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Quality Control And Inspection Methods For Phosphating Of Ferrous Metals

Phosphate after the workpiece, according to its use, its quality indicators for sub-inspection. The main quality control indicators, including the appearance of phosphating film, phosphate film thickness or film weight, phosphate film or post-treatment of the three common indicators of corrosion resistance. According to the phosphating use sometimes also test: phosphating and film supporting, phosphating film hardness, friction coefficient, anti-scratch and other indicators. On the three common indicators of phosphating, can refer to the following standards and methods. Phosphate film appearance: the use of visual inspection, the relevant standard GB / T 11376-1997 "metal phosphate conversion film" and GB / T 6807-2001 "steel workpiece before painting phosphating treatment technology conditions."

Phosphate film thickness or film weight: film thickness measurement using GB / T 6462-2005 "metal and oxide coating thickness measurement microscopy", can also be used thickness gauge, in accordance with GB / T 4956-2003 "magnetic metal matrix on the Magnetic cover layer thickness measurement magnetic method "or GB / T 4957-2003" non-magnetic metal substrate on the non-conductive coating to measure eddy current method. " Membrane weight measurement by weight method, according to GB / T 6807-2001 "steel workpiece painting before phosphating treatment technology conditions" or GB / T 9792-2003 "metal materials on the conversion film per unit area of the quality of the method of weight method" The Corrosion resistance: Detection of corrosion resistance of the phosphating film itself can be carried out by copper sulfate dripping method, after drying in the oil is not immersed on the workpiece 3-5% CuSO4 solution, more than 1min does not appear red spots for qualified.

Sodium chloride salt water immersion method and salt spray test method: drip method and salt water immersion method can be in accordance with GB / T6807-2001 "steel work before painting phosphating treatment technology conditions", phosphating film after post-treatment such as oil, wax , Painted after the general salt spray test. Salt spray test can be in accordance with GB / T1771-1991 "paint and varnish resistance to neutral salt spray performance determination" or GB / T10125-1997 "artificial atmosphere corrosion test salt spray test."

1.paint before the primer with phosphating

The main purpose is to improve the adhesion of the paint film and the corrosion resistance of the coating system, so the focus is on the performance of the film with the film. General inspection of phosphating quality indicators include film appearance, film thickness and performance after supporting the film. Membrane appearance should be uniform and complete intact phosphating film, the appearance should be uniform fine and complete phosphating film, the zinc-iron phosphate, the appearance should be a complete red and blue color film. Phosphate film should not be too thick, the general membrane weight should be less than 7.5g / m2, preferably 1.5 ~ 3.0g / m2, for zinc iron phosphate film weight 0.5 ~ 1.0g / m2 is appropriate, too thick and rough phosphorus The film is unfavorable. Corrosion resistance indicators include corrosion resistance of the phosphating film itself and should not appear yellowing rust before painting. Phosphating and paint with the corrosion resistance is the most important, it reflects the phosphate film and paint after the overall corrosion resistance. Phosphating film and paint in addition to the detection of corrosion resistance, the general need to determine the mechanical properties of the film, such as: adhesion, impact strength, bending capacity (flexibility) and so on.

Paint before the primer with the quality of phosphate and the detection method should generally refer to the national standard GB / T 6807-2001 "steel workpiece before painting the technical conditions of phosphating treatment," the standard of the phosphate film of the quality indicators and Testing and evaluation methods are more detailed provisions, the main contents are as follows:

(1) phosphating film appearance should be dense crystal, continuous uniform light gray to dark gray film, for the light iron phosphate should be continuous color film. The following defects are permitted: slight water marks, chromate traces, slight hang ash phenomena, and the phosphating film defects due to the different surface conditions such as heat treatment welding and processing. For the following is not allowed to appear defects: phosphating film appears yellow rust, phosphating film loose, phosphating exposed bottom of the local film, serious hanging ash.

(2) paint with phosphating film weight should be less than 7.5g / m2.

(3) corrosion resistance of phosphating film using salt water immersion method, phosphating the workpiece in 3% NaCl aqueous solution, at 15 ~ 25 ℃ temperature, soaking 1h should not be rust. Phosphating and film with the corrosion resistance of the test is to phosphating the workpiece coated 25 ~ 35μm A04-9 white amino paint, scratches after salt spray test (according to GB / T 1771-1991) by 24h salt spray Test (iron phosphate is 8h salt spray test) paint should be no blistering, rust, shedding phenomenon.

GB / T 6807-2001 on the copper sulfate drip method is not required to be tested items, that can be used as a process between the quality of the rapid test method, and phosphating and paint with the corrosion resistance as a must check items.

  For the paint before the test indicators and methods can also refer to GB / T 11376-1997 "metal phosphate conversion film."

  Therefore, from the standard provisions of the inspection items, paint before the primer with phosphating should be dense, uniform, thin layer of phosphate film, should focus on testing phosphating and paint after supporting the corrosion resistance and mechanical and physical properties.

2.on the rust, corrosion with phosphating

For this type of phosphating, its main purpose is to corrosion protection, corrosion resistance is the most important indicators. General quality inspection indicators include copper sulfate drip to more than 1min, salt water is greater than 2h, salt spray test is greater than 1.5h. For oil or wax after the corrosion resistance test, it is best to use salt spray test, the specific should meet the salt spray time, both agreed by the supply and demand.

3.lubrication, wear-resistant anti-friction phosphating

Phosphating from the role of lubrication is mainly used in cold processing, generally zinc. Wear-resistant anti-friction and phosphating is used for load friction movement of the workpiece, the conventional manganese-based phosphating.

For the phosphating of the lubricating effect, the main test appearance, film weight, corrosion resistance and saponification after the smoothness, and sometimes to determine the friction coefficient. Phosphate film should be uniform and complete appearance, the general membrane weight greater than 5g / m2, to ensure that a certain film thickness, after saponification, significantly reduce the friction, reduce mold damage, reduce the workpiece when cold cracking.

For wear-resistant anti-friction phosphating, usually manganese-based phosphating, the phosphating film should be a uniform appearance of dark gray or black film. For the small parts with the gap, the film should be in the 1 ~ 3g / m2, moving with the gap between the workpiece, the membrane weight should be 5g / m2 or more. Requirements of such phosphating have a higher hardness and scratch resistance, the specific indicators can be agreed by both supply and demand. At the same time wear anti-friction phosphating should have good corrosion resistance, usually salt spray should be more than 1.5h. For lubrication, wear-resistant anti-friction phosphating the same can refer to GB / T11376-1997.

4.Phosphorus for other uses

Phosphating in addition to the above three areas, but also for electrical insulation, decorative aspects. The routine quality inspection indicators for the appearance, film weight and corrosion resistance. For electrical insulation phosphating, it is required to detect the surface resistance per unit area. On the decorative phosphating according to different requirements for dyeing, requiring different color chromaticity and corrosion resistance, the detection methods and control of these indicators are generally agreed by the supply and demand sides.

Phosphating quality indicators of the detection and control, according to their use to have different requirements, in addition to the conventional appearance, film weight, some phosphating corrosion resistance standards can be followed, most of the indicators and testing Methods are agreed by the supply and demand sides.

GB / T10125-1997 "artificial atmosphere corrosion test salt spray test" the current standard is GB / T10125-2012.

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