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Valve phosphating treatment process

一、Principle of phosphating treatment

Phosphatization is a chemical and electrochemical reaction to form a phosphate chemical conversion film. When the metal (valve) is immersed in a phosphate solution containing manganese, iron and zinc, a series of complex chemical reactions occur on the metal surface. In this process, the atoms on the metal surface interact with phosphate ions, metal ions, etc. in the phosphate solution to generate a layer of water-insoluble phosphate crystalline film. This layer of phosphate protective film has good corrosion resistance, wear resistance, insulation and other properties, can effectively protect the valve surface from the erosion of the external environment.

二、Process Flow

(一) Surface Pre-treatment

1、Degreasing:

Purpose: to remove oil, grease and other organic impurities on the surface of the valve to ensure the effect of subsequent treatment.

2、Descaling:

Purpose: to remove rust and oxidized skin on the surface of the valve, so that the metal surface reveals a fresh metal matrix, in order to facilitate phosphating treatment.

3、Water washing:

Purpose: rinse the valve surface with water to remove residual degreasing agent and rust remover to ensure that the valve surface is clean.

(二) Phosphating treatment

1、Phosphating solution formulation:

According to different phosphating requirements, choose the appropriate phosphating solution formula. Common phosphating solution formulations include zinc phosphating solution, manganese phosphating solution, iron phosphating solution and so on. - Phosphoric acid, phosphate, accelerator and other raw materials according to a certain proportion of water, mix well, formulated into phosphate solution.

2、Phosphating operation:

Put the pre-treated valve into the phosphating solution to ensure that the valve is completely submerged in the phosphating solution. According to the formula of the phosphating solution and process requirements, control the temperature and time of phosphating treatment. Generally speaking, the phosphating temperature between 30 ℃ - 60 ℃, phosphating time between 10 minutes - 30 minutes. In the phosphating process, the phosphate ions in the phosphating solution and the metal surface of the chemical reaction to generate phosphate crystals, and gradually form a layer of uniform, dense phosphate film on the surface of the valve.

3、Washing:

Purpose: rinse the valve surface with water to remove the residual phosphating solution, to prevent the phosphating solution on the surface of the valve caused by corrosion.

4、Drying:

Purpose: to make the valve surface water evaporation, to ensure that the phosphating film is dry and firm, to improve the corrosion resistance of the phosphating film.

5、Closed treatment (optional): Purpose: In order to further improve the corrosion resistance of the phosphating film, can be closed to the valve after phosphating treatment.

三、Process parameters

1、Temperature: the temperature of phosphating treatment has a great influence on the speed of phosphating reaction and the quality of phosphating film. Temperature is too low, phosphate reaction rate is slow, phosphate film crystallization rough, poor corrosion resistance; temperature is too high, phosphate reaction rate is too fast, phosphate film crystallization coarse, easy to hang ash and other defects. Generally speaking, the phosphating temperature between 30 ℃ - 60 ℃ is appropriate

2、Time: phosphating time is also an important factor affecting the quality of phosphating film. Time is too short, the phosphating reaction is incomplete, phosphate film thin, poor corrosion resistance; time is too long, phosphate film crystallization coarse, easy to hang ash and other defects. Generally speaking, phosphating time between 10 minutes - 30 minutes is appropriate.

3、Phosphate concentration: phosphate solution in the phosphate, phosphate and accelerator concentration of phosphate reaction rate and phosphate film quality also has a great impact. Concentration is too low, the phosphate reaction rate is slow, phosphate film thin, poor corrosion resistance; concentration is too high, the phosphate reaction rate is too fast, phosphate film crystallization coarse, easy to appear hanging ash and other defects.

四、Quality control

1、Appearance inspection:

The surface of the valve after phosphating should be uniform, dense, without obvious defects and impurities.

The color of the phosphating film should meet the requirements, generally gray or black.

Observe the surface of the valve with the naked eye, there should be no blistering, flaking, cracks and other defects.

2、Membrane thickness test:

Using a film thickness meter to detect the thickness of the phosphating film, the general requirements of the film thickness between 2μm - 10μm. Film thickness is too thin, poor corrosion resistance; film thickness is too thick, easy to hang gray and other defects.

3、Corrosion resistance test:

Through the salt spray test, hot and humid test and other methods to detect the corrosion resistance of the phosphating film.

Salt spray test is the phosphating of the valve into the salt spray test chamber, at a certain temperature and humidity conditions, continuous spray for a certain period of time, to observe whether the valve surface corrosion.

Damp heat test is to put the phosphated valve into the damp heat test chamber, at a certain temperature and humidity conditions, keep for a certain period of time, observe whether the valve surface corrosion.

4、Adhesion test:

The use of scratching or drawing method, detecting the adhesion of the phosphating film and the metal substrate.

Adhesion should meet the requirements, otherwise it will affect the service life of the phosphating film.