Classifications

• • 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
  • B05D3/06—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 exposure to radiation
  • B05D3/068—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 exposure to radiation using ionising radiations (gamma, X, electrons)
• • 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
  • B05D1/00—Processes for applying liquids or other fluent materials
  • B05D1/62—Plasma-deposition of organic layers
• • 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
  • B05D2350/00—Pretreatment of the substrate
  • B05D2350/60—Adding a layer before coating
  • B05D2350/63—Adding a layer before coating ceramic layer

Definitions

• the invention relates to a method for sealing a porous coating made of hard material, such as aluminum oxide, tungsten carbide, chromium, applied to a body in the plasma spraying method.
• hard material such as aluminum oxide, tungsten carbide, chromium
• metallic objects which must have a very high resistance to abrasion, in the plasma to provide the spraying method with a coating of a hard material, suitable metals, oxides and carbides being suitable as hard materials.
• the coating material is fed to the plasma spray nozzle in the form of a powder, melted in the plasma jet on the surface of the individual grains and thus reaches the surface to be coated, where the hard material forms a more or less porous coating.
• the cavities contained in this coating are generally to a greater or lesser extent capillaries. While the resistance of metallic bodies that have been coated in this way to purely mechanical wear is generally good, the resistance to chemical attacks is often inadequate, since acids can reach the metallic body through the cavities of the coating, for example. attack it and cause the coating to peel
• the object of the invention is to close the voids in the coating so that chemically aggressive substances cannot reach the surface of the metallic body.
• This object is achieved according to the invention in that the coating is impregnated with a liquid curable, in particular crosslinkable, plastic or lacquer, and in that this plastic layer or lacquer layer is crosslinked, at least in its outwardly facing region, by irradiation with electrons.
• the advantage of the invention is that a completely closed layer of the cured, in particular cross-linked plastic or lacquer is created within the porous coating, which prevents the entry of acids or other aggre sensitive substances to the surface of the metallic body with suitable selection of the plastic with certainty prevented. It is not absolutely necessary that the plastic or lacquer layer, which is simply referred to as a plastic layer in the following, is cross-linked to its full depth, but it is sufficient if the cross-linking takes place only in an outer region.
• Another advantage of the invention is that the crosslinking by means of electron radiation can take place very quickly, in the presence of suitable systems, for example in a few seconds or at most a few minutes, and that the plastic layer and thus the body carrying the coating are not noticeably heated as a result of the electron radiation . It is therefore also possible to treat bodies sensitive to temperature increases with the method according to the invention. If it is intended to subject the body to processing after crosslinking, for example grinding the coated surface, then the crosslinking is carried out in such a way that the crosslinking in the applied plastic layer extends at least so deep that no areas which have not yet been crosslinked in the subsequent processing the plastic layer can be reached.
• the coated bodies can be processed further immediately after the electron irradiation. Depending on the type of the coated object, it may then be sufficient if areas of the plastic which are not yet crosslinked in the depth are still completely crosslinked under the influence of a sufficiently high ambient temperature in the course of the following days or weeks.
• the body is heated to approximately 80 ° C. before the liquid plastic is applied, and that the plastic subsequently applied to the heated body, in particular sprayed on.
• the relatively low temperature for example, 80 ° C, which can be withstood even by sensitive bodies without danger
• the air contained in the cavities of the hard material coating is largely expelled and the liquid plastic penetrates into it Depth of the porous layer is facilitated.
• the plastic is applied while the body is still warm, so that the liquid plastic can penetrate into deeper areas of the porous layer when the air still contained in the pores cools.
• the amount of liquid plastic applied can be adapted to the particular requirements in a particularly simple manner by spraying.
• a liquid plastic of low viscosity preferably a plastic that is more liquid than water. This facilitates the penetration of the plastic into the cavities in the hard material coating.
• the method is applied in such a way that only a single plastic coating is provided, which then generally takes up the entire thickness of the hard material coating.
• the porous coating is first soaked only in its area adjacent to the metallic body, and that after curing by electron radiation the body is in turn soaked with a plastic which is also crosslinked by electron radiation.
• the same plastic can be used here if, in special cases, for example, a desired crosslinking to a relatively great depth cannot take place in a single irradiation process because the plastic layer is too thick for this; however, different plastics are used in other embodiments of the invention.
• the outer plastic layer can be chosen so that a particularly low coefficient of friction of the body results; in this case the outer, fully crosslinked plastic layer can in particular be polytetrafluoroethylene.
• the penetration of the plastic can only be brought about into the area of the porous coating adjacent to the metallic body by applying only a limited amount of plastic required to fill the capillaries adjacent to the metallic body, which is then heated by appropriate heating as a result of gravity seeps down, being due to the limited amount of the liquid plastic, the upper areas can be cleared of the plastic again and can be filled with another plastic after the plastic has hardened.
• the entire coating can be filled with a certain plastic and the workpiece heated to a temperature at which the liquid plastic evaporates from the area near the surface, at which temperature the remaining plastic is already cured can.
• Another plastic can then be introduced into the area of the porous layer which has become free due to evaporation of the plastic and can be cured by electron radiation.
• the heating can be carried out in such a way that this area of the layer located on the surface heats up more than the area of the porous layer adjacent to the metallic body.
• An important advantage of the invention lies in the following: If a body coated with hard material, for example a cylinder of a printing press, has to be ground to achieve a sufficiently smooth surface, whole grains of the coating material are often torn out of the coating, so that a certain amount of Roughing depth cannot be fallen below.
• the body is in accordance with the invention Provided sealer, the cross-linked plastic layer holds the grains of the hard material coating firmly, especially if it extends to greater depths of the coating, so that individual grains that protrude too far outward are partially removed as desired, but not completely be torn out of the coating.
• a metallic body which in the exemplary embodiment is a printing cylinder of a printing press, and which consists of steel and has dimensions of 180 cm in length and 85 cm in diameter, is coated with a layer of tungsten carbide in the plasma spraying process. This coating has a thickness of approximately 100 pm.
• the plasma spraying process or, as it is also called, plasma spraying, and the devices required for this are known.
• a gas is fed to an arc plasma torch and dissociated and ionized in the arc depending on the type of gas. Shortly before the nozzle emerges, the pulverized spray material, i.e. the hard material, is fed to the plasma flowing out at high speed with the aid of a carrier gas. Argon is often used as the plasma gas.
• the body provided with the hard material coating is then heated in such a way that the temperature of the body decreases somewhat from the inside to the outside.
• the heating causes most of the air contained in the pores of the surface layer to escape.
• the coated body with a liquid Sprayed plastic which is specified below. This plastic is drawn into the pores of the coating, at least in part also as a result of capillary action, not least because the liquid plastic penetrates into the warmer areas of the coating, that is to say inside, with further liquefaction.
• Spraying takes place immediately after the workpiece has been heated to approximately 80 ° C., so that the air that has escaped from the pores of the coating does not penetrate again in the meantime.
• the workpiece is irradiated by electrons.
• a system suitable for such radiation is sold by Otto Dürr Anlagenbau GmbH, D-7000 Stuttgart under the type designation ESH 150.
• This system generates electrons with an energy of 150 keV, whereby the body to be irradiated can be in the free atmosphere and is only flushed with a suitable inert gas to keep out the oxygen in the air in the area in which the electrons strike the body .
• Nitrogen is an example of an inert gas.
• the power of the electron beam available for irradiation is 7.5 KW.
• the sealing by the plastic cross-linked or hardened by means of electron bombardment is extremely effective.
• An unsealed, plasma sprayed layer is removed, for example, in a single operation by sandblasting with corundum. If a hardened plastic layer according to the invention is introduced into the hard material layer, about six such sandblasting processes are required to remove this combined layer.
• the cross-linked plastic layer makes it possible for the first time to use workpieces with surfaces sprayed with a plasma spray in the chemical sector, where without the hardened plastic layer the hard material coating would be damaged by corrosion of the metal body supporting this layer. An impregnation of the hard material layer with an uncured plastic, however, could not prevent corrosion of the metal body with certainty.
• a high-molecular plastic which essentially consists of polyethylene glycol dimethacrylate or trimethylol propane trimethacrylate with the addition of aliphatic and / or aromatic hydrocarbons, especially amines, and which contains the usual additives of plasticizer, polymer Thickener, peroxide, toluidine, saccharin, fillers, pigments, stabilizers and the like, some based on Si.

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• Health & Medical Sciences (AREA)
• General Health & Medical Sciences (AREA)
• Toxicology (AREA)
• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Application Of Or Painting With Fluid Materials (AREA)

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Citations (4)

• 1981
  • 1981-11-05 DE DE19813143874 patent/DE3143874C2/de not_active Expired
• 1982
  • 1982-10-29 EP EP19820110003 patent/EP0079007B1/fr not_active Expired

Patent Citations (4)

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