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
  • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
  • C23C4/12—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge characterised by the method of spraying
  • C23C4/131—Wire arc spraying

Definitions

• the invention relates to the use of a gas mixture as a carrier gas for arc spraying. Furthermore, the invention relates to a method for arc spraying, wherein a spray material is melted in an arc and atomized in a carrier gas to spray particles and the spray particles are conveyed with the carrier gas to the workpiece, where of the spray particles, the coating is formed.
• Arc spraying is one of the thermal spray processes. In all methods of thermal spraying, spray particles are directed onto a workpiece by means of a carrier gas. The spray particles form the coating on the workpiece. The spray particles adhere to the surface of the workpiece and to one another due to the kinetic energy and heat that they have on impacting the workpiece.
• arc spraying a thermal spraying process, two wires are melted in an arc and atomized to spray particles by means of a carrier gas and then transported to the workpiece. The electric arc burns between the two wires. As wires therefore only electrically conductive materials come into question. The two wires can be made of the same or different materials. Instead of wires, two metallic tubes can also be used. The arc is normally generated between the two wire ends, which are fed to each other in the spray gun, by the application of a voltage with a contact ignition. Arc spraying is primarily used to produce coatings that serve as wear or corrosion protection.
• the disadvantage of arc spraying is the influence of oxygen on the spray material. Due to the high temperatures that prevail in the vicinity of the arc, the oxygen has a strong oxidizing effect. Oxygen enters the spray material during arc spraying either by the carrier gas, which is often used for compressed air, or by the swirling with the carrier gas ambient air. Depending on the energy present, the molten and atomized spray particles burn completely or the metal particles oxidize to metal oxides. The completely burned spray particles are no longer available for the coating, it is called burning. The burnup thus reduces the efficiency for the application of the spray material to the workpiece. The efficiency is defined as the ratio between the spray material forming the coating to the total molten spray material.
• the metal oxides together with the metallic spray particles, reach the workpiece and become part of the coating there.
• these metal oxides lead to a deterioration of the coating quality.
• nitrogen is used as the carrier gas. Nitrogen reduces the oxidation of the spray particles. However, oxidation is insufficiently suppressed by the use of nitrogen, and the coatings often fail to meet the quality requirements.
• the invention has for its object to provide a method that allows high efficiency for the application of the spray material and which leads to high quality coatings.
• a gas mixture is used as a carrier gas for arc spraying, which contains hydrogen.
• the hydrogen in the carrier gas increases the temperature in the arc, causing more spray material to be melted in the arc and atomized and transported by the carrier gas.
• Higher deposition rates enable higher order rates and thus faster layer production. This leads to a higher efficiency of the arc spraying, which has an advantageous effect especially when coating large areas and when spraying thick layers.
• the efficiency for the application of the coating increases, ie the proportion of molten Spray material which forms the coating increases with respect to the total molten spray material. This is due to a reduction in burnup.
• the gas mixture contains 1 to 30% by volume, preferably 2 to 20% by volume, of hydrogen.
• a hydrogen content of less than or equal to 30% by volume, preferably less than or equal to 20% by volume is chosen, since the danger of an explosion increases with increasing hydrogen content.
• the optimum hydrogen content of the carrier gas mixture depends on the specific injection task present and can be determined by simple trial and error.
• the gas mixture contains from 2 to 10% by volume, preferably from 3 to 7% by volume, of hydrogen. Hydrogen contents of this order of magnitude are particularly suitable when non-ferrous metals are used as the spray material. In another particularly advantageous embodiment, the gas mixture contains 10 to 20 vol .-%, preferably 10 to 18 vol .-% hydrogen. Gas mixtures with these hydrogen contents are particularly advantageous when using high-alloy steels as the spray material.
• the gas mixture contains nitrogen. Since nitrogen is an inert gas, the use of nitrogen as the carrier gas reduces the burnup and prevents the formation of metal oxides or of other metal compounds.
• the oxygen from the ambient air, which is introduced by turbulence during the injection process in the mixture of spray particles and carrier gas is bound by the hydrogen. Therefore, the binary mixtures of hydrogen and nitrogen are particularly suitable for the invention.
• the gas mixture contains argon. Since argon is an inert gas, the hydrogen-argon mixtures are also suitable for the invention. Advantageous are v.a. also the teneren mixtures of hydrogen, nitrogen and argon.
• the object is further achieved by a method for arc spraying, which is characterized in that hydrogen is contained in the carrier gas or hydrogen is added to the carrier gas as a further component.
• This inventive method shows all the aforementioned advantages.
• the hydrogen volume fractions are specified in the preceding sections.
• Hydrogen-containing gas mixtures can be obtained from gas suppliers.
• the carrier gas may be stored in a buffer after the addition of hydrogen, or the hydrogen may be introduced separately from the other carrier gas components into the spray gun where the mixing takes place.
• a gas mixture of hydrogen and nitrogen is used.
• the oxygen introduced by the hydrogen is bound by the hydrogen during the injection process from the environment.
• hydrogen is mixed into air.
• the addition of hydrogen to air significantly improves the properties of the carrier gas hydrogen and air in comparison to the use of pure air, since the hydrogen binds at least a portion of the oxygen and thus at least partially adjust the advantages.
• a deposition rate of at least 10 kg / h is used. Possible melting rates of 20 kg / h and more. As the deposition rate increases, the problems of burnup and oxide formation increase. With the method according to the invention, however, these problems are solved even at high Abschmelz transaction.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Physics & Mathematics (AREA)
• Plasma & Fusion (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Coating By Spraying Or Casting (AREA)

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Cited By (2)

Citations (11)

• 2004
  • 2004-12-21 DE DE102004061569A patent/DE102004061569A1/de not_active Withdrawn
• 2005
  • 2005-12-15 EP EP05027513A patent/EP1674590A1/fr not_active Ceased

Patent Citations (11)

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