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          Acid washing passivation formula for stainless steel castings

          From:Changzhou HongHuiHe Machinery Manufacturing Co., Ltd.  Add Time:2018/7/20 13:03:30

          Pickling and passivation of stainless steel castings

          1, subject content

          This regulation specifies the requirements, methods and matters needing attention for cleaning, pickling and passivation of stainless steel parts.

          2. Scope of application

          This regulation applies to pickling and passivation of chromium and nickel austenitic stainless steel parts.

          3, pickling and passivation process

          Vibration grinding - to dust (flushed with cold water) - to remove oil (sand or shot by craft) - rinse (with cold water or hot water) - acid washing (2-3 times) - Vibration Lapping - flushing (cold water or hot water) inspection - passivation - flushing (cold water or hot water rinse) neutralization - test.

          4, pretreatment before pickling and passivation

          4.1 after finishing the finished stainless steel parts according to the requirements of the finishing process card, only after acid inspection and passivation pretreatment can be carried out for qualified inspection items.

          4.2 the weld and its side welding slag and splash are cleaned up. The surface of the product should be sandblasting or shot (see the product process card) to remove the dirt and other stains.

          4.3 remove the foreign objects on both sides of the weld, clean up with stainless steel wire brush, stainless steel shovel or grinding wheel. Clean water with clean water (the content of chlorine ion in water is not more than 25mg/l).

          5, acid washing and passivation solution formula

          Acid washing solution formula / mass fraction (%)

          Formulation hydrochloric acid, hydrofluoric acid water inhibitor, mist inhibitor, acidizing time, temperature

          2010 - 700.15 - 10-20min 40 C

          Passivation solution formula / mass fraction (%)

          Formula, nitric acid, hydrofluoric acid, sodium bichromate, water temperature, treatment time, application area

          105 - 8540 C austenitic stainless steel 15-30min

          (1) the corrosion inhibitor is orrotopin;

          2. The mist suppressant is urea, which inhibits the volatilization of acid mist.

          (3) the iron content in the passivation solution is less than equal to 40mg/L.

          6, pickling and passivation operation

          6.1 only parts that have been pre processed can be pickled and passivated.

          6.2 acid pickling is mainly used for overall treatment of small unprocessed parts, and immersion or spray method can be used. When the solution temperature is 21-60 degrees, check every 10 minutes until the uniform white etching is achieved.

          6.3 passivation solution is mainly suitable for the whole treatment of small containers or parts. It is possible to use immersion or spray brush. When the temperature of the solution is at 48-60, it is checked once every 8 minutes, and when the solution is at 21-47, it is checked every 20 minutes until a uniform passivation film is formed on the surface.

          6.4 pickling passivation parts must be rinsed with clean water, and finally test any part of the wash with acid litmus test paper to make the pH between 6.5-7.5, dry or dry with compressed air.

          6.5 containers and parts are pickled and passivated after being pickled and removed.

          7, key points of pickling and passivation

          7.1 no obvious corrosion marks should be observed during pickling.

          7.2 the oxide scale must be thoroughly removed, and the heat affected zone and the hot working surface of the weld must not be oxidized.

          7.3 the spatter slag of the weld must be thoroughly removed.

          On the 7.4 surface, there must be no color uneven markings.

          No carbon steel particles are not adhered to the surface of 7.5 stainless steel

          8. Precautions

          8.1 when mixing the liquid, the water should be put proportionally into the acid proof container, then slowly add acid to the ratio, so as to prevent the acid falling too fast and cause splashing and hurting people.

          8.2 pickling and passivation, the first operation should be done on the local part of the small part or similar material.

          8.3 during the pickling process, operators must be careful and careful to observe in time to prevent excessive surface corrosion.

          8.4 operators must wear acid proof clothing, gloves, masks and eye protectors while operating. Acid pickling in containers must be carried out with qualified gas masks and conducted under special guardianship.

          8.5 the heat treatment requirements are treated by heat treatment card after heat treatment and pickling passivation treatment.

          8.6 the above pickling and passivation formula and operation, concentration, volume ratio, liquid temperature and operating time can be adjusted according to circumstances. The pickling and passivation solution can be used repeatedly, but the proper concentration and volume ratio must be ensured.

          9. The methods for the quality inspection of acid pickling:

          9.1 naked eye examination, check the above 7.1-7.5 requirements.

          9.2 check whether the surface of stainless steel is sticky carbon steel particles, chemical inspection can be used to dissolve 8 grams of copper sulphate in 500 ml water, add 2-3 ml of sulphuric acid, drop this liquid on the surface of the workpiece, keep wet, such as no steel precipitation in 6 minutes that is considered qualified.

          10. Passivation quality test:

          If the sample is required to be checked with blue point method, the solution is made up of 1 grams of +3 milliliter 65 - 85%HNO3+100 milliliter water of the red blood salt and impregnated with filter paper, attached to the surface, and can be directly painted on the surface of the test, such as the surface passivation film is not finished or the iron ion pollution, that is blue. If there is no blue point in 30 seconds, it is considered to be qualified.

          11. Surface residual acidity test:

          After the surface treatment of stainless steel parts, the surface can not have residual acid, inspection can be dipped in the PH test paper on the surface of the workpiece, the color of the test paper is not constant red that is qualified.

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