Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F19/00—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers
  • F28F19/02—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers by using coatings, e.g. vitreous or enamel coatings
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
  • B05D3/10—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by other chemical means
  • B05D3/107—Post-treatment of applied coatings
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F19/00—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D2202/00—Metallic substrate
  • B05D2202/20—Metallic substrate based on light metals
  • B05D2202/25—Metallic substrate based on light metals based on Al
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F2245/00—Coatings; Surface treatments
  • F28F2245/02—Coatings; Surface treatments hydrophilic

Definitions

• the invention relates to a method for the surface treatment of heat exchanger surfaces made of aluminum, which are provided with a corrosion-protective coating.
• heat exchangers are designed for the purpose of increasing the heat output or the cooling effect in such a way that the heat-emitting or cooling surfaces are as large as possible.
• the distance between the individual slats is chosen to be extremely small. If the heat exchanger is used for cooling purposes, air moisture condenses on the surface of the heat exchanger, especially in the fins. The more hydrophobic the fin surfaces are, the easier the condensed water forms water drops that clog the fin gaps, increase the resistance to air and thus reduce the heat exchange rate.
• Another disadvantage is that the water droplets sticking in the lamellar columns from the fan of the heat exchanger into the air blow and be easily pushed out of the water collecting container in the bottom of the device. If necessary, the surroundings of the heat exchanger can be sprayed wet.
• the object of the present invention is to provide a method which imparts good hydrophilic properties to the aluminum surfaces of heat exchangers without the corrosion protection being impaired and without the disadvantages of the known methods being accepted.
• the object is achieved by designing the method of the type mentioned at the outset in accordance with the invention in such a way that the anti-corrosion coating is after-treated with a dispersion which contains fine alumina particles.
• the corrosion protective coating on the aluminum surface can be an anodized or boehmite layer, a chromate coating or the like.
• the base layer initially formed on the heat exchanger surfaces causes corrosion Stability achieved, which receives hydrophilic properties by forming a layer of fine alumina particles by applying an aqueous dispersion containing alumina fine particles.
• the known methods can be used for the corrosion-protective base layers applied within the invention.
• the fine alumina particles used in the process according to the invention should preferably have a particle size of 1 to 100 nanometers (10 m).
• the fine alumina particles adhere to the coating-treated surface and form such a bond that once applied fine alumina particles are practically no longer redispersible and therefore removable.
• the hydrophilic property hardly changes over time, so that a permanently hydrophilic surface is retained.
• a preferred embodiment of the invention consists in aftertreatment with a dispersion which additionally contains surfactant.
• Anionic, nonionic, and possibly also zwitterionic surfactants are particularly suitable. Their presence stabilizes the dispersion on the one hand and improves the wettability of the anti-corrosion coating on the other.
• Another advantageous embodiment of the invention provides for aftertreatment with a dispersion which additionally contains fine particles of silica or silicate.
• the particle size should be of the same order of magnitude as that for the alumina.
• the additional content of the components mentioned creates a layer on the coated surface with a structure close to the mullite (3 Al 2 O 3 2 Si0 2 ). This is special from the coated surface difficult to remove, hardly changes over time and creates a permanent hydrophilic surface.
• post-treatment can be carried out with an aqueous dispersion which contains tannin.
• an aqueous dispersion which contains tannin.
• This further improves the hydrophilic property of the coated surface.
• an aqueous dispersion is used which contains fine alumina particles, fine silica particles and tannin.
• the process according to the invention can also be designed in such a way that aftertreatment is carried out with a dispersion which contains water-soluble synthetic resin.
• the admixture of water-soluble synthetic resins elegantly permits the viscosity control of the aqueous dispersion and thus facilitates the regulation of the application quantity.
• the resin content should be comparatively small.
• the tannin possibly used in the invention means tannin or tannic acid, whereby hydrolyzable tannin or condensable tannin or precursors containing these forms partially dissolved can also be used, e.g. Depsid, Gallotannin, Chinese Tannin, Turkish Tannin, Hamamelitannin, Tannic Acid of Karako Maple, Chebulinic Acid, Sumachannin, Tannin from Japanese GallApple, Ellagic Acid Tannin, Catechin, Catechintannic Acid and Tannic Acid from Quebrana [Quebrachogerbic Acid].
• the layer weight produced with the method according to the invention should be approximately 0.01 to 5 g / m 2 (in the dried state). With less than 0.01 g / m 2 , a sufficiently hydrophilic surface can hardly be achieved. More than 5 g / m 2 reach the limit of economy. With an application amount of 0.1 to 1 g / m 2 you get one Contact angle when wetted with water of less than 30 °, which indicates an effectively hydrophilic property.
• the first batch was obtained by removing the degreased and rinsed sheets in an aqueous resin solution by reacting 220 g of ethylene-acrylic acid copolymer resin, 43 g of 28% ammonia water and 73.7 g of deionized water in a pressure vessel at a temperature of 130 ° C with stirring for about 1 hour, then cooling and diluting with 28% ammonia water to a solids content of 22% while simultaneously adjusting the pH to 9.5 + 0.5 and again diluting with deionized water to 10%. -% solids had been prepared, immersed at 20 ° C for 10 seconds. It was then squeezed off with a rubber roller, the moisture was removed while drying in a drying oven at 130 ° C. for 2 minutes and a corrosion-resistant surface layer of 1.2 g / m 2 was formed.
• the second batch was obtained by immersing degreased and cleaned aluminum panels in an acidic chromate solution at 50 ° C for 1 minute.
• a chromate coating was formed with a layer weight of approx. 80 mg / m (calculated as chromium). The sheets treated in this way were finally rinsed and dried.
• Dispersions were prepared for the aftertreatment of the aforementioned sheets.
• test panels were then subjected to a salt water spray test (according to JIS-Z-2371) to determine the corrosion resistance.
• the hydrophilic properties were assessed by measuring the contact angle. For this purpose, a small water drop of 1 to 2 mm in diameter standing on the surface was measured with the aid of a goniometric contact angle meter G-I for normal temperatures (manufactured by Elema Optics Co., Ltd.). The values after the immediate surface treatment (initially) and after immersion in running water for one week were measured (after 1 week).

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Paints Or Removers (AREA)
• Laminated Bodies (AREA)

Applications Claiming Priority (2)

Publications (2)

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ID=14282720

Family Applications (1)

Country Status (5)

Cited By (6)

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Citations (5)

• 1983
  • 1983-06-08 JP JP58100770A patent/JPS59229197A/ja active Pending
• 1984
  • 1984-06-01 AU AU28946/84A patent/AU2894684A/en not_active Abandoned
  • 1984-06-05 EP EP84106430A patent/EP0128514A3/fr not_active Withdrawn
  • 1984-06-05 DE DE19843420852 patent/DE3420852A1/de not_active Withdrawn
  • 1984-06-07 BR BR8402758A patent/BR8402758A/pt unknown

Patent Citations (5)

Non-Patent Citations (1)

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