FR2828418A1 - Device for the production of spherical balls by passing droplets through a cooling tower incorporating an outlet chamber and an ultrasound generator to agitate the molten material prior to granulation - Google Patents

Abstract

A device for the production of spherical balls by passing a jet of molten material through vibrating orifices (8) of a granulation crucible (4) to form droplets that solidify during their fall through a cooling tower (16) filled with an inert gas, incorporates an outlet chamber (20) in the fusion vessel (1) and an ultrasound generator (21, 22) to agitate the molten material contained in the outlet chamber before its transfer into the granulation crucible. The inert gas in the cooling tower contains a predetermined quantity of oxygen. The quantity of oxygen in the inert gas is less than about 15 to 150 ppm. The volume of the outlet chamber is less than about 20% of the volume of the fusion vessel.

Description

<Desc / Clms Page number 1>

Technical device for selecting spherical balls Technical field of the invention The invention relates to a device for selecting spherical balls comprising means for feeding the balls onto a first inclined plane.

STATE OF THE ART There are many granulation processes and devices, applied in many industrial fields, whether in metallurgy, fertilizers, the food or pharmaceutical industry, etc. They all aim to transform into balls of previously molten materials, which have, in air or under neutral gas, low viscosity, good surface tension, good ease of flow through orifices and are capable of being solidified by cooling.

By way of example, the document WO-A-8101811, corresponding to US Pat. No. 4,428,894, describes a method and a device for manufacturing metal granules, 0.1 to 5 mm in diameter, from a metal bath in fusion.

According to this known method, a jet of molten metal is formed, it is passed through a vibrating orifice to divide the jet into individual drops, the drops of the jet are dropped by gravity through an atmosphere of inert gas, so as to by cooling, the solidification of the granular drops.

Whatever the material (organic product, metal ...) granulated by this type of technique, it often happens that a certain percentage of production is

<Desc / Clms Page number 2>

 constituted by strongly deformed balls or by balls glued together, often in pairs, such a pair being called a dumbbell.

However, it is essential, for certain applications, to produce beads, more specifically microbeads, which not only have a uniform diameter but are also perfectly spherical and isolated. In the mechanical industry, when the balls are made of a material of relatively high hardness, selection or sorting devices are generally used, comprising sieves, rollers, etc. This is particularly the case for balls for bearings, for pens, etc. The balls can then withstand impacts and friction without their surface being marked.

On the other hand, in certain cases, the sphericity and the surface condition of the balls must not be altered by the selection device. This is particularly the case for solder alloy balls intended to be used in electronics to form connections, for example for BGA (Ball Grid Array) type housings. Indeed, the materials used in welding alloys are soft metals and the surface condition of a ball made up of such metals can be very easily altered.

OBJECT OF THE INVENTION The object of the invention is to provide a device for selecting spherical balls making it possible to sort balls of uniform diameter, so as to separate all of the balls which are not perfectly spherical.

<Desc / Clms Page number 3>

According to the invention, this object is achieved by the fact that the device comprises a succession of inclined planes, separated by spaces of predetermined dimensions, at least the first inclined plane, in the direction of movement of the balls, having a surface whose roughness is greater than that of the following inclines.

According to a preferred embodiment, the means for bringing the balls onto the first inclined plane comprise a rolling plane, abutment means, ejection means for ejecting from the rolling plane, by jerks, the balls coming into abutment against the stop means.

The ejection means preferably comprise a hollow ramp, driven in a lateral movement back and forth and provided with a plurality of air ejectors distributed uniformly along the ramp.

According to another characteristic of the invention, the means for bringing the balls onto the first inclined plane comprise a conveyor belt having a face inclined in the same direction as the inclined planes and a direction of rotation opposite to the direction of rolling of the balls on said face.

Another object of the invention relates to the elimination of the beads stuck together.

According to a development of the invention, this other object is achieved by the fact that the device comprises, downstream of the inclined planes, a toothed wheel driven in a rotational movement about an inclined axis and comprising longitudinal grooves, the dimensions allow the rolling of an insulated ball and prevent the rolling of a pair of glued balls.

<Desc / Clms Page number 4>

Brief description of the drawings Other advantages and characteristics will emerge more clearly from the description which follows of particular embodiments of the invention given by way of nonlimiting examples, and represented in the appended drawings, in which: FIG. 1 represents , in schematic form, a particular embodiment of a device according to the invention.

FIGS. 2 and 3 show in more detail, respectively in side view and in plan view, a particular embodiment of the part of the device located upstream of the inclined planes of the device according to FIG. 1.

FIG. 4 represents a particular embodiment of the rolling plane leaving the hopper of a device according to FIG. 3, seen from the free end of the rolling plane.

Figures 5 and 6 illustrate the respective positions of the mobile ramp and the hopper exit rolling plane for two extreme positions of the ramp.

FIG. 7 represents, in section, the toothed wheel of the device according to FIG. 1.

FIG. 8 illustrates the positioning of a pair of balls locked inside a groove of the toothed wheel according to FIG. 7.

Description of particular embodiments It has already been proposed to sort spherical products of different diameters or having significant malformations by means of an inclined plane, the sorting being carried out as a function of the speeds acquired by the different balls.

<Desc / Clms Page number 5>

According to the invention, this type of sorting is suitable for sorting balls which already, before the sorting operation, all have the same diameter, with close tolerances, but whose sphericity varies, within a relatively narrow range. The purpose of sorting is then to eliminate all the balls which are not perfectly spherical and which do not have a perfect surface condition.

In the embodiment shown in FIG. 1, the device comprises a tank, in the form of a hopper 1, in which the balls to be sorted are placed. Such a tank is, for example, disposed at the outlet of a device for manufacturing metallic granules of the type described in document WO-A-8101811. The balls are brought on a succession of inclined planes 2a, 2b, 2c and 2d. Each inclined plane is located slightly below the previous inclined plane and a horizontal space and separates two successive inclined planes. The empty spaces between the inclined planes make it possible to eliminate the balls which reach the end of an inclined plane without having acquired sufficient speed to pass onto the next inclined plane without falling between the two successive inclined planes.

The inclined planes do not all have the same surface condition and this is perfectly controlled for each diameter of balls to be sorted. Indeed, the speed of the balls depends on the combined effects of several types of forces, in particular gravity, friction forces, aerodynamic forces, interaction with the rolling surfaces, etc. The inclined planes are, preferably, constituted by sheets whose surface has a controlled roughness, greater for at least one of the first inclined planes, in the direction of movement of the balls. The roughness of the first inclined plane 2a is greater than that of the following inclined planes, so as to more significantly slow down the balls having surface defects. The trajectory of such

<Desc / Clms Page number 6>

 ball on a surface which also has well-defined faults is more complex, which tends to slow down the ball, causing it to fall between the inclined planes 2a and 2b for example. The surface of the inclined planes is treated by any suitable means, for example by sandblasting or micro-blasting, to obtain the desired roughness. In a preferred embodiment, the first two inclined planes 2a and 2b have a large roughness, which may be lower for the second. The last inclined plane 2d, possibly the last two inclined planes 2c and 2d, can have a perfectly smooth surface.

The interaction between the surface defects of the balls and the surface condition of the inclined planes thus makes it possible to quickly eliminate the defective balls.

The slope of each inclined plane and the spaces separating two successive inclined planes are determined, as a function of the diameter of the balls, so that the balls of very good sphericity roll on the inclined planes with sufficient speed to pass from one inclined plane to the next. . Each inclined plane comprises, at its upstream part, an upward curvature, intended to attenuate the shocks upon reception of the balls on the inclined plane and to avoid any rebound of the balls.

For example, for the selection of solder alloy microbeads, the diameter of which is typically less than SOOm, each inclined plane has, in projection on the horizontal, a length L, which can be of the order of 10 to 15cm, and a width which can be of the order of lm. The vertical space e2 separating two successive inclined planes can be less than or equal to 1 cm, while the horizontal space e1 can be of the order of 1cm to 3cm. The number of inclined planes is inversely proportional to the size of the balls, preferably between 2 and 5. Furthermore, the heavier the balls, the faster they roll. In

<Desc / Clms Page number 7>

 Consequently, the inclination of the inclined planes must be low to allow good selection.

The balls leaving the hopper 1 are brought to the first inclined plane 2a by means of a rolling plane 3, slightly inclined, extending the bottom of the hopper 1. The balls exit at the base of the hopper 1 by a narrow passage 4, under the action of gravity forces, so as to constitute a single layer of balls rolling on the running surface. At the free end of the running surface 3, the balls abut against a stop 5. In FIGS. 1 to 3, the stop 5 is constituted by a cylinder disposed at least over the entire width of the running surface 3, perpendicularly in the direction of flow of the balls on the rolling surface 3. The balls are thus aligned in front of the stop 5. A space, less than the diameter of a ball, separates the free end of the rolling plane 3 from the stop 5 .

The balls aligned in front of the stop 5 are ejected by jerking from the running surface. The ejection is preferably carried out by a ramp 6, constituted by a hollow tube in which a continuous flow of compressed dry air or inert gas (nitrogen, argon, etc.) circulates. The ramp 6 is arranged parallel to the stop 5, below the free end of the running surface 3. It has a plurality of air nozzles 7, directed towards the space between the free end of the working plane bearing and the stop, uniformly distributed along the ramp 6 and constituting ejectors intended to lift, preferably by jerking, the row of balls aligned in front of the stop 5.

To ensure the ejection of the balls by jerks, the ramp 6 is driven, by a jack (not shown), with a lateral movement back and forth,

<Desc / Clms Page number 8>

 perpendicular to the direction of flow of the balls (from left to right in Figures 3.5 and 6) on the running surface 3. The respective positions of the ramp 6 and the running surface 3 for two extreme positions of the ramp during its back-and-forth movement are shown in Figures 5 and 6. The running surface 3 has, at least at its free end, obstacles 8, of uniform thickness (Figure 4), triangular in top view , which divide it into a plurality of corridors 9 of decreasing width. The obstacles 8 protrude slightly at the free end of the running surface. The base of the triangular section of an obstacle 8, parallel to the free end of the running surface 3, has a length 11, and the vertices of two adjacent obstacles are separated by a distance 12 (FIG. 5). The basic angles of the triangular obstacles 8 constitute the limits of the displacement of the air nozzles 7 in the two extreme positions of the ramp 6 (FIGS. 5 and 6).

Thus, at the end of the race, when the ramp 6 is in one of these extreme positions, all the air nozzles 7 are placed under one end of an obstacle 8. The air jets leaving the ramp 6 by the air nozzles 7 are then channeled under the obstacles 8 and cannot eject the balls arranged in the lanes 9, on the running surface 3. On the other hand, during the movement of the ramp 6, the air jets leaving the air nozzles associated with each of the lanes cause the row of balls ejecting against the stop 5 to be ejected.

The ejection is done gradually as the air nozzles move. A stop time of the ramp at both ends allows intermittent ejection, in jerks, thus making it possible to completely free up the space, downstream, before the ejection of a new row of balls and limiting the interactions between the balls likely to alter their surface condition. The

<Desc / Clms Page number 9>

 quantity of balls present on each rolling zone is thus regulated and limited.

In a preferred embodiment, 8 obstacles delimit 7 lanes 9. The length 11 of the triangular base of the obstacles 8 can be of the order of 20 to 30mm, for a distance 12 of the order of 130mm. The duration of movement of the ramp between its two extreme positions can, for example, be between 1 s and a few seconds (frequency between 0.1 and 1 Hz).

The ejected balls are directed by a deflector 10 on an inclined face of a conveyor belt 11. The deflector 10, preferably of curved shape, delimits with the stop 5 a passage for the ejected balls, which then fall on an inclined face of the treadmill 11, arranged below the assembly constituted by the running surface 3, the stop 5, the ramp 6 and the deflector 10. The face of the treadmill on which the ejected balls fall is inclined in the same direction as inclined planes 2a to 2d. The direction of rotation of the treadmill 11 is opposite to the direction of rolling of the balls on this face of the treadmill (Figure 1).

The balls having a good sphericity roll on the inclined face of the treadmill, in the direction of the first inclined plane 2a. The speed of movement of the conveyor belt is chosen so that the spherical balls rolling on its inclined face in the opposite direction of its movement reach the first inclined plane. For example, the speed of the treadmill can be of the order of 0.5 to 5 m / min, preferably 2 m / min. The treadmill makes a first selection. Indeed, the balls having large surface defects or the double balls, which cannot roll or roll too slowly on the inclined face of the treadmill, are evacuated backwards by the treadmill and fall into a

<Desc / Clms Page number 10>

 first tank 12, while the balls having a good sphericity roll in the opposite direction, as far as the first inclined plane.

At the exit of the last inclined plane 2d, the selected balls fall into a hopper 13. A movable strip 14 can be arranged between the last inclined plane 2d and the hopper 13, so as to make a final selection between the balls before their reception in the hopper. In FIG. 1, the strip 14 has an upper edge connecting two walls, one of which directs the faster balls towards the hopper 14, while the other discharges the slower balls, which fall upstream of the upper edge .

The device described above makes it possible to select spherical balls of uniform diameter according to their surface condition. Only the balls with a perfect surface finish reach the hopper 13. However, it can happen that glued balls reach the hopper 13. In practice, out of approximately one million balls, 2 or 3 pairs of glued balls reach up to 'to the hopper. This is the case in particular when a pair 18 of glued balls falls on the conveyor belt 11, then on the different inclined planes, so that the rolling of the pair is not slowed down, for example when the axis S of longitudinal symmetry of the pair (Figure 8) is perfectly perpendicular to the direction of movement of the balls. To also eliminate the glued balls capable of reaching the hopper 13, the device is preferably supplemented by a toothed wheel 15 of large diameter, for example of the order of 30 cm, arranged downstream of the inclined planes.

In the particular embodiment of Figure 1, the hopper 13, funnel-shaped, allows the flow of the balls on the upper part of the wheel

<Desc / Clms Page number 11>

 toothed 15. This has a slow rotational movement around an inclined axis 16 and has longitudinal grooves 17 whose dimensions allow the rolling of an isolated ball and prevent the rolling of a pair 18 of balls glued (Figures 7 and 8). The flawless balls roll in the grooves 17 of the toothed wheel and are collected in a second tank 19 arranged downstream of the toothed wheel. The pairs 18 of glued balls locked in the grooves rotate with the gear wheel around the axis 16 and fall by gravity into a third tank 20 when the gear wheel has made a U-turn and the groove in which the pair is located 18 has reached the lower part of the toothed wheel, above the third tank.

The toothed wheel 15 preferably has several hundred grooves. The bottom of the grooves 17 has approximately 1.2 to 1.5 times the diameter of the balls, so that a pair of glued balls cannot be placed perpendicular to the groove and roll therein. To facilitate the deposition of the balls in the grooves 17, the top of the teeth of the toothed wheel is preferably pointed with a slight rounded shape.

A deflector (not shown) in the form of an arc of a circle matching the outside diameter of the toothed wheel can be placed perpendicular to the grooves 17, so as to serve as a barrier in the event of congestion at the outlet of the hopper 13.

The invention is not limited to the particular embodiments described and shown. In particular, the shape, dimensions, arrangement and number of inclined planes can be adapted to the dimensions of the balls to be selected. The stop 7 may not be cylindrical. The curved shapes are nevertheless

<Desc / Clms Page number 12>

 advantageous, sharp edges liable to deteriorate the surface condition of the balls.

Claims (8)

Claims 1. Device for selecting spherical balls comprising means for feeding the balls on a first inclined plane (2a), device characterized in that it comprises a succession of inclined planes (2a, 2b, 2c, 2d), separated by spaces (e1, e2) of predetermined dimensions, at least the first inclined plane (2a), in the direction of movement of the balls, having a surface whose roughness is greater than that of the following inclined planes. 2. Device according to claim 1, characterized in that at least the last inclined plane (2d) has a perfectly smooth surface. 3. Device according to one of claims 1 and 2, characterized in that the means for bringing the balls onto the first inclined plane comprise a rolling plane (3), stop means (5), means of ejection (6,7) to eject from the running surface, by jerks, the balls abutting against the abutment means. 4. Device according to claim 3, characterized in that the ejection means comprise a hollow ramp (6), driven in a lateral movement back and forth and provided with a plurality of air ejectors ( 7) distributed evenly along the ramp. 5. Device according to any one of claims 1 to 4, characterized in that the means for bringing the balls onto the first inclined plane (2a) comprise a conveyor belt (11) having a face inclined in the same direction as the <Desc / Clms Page number 14>  inclined planes and a direction of rotation opposite to the direction of rolling of the balls on said face. 6. Device according to claim 5, characterized in that the means for bringing the balls onto the first inclined plane (2a) comprise deflector means (10) for directing the balls ejected onto the inclined face of the conveyor belt (11). 7. Device according to any one of claims 1 to 6, characterized in that it comprises, downstream of the inclined planes (2a, 2b, 2c, 2d), a toothed wheel (15) driven by a rotational movement around an inclined axis (16) and having longitudinal grooves (17) whose dimensions allow the rolling of an isolated ball and prevent the rolling of a pair (18) of glued balls. 8. Device according to claim 7, characterized in that it comprises first receiving means (19) for the flawless balls rolling in the grooves (17) of the toothed wheel (15), the pairs (18) of balls glued blocked in the grooves (17) falling by gravity into second receiving means (20) during the rotation of the toothed wheel (15).