Inoculant with surface particles

Abstract

The present invention relates to a particulate inoculant for treating liquid cast-iron, comprising, on the one hand, support particles made of a fusible material in the liquid cast-iron, and on the other hand, surface particles made of a material that promotes the germination and the growth of graphite, disposed and distributed in a discontinuous manner at the surface of the support particles, the surface particles presenting a grain size distribution such that their diameter d50 is smaller than or equal to one-tenth of the diameter d50 of the support particles.

Claims

1. A powdered particulate inoculant for treating liquid cast-iron, comprising: support particles made of a fusible material in the liquid cast-iron, and surface particles made of a material that promotes germination and growth of graphite, disposed and distributed in a discontinuous manner at a surface of the support particles, wherein the support particles comprise at least a ferro-silicon alloy, aluminum and calcium, wherein silicon is present in at least 40% by mass to the mass of said support particles, and aluminum and calcium are present in an alloyed form and each in amount of between 0.2 and 5% by mass relative to the mass of the support particles, the material of the surface particles is different from the material of the support particles, and the surface particles present a grain size distribution such that their diameter d50 is smaller than or equal to one-tenth of a diameter d50 of the support particles, and wherein, until an introduction of the cast-iron, the surface particles occupy up to 90% of the surface of the support particles.

2. The inoculant according to claim 1, wherein the support particles are made of a material that promotes the association of carbon with iron in the form of graphite.

3. The inoculant according to claim 1, wherein the support particles comprise, in an alloyed form, at least one additive element between 0.2 and 5% by mass for each additive element, relative to the mass of the support particles.

4. The inoculant according to claim 1, wherein the support particles comprise, in an alloyed form, at least one element for treating shrinkage cavities, in an amount comprised between 0.5 and 6% by mass, relative to the mass of the support particles.

5. The inoculant according to claim 1, wherein a proportion of the surface particles comprises between 1 and 8% by mass, relative to a mass of the inoculant.

6. The inoculant according to claim 1, wherein, until an introduction of the cast-iron, the surface particles occupy between 80 and 90% of the surface of the support particles.

7. The inoculant according to claim 1, wherein the surface particles comprise at least one of, separately or in a mixture, metallic elements including aluminum, bismuth and manganese, silicides including iron silicides, rare earth silicides and calcium silicides, oxides including aluminum oxides, calcium oxides, silicon oxides or barium oxides, metallic sulfides including iron sulfides, calcium sulfides and rare earth sulfides, barium sulfates and carbon black.

8. The inoculant of claim 7, wherein the surface particles comprise at least one of aluminum oxides, calcium oxides, silicon oxides, barium oxides, and barium sulfate.

9. The inoculant according to claim 1, wherein the surface particles are inlaid in the surface of the support particles.

10. The inoculant according to claim 1, wherein the surface particles are bonded by means of a binder at the surface of the support particles.

11. A method of manufacturing an inoculant for treating liquid cast-iron according to claim 1, comprising: providing support particles made of a fusible material in the liquid cast-iron, presenting a grain size distribution ranging from 0.2 to 7 mm, providing surface particles presenting a grain size distribution such that their diameter d50 is smaller than or equal to one-tenth of a diameter d50 of the support particles, and dry mixing the support particles and the surface particles at high speed so as to obtain a deposit by inlaying the surface particles at the surface of the support particles, according to a discontinuous distribution.

12. The method according to claim 11, wherein the surface particles are made of a material comprising at least one of aluminum, bismuth, silicides including iron silicides, rare earth silicides and calcium silicides, oxides including aluminum oxides, calcium oxides, silicon oxides or barium oxides, metallic sulfides including iron sulfides, calcium sulfides and rare earth sulfides, sulfates including barium sulfates and carbon black.

13. The method of manufacturing an inoculant according to claim 1, further comprising: providing support particles made of a fusible material in the liquid cast-iron, presenting a grain size distribution ranging from 0.2 to 7 mm, and providing surface particles presenting a grain size distribution such that their diameter d50 is smaller than or equal to one-tenth of the diameter d50 of the support particles, providing a binder in a solvent, mixing the support particles, the surface particles and the binder, to obtain a deposit by binding the surface particles at the surface of the support particles, according to a discontinuous distribution and removing the solvent from the binder.

14. The method according to claim 13, wherein the binder comprises at least one of organic and polymer binders including polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), polyvinylpyrrolidone (PVP), and cement.

15. A powdered particulate inoculant for treating liquid cast-iron, comprising: support particles made of a fusible material in the liquid cast-iron, comprising at least a ferro-silicon alloy, aluminum and calcium, wherein silicon is present in at least 40% by mass to the mass of said support particles, and aluminum and calcium are present in an alloyed form and each in amount of between 0.2 and 5% by mass relative to the mass of the support particles, and surface particles made of a material that is different from the material of the support particles, and that promotes the germination and the growth of graphite, disposed and distributed in a discontinuous manner at a surface of the support particles, wherein the support particles present a grain size distribution ranging from 0.2 to 7 mm, wherein the surface particles present a grain size distribution such that their diameter d50 is smaller than or equal to one-tenth of a diameter d50 of the support particles, and wherein, until an introduction of the cast-iron, the surface particles occupy up to 90% of the surface of the support particles.

16. The inoculant of claim 15, wherein the surface particles comprise at least one oxide or a sulfate.

17. The inoculant of claim 16, wherein said oxide is selected from the group consisting of aluminum oxides, calcium oxides, silicon oxides, and barium oxides; and said sulfate is a barium sulfate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will be better understood upon reading the detailed description and the implementation examples that follow, with reference to the appended drawing wherein:

(2) FIG. 1 is an overall view, taken from the scanning electron microscope, of a particulate inoculant batch according to the invention comprising support particles (black) to the surface of which are fixed the surface particles (white) conferring a high inoculating capacity to the entire set,

(3) FIG. 2 is a zoom of FIG. 1 on an inoculating particle according to the invention.

DETAILED DESCRIPTION

(4) An inoculant according to the invention can be manufactured in the following manner.

(5) About 500 kg of a FeSi alloy containing 1% by mass of aluminum and 1.5% by mass of calcium and presenting a grain size distribution comprised between 0.4 to 2 mm, are introduced in a fluidized-bed reactor. The FeSi alloy being fluidized by air injection.

(6) The minimum speed of fluidization is determined in the conventional way, then the air flow rate is kept substantially constant and higher than this minimum speed.

(7) The temperature inside the reactor is raised to about 100 C. This temperature will enable the removal of the water injected subsequently.

(8) The particles of this alloy will form the support particles to the surface of which will be fixed the inoculant particles.

(9) In the present example, the surface particles may comprise calcium silicide (CaSi) and metallic aluminum particles both presenting grain size distributions smaller than 400 micrometers.

(10) 5% by mass of these surface particles will be used, namely about 25 kilograms of this mixture of CaSi and Al particles.

(11) In order to allow their fixation on the support particles, the surface particles to be fixed are mixed beforehand with a binder in an aqueous solution, then injected in the reactor for about 30 minutes at the temperature of 100 C.

(12) Once the mixture of particles and binder is completely injected, the surface particles, support particles and binder set are fluidized and heated until the complete evaporation of the introduced water. The water evaporation can be controlled by any common method, in particular by measuring the humidity of the air coming out of the reactor.

(13) Afterwards, the inoculant of the invention is recovered and characterized in order to assess the effectiveness of the coating. In particular, this characterization can be carried out by monitoring with the scanning electron microscope.

(14) The binder used can be of the organic or polymer type, such as for example binders of the type polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC) and polyvinylpyrrolidone (PVP), etc. Of course, this list is not restrictive.

(15) Of course, the amount of water used for diluting the binder depends on the solubility of the latter in water and should be adapted accordingly.

(16) It is also possible to consider the use of mineral binders, in particular of the sodium silicate type, as well as hydraulic binders of the cement or lime type.

(17) Of course, the nature of the used binder can depend on the supports and inoculant materials used.

(18) The amount of binder used will be calculated so as to allow as best as possible the almost complete fixation of the surface particles with no significant excess which could afterwards damage the final performances of the inoculant according to the invention.

(19) Of course, this used amount of binder will depend on its bonding capacity and should be also adapted accordingly. In particular, we can proceed by tests and visual checking, in particular by using a scanning electron microscope. Typically, the amount of binder used can be comprised between 0.001 and 1% by mass of binder, relative to the total mass of the particles (the support particles and the surface particles).

(20) According to another possible example of inoculants manufacturing according to the invention, about 500 kg of FeSi.sub.70 containing 1% by mass of Al and 1.5% by mass of Ca, with a grain size distribution comprised between 0.2 and 0.5 mm, are introduced in a fluidized-bed reactor. The FeSi alloy is fluidized by air injection. The temperature inside the reactor is raised to 100 C. These particles constitute the support particles. A suspension is made from PVP and water. 8% of surface particles, containing bismuth Bi and ferrosilico-rare earths FeSiRE alloy, both with a grain size distribution smaller than 200 m, are added to the water+PVP solution, then put in suspension. Afterwards, this suspension is injected in an amount of 10% by mass in the reactor for about 40 min at a temperature of 100 C. When the mixture is completely injected, the temperature inside the reactor is maintained at 100 C. until the product is completely dried.

(21) According to still another possible example of inoculant manufacturing according to the invention, about 1000 kg of FeSi.sub.70 containing 1% by mass of Al and 1.5% by mass of Ca, with a grain size distribution comprised between 2 and 7 mm and about 50 kg of Aluminum powder with a grain size distribution smaller than 300 m are introduced in a fluidized-bed reactor. All particles are fluidized by injection of depleted air. The temperature inside the reactor is raised to 100 C. A suspension is carried out with PVP and water. Afterwards, this suspension is injected in an amount of 10% by mass in the reactor for about 40 min at a temperature of 100 C. When the mixture is completely injected, the temperature inside the reactor is maintained at 100 C. until the product is completely dried.

(22) Of course, the implementation of the method is not limited to the use of a fluidized-bed reactor and other coating techniques may be used. In particular, mention can be made to the following methods.

(23) A first method comprises using a high-speed mixer, for example in the order of 1000 to 1500 rpm.

(24) The mixing speed allows the mechanical inlaying of the fine surface particles in the particles larger than FeSi (support particles). Such a mechanical inlaying does not require the use of a binder and therefore, it is referred to as a cold and dry coating. The FeSi.sub.75-type support particles containing mainly the FeSi.sub.2,4 and Si phases, can be inlaid directly by the surface particles.

(25) A second method comprises using a high-shear mixer.

(26) In this case, the mixing is performed at a relatively high speed (for example between 50 and 500 rpm) in a mixer-granulator type mixer, in the presence of a binder (the aforementioned examples). After mixing, a drying step is carried out in order to remove the water from the binder.

(27) The mixer may be equipped with drying means. In particular, these may comprise a burner manifold, for example gas burner manifold, which heat the exterior of the mixer by induction; of a heating belt, for example made of silica, surrounding in particular the walls of the mixer; or still of any other system that can raise the temperature of the powder inside the mixer to a temperature comprised between 80 and 150 C. in order to remove the water.

(28) The mixing systems used, of the drum or granulator type, must enable a movement of the powder inside said mixer resulting to an effective stirring and a certain uniformity of the bonding.

(29) To this end, the mixer may be equipped with stirring fins on its walls or still a mixer-granulator with a rotation system which is central or offset according to one or two axes.

(30) The method of the invention may be carried out equally in a continuous or a discontinuous manner by batches.

(31) During the implementation, the support and surface particles may be added either together or separately.

(32) When they are added together, they can be advantageously premixed before adding the binder for ensuring the bonding.

(33) When they are added separately, the support particles will be preferably introduced at first before adding the surface particles, preferably in a continuous manner, the binder being also introduced preferably in a continuous manner.

(34) It should be also noted that, although the invention has been illustrated with FeSi-based support particles, it is of course possible to use other materials that are commonly used in the casting industry, and in particular support particles of the SiC or graphite type. If so, all it needs is to transpose the manufacture examples to these materials.

(35) The results that have been achieved with such an inoculant according to the invention have been tested on a cast-iron bath.

(36) As is the case with the manufacturing method, the examples are given for the most common cases of use with an inoculant according the invention whose support particle is of the FeSi type.

(37) This is in no way preventing the use of inoculants according to the invention comprising other types of support particles such as silicon carbide or graphite, these materials being however less frequently used in the casting industry.

Example 1: Inoculant According to the Prior Art (Reference)

(38) A spheroidal graphite cast-iron bath has been treated at a rate of 0.3% by weight with an inoculant alloy of the type FeSi.sub.75 and containing 0.8% by mass of aluminum and 0.7% by mass of calcium.

(39) The treatment is performed by adding the inoculant in the cast-iron ladle, before filling the mold.

(40) The amount of equivalent carbon (Ceq) of the cast-iron is at 4.32% (calculated according to the simplified formula: Ceq=% C+(% Si+% P) wherein % C, % Si and % P are the carbon, silicon and phosphorus contents of the cast-iron).

(41) The residual magnesium of the cast-iron is at 400 thousandths.

(42) Afterwards, the cast-iron has been cast in a BCIRA-type mold.

(43) At a thickness of 6 mm, the treated cast-iron presents the following characteristics:

(44) Structure of the matrix: 55% of pearlite, 15% of ferrite, 30% of cementite

(45) Number of nodules per mm.sup.2: 270

(46) VI-type graphite: 57%

(47) Average nodularity: 85%

(48) Average diameter: 16.2 microns

Example 2: Inoculant According to the Invention

(49) A spheroidal graphite cast-iron bath has been treated at a rate of 0.3% by mass with an inoculant according to the invention having the following composition:

(50) Alloy of support particles: FeSi.sub.75, and containing 0.8% by mass of aluminum and 0.7% by mass of calcium,

(51) Surface particles: 1.5% by mass of CaSi particles having a size smaller than 50 microns and 1.5% by mass of metallic aluminum particles having a size smaller than 50 microns,

(52) Binder: 10% by mass of an aqueous solution of PVP,

(53) Bonding deposit of surface particles carried out by fluidization at 100 C.

(54) The treatment is performed by adding the inoculant in the cast-iron ladle, before filling the mold.

(55) The amount of equivalent carbon (Ceq) of the cast-iron is at 4.32%.

(56) The residual magnesium of the cast-iron is at 400 thousandths.

(57) Afterwards, the cast-iron has been cast in a BCIRA-type mold.

(58) At a thickness of 6 mm, the treated cast-iron presents the following characteristics:

(59) Structure of the matrix: 45% of pearlite, 50% of ferrite, 5% of cementite

(60) Number of nodules per mm.sup.2: 540

(61) VI-type graphite: 59%

(62) Average nodularity: 92%

(63) Average diameter: 18.7 m

Example 3: Inoculant According to the Invention

(64) A spheroidal graphite cast-iron bath has been treated at 0.3% by mass with a product constituted by:

(65) a support alloy: FeSi.sub.75 with Al=0.8% by mass and Ca=0.7% by mass,

(66) surface particles: 2.5% by mass of Bismuth Bi particles having a size <100 m, and 2.5% by mass of particles of the ferrosilico-rare earths (FeSiRE) alloy having a size <100 m,

(67) Binder: 10% by mass of an aqueous solution of PVP,

(68) Bonding deposit of surface particles carried out by fluidization at 100 C.

(69) The treatment is performed by adding the inoculant in the cast-iron ladle, before filling the mold.

(70) The amount of equivalent carbon (Ceq) of the cast-iron is at 4.32%. The residual magnesium is at 420 thousandths.

(71) The cast-iron is cast in a BCIRA-type mold.

(72) At the thickness of 6 mm, the cast-iron presents the following characteristics:

(73) Structure of the matrix: 50% of pearlite, 50% of ferrite, 0% of cementite

(74) Number of nodules per mm.sup.2: 570

(75) VI-type graphite: 62%

(76) Average nodularity: 92%

(77) Average diameter: 17.8 m

Example 4: Inoculant According to the Prior Art

(78) A spheroidal graphite cast-iron bath has been treated at a rate of 0.3% by mass with a FeSi.sub.75-type inoculant elaborated in the conventional way and containing 1.2% by mass of aluminum, 1.5% by mass of calcium and 1.5% by mass of zirconium.

(79) The treatment is performed by adding the inoculant in the cast-iron ladle, before filling the mold.

(80) The amount of equivalent carbon (Ceq) of the cast-iron is at 4.32%.

(81) The residual magnesium of the cast-iron is at 400 thousandths.

(82) Afterwards, the cast-iron has been cast in a BCIRA-type mold.

(83) At a thickness of 6 mm, the treated cast-iron presents the following characteristics:

(84) Structure of the matrix: 45% of pearlite, 50% of ferrite, 5% of cementite

(85) Number of nodules per mm.sup.2: 505

(86) VI-type graphite: 59%

(87) Average nodularity: 87%

(88) Average diameter: 18.9 microns

(89) Thus, in order to obtain substantially the same results, it would be necessary to increase considerably the amounts of inoculating components and introduce zirconium, compared to an inoculant having a structure according to our invention,

Example 5: Inoculant According to the Prior Art

(90) A lamellar graphite cast-iron bath has been treated at a 0.3% by weight with a FeSi.sub.75-based product with Al=1.0% by weight and Ca=1.5% by weight.

(91) The treatment is performed by adding the inoculant in the cast-iron ladle, before filling the mold.

(92) The amount of equivalent carbon (Ceq) of the cast-iron is at 4.3%.

(93) The cast-iron is cast in a BCIRA-type mold.

(94) At the thickness of 6 mm, the cast-iron presents the following characteristics:

(95) Number of eutectic cells/mm.sup.2: 0.2

(96) Cementite: 40%

Example 6: Inoculant According to the Invention

(97) A lamellar graphite cast-iron bath has been treated at 0.3% by mass with a product constituted by:

(98) a support alloy: FeSi.sub.75 with Al=1.0% by mass and Ca=1.5% by mass.

(99) surface particles: 5% by mass of barium sulfate BaSO.sub.4 particles having a size <100 m,

(100) a binder: 5% by mass of an aqueous solution of cement,

(101) a bonding deposit of surface particles carried out by fluidization at 100 C.

(102) The treatment is performed by adding the inoculant in the casting ladle before filling the mold.

(103) The amount of equivalent carbon (Ceq) of the cast-iron is at 4.3%.

(104) The cast-iron is cast in a BCIRA-type mold.

(105) At the thickness of 6 mm, the cast-iron presents the following characteristics:

(106) Number of eutectic cells per mm.sup.2: 2

(107) No cementite

Example 7: Inoculant According to the Prior Art

(108) A lamellar graphite cast-iron bath has been treated at 0.3% by mass with a FeSi.sub.75-based product with Al=1.0% by mass, Ca=1.5% by mass and Zr=1.5% by mass.

(109) The treatment is performed by adding the inoculant in the cast-iron ladle before filling the mold.

(110) The amount of equivalent carbon (Ceq) of the cast-iron is at 4.3%.

(111) The cast-iron is cast in a BCIRA-type mold.

(112) At the thickness of 6 mm, the cast-iron presents the following characteristics:

(113) Number of eutectic cells per mm.sup.2: 1.5

(114) Cementite: 5%

Example 8: Parts with Different ThicknessesInoculant According to the Invention

(115) A spheroidal graphite cast-iron bath has been treated at 0.3% by mass with a product constituted by:

(116) a support alloy: FeSi.sub.75 with Al=1.0% by mass and Ca=1.0% by mass,

(117) surface particles: 5% of a mixture of aluminum powders (size <75 m) and CaSi (size <75 m),

(118) Binder: 2% by mass of an aqueous solution of PVP,

(119) Bonding deposit of surface particles is carried out by fluidization at 100 C.

(120) The treatment is performed by adding the inoculant to the jet when filling the mold.

(121) The amount of equivalent carbon (Ceq) of the cast-iron is at 4.32%.

(122) Afterwards, the cast-iron is cast in a mold intended for manufacturing a part having different thicknesses: 4 mm and 25 mm.

(123) On the cast part, on the 4 mm-thick portion, the cast-iron presents the following characteristics:

(124) Number of nodules per mm.sup.2: 502

(125) Average diameter: 17 m

(126) VI-type graphite: 85%

(127) Nodularity: 98%

(128) Cementite: 0%

(129) Ferrite: 48%

(130) Pearlite: 52%

(131) On the cast part, on the 25 mm-thick portion, the cast-iron presents the following characteristics:

(132) Number of nodules/mm.sup.2: 250

(133) Average diameter: 23 m

(134) VI-type graphite: 87%

(135) Nodularity: 98.5%

(136) Cementite: 0%

(137) Ferrite: 50%

(138) Pearlite: 50%

Example 9: Parts with Different ThicknessesInoculant According to the Prior Art

(139) A spheroidal graphite cast-iron bath has been treated at 0.3% by mass with a FeSi.sub.75 alloy obtained in the conventional manner, containing 1.0% of Al, 1.0% of Ca and 1.5% by mass of Zr.

(140) The treatment is performed by adding the inoculant to the jet when filling the mold.

(141) The amount of equivalent carbon (Ceq) of the cast-iron is at 4.31%.

(142) Afterwards, the cast-iron is cast in a mold intended for manufacturing a part having different thicknesses: 4 mm and 25 mm.

(143) On the cast part, on the 4 mm-thick portion, the cast-iron presents the following characteristics:

(144) Number of nodules/mm.sup.2: 350

(145) Average diameter: 19 m

(146) VI-type graphite: 70%

(147) Nodularity: 95%

(148) Cementite: 30%

(149) Ferrite: 40%

(150) Pearlite: 30%

(151) On the cast part, on the 25 mm-thick portion, the cast-iron presents the following characteristics:

(152) Number of nodules/mm.sup.2: 150

(153) Average diameter: 25 m

(154) VI-type graphite: 73%

(155) Nodularity: 95.5%

(156) Cementite: 0%

(157) Ferrite: 50%

(158) Pearlite: 50%

(159) Thus, it is possible with the inoculants, according to the invention, to effectively inoculate the different portions of a part having different thicknesses, while it can be hardly achieved with an inoculant manufactured according to the prior art.

Example 10: Large-Thickness PartsInoculant According to the Invention

(160) A spheroidal graphite cast-iron bath has been treated at 0.3% by mass with a product constituted by:

(161) a support alloy: FeSi.sub.75 with Al=1.0% by mass and ca=1.0% by mass,

(162) surface particles: 5% of a mixture of aluminum powders (size <75 m) and of CaSi (size<75 m),

(163) Binder: 10% by mass of an aqueous solution of cement,

(164) Bonding deposit of surface particles carried out by fluidization at 100 C.

(165) The treatment is performed by adding the inoculant in the casting bath during the filling of the mold.

(166) The amount of equivalent carbon (Ceq) of the cast-iron is at 4.33%.

(167) Afterwards, the cast-iron is cast in a mold intended for manufacturing a large-thickness part (170 mm).

(168) On the 170 mm-thick cast part, at the center of the part, the cast-iron presents the following characteristics:

(169) Number of nodules/mm.sup.2: 160

(170) VI-type graphite: 65%

(171) Average diameter: 25 m

(172) Nodularity: 99.2%

(173) Cementite: 0%

(174) Ferrite: 50%

(175) Pearlite: 50%

Example 11: Large-Thickness PartsAn Inoculant According to the Prior Art

(176) A spheroidal graphite cast-iron bath has been treated at 0.3% by mass with a FeSi.sub.75 alloy obtained in the conventional manner, containing 1.0% of Bi, and 0.6% of rare earth elements.

(177) The treatment is performed by adding the inoculant in the casting bath during the filling of the mold.

(178) The amount of equivalent carbon (Ceq) of the cast-iron is at 4.31%.

(179) Afterwards, the cast-iron is cast in a mold intended for manufacturing a large-thickness part: 170 mm.

(180) On the cast part, at the middle of the 170 mm-thick part, the cast-iron presents the following characteristics:

(181) Number of nodules/mm.sup.2: 155

(182) Average diameter: 22 m

(183) VI-type graphite: 50%

(184) Nodularity: 85%

(185) Cementite: 0%

(186) Ferrite: 52%

(187) Pearlite: 48%

(188) Thus, it is possible with the inoculants, according to the invention, to effectively inoculate large-thickness parts, while preserving a good nodularity of the graphite.

(189) Although the invention has been described with a particular embodiment, it goes without saying that it is not limited thereto and that it comprises all technical equivalents of the described means, as well as their combinations if these are within the scope of the invention.