Quality Analysis of Surface Coating Process of Steel Barrel for Sauce

Quality Analysis of Surface Coating Process of Steel Barrel for Sauce

Zhang Yumin

【Abstract】The paper analyzes the performance of coatings on the surface of steel drums for sauces, the problems and solutions of surface treatment before painting, the coating process and the environment requirements during painting.

[Keywords] steel drum for sauce; surface coating; process technology

The quality of the coating on the surface of the steel drum for the sauce depends not only on the surface quality of the paint and the steel drum itself, but also on the whole process of the coating formation. Proper selection of reasonable coating technology is a necessary condition to improve the surface coating quality of steel drums for sauces.

l Coating steel surface coating requirements for coating performance

The purpose of coating the surface of the steel drum for the sauce is to protect it and decorate it. Its specific requirements for coatings are bright color, strong adhesion and smooth surface. Therefore, it is important to correctly select the type of coating and the coating system. Generally, electrostatic spraying (dusting and painting) or high-pressure airless spraying is used.

2 Strictly carry out surface pretreatment before coating steel drum for sauce

The raw material for the steel drum for sauce is exposed to air during production and transportation, and it is prone to corrosion, adhesion to foreign matter, scale, oil, processing debris, dust, etc. Therefore, the surface treatment must be carried out before the steel drum is painted, and the unfavorable factors affecting the quality of the steel drum coating are eliminated by the degreasing phosphating, cleaning and drying process, thereby improving the coating quality of the steel drum for the sauce. Problems and solutions often encountered in the surface treatment process before painting.

(1) Degreasing is not clean.

a) The concentration of the degreased oil is low; the concentration should be increased.

b) Short oil removal time; extended time.

c) The temperature of the oil removal is low; the temperature is raised.

d) The local grease is too thick; the pretreatment (manual or mechanical) is added.

e) The grease layer on the surface of the oil sump is thick; the oil layer is taken out.

f) The nozzle is clogged during the spraying process; the cleaning is opened.

g) The processing capacity of the workpiece is large; the concentration of the degreased oil is stabilized by adding the agent in time.

(2) Derusting is not complete.

a) The concentration of the descaling solution is low; the concentration is increased.

b) Short derusting time; increase time.

c) The scale formed by high temperature is too thick; the auxiliary mechanical rust is increased.

d) The iron ion content in the descaling solution is too high, and the anti-rust liquid is invalid; replace the new tank.

(3) There is too much acid in the derusting liquid or hydrogen embrittlement or corrosion after the workpiece is rusted:

a) The concentration is too high; diluted with water.

b) Insufficient additives; add additives.

c) The time is too long; the time is reduced.

(4) The phosphating film is rough in crystals.

a) The free acidity is high; the free acidity is reduced by a neutralizing agent.

b) Residual acid; enhanced neutralization and washing.

c) Over-corrosion of the workpiece surface; control concentration.

(5) The phosphating film is too thin and has no obvious crystallization.

a) The free acidity is low; after adding the phosphating solution, the neutralizer is added.

b) High total acidity; diluted with water.

c) The surface of the workpiece has a hardened layer; the pickling is strengthened.

d) The temperature is too low; increase the temperature.

e) The ferrous ion content is too low; the ferrous ion is increased.

(6) The phosphating film has poor corrosion resistance and rusting occurs.

a) Phosphating film is coarse; reducing free acidity.

b) low total acidity; increase phosphating solution.

c) There is residual liquid on the surface of the workpiece; strengthen the neutralization and wash.

d) The phosphating temperature is low; the temperature is raised.

e) Phosphating time is short; increase time.

f) The workpiece has overlap during the drying process; the separation is placed.

g) There is water accumulation in the workpiece; change the placement angle of the workpiece.

(7) After the phosphating, the workpiece has ash hanging phenomenon.

a) Free acidity is too low; increase free acidity.

b) Washing is not clean; strengthen washing.

(8) Phosphating film is not uniform:

a) Degreasing is not clean; strengthen degreasing.

b) The surface of the workpiece has a hardened layer; the pickling is strengthened.

c) The ferrous ion content is too high; treated with hydrogen peroxide.

d) The pickling bath is brought into the phosphating solution; the neutralized water washing is strengthened.

The above experience can be solved by formulating process indicators and process codes and operating procedures and then configuring the corresponding process equipment to minimize defects.

3 Strict coating process for steel surface coating of steel drum

The paint is evenly sprayed on the surface of a clean steel drum. After drying, a good protective film, the paint film, can be obtained. The formation process of the entire paint film can be divided into two stages, a coating process and a dry film forming process.

(1) Coating process. Coating refers to the process of uniformly coating a coating on the surface of a steel drum to a desired thickness. This process is typically done by an automatic sprayer. The uniformity of coating is very important. If it is not uniform, it will reduce the corrosion resistance when it is too thin, and it will be easy to sag and wrinkle when it is too thick.

(2) Dry film formation process of surface coating of steel drum for sauce. The dry film formation process is a comprehensive physical and chemical process including solvent evaporation, condensation, oxidative polymerization, etc. The whole process has both physical and chemical effects, and can be roughly divided into two stages:

a) Solvent evaporation stage. Generally occurs in the early stage of drying, immediately after painting, a large amount of solvent is volatilized and the volatilization process is carried out almost on a free surface. Due to the volatilization of the solvent, the concentration of the paint film on the surface of the steel drum changes, so that the paint loses fluidity.

b) Chemical reaction stage. On the surface of the steel drum for the sauce, the solvent loses fluidity after evaporation. Under the action of heat energy, some of the polymer compounds are formed by condensation reaction, and other paint bases are oxidized in the air, and polymerization is carried out to form a network structure. The polymer compound, this process is a relatively complicated chemical reaction process, but in the end, it is a polymer compound having a network structure with different degrees of polymerization. This polymer compound has good properties, and almost all the protective properties of the film are provided by it. Therefore, heat and time are essential in the drying process of the coating on the surface of the steel drum for the sauce. Without sufficient heat and sufficient time, the coating does not get enough chemical reaction energy or the reaction cannot be completely carried out. . The so-called selection of appropriate drying specifications is to set a reasonable configuration of drying temperature and drying time in order to obtain sufficient heat, so that the paint film can reach the optimal structure for protecting steel drums and decorative steel drums.

4 timely treatment of surface coating defects of steel drums for sauce

Defects found in the inspection of the coating process and the final coating properties shall be promptly disposed of and corresponding measures shall be taken to remedy the coating quality on the surface of the steel drum for the sauce.

Coating film defects during the coating process or after coating are generally related to the pre-coating state of the steel drum surface, the coating process, the paint quality, the coating method and operation, the coating equipment and the environment. Common defects include sag, sag and flow marks, coarse granules and sputum, poor bottom and cover, pinholes, orange peel, wrinkles, poor drying, rust, and brittleness.
Scientific and rational codes of practice and operating procedures must be developed and equipment levels and management strengthened. Paint defects must be controlled before problems arise.

5 Environmental requirements for surface coating of steel drums for sauces

(1) The lighting in the spray drying room is good and the brightness is uniform. Appropriate brightness should be provided in the coating operation area (spraying room) on the surface of the steel drum, but direct sunlight and too strong light should be avoided to facilitate operation.

(2) The temperature and humidity in the spray booth are moderate. The temperature and humidity of the air have a great influence on the surface coating performance of the steel drum. If it is not properly controlled, it will cause various defects in the surface coating of the steel drum. Different coatings require different temperatures and humidity during coating due to their different volatility and workability (Table 1).

Table 1 Temperature and humidity requirements for some coatings

(3) Spray indoor air should be clean. The indoor air sprayed on the surface of the steel drum should be kept dry, clean, dust-free or dust-free. When spraying, the dust in the spray booth adheres to the paint film on the surface of the steel drum, which not only affects the appearance quality of the steel drum, but also reduces the coating performance and durability of the steel drum surface. The indoor air should be strictly controlled during production.

(4) The spray drying room should be well ventilated and properly ventilated. The air in the spray drying chamber should be continuously flowing, on the one hand, the coating drying can be accelerated; on the other hand, the concentration of harmful substances in the spray drying chamber can be diluted to improve the sanitary conditions in the workshop.

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