Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D13/00—Electrophoretic coating characterised by the process

Definitions

• the present invention provides a method of applying a particular high temperature resistant coating to a steel part.
• a method of applying a coating to a steel part comprises electrophoretically applying a coating of aluminum powder and organic resin to the part, heating the part to drive off the organic resin, and subsequently impregnating the coating with a high temperature resistant base material.
• the high temperature resistant base material is preferably potassium silicate. In this case it is preferable to stove the impregnated coating.
• the initial coating is performed from an aqueous solution.
• the electrophoretic coating may be performed from a solution comprising one part of an acrylic resin, from 2 to 20 parts by weight offine powdered aluminum and water to make a workable consistency.
• EXAMPLE 1 100 grams of a 50 percent aqueous solution of acrylic resin known as Synocryl 84/S and obtained from Messrs. Cray Valley Products was mixed with 400 grams fine powdered grease free aluminum of particle size to'l0 microns (400 grade) and 250 grams of water. The mixture was ball milled for one hour to produce a homogenous mixture.
• Test panels of 12 percent chromium steel were immersed in the mixture and an electric potential applied between the panels and a fixed electrode so that the panels were given negative polarity and consequently were coated with the aluminum and resin by electrophoresis.
• a current density of 0.1 amps per square inch gave best results, and the coatingwas continued for 30 seconds to give a coating of between 0.4 and 0.8 thousandths of an inch thickness.
• test panels were then removed from the mixture and the coating was stoved for 30 minutes at 150C.
• the panels were then further heated to 560C; this caused the acrylic resin to be driven off and also diffused the aluminum coating. This temperature was maintained for two hours.
• the panels were then provided with a porous aluminum coating, to complete the coating the panels were allowed to cool to 100C and an aqueous solution of potassium silicate comprising 1 part by volume of the silicate in 2 parts by volume of water was brushed onto the coating until it had completely filled the pores of the aluminum. The panels were then finally stoved for 30 minutes at 150C.
• the actual potassium silicate used was Crosfield Grade 66 having a mean molecular ratio of SiO :K O of 3.21 and a specific gravity of 1.33.
• Test panels which had been thus coated were then subjected to corrosive conditions to evaluate the coating. Each panel was subjected to 10 cycles of a heating programme which involved two hours heating at 450C followed by 22 hours of neutral salt spray at room temperature. After this test the test panels were in good condition and the coating was almost undamaged as was the steel substrate. The panels were also tested by immersion in various fluids which are often used in or adjacent to gas turbine engines such as lubricating oils, kerosene and petroleum fuels and various hydraulic fluids, and the coating was found to be resistant to all these fluids.
• EXAMPLE 2 Further tests were carried out on panels whose coating had been produced using the same mixtures but a different heating cycle. In this case the panels were electrophoretically coated, stoved for 30 minutes at 150C and then heated to 350C to drive off the acrylic resin. The porous coating was then impregnated and heat treated as before. We found equally satisfactory results with these test panels.
• EXAMPLE 3 Further test panels were coated using a mixture comprising 31 grams of Synolac 84l/S as described above, 41.6 grams of the 400 grade aluminum powder and 27.3 grams of distilled water. The test pieces were coated by electrophoresis (or electro-printing) using an electrical current in the range of 5 to milliamps per square inch.
• test panels were then stoved and further coated as described in the previous examples, and were found to give satisfactory results in similar tests. It was additionally found that the mixture itself was less liable to settling out of the solid constituents than the previous mixture.
• the process of electrophoresis or electro-printing may be carried out using a contrast current or a contrast voltage supply; in the latter case the current will vary over the coating process.
• the parameters of current and voltage which give the best results for a particular mixture are best determined by experiment, but we find that the current used will normally fall within the range 5 to 100 milliamps per square inch of surface to be cov ered.
• the coating should be such as to be electrically conductive so as to give galvanic resistance to corrosion. It is possible to arrange that the coating is conductive by the addition of a final heat treatment step in which the panel involved is heated to 560C for 2 hours, as was seen in the following example.
• EXAMPLE 4 Test panels were made and coated in exactly the same manner as Example 1, but in this case after the final stoving the panels were further heat treated to 560C in air for 2 hours. The panels were tested and it was found that the coatings were electrically conductive and gave even better protection than the panels of Example 1.
• a method of applying a coating to a steel part comprising the steps of firstly electrophoretically applying a coating of a mixture of aluminum powder and organic resin to the part, secondly heating the part to drive off the organic resin, and thirdly impregnating the coating with a high temperature resistant base material.
• a method as claimed in claim 4 and in which said subsequent heating comprises heating in air to 560C for 2 hours.
• a method of applying a high temperature and corrosion resistant coating to a steel part comprising the steps of:

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Paints Or Removers (AREA)
• Laminated Bodies (AREA)

Applications Claiming Priority (1)

Publications (1)

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Family Applications (1)

Country Status (6)

Cited By (9)

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Citations (2)

• 1971
  • 1971-06-17 GB GB2836971A patent/GB1341899A/en not_active Expired
• 1972
  • 1972-06-12 US US00261814A patent/US3787305A/en not_active Expired - Lifetime
  • 1972-06-17 IT IT25857/72A patent/IT959840B/it active
  • 1972-06-17 JP JP6091672A patent/JPS5339451B1/ja active Pending
  • 1972-06-19 DE DE2229896A patent/DE2229896C3/de not_active Expired
  • 1972-06-19 FR FR7222032A patent/FR2142078B1/fr not_active Expired

Patent Citations (2)

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