The home appliance industry is a large application field of powder coating in China, and the powder coating technology is relatively mature. The powder coating production line for home appliances consists of four main equipment units, including pre-treatment equipment, moisture drying equipment, powder spraying equipment and powder curing equipment.
the home appliance industry is a major application area for powder coatings in china, and powder coating technology is relatively mature. the household appliance powder coating production line consists of four main equipment units, including pre-treatment equipment, moisture drying equipment, powder spraying equipment, and powder curing equipment.
The powder coating production line for household appliances has the following characteristics:
the powder coating production line for household appliances has the following characteristics:
1) High output, mostly continuous production;
1) high yield, mostly continuous production;
2) The workpiece is relatively light, and the suspension conveying method is mostly adopted
2) the workpiece is relatively light and is often transported by hanging;
3) The size of the workpiece is small, and most of them adopt single-point hanging mode
3) the workpiece size is relatively small, and most of them use a single point hanging method;
4) The structure of the parts is relatively simple, and the pre-treatment mostly adopts the spray structure;
4) the structure of the parts is relatively **and the pre-treatment mostly adopts a spray type structure;
5) The workpiece is mostly a cold plate, the rust is light, and there is no need to set up the rust removal process
5) the workpieces are mostly cold plates with light rust, and there is no need to set up an online rust removal process;
6) The production line is relatively simple, and the management and maintenance are relatively easy.
6) the production line is relatively **and management and maintenance are relatively easy.
1. Main equipment and process parameters.
1. main equipment and process parameters
1.1 Pre-treatment equipment.
1.1 pre processing equipment
1.1.1 Purpose and Function.
1.1.1 purpose and function
The purpose of pre-coating treatment is to remove oil, oxide scale, dust and other dirt from the workpiece to provide a good substrate suitable for coating. Its functions are mainly reflected in the following aspects: (1) enhance the adhesion of the coating film to the surface of the coated object;(2) Improve the protective performance of the coating film on the coated object;(3) Provide a smooth and good substrate surface for the coating film.
the purpose of pre-treatment before painting is to remove dirt such as oil, oxide skin, and dust from the workpiece, in order to provide a good substrate suitable for painting. its function is mainly reflected in the following aspects: (1) enhancing the adhesion of the coating film to the surface of the coated object; (2) improve the protective performance of the coating on the coated object; (3) provide a smooth and good substrate surface for the coating.
1.1.2 Pre-treatment form.
1.1.2 pre processing form
Pre-treatment can be divided into mechanical and chemical treatment, mechanical treatment includes: sandblasting, shot blasting;Chemical treatment includes: tank immersion type, spray type.
pre treatment can be divided into mechanical and chemical treatments, with mechanical treatments including sandblasting and shot blasting; chemical treatment includes tank immersion and spray.
1.1.3. Pretreatment process and typical process.
1.1.3 pre treatment process and typical processes
There are various pretreatment processes, and the following factors should be considered in the determination of the process:
there are various pre-treatment processes, and the determination of the process should consider the following factors:
1) Composition and composition of the substrate;
1) the composition and composition of the substrate;
2) The structural shape and surface state of the workpiece;
2) the structural shape and surface condition of the workpiece;
3) Composition and cleanliness requirements of surface soil;
3) the composition and cleanliness requirements of surface dirt;
4) Yield and quality requirements;
4) production and quality requirements;
5) Compatibility with the subsequent process.
5) compatibility with subsequent processes.
The main processes of pretreatment include degreasing, washing, surface adjustment, phosphating, washing, deionization washing and other processes. It can be increased or decreased according to the different workpieces, different products, and changes in the above five factors.
the main pre-treatment processes include degreasing, water washing, surface adjustment, phosphating, water washing, deionized water washing, and other processes. adjustments can be made based on different workpieces, products, and changes in the aforementioned five factors.
The plates in the household appliance industry are generally cold plates, with less oil pollution, and the degreasing process is generally set up with two stages, mainly zinc-based phosphating, and there are also silane treatment processes.
the boards in the home appliance industry are generally cold boards with less oil pollution. the degreasing process usually involves two steps, mainly zinc based phosphating. currently, some also use silane treatment technology.
The typical pretreatment process of household appliance powder coating is as follows:
the typical pre-treatment process for powder coating of household appliances is as follows:
1) The pre-coating treatment process of the water dispenser shell.
1) pre coating treatment process for the shell of a water dispenser
Hot water wash (30s, 50 65) Pre-degreasing (60s, 50 65) Degreasing (150s, 50 65) Water wash 1 (inline row) Water wash 1 30s, room temperature (RT) Water wash 2 (30s, RT) Fresh water direct spray Surface tone (30s, rt) Phosphating (150s, 50 60) Water wash 3 (30s, rt) Water wash 4 (30s, rt) Fresh pure water direct injection.
hot water washing (30s, 50-65 ℃)pre degreasing (60s, 50-65 ℃)degreasing (150s, 50-65 ℃)water washing 1 (direct discharge) →water washing 1 [30s, room temperature (rt)] water washing 2 (30s, rt) →fresh water direct spraying → surface adjustment (30s, rt) →phosphating (150s, 50-60 ℃)water washing 3 (30s, rt) →water washing 4 (30s, rt) →fresh pure water direct spraying.
2) Air conditioner shell coating pre-treatment process.
2) pre coating treatment process for air conditioner housing
Hot water wash (40s, 50 65) Pre-degreasing (80s, 50 65) Degreasing (120s, 50 65) Wash 1 (45s, rt) Wash 2 (50s, rt) Fresh water direct spray Surface tone (45s, RT) Phosphating (150s, 38 45) Water wash 3 (45s, rt) Water wash 4 (50s, rt) Pure water wash (50s, rt) Fresh pure water direct injection.
hot water washing (40s, 50-65 ℃)pre degreasing (80s, 50-65 ℃)degreasing (120s, 50-65 ℃)water washing 1 (45s, rt) →water washing 2 (50s, rt) →fresh water direct spraying → surface adjustment (45s, rt) →phosphating (150s, 38-45 ℃)water washing 3 (45s, rt) →water washing 4 (50s, rt) →pure water washing (50s, rt) →fresh pure water direct spraying.
3) A special coating pre-treatment process.
3) a special pre-treatment process for painting
Degreasing phosphating (90s, 120 140) water wash 1 (60s, 120 140) pure water spray (5s, RT) water wash 2 (60s, rt) pure water spray (5s, RT).
degreasing phosphating (90s, 120-140 ℃)water washing 1 (60s, 120-140 ℃)pure water spraying (5s, rt) →water washing 2 (60s, rt) →pure water spraying (5s, rt)
1.1.4. Design and layout of pre-treatment equipment.
1.1.4 design and layout of pre-treatment equipment
The pretreatment of the powder coating production line of household appliances mostly adopts spray structure, and the main equipment includes channels, liquid tanks, spray pipelines, heat exchange pipelines and exhaust systems, as shown in Figure 1.
the pre-treatment of household appliance powder coating production lines often adopts a spray type structure, with main equipment including channels, liquid tanks, spray pipelines, heat exchange pipelines, and exhaust systems, as shown in figure 1.
*。picture
1) Pre-treatment channel.
1) preprocessing channel
Channel structure: commonly used steel plate welding, internal baffle partition to prevent liquid splashing, there should be enough transition area to prevent liquid channeling, and set up a maintenance channel, which is conducive to replacing the internal nozzle and cleaning up the accumulated dirt inside the channel.
channel structure: commonly welded steel plates are used, with internal baffles to prevent liquid splashing. there should be sufficient transition areas to prevent liquid leakage, and maintenance channels should be set up to facilitate the replacement of internal nozzles and cleaning of accumulated dirt inside the channels.
Some channels are not welded, but replaced by bending, biting, gluing and other methods to save on-site welding workload.
some channels are not solderable and are replaced by methods such as bending, biting, and gluing to s**e on-site welding workload.
Channel length l = inlet and outlet length + spray zone length + transition section length.
channel length l=length of inlet and outlet+length of spray area+length of transition section
Spray zone length = process time process speed.
spray area length=process time × process speed
The length of the inlet and outlet is mainly determined according to the length of the workpiece, the length of the spray splash and the overflow of hot steamThe length of the transition section is determined by the length of the workpiece, the drip time, and the length of the spray splashThe width b is determined by the width f of the workpiece, and the installation distance of the sprinkler line needs to be considered.
the length of the inlet and outlet is mainly determined based on the length of the workpiece, the length of the spray splash, and the situation of hot steam overflow; the length of the transition section is determined by the length of the workpiece, dripping time, and spray splashing length; the width b is determined by the width f of the workpiece and needs to consider the installation distance of the spray pipeline.
The height h is determined by the height e of the workpiece, taking into account the installation method of the sprinkler line, and different installation allowances should be considered when the sprinkler main is installed at the top or bottom.
the height h is determined by the height e of the workpiece, while considering the installation method of the spray pipeline. when the spray main pipe is installed at the top or bottom, different installation allowances should be considered.
Key points in the design of the pre-treatment channel:
key points of pre-processing channel design:
The length of the transition section is appropriate, the front and rear leaching areas are set reasonably, and there is no channeling
the length of the transition section is appropriate, and the setting of the front and rear drainage areas is reasonable, without any liquid channeling phenomenon;
Proper opening of the door is conducive to observing the degreasing and phosphating effect, but it can not affect the product quality
opening the door appropriately is beneficial for observing the degreasing and phosphating effects, but it should not affect product quality;
The right length of the inlet and outlet prevents the spray from spilling out of the equipment and does not waste material
appropriate length of inlet and outlet to prevent spray liquid from splashing out of the equipment and not wasting materials;
The catenary running channel must be sealed to prevent the catenary from being corroded by hot gases.
the running channel of the suspension chain must be sealed to prevent the corrosion of the suspension chain caused by hot gas.
2) Liquid tank. 2) liquid tank
The volume of the liquid tank is determined by the flow rate of the spray pump and the internal heating device
the volume of the liquid tank is determined by the flow rate of the spray pump and the internal heating device;
The length, width and height are determined according to the size of the tunnel, the requirements of the operating surface, the installation form of the pump, etc.;
the length, width, and height are determined based on the tunnel size, operating surface requirements, and pump installation form;
Thermal insulation materials should be added to the hot tank with temperature requirements;
insulation materials should be added to heat sinks with temperature requirements;
The pump inlet should have a filter device to prevent the pump from clogging, and the heating heat source can be steam, electricity and natural gas.
the pump inlet should h**e a filtering device to prevent pump blockage, and the heating source can be steam, electricity, or natural gas.
Key points in the design of the liquid bath:
key points of liquid tank design:
The structure of the tank should be reasonable to prevent the degreasing foam and hot air from overflowing from the tank cover
the structure in the tank shall be reasonable to prevent the degreasing foam and hot gas from overflowing from the tank cover;
There should be a filter device in the tank to prevent the pump from clogging;
there should be a filtering device inside the tank to prevent pump blockage;
In order to save water consumption, the water washing tank should be able to meet the requirements of countercurrent water replenishment;
to s**e water consumption, the water washing tank should be able to meet the requirements of countercurrent water replenishment;
The design of the heater in the tank is reasonable, and other requirements such as installation and maintenance should be considered in addition to meeting the heating requirements.
the design of the heater inside the tank is reasonable, and in addition to meeting the heating requirements, other requirements such as installation and maintenance should also be considered.
3) Sprinkler lines.
3) spray pipeline
The number of nozzles is determined by the height of the workpiece and the spray requirements, the bottom nozzle is dispensable according to the shape of the workpiece, and the nozzle spacing is determined by the spray angle of the nozzle. The nozzle is usually V-shaped, hollow cone, which can be selected according to the situation.
the number of nozzles is determined by the height of the workpiece and the spraying requirements. the bottom nozzle can be optional according to the shape of the workpiece, and the nozzle spacing is determined by the spraying angle of the nozzle. nozzles usually h**e v-shaped or hollow conical shapes, which can be selected according to the situation.
The flow rate of the spray pump is determined by the total number of nozzles, and the spray pressure is calculated from the process requirements and the loss of the pipe.
the flow rate of the spray pump is determined by the total number of nozzles, and the spray pressure is calculated based on process requirements and pipeline losses.
The direction of the sprinkler line is determined according to the customer's preferences and Xi, and the upward or downward mode can be selected, each with its own advantages and disadvantages.
the direction of the spray pipeline is determined according to the customer's preferences and habits, and can be selected as either up or down, each with its own advantages and disadvantages.
The phosphate spray pipe should adopt a quick-release structure. There are horizontal and vertical spray pumps, and it is recommended to choose vertical pumps for phosphorus chemical level, and other stations can be selected at will.
the phosphating spray pipe should adopt a quick detachable structure. spray pumps come in both horizontal and vertical forms. it is recommended to choose a vertical pump for the phosphating station, while other stations can be freely selected.
Key points in the design of the sprinkler line:
key points in spray pipeline design:
The pressure and flow rate of the phosphating section must be reasonable in order to generate a good phosphating film
the pressure and flow rate of the phosphating section must be reasonable in order to generate a good phosphating film;
The phosphating spray line should be easy to maintain and clean.
the phosphating spray pipeline should be easy to maintain and clean.
4) Exhaust system.
4) exhaust system
The function of the exhaust system is to prevent the tank liquid vapor in the injection zone from spreading to the workshop;The exhaust air volume of the fan is determined by the amount of mixed gas overflow at the opening, and the air pressure of the fan is determined by the resistance of the air ductThe key point in the design of the exhaust system is that the liquid must not be pumped out and discharged.
the function of the exhaust system is to prevent the diffusion of tank liquid vapor from the spraying area to the workshop; the exhaust volume of the fan is determined by the amount of mixed gas overflow at the opening, and the wind pressure of the fan is determined by the resistance of the air duct; the key point in designing an exhaust system is not to extract and drain the liquid.
5) Flat layout.
5) plan layout
The factors that determine the layout of the pre-coating treatment plane are the size of the equipment, the direction of logistics, and the area of the plant.
the factors that determine the layout of the pre-treatment plan for painting are equipment size, logistics direction, and factory area.
The pre-treatment plane layout generally has straight-through type, U-shape, and L-type.
the pre-treatment plane layout generally includes straight through, u-shaped, and l-shaped.
1.1.5. Pre-treatment process operation and parameter control.
1.1.5 pre treatment process operation and parameter control
The important processes of pretreatment include degreasing, surface conditioning, and phosphating, and the control of process parameters is very important.
the important pre-treatment processes include degreasing, surface adjustment, and phosphating, and the control of process parameters is crucial.
1) Degreasing. 1) defatting
The degreasing mechanism is the saponification, solubilization, wetting, dispersion, emulsification and other effects of degreasing agents on various types of oils, so that the oils and fats are separated from the surface of the workpiece and become soluble substances or are emulsified, dispersed and uniformly and stably existing in the bath.
the degreasing mechanism is achieved through the saponification, solubilization, wetting, dispersion, and emulsification of various oils and fats by degreasing agents, thereby causing the oils and fats to detach from the surface of the workpiece, become soluble substances, or be emulsified, dispersed and uniformly and stably present in the tank liquid.
The evaluation standard of degreasing quality is that there should be no visual grease, emulsion and other dirt on the surface of the degreased workpiece, and the surface should be completely wetted with water after washing.
the evaluation standard for degreasing quality is that the surface of the degreased workpiece should be free of visual grease, emulsion, and other dirt. after washing, the surface should be completely wetted with water.
The quality of degreasing depends mainly on factors such as free alkalinity (FAL), total alkalinity (TAL), temperature of the degreasing solution, treatment time, mechanical action and oil content of the degreasing solution.
the quality of degreasing mainly depends on factors such as free alkalinity (fal), total alkalinity (tal), temperature of degreasing solution, processing time, mechanical action, and oil content of degreasing solution.
The main parameters of the degreasing process control:
the main parameters for controlling the degreasing process are:
fal(12～14)；
fal (12-14);
Temperature 50 65;
temperature: 50-65 ℃;
Time 30 150s;
time: 30-150 seconds;
Pressure 01～0.12mpa；
pressure range from 0.1 to 0.12 mpa;
Oil content 5 10g l;
oil content 5-10g/l;
tal 14～20；
tal 14-20;
The ratio of tal fal is 25。
the ratio of tal/fal is less than 2.5.
The test method of degreasing quality can be the water film method, the wiping method, and the test strip method.
the inspection methods for degreasing quality can be water film method, wiping method, or test **method.
The consumption of the degreasing solution is about 25 g m2 and should be replaced regularly.
the consumption of degreasing solution is about 25g/m2 and should be replaced regularly.
The spray pressure at the degreasing station is generally higher to facilitate clean and thorough degreasing.
the spray pressure at the degreasing station is generally higher to facilitate clean and thorough oil removal.
2) Tone. 2) table tuning
The surface conditioner can eliminate the unevenness of the surface state of the workpiece caused by alkali degreasing or pickling rust removal, so that a large number of ultra-fine crystalline centers can be formed on the metal surface, thereby accelerating the speed of phosphating reaction and conducive to the formation of phosphating film.
surface adjustment agents can eliminate the unevenness of surface conditions caused by alkaline degreasing or acid pickling rust removal on the workpiece surface, forming a large number of extremely fine crystal centers on the metal surface, thereby accelerating the rate of phosphating reaction and facilitating the formation of phosphating film.
The main parameters of the surface conditioning process control are pressure and pH value (8 9), and the concentration of surface conditioning liquid is generally controlled at 02%～0.3%, the water conductivity of the distribution tank should not be too high, generally 200 s cm. The consumption of surface conditioning is controlled at 05 2g m2, which needs to be replaced regularly (about a week).
the main parameters for controlling the surface adjustment process are pressure and ph value (8-9). the concentration of the surface adjustment solution is generally controlled between 0.2% and 0.3%. the conductivity of the tank water should not be too high, generally less than 200 μ s/cm. the consumption of the adjustment solution should be controlled between 0.5-2g/m2 and needs to be replaced regularly (about a week).
3) Phosphating. 3) phosphating
Phosphating is a process of chemical and electrochemical reactions to form a phosphate chemical conversion film, and the phosphate chemical conversion film formed is called a phosphate film.
phosphating is a process of chemical and electrochemical reactions to form a phosphate chemical conversion film, and the resulting phosphate chemical conversion film is called a phosphating film.
Phosphating is a very important part of the whole pretreatment process, and its reaction mechanism is complex and there are many influencing factors, so the control of phosphating bath is much more complex than that of other baths.
phosphating is an important part of the entire pre-treatment process, with a complex reaction mechanism and multiple influencing factors. therefore, the control of the phosphating tank liquid is much more complex compared to other tank liquids.
The parameters that need to be controlled in the phosphating process are pressure, total acidity (TA, generally 13 32 points H+ concentration), free acidity (FA, generally 0.).3 or so, H+ concentration), temperature (low temperature phosphating, below 50) pH value (zinc phosphating is 2 25. Iron phosphating is 4 45) The control of phosphate slag is below 500 700mg kg.
the parameters that need to be controlled in the phosphating process include pressure, total acidity (ta, generally 13-32 points h+concentration), free acidity (fa, generally around 0.3 points h+concentration), temperature (low-temperature phosphating, below 50 ℃)ph value (zinc based phosphating is 2-2.5, iron based phosphating is 4-4.5), and the control of phosphating slag is below 500-700mg/kg.
If the TA is too high, the phosphate film crystallization is rough and the sediment is moreIf the ta is too low, the phosphating reaction will slow down, the phosphating film will be difficult to generate, and the resulting phosphating film will be thin. Fa is high, the phosphating speed is slow, the film-forming time is long, and the phosphating crystals are coarse and porousIf the FA is too low, the phosphate film is thin, and sometimes the film cannot be formed.
ta is too high, the crystallization of the phosphating film is rough, and there is a lot of sediment; if ta is too low, the phosphating reaction slows down, *it difficult to form a phosphating film, resulting in a thin phosphating film. high fa, slow phosphating speed, long film formation time, coarse and porous phosphating crystals; fa is too low, the phosphating film is thin, and sometimes it cannot form a film.
The spray pressure and flow rate of the phosphating process have a great influence on the phosphating film formation, and the high flow rate and low pressure are conducive to the phosphating film formation. Phosphate slag also has a great impact on film formation, and the phosphate tank should be removed daily. The phosphate spray pipe should be connected with quick release, which is easy to remove slag.
the spray pressure and flow rate of the phosphating process h**e a significant impact on the phosphating film formation, and high flow rate and low pressure are beneficial for phosphating film formation. phosphating slag also has a significant impact on film formation, and the phosphating tank should remove slag daily. the phosphating spray pipe should be connected quickly and easily for slag removal.
During normal production, with the increase of the processing capacity of phosphorus chemical parts, the composition of the liquid medicine is constantly changing, so the main phosphate and accelerator need to be continuously supplemented. The consumption control of phosphating solution is generally as follows: the main agent is 10 16 g m2, and the accelerator is 25～5g/m2。
during normal production, as the processing volume of phosphating workpieces increases, the composition of the solution constantly changes, so the phosphating main agent and promoter need to be constantly supplemented. the consumption control of phosphating solution is generally 10-16 g/m2 for the main agent and 2.5-5g/m2 for the promoter.
The method of testing the quality of the phosphate film is to first make visual observation to check the hue, gloss and color of the phosphate film, and then use a 10 100 magnifying glass to observe and check whether the phosphate film is continuous, uniform, no rust spots, no white spots, no handprints, etc.
the quality inspection method for phosphating film is to first visually observe the color tone, luster, color, etc. of the phosphating film, and then use 10-100 × observe with a magnifying glass to check if the phosphating film is continuous, uniform, free of rust spots, white spots, fingerprints, etc.
The corrosion resistance test of the phosphate film can be titrated with copper sulfate, and no corrosion occurs for more than 1min.
the corrosion resistance of the phosphating film can be tested using copper sulfate titration, and it is qualified if there is no corrosion for more than 1 minute.
4) Wash. 4) water washing
The purpose of washing is to remove the residual liquid brought out by the workpiece from the previous process, and the quality of washing directly affects the quality of the sprayed workpiece and the stability of the whole tank liquid.
the purpose of water washing is to remove the residual liquid carried out by the workpiece from the previous process. the quality of water washing directly affects the quality of the sprayed workpiece and the stability of the entire tank liquid.
The parameters controlled by the washing process are pH, pressure, time, and a certain amount of overflow water is required at the same time.
the parameters controlled for the washing process are ph value, pressure, and time, and a certain amount of overflow water needs to be maintained simultaneously.
The key control points in the washing process are the first water wash after degreasing and the first water wash after phosphating.
the key control points of the water washing process are the first water washing after degreasing and the first water washing after phosphating.
In addition, the water of several washes needs to be changed frequently, especially the quality of the water in the final pure water wash, which generally has a salt content of 100mg l.
in addition, the water used for several washes needs to be changed frequently, especially the quality of the water in the last pure water wash tank. generally, the salt content should be less than 100mg/l.