CN108193214B

CN108193214B - Method for stabilizing and compatible degreasing and chromizing agent for slag reduction in aluminum industry

Info

Publication number: CN108193214B
Application number: CN201711471771.9A
Authority: CN
Inventors: 熊映明
Original assignee: Foshan Sanshui Xiongying Innovation Center For Aluminum Surface Technnologies Co ltd
Current assignee: Foshan Sanshui Xiongying Innovation Center For Aluminum Surface Technnologies Co ltd
Priority date: 2017-12-29
Filing date: 2017-12-29
Publication date: 2020-06-23
Anticipated expiration: 2037-12-29
Also published as: CN108193214A

Abstract

The invention discloses a method for stabilizing and compatible degreasing and chromizing agents for slag reduction in aluminum industry, which comprises a degreasing tank and a chromizing tank, wherein degreasing liquid is arranged in the degreasing tank, the chromizing tank is internally provided with chromizing liquid, the degreasing liquid is a solution of nitric acid and hydrofluoric acid, the chromizing liquid is a solution of chromic anhydride, hydrofluoric acid and nitric acid, the degreasing liquid and the chromizing liquid are compatible, and the degreasing tank and the chromizing tank do not generate precipitates in the long-term operation process. The stable components are selected to ensure that the oil removing groove and the chromizing groove do not generate sediment in long-term operation, and the surface of the aluminum material is not easy to be coated with ash and generate crystal precipitates. The deoiling liquid is compatible with the chromizing liquid, when the deoiling liquid is inevitably carried into the chromizing liquid by the aluminum product, the operation of the chromizing liquid and the chromizing effect of the aluminum product are not influenced, and no precipitation crystallization is generated in the chromizing tank.

Description

Method for stabilizing and compatible degreasing and chromizing agent for slag reduction in aluminum industry

Technical Field

The invention relates to the technical field of metal surface treatment, in particular to a method for stabilizing and compatible degreasing and chromizing agents for slag reduction in aluminum industry.

Background

The aluminum and the aluminum alloy have the advantages of excellent processing performance, good corrosion resistance, beautiful surface, high recovery rate and the like, are widely applied to the industries of buildings, transportation, machinery, electric power and the like, and have more obvious trend of expanding the application of the aluminum by replacing the steel with the aluminum in recent years. The aluminum processing industry is a traditional industry, and more particularly, the sunrise industry which is full of bobby vitality. According to statistics, developed countries in Europe and America consume more than 32kg of aluminum materials per year, but China only has about 13kg of aluminum materials per year and is only about one third of developed countries, and domestic aluminum material consumption has huge growth space, but under the new economic normal state, the problems of high energy consumption, large total pollution discharge amount and low resource recovery rate also become bottlenecks and obstacles for industry development.

The production in the aluminum industry comprises the working procedures of electrolysis, casting, pressure processing, surface treatment and the like, and waste water and waste residues are generated in different degrees in all the working procedures during production. A large amount of aluminum ash is generated during electrolysis and casting, alkaline waste liquid is corroded by alkali in the extrusion process, and various waste water and waste residues containing acid, alkali, treatment agents, chromium, nickel heavy metal ions and other complex components are generated in the surface treatment process.

Modern aluminum processing enterprises have the urgent need of treating waste water and waste residue after spraying pretreatment, but the existing treatment method is too simple, and the chromium-containing waste water and waste residue generated by the chromizing process and the fluorine-containing waste water and waste residue generated by the chromium-free process all face the environmental protection pressure of treating the toxic waste water and waste residue. The society will pay for expensive disposal costs to dispose of these wastes.

The spraying pretreatment of the chromium-containing toxic waste residue generated by oil removal and chromizing accounts for 20 percent of the total amount of the waste residue generated by surface treatment of aluminum processing enterprises.

The powder spraying aluminum profile has the advantages of beautiful surface, rich colors, good corrosion resistance and weather resistance, and the like, and becomes the largest surface treatment variety of the aluminum profile, and accounts for more than 60 percent of the total amount. The surface of the section bar is pretreated before spraying, a layer of compact conversion coating is generated on the surface of the aluminum material through chemical reaction, the conversion coating has certain corrosion resistance, and more importantly, the base material and the spraying coating can be firmly combined together.

Chromium-containing wastewater is generated after spraying chromizing pretreatment, chromium belongs to a class of pollutants, the wastewater is collected and treated independently, and the wastewater can be discharged after reaching the standard. The waste water containing hexavalent chromium is generally treated by an oxidation-reduction method, i.e. reducing agents such as ferrous sulfate and sodium pyrosulfite are used to treat Cr in the waste water⁶+ reduction to Cr³⁺Then, the pH value of the wastewater is adjusted to 7-8, and alkali and flocculating agent are added to lead Cr to be³⁺Formation of Cr (OH)₃Precipitating, and dehydrating by flocculation, sedimentation and filter pressing to form chromium hydroxide (trivalent chromium) chromium slag. The flow of the chromium-containing wastewater treatment is shown in FIG. 3. The chromium slag belongs to dangerous waste and must be legally transferred to a qualified third-party institution for standard disposal.

In a word, the treatment and disposal cost of the chromium-containing wastewater and waste residue is high, the enterprise is heavily burdened, and the method has environmental hazard, regardless of 'talking about chromium color change' of governments or enterprises.

In order to solve the pollution problem caused by the chromizing process, a large amount of chromium-free process substitution researches are carried out at home and abroad for many years and are generally applied to the aluminum profile industry. The chromium-free process mainly comprises two technical routes, namely a titanium-zirconium system and a silane system, and the chromium-free passivation process of fluotitanic acid and fluozirconic acid of the titanium-zirconium system is mainly applied in Chinese aluminum section factories. The quality of the passive film and the spraying layer of the process can basically meet the requirement of GB 5237, but the passive film and the spraying layer are inferior to a chromized film in certain indexes and overall stability, and the passive film and the spraying layer are not subjected to outdoor long-term inspection. And the chromium-free passivation process has strict control requirements, the conversion film has no color, the quality of the film layer is difficult to judge on site, and the product is likely to be unqualified if careless. In order to ensure the product quality, the fluorocarbon paint spraying section bar and the curtain wall veneer still adopt the chromizing process. More importantly, chromium-free reagents such as fluotitanic acid and fluozirconic acid contain fluorine, and the pollution problem of the fluorine is caused by using the chromium-free chemical reagents with strong toxicity. The front door drives wolf and the back door drives tiger, and the process of replacing pollution by the same non-environment-friendly process is not the optimal choice.

Among all the chemical conversion coatings, the chromized coating has the best corrosion resistance and has a self-repairing function, which is related to the retention of hexavalent chromium in the coating structure, and the corrosion resistance of other chemical conversion coatings can not reach the level of the chromized coating. Therefore, the chromizing process is still irreplaceable as long as the problem of hexavalent chromium wastewater and waste residue pollution of the chromizing process is solved.

The chromate chemical conversion treatment is the most common aluminum product pretreatment process, has been applied for decades at home and abroad, has mature technology, easy control of the process, good quality of a chromizing film layer and very stable quality of a spraying layer. However, hexavalent chromium contained in the chromating solution and the conversion coating has strong toxicity, and governments have set a series of policies to limit the adoption of the process in some fields, the most important of which is that: on 13.2.2003, the "RoHS directive" for restricting the use of 6 toxic and harmful substances such as hexavalent chromium in electrical and electronic equipment, which is passed through by the european union, is mainly directed to electrical and electronic equipment products. However, in other fields, such as aerospace, building aluminum alloy doors, windows and curtain walls, no relevant foreign policy report is found at present. In Europe and America, the spraying pretreatment of aluminum profiles and curtain wall aluminum plates also adopts a great deal of chromizing treatment process.

In recent years, national environmental protection regulation is becoming stricter, and many local governments in China take the environmental hazards of hexavalent chromium and trivalent chromium in the traditional chromate passivation to waste water and waste residue and the difficulty in treatment and regulation into consideration, and develop an environmental protection policy of strictly limiting the adoption of the traditional chromium-containing passivation process. The Buddha mountain is the most concentrated area of aluminum products in China, the aluminum profile industry is one of the pillar industries in the Buddha mountain market, how to actively and scientifically deal with the national environmental protection laws and regulations, guide enterprises to grasp opportunity transformation and upgrade, accelerate the popularization and application of a spraying pretreatment process without generating waste water and waste residues, protect the environment and benefit descendants, and the Buddha mountain aluminum profile is worthy of common discussion and thinking of governments and enterprises.

In the prior art, the spraying pretreatment process flow is as follows: hanging workpieces → acid etching and degreasing → water washing → chromizing → water washing → draining → drying → coating. The production line for the aluminum profile coating pretreatment is divided into 2 types of vertical lines and horizontal lines, wherein the vertical lines adopt a full-automatic spraying mode; the horizontal wire was dipped all at once as shown in fig. 6.

The No. 1 acid oil removing tank is generally selected from sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid, hydrofluoric acid, sodium fluoride, ammonium bifluoride and a proper amount of surfactant for oil removal. When the aluminum material is deoiled, the aluminum is subjected to the following chemical reaction in deoiling liquid containing mixed acid and fluorine:

1. removing natural oxide film

Al₂O₃+6H⁺＝2Al³⁺+3H₂O (1)

2. Melting aluminum and deburring

2Al+6H⁺＝2Al³⁺+3H₂↑ (2)

3. Aluminum-fluorine complexing and stable deoiling liquid

6Al³⁺+F^-+H₂O＝AlF₆ ^3-+Al(OH)F₅ ^3-+Al(OH)₂F₄ ^3-

+Al(OH)₃F₃ ^3-+Al(OH)₄F₂ ^3-+Al(OH)₅F^3-+6H⁺(3)

4. Passivating the aluminum surface and reducing the dissolved aluminum

2Al+3NO₃ ^-＝Al₂O₃+3NO₂ ^-(4)

According to the formulas (1) and (2), the higher the acid concentration is, the faster the aluminum dissolving speed is; according to the formulas (3) and (4), the surface of the aluminum material is passivated, the amount of dissolved aluminum is restricted, and the pressure of crystal precipitation of bath solution is reduced; meanwhile, due to the existence of high-concentration nitric acid, aluminum exists in the forms of fluoroaluminate and hydroxyfluoroaluminate instead of being precipitated and separated out by aluminum fluoride or aluminum phosphate, the bath solution is stable, does not decompose, does not scale and can run for a long time.

4# chromizing tank, typically containing CrO₃Potassium dichromate K₂Cr₂O₇Sodium fluoride, nitric acid, potassium ferricyanide K₃Fe(CN)₆Sodium silicate Na₂SiO₃Hydrofluoric acid, boric acid, sodium molybdate, a stabilizer (prepared by mixing 2 organic acids containing carboxyl and hydroxyl), and the like. When the aluminum material is chromized, a layer of passivation film which is difficult to dissolve in water and mainly consists of chromate is formed on the surface of the metal. The 4# groove chromizing film-forming process is relatively complex, and the reaction mechanism is as follows:

1. dissolving aluminum and precipitating hydrogen on the surface of aluminum material

2Al+6HF＝2AlF₃+3H₂↑ (5)

AlF₃Reacting according to (3) to produce fluoroaluminic acid and hydroxyfluoroaluminic acid

2. The separated hydrogen reduces the hexavalent chromium into trivalent chromium, and the trivalent chromium is deposited on the surface of the aluminum in the form of chromium hydroxide colloid due to the increase of the pH value at the two-phase interface of the aluminum alloy and the chromizing liquid

3H₂+2CrO₃＝2Cr(OH)₃↓ (6)

3. The chromium hydroxide colloid is combined with hexavalent chromium to form trivalent chromium and hexavalent chromium oxide on the surface of aluminum

2Cr(OH)₃+CrO₃＝Cr(OH)₃·Cr(OH)·CrO₄↓

+H₂O＝Cr(OH)₃·Cr(OH)₂·HCrO₄↓ (7)

4. The pH value of the interface of two phases of the aluminum alloy and the chromizing liquid is increased, so that aluminum ions and hydroxide radicals generate gelatinous aluminum hydroxide, and the aluminum hydroxide is dehydrated on the surface of the aluminum alloy to form an alumina film which is difficult to dissolve in water

2Al³⁺+6OH^-＝2Al(OH)₃↓＝Al₂O₃↓+3H₂O (8)

5. The fluoroaluminate electrically adsorbed on the surface of the aluminum alloy reacts with trivalent chromium to generate a chromium fluoroaluminate film

Cr³⁺+AlF₆ ^3-＝CrAlF₆↓ (9)

6. Molybdate is used as an oxidative promoter, and the molybdate and aluminum ions form an aluminum molybdate compound protective film on the surface of aluminum

3H₂MoO₄+2Al³⁺＝Al₂(MoO₄)₃↓+6H⁺(10)

7. With potassium ferricyanide K₃Fe(CN)₆As an oxidation promoter, potassium ferricyanide and aluminum ions form an aluminum ferricyanide composite protective film on the surface of aluminum

Fe(CN)₆ ^3-+Al³⁺＝AlFe(CN)₆↓ (11)

8. Nitric acid is used as a bath solution stabilizer and a dust remover to remove the virtual dust on the surface of the aluminum profile chromizing film, limit the precipitation of sludge in the chromizing bath and oxidize trivalent chromium to hexavalent chromium.

The composition of the chromate conversion coating is substantially CrAlF₆·AlFe(CN)₆·Al₂(MoO₄)₃·Cr(OH)₃·Cr(OH)₂·CrO₄·Al₂O₃·H₂O, the newly generated conversion film exists in a colloid state, the hardness and the wear resistance are poor, the conversion film is dehydrated and hardened after being dried, has hydrophobicity, and has good bonding force with an aluminum material substrate and corrosion resistance, and is a good bottom layer of an organic coating.

According to the figure 6, the chromizing aluminum material is produced, and long-term operation shows that crystals exist at the bottom of the oil removing groove, chromium-containing sludge exists at the bottom of the chromizing groove, the chromium-containing sludge needs to be cleaned regularly, the sludge contains highly toxic hexavalent chromium, and the operation is very dangerous.

Ammonium fluoride, ammonium bifluoride, sodium fluoride and phosphoric acid in the acidic oil removal tank are components which cause the surface of the aluminum material to be easy to be coated with ash and generate crystal precipitates. When the acidity value of the bath solution is not enough, acid corrosion ash is easily generated on the surface of the aluminum material, and the oil removal effect is influenced; sodium ions in the sodium fluoride are easy to generate sodium fluoroaluminate precipitate, and the tank liquor needs to be cleaned; phosphoric acid is easy to generate aluminum phosphate precipitate, and the tank liquor needs to be cleaned.

Potassium dichromate K in chromizing tank₂Cr₂O₇Sodium fluoride, potassium ferricyanide K₃Fe(CN)₆Sodium silicate Na₂SiO₃The sodium molybdate is a component which makes the surface of the aluminum material easy to be coated with ash and easy to generate crystal precipitates. The components contain sodium and potassium, sodium fluoroaluminate and potassium fluoroaluminate precipitates are easy to generate, and a tank needs to be cleaned; meanwhile, the products can make the bath solution unclear and the chromizing film is easy to be coated with ash, thereby affecting the chromizing quality.

The stabilizer in the chromizing tank is prepared and combined by 2 organic acids containing carboxyl and hydroxyl, and is an unstable component easy to be oxidized and decomposed in the chromizing liquid. These are reducing components in the presence of chromium-containing anhydrides (CrO)₃) Hydrofluoric acid, nitric acid and boric acid are easily decomposed by an oxidant, and the stability of the chromizing liquid is affected.

Disclosure of Invention

The invention aims to provide a method for stabilizing and compatible degreasing and chromizing agents for slag reduction in aluminum industry, which has the characteristic that degreasing liquid and chromizing liquid are compatible with each other.

The invention aims to provide a system adopting a stabilizing and compatible method of an oil removing and chromizing agent for slag reduction in aluminum industry, which has the characteristics that degreasing liquid and chromizing liquid are compatible with each other and groove cleaning is not needed.

In order to achieve the purpose, the invention adopts the following technical scheme:

the utility model provides an aluminium industry subtracts stable and compatible method of deoiling and chromizing medicament of sediment, includes except that oil groove and chromizing groove, it has deoiling liquid to remove in the oil groove, it has the chromizing liquid to change the inslot to chromize, deoiling liquid is the solution of nitric acid and hydrofluoric acid, the chromizing liquid is the solution of chromic anhydride, hydrofluoric acid and nitric acid, it is compatible with chromizing liquid to remove oil liquid, deoiling groove and chromizing groove do not have the sediment in the long-term operation process and produce.

Further, the control indexes of the deoiling liquid are as follows: 68 wt% nitric acid 40-60 g/L, 50 wt% hydrofluoric acid 5-15 g/L, and acid concentration 1.0-1.5 equivalent.

Furthermore, in the long-term operation process of the oil removing groove, the adding agents are solutions of nitric acid and hydrofluoric acid, and 68 wt% of nitric acid/50 wt% of hydrofluoric acid in the adding agents of the oil removing groove is 1.5-2.5.

Further, the control indexes of the chromizing liquid are as follows: chromic anhydride CrO32.5-3.5 g/L, 50 wt% hydrofluoric acid 0.4-0.8 g/L, 68 wt% nitric acid 5-7 g/L, pH 1.8.8-2.2.

Furthermore, in the long-term operation process of the chromizing liquid, the adding agent is a solution of nitric acid and hydrofluoric acid, and the adding agent of the chromizing liquid is 68 wt% of nitric acid/50 wt% of hydrofluoric acid which is 8-12.

Further, the mutual compatibility of the deoiling liquid and the chromizing liquid means that:

when part of deoiling liquid in the deoiling tank is brought into the chromizing tank, the operation of the chromizing tank is not influenced, and the chromizing capacity of the chromizing liquid is not influenced;

when part of chromizing liquid in the chromizing tank is brought into the oil removing tank, the operation of the oil removing tank is not influenced, and the oil removing capability of the oil removing liquid is not influenced.

The spraying pretreatment process flow comprises the following steps: hanging workpieces → acid etching and degreasing → water washing → chromizing → water washing → draining → drying → coating.

The invention has the beneficial effects that:

1. the degreasing liquid adopts a solution of nitric acid and hydrofluoric acid, and stable components are selected to ensure that the degreasing liquid does not generate precipitation after long-term operation, and the surface of the aluminum material is not easy to be coated with ash and is not easy to generate crystallized precipitates.

2. The chromizing liquid adopts a solution of chromic anhydride, hydrofluoric acid and nitric acid, and stable components are selected to ensure that the chromizing liquid does not generate precipitate after long-term operation, and the surface of the aluminum material is not easy to hang ash and generate crystallized precipitates. And the risk of cleaning the tank is avoided by avoiding the generation of sodium fluoroaluminate and potassium fluoroaluminate precipitates and the decomposition of organic matters.

3. Careful selection of the components ensures that the long-term operation of the oil removal bath does not affect the stability of the chromizing bath. The deoiling liquid is compatible with the chromizing liquid, when the deoiling liquid is inevitably carried into the chromizing liquid by the aluminum material, the operation of the chromizing liquid and the chromizing effect of the aluminum material are not influenced, and no precipitation and crystallization exist in the chromizing tank.

4. The stability component that ensures the chromizing cell is compatible with the oil removal cell is carefully selected. The invention firstly focuses on the compatibility of the selected components to the deoiling liquid on the premise of selecting the components of the chromizing liquid, stabilizing the tank liquid and not precipitating and crystallizing.

5. The ratio of the two acids of the oil removal tank additive is carefully selected. The production of the chromizing aluminum material is found in long-term operation that even if the degreasing agent only contains nitric acid and hydrofluoric acid, the tank bottom of the degreasing tank still has the risk of precipitating aluminum fluoride, the cleaning is required regularly, sludge contains extremely toxic fluoride, and the operation is very dangerous. According to the invention, the weight ratio of 68 wt% nitric acid to 50 wt% hydrofluoric acid in the degreasing liquid is controlled to be 1.5-2.5, so that the risk of precipitation in the degreasing tank is thoroughly eliminated.

6. The ratio of the two acids of the chromizing vessel charge was carefully selected. The production of the chromizing aluminum material is found in long-term operation that even if the chromizing agent only contains chromic anhydride, nitric acid and hydrofluoric acid, the bottom of a chromizing tank still has the risk of separating out aluminum fluoride and chromium fluoroaluminate, the bottom needs to be cleaned regularly, sludge contains virulent fluoride and hexavalent chromium, and the operation is very dangerous. According to the invention, the weight ratio of 68 wt% nitric acid to 50 wt% hydrofluoric acid in the additive in the chromizing liquid is controlled to be 8-12, so that the risk of precipitation in the chemical tank is thoroughly eliminated.

Drawings

FIG. 1 aluminum ash component detection report;

FIG. 2 shows a source of aluminum-containing waste residues in a large aluminum plant;

FIG. 3 is a flow chart of chromium-containing wastewater treatment;

FIG. 4 shows a nickel-containing wastewater treatment process;

FIG. 5 is a flow of waste water and residue treatment;

FIG. 6 is a diagram of a conventional spray chromizing process and slot placement.

Detailed Description

The invention relates to a method for stabilizing and compatible degreasing and chromizing agents for slag reduction in aluminum industry, which is a new process after unprecedented system research is carried out on a spraying pretreatment process with large waste water and slag amount and huge environmental protection pressure of the existing aluminum processing enterprises after the production confusion of the aluminum processing enterprises is fully known and the spraying pretreatment process is researched and developed for many years.

Quantitative and qualitative analysis of oil removal and chromizing stabilization and compatible agents.

1. Qualitative and quantitative analysis of each component of deoiling liquid

In the prior art, sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid, hydrofluoric acid, sodium fluoride, ammonium bifluoride and a proper amount of surfactant are generally selected to remove oil. The quantitative and qualitative analysis of each component is as follows:

sulfuric acid: the sulfuric acid is a basic component for acidic oil removal, and has the functions of providing an acidity value, dissolving a natural oxidation film and dissolving aluminum. The sulfuric acid is mainly used for maintaining a certain free acidity of the deoiling liquid, keeping the solution stable, promoting the dissolution of aluminum and enabling the aluminum surface to present an active area which is beneficial to the film formation of chromate. The oil removal effect is weakened due to the over-low sulfuric acid content and over-long oil removal time; the concentration of the sulfuric acid is too high, the aluminum dissolution is too fast, and the pressure of wastewater treatment is too large. Therefore, the content of sulfuric acid should be controlled within the range of 10-20 g/L (98% sulfuric acid);

phosphoric acid: phosphoric acid is a basic component for acidic oil removal, has the functions of providing acidity value, dissolving a natural oxidation film and dissolving aluminum, and is a basic component for acidic oil removal. The phosphoric acid is mainly used for maintaining a certain free acidity of the deoiling liquid, keeping the solution stable, promoting the dissolution of aluminum and enabling the aluminum surface to present an active area which is beneficial to the film formation of chromate. The phosphoric acid content is too low, the dissolving capacity is weakened, and the oil removing time is too long; the concentration of phosphoric acid is too high, aluminum is dissolved too fast, aluminum phosphate precipitation risks occur, and the wastewater treatment pressure is too high. Therefore, the content of phosphoric acid should be controlled within the range of 5-15 g/L (85% phosphoric acid);

nitric acid: nitric acid is a basic component for removing oil in an acidic way, and has the functions of providing an acidity value, dissolving a natural oxidation film and dissolving aluminum. The nitric acid is mainly used for maintaining a certain free acidity of the deoiling liquid, keeping the solution stable, promoting the surface of the aluminum to be passivated, removing ash and enabling the surface of the aluminum to present an active area which is beneficial to the film formation of chromate. The content of nitric acid is too low, the passivation capability is weakened, the amount of aluminum dissolved is increased, and the risk of generating aluminum phosphate and aluminum fluoride exists; the concentration of nitric acid is too high, ammonia nitrogen in the wastewater is increased, and the environmental protection treatment pressure is too large. Therefore, the content of the nitric acid is controlled within the range of 20-30 g/L (68% nitric acid);

hydrochloric acid: hydrochloric acid is a basic component for acidic oil removal, and has the functions of providing an acidity value, dissolving a natural oxidation film and dissolving aluminum. The sulfuric acid is mainly used for maintaining a certain free acidity of the deoiling liquid, keeping the solution stable, promoting the dissolution of aluminum and enabling the aluminum surface to present an active area which is beneficial to the film formation of chromate. The hydrochloric acid content is too low, the oil removing time is too long, and the oil removing effect is weakened; the hydrochloric acid concentration is too high, the aluminum dissolution is too fast, the aluminum surface is gray and dark, and the wastewater treatment pressure is too high. Therefore, the content of hydrochloric acid should be controlled within the range of 5-10 g/L (30% hydrochloric acid);

hydrofluoric acid (sodium fluoride, ammonium bifluoride): hydrofluoric acid is an activating agent of the degreasing liquid, quickly dissolves a natural oxide film and aluminum, and is an indispensable promoting component of the degreasing liquid. Hydrofluoric acid is mainly used to maintain a certain free acidity of the solution, keep the solution stable, promote the dissolution of aluminum and complex Al³⁺The aluminum surface is made to exhibit an active zone which is favorable for chromate film formation. F^-And NO3^-Has a certain proportion relation with the content of F^-/NO₃ ^-The optimal ratio range of (A) is 0.25-0.35, and the ratio seriously influences the oil removal effect and the stability of the bath solution. F^-When the content is too low, the oil removal reaction time is longer, and the dissolution on the surface of aluminum is uneven; f^-When the content is too high, the aluminum alloy reacts with aluminum to generate hydrogen violently, the glossiness of the surface of the aluminum profile is reduced, the aluminum dissolving amount is too large, and aluminum fluoride precipitation is easy to occur. Therefore, the content of hydrofluoric acid should be strictly controlled within the range of 5-15 g/L (50% hydrofluoric acid);

surfactant (b): the surfactant is a basic component for acid oil removal, and is used for emulsifying oil stains on the surface of the aluminum material to ensure that the surface is uniform, and the concentration of the surfactant is 0.005-0.010 g/L

Acidity value: the acidity value of the deoiling liquid has obvious influence on the deoiling effect. If the acidity value of the deoiling liquid is low, the dissolution speed of the aluminum alloy is slow, and the deoiling effect is poor; the degreasing liquid has high acidity value, high aluminum alloy dissolving speed and good degreasing effect. Therefore, the acidity value of the deoiling liquid should be strictly controlled within the range of 1.0-1.5 equivalent;

oil removal temperature: the temperature of the degreasing liquid has certain influence on the degreasing effect. When the temperature is lower than 5 ℃, the reaction speed is too slow, and the oil removal effect is weakened; when the temperature is higher than 40 ℃, the film forming speed is too fast, and the aluminum dissolution is too fast. Therefore, the temperature of the degreasing fluid is preferably controlled within the range of 10-30 ℃, and the degreasing fluid can be used at normal temperature under ordinary conditions.

2. Quantitative and qualitative analysis of each component of chromizing tank

In the prior art, the chromizing tank generally contains CrO₃Potassium dichromate K₂Cr₂O₇Sodium fluoride, potassium ferricyanide K₃Fe(CN)₆Sodium silicate Na₂SiO₃Hydrofluoric acid, nitric acid, boric acid, sodium molybdate, a stabilizer (prepared by mixing two organic acids containing carboxyl and hydroxyl), and the like. The quantitative and qualitative analysis of each component is as follows:

chromic anhydride: chromic anhydride is a basic component of passivation, is an oxidizing agent in the chromizing liquid, and has important influence on the forming speed and appearance quality of the chromizing film. When the content of chromic anhydride is too low, the film forming speed is slow, the film is incomplete, the color is light, and the corrosion resistance is reduced; when the content of chromic anhydride is too high, the reaction speed is too high, the film layer is coarse in crystallization, loose and not compact, easy to pulverize, deep in color and luster, poor in binding force, and the environmental pollution and the waste water treatment cost are increased. Therefore, the content of chromic anhydride is controlled to be 1.5-4.0 g/L;

hydrofluoric acid: hydrofluoric acid is an activator for the chromizing liquid, has a catalytic effect on the film-forming reaction, and is an essential accelerating component for forming a chromized film. Hydrofluoric acid is mainly used to maintain a certain free acidity of the solution, keep the solution stable, promote the dissolution of aluminum and complex Al³⁺The aluminum surface is made to exhibit an active zone which is favorable for chromate film formation. F^-In a certain proportion relation with the content of CrO3, F^-/CrO₃The optimal ratio range of (A) is 0.05-0.15, and the size of the ratio seriously influences the adhesiveness and the corrosion resistance of the chromate conversion film. F^-When the content is too low, the film forming reaction time is longer, the film layer is thinner, the corrosion resistance is poor, and even the film can not be formed; f^-When the content is too high, the aluminum alloy reacts with aluminum to generate hydrogen violently, the glossiness of the surface of the aluminum profile is reduced, a film layer is rough and loose, the adhesive force is reduced, meanwhile, the chromizing liquid is unstable, and chromium-containing sludge is easily formed at the bottom of the tank. Therefore, the content of hydrofluoric acid should be strictly controlledIn the range of 0.5-1.0 g/L;

nitric acid: nitric acid is a basic component of the chromizing liquid and has the functions of providing an acidity value, dissolving chromized ash, dissolving sludge at the bottom of a chromizing tank, preventing crystallization and oxidizing trivalent chromium. The nitric acid is mainly used for maintaining a certain free acidity of the chromizing liquid, keeping the solution stable, promoting the surface of aluminum to be passivated and ash to make the surface of aluminum present an active area which is beneficial to the film formation of chromate. The content of nitric acid is too low, the dissolving capacity is weakened, the amount of aluminum dissolved is increased, and the risk of generating chromated sludge at the bottom of the tank is generated; the concentration of nitric acid is too high, the chromizing film is too thin, ammonia nitrogen in the wastewater is increased, and the environmental protection treatment pressure is too large. Therefore, the content of the nitric acid is controlled to be within the range of 5-10 g/L (the nitric acid refers to nitric acid with the weight fraction of 68%);

boric acid: boric acid mainly plays a buffering role in the chromizing liquid, so that the pH value of the solution is kept relatively stable. The boric acid can continuously ionize hydrogen ions to supplement the hydrogen ions consumed in the production process, so that the hydrogen ion concentration of the solution is prevented from being sharply reduced, and the solution is prevented from being unstable due to the obvious increase of the pH value of the solution. Meanwhile, boric acid can control the oxidation reaction speed of the solution and improve the appearance of the film layer, so that the conversion film is uniform and compact. The boric acid content is too low, the buffering effect is weak, and the effect is not obvious; the boric acid content is too high, so that the film forming reaction speed is slowed down, and the color of a film layer is lightened. The dosage of the boric acid is preferably 0.3-1.2 g/L;

sodium molybdate: sodium molybdate is an accelerant for forming a chromizing film, has strong oxidizing property in an acid chromate medium, plays a role in accelerating depolarization of a cathode, and improves the current density of the micro battery, thereby accelerating the film forming speed, reducing the reaction temperature and shortening the film forming time. In addition, sodium molybdate also participates in film forming reaction to generate aluminum molybdate compound to be deposited on the chromate film, so that the incompactness of the chromate film is compensated, and the corrosion resistance of the chromate conversion film is improved. The content of sodium molybdate is low, the film forming speed is slow, the film is thin, and the color is light; high content of sodium molybdate, fast film forming speed, deep color, good corrosion resistance, but increased cost. The content of sodium molybdate is controlled within the range of 0.2-0.8 g/L;

a stabilizer: the stabilizer is prepared from two organic acids containing carboxyl and hydroxylIs mainly used for mixing with excessive Al³⁺Form stable chelate, control and reduce the film forming reaction speed, mask the interference of impurities in the solution and improve the stability of the chromizing liquid. Meanwhile, the corrosion inhibitor can be adsorbed on the surface of an aluminum matrix through physical and chemical effects, and has higher coverage due to the synergistic effect of the physical and chemical effects, so that the corrosion inhibition effect is improved, and Al is effectively inhibited³⁺The generation of sediment is reduced, and the surface of the workpiece is prevented from being coated with ash. The content of the stabilizer is too low, the chelating effect is poor, and the effect of inhibiting sediments cannot be achieved; too high a content of the stabilizer may prevent the chromizing film-forming reaction from proceeding normally. The content of the stabilizer is generally 0.7-2.5 g/L;

chromizing pH value: the pH value of the chromizing liquid has a remarkable influence on the formation and quality of the chromizing film. If the pH value of the solution is lower, the dissolving speed of the metal is increased, the film forming reaction is accelerated, the film layer is rough and loose, and the adhesive force is poor; if the pH value of the solution is higher, the dissolution speed of the metal is reduced, the film forming reaction is slowed down, the film layer is thinner, the color is light, and the corrosion resistance is poor. Therefore, the pH value of the chromizing liquid is strictly controlled within the range of 1.8-2.2, and nitric acid or ammonia water is generally adopted to adjust the pH value of the chromizing liquid;

chromizing temperature: the solution temperature has a large influence on the performance of the chromized film. When the temperature is lower than 5 ℃, the reaction speed is too slow, the film layer is thin, the color is light, even the film cannot be formed, and the corrosion resistance is poor; when the temperature is higher than 40 ℃, the film forming speed is too fast, the film is rough and loose, powder is easy to generate, and the adhesive force is poor. Therefore, the temperature of the solution is preferably controlled within the range of 20-35 ℃, and the solution can be generally controlled at normal temperature.

And secondly, carrying out quantitative experiments on oil removal and chromizing stability and compatible reagents.

1. Selection scheme for stabilizing oil removing liquid medicament

In the prior art, the acidic degreasing liquid is generally prepared from sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid, hydrofluoric acid, sodium fluoride, ammonium bifluoride and a proper amount of surfactant. The medicament component selection scheme is as follows:

selecting the components which are difficult to form dust on the surface of the aluminum material and difficult to generate crystal precipitates: sulfuric acid, nitric acid, hydrochloric acid, hydrofluoric acid and a proper amount of surfactant;

removing components which are easy to form ash on the surface of the aluminum material and easy to generate crystallized precipitates: ammonium fluoride, ammonium bifluoride, sodium fluoride and phosphoric acid. When the acidity value of the bath solution is not enough, acid corrosion ash is easily generated on the surface of the aluminum material, and the oil removal effect is influenced; sodium ions in the sodium fluoride are easy to generate sodium fluoroaluminate precipitate, and the tank liquor needs to be cleaned; phosphoric acid is easy to generate aluminum phosphate precipitate, and tank liquor needs to be cleaned, so from the viewpoint of oil removal effect and tank liquor stability, ammonium fluoride, ammonium bifluoride, sodium fluoride and phosphoric acid are removed from oil removal components.

2. Option for stabilization of chromizing liquid medicament

In the prior art, chromic anhydride (CrO) is generally selected as the chromizing liquid₃) Potassium dichromate (K)₂Cr₂O₇) Sodium fluoride, potassium ferricyanide [ K ]₃Fe(CN)₆]Sodium silicate (Na)₂SiO₃) Hydrofluoric acid, nitric acid, boric acid, sodium molybdate and a stabilizer (prepared and combined by two organic acids containing carboxyl and hydroxyl), wherein the selection scheme of the components of the medicament is as follows:

a. selecting the components which are difficult to form dust on the surface of the aluminum material and difficult to generate crystal precipitates: chromic anhydride, hydrofluoric acid, nitric acid and boric acid;

b. removing components which are easy to form ash on the surface of the aluminum material and easy to generate crystallized precipitates: potassium dichromate, sodium fluoride, potassium ferricyanide, sodium silicate and sodium molybdate. The components contain sodium and potassium, sodium fluoroaluminate and potassium fluoroaluminate precipitates are easy to generate, and a tank needs to be cleaned; meanwhile, the products can make the bath solution unclear, and the chromizing film is easy to be coated with ash, which affects the chromizing quality and should be removed from the chromizing solution components;

c. eliminating unstable and easily oxidized and decomposed components in the chromizing liquid: the stabilizer is prepared and combined by two organic acids containing carboxyl and hydroxyl, which are reducing agent components, are easy to be decomposed by an oxidant in bath solution containing chromic anhydride, hydrofluoric acid, nitric acid and boric acid, influence the stability of the chromating solution and are removed from the chromating solution components.

According to the selection result, the oil removing groove selects sulfuric acid, nitric acid, hydrochloric acid, hydrofluoric acid and a proper amount of surfactant; chromic acid anhydride, hydrofluoric acid, nitric acid and boric acid are selected as the chromizing tank. These options ensure long-term stability of bath solution without cleaning the bath during degreasing and chromizing.

However, in practical production, after the aluminum material is deoiled, the aluminum material is subjected to two flowing water washes and enters a chromizing tank for chromizing, and partial deoiling liquid may be brought into the chromizing tank to influence the chromizing effect and the stability of the chromizing liquid, even produce precipitates. Therefore, for complete stabilization of the bath solution, a drug compatible design must be made.

3. Selection of components of deoiling liquid compatible with chromizing liquid medicament

The oil removing tank can select stable components of oil removing liquid, such as sulfuric acid, nitric acid, hydrochloric acid, hydrofluoric acid and a proper amount of surfactant; the components can bring the aluminum material into the chromizing tank after passing through the oil removing tank and the two flowing rinsing tanks, influence the chromizing capacity and the stability of the chromizing tank, and need to be compatible in design to ensure the long-term stable work of the chromizing tank. The experiments were as follows:

a. the additive amount of the deoiling liquid is 30g/L of 68 wt% nitric acid, 10g/L of concentrated sulfuric acid (weight fraction is 98%), 5g/L of hydrochloric acid solution (weight fraction is 30%), 10g/L of 50 wt% hydrofluoric acid and 0.001g/L of TX-10 phosphate; the addition amount of the chromizing liquid is 3g/L of chromic anhydride, 0.7g/L of 50 wt% hydrofluoric acid, 8.5g/L of 68 wt% nitric acid and 0.8g/L of boric acid. Soaking the aluminum material in degreasing liquid for degreasing for 3 minutes, carrying out two times of 30-second flowing water washing, carrying out chromizing for 3 minutes by using a chromizing liquid, carrying out two times of 30-second flowing water washing, airing, observing the surface color of the aluminum material, and recording the number of an original plate to be 0 #.

The chromizing liquid contains nitric acid and hydrofluoric acid, so that the nitric acid and the hydrofluoric acid in the deoiling liquid can be brought into the chromizing liquid and are completely compatible; but sulfuric acid, hydrochloric acid and TX-10 chromizing liquid in the deoiling liquid do not exist, and a compatible experiment is required to be carried out to observe the influence of the sulfuric acid, the hydrochloric acid and the TX-10 on the working capacity and the stability of the chromizing liquid.

b. Taking out 5 parts of the chromizing liquid in experiment a, and respectively adding 1.0g/L, 2.0g/L, 3.0g/L, 4.0g/L and 5.0g/L of concentrated sulfuric acid (98%); soaking the aluminum material in a degreasing liquid for degreasing for 3 minutes, carrying out two 30-second flowing water washing, carrying out chromizing on the aluminum material by using the 5 parts of chromizing liquid for 3 minutes, carrying out two 30-second flowing water washing, airing, observing the surface color of the aluminum material, recording the numbers 1#, 2#, 3#, 4#, and 5# of the chromizing plates, comparing the appearance colors of the chromizing plates from 0# to 5#, finding that the chromizing plates from 1# to 5# fade, and the chromizing capability is seriously affected by sulfuric acid, wherein even if the concentration of the sulfuric acid is as low as 1g/L, the chromizing film is hardly colored, so that the sulfuric acid in the degreasing liquid is incompatible with the chromizing liquid, and the sulfuric acid component in a degreasing tank is required to be.

c. 5 parts of the chromizing liquid in experiment a are taken out, and 1.0g/L, 2.0g/L, 3.0g/L, 4.0g/L and 5.0g/L of hydrochloric acid solution (30%) are respectively added; soaking the aluminum material in deoiling liquid for 3 minutes, carrying out two 30-second flowing water washing, carrying out chromizing on the aluminum material by using the 5 parts of chromizing liquid for 3 minutes, carrying out 30-second flowing water washing, airing, observing the surface color of the aluminum material, recording the numbers 6#, 7#, 8#, 9# and 10# of the chromizing plates, comparing the appearance colors of the chromizing plates 0 and 5# to 10# of the aluminum material, finding that the 6# to 10# chromizing plates fade, and the chromizing capability is seriously influenced by hydrochloric acid, wherein even if the concentration of the hydrochloric acid is as low as 1g/L, the chromizing film is hardly colored, so that the hydrochloric acid of the deoiling liquid is incompatible with the chromizing liquid, and the components of the hydrochloric acid are required to be removed.

d. Taking out 5 parts of the chromizing liquid in experiment a, and respectively adding TX-100.0001 g/L, 0.0002g/L, 0.0003g/L, 0.0004g/L and 0.0005 g/L; removing oil from the aluminum material in a degreasing liquid for 3 minutes, carrying out two 30-second flowing water washing on the aluminum material, carrying out chromizing on the aluminum material by using the 5 parts of chromizing liquid for 3 minutes, carrying out two 30-second flowing water washing on the aluminum material, airing, observing the surface color of the aluminum material, recording the numbers 11#, 12#, 13#, 14# and 15# of the chromizing plates, and comparing the appearance colors of the chromizing plates 0 and 10-15 #, finding that the chromizing plates 11# to 15# do not fade; after powder spraying and curing, water boiling, cupping and impact detection are carried out, and the result shows that the chromized film has insufficient adhesive force and is unqualified in detection. Therefore, the TX-10 seriously influences the adhesive force of the chromizing film, and even if the concentration is as low as 0.0001g/L, the adhesive force of the chromizing film is not qualified, so that the TX-10 in the deoiling liquid is incompatible with the chromizing liquid, and the surfactant component is removed.

According to the results of experiments a to d, the degreasing fluid can be selected from the components of a chromizing fluid compatible medicament: nitric acid, hydrofluoric acid; other components affect either the stability of the chromizing liquid or the quality of the chromizing film.

4. Selection of components of chromizing liquid compatible with degreasing liquid medicament

e. The addition amount of the deoiling liquid is 40g/L of 68 wt% nitric acid and 10g/L of 50 wt% hydrofluoric acid; the addition amount of the chromizing liquid is 3g/L of chromic anhydride, 0.7g/L of 50 wt% hydrofluoric acid, 8.5g/L of 68 wt% nitric acid and 0.8g/L of boric acid. Removing oil from the aluminum material in deoiling liquid for 3 minutes, performing two times of 30-second flowing water washing, performing chromizing by using a chromizing liquid for 3 minutes, performing two times of 30-second flowing water washing, then drying, observing the surface color of the aluminum material, and recording the number 00# of an original plate.

In order to save water, the aluminum material is cleaned after being chromized, the cleaning water can supplement water for the deoiling liquid, and the cleaning water inevitably contains the chromizing liquid component, so that the deoiling effect is not influenced when the chromizing liquid is compatible with the deoiling liquid. The degreasing liquid contains nitric acid and hydrofluoric acid, so that the nitric acid and the hydrofluoric acid of the chromizing liquid are completely compatible with the degreasing liquid; but chromic anhydride and boric acid deoiling liquid of the chromizing liquid do not exist, and a compatible experiment is needed to observe the influence of the chromic anhydride and the boric acid on the working capacity and stability of the deoiling liquid.

f. 5 parts of the deoiling liquid in experiment e are taken out and CrO is added respectively₃0.2g/L, 0.4g/L, 0.6g/L, 0.8g/L, 1.0 g/L; removing oil from the aluminum material by the 5 parts of deoiling liquid for 3 minutes, carrying out two 30-second flowing water washing, carrying out chromizing by a chromizing liquid for 3 minutes, carrying out two 30-second flowing water washing, airing, observing the surface color of the aluminum material, recording the numbers 16#, 17#, 18#, 19#, and 20# of the chromizing plate, and comparing the appearance colors of the chromizing plate 00# and the chromizing plate 16# to 20# to find that the 16# to 20# of the chromizing plate does not fade; after powder spraying and curing, water boiling, cupping and impact detection are carried out, and the adhesion of the chromizing film is not affected and the detection is qualified. Therefore, CrO is added into the deoiling liquid₃Does not affect the adhesion of the chromized film, CrO₃Is compatible with deoiling liquid.

g. Taking out 5 parts of deoiling liquid in experiment e, and respectively adding 0.1g/L, 0.2g/L, 0.3g/L, 0.4g/L and 0.5g/L of boric acid; removing oil from the 5 parts of deoiling liquid for 3 minutes, carrying out two times of 30-second flowing water washing on the aluminum material, carrying out chromizing on the aluminum material for 3 minutes by using a chromizing liquid, carrying out two times of 30-second flowing water washing on the aluminum material, airing, observing the surface color of the aluminum material, recording the numbers 21#, 22#, 23#, 24#, and 25# of the chromizing plate, and comparing the appearance colors of the chromizing plate 00# and the chromizing plate 21-25 #, wherein the chromizing plate 21-25 # is not faded; after powder spraying and curing, water boiling, cupping and impact detection are carried out, and the adhesion of the chromizing film is not affected and the detection is qualified. Therefore, the boric acid is added into the degreasing liquid, the adhesive force of the chromating film is not influenced, and the boric acid is compatible with the degreasing liquid. However, after the boric acid is added, the oil removing capability is obviously weakened, the reaction speed is reduced, the appearance effect is poor after the aluminum material is subjected to oil removing, and the boric acid can be removed, so that the chromizing liquid is completely compatible with the deoiling liquid.

According to experiments a-g, the compatible selection of the chemical components of the deoiling liquid and the chromizing liquid is as follows:

the deoiling liquid is nitric acid and hydrofluoric acid, and the chromizing liquid is chromic anhydride, nitric acid and hydrofluoric acid. Therefore, national standard detection of various abilities of the chromized film after medicament compatibility is carried out:

h. the addition amount of the deoiling liquid is 40g/L of 68 wt% nitric acid and 10g/L of 50 wt% hydrofluoric acid; the addition amount of chromic anhydride CrO in the chromizing liquid₃3g/L, 50 wt% hydrofluoric acid 0.8g/L, and 68 wt% nitric acid 7 g/L. Removing oil from the aluminum material in deoiling liquid for 3 minutes, performing two times of 30-second flowing water washing, performing chromizing by using a chromizing liquid for 3 minutes, performing two times of 30-second flowing water washing, then drying, observing the surface color of the aluminum material, and recording the number 001# of an original plate.

Observing the appearance color of the chromizing plate 001#, then spraying powder, curing, performing water boiling, cupping and impact detection, and detecting the adhesion of the chromizing film, wherein the result shows that all detection indexes are all qualified.

Although the degreasing liquid only contains nitric acid and hydrofluoric acid, the risk of generating aluminum fluoride precipitate exists, and an appropriate nitric acid/hydrofluoric acid interval needs to be determined, so that the generation of aluminum fluoride is hindered by utilizing the dissolving capacity of nitric acid. The experiments were as follows:

i. the addition amount of the deoiling liquid is 40g/L of 68 wt% nitric acid and 10g/L of 50 wt% hydrofluoric acid; the addition amount of chromic anhydride CrO in the chromizing liquid₃3g/L, 50 wt% hydrofluoric acid 0.7g/L, and 68 wt% nitric acid 8.5 g/L. The aluminum material is degreased for 3 minutes in deoiling liquid, and is respectively subjected to two 30-second flowing water washing, chromizing for 3 minutes in chromizing liquid, and then is respectively subjected to two 30-second flowing water washing. Controlling the acidity value of the degreasing liquid to be 1.0-1.5 equivalent, selecting the weight ratio of 68 wt% nitric acid/50 wt% hydrofluoric acid as the additive liquid to be 1-3: 1, repeating the experiment. Although the chromized film passed the national standard, 68 wt% nitric acid/50 wt% hydrofluoric acid weightWhen the ratio is low, the reaction is too fast, the dissolved aluminum is too much, and precipitates are separated out in an oil removing groove; the weight ratio of 68 wt% nitric acid to 50 wt% hydrofluoric acid is increased, and the precipitate disappears; when the weight ratio of 68 wt% nitric acid to 50 wt% hydrofluoric acid is too high, the reaction is slowed down and the oil removal effect is not good. 1 the appropriate addition material for the oil removing liquid has a weight ratio of nitric acid concentration (68%)/50 wt% hydrofluoric acid of 1.5-2.5.

As with the degreasing fluid, although the chromizing fluid only contains chromic anhydride, nitric acid and hydrofluoric acid, there is still a risk of generating aluminum fluoride and chromium fluoroaluminate precipitates, and it is necessary to determine an appropriate nitric acid/hydrofluoric acid interval to utilize the dissolving capacity of nitric acid to hinder the generation of the aluminum fluoride and chromium fluoroaluminate precipitates:

j. the addition amount of the deoiling liquid is 40g/L of 68 wt% nitric acid and 10g/L of 50 wt% hydrofluoric acid; the addition amount of the chromizing liquid is 3g/L of chromic anhydride, 0.7g/L of 50 wt% hydrofluoric acid and 8.5g/L of 68 wt% nitric acid. The aluminum material is degreased in an oil removing groove for 3 minutes, and is subjected to two times of 30-second flowing water washing, chromizing by a chromizing liquid for 3 minutes, and then two times of 30-second flowing water washing. The acidity value of the deoiling liquid is controlled to be 1.0-1.5 equivalent, the concentration of chromic anhydride in the chromizing liquid is controlled to be 2.5-3.5 g/L, and the weight ratio of 68 wt% nitric acid to 50 wt% hydrofluoric acid added into the chromizing liquid is 5-15: 1, repeating the experiment. Although the chromating film is qualified according to national standard detection, when the weight ratio of the 68 wt% nitric acid to the 50 wt% hydrofluoric acid is low, chromating is too fast, aluminum fluoride or chromium fluoroaluminate precipitates in a chromating tank, the weight ratio of the 68 wt% nitric acid to the 50 wt% hydrofluoric acid is increased, and the precipitates disappear; when the weight ratio of the 68 wt% nitric acid to the 50 wt% hydrofluoric acid is too high, the color of the chromized film becomes light, the weight of the film becomes light, and the national standard detection of the chromized film is unqualified. The proper weight ratio of the two acids of the additive of the chromizing liquid is 68 wt% nitric acid/50 wt% hydrofluoric acid and is 8-12.

Third, the stability and compatibility of the degreasing liquid and the chromizing liquid medicament are designed and the experimental result is analyzed

According to the experiments a to j and the detection results, the following analysis can be performed:

1. the degreasing liquid is composed of nitric acid and hydrofluoric acid, and the bath liquid is stable and compatible with the chromizing liquid. The weight ratio of 68 wt% nitric acid to 50 wt% hydrofluoric acid in the additive of the degreasing liquid is controlled to be 1.5-2.5, so that the degreasing liquid can be kept to operate stably for a long time, and aluminum fluoride precipitates are not generated.

2. The components of the chromizing liquid are selected from chromic anhydride, nitric acid and hydrofluoric acid, and the bath liquid is stable and compatible with deoiling liquid. The weight ratio of 68 wt% nitric acid to 50 wt% hydrofluoric acid in the additive of the chromizing liquid is controlled to be 8-12, so that the long-term stable operation of the degreasing liquid can be maintained, and aluminum fluoride and chromium fluoroaluminate precipitates are not generated.

The technical solution of the present invention is further described below with reference to the accompanying drawings and the detailed description.

The invention provides a method for stabilizing and compatible degreasing and chromizing agents for slag reduction in aluminum industry, which comprises a degreasing tank and a chromizing tank, wherein degreasing liquid is arranged in the degreasing tank, the chromizing tank is internally provided with chromizing liquid, the degreasing liquid is a solution of nitric acid and hydrofluoric acid, the chromizing liquid is a solution of chromic anhydride, hydrofluoric acid and nitric acid, the degreasing liquid and the chromizing liquid are compatible, and the degreasing tank and the chromizing tank do not generate precipitates in the long-term operation process.

The degreasing liquid adopts a solution of nitric acid and hydrofluoric acid, and stable components are selected to ensure that the degreasing liquid does not generate precipitation after long-term operation, and the surface of the aluminum material is not easy to be coated with ash and is not easy to generate crystallized precipitates.

The chromizing liquid adopts a solution of chromic anhydride, hydrofluoric acid and nitric acid, and stable components are selected to ensure that the chromizing liquid does not generate precipitate after long-term operation, and the surface of the aluminum material is not easy to hang ash and generate crystallized precipitates. And the risk of cleaning the tank is avoided by avoiding the generation of sodium fluoroaluminate and potassium fluoroaluminate precipitates and the decomposition of organic matters.

The mutual compatibility of the deoiling liquid and the chromizing liquid means that: when part of deoiling liquid in the deoiling tank is brought into the chromizing tank, the operation of the chromizing tank is not influenced, and the chromizing capacity of the chromizing liquid is not influenced; when part of chromizing liquid in the chromizing tank is brought into the oil removing tank, the operation of the oil removing tank is not influenced, and the oil removing capability of the oil removing liquid is not influenced.

Careful selection of the components ensures that the long-term operation of the oil removal bath does not affect the stability of the chromizing bath. The deoiling liquid is compatible with the chromizing liquid, when the deoiling liquid is inevitably carried into the chromizing liquid by the aluminum material, the operation of the chromizing liquid and the chromizing effect of the aluminum material are not influenced, and no precipitation and crystallization exist in the chromizing tank. The stability component that ensures the chromizing cell is compatible with the oil removal cell is carefully selected. The invention firstly focuses on the compatibility of the selected components to the deoiling liquid on the premise of selecting the components of the chromizing liquid, stabilizing the tank liquid and not precipitating and crystallizing.

Furthermore, in the long-term operation process of the oil removing groove, the added agents are solutions of nitric acid and hydrofluoric acid, and 68 wt% of nitric acid/50 wt% of hydrofluoric acid in the added agents of the oil removing groove is 1.5-2.5. The ratio of the two acids of the oil removal tank additive is carefully selected. The risk of precipitation generated in the oil removing groove is thoroughly eliminated by controlling the weight ratio of 68 wt% nitric acid to 50 wt% hydrofluoric acid in the oil removing liquid to be 1.5-2.5.

Further, the control indexes of the chromizing liquid are as follows: chromic anhydride CrO32.5-3.5 g/L, 50 wt% hydrofluoric acid 0.4-0.8 g/L, 68 wt% nitric acid 5-7 g/L, pH 1.8.8-2.2. The addition amount of the chromic anhydride is controlled, so that the film layer has enough thickness and enough compactness. The film forming speed is controlled within a reasonable range by controlling the pH value of the chromizing liquid, and the film quality is improved.

Furthermore, in the long-term operation process of the chromizing liquid, the added medicament is a solution of nitric acid and hydrofluoric acid, and the added medicament of the chromizing liquid is 68 wt% of nitric acid/50 wt% of hydrofluoric acid which is 8-12. The ratio of the two acids of the chromizing vessel charge was carefully selected. The risk of precipitation generated in the chemical tank is thoroughly eliminated by controlling the weight ratio of 68 wt% nitric acid to 50 wt% hydrofluoric acid in the additive in the chromizing liquid to be 8-12.

The invention is further illustrated by the following specific examples.

The components of the degreasing solution and the chromizing solution in examples 1 to 5 are shown in the following tables.

In examples 1 to 5, the acidity values of the degreasing solutions were all within a range of 1.0 to 1.5, and the pH values of the chromating solutions were all within a range of 1.8 to 2.2. When the oil removing tank runs for a long time, the weight ratio of 68 wt% nitric acid to 50 wt% hydrofluoric acid in the additive agent of the oil removing liquid is 1.5-2.5; when the chromizing liquid runs for a long time, the weight ratio of 68 wt% nitric acid to 50 wt% hydrofluoric acid in the additive agent of the chromizing liquid is 8-12.

In the embodiments 1 to 5, the aluminum material treatment processes are as follows: the aluminum material is degreased for 3 minutes in the degreasing liquid of the degreasing tank, is subjected to 30-second flowing water washing in two washing tanks respectively, is subjected to chromizing in the chromizing liquid of the chromizing tank for 3 minutes, and is subjected to 30-second flowing water washing in two washing tanks respectively. And (5) drying the aluminum material, and detecting. Observing the appearance color of the aluminum product after chromizing, then spraying powder, curing, performing water boiling, cupping and impact detection, and detecting the adhesion of the chromized film, wherein the result shows that all detection indexes are all qualified.

In examples 1 to 5, the oil removing tank and the chromizing tank were operated for 45 days without precipitation and crystallization.

The technical principle of the present invention is described above in connection with specific embodiments. The description is made for the purpose of illustrating the principles of the invention and should not be construed in any way as limiting the scope of the invention. Based on the explanations herein, those skilled in the art will be able to conceive of other embodiments of the present invention without inventive effort, which would fall within the scope of the present invention.

Claims

1. A method for stabilizing and compatible degreasing and chromizing agents for slag reduction in aluminum industry is characterized by comprising an oil removing tank and a chromizing tank, wherein degreasing liquid is arranged in the oil removing tank, the chromizing tank is internally provided with chromizing liquid, the degreasing liquid is a solution of nitric acid and hydrofluoric acid, the chromizing liquid is a solution of chromic anhydride, hydrofluoric acid and nitric acid, the degreasing liquid and the chromizing liquid are compatible, and the oil removing tank and the chromizing tank do not generate precipitates in the long-term operation process;

the control indexes of the deoiling liquid are as follows: 68 wt% nitric acid 40-60 g/L, 50 wt% hydrofluoric acid 5-15 g/L, acid concentration 1.0-1.5 equivalent;

in the long-term operation process of the oil removing groove, the added medicaments are solutions of nitric acid and hydrofluoric acid, and 68 wt% of nitric acid/50 wt% of hydrofluoric acid in the added medicaments in the oil removing groove is 1.5-2.5;

the control indexes of the chromizing liquid are as follows: chromic anhydride CrO32.5-3.5 g/L, 50 wt% hydrofluoric acid 0.4-0.8 g/L, 68 wt% nitric acid 5-7 g/L, pH 1.8.8-2.2;

the mutual compatibility of the deoiling liquid and the chromizing liquid means that:

2. The method of claim 1, wherein the chemical is a solution of nitric acid and hydrofluoric acid during long-term operation of the chromizing liquid, and the chemical added to the chromizing tank is 68 wt% nitric acid/50 wt% hydrofluoric acid-8-12.