seal 69. The plasma generator 68 is coupled to a mechanism 70 intended to set it in motion in the longitudinal direction.

In the upper part of the melting compartment 62 there is an opening 71 for the removal of excess gas from the chamber 43;in the lower part of the melting compartment 62 there is an opening 72 communicating with a detachable container 73 intended for accumulation of granules.

The plasma generator 68 is built into the conical wall 74 of the lid 67 at an angle of 20 to 700 to the axis of the opening 64, i.e.

to the axis of the chamber 43. According to Figure 3, the heat source 68 is an arc plasmatron constructed as a tube extending through the seal 69 at an angle of 45" to the axis of the opening 64. Provided in the narrowing portion of the conical wall 74, coaxially with the opening 64, is an inspection window 75. The front wall 65 has a concave coneshaped surface so as to reduce the volume of the sealed chamber 43.

The lid 67 is provided with a drive mechanism comprising a drive screw 81 mounted on the wall 65 and secured in supports 82, and a nut 83 secured to said lid 67. The drive screw 81 also acts as an axle around which the lid 67 pivots when the hatch 66 is opened.

The plasma generator 68 is displaced from the axis of the opening 64 by no more than 1/3 of the diameter of said opening 64 (according to Figure 4, the displacement is equal to 1/4 of the diameter of the opening 64).

The apparatus according to the invention is further equipped with power sources, vacuum pumps, a system for the supply, purification and circulation of inert gas, automatic control units and other means which are necessary for normal functioning of the device, but not shown in Figures 3 and 4.

The granulation apparatus described above operates as follows.

Cylindrical billets 76 are placed through the hatch 61 in the magazine 45; 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 from the rear.

By 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 proportional to the diameter of the billet 76; the displacement is also dependent upon the cross-sectional area of the plasma jet 77, the physical properties of the billet material and some other parameters. The lid 67 is closed and the chamber 43 is evacuated through the line 58. The valve 59 is then closed and the chamber 43 is filled with an inert gas through the opening 60. The drives 49 and 55 are brought into play, and the billet 76 is introduced through the opening 64 into the melting compartment 62. The plasma generator 68 is switched on and its plasma jet 77 is directed at the end face 78 of the billet 76 to heat it to the melting point of the billet material.

The centrifugal forces resulting from the rotation of the billet 76 about its longitudinal axis tear the molten metal from the end face 78 of the billet 76, which molten metal is uniformly sprayed inside the melting compartment 62. The inert gas pressure in the chamber 43 is maintained at a level sufficient to ensure cooling and complete solidification of particles of molten metal in the course of their flight from the end face 78 Qf the billet 76 to the cylindrical wall of the chamber 43. The gas, which is continuously supplied to the chamber 43 with the plasma jet 77, is released through the opening 71. The speed of the mechanism 51 is selected so as to ensure uniform heating of the end face 78 of the billet 76, i.e. a constant spacing between said end face 78 and the generator 68.Solidified particles 79 fall to the bottom of the compartment 62 and through 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 76 from the magazine 45 is placed on the rolls 47, and the above sequence of events is repeated.

The apparatus under review features a more uniform distribution of the thermal flux produced by the heat source 68 over the end face 78 of the billet 76. This is due to the fact that the plasma jet 77 is directed at an angle of 200 to 700 to said end face 78 and by that said plasma jet 77 is displaced with respect to the axis of the rotating billet 76. As a result, it is possible to significantly increase the billet diameter and thus raise the output of the apparatus. It is advisable that the billet 76 should be rotated in the direction opposite to that of the plasma jet 77, as shown in Figure 4. As a result, particles of molten material torn from the end face 78 are acted upon not only by the centrifugal forces, but also by the velocity head of the plasma het 77.This makes it possible to produce smaller granules 79 or reduce the speed of rotation of the billet 76, which, in turn, makes it possible to simplify the billet rotating mechanism 46. For example, in conventional apparatus a billet with a diameter of 50 mm must be rotated at a speed of 12,000 to 18,000 rpm to produce granules with a diameter of 100 to 200 m'i The apparatus of this invention makes it possible to reduce the speed of rotation of the billet at least two-fold, while producing granules of the same size.

An important feature about the proposed apparatus is that it makes is possible to remove the unmelted part of the billet from the compartment 44 to the compartment 62 without interferring with the generator 68, and that it provides a good view of the end face 78 of the billet 76 from the inspection window 75.

Apart from facilitating maintenance of the apparatus, this feature provides for a better control of some process parameters. It is possible, for example, to measure the temperature of the end face exposed to the plasma jet by using a pyrometer; it is possible to control the size, shape and location of the heat affected zone, etc.

It is best to arrange the generator 68 at an angle of 20 to 70 to the axis of the opening 64. With an angle of less than 200 and the generator fixed relative to the end of the billet, no positive effect is produced, i.e. it is impossible to facilitate maintenance and increase output. With an angle of more than 700, particles of molten material may reach the generator 68, which may interfere with operation of the apparatus.

The embodiment of Figures 3 and 4 may be modified in the following ways.

For example, when processing billets of very large diameters (200 to 400 mm and more), use should be made of a number of heat sources. One may use, for example, three direct-action arc plasma generators powered by three-phase alternating current so that the billet is a common zero point of three starconnected plasma arcs. Each of the three generators should be displaced to a different degree from the axis of the opening for introducing the billet into the melting chamber.

Keeping in mind the great mass of each billet, it may be practicable to dispense with the charging magazine and process billets one by one. In such a case it is preferable that the billet rotating mechanism should be construct ed as a vertical spindle with a billet clamping chuck.

The apparatus in accordance with the invention makes it possible to handle billets with diameters that are 3 to 4 times greater than the diameters of billets processed. in con ventional apparatus; this accounts for a two to three-fold increase in the output, while maintaining the same dimensions, uniformity and chemical composition of the granules. In addition, the proposed apparatus is much simpler to maintain than conventional apparat us, and provides for a better control of process parameters.

While particular embodiments of the present invention have been shown and described, various modification thereof will be apparent to those skilled in the art and therefore it is not intended that the invention should be limited to the disclosed embodiments or to the details thereof and the departures may be made there from within the scope of the invention as defined in the claims.

WHAT WE CLAIM IS: 1. A method for producing granules from a rod-shaped billet, comprising melting the end face of a free end of the billet with the use of a concentrated heat source, rotating the rod shaped billet about the longitudinal axis thereof during melting, and, as the free end of the billet melts, moving the billet along the longitudinal axis thereof towards the concen trated heat source so that molten particles of the billet are sprayed and solidify in the form of granules, the direction of the concentrated heat source being along an axis which subtends an angle with respect to the longitudinal axis of the billet within a range of 0 to 700, and the axis of the concentrated heat source being displaced during melting, from a starting position in which the concentrated heat source is directed at the center of the molten end face of the billet, to positions parallel to said start ing position and in which the concentrated heat source is directed at the billet along a radius of the end face and as far as the periphery of the billet.

2. An apparatus for producing granules from a rod-shaped billet, comprising a sealed chamber with a lid and a concentrated heat source built into that lid on one side of the chamber, and an opening on the opposite side of the chamber for feeding a free end of a billet into the chamb er towards the concentrated heat source; a mechanism for rotating the billet from the longitudinal axis thereof which is arranged coaxially with the axis of the chamber, and for moving the billet along that axis; said concentrated heat source being built into said lid for providing a source of concentrated heat along an axis which subtends an angle within a range of 0 to 700 with respect to the longitudinal axis of the billet; a sight glass for observing the end face of the billet as it is being melted; the lid being arranged so that the concentrated heat source is displaceable from a starting position in which the concentrated heat source is, in use, directed at the centre of the billet to positions parallel to said starting position and in which the concentrated heat source is directed at the billet along a radius of the end face and as far as the periphery of the billet.

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

4. An apparatus for producing granules as claimed in Claim 2, wherein the chamber lid is shaped as a conical funnel coaxial with the opening for feeding the billet and expanding towards that opening, the sight glass being arranged at the apex of the conical lid, and the concentrated heat source being built into the inclined lateral wall of the lid.

5. A method for producing granules as setforth in Claim 1, substantially as hereinbefore described with reference to the accompanying drawings.

6. An apparatus for producing granules as set forth in Claims 2, 3 and 4, substantially as hereinbefore described with reference to Figures 1 and 2 or to Figures 3 and 4 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. one. In such a case it is preferable that the billet rotating mechanism should be construct ed as a vertical spindle with a billet clamping chuck. The apparatus in accordance with the invention makes it possible to handle billets with diameters that are 3 to 4 times greater than the diameters of billets processed. in con ventional apparatus; this accounts for a two to three-fold increase in the output, while maintaining the same dimensions, uniformity and chemical composition of the granules. In addition, the proposed apparatus is much simpler to maintain than conventional apparat us, and provides for a better control of process parameters. While particular embodiments of the present invention have been shown and described, various modification thereof will be apparent to those skilled in the art and therefore it is not intended that the invention should be limited to the disclosed embodiments or to the details thereof and the departures may be made there from within the scope of the invention as defined in the claims. WHAT WE CLAIM IS:

1. A method for producing granules from a rod-shaped billet, comprising melting the end face of a free end of the billet with the use of a concentrated heat source, rotating the rod shaped billet about the longitudinal axis thereof during melting, and, as the free end of the billet melts, moving the billet along the longitudinal axis thereof towards the concen trated heat source so that molten particles of the billet are sprayed and solidify in the form of granules, the direction of the concentrated heat source being along an axis which subtends an angle with respect to the longitudinal axis of the billet within a range of 0 to 700, and the axis of the concentrated heat source being displaced during melting, from a starting position in which the concentrated heat source is directed at the center of the molten end face of the billet, to positions parallel to said start ing position and in which the concentrated heat source is directed at the billet along a radius of the end face and as far as the periphery of the billet.