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
  • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B31/00—Machines or devices designed for polishing or abrading surfaces on work by means of tumbling apparatus or other apparatus in which the work and/or the abrasive material is loose; Accessories therefor
  • B24B31/12—Accessories; Protective equipment or safety devices; Installations for exhaustion of dust or for sound absorption specially adapted for machines covered by group B24B31/00
  • B24B31/14—Abrading-bodies specially designed for tumbling apparatus, e.g. abrading-balls

Definitions

• heat resistant and corrosion resistant ferrous or non-ferrous refractory alloys for example 18/8 nickel- chromium stainless steels and nickel-cobalt base creep- resistant alloys
• heat treatment or are used under conditions of high temperature an oxide scale is often formed on them. It is usually necessary to remove this scale in order to facilitate subsequent operation such as welding, brazing, close fitting assembly or size or defect inspection processes.
• Known methods of scale removal include mechanical methods and chemical methods.
• Known mechanical scale removal methods include shot blasting, abrasive grit blasting, blasting with aqueous abrasive suspensions, grinding, linishing and buffing. These methods are time-consuming, labour- intensive and incur metal loss.
• One method involves contacting the article with neutral or alkaline molten salts, the latter often in the presence of sodium hydride. Such methods tend sometimes to be ineffective and are dangerous to operate.
• Another method involves pickling the article in an acid solution generally containing an inhibitor.
• the method may be supplemented with alternating treatments in an aqueous alkaline oxidising bath such as a caustic/permanganate composition.
• aqueous alkaline oxidising bath such as a caustic/permanganate composition.
• a difficulty with many methods of scale removal is that there is a tendency for the method either to result in incomplete removal of scale or to result in the removal of substantial amounts of the metal substrate. It has been our object to devise a method that is capable of giving very efficient removal of scale with minimum removal of metal.
• scale on a metal article is removed by contact of the article in a vessel with an aqueous acidic scale removing composition, and in this method the vessel contains solid bodies wetted by the composition and the contact of the article with the solution is effected by agitating the wetted bodies against the article.
• the bodies generally have dimensions of between 0.2 and 20 mm.
• the amount should be less than the amount required to form a continuous phase in which the bodies could be suspended.
• the amount of composition is less than 75%, and preferably less than 50%, of the volume required to fill the voids.
• the volume of composition must be sufficient to wet all the bodies in the vessel and may be, for instance, at least 10% of the volume required to fill all the voids.
• the solid bodies may be made of, for example, ceramic, refractory, abrasive or metallic.
• the bodies may be any suitable shape and size. They may be spherical but preferably are polyhedral, having a small number of faces, e.g. up to eight. Thus, for example, the bodies may be right triangular prisms or cubes. Alternatively, the bodies may be obtained by crushing a block of a suitable material, e.g. fused alumina.
• the minimum dimension of the bodies is preferably at least 0.5, and usually at least 2 mm. The maximum dimension may be no more than 20, 10 or even 6 mm.
• the agitation may involve barrelling or tumbling but preferably the vessel is a trough containing a bed of the bodies, the article is submerged in the bed and the bodies are agitated by agitating the trough.
• the trough may be vibrated and if the trough is circular, or, more preferably, spiral or annular shaped it may be vibrated with a rotational motion.
• Suitable apparatus for use in the method is known and is readily available under the trade name "Spiratron” which is manufactured by Cetema Limited of School Lane, Knowsley Industrial Estate, Prescot, Merseyside, England.
• the composition is preferably above ambient temperature during the process, suitably at a temperature of 40 to 100°C, e.g. about 80°C.
• a temperature of 40 to 100°C e.g. about 80°C.
• the composition is heated outside the vessel by a heater, is circulated through the vessel for contact with the article, and is recycled to the heater, where it is reheated and then circulated through the vessel again.
• the composition may be continuously trickled into the vessel from a heater, continuously removed from the vessel and recycled to the heater.
• the total treatment of the article may involve alternation of the described method with contact with an oxidising alkaline solution.
• the method may comprise contacting the article with the said wetted and agitated bodies in the vessel, removing the article from the vessel, contacting the article with an oxidising alkaline solution and then repeating the contact of the article in the vessel with the wetted and agitated bodies.
• the alkaline oxidising solution typically contains sodium hydroxide and potassium permanganate and is usually hot, e.g. 95°C. Generally it is a static solution and contact is achieved by immersing the article in the solution. Generally the article is rinsed between each treatment.
• the invention is of particular value when the scale removing composition is an acidic solution of a chelating agent, often a solution of an acidic chelating agent.
• Suitable chelating agents are tartaric acid, citric acid, ethylenediaminetetraacetic acid and nitrilotriacetic acid.
• the composition should be mildly acid and so will usually have a pH of at least 2, e.g. from 2.5 to 6. It may include components additional to the chelating agent and any necessary acid to generate the chosen pH, for instance reducing agents, surfactants and corrosion inhibitors.
• chelating compositions known for scale removal of refractory oxides can be used in the invention but the method of the invention results in very much more effective scale removal than has previously been attainable.
• the weight loss of scale from the blade amounted to approximately 550 mg. Further weight loss from the cleaned blade in the agitated hot wetted medium was at the rate of approximately 5 mg per hour. Using a solution of sodium silicate for 10 hours in the same vibrated medium produced no apparent cleaning effect.
• a suitable solution for use as the chelating solution defined in this example is the material sold commercially by Ardrox Limited, of Furlong Road, Bourne End, Buckinghamshire, England as their product Ardrox 1871. "Ardrox” is a trade mark.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)

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Citations (4)

• 1982
  • 1982-03-17 EP EP82301375A patent/EP0061298A1/fr not_active Withdrawn

Patent Citations (4)

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