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
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/73—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals characterised by the process
• • 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
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
  • C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions

Definitions

• Schramm ABSTRACT A method for treating steel, galvanized steel, zinc and aluminum sheet and strip with an HF-CrO, containing solution wherein the solution is applied so that no more than about 50 percent of the applied solution is returned to the treating bath and about 0.1-6 grams/square meter HF and about 0.06-3 grams/square meter CrO are retained on the metal surface to give a pickling efiect or metal removal of about 0.1 to 2 grams/square meter.
• the present invention relates to an improved process for the chemical surface treatment of steel, galvanized steel, zinc and aluminum and more particularly relates to a process which is suitable for the preparation of these materials for the application of organic coatings.
• the quantities of hydrofluoric acid and chromic acid required according to the method of the present invention are brought into contact with the metal surface in the form of an aqueous solution.
• the quantity of the solution and the condi tions of application are so selected that at least 50 percent, but preferably 80 percent of the solution applied to the metal surface will remain upon that surface for the duration of the pickling reaction. ln the conventional immersion or spraying process after the reaction with the metal surface more than 90 percent of the treatment solution will be returned to the storage tank and reused for the next phase of the process.
• the concentrations of hydrofluoric and chromic acid in the pickling solution, according to the method of the present invention, are desirably in the range of 5 to 30 g./l. HF and 3 to 15 g./l. CrO Usually, 20 to 400 ml./m. aqueous solution is sufficient to ensure the application of the required HF and CrO quantities to the metal surfaces.
• the lower quantities are appropriately applied when using higher concentrations of hydrofluoric-chromic acid solutions. These quantities, how'- ever, generally increase when the HF and CrO concentrations are decreasing toward the lower limit.
• the concentrations of HF and CrO in the quantity of liquid applied to the metal surfaces should be so selected that under given temperature conditions and reaction times a pickling effect or metal removal of 0.1 to 2 g./m. will be ensured. Below O.l g./m. the roughening of the metal surface will be insufficient, therefore, adhesion difficulties may appear during subsequent coating with organic materials. On the other hand, pickling effects higher than 2 g./m. will lead to the deposition of pickling residues, particularly on steel and aluminum, and this may be equally detrimental as far as the adhesion of organic coating layers is concerned. At the same time the consumption rate of the chemical ingredient will increase. With a pickling effect in the range of 0.1 and 2 g./m. the metal surfaces will show a uniform roughening effect without any noticeable layer formation or pickling residues.
• the pickling effect is also a function of the composition of the treatment solution, the temperature and the reaction time.
• the influence of the composition of the treatment solution, and therefore, the influence upon the pickling effect of the quantities of HF and CrO applied to the metal surfaces may be seen from tables 1-3.
• the pickling efiect was determined from the weight difference of the sample sheets before and after the treatment.
• the temperature of the pickling solution should be between 15 and 40 C., even though the process may be carried out at higher temperatures as well.
• the temperature should not exceed about 60 C., as inthis range it is rather difficult to control the desired pickling effect.
• the process according to the present invention may be carried out by flooding, pouring or spraying as well as by roller application.
• a higher recycling rate of the treatment solution from the metal surface into the storage tank should be taken into account.
• the recycled quantity may be reduced by using less excess solution quantities and by distributing the solution on the metal surface in a uniform manner with rollers, squeezers or by some appropriate blowing arrangement.
• the diameter, the efficiency and the number of jets as well as the spraying pressure should be so selected that a uniform film will be formed on the metal surface, without any substantial quantities of solution passing by the treated material or running off.
• the distance between the jets and the metal sheet should be 10 to 25 cm.
• several tubes provided with jets may be arranged in series, the jets being located at angles which will ensure uniformity.
• the reaction solution may be used directly from storage tank to metal surface without any dilution.
• a correspondingly higher concentrated solution may be injected into a water-fed spraying system.
• the blending ratio of water to concentrate should be so adjusted that the solution quantity of liquid applied to the upper or the lower side of the metal may be identical or not.
• the CrO and free acid contents should be controlled by means of conventional analytical methods.
• the replenishment should be carried out preferably with CrO to Cr (VI) consistency and with HF to free acid consistency.
• the replenishing materials may be added to the bath either individually or in premixed condition.
• the excess solution remaining on the metal surface may be removed by squeeze rollers, a blowing arrangement or by some other appropriate devices, and the resultant solution film is dried.
• the prerequisite for this particularly advantageous method of operation is that the pickling solution should contain maximum 1 part by weight of HF per every part by weight of CrO It should be particularly noted, that in this method of operation the two customary stages, i.e., the water rinse and the after-rinse with CrO; containing solutions will not be required, this again represents considerable savings on installations, floor space and expenditures otherwise required for the treatment of chromic acid containing efiluents.
• the solution film is removed from the metal surface to such an extent, e.g., by means of rubber squeeze rollers, that after drying a coating will be obtained which contains 6 to mgJm.
• the HF/CrO ratio in the pickling solution is adjusted to values above 1. ln this instance, in the treatment of steel and zinc surfaces under appropriate experimental conditions, for example under extended reaction times, and also in the treatment of aluminum, the total chromic acid quantities applied to the metal surface are being used up in the pickling reaction.
• the solution which remains after the reaction may be then removed by squeezing and/or water rinsing. As in this instance the solution does not contain any more hexavalent chromium, this solution may be immediately neutralized without any specific effluent treatment, therefore, the expenditures otherwise required for a chromic acid reduction process will be saved.
• an aqueous solution containing Cr (VI) is used for after-rinsing, whereby 6 to 120 mg./m. hexavalent chromium, calculated as CrO will be applied to the surface.
• the solution is then dried.
• the Cr(Vl) content of the solution calculated as CrO should be preferably between 0.6 and 6 g.ll., where the higher contents are used preferably whenever a squeezing process is employed to ensure the uniformity of the adhering solution film.
• the hexavalent chromium may be added to the bath for example in the form of chromic acid andlor zinc, calcium, aluminum and chromium-lIl-chromate.
• the after-rinse As far as the after-rinse is concerned, it is sufiicient to bring the metal surface into contact for only a few seconds with the Cr(VI) containing solution.
• the temperature of the after-rinse may range from room temperature to about 60 C.
• the liquid film remaining on the metal surface is dried. This may be followed by the application of lacquers, adhesives for plastic films and such.
• the pickling solution which contains CrO and HF according to the process of the present invention, should be applied as far as possible to degreased surfaces.
• aqueous solutions of alkali cleaning agents which contain alkali hydroxides, alkali carbonates, alkali ortho and condensed phosphates, alkali silicates, alkali borates, complex-forming as well as surface active substances, and which may be applied to the metal surfaces by immersion, flooding or spraying and preferably at elevated temperatures.
• the degreasing process may be omitted whenever the metal to be treated is substantially grease-free, such as for example freshly galvanized steel.
• the process according to the present invention is particularly suitable for the treatment of continuous rolls and sheet metals.
• EXAMPLE 1 A 300-mm. wide steel band is treated in the following manner in a continuous arrangement:
• the upper as well as the lower surface of the steel band have indicated clean, uniform and mat pickling effect.
• the content of hexavalent chromium was about 30 mg. CrO per m. of surface.
• the pickling effect was evaluated on steel samples secured onto the steel band. These samples were the quality UST 1405 m. according to Gennan Industrial Standard (DIN) 1623, page 1. The result was found to be in the range of 0.5 and 0.6 g./m.
• the samples were subsequently lacquered by using a conventional lacquer of acrylate resin base. Following a storage period of 3 days, the samples were scratched and subjected to a salt-spray test according to ASTM 13 117-64. The results of this test are given in table 5.
• EXAMPLE 3 Samples of steel, hot galvanized steel and AlMg were degreased and rinsed in the manner described in example l. These samples (series A) were pickled by an ordinary spray process, i.e., with a recycling ratio of over 90 percent, for ll seconds at 25 C., using a solution containing 0.5 g./l. C10; and 2.5 g./l. HF. Subsequently, the samples were rinsed, after rinsed and dried in the manner described in example 1.
• a process for the chemical surface treatment of metals which comprises pickling the metal surface to be treated with an aqueous solution containing HF and C10 applying said solution so that at least about 50 percent by volume remains on the metal surface, with no more than about 50 percent by volume being returned to the main body of the treating solution, retaining from about 0.1 to 6 grams/square meter HF and 0.6 to 3 grams/square meter CrO on the metal surface and effecting pickling of the metal surface to the extent of removing from about 0.1 to 2 grams of metal/square meter of treated metal surface.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemical Treatment Of Metals (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
• Coating With Molten Metal (AREA)
• Electroplating Methods And Accessories (AREA)

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Cited By (7)

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Citations (4)

• 1969
  • 1969-12-01 FR FR6941338A patent/FR2043646A1/fr active Pending
  • 1969-12-03 BE BE742605D patent/BE742605A/xx unknown
• 1970
  • 1970-03-13 ES ES377462A patent/ES377462A1/es not_active Expired
  • 1970-03-25 AT AT274570A patent/AT293130B/de not_active IP Right Cessation
  • 1970-05-13 GB GB23255/70A patent/GB1294490A/en not_active Expired
  • 1970-05-19 NL NL7007232A patent/NL7007232A/xx not_active Application Discontinuation
  • 1970-05-19 CS CS3490A patent/CS167286B2/cs unknown
  • 1970-05-21 US US39523A patent/US3632447A/en not_active Expired - Lifetime
  • 1970-05-22 SE SE07083/70A patent/SE356080B/xx unknown
  • 1970-05-22 BR BR219226/70A patent/BR7019226D0/pt unknown

Patent Citations (4)

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