GB2168725A

GB2168725A - Manufacture of metal granules

Info

Publication number: GB2168725A
Application number: GB08531684A
Authority: GB
Inventors: Rudolf Koppatz
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-12-21
Filing date: 1985-12-23
Publication date: 1986-06-25
Also published as: GB8531684D0; DE3538267A1

Abstract

Molten metal is placed in a dropper tub the bottom of which is provided with dropper nozzles and flows through the dropper nozzles in the form of drops onto a movable surface. In order to provide a predetermined size and shape of granules, and in particular also to produce relatively small granules, the molten metal present in the dropper tub is caused to vibrate during the pouring process. The amplitude and frequency of vibration are adjusted as a function of the marginal conditions (as herein defined) and of the granule size to be produced. In order to produce relatively small drops, the amplitude is reduced and/or the frequency increased, while to achieve larger drops, the amplitude is increased and/or the frequency reduced. Either the dropper is vibrated or the melt surface is vibrated by a gas.

Description

SPECIFICATION Manufacture of metal granules This invention relates to a method of and apparatus for manufacturing metal granules in which a bath of molten metal is placed in a droppertub the bottom of which is provided with dropper nozzles and the molten metal flows through the dropper nozzles in the form of drops onto a movable surface.

In a known method ofthe kind referred to, the dropper process takes place underforce of gravity and can be assisted by a percussion mechanism. The size of the granules can be varied only slightly by varying the size and configuration ofthe nozzles located in the dropper tub. Nevertheless, it is possible at best to obtain granules down to a minimum size of approx. 6 mm. With this arrangement, irregularities in shape and size must be expected and often there may even be small tails on the granules. No control of the size and shape ofthe granules is possible. The resulting end products more or less depend on the conditions of the molten metal, namely its temperature, viscosity, surface tension and its alloy condition.

The invention is concerned with providing a method bywhich it is possible to achieve a definite size and shape of granules and in particular to produce small or extremely small granules.

According to the invention, this is achieved by subjecting the molten metal present in the dropper tub during the pouring process to vibration, the amplitude and frequency of which is adjustable as a function of marginal conditions (as hereinafter defined) and of the granule size required to achieve smaller granules, the amplitude of vibration is reduced and/orthefrequency increased while to achieve larger granules the amplitude is increased andlorthefrequencyis reduced.

For the drops to develop as desired, a predetermined minimum rate of acceleration is required in the molten metal relativetothedroppertuborthe dropper nozzles, according to said marginal condi tions which may be defined as the selected size ofthe dropper nozzles, the temperature, the viscosity, the surfacetension,the alloying condition of the molten metal and such like.

The molten metal can be made to vibrate in various ways. Preferably, vibrations are applied to the dropper tub which transmits them to the molten metal.

Transmission ofthevibrations to the molten metal can take place if the liquid metal inside the dropper tub is maintained in an unstable state of suspension and only contacts the bottom and walls ofthe dropper tub afterthe latter has reachedthe lowest pointofthe vibration code, in other words, during its upward movement. Because ofthe state of suspension, the material srtess on the hot droppertub is relieved and its effective life is prolonged.

Alternatively, the molten metal can be made to vibrate by subjecting the surface of the molten batch in the droppertub to the action of a vibrating gas column, the strength and frequency ofthe pressure surges being adjustable according to the said margin al conditions and the size granules be be obtained. If the droppertub is fed with molten metal feed by a siphon-like action the surface ofthe molten metal can be lowered under pressure and raised under a vacuum so that the desired vibration effect can be adjusted.

Preferably, the acceleration exerted on the molten metal by the vibrations is greaterthan 1.2 times the acceleration due to gravity; however, values of 3 to 5 or more times the earth's acceleration are possible.

The desired size of granule can be adjusted by adjusting the amplitude and frequency of the vibrations.

An inert gas is preferably used as the gas column and this does not reactwith the molten metal but only acts on it mechanically.

Apparatusforcarrying out the method comprises a droppertubwith its bottom provided with dropper nozzles from which the molten metal flows dropwise onto a movable surface, the droppertub according to the invention being mounted forvariable oscillation.

At the sametime, the droppertub can be mounted on a lever mechanism engaged by an actuating rod connected to a rotating eccentric member, both the rotary speed of the eccentric mem ber and also its degree of eccentricity being variable. Rotation of the eccentric member causes a periodic upwards and downwards movementofthedroppertobsothat, upon reversal of the oscillating movement, the molten metal batch present in the droppertub is accelerated.

Dependent upon the degree of acceleration, an exactly defined quantity of molten metal passes through the dropper nozzles and at each vibration forms equalsized drops which fall onto the movable surface. the granules resulting from the drops always havethe sameshape.

It is expedientforthe eccentric member to comprise an adjustable disc which makes it possible to adjust the eccentricity and so alterthe amplitude of vibration.

Adjustment of the amplitude is also possible by adjusting the point of articulation of the actuating rod to the lever mechanism.

Preferably, the droppertub is mounted on a lever mechanism one arm ofwhich rests on a supporting surface with its underside engaged by an adjustable lifting mechanism by which the arm can be periodically lifted from the supporting surface. The height of the latter can be adjusted so that the degree of downward movementofthe lever arm and thus the amplitude of vibration can be adjusted. Alternatively, the lever arm may have an abutment, the height of which is adjustable.

In order to improve thefunctional efficency ofthe apparatus the lever arm can be subjected to the action of an opposing force which counteracts the weight of the dropper tub. The opposing-force is intended to provide a moment which counteractsthe torque which the dead weight of the dropping tub exerts on the lever mechanism so thatthe latterwhich causes the oscillation ofthe droppertub does not have to lift the entire weight of the relatively heavy dropper tub at every stroke. It is convenient if the opposing-force is exerted by adjustable mechanism so thatthe optimum trimming ofthe apparatus is possible in accordance with relevant operating conditions.

Preferably, the mechanism exerting the opposingforce consists of a spring which exerts a given force on the lever mechanism. The spring can apply traction of compression to the lever mechanism orcan in some other way create torque about the pivot point ofthe lever mechanism, the direction ofthetorque requiring to be so adjusted that it counteracts the weight ofthe dropper tub.

It is possible with the opposing-force mechanism to trim the apparatus to the extent that the weight ofthe droppertub is exactly compensated. In such a case, however, it is necessary to provide, in addition to the opposing-force mechanism, a restoring spring which acts in the direction ofthe weight ofthe dropper tub, so that the droppertub, after it has been raised by the lifting mechanism, can move backto its lower starting position. Also the restoring spring can be adjustable.

The opposing trimming facility makes it possible to impart increased restoring acceleration to the dropper tub.

Theapparatusforcarrying outthe alternative method may be so constructed that the dropper tub has an enclosed space above at least part of the molten metal and provided with an inert gas connectionthrough which the space can be subjected to pressure surges of adjustable magnitude and frequency. The pressure surges so act on the batch of molten metal that, according to the waythey are set, equally sized drops always emerge from the dropper nozzles in the dropper tub.

The pressure surges in the gas column may be generated by connecting the inert gas line to a cylinder containing a piston of adjustable length and frequency of stroke.

The invention is illustrated byway of example in the accompanying drawings and is described in detail hereinafter with reference to said drawings, in which: Fig. lisa diagrammatic view of one embodiment of the invention in the form ofapparatusfor manufacturing metal granules; Fig. 2 is a partial view of another embodiment; Fig. 3 shows another embodiment ofthe invention; Fig. 4 shows an embodiment of the invention in which an oscillating column of gas acts on a batch of molten metal in a dropper tub; and Fig. 5 is a further development of the embodiment shown in Fig. 3 provided with trimming mechanism.

The apparatus shown diagrammatically in Fig. 1 serves two carry outthe method according to the invention.Adroppertub 1 which is shown in section butwithoutshowing the dropper nozzles provided in its bottom, is mounted for movement by a lever mechanism 2. The lever mechanism 2 in this embodiment comprises a parallelogram linkage constituted bytwo links 3,4. The ends ofthe links shown on the left in Fig. 1 are pivotally mounted on a rigid support 5.

The upper link3 ofthe parallelogram linkage is extended beyond a pivot point 6 on the droppertub 1 to form an arm 7.

Belowthe arm 7 is a flywheel 8which can be driven at a variable speed and carries an adjustable disc9 which includes an eccentric member 10. An actuating rod 11 connects the eccentric member 10 to a block 12 disposed on the arm 7 in longitudinally displaceable and locable manner. Locking is performed by a screw 13 which passes through the block 12. According to the size ofthe droppertub and the volume of metal, it is possible to provide, for example by means of a counterweight, an equalisation of masses which is arrived at by calculation.

Fig. 2 ofthe drawings shows the free end ofthe arm 7 in the form of a lever arm 14and which mounts the droppertub for oscillation via the lever mechanism 2.

Cooperating with this lever arm is an eccentric journal 15 which, upon rotation oftheflywheel 8which carries the adjusting disc 9, moves along a circular path about the central axis of the flywheel. The free end of the lever arm 14 has a downwardly directed abutment 16 forengagementwith a supporting surface 17 which is wedge-shaped and is mounted for displacement in the direction ofthe arrow 19 on a rigid track 18.

During rotation ofthe eccentric journal 15, it moves upwardly from the position shown in Fig. 2 to a position against the underside of the lever arm 14. The amplitude of oscillations ofthe lever arm and thus the dropper tub depends upon the distance between the lower position of the lever arm 14 and the top dead centre position ofthe eccentricjournal 15 and can therefore, be varied by displacement ofthe wedgeshaped supporting surface.

It is also possible however, to providethe lever arm 15 with a vertically adjustable abutmentto limit the downward movement ofthe droppertub. In the embodiment shown in Fig. 3, such an abutment is provided by a threaded rod 20, the lower end of which is engageable with a fixed support 21. An eccentric journal 22 shown diagrammatically in Fig. 3 moves in a clockwise direction about the central axis 23 of the flywheel 8, during which it engages the underside of the leverarm 14and lifts itto impartthe desired the molten metal in the tub.

Fig.4showsapparatusforcarrying outanalterna- tive process. In this case, the dropper tub 24 has an enclosed space 25 which communicates through an inert gas connection 27 on an inert gas line 26 with a cylinder 28 containing a piston 29 reciprocable by the flywheel 8 through an eccentric journal and a connecting rod 30. Rotation ofthevariable speed flywheel moves the piston 29 to and fro in the cylinder28, as a result of which pressure surges are transmitted to the gasspace 25to vibrate the gas column acting on the surface ofthe molten metal in the dropper tub. The intensity and frequency ofthe pressure surges can be adjusted by varying the eccentricity of the eccentric journal and the rotary speed ofthe flywheel.

The space 25 is isolated from the molten metal inlet by a weir 31 which prevents the inert gas from passing out ofthe space 25 into the molten metal inlet 32.

Fig. 5 shows a further alternative form of apparatus which is based on the structural principle employed in the embodiment shown in Fig. 3.

Withthisdesign,the lever 14takestheform of a double-armed lever pivotable about a pivot mounting 33. The droppertub 1 is carried on arm 34ofthe lever shown on the right in the drawing. Adjacent its free end, the lever arm 34 is provided with an adjustable abutment 35 which limits its downward movement, and is subjected to the action of an eccentric member 41 which periodically raises and lowers the lever arm 34 and with it,thedroppertub 1.

The oppositely disposed left-hand lever arm36 is subjected from above to the action of a thrust spring 37,theforce of which exerts a torque on the double-armed lever 14 about its pivot 33 in opposition to the torque generated by the weight ofthe dropper tub. The thrust spring 37 includes mechanism 38 by which the force ofthe thrust spring 37 can be adjusted.

Thus it is possible to trim the apparatus in a manner to ensure optimum adpation to the relevant working conditions. Normally, the trimming is such that the thrust spring 37 completely compensates for the weight of the dropper tub 1. With this type of trimming, however, a restoring force is required to press the right-hand lever arm 34 downwards in the direction ofthe weight of the droppertub 1. This restoring force can be generated by means of a restoring spring 39 which engages the left-hand lever arm 36 from below. The force ofthe restoring spring 39 can beadjustedtotherelevantworking conditions by mechanism 40.

As shown by broken lines on the right-hand side of Fig. 5, the restoring spring 39 can instead, engage the right-hand lever arm 34 but in this case it must do so from above in order to generate torque in the correct direction.

The springs which engage the lever 4 do not increase its moment of inertia so thatthe manner of oscillation is not negatively affected thereby. Instead, the possibility of trimming the lever mechanism by means of the thrust spring 37 and counter-trimming by means of the restoring spring 39 improve the manner of vibration of the lever mechanism and thus that of the dropper tub 1 which it supports.

The droppertubs shown in the drawing can, for example, be provided with dropper nozzles at their lower ends with a bore diameter of 1.6mum. They can be caused to vibrate at about 100 to 1000 vibrations per minute. The amplitude of these vibrations can be approx. 1 to 2 mm and more. The vibrations exert on the molten metal in the droppertub an acceleration which, as a function of the number of vibrations per minute and their amplitude, is 2to 4 or more times as great as the acceleration duetothe earth's gravity.

With a fixed adjustment of the number of oscillations and a preset amplitude, drops and thus granules of constant size and shape will be produced.

Claims

CLAIMS:

1. A method of manufacturing metal granules, in which a batch of molten metal is placed in a dropper tubthe bottom ofwhich isprovidedwith dropper nozzles through which the molten metal runs out in the form of drops onto a movable surface, characterised in that, during the pouring process, the molten metal present in the dropping tub is subjected to vibrations, the amplitude and frequency of which are adjustable as afunction ofthe marginal conditions (as herein defined) and the size of granules to be obtained, in such a way thatto obtain smaller granules the amplitude is reduced and/orthefrequencyis increased while to obtain larger granules the amplitude is increased and/orthefrequency is reduced.

2. A method according to claim 1, characterised in thatthe droppertub is caused to vibrate and the vibrationstransmitted to the molten batch.

3. A method according to claim 1, characterised in that the surface of the molten batch in the dropping tub is exposed to the action of a vibrating column of gas.

4. A method according to claim 3, characterised in that an inert gas is used as the column of gas.

5. A method according to any one of claim 1 to 4, characterised in that the acceleration to which the molten batch is subjected due to the vibrations is greaterthan 1.2 times the acceleration caused by gravity.

6. Apparatus for carrying outthe method according to claim 1 or 2, comprising a dropping tubthe bottom of which is provided with dropper nozzles from which the molten metal flows dropwise onto a movable surface, characterised in thatthe dropper tub is movably mounted on means for subjecting it to variable vibrations.

7. Apparatus according to claim 6, characterised in thatthe dropper tub is mounted on a lever mechanism engaged by an actuating rod operatively connected to an eccentric member, the rotary speed and degree of eccentricity of which are variable.

8. Apparatus according to claim 7, characterised in that the eccentric member includes an adjusting disc for varying its eccentricity.

9. Apparatus according to claim 7 or 8, characterised in that the point of engagement ofthe actuating rod with the lever mechanism is adjustable.

10. Apparatus according to claim 6, characterised in thatthe droppertub is mounted on a lever mechanism ofwhich one lever arm rests on a supporting surface and is subject to the action of an adjustable lifting mechanism by which it can be periodically lifted from said surface.

11. Apparatus according to claim 10, characterised in thatthe height of the supporting surface is adjustable.

12. Apparatus according to claim 10, characterised in that said lever arm has an adjustable abutmentfor engagement with said supporting surface.

13. Apparatus according to any one of claims 10 to 12, characterised in that said lever arm is acted upon by mechanism which counteracts the weight of the droppertub.

14. Apparatus according to claim 13, characterised in that said mechanism is adjustable.

15. Apparatus according to claim 730r14, char- acterised inthatthe said mechanism includes a thrust spring.

16. Apparatus according to any one of claims 13 to 15, characterised in that a restoring spring is provided which acts on said lever arm in the same direction as the weight of the droppertub.

17. Apparatus accordingto claim 16, characterised in thattheforce ofthe restoring spring is adjustable.

18. Apparatus for carrying outthe method accord- ing to claim 3, comprising a droppertub provided with dropper nozzles at its lower end from which the molten metal flows dropwise onto a movable surface and an inletforthe molten metal, characterised in that the dropper tub has an enclosed space above at least a part the molten metal, said space being filled with an inert gas which is subjected to pressure surges of adjustable strength and frequency.

19. Apparatus according to claim 18, characterised in that said space is connected via an inert gas line to a cylinder containing a piston the length and frequency of stroke of which are adjustable.

20. Apparatus according to claim 18 or19. char- acterised in thatthe inert gas space in the droppertub is separated by a weirfrom the molten metal inlet.

21. A method of manufacturing metal granules substantially as herein described with reference to Figs. 1 to 3 or Fig. 4 of the accompanying drawings.

22. Apparatus for manufacturing metal granules, substantially as hereinbefore described with refer ence to and as shown in Figs. 1 to 3 and 5 or Fig.4 of the accompanying drawings.