Aluminum Alloys spray a lot of pre-treatment process , depending on the circumstances , such as the spatial location of plant condition that the size of the workpiece material ( cold-rolled plate , hot-rolled plate, galvanized sheet , aluminum , glass, steel , etc. ) , the surface condition ( corrosion , anti-rust oil , debris ) , production volume , quality requirements and other options . Different manufacturers use different processes . If the overall passenger car production processes and quality requirements is basically the same , pre-treatment processes generally have the following two ways:
1 , parts pre-treatment
The typical process:
Pre- degreasing degreasing → ??washing → ??I → II → pickling → ??washing → ??washing in and III → table adjustment phosphate → washing IV → passivation
Our factory can be adjusted to the actual situation :
As pretreatment parts , acid rust is essential. However, the former process , the best corrosion member and non- corrosion member separate pieces pickling corrosion , non- corrosion member is preferably not to be pickled .
2 , pre-treatment products
Pre-treatment of the entire product is immersed in the bath products for surface treatment , there are a lot of manufacturers to adopt . Transfer process between a manual control and automatic control of two . Is the use of more advanced PLC program automatic control, can realize automatic transfer between processes . General process is: degreasing → ??washing → table adjustment phosphate → washing .
Processing used before spraying device is a combination spray cleaning machine , by means of spraying the cleaning principle mechanical and chemical action , to complete degreasing , phosphating , passivation, cleaning processes .
Joint typical spray cleaning machine processes are: degreasing , washing, table transfer, phosphating , passivation , washed with pure water .
Its structure is characterized by: each step pre-treatment production line sprinkler pipe arranged in a tunnel , spray each sump pump to provide. Various processes have openings plate separated to prevent channeling fluid. The form of the heating tank heating tank and outside the tank . Within the heater exhaust pipe, coiled pipe , corrugated board, etc. ; outside heater tube , plate heaters. Heating medium hot water, steam , oil and so on. In degreasing , phosphating processes , respectively, with degreasing systems and slag removal system . To prevent the heating section of the tunnel openings at the top and overflow steam exhaust fan in the tunnel at the top with .
The process control elements are as follows :
1 , skim
Degreasing degreasing agent mechanism is by saponification of various oils , solubilizing , wetting , dispersing , emulsifying effect, so that grease from the surface from , the material becomes soluble or emulsified uniformly dispersed stably in the groove fluid . Quality is evaluated based on skim skim the surface of the workpiece can not have a visual oil, emulsions and other dirt , the surface should be washed thoroughly wetted by water as the standard . The quality depends skim free alkalinity , the temperature of the degreasing liquid , the processing time , mechanical and degreasing liquid oil and other factors :
( 1 ) free alkalinity (FAL)
Degreasing agents in order to ensure the best results the appropriate concentration . Generally only need to detect degreasing fluid free alkalinity , FAL is too low, degreasing effect is relatively poor ; FAL too high, not only caused material waste , but also to increase the burden of back- washing , pollution will be severe after the sequence tables reconcile phosphorus technology .
( 2 ) the temperature of the degreasing liquid
Any one have the best degreasing degreasing liquid temperature, the temperature is lower than process requirements, can not be fully degreasing effect ; temperature is too high , not only increases energy consumption, but also bring some side effects. Such as degreasing agent evaporates too quickly , the workpiece surface is dry from the bath due to faster , easily causing artifacts return to rust , alkali spots , oxidation and other ills affecting the quality phosphide after the procedure . Automatic temperature control also needs to be checked regularly .
( 3 ) Processing time
Degreasing liquid oil on the workpiece must be full contact , there is sufficient contact time in order to ensure a good degreasing effect . But skim too long, blunt workpiece surface will increase , affecting phosphate film formation.
( 4 ) the impact of mechanical action
Degreasing process, supplemented by mechanical action , using pump circulation or workpiece moves , it can strengthen the degreasing effect and shorten the immersion cleaning time ; spray skim skim faster than dipping more than 10 times faster .
( 5 ) degreasing liquid oil content:
With the recycling of the bath , bath oil content will continue to increase inside , when a certain percentage, the degreasing effect of degreasing agents and cleaning efficiency will be significantly decreased , even if the bath by adding the drug to maintain a high concentration , the surface to be treated the cleanliness is still not improved. Degreasing liquid has been aging deterioration , must replace the entire tank . Production is generally based on the use of bath time and processing workload timely exchange slot.
2 , acid
Product manufacturing rolled steel molding or storage in the transport process , the surface will produce rust. As loose rust layer structure , and substrate adhesion is not strong, and can be composed of iron oxide and aluminum primary cells, to further promote aluminum corrosion, the coating will soon be destroyed, so it must be before painting Ex . Product is commonly used pickling rust, it does not make aluminum workpiece deformation , corrosion every corner can be cleaned, rust fast , relatively low cost. Mainly after pickling pickling quality of the workpiece should not be seen visually oxides, rust and corrosion phenomena over the standard , the impact effect of rust main factors :
( 1 ) free acidity (FA)
Determination of free acidity of the pickling tank FA, is to verify the effect of the level of the pickling tank rust most direct and effective evaluation. Low free acidity , rust poor results. Free acidity is too high, the work environment mist larger content is not conducive to labor protection ; aluminum surface is easy to produce "over eclipse " phenomenon ; and residual acid cleaning more difficult, easily lead to subsequent contamination of the bath .
( 2 ) temperature and time
Most pickling is carried out at room temperature , when heated pickling , the general control between 40 ℃ ~ 70 ℃ , while the temperature of the pickling capabilities greater impact, but the temperature is too high will increase the workpiece , corrosion of the equipment , the impact of the work environment is also very unfavorable ; and in the complete removal of rust under the premise of pickling time should be as short as possible to reduce the aluminum corrosion and hydrogen embrittlement . Therefore, the process should be strictly controlled bath temperature and workpiece processing time.
( 3 ) Pollution aging
Acid in rust process, will continue to bring oil or other impurities , which can be suspended impurities fishing manner by scraping to remove ; when soluble iron ions above a certain level , the bath will not only greatly reduce the effects of rust , and the excess iron ions with the surface of the raffinate tank mixed phosphate , phosphate bath pollution accelerated aging, seriously affect the quality of the workpiece phosphate , general acid content of iron ions should be controlled in not more than 6 % 10% is appropriate. Control targets must be replaced over the bath .
3, Table tune
Surface modifier can remove the workpiece surface due to alkali degreasing or pickling rust caused by the unevenness of the surface condition , the aluminum surface to form a large number of fine crystalline center , thus speeding up the reaction rate phosphate , beneficial phosphate film formation.
( 1 ) Water Quality
Used bath water in the aquifer as a serious rust , calcium and magnesium ion content greater surface conditioning liquid will affect the stability of the bath can be prepared in advance to add a water softener to remove liquid water on the surface conditioning effects .
( 2 ) use of time
General Table transfers colloidal titanium salt is used , the existence of colloidal activity , when the use of longer or more impurities contained in the colloidal ions lose activity , time stable colloidal state is destroyed , bath layered sediment , were flocculent In this case you must replace the bath .
4 , phosphate
Phosphate is a chemical and electrochemical reaction to form phosphate chemical conversion coating process , the formation of phosphate chemical conversion film called phosphate coating . Bus Painting commonly used low-temperature zinc phosphating solution . Phosphide main purpose is to provide protection to the aluminum substrate , to a certain extent, to prevent corrosion of aluminum ; used primer before painting , to improve the film layer attached focus and corrosion resistance . Phosphate pre-treatment process is the most important aspect of the reaction mechanism is complex and influenced by many factors , so the phosphate bath relative to the other bath is much more complex production process control .
( 1 ) acid ratio ( total acidity and free acidity ratio )
Phosphate acid ratio improved to accelerate the reaction rate, the phosphate coating thin and delicate, but the acid ratio is too high layer is too thin , it can lead phosphate workpiece hanging gray ; acid ratio is too low, the reaction is slow phosphide , phosphorus of crystal thick porous , corrosion resistance is low, prone to yellow rust phosphating workpiece . Generally phosphating liquid system or a different formula than the size of its acid requirements are also different .
( 2) Temperature
An appropriate increase in the bath temperature , film speed, but the temperature is too high, the changes will affect the acid ratio , thereby affecting the stability of the bath , while thick film nuclei , increasing the amount of the slag bath .
( 3 ) the amount of sediment
As the reaction continued for phosphate , the bath will gradually increase the amount of sediment , the excess sludge can affect the surface of the interface reaction , resulting phosphate film blur, gray hanging serious , or even film , so bath to according to the amount of the workpiece handling and use of timely trough time for slag desludging .
( 4 ) nitrite NO-2 ( accelerator concentration )
NO-2 can accelerate the phosphating reaction speed, increase the density of phosphate coatings and corrosion resistance , the content is too high to make the film prone to the phenomenon of white spots or hair color ; too low, the film is slow , phosphate coating Yi raw yellow rust .
( 5 ) SO2-4 sulfate
Acid concentration is too high or washing lotion are easily lead to poor control of phosphate bath of sulfuric acid ions increased , the high phosphate sulfate ions will slow down the reaction rate, the coarse grain porous phosphate film , hanging ash serious , phosphate coating corrosion resistance decreases.
( 6 ) ferrous ions Fe2 +:
Phosphating solution containing ferrous ions is too high , makes the room temperature phosphate coating corrosion resistance decreased ; make phosphate coating coarse grains in the temperature , the surface floating lime , corrosion resistance decreased ; phosphating sludge will increase in volume and temperature large , the solution becomes cloudy , and the free acidity increased.
5 , passivation ( closed )
The purpose of the passivation film is a closed porosity phosphate , phosphate coating to improve the corrosion resistance , especially to improve the overall coating adhesion and corrosion resistance . The general use of chrome and chrome- containing treatment in two ways, however, some type of passivation with alkaline salts (most phosphate , carbonate , nitrite , phosphate, etc. ) , these substances serious damage paint film 's long-term adhesion and corrosion resistance .
6 , washing
The purpose of washing is to remove from the surface brought out on a bath residue , washed their quality can directly affect the quality of the workpiece and the entire phosphating bath stability. Washing bath generally control the following:
( A ) sludge residue content is not too high . Prone to high levels of ash hung workpiece surface .
( 2 ) the bath surface should be without suspended impurities. General washing method using overflow washing, in order to ensure the bath surface without suspended oil or other impurities.
( 3 ) PH value should be close to neutral bath . PH value is too high or too low are likely to cause bath string grooves , thus affecting subsequent stability of the bath .
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