Classification of phosphating
1, zinc phosphating: also known as gray phosphorus, the formation of gray - dark gray phosphating film, phosphating film weight 1.5-3.5g / m2, mainly used for coating the bottom layer, improve the adhesion of the coating and anti-corrosion ability.
2, iron phosphating: also known as color phosphorus, the formation of blue - golden - rainbow color phosphating film, phosphating film weight 0.3-0.6g / m2, mainly used for coating the bottom layer, improve the adhesion and corrosion resistance of the coating.
3, manganese phosphating: also known as black phosphating, the formation of dark ash - black phosphating film, phosphating film weight 5.0-20g / m2, soaked in anti-rust oil or saponification, for long-term rust prevention of parts.
4, multi-functional phosphating: also known as three-in-one phosphating, one-time completion of oil removal, rust removal, phosphating functions, the formation of blue - blue violet - gray phosphating film, used for large equipment, small batch production and pre-painting treatment.
Anti-rust phosphating process
The early application of the phosphating process is anti-rust, and the steel parts are phosphating to form a phosphating film to play a rust-proof role. After phosphating anti-rust treatment of the workpiece rust prevention period of up to a few months or even a few years (for oiled workpieces), widely used in the process, transportation, packaging storage and use of the process of rust prevention, rust phosphating mainly has iron phosphating, zinc phosphating, manganese phosphating three varieties.
The main bath component of iron phosphating is ferrous phosphate solution, which does not contain oxidation accelerators and has a high free acidity. This iron phosphating treatment temperature is higher than 95 °C, the processing time is more than 30min, the phosphating film is greater than 10g/m², and it has the dual functions of rust removal and phosphating. This high-temperature iron phosphating is now rarely used because the phosphating rate is too slow.
Manganese phosphating has the best performance as anti-rust phosphating, and the microstructure of the phosphating membrane is densely stacked with particles, which is the most widely used anti-rust phosphating. Additive or non-accelerator can be added, if the addition of nitrate or nitroguanidine accelerator can speed up the phosphating film formation. Usually the treatment temperature is 80~ 100 °C, the treatment time is 10 ~ 20min, and the membrane weight is more than 7.5 g/m². Zinc phosphating is also a widely used anti-rust phosphating, usually using nitrate as a promoter, the treatment temperature is 80 ~ 90 °C, the processing time is 10 ~ 15min, the phosphating membrane is greater than 7.5g / m², and the microstructure of the phosphating membrane is generally a tight stacking type of needles.
Anti-rust phosphating general process:
Degreasing and rust removal - water cleaning - surface adjustment and activation - phosphating - water cleaning - chromate treatment - drying - greasing or dyeing treatment
The workpiece treated with a strong alkali and strong acid will lead to the coarsening of the phosphating film, and the grain can be refined by surface adjustment activation. Zinc phosphating can be adjusted with oxalic acid and colloidal titanium. Manganese phosphating can be activated by an insoluble manganese phosphate suspension. Iron phosphating generally does not require adjustment of the activation treatment. The phosphating of the workpiece can be greatly improved by chromate sealing, such as oiling or dyeing treatment can improve the rust resistance several times or even dozens.
Wear-resistant friction-reducing lubrication phosphating process
For workpieces such as engine piston rings, gears, and refrigeration compressors, it not only bears a load, but also has motion friction, requiring the workpiece to be able to reduce friction and resist friction. Manganese phosphating film has high hardness and thermal stability, can withstand wear, phosphating film has a good anti-friction lubrication effect. Therefore, it is widely used in piston rings, bearing bearings, compressors and other parts. This kind of wear-resistant molar phosphating treatment temperature is 70~ 100 °C, the processing time is 10 ~ 20min, and the phosphating film is greater than 7.5g/m².
In the cold processing industry such as: takeover, drawing, extrusion, deep stretching and other processes, the phosphating film is required to provide friction reduction lubrication performance, generally using zinc phosphating, one is the zinc phosphating film saponification to form a very lubric zinc stearate layer, the second is that the zinc phosphating operation temperature is relatively low, can be phosphating treatment under 40, 60 or 90 °C conditions, phosphating time 4 ~ 10min, sometimes even tens of seconds, phosphating film weight requirements ≥3g / m² can be.
The process flow is:
Wear-resistant anti-phosphating Anti-friction lubrication phosphating (cold working)
Degreasing degreasing descaling Degreasing degreasing water cleaning Water cleaning
Manganese phosphating Zinc phosphating
Water cleaning Water cleaning
Drying saponification (sodium stearate)
Grease to dry
Pre-paint phosphating process
The phosphating treatment before applying the primer will improve the adhesion of the paint film to the matrix metal, improve the corrosion resistance of the entire coating system, and provide protection between processes to avoid the formation of secondary rust. Therefore, the primary problem of phosphating before paint is that the phosphating film must have excellent matching with the primer, and the rust resistance of the phosphating film itself is secondary, and the phosphating film is fine and dense, and the film is thin. When the phosphating film is thick, it will have a negative effect on the comprehensive performance of the paint film. The selection of the phosphating system and process is mainly determined by: the material of the workpiece, the degree of oil rust, the geometry; the time interval between phosphating and painting; the variety and construction method of the primer and the relevant site equipment conditions.
In general, low carbon steel is easy to phosphating treatment, and the phosphating film forming performance is better. For rusty (oxide scale) workpieces must go through the pickling process, and the pickling workpiece will bring a lot of trouble to phosphating, such as rusting and yellowing between processes, removal of residual acid, and roughing of phosphating film. After pickling, the workpiece is generally subjected to surface adjustment before zinc and zinc-manganese phosphating.
In intermittent production occasions, due to conditions, phosphorus chemical parts must be stored for a period of time before they can be painted, so the phosphating film itself is required to have good rust resistance. If the storage period is more than 10 days, it should generally be used to phosphate at medium temperature, such as medium temperature zinc system, medium temperature zinc manganese system, medium temperature zinc calcium system, etc., and the thickness of the phosphating film should preferably be between 2.0 and 4.5g/m². The phosphating workpiece should be dried immediately, and should not be dried naturally to avoid the formation of rust in the cracks and welds. If the storage period is only 3 to 5 days, it can be phosphating with low temperature zinc and light iron, and the drying effect will be better than that of natural cool drying.
(1) Single-chamber spray phosphating process
There is only one spray chamber for the entire pretreatment process, and there are multiple reservoirs under the spray chamber, and different treatment fluids are sprayed into the workpiece and then flowed back into their respective tanks. For example, first spray the degreasing solution, after the degreasing liquid flows back to the degreasing tank, close the valve; then spray water washing, close the water washing valve after the completion of the water washing; the next step is to spray the phosphating liquid, this single-chamber treatment method can be implemented as follows:
Degreasing - phosphating "two-in-one" (light iron system) - water cleaning - (chromium sealing) - out of the piece
Degreasing - water cleaning - phosphating - water cleaning - (chromium sealing) - out of the piece
Degreasing - water cleaning - surface adjustment - phosphating - water cleaning - (chromium sealing) - out
This phosphating process generally does not advocate the arrangement of pickling processes, so as not to cause corrosion of the equipment or rust between processes. Single-chamber process equipment occupies less space, is simple and easy, but wastes a lot, and is only suitable for intermittent production occasions with few batches. Another method similar to this, the use of a small capacity tank outside the treatment liquid, through the pump and pipeline pumping after mixing with hot water spray on the workpiece to achieve degreasing, phosphating effect, spraying after the liquid is not recovered, this method is simpler, but the waste is greater.
(2) Multi-chamber "standard" station phosphating process:
(1) Pre-degreasing 50~70°C 1~2min
(2) Degreasing 50 to 70°C 2 to 4min
(3) Water cleaning 1 ~ 2 channels Room temperature 0.5 ~ 1.0min
(4) Surface adjustment Room temperature 0.5 ~ 1.0min
(5) Phosphating 35~60°C 2~6min
(6) Water cleaning < 2 channels room temperature 0.5 ~ 1.0min
(7) Deionized water washing room temperature 0.5 ~ 1.0min
(8) Chromate treatment 40 ~ 70 °C 0.5 ~ 1.0min
(9) Drying below 180°C
The treatment method can be full spray, full soak, spray -soak combination three ways. For the household appliance industry, the general use of full spraying method, it is high efficiency, the entire pre-treatment only needs ten minutes to complete, saving site equipment. The automotive industry is popular for a combination of spray-soak.
The surface adjustment process is not required, and the same effect can be achieved by adding surface adjustment to the degreasing tank. Deionized wash after phosphating is essential. Phosphating chromate treatment can improve the corrosion resistance of the entire coating system, but it should be used with caution due to the environmental pollution problem of chromium.
(3) Phosphating treatment process of mixed parts (rust workpiece)
(1) Degreasing 40 to 70°C 3 to 8min
(2) Water cleaning room temperature 0.5 ~ 1.0min
(3) Pickling 40 ~70 °C 3 ~8 min
(4) Water cleaning Room temperature 0.5min
(5) Neutralization room temperature 0.5 ~ 1.0min
(6) Surface adjustment Room temperature 0.5min
(7) Phosphating 35~60°C 3~10min
(8) Water cleaning Room temperature 0.5 ~ 1.0min
(9) Wash with water at room temperature of 0.5 to 1.0min
(10) Chromate washing 40 ~ 70 °C 0.5 ~ 1.0min
(11) Drying < 180 °C
Unless there is a sufficient reason, the pickling process generally does not use spray treatment, spraying will bring a series of problems such as equipment corrosion and rust between workpiece processes. All other processes can be constructed using a full spray or a combination of spray-dip.
For mixed parts (rust-free workpieces, rusty, oxidized scaling workpieces mixed at the same time), the use of degreasing and rust removal "two-in-one" instead of step-by-step degreasing and rust removal method has been applied for decades, and the same satisfactory effect can be obtained. For pickling and degreasing and rust removal" "two-in-one" generally use non-volatile inorganic acids is more appropriate.
Phosphating process operation ideas
(1), degreasing and oil removal: before phosphating, the grease on the surface of the workpiece should be cleaned, otherwise it will affect the uniformity, corrosion resistance and coating adhesion of the phosphating film.
(2), acid rust removal: after removing oil, the rust layer and oxide film on the surface of the workpiece should be removed, so as not to affect the uniform growth of the phosphating film.
(3), neutralization: through the acid-base neutralization reaction principle, wash the inner surface of the pipe, weld the residual acid, improve the corrosion resistance of the phosphating film.
(4) Specification: Cover the surface of the workpiece with a layer of activation center, which is conducive to depositing the phosphating film on the surface of the workpiece; in addition, the pH of the workpiece surface is appropriate, and it is in the best state of the film-forming reaction.
(5), phosphating post-treatment: In order to improve the performance of phosphating film, various post-treatments can be carried out according to different uses, such as manganese phosphating after soaking anti-rust oil or saponification as long-term rust prevention, iron phosphating after passivation treatment to improve the rust resistance of phosphating film.
(6), drying: the temperature does not exceed 140 °C, otherwise it will destroy the integrity of the phosphating film and reduce the corrosion resistance of the phosphating film.
(7), washing: keep the overflow water washing, to ensure adequate washing, reduce the serial groove pollution and improve the corrosion resistance of the phosphating film.