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
  • C23G1/10—Other heavy metals
• • 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
  • C23G1/08—Iron or steel
  • C23G1/086—Iron or steel solutions containing HF

Definitions

• the invention relates to a method for pickling workpieces made of high-alloy materials according to the preamble of the main claim.
• air is blown into the bath in an amount of at least 3 cbm per hour per cbm bath and an amount of stabilized H2O2 between 0.3 and 1 g per liter per hour is controlled on the basis of a redox potential in the bath of greater than or equal to 350 mV.
• additions to the starting materials are listed as under a), c) and e) in order to maintain their concentration in the bath at an optimal level and to keep the pH value of the bath less than 1 preferably between 0 and 0.5.
• the method should be advantageous in several respects, since it does not require nitric acid and thus avoids the problems associated with nitric acid (NOx smoke, complex washing system, NOx content in the waste water).
• the content of expensive hydrogen peroxide has been reduced to a value of preferably 2 to 5 g per liter.
• a stabilized H2O2 This stabilization allows the H2O2 content to be reduced as indicated.
• the actual pickling attack takes place instead of using the nitric acid via the added trivalent iron. At least 15 g per liter should preferably be added for the new batch.
• the pickling process should generally be for everyone Treatment conditions of the usual high-alloy materials can be used and produce excellent surfaces, which are said to be even better in comparison to the traditional nitric-hydrofluoric acid pickling.
• a disadvantage of this method is the large amount of air that has to be blown in and that has a not inconsiderable cost impact on the total expenditure. More expensive is the extra stabilized H2O2 compared to the conventional and the high concentration of hydrofluoric acid and sulfuric acid, which wipes out part of the profit due to the reduced H2O2 content.
• a high concentration of acid also means high disposal costs with regard to the amount of lime and waste to be landfilled.
• blowing in air also has the disadvantage that the sludge is whirled up in the bath and the particles are deposited in finely divided form on the pickling material. The cold air that is blown in also constantly cools the pool down, so that either the air has to be preheated or the bath has to be overheated.
• the object of the invention is to provide an improved generic method for pickling workpieces made of high-alloy materials, which is cheaper in terms of its total costs compared to the known prior art and can be safely handled in a simple manner without complex control.
• the pickling times are not extended compared to conventional nitric hydrofluoric acid pickling and the surface quality also shows no differences.
• the air blowing deemed necessary according to the prior art can be omitted, as can the use of an extra stabilized H2O2.
• the other recommended additives are also not required. So that there is no pickling damage, especially in the case of sensitive materials such as 1.4876, the proportion of hydrogen peroxide is run in excess according to the invention, so that a driving style in the transpassive area is ensured.
• a ratio of 2: 2: 3 in the initial concentration in the pickling bath of sulfuric acid to hydrofluoric acid to hydrogen peroxide has proven to be particularly favorable. This means that depending on the size of the surface to be pickled, concentration reductions of up to 1% by weight for H2SO4 and HF and 1.5% by weight for H2O2 are possible. This low value preferably applies to a bath temperature of 40 - 50 degrees Celsius. If you apply the bath with the advantageous ratio of the concentration - expressed in percent by weight - of 2: 2: 3, then it lies strippable surface already higher than a classic 16% nitrate-4% hydrofluoric acid stain. If the bath is to be operated at room temperature, then the concentration is increased to 2% by weight for H2SO4 and HF and 3% by weight for H2O2 compared to the increased bath temperature. The advantageous ratio of 2: 2: 3 is retained.
• the strong simplification of the proposed method has a favorable effect on the total costs based on 1 square meter of pickled surface. It is almost 50% lower than that of a conventional stain. These total costs take into account the costs for the chemicals when a bath is newly prepared, the amount of lime for the neutralization and the landfill costs.
• the elimination of nitric acid also eliminates the expenses related to the precipitation of NOx.
• the wastewater is no longer polluted with regard to the nitrate content. These costs are not even taken into account in the comparison.
• the lowered acid concentration also has an advantageous effect on the stability of the H2O2, so that the addition of extra stabilized H2O2 is not necessary.
• the bath can be operated in different ways.
• One possibility is to remodel the bathroom, drive it to the point of exhaustion, drain it and then remake it. If you want to use the bathroom for longer, it is necessary to replace the used chemicals.
• sulfuric and hydrofluoric acids are concerned, this is done via an interval concentration measurement, be it semi or fully automatic.
• the consumption of hydrogen peroxide is visually noticeable on the one hand - the sparkling wine sparkles - and on the other hand via an indicator.
• a test strip is used, for example, which the insufficient Oxidation of Fe2+ in Fe3+ indicates. If no more Fe3+ is formed, the test strip turns increasingly brown. It can also be seen from the fact that the pickling material begins to turn brown in places.
• the diminishing effect of H2O2 can also be determined by measuring the redox potential. Even with the appropriate addition, sooner or later the bathroom will be exhausted because the increasing sludge accumulating on the bottom reacts with the H2O2 and reduces its effect. You can remedy this by constantly removing the mud and regenerating the bath. Then a newly prepared bath can be operated for a correspondingly longer time. Another possibility for regeneration is to continuously pump off a part of the pickling bath, to filter it and to feed the cleaned pickling liquid again.
• the proposed bath composition is suitable for all common high-alloy steels in accordance with the DIN designation 1.4301, 1.4306, 1.4404, 1.4541, 1.4550, 1.4571. 1.4876, 1.4910, 2.4663, d. H. starting from a simple 18/8 steel to the molybdenum-containing titanium-stabilized stainless steel up to the nickel-based alloy.
• Oxidized annealed tubes measuring 33 x 3.5 mm made of 1.4571 (containing molybdenum, titanium stabilized) were immersed as a bundle, ie with a number of 148 pieces and a total weight of 4366 kg, in a newly prepared bath.
• the bathroom has a capacity of 20,000 liters.
• the bath temperature was regulated in a range from 40 to 50 degrees Celsius.
• the starting composition was a) H2SO4 (96%) 0.2% by weight HF (73-75%) 0.2% by weight H2O2 (30%) 0.3% by weight
• the tube bundle was immersed in a rinsing bath and then the inside and outside surface was additionally sprayed off by holding a hose.
• the spraying should remove the remaining dirt particles and prevent staining.
• the surfaces examined were flawless and showed no irregularities such as over-pickling or dark spots.
• the mentioned example of stripping oxidized annealed pipes is the worst case in which the pickling time is particularly long and the pickling liquid is heavily used. If, on the other hand, contaminated or blasted or bright-annealed pipes are cleaned, the required pickling times are considerably shorter and the service life of the bath correspondingly longer.
• a starting composition was chosen at a bath temperature of 40 degrees Celsius 1% by weight HCl (16%) 1 wt.% H2O2 or at room temperature 1% by weight HCl (11.7%) 1% by weight HF (2.6%) (HNO3) (2.6%) 2 wt.% H2O2

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

Applications Claiming Priority (4)

Publications (1)

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Family Applications (1)

Country Status (3)

Cited By (5)

Citations (6)

Family Cites Families (1)

• 1994
  • 1994-05-13 DE DE19944417284 patent/DE4417284C2/de not_active Expired - Lifetime
  • 1994-05-18 EP EP94250130A patent/EP0626469A1/de not_active Withdrawn
  • 1994-05-24 CZ CZ941269A patent/CZ126994A3/cs unknown

Patent Citations (6)

Non-Patent Citations (6)

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