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Classification and process control of aluminum chromizing process

Release time:

2023-03-15 11:48

Classification and process control of aluminum chromizing process

 

◆aluminum hexavalent chromium passivation-----Containing hexavalent chromium, hexavalent chromium is a cancer substance, not environmentally friendly, but its passivation film corrosion resistance is quite excellent, the market price is cheap, the traditional chromium process, the formula technology content is not high.

◆aluminum trivalent chromium passivation-----No hexavalent chromium, passivation film in line with EUROHSRequirements, its passivation film corrosion resistance and hexavalent chromium passivation equivalent, the market price is higher, the formula technology content is higher.

Development Trend and Adaptability of Aluminium Chromization

         1,The traditional chromizing process contains toxic hexavalent chromiumCr6 , has been listed as a key monitoring object of the environmental protection department, the use of hexavalent chromium passivation process manufacturers are less and less, has been basically not used.

2. Hexavalent chromium passivation containing hexavalent chromium is not environmentally friendly, and the passivation film formed by traditional hexavalent chromium is not in line with the EU.ROHSEnvironmental requirements. However, the passivation film formed by the trivalent chromium passivation process does not contain hexavalent chromium and is in line with the EU.ROHSEnvironmental protection requirements, so trivalent chromium passivation can be used for aluminum passivation with environmental protection requirements.

3. Aluminum chromium-free passivation has gradually replaced the traditional hexavalent chromium and trivalent chromium passivation for the pretreatment of aluminum coating. However, the corrosion resistance of bare aluminum chromium-free passivation film is not as good as that of hexavalent chromium or trivalent chromium passivation. Therefore, the traditional hexavalent chromium passivation or trivalent chromium passivation is mostly used for aluminum direct corrosion protection. From the perspective of environmental protection, trivalent chromium passivation process is mostly used.

 

 

Aluminum chromate passivation process flow description

Process flow

 

(1) Standard process flow of spray mode

Pre-degreasing -- main degreasing -- Water Wash -- Water Wash -- Live 化 -- Water Wash -- Wash -- Chromium 化 -- Water Wash --Water Wash -- Pure water washing -- moisture drying --

(2) Standard process flow of soaking method

off Grease -- Water Wash -- activation -- Wash --Water Wash --Chromium 化 --Water Wash -- Water Wash -- Pure water washing --

(3) Simple process flow of soaking method

aluminum acid degreasing -- Water Wash -- Water Wash -- Chromium 化 -- Water Wash --

Process Description

 

(1) If there is no pure water device, the pure water washing process can be canceled, which does not have much impact on the quality. Pure water washing can improve the salt spray test time of the coating and make the salt spray test more guaranteed, especially when the chloride ion or calcium and magnesium ion in tap water is high.

(2) The best temperature for moisture drying is60~100℃, the temperature is too high to exceed150℃ or long time baking, the chromium-free passivation film will be damaged, but the chromium-free passivation film can be combined with the paint after coating.250Baking is no problem.

(3) Determination of degreasing time:

Total degreasing time spraying ≥2-3min

Ultrasonic immersion ≥2-3min; swimming immersion ≥4-6min

Pure immersion is ≥8-10min

(4) Water washing time:

The time of each water washing is generally specified as ≥0.5min

The total washing time after each process is ≥1min

(5) Hexavalent chromium passivation process conditions and time provisions:

Process conditions: normal temperature

Process time:

Spraying time ≥1.5-2.5min

Soaking time ≥3-4min

Pure soak ≥5-8min

(6) Trivalent chromium passivation process conditions and time provisions:

Process conditions: normal temperature -45 ℃

Process time:

Spraying time ≥2-3min

Soaking time ≥4-5min

Pure soak ≥8-10min

Effect of temperature on passivation film: Trivalent chromium passivation heating will increase the thickness of the passivation film.

 

 

Process, passivation, time, washing, soaking, environmental protection, traditional, passivation process, process flow

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