IL98540A - Method of coating articles - Google Patents

Description

J METHOD OF COATING ARTICLES METHOD QF_COATI G ARTICLES The present invention relates to a method of coating an article, and particularly to a method which utilizes a magnetic field for this purpose.

It is known that diverse methods are employed for coating an article , The use of an fluidized bed for coating articles is known, primarily as a means of effecting articles mowing. For example. Erith T. Clayton (U.S. Pat. No. 3,132,043) uses pressure and impacts of shot in tumbling barrel to coat metallic articles with a fluid or dry film formers and heating to 200-300°. Clayton, Erith T. (Brit. Pat. No. 1,184,098 CI. C 23c) use a plating of metallic articles by tumbling in an aq. slurry of metal powder with glass bead impact media and addition of the certain or. promoter addns., amounting to 0.005-100 wt.% powder, metal. Fritz J. Nagel (Prod. Eng. 35 (16), 84-91, 1964) uses to coat metallic articles with polymer material a transference a energy of pressed air to the coated material. In this method is used a heating process of coated articles also. In method of Lauterbach, Horst (Ger. Offen. 2,925,343 CI. B05D7/14) edges, corners, points, etc. of ferrous metal articles are coated uniformly by applying coating compns. contg. ferromagnetic pigments in a magnetic field. Heating process is used in this method also.

What is needed is a method of coating that does not require additional heating treatment and addition of different chemical components to improve of coating properties. What is also needed is an economical way of coating producing without using of vibrated parts of devices and devices of pressed air. What is also needed is a coating devices without external mowed parts.

According to the present invention, there is provided a method of coating an article with a coating material, comprising: introducing a mixture of the coating material in particle or liquid form with soft magnetic material into a confined working volume containing the article to be coated, the soft magnetic material being of non-spherical configuration so as to produce magnetic dipoles when subjected to an external magnetic field; and subjecting the confined working volume to a changing magnetic field to produce a fluidized bad of the mixture and to cause the coating material to bond by impact to the article to be coated.

The above method may be applied for coating all kinds of powder or liquid material, both metallic and non-metallic, magnetic and non-magnetic, electrically-conductive and non-electrically-conductive, including ceramics, carbides, borides, oxides of metal, and polymers. As a result, it is possible to produce coating with a wide range of different properties. As examples, the method may be used for producing coatings for protection against corrosion, high temperature, wear and tear, for increasing hardness and durability of working surfaces, for changing reflective characteristics of surfaces, and for providing decorative characteristics. The method of the present invention is particularly useful for applying protective coatings to nails, and to the inner surfaces, as well as to the outer surfaces, of long tubes.

In the preferred embodiments of the invention described below, the soft magnetic material has a length-to-width ratio of from 2 to 30; in addition, the soft magnetic material constitutes 2-25% of the confined working volume, and the coating material constitutes 2-40% of the confined working volume.

The magnetic field is preferably a rotary field, such as produced by a three-phase, 50 Hz power supply. The magnetic flux density (B) is preferably between 0.01 and 0.1 T (Tesla).

According to some preferred embodiments, there are a plurality of articles to be coated mixed with the coating material and the soft magnetic material in the confined volume. In this embodiment, the plurality of articles to be coated occupy 10-15% of the confined working volume.

According to one of the latter embodiments, the soft magnetic material is or includes the articles to be coated, e.g., small elongated nails of steel or iron. In such case, the soft magnetic material preferably occupies 4-30% of the confined working volume.

According to yet another described embodiment, the article to be coated is longer in one dimension than the confined working volume and is gradually moved through the confined volume. The article is also preferably rotated in the direction opposite to the direction of rotation of the magnetic field.

According to the further described embodiment, the article to be coated is a hollow tube whose inner surface is to be coated. In this case, the interior of the hollow tube defines the confined working volume receiving the mixture in which the fluidized bed is formed.

According to a still further described embodiment, the method includes the further step of subjecting the confined volume to an electrical discharge to produce either a plasma of charged particles, or a corona discharge, at the same time it is subjected to the magnetic field. Where the article to be coated is of electrically-conductive material, the electrical discharge may be produced between it and another electrode included within the confined working volume.

Further features and advantages of the invention will be apparent from the description below.

The invention is herein described, by way of example only, with reference to a number of examples to be described more fully below, and also with reference to the accompanying drawings, wherein: Fig. 1 diagrammatically illustrates apparatus constructed in accordance with the present invention showing the coating material before it is subjected to the magnetic field; Fig. 2 illustrates the apparatus of Fig. 1 at the time the magnetic field is applied; Fig. 3 illustrates the apparatus for coating a plurality of small articles; Fig. 4 illustrates the apparatus for coating steel nails and the like; Fig. 5 illustrates the apparatus for coating an article longer than the confined working volume; Fig. 6 illustrates the apparatus for coating the interior surface of a long tube; Fig. 7 illustrates the apparatus of Fig. 1 and 2 but modified to also subject the coating material to an electrical plasma or corona discharge at the time it is subjected to the magnetic field; The apparatus illustrated in Figs. 1 and 2 includes a confined working volume, generally designated 2, which receives the article 3 to be coated. Also disposed within the confined working volume 2 is a mixture of the material to be coated, in the form of fine particles or powder 4, together with particles of a soft magnetic material 5. The particles 5 of soft magnetic material, such as soft iron or steel, are of a non-spherical or asymmetrical configuration; that is, they have a dimension along one axis (length) which is longer than the dimension along the other axes (width). Thus, the particles 5 of soft magnetic material form magnetic dipoles when subjected to an external magnetic field. Such a magnetic field is produced by electromagnets 6 disposed externally of the confined working volume 2.

Fig. 1 illustrates the above-described setup when electromagnet 6 is not energized, so that no magnetic field is produced within the confined working volume 2. Accordingly, the mixture of the coating material particles 4 and the soft magnetic particles 5 rests loosely at the bottom of the confined working volume 2. The article 3 to be coated may be supported in any suitable manner within the confined working volume 2.

Electromagnet 6 is energized with a three-phase current to produce a rotating magnetic field within the confined working volume 2. The so-produced magnetic field is sufficiently intense to cause the non-spherical or asymmetric particles 5 of soft magnetic material to overcome the gravitational force and thereby to produce a fluidized bad of these particles 5, together with the coating material particles 4, within the confined working volume 2. The particles 4 and 5 of the fluidized bed are moved vigorously in all directions within the confined working volume 2 and bombard the other surface of the workpiece article 3 with sufficient impact so as to become bonded to its outer surface.

Preferably, the non-spherical magnetic particles 5 have a length-to-width ratio of from 2 to 30, and constitute from 2-25% of the confined working volume 2, whereas the coating material particles 4 constitute 2-40% of the confined working volume. The magnetic field produced by electromagnetic 6 preferably has a field intensity (B) within the range of 0.01-0.1 Tesla.

Fig. 3 illustrates a setup including a confined working volume 12 containing a plurality of articles , therein designated 13, to be coated with the fluidized bed of coating particles 14 and soft magnetic material particles 15 produced by energizing electromagnet 16 to produce the rotating magnetic field within the volume 12. Preferably, the plurality of articles 15 to be coated occupy about 10-15% of the confined working volume 12. They may be suitably supported within this volume, or merely mixed with the mixture of particles 14 and 15 so as to become part of the fluidized bed.

Fig. 4 illustrates a setup wherein the soft magnetic material is or includes the articles to be coated, such as small steel nails, shown at 25, or the like. In this case, the soft steel nails 25 are mixed with the coating particles 24 in the confined working volume 22 and form part of the fluidized bed within that volume upon energizing the electromagnet 26.

Following are several examples of practicing the method as illustrated in Fig. 4: EXAMPXEX The example coated soft steel nails 25 having a length : width ratio 15.1 and occupying 6% of the confined working volume 22. The coating particles 24 were a mixture of zinc powder and white sand, each occupying 3% of the confined working volume 2. In this example, the nails thus constituted both the articles being coated and the soft magnetic particles. Three-phase, 50 Hz electric current was applied to the electromagnet 6 to produce a rotating magnetic field having a field intensity (B) of about 0.01 T for a period of about 25 minutes. The articles 25 were coated with a coating thickness of 16-25 · microns, and the first signs of corrosion were observed only at about 120 hours under ambient conditions.

EXAMPLES.

The articles to be coated were also nails of two sizes: some of length : width ratio of 5 and the others of 15. They occupied about 6% of the confined working volume 22. The coating particles 24 were a mixture of copper powder and white sand, each occupying 3% of the confined working volume 2. Three-phase, 50 Hz electric current was applied to the electromagnet 6 to produce a rotating magnetic field having a field intensity (B) of about 0.01 T for a period of ten minutes. The results a coating of 26-31 microns, which did not reveal signs of corrosion until after 240 hours.

EXAMPLE.! This example is the same as in Example 2, except that the coating materials 24 were a mixture of zinc powder and white sand, each occupying 3% of the confined working volume 22, and the electromagnet 26 was energized for a period of 15 minutes. The results were similar to those of Example 2.

EXAMPXEJ.

This example was also the same as in Example 2, except that the mixture included particles 24 of zinc powder and glass powder. The zinc powder constituted about 15% of the confined working volume 2; the glass powder constituted about 3% of that volume, and the nails constituted about 6% of the confined working volume. Three-phase, 50 Hz electric current was applied to produce a magnetic field intensity of 0.02 T for a period of 25 minutes. This produced coatings of 40-45 microns on the larger samples, and 60-63 microns on the smaller samples, which coatings withstood signs of corrosion for a period in excess of 300 hours.

Fig. 5 illustrates the setup wherein the article to be coated, generally designated 33, is longer in one dimension that the confined working volume 32. For purposes of example, Fig. 5 illustrates the article 33 as a hollow or solid rod whose outer surface is to be coated. As the fluidized bed of coating particles 34 and soft magnetic particles 35 is produced by the energization of the electromagnet 36, the article 33 is gradually moved through the confined working volume 32 so that its outer surface is coated by the impacted particles. Preferably, article 33 is rotated in the direction opposite to the direction of rotation of the magnetic field produced by electromagnet 36.

Fig. 6 illustrates an arrangement wherein the article, therein designated 43, is in the form of a hollow tube whose inner face 43a is to be coated. In this case, the interior of the hollow tube 43 defines the confined working volume receiving the mixture of coating particles 44 and the soft magnetic particles 45 producing the fluidized bed by the energization of the electromagnet 46, which fluidized bed coats the inner surface 43a of the tube 43 by impact, as described above. As described with respect to Fig. 5, the hollow tube 43 is gradually moved through the space occupied by the electromagnet 46, and is preferably rotated in the direction opposite to that of the rotational magnetic field produced by that electromagnet.

Following are a number of examples of coating the interior of a hollow tube according to the setup illustrated in Fig. 6: EXAMELEJ.

Hollow tube 42 is of steel having an inner diameter of 50 mm and a length of 400 mm; the coating particles 44 are of copper of 20-50 microns, and occupy about 5% of the interior of the hollow tube 43, which interior defines the confined working volume; the soft magnetic particles 45 are of mild carbon steel of rod-shape configuration, having a length of about 30 mm and a diameter of about 2 mm, and occupy about 10% of the interior of the hollow tube 43; and the magnetic field produced by electromagnet 46 has a field intensity (B) of 0.02 T, and is energized by 50 Hz three-phase current. In this example, the coating rate was between 90 and 140 cm2 per minute, and provided a coating thickness of about 50-80 microns.

EXAMRLE_d This example was substantially the same as the same as Example 5 above, except that the hollow tube 43 was of aluminum.

EXAMELEJZ In this example, the hollow tube 43 is of copper having an inner diameter of about 100 mm and a length of about 400 mm; the coating material 44 is zinc having a particle size of 20-50 microns and occupying about 10% of the volume of the interior of the hollow tube; and the soft magnetic particles 45 are the same as in Examples 1 and 2 above. The magnetic field intensity (B) produced by electromagnet 46 is 0.03 Tesla.

EXAMPXEJ.

In this example, the hollow tube 43 is of titanium, and the coating particles 44 are boron carbide having a size of 20-50 microns, and occupy about 10% of the volume of the interior of the tube 43. The soft magnetic particles 45 are the same as in Example 1.

Examples 5, 6 and 7 can also be used for coating solid or hollow articles completely enclosed within the confined working volume according to the setup of Figs. 1 and 2.

Fig. 7 illustrates a further setup that may be used. In this setup, the confined working volume, therein designated 52, is subjected to both a magnetic film produced by the electromagnet 56, and also to an electrical discharge to produce a plasma of ionized particles at the same time the magnetic field is produced. In this case, the article 53 to be coated is electrically-conductive, such as of copper, steel, aluminum, or the like, and serves as one of the electrodes in the electrical discharge producing the plasma. Therefore, the article 53 is connected to one side of the power supply 57. The other side of the power supply 57 is connected to two additional electrodes 58, 59, within the confined working volume 52 to produce the plasma therein at the time electromagnet 56 produces the magnetic field therein.

E AMPLES As an example, the coating particles 54 and the soft magnetic material particles 55 may be of the same material, and in the same volumes, as described above with respect to Example 5, except that the coating material particles 54 occupy about 12-14% of the volume 52, and the magnetic particles 55 occupy about 6-8% of that volume. The power supply 57 applies electric pulses to the electrodes 58, 59 and the electrically-conductive article 53 to be coated, a pulse period of 90-200 μ8 and a current of magnitude of 1-1.5 kA, and at a frequency of 300-800 Hz. The coating thickness was 140-200 microns, and the adhesion was 170 mPa.

As a variation particularly for the setup of Figs. 1 and 2, the electrodes may be energized to produce a corona discharge, rather than a spark discharge. In one experiment, the materials and the conditions were the same as in immediately preceding described example, except that the setup was according to Figs. 1 and 2 and the working electrode was the cathode (rather than the anode); the voltage was 2.5 kV, and the current was 3 raA. The coating thickness in this example was about 50% larger than in the immediately preceding example. Thus, an experiment was performed with boron carbide coated on aluminum, in which case the thickness of the boron carbide coating was 60 microns when the fluidized bed was produced in the presence of corona discharge.

While the invention has been described above with respect to fluidized beds including solid coating particles, it will be appreciated that the invention could also be practised using a liquid, such as paint. Many other variations, modifications and applications of the invention will be apparent.

Claims (13)

iAliS_CLAIMED_LS.:.

1. A method of coating an article with a coating material, comprising: introducing a mixture of said coating material in particle or liquid form with soft magnetic material into a confined working volume containing the article to be coated, the soft magnetic material being of non-spherical configuration so as to produce magnetic dipoles when subjected to an external magnetic field; and subjecting said confined working volume to a changing magnetic field to produce a fluidized bed of said mixture and to cause said coating material to bond by impact to the article to be coated.

2. The method according to Claim 1 , wherein said soft magnetic material has a length-to- width ratio of from 2 to 30.

3. The method according to either of Claims 1 or 2, wherein said coating material constitutes 2-40% of said confined working volume.

4. The method according to any one of Claims 1-3, wherein said soft magnetic material constitutes 2-25% of said confined working volume.

5. The method according to any one of Claims 1 -4, wherein said changing magnetic field is a rotating magnetic field.

6. The method according to mixed with said coating material and said soft magnetic material in said confined working volume.

7. The method according to Claim 6, wherein said plurality of articles to be coated occupy 10-15% of said confined working volume.

8. The method according to Claim 6, wherein said articles to be coated are of said soft magnetic material and occupy 4-50% of said confined working volume.

9. The method according to Claim 5, wherein the article to be coated is longer in one dimension than said confined working volume and is gradually moved through said confined working volume.

10. The method according to Claim 9, wherein the article to be coated is rotated in the direction opposite to the direction of rotation of the magnetic field.

11. 1 1. The method according to Claim 10, wherein the article to be coated is a hollow tube whose inner face is to be coated, the interior of said hollow tube defining said confined working volume receiving said mixture.

12. The method according to any one of Claims 1-1 1, including the further step of subjecting said confined working volume to an electrical discharge at the same time it is subjected to said magnetic field, wherein said changing magnetic field is a rotating magnetic field.

13. The method according to Claim 12, where the electrical discharge creates a plasma of charged particles within the confined working area.