Title:
METHOD AND DEVICE FOR CONTINUOUSLY PRODUCING GLASS-SHEATHED METAL WIRES BY SUPPLYING METAL PARTICLES
Kind Code:
A1


Abstract:
The method allows the continuous, very regular production of glass-coated metal wire on the basis of the TAYLOR-ULITOVSKY principle.

The feeding of the molten bath (12) by the guide tube (45) is made by means of a regulated dispensing system (40) allowing the very regular, precise adding of metal particles at a rate corresponding to the rate of wire drawing without disturbing the molten metal bath (14). The system is advantageously completed with a vacuum system (38), a pyrometer (30), a magnet (47), an automatic travel system (25) for the glass tube (20), a spooling system (11) and a water spray (34). Application to the manufacture of metal wire and in particular to glass-coated ferromagnetic wire.




Inventors:
Adenot-engelvin, Anne-lise (Tours, FR)
Bertin, Frederic (Tours, FR)
Herve, Vincent (Romorantin, FR)
Application Number:
11/576000
Publication Date:
09/13/2007
Filing Date:
10/13/2005
Assignee:
COMMISSARIAT A L'ENERGIE ATOMIQUE (25 rue Leblanc, Paris 15ème, FR)
Primary Class:
Other Classes:
164/268, 164/254
International Classes:
B22D11/00
View Patent Images:
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Primary Examiner:
PATEL, DEVANG R
Attorney, Agent or Firm:
PEARNE & GORDON LLP (1801 EAST 9TH STREET, SUITE 1200, CLEVELAND, OH, 44114-3108, US)
Claims:
1. Method for the continuous, stable production of glass-coated metal wire (10), consisting of: adding metal to a glass tube (20) inside which a tube (45) to feed metal is positioned and is fixed with respect to the glass tube (20) which is mobile, whose outer diameter is smaller than the inner diameter of the glass tube (20) and is fully inert against a molten metal bath (14) for which it is intended to be used and does not soften at the working temperature, intended to receive the metal required for fabricating a glass-coated metal wire (10), its lower end lying at a short determined distance from the molten metal bath (14); heating the metal to melting point inside the glass tube (20), in its lower part, for the purpose of creating the molten metal bath (14) in the lower part of the glass tube (20) to soften it and allow the continuous feeding of metal, so that the size of the molten metal bath (14) remains substantially constant during drawing of the wire (10); and continuously drawing the assembly formed of the molten metal surrounded by glass derived from the lower part of the glass tube (20), while gradually lowering the glass tube (20) as and when it is consumed by drawing the coated wire obtained, characterized in that, during the continuous wire production, it consists of feeding the molten metal bath with metal continuously and regularly by means of a regulated, metal particles dispensing system and via the tube intended for metal feeding which is a guide tube (15) for the particles towards the molten metal bath (14).

2. Device for the continuous, stable production of glass-coated metal wire (10) chiefly comprising: a glass tube (20) sealed at its base, of determined diameter containing a molten metal bath (14); a tube intended to feed metal placed in the glass tube (20), whose outer diameter is smaller than the inner diameter of the glass tube (20) and which does not soften at the melting temperature of the metal to be melted, this tube having a lower end placed close to the lower part of the glass tube (20); heating means (23) to melt the metal mass (12) placed in the glass tube (20) and to maintain a molten metal bath (14) in the liquid state, softening a lower part of the glass tube (20); and means for moving the glass tube (20) to lower it gradually as and when it is consumed by drawing of the wire (10); characterized in that it comprises a regulated dispensing system (40,50,60) of metal particles to feed the molten metal bath (14) continuously and regularly, the tube intended to feed the metal is a guide tube (45) for the particles towards the molten metal bath (14).

3. Device according to claim 2, characterized in that it is completed by: a water spray (34) placed underneath the heating means (23); a spooling system (11) to wind the manufactured wire (10); vacuum means (38) to regulate the flow of metal; and means for controlling the temperature of the molten bath (14), in the form of a pyrometer (30).

4. Device according to claim 2, characterized in that the regulated dispensing system uses a metering unit with rotating spindle (50).

5. Device according to claim 2, characterized in that the regulated dispensing system uses an automatic strip cutter (60).

6. Device according to claim 2, characterized in that the regulated dispensing system uses a worm screw metering unit.

7. Device according to claim 2, characterized in that the regulated dispensing system uses a vibratory metering unit.

8. Device according to claim 2, characterized in that the regulated dispensing system uses a notched belt metering unit.

Description:

AREA OF THE INVENTION

The invention concerns the stable, continuous production of glass-coated metal wire, and in particular when the two constituent materials of the wire are heated and melted to undergo continuous drawing into their final shape.

PRIOR ART AND PROBLEM RAISED

All the prior art processes to manufacture glass-coated metal wire are based on a process developed and described for the first time by TAYLOR-ULITOVSKY in 1924. It consists of the following principle.

With reference to FIG. 1, a certain quantity of metal is previously inserted into a glass tube 5 whose base is sealed. The lower part of this glass tube 5 is placed in the vicinity of a high frequency inductor 24, which causes melting of the metal 4 placed in the glass tube. The glass softens under thermal conduction. The drawing operation of the microwire, consisting of the metal wire inside its glass coating 5, is primed manually using a capillary. The wire 1 thus initiated is then placed on a winding device 11 so that it can be continuously drawn. To define and obtain the properties of the wire 1, the different parameters of the process need to be stabilized, such as the temperature of the molten metal bath 4, the spooling speed and the rate of travel of the glass tube 5 moved forward by a travel device 6. When the wire is being drawn, the temperature of the molten metal bath 4 can be measured by a pyrometer 30. The adjustment of this temperature is achieved using a vacuum pressure system 8 associated with the glass tube 5. When this vacuum pressure is modified (in the order of 300 Pa) inside the glass tube 5, the metal bath 4 is drawn towards or away from the most intense heating area of the inductor 24, and therefore its temperature is reduced. This parameter affects geometric characteristics as follows: the higher the temperature of the molten metal, the smaller the metal diameter of the wire 1 obtained. A spooling system 11 containing three spool supports is associated with the drawing process. It is an automatic turntable system provided to conduct changeover from one spool to another without generating any wire breakage. Spool speeds can be set, varying between 0.3 to 40 m/s, and having a direct influence on the geometric properties of the wire 1. The diameters of the metal core and total wire 1 decrease when spooling speed is increased. The travel device 6 is positioned for centering and causing vertical movement of the glass tube 5. The travel rates can be adjusted from 0.5 to 5 mm/min, and cause the metal diameter and total diameter of the wire 1 to change linear fashion. Wires whose total diameter may vary from 6 to 25 μm and over, with a metal core possibly measuring 2 to 18 μm, are routinely obtained with this drawing process.

Several routes have been developed to ensure uninterrupted drawing of the wire over an extended period. For example, mention may be made of French patent FR-1 361 929 consisting of using a metal rod acting as metal feed in the tube and connected to a vertical travel mechanism. A derivate process was imagined and described in Russian patent SU 0 888 075. This document uses two high frequency inductors allowing the molten bath to be fed with a metal drop.

Finally, with reference to FIG. 2, the device and manufacturing process described in French patent application 2 823 744 describe a device consisting of two high frequency inductors 23 and 24 placed one over the other and around a glass tube 20. One is positioned in the lower part and allows heating of the molten metal bath 14, and the other is positioned in the upper part around the glass tube 20 and ensures constant maintaining of the temperature of a metal reserve in the liquid state 12. This liquid metal reserve 12 is placed in a quartz tube 15 which ends in a nozzle 13 so as to continuously feed the molten metal bath 14. Therefore, metal feeding is achieved by placing the liquid metal reserve in contact with the molten metal bath 14. By acting on a vacuum system 38 connected to the liquid metal reserve 12, it is possible to cause the desired quantity of metal to flow.

This process raises technical difficulties however for its implementation. The use of heating by induction for the liquid metal reserve 12 causes abrasion of the walls of the feed tube 15 by flows of material i.e. electromagnetic agitation set up in the molten metal bath. The quartz particles torn from the walls of the feed tube 15 therefore collect in the nozzle 13 obstructing it and making it impossible to control the dropping of the metal from the molten metal reserve.

In addition, vacuum control of the liquid metal in the liquid metal reserve 12 is technically very difficult to control. Adjusting pressure by a few Pascals, to adjust metering, is difficult to perform on account of the hot gas flows over the liquid metal reserve 12. Additionally, the use of the two inductors 23 and 24 raises problems of coupling one inductor to the other. Finally, deoxidization of the feed tube 15 causes pollution of the metal over extended production periods.

All these continuous feed processes have disadvantages in that they may have detrimental effects on the drawing process of the coated wire. The major risks to be avoided are:

    • uncontrolled, non-reproducible metal feeding, leading to disturbances in the molten metal bath and hence to major variations in wire geometry;
    • splashing of metal at the time of metal feeding;
    • pollution of the alloy over the long term; and
    • wire breakage necessitating re-initialization of the process.

The purpose of the invention is therefore to overcome these disadvantage.

In the prior art there are various techniques for obtaining metal particles which can be used in prior art devices. They include gas atomization using a neutral or scarcely oxidizing gas stream under high pressure, atomization using a rotating electrode, forging, mechanical crushing, machining (more precisely lathe turning and milling) and strip formation using a rotating water bath.

SUMMARY OF THE INVENTION

For this purpose, one first main object of the invention is a continuous, stable method for producing glass-coated metal wire, consisting of:

    • adding metal to a glass tube, inside which a tube to feed metal is placed that is fixed with respect to the mobile glass tube and whose outer diameter is smaller than the inner diameter of the glass tube, that is fully inert against a bath of molten metal, does not soften at the metal working temperature and is intended to receive the metal required for manufacturing glass-coated metal wire, its end part being positioned at a short, determined distance from the molten metal bath;
    • heating the metal to its melting point inside the glass tube, in its lower part, for the purpose of creating a molten metal bath, softening it and feeding it continuously so that its dimensions remain substantially constant during drawing of the wire;
    • drawing continuously the assembly consisting of the molten metal surrounded by the glass derived from the lower part of the glass tube, while lowering the glass tube gradually, as and when it is consumed by drawing of the coated wire obtained.

According to the invention, during the continuous manufacture of the wire, the method consists of feeding metal continuously and regularly by means of a regulated dispensing system of metal particles and via the tube to feed metal which is a guide tube for the particles towards the molten bath.

A second main object of the invention is a device for the continuous production of glass-coated metal wire, using a glass tube sealed at its base and of determined diameter, mainly consisting of:

    • a tube to feed metal placed inside a glass tube containing a metal mass, whose outer diameter is smaller than the inner diameter of the glass tube and does not soften at the melting point of the metal to be melted, this tube having a lower end placed very close to the molten metal bath;
    • heating means to melt a metal mass placed in the glass tube, and to maintain the formed molten metal bath by softening a lower part of the glass tube;
    • means for moving the glass tube, to lower it gradually as and when it is consumed by drawing of the wire.

According to the invention, the device comprises a regulated, metal particle dispensing system to feed the metal bath continuously and regularly throughout drawing, the tube intended to supply the metal is a guide tube for the particles towards the molten metal bath.

To complete said device, the following are used:

    • water spray means to solidify the coated metal wire just drawn;
    • a spooling system for the wire produced;
    • vacuum means to regulate the metal flow; and
    • temperature control means using a pyrometer.

In a first preferred embodiment of the invention, the regulated dispensing system consists of a metering unit with rotating spindle.

In a second embodiment, this regulated dispensing system consists of an automatic strip cutter.

In a third embodiment of the device, the regulated dispensing system consists of a worm screw metering unit.

In a fourth embodiment, the regulated dispensing system consists of a vibratory metering unit.

Finally, in a fifth embodiment, the regulated dispensing system consists of a notched belt metering unit.

LIST OF FIGURES

The invention and its different technical characteristics will be better understood on reading the description below to which several figures are appended respectively showing:

FIG. 1, already described, a cross-section of the continuous fabrication method for coated metal wire according to the TAYLOR-ULITOVSKY technique;

FIG. 2, already described, a cross-section of a continuous production device for metal wire according to the prior art;

FIG. 3, a cross-section of a first embodiment of the continuous manufacturing device for metal wire according to the invention,

FIG. 4, a cross-section of a second embodiment of the device according to the invention

FIG. 5, a third embodiment of the device according to the invention;

FIG. 6, a fourth embodiment of the device according to the invention,

FIG. 7, a fifth embodiment of the device according to the invention; and

FIG. 8, a sixth embodiment of the device according to the invention.

DETAILED DESCRIPTION OF THREE EMBODIMENTS OF THE INVENTION

The method of the invention is based on the wire drawing process according to the TAYLOR-ULITOVSKY technique, with feeding of the molten metal bath by a supply of solid metal particles whose individual weight represents less than 0.5% of the weight of the molten metal. The particle feed rate is related to metal consumption during wire drawing. It must be adjustable, which is ensured by a regulated, particle dispensing system associated with the manufacturing method. The method of the invention allows the production of glass-coated metal microwires over extended periods under conditions that are absolutely fixed and stable in time, limiting actions by the operator on the device used to implement the process.

In addition, this method solves the problems encountered in the prior art. Particle fabrication remains easy to conduct and at satisfactory cost. It is therefore possible to ensure accurate and regular compensation of consumed metal without disturbing the molten metal bath, and hence without modifying the geometric properties of the wires.

FIGS. 3 to 8 show six embodiments of the device according to the invention, in which only the metal particle dispensing system changes, the remainder of the installation being the same for these six embodiments. Consequently this common part will only be described once with reference to FIG. 3.

A glass tube 20 is used, sealed in its lower part and having two open ends 28 and 29 in its upper part. The first open end 28 is connected to the vacuum system 38 while the second 29, forming the vertical upper part of the glass tube 20, is used to feed the molten metal bath 14 with particles. The inner diameter of the glass tube 20 lies between 8 and 50 mm, with a wall thickness of 0.8 to 5 mm and a length of between 0.5 to 1 m.

In the glass tube 20, an initial mass of metal is placed in the order of ten grams, depending on the size of the glass tube 20. This metal is either an assembly of solid alloy pieces, or consists of a certain quantity of metal particles used for feeding The glass tube 20 is then fixed in travel means 25 to cause the tube to be gradually lowered.

The device is completed by an inductor 24 positioned underneath the glass tube and centered, so that it can heat the molten metal bath 14 with maximum yield, this bath being placed in the lower part of the glass tube 20. A pyrometer 30 is also used at this level to control the temperature. The device is completed by a water spray 34 to solidify the coated metal wire 10 so produced, this wire being automatically stored on a spool device 11.

According to the invention, a guide tube 45 is used whose outer diameter is smaller than the inner diameter of the glass tube 20 and is positioned inside the latter, this guide tube 45 not being intended to contain a liquid metal reserve. A packing seal 33 is used to center it in the upper part of the glass tube 20. This allows the glass tube 20 to slide with respect to the guide tube 45. The lower end of the guide tube 45 comes to lie just above the molten metal bath 14. According to the invention, the guide tube 45 has an upper part placed at the outlet of a metering unit with rotating spindle 41 enclosed in a chamber 49 and fed by a hopper 42 in which the metal particles are stored. The assembly forms the regulated dispensing system referenced 40.

Metal particles are therefore sent into the guide tube 45, and move down this tube to feed the molten metal bath 14.

The variant of embodiment described in FIG. 4 only concerns the regulated dispensing system, denoted 50 in this figure. This system comprises a motor 51 whose output shaft 53 moves at relatively low speed. This output shaft 53 drives in rotation, about a grooved spindle, a device having a rotating shaft 54 and located underneath a hopper 52 containing the metal particles to be sent into the guide tube 45, this guide tube being fully straight. In this case, by way of example, the metal particles are advantageously beads having a diameter of around 1.5 mm representing 15 mg of metal. By causing the motor 51 to rotate at a speed of 15.3 rpm, the grooved spindle conveys the particles and it is hence possible to feed the metal bath 14 with 230 mg of metal per minute.

The third embodiment of the regulated dispensing system is shown FIG. 5 under reference 60. More precisely, this system consists of an automatic strip cutter comprising a spool of strip 61 from which a strip 62 is unwound and is inserted in an automatic strip cutting device 63 to ensure the supply of flat metal particles e.g. at least 5 mm long, at a rate of less than 2 metal cuttings per second, in relation to the desired rate of metal consumption. The cuttings are very precise, reproducible and repeatable to within 100 μm.

FIG. 6 shows a fourth embodiment of the regulated dispensing system, which is a worm screw metering unit 70. This metering unit comprises a speed-regulated motor 71 driving a worm screw 73 fed with metal particles by a hopper 72 and whose end comes to lie above a guide tube 45.

FIG. 7 shows a fifth embodiment of the regulated dispensing system in the form of a vibratory metering unit 80. This metering unit also uses a speed regulated motor 81 driving a trough 83 in vibration via a vibrating device 84. A hopper 82 feeds the trough with metal particles. The end of this trough lies above the guide tube 45.

The sixth and final described embodiment of the regulated dispensing system is shown FIG. 8 and uses a notched belt device 90. This belt uses a speed regulated motor 91 driving an endless notched belt 93. This belt is fed by a hopper 92, each metal particle falling into a notch of the notched belt 93 which forms a driving means for each of these particles. This device can be used to convey the particles forward at low speed at the desired rate.

In the method implemented in the described devices, the metal particles used may have different geometric shapes i.e. spherical, powder, bead, thread, strip or any other (crushings, flats, flakes . . . ). Their shape is directly related to the mode of manufacture used and chosen in relation to the downstream dispensing system. So that the continuous process can operate under good conditions, it is preferable that the weight of a fed particle should lie between 0.5 and 30 mg for an initial weight of the molten metal bath of 6 grams, i.e. 0.01 to 0.5% of the initial weight of the molten metal present in the glass tube 20. If the weight of a fed particle is too low, e.g. less than 0.5 mg, the transfer of material between the particles, at ambient temperature, and the molten metal bath will not be achieved owing to poor heat transfer. This is mainly due to insufficient coupling of the particle with the electromagnetic field set up by the inductor 24. The coupling of this particle is related to the frequency of the inductor 24, to the size and shape of the particle. For example, with an inductor frequency in the order of 400 kHz, good coupling is obtained with the use of spherical particles greater than 0.5 mm in diameter. If the weight of a fed particle is too high e.g. greater than 30 mg, thermal disturbances will be observed in the molten metal bath e.g. temperature variations of more than 10° C., leading to major geometric variations in wire diameter, or the splashing of liquid metal due to impacts of the particles on the molten metal bath.

Regarding the composition of the particles, it is to be noted that to prevent undue stoppage of the wire manufacturing process, it is important to define an oxygen level to be maintained so that there is no oxidization of the metal particles in the molten metal bath. For this purpose it can be proposed, for an alloy of cobalt, iron silicon and boron, that the limit oxygen level should be 500 parts per million (ppm), this level to be observed and not exceeded when forming the particles.

For practical reasons, it is to be noted that it may be of advantage to use metal particles of different compositions to form the final composition of the molten metal bath, and hence of the manufactured wire. It is then possible either to use two, synchronized, regulated dispensing systems in parallel, with different respective compositions, or to use a single system but ensuring that equal weights of particles of the two types are used.

In the manufacturing method of the invention, the obtaining of the particles may be the same as in the prior art. For example, mention may be made of gas atomization using a neutral or scarcely oxidizing gas stream under high pressure (powder), atomization using a rotating electrode (powder), forging (beads), mechanical crushing, machining (more precisely, lathe turning and milling to obtain chips) and obtaining strips with a rotating-water-bath method.

Regarding the feeding of metal particles, this is dependent upon consumption during wire drawing. The particles must be dispensed in relation to this consumption rate. This rate can be characterized by regular intervals between the feeding of one or more particles ranging from 2 to 60 seconds. This feeding must be made taking into account the fact that the total weight of the fed particles must never exceed the limit of 0.5% by weight of the weight of molten metal in the tube, in order to limit any thermal disturbance.

The importance is stressed of controlling the geometry and weight parameters of the fed particles with respect to the choice of regulated dispensing system used. The metal feed must be best controlled in order to offset metal consumption properly when wire drawing.

Regarding the different types of regulated dispensing systems used, the choice is to be made in relation to the weight and shape of the particles, to the accuracy and reproducibility of the desired metering, and to the cost of the dispensing device.

Regarding guiding of the particles, it is to be noted that it is important to always maintain the same pathways towards the molten metal bath. For this purpose, the guide tube 45 must have an inner diameter that is slightly larger than the height of the fed particles. It is then necessary to adjust the distance between the lower end of the guide tube 45 and the molten metal bath 14. This distance must be slightly smaller than the diameter of the fed particles. If these particles do not arrive at the center of the molten metal, they may arrive at a lateral area of the glass tube 20, in which the glass is in the viscous state, and may remain blocked at this point. If one of these particles is present in this area, this may lead to disturbed glass flow and cause wire breakage. Therefore, by adjusting this distance it is possible to ensure proper transfer of the particles towards the molten metal bath. The guide tube 45 must therefore be able to withstand temperatures close to those of the molten metal bath. If the temperature of this molten metal bath is in the order of 1100° C. to 1300° C., quartz is a suitable material to be used to form this guide tube 45.

To ensure the adding of the metal particles, a magnet 47 may be placed around the glass tube 20 a few centimeters above the inductor 24, if the fed metal particles are magnetic. Said magnet 47 can slow down the falling of the particles and therefore prevent splashing of the molten metal on the walls, thereby also ensuring the proper transfer of materials between the particles and the molten metal bath. If the particles are not magnetic, the shape and material of the guide tube 45 can be modified to slow down the particle falling rate.

For continuous wire production according to the invention, it is useful to verify the seal of the assembly to allow temperature control by the vacuum means, then the initial metal mass must be melted in order to form a molten metal bath. It is also necessary previously to place in rotation the receiving spool of the winding system 11, and to set in operation the travel system 25 for the glass tube 20. The temperature of the molten metal bath must then be fixed using the vacuum system 38 assisted by the pyrometer 30, thereby stabilizing the process. Finally, the water spray 34 is used to solidify the wire 10. The dispensing rate of the regulated dispensing system must be adjusted in relation to the desired consumption rate.

EXAMPLES OF EMBODIMENT

One embodiment, using a device with rotating spindle as regulated dispensing system, uses an alloy consisting of an ingot of cobalt, iron, nickel molybdenum, boron and silicon having a density of 7.5 g per cubic centimeter, known as such. 6 g of this alloy are previously placed in the glass tube 20 which is borosilicated and formed of material of Pyrex 7740 type, 600 mm long and inner diameter of 12.6 mm, the thickness of the glass wall being 1.2 mm. The inductor used may be of single spiral type, slightly incurved, with an outer diameter of 50 mm and an inner diameter of 8 mm, supplied by a 440 kHz frequency generator. The guide tube may have a length of 700 mm, an outer diameter of 4 mm and an inner diameter of 2 mm.

To draw a wire whose metal diameter is 8 μm in this example, the temperature of the metal alloy is maintained at 1200° C. in the glass tube, while the travel rate of the tube is 1.6 mm per minute and the spooling rate is 9 m/s. The wire is drawn under these conditions to a total diameter of 12 μm and a metal core of 8 μm. The consumption of metal during drawing of the wire then occurs at a mean rate of 203 mg/min. Finally, the particles used are spherical powders having the same composition as the metal initially placed in the glass tube, and can be obtained by water atomization.

In a first example, if particles of 15 mg weight are used (i.e. a mean diameter of 1.5 mm), the lower end of the guide tube is placed at a maximum distance of 1 mm from the molten metal bath. The rotation speed of the motor of the feed device is set as 13.3 rpm to compensate for metal consumption of 203 mg/min. Every 4.5 seconds, a metal particle of 15 mg falls to feed the molten metal bath, over an operating time defined by the operator in relation to the desired number of kilometers of wire.

In a second example, the same experimental conditions as previously are fixed. If metal particles having a weight of 25 mg are now used (i.e. a mean diameter of 1.9 mm) the lower end of the guide tube must then be positioned at a maximum distance of 1.5 mm from the molten metal bath. The motor of the feed device is then set a rotating speed of 8 rpm to compensate for metal consumption of 203 mg/min, i.e. the falling of a particle of 25 mg every 7.5 seconds.

To draw a wire of metal diameter 6 μm, the drawing method is now used with the following parameters.

The temperature of the metal alloy is now maintained at 1280° C. in the glass tube, the travel rate of the tube is set at 1.8 mm/min, and the spooling rate is 5.5 m/s.

The wire drawn under these experimental conditions therefore has different geometrical characteristics i.e. a total diameter of 16 μm and a metal core of 6 μm. Metal consumption on wire drawing is 70 mg/min.

In a first example, if spherical particles of weight 5 mg (i.e. a mean diameter of 1 mm ) are used, the lower end of the guide tube lies at a maximum distance of 0.5 mm from the molten metal bath. The motor speed of the feed device is then set at 14 rpm to compensate for metal consumption of 70 mg/min. Every 4.2 seconds, a metal particle of weight 5 mg falls to feed the molten metal bath.

In a second example, spherical metal particles are used of weight 25 mg (i.e. a mean diameter of 1.9 mm), the lower end of the guide tube is positioned at a maximum distance of 1.5 mm from the molten metal bath. The motor of the feed device is therefore set at a rotation speed of 2.8 rpm to compensate metal consumption of 70 mg/min, i.e. the falling of particle of 25 mg every 21 seconds.