The phosphatized workpiece is subjected to a sub-test for its quality index according to its use. The main quality control indicators include the appearance of phosphating film, the thickness of phosphating film or film weight, the phosphating film or the corrosion resistance after post-treatment. According to the phosphating use, it is sometimes necessary to detect: phosphating and paint film matching, phosphating film hardness, friction coefficient, anti-scratch and other indicators. For the tri-common index of phosphorus, the following standards and methods can be referred to.
Appearance of phosphating film: using visual method, relevant standard GB 11376-89 "metal phosphate conversion film" and GB 6807-86 "technical conditions for phosphating treatment of steel workpiece before painting".
Phosphating film thickness or film weight: film thickness measurement using GB 6462 "metal oxide coating cross-section thickness microscopy", can also be used thickness gauge, according to GB 4956 "magnetic metal substrate on the thickness of non-magnetic coating layer measurement magnetic Method" or GB 4957 "Measurement of eddy currents by non-conductive coating on non-magnetic metal substrates". The weight of the membrane is measured by the gravimetric method, which can be in accordance with GB 6807 "Technical Conditions for Phosphating Treatment of Steel Workpieces before Painting" or GB 9792 "Determination of Film Layer Quality per Unit Area of ​​Conversion Coatings on Metallic Materials".
Corrosion resistance: The corrosion resistance of the phosphating film itself can be measured by a copper sulfate dropping method, a sodium chloride salt immersion method and a salt spray test method. The drip method and the salt water immersion method can be carried out according to GB 6807-86 "Technical conditions for phosphating treatment of steel parts before painting". After the phosphating film is post-treated, such as oiling, waxing, and painting, the salt spray test is generally carried out. The salt spray test can be carried out according to GB 1771-79 "Determination of salt spray resistance of paint film" or GB 6458 "Neutral salt spray test of metal cover layer".
Phosphating with primer before painting
The phosphating treatment for pre-painting primers is mainly to improve the adhesion of the paint film and the corrosion resistance of the coating system, so the focus is on the compatibility with the paint film. Generally, the phosphating quality testing indicators include the appearance of the film, the film thickness and the performance after matching with the film. The appearance of the film should be a uniform and fine phosphating film. For the light iron phosphating, the appearance should be a uniform fine and complete phosphating film. For the light iron phosphating, the appearance should be a complete red and blue color film. The phosphating film should not be too thick. Generally, the film weight should be less than 7.5g/m2, preferably 1.5-3.0g/m2, and the light iron phosphating film should be 0.5-1.0g/m2, too thick and rough. The film is unfavorable for painting. The corrosion resistance index includes the corrosion resistance of the phosphating film itself and the yellowing and rusting phenomenon should not occur before painting. Corrosion resistance after phosphating and lacquering is the most important, which reflects the overall corrosion resistance of the phosphating film in combination with the lacquer. In addition to the detection of corrosion resistance, the phosphating film is usually tested for mechanical properties such as adhesion, impact strength, and bending resistance (flexibility). The quality index and testing method for phosphating before painting can generally refer to the national standard GB 6807-86 "Technical conditions for phosphating treatment of steel workpiece before painting", the quality index and testing evaluation of the standard for phosphating film The method has more detailed regulations, and its main contents are as follows:
(1) The appearance of the phosphating film should be a crystalline dense, continuous uniform light gray to dark gray film, and should be a continuous color film for light iron phosphating. The following defects are allowed; slight water marks, chromate marks, slight ash ashing, phosphating film defects due to different surface conditions such as heat treatment welding and processing. For the following, defects are not allowed: the phosphating film is yellowish and rusted, the phosphating film is loose, and the phosphating exposed bottom is partially film-free, and the ash is seriously hanged.
(2) The phosphating film for painting should have a weight less than 7.5 g/m2.
(3) The corrosion resistance of the phosphating film is immersed in a salt water immersion method. The phosphating workpiece is immersed in a 3% NaCl aqueous solution at a temperature of 15 to 25 ° C for 1 hour. Corrosion resistance test after phosphating with paint film is to coat the phosphating workpiece with 25~35μm A04-9 white amino lacquer, and after salting, carry out salt spray test (according to GB 1771-79) after 24h salt spray test ( Iron phosphating is 8h salt spray test) The paint film should be free from blistering, rusting and falling off.
GB 6807-86 is not a necessary test for the copper sulfate drip method. It is considered as a rapid test method for the phosphating quality between processes, and the corrosion resistance after phosphating and painting is a mandatory item.
For the test indicators and methods for phosphating before lacquer, refer to GB 11376-89 "Phosphate Conversion Coatings for Metals".
Therefore, from the standard inspection items, the phosphating before lacquering should be a dense, uniform, thin-layer phosphating film. The corrosion resistance and mechanical and physical properties of phosphating and paint should be emphasized.
2 Phosphating against rust and corrosion
For this type of phosphating, its main purpose is to protect against corrosion, and its corrosion resistance is the most important indicator. The general quality test indicators include copper sulfate droplets greater than 1 min, salt water resistance greater than 2 h, and salt spray test greater than 1.5 h. For the corrosion resistance test after oiling or waxing, it is best to use the salt spray test. The specific salt spray resistance time should be agreed upon by the supplier and the buyer.
3 lubrication, wear-resistant anti-friction phosphating
The phosphating for lubrication is mainly used in cold working, generally zinc. Wear-resisting anti-friction phosphating is a workpiece used for load-friction movement, and conventional manganese phosphating.
For the phosphating of the lubricating action, the appearance, the film weight, the corrosion resistance, and the smoothness after saponification are mainly examined, and the friction coefficient is sometimes measured. The appearance of the phosphating film should be uniform and complete. Generally, the film is larger than 5g/m2 to ensure a certain film thickness. After saponification, the friction is obviously reduced, the mold damage is reduced, and the cracking of the workpiece during cold working is reduced.
For wear-resistant antifriction phosphating, generally manganese phosphating, the appearance of the phosphating film should be a uniform and complete dark gray or black film. For parts with small clearance, the film weight should be 1~3g/m2, and the workpiece with large dynamic matching clearance should have a film weight of 5g/m2 or more. Such phosphating is required to have higher hardness and scratch resistance, and specific indicators can be agreed between the supplier and the buyer. At the same time, the wear-resisting anti-friction phosphating should have good corrosion resistance, and the salt spray resistance should be above 1.5h. For lubrication, wear-resisting and anti-friction phosphating, reference is also made to GB 11976-89.
4 Phosphating for other purposes
In addition to the above three fields, phosphating can also be used for electrical insulation and decorative aspects. Its conventional quality testing indicators are appearance, film weight and corrosion resistance. For electrical insulation phosphating, it is required to detect the surface resistance per unit area. For decorative phosphating, it is necessary to dye according to different requirements, and different color chromaticity and corrosion resistance are required. The detection method and control range of these indicators are generally agreed by the supplier and the buyer. The detection and control of phosphating quality indicators are subject to various requirements depending on the application. Except for the conventional appearance, membrane weight, and some phosphating corrosion resistance standards, most indicators and tests are The methods are all agreed by the supplier and the buyer.
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