1.0 Scope of Application

This process is suitable for the surface treatment of steel products before coating, so that the surface of the product generates a layer of water-insoluble color phosphating film, in order to inhibit the corrosion under the coating film and make the coating and the substrate have a good binding force. Treatment can be soaked or sprayed in two ways, room temperature treatment.

　2.0 materials and reagents

KRB-L100 color phosphating agent

0.1N sodium hydroxide standard solution

Bromophenol blue and phenolphthalein indicator

　3.0 equipment

Phosphating bath: lined with resin glass fiber reinforced plastic anti-corrosion layer

　　4.0 process

General process: rust and oil removal → water washing → water washing → phosphating → (water washing) drying or drying → spraying, etc.

Phosphating: 5-10% of KRB-L100 phosphating solution and 90%-95% of water are used to form color phosphating working solution. The workpiece is immersed therein for 3-10 minutes.

Drying: drying, sun drying or blow drying, pay attention to eliminate excessive water in the workpiece.

Inspection: The appearance of the phosphating film shall be of various colors with a certain degree of color, and there shall be no rust, loose film, viscous residue and a large amount of ash.

Clean the surface of the workpiece: the surface of the workpiece after cleaning should be free of rust, dust particles and sticky residue, and then coated. The time interval between completion of phosphating and painting shall not exceed 16 hours.

　Note:

A, with the color of phosphating film to master the phosphating time and supplementary materials.

B, control the free acidity of phosphating solution is not less than 0.7 points, when the free acidity is insufficient, the phosphating agent should be supplemented, each supplemented KRB-L100 2kg/m3, can improve the free acidity of 0.1 points.

C, in the working process of iron from the workpiece into the solution, so the iron content and total acidity of phosphating solution will gradually increase. At this time, the workpiece film (on the color) speed will slow down, if after phosphating with liquid drying is also prone to hanging ash. When the iron content in the phosphating solution is greater than 1.5g/L, the operation of washing, repassivation and drying after phosphating should be adopted. When the iron content is ≥ 3.0g/L, or the total acidity is ≥ 36 points, it is recommended to replace the phosphating solution partially or completely.

Analysis and detection methods of 5.0 solution

　1. Chemical titration

Total acidity a: suck 5.00ml of phosphating solution with a graduated pipette, inject it into a conical flask, add 50ml of water and 2 drops of phenolphthalein indicator, titrate with 0.1N NaOH (sodium hydroxide) standard solution until stable red is taken as the end point, and record the milliliters v of standard solution consumed by titration.

a = 2V (point)

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 yellow disappears (blue and green under fluorescent lamp; Under iodine tungsten lamp or sunlight, it is blue with purple red) as the end point, and record the milliliter number v of standard solution consumed in titration.

B = V (point)

The free acidity of the working solution prepared according to the concentration of 5% should be greater than the 1.0 point and the PH value should be less than 3.5.

2. Cold plate test piece method

After completely degreasing a small piece of cold plate (you can scrub it thoroughly with a rag in the degreasing tank), immerse it in the phosphating tank for 1 minute and then take it out to the side and place it upright. After the test piece is naturally dried, observe the color of the test piece:

A, the color of the test piece is dark, dark purple and dark green, the phosphating tank concentration is too high.

B, the color of the test piece is blue-purple, then the concentration of the phosphating tank is moderate.

C, the color of the test piece is light, blue and white, the concentration is insufficient, need to add phosphating agent.