Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
  • C23C2/26—After-treatment
  • C23C2/265—After-treatment by applying solid particles to the molten coating

Definitions

• the invention relates to a method for treating a metal sheet coating layer in which a powder is sprayed onto the metal layer when it is, at least partially, in the liquid state.
• This process is commonly used during the galvanization of steel sheets.
• the sheet is dipped in a bath of liquid metal, the sheet is extracted from the bath to entrain a layer of said liquid metal on the sheet, a powder is sprayed onto said entrained liquid layer and then said layer is solidified.
• the thickness of the entrained metal layer can be adjusted before spraying the powder.
• a variant of this galvanizing process consists in spraying the powder well after the quenching: the sheet is then heated to at least partially melt the coating layer, the powder is sprayed onto the molten layer, then solidified.
• the powder is inserted into the metal layer, that is to say generally dispersed or dissolved.
• the sheets coated according to this process for example have a better surface appearance (disappearance of flowering) or are easier to shape (better stampability).
• oxide powders or mixtures of metallic powders and oxide powders.
• the quality of such coating depends, among other things, on the morphology of the powder and the conditions of projection onto the sheet; these two parameters indeed determine the homogeneity of the distribution of the material projected on the one hand on the surface of the molten metal layer, on the other hand in the depth of this layer.
• patent JP 02 093053 proposes using atomized powders.
• the powder spraying process should be adapted and controlled to achieve an identical and homogeneous distribution of all the basic powder components in the treated metal layer.
• the object of the invention is to treat a metal layer by spraying powder homogeneously in the depth, and, when the treatment powder comprises several basic components, to distribute them in a very homogeneous manner throughout the metal layer.
• the subject of the invention is a method of treating a metal layer for coating sheet metal, in particular in a line for galvanizing sheet metal, in which a powder is sprayed onto said metal layer when it is, at least partially, liquid state, characterized in that said powder is prepared by atomization in a manner suitable for it to be in the form of atomization agglomerates gathering elementary grains to be dispersed and / or dissolved in said metal layer in the liquid state and so that the average size of said agglomerates is greater than the thickness of said metallic layer in the liquid state.
• the installation for coating sheet metal by dipping with powder spraying is known in itself and will not be described here in detail; it comprises, in particular a sheet dipping bath, wiping means for regulating the thickness of the metal layer on the sheet at the outlet of the bath, and a device for spraying powder onto the metal layer still in the molten state after spinning.
• the atomization installation is supplied from a composition of these basic powders, for example suspensions and / or liquid solutions of these basic powders.
• suspensions in particular colloidal, and / or from solutions containing the basic components of the material to be sprayed.
• the feed composition is atomized to form an atomized powder, composed of agglomerates uniting elementary grains of base powder, possibly of different natures and of different morphologies.
• atomization can be used to preformulate a mixture, in the sense that the atomization conditions are adapted in a manner known in itself to obtain, within of each agglomerate of the powder to be sprayed, a mixture of grains of the different components in the said proportions.
• the atomization conditions are determined in a manner known per se to obtain, according to the invention, agglomerates having an average size greater than the thickness of the molten metal layer after spinning.
• the atomized powder because it consists of large agglomerates, can be handled with even less explosive or toxic risks.
• the agglomerates consist of elementary grains which are sufficiently fine to ensure a homogeneous dispersion of the material to be sprayed into the metal layer.
• these elementary grains have an average size less than about half the thickness of the molten metal layer.
• the atomization conditions are adapted in a manner known per se so that the ratio (average size of the agglomerates) / (average size of elementary grains) is greater than approximately 4.
• a binder is added as necessary to reinforce, if necessary, the cohesion of the agglomerates of the atomized powder.
• polyvinyl alcohol can in particular be used.
• the atomization conditions as well as the nature and the proportion of binder in the feed composition are also determined in a manner known per se, in order to obtain cohesion of the agglomerates, admittedly weak but sufficient.
• sufficient cohesion is meant a cohesion which is preserved in all the operations for handling the powder situated between the atomization itself and the projection onto the sheet at the outlet of the coating bath.
• weak cohesion is meant a cohesion which disappears under the impact of projection of the agglomerate on the sheet, in order to ensure the dispersion of the elementary grains of the agglomerate in the metallic layer in the molten state.
• the measurement of porosity namely the ratio (total volume of pores) / (total volume of an agglomerate), is a known means of evaluating the cohesion of the agglomerates.
• the proportion of binder and the atomization conditions are adapted to obtain agglomerates of porosity greater than about 30%, the porosity measured taking into account only the pores of size greater than 0.01 ⁇ m.
• the coating is carried out by dipping a sheet metal with powder spraying in a manner known per se, with the difference that the powder spraying device is supplied with the atomized powder described above.
• the sheet to be coated is here a steel sheet.
• the metallic coating bath is here a zinc bath.
• the sheet to be coated is therefore quenched, it is wrung to obtain in a manner known per se a predetermined thickness of metallic layer entrained on the sheet, then, while the metallic layer is still in the molten state, projects the atomized powder onto said layer.
• the temperature of the metal layer is at least about 10 ° C higher than that of its melting temperature.
• the spray conditions of the atomized powder are adapted so that the agglomerates that compose it break under the effect of the impact of projection against the sheet, which releases and disperses the elementary grains in the molten metal layer.
• the average size of the agglomerates of the atomized powder being greater than the thickness of the metal layer, it is easier than in the prior art to spray said powder with sufficient energy for the elementary grains to disperse in the depth of the layer, in the vicinity of the sheet metal substrate, which represents an essential advantage of the invention.
• the material to be sprayed contains several components and the atomization operation is used to preformulate a mixture of these components, the constraints on controlling the spraying installation are therefore reduced; in fact, the mixture being preformulated, it is much easier to obtain than in the methods of the prior art a uniform and homogeneous distribution of the elementary grains of the material to be sprayed into the metal layer.
• the elementary grains of core are particles of silica and the coating material consists of particles of metal of the same nature as that of the dip bath of the sheet, here for example, particles of zinc.
• the periphery of the agglomerates melts first, releasing the oxide particles it contains to the core to disperse them in the molten metal layer.
• the powder to be sprayed thanks to its method of preparation (atomization) and the size of its agglomerates, makes it possible to treat metallic layers (in the molten state) easily and in a very homogeneous manner.
• the purpose of this example is to illustrate the invention in the case of a treatment of a metallic coating layer with a metallic zinc powder.
• this treatment takes place in a galvanizing operation, where, after quenching, the metal layer to be treated has a thickness of approximately 10 ⁇ m.
• a zinc powder As a base powder, a zinc powder is used, the grains of which have an average size of approximately 4.5 ⁇ m.
• a suspension of this base powder is prepared and polyvinyl alcohol is diluted to about 3% by weight (relative to the weight of base powder).
• This suspension (or feed composition) is atomized so as to obtain batches of powder to be sprayed having agglomerates of average size between 24 ⁇ m and 56 ⁇ m.
• the porosity of the powders obtained is approximately 33.8% and the internal porosity has an average diameter of 0.06 ⁇ m.
• the metal layer is still treated in the liquid state by spraying a batch of powder and then solidified.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Coating By Spraying Or Casting (AREA)
• Other Surface Treatments For Metallic Materials (AREA)
• Coating With Molten Metal (AREA)
• Laminated Bodies (AREA)
• Powder Metallurgy (AREA)
• Manufacture Of Metal Powder And Suspensions Thereof (AREA)

Applications Claiming Priority (2)

Publications (2)

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Family Applications (1)

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Cited By (1)

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Citations (3)

Family Cites Families (6)

• 1995
  • 1995-10-19 FR FR9512273A patent/FR2740145B1/fr not_active Expired - Fee Related
• 1996
  • 1996-10-01 ES ES96402089T patent/ES2142556T3/es not_active Expired - Lifetime
  • 1996-10-01 EP EP96402089A patent/EP0769567B1/de not_active Expired - Lifetime
  • 1996-10-01 DE DE69606132T patent/DE69606132T2/de not_active Expired - Lifetime
  • 1996-10-01 AT AT96402089T patent/ATE188748T1/de active
  • 1996-10-15 CA CA002187860A patent/CA2187860C/fr not_active Expired - Fee Related
  • 1996-10-16 US US08/733,071 patent/US5711990A/en not_active Expired - Lifetime
  • 1996-10-18 JP JP29758396A patent/JP3875325B2/ja not_active Expired - Fee Related

Patent Citations (3)

Non-Patent Citations (2)

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