Study on the process of coating PVF coating on steel drums for new foods (4)

Study on the process of coating PVF coating on steel drums for new foods (4)

Fourth, quality inspection methods

The surface of the qualified coating is flat, free from cracks, dirt and flaws, uniform in color, no crispness, no traces on the nails, no squeaking and peeling with nails at the corners, and further cannot be smashed with a knife. Broken into the mouth.

Polyvinyl fluoride coatings have excellent anti-corrosion properties, and more than 100 chemical products have been tested. Due to the different methods of surface treatment, spraying, baking, etc. used by the barrel manufacturers, the PVF coating film has an effect. Therefore, we believe that it is necessary to carry out the dressing test before and during the pre-installation of each new product, and strive to eliminate the hidden dangers of product quality in the factory.

1. Anti-corrosion coating should also be checked by pinhole to avoid the anti-corrosion effect due to the presence of pinholes. The pinhole test method is as follows:

a, 5% copper sulfate solution is immersed at room temperature for more than 24 hours, and copper is precipitated on the surface, indicating that there is pinhole at the place.

b. 1000 volt hand-swing megohmmeter, one pole is in contact with the workpiece metal, and the brush with one pole connected to the salt water moves on the surface of the coating. When the pointer jumps, it indicates that there is a pinhole in the location. It can also be replaced by a 1.5 volt dry cell with a sensitive galvanometer or microampere meter.

c, pinhole detection equipment, can be directly purchased from the market, such as electric spark pinhole detection equipment.

2. Adhesion test (cross-cut method) Six parallel scratches with a length of 10 to 20 cm and a pitch of 1 mm are cut on the paint film, and then rotated 90°, and cut into squares by the same method. The adhesion requirement of PVF coatings is above Grade I. For details, please refer to the national standard GB325-91.

Five, the treatment of common defects

1. Common quality problems and treatment methods: (see table below)

Common defects and improvement methods

unpleasant sight

cause

Improve methods

Hemp, wavy surface

(1) The airflow of the spray gun is too urgent

(2) The spray gun is too close

(3) Spraying too thick at one time

(1) Reduce the air pressure

(2) Pulling the distance, the muzzle keeps moving

(3) Spray thin

Honeycomb small round pit

(4) The primer is decomposed or not dried

(5) Solvent evaporation

(4) Switch to PVF coating

(5) Do not use low-boiling solvent, dilute with dimethyl ester

Coking

(6) Decomposition caused by excessive temperature

(7) overheated

(8) Decomposition caused by old patent leather or original coke

(6) Properly lower the furnace temperature for easy control

(7) Released in time

(8) thoroughly remove the net beforehand, and the coke on the hanger is also cleaned.

Membrane soft

(9) Residual solvent

(10) Spraying over thick evaporation difficulties

(9) Extend the baking time

(10) Prevent local multi-spray and sag

Stripping

(11) Residual solvent

(12) Inappropriate primer

(13) The surface treatment is not good

(11) Dry more time or increase the furnace temperature

(12) Switch to PVF primer

(13) If it is unqualified, it should be coated in time after surface treatment.

Blank point

(14) There are oil stains and water droplets

(14) Wipe the barrel with alcohol

Pinhole

(15) The coating is too thin

(16) Partial coating thin

(17) Thin coating at acute angle

(18) The corner is impacted

(15) Repaint once

(16) Recoating part

(17) Pre-rounding the horns, eliminating burrs, etc.

(18) Separate after quenching

Edge crack

(19) Low furnace temperature

(20) The starting temperature is too low

(21) The latent solvent volatilizes too early

(22) too low boiling point solvent

(19) Increase the furnace temperature

(20) If the temperature is not enough, do not enter the furnace, first close the door to heat up

(21) Stop the blast

(22) Switch to dimethyl ester or diethyl ester

Cracked, wrinkled

(23) The furnace temperature is too low

(24) The starting temperature is too low

(25) Uneven temperature in the furnace room

(23) greatly improve the furnace temperature

(24) Close the door to raise the temperature so that the furnace temperature is too high, and the furnace moves quickly.

(25) Increase thermal power

Color difference

(26) Uneven temperature in the furnace

(27) Large difference in wall thickness

(26) Blasting or rotating work

(27) Make the thick wall more heated

Coarse grain

(28) The coating has coarse particles

(29) The paint is not evenly mixed

(28)180 mesh screen filtration

(29) Stir thoroughly during dilution

2. Repair and withdrawal of the coating:

The quality of the spray is unqualified, and it is much easier to rework before baking. It can be washed with alcohol or gasoline. It is much more difficult to remove the coating after baking and plasticizing. In view of this, try to use the thermoplastic characteristics of the polyvinyl fluoride coating, and adopt a repair method instead of the removal. However, there are often four cases to consider retreating: large areas of dry coke, the appearance needs to look good, the mating surface requirements are flat and have been coated many times or repeated.