1. Scope of application

This process is suitable for the surface treatment of steel products before coating, so that a layer of water-insoluble gray phosphate film is generated on the surface of the product, so as to improve the adhesion of the coating to the metal surface and inhibit the corrosion under the film of the coating. The treatment can be carried out by both immersion and spray methods, both at room temperature.

2. Materials

KRB-L101A phosphating agent A;

KRB-L101B phosphating agent B

neutralizer

3. Reagents

0.1N sodium hydroxide standard solution

0.1N or 0.2N sulfuric acid standard solution

phenolphthalein indicator

Bromophenol blue indicator

sulfamic acid

4. Equipment

Phosphating tank: steel tank or cement tank with lining. The bottom of the groove is provided with 200-300 high brackets.

5. Technological process

Oil removal → water washing → water washing → rust removal → water washing → water washing → surface adjustment → phosphating → water washing → air drying or drying → spraying, etc.

A, build bath:

Calculate the working volume m3 of phosphating tank, first inject 3/4 tank clear water, add 100kg of KRB-L100 phosphating agent, stir evenly, then add 3~4kg/m3 of neutralizing agent and 2kg/m3 of accelerating agent, stir evenly, detect the free acidity of phosphating solution, then carefully adjust the free acidity to about 0.8 with neutralizing agent, and add water to the working liquid level. The initial phosphating solution may not be ideal for some workpieces, and it takes a short "maturity period" to enter the steady state. The curing process is to treat some steel surfaces (about 50~200 m2/m3) with the initial phosphating solution. When the phosphating solution appears light brown and FePO4 alum flower appears, the curing is basically completed. At this time, the appearance and protective ability of the phosphating film will be further improved and the solution will enter a steady state.

B. Control indicators

Total acidity a

25~30 points for dense loading of the workpiece a value can be as high as 45 points, or even higher.

free acidity B

0.3~0.7 points. Under the normal operation of supplementing phosphating agent in a small amount (not more than 8kg/m3 each time), the B value of phosphating solution can automatically establish balance, and generally no acid-base correction is required.

Accelerator c

2-4 points. Since the commercially available fermentation tubes are not standardized, even the fermentation tubes provided by different manufacturers with the same nominal volume of ml vary greatly, so the range of c value should be determined by the user according to their own production situation.

C. Maintenance and adjustment of solution

Each additional phosphating agent 4.5kg/m3 can improve the total acidity of phosphating solution 1 point. At the same time, the KRB-201# accelerator with 10% of phosphating agent can maintain the basic balance of solution components.

D. Phosphating process

Attention should be paid to shaking the workpiece to exclude air bags. For densely loaded workpieces or elongated tubular members, the workpieces shall be raised to the liquid surface and then immersed in the solution several times to renew the solution contacting the workpieces. Phosphating time is generally 10 minutes of immersion, spray 3 minutes, dense loading parts should be appropriate to extend the phosphating time. After phosphating is completed, the solution brought by the workpiece should be fully poured (leached).

E. Inspection

The appearance of the phosphating film should be light gray to dark gray, and a small amount of color film is allowed locally, but it does not affect the uniform coverage of the coating film.

Loose and rough phosphating coating, rust, unphosphated coating and serious ash hanging are not allowed.

6. Solution analysis and detection methods

Total acidity a: suck 10 ml of phosphating solution with a graduated pipette, inject it into a conical flask, add 10 ml of water and 2 drops of phenolphthalein indicator, titrate with 0.1N NaOH standard solution to a stable light red as the end point, and record the milliliter number v of standard solution consumed by titration. Total acidity = V (points).

Free acidity B: suck 10.00ml of phosphating solution with a graduated pipette, inject it into a conical flask, add 50ml of water and 4 drops of bromophenol blue indicator, and titrate with 0.1N NaOH standard solution until blue is slightly greenish (observed under fluorescent lamp) or blue is purplish red (detected under iodine tungsten lamp) as the end point. Note the number of milliliters V of standard solution consumed for titration. Free acidity = V (point).

Accelerator point C: fill the 10.00ml fermentation tube with phosphating solution, add about 1g of solid sodium sulfamate, quickly press and hold the nozzle, turn the fermentation tube upside down, make the solid fall into the bottom of the tube, put the fermentation tube straight, and count the milliliters of gas at the top of the tube after one minute, which is the C value.

Attached: technical indicators and processing conditions: