Basic material of 1.2.2 powder electrostatic spraying
Indoor epoxy polyester powder coating. It is the main component of epoxy resin, polyester resin, curing agent, pigment, filler, additives (such as leveling agent, curing agent, corner modifier). After heating curing powder on the surface of the workpiece to form coating. Auxiliary material is compressed air, clean and dry, oil free water content of less than 1.3g/m3, oil content of less than 1 * 10-5% (mass fraction)
Construction technology of 1.2.3 powder electrostatic spraying
Electrostatic high pressure 60-90kV. The high voltage is easy to cause the powder rebound and edge pitting rate of the powder of low voltage is too low.
Electrostatic current 10 ~ 20 A. The current is too high to produce discharge breakdown powder coating; the current is too low and the powder rate is low
The faster the velocity of flow pressure 0.30-0.55MPa. the higher the deposition rate of the powder is, the faster the thickness of the coating can be obtained, but it will increase the amount of powder and the wear rate of the gun.
Atomizing pressure 0.30 ~ 0.45MPa. Proper increase of atomization pressure can keep the thickness of powder coating even, but it will make the powder feeding parts wear quickly. It can improve the covering ability of the powder by reducing the atomization pressure, but it is too low to make the powder feeding parts blocked.
Gun pressure 0.5MPa. Gun pressure is too high will accelerate the wear of the gun head, too low and easy to cause the gun plug.
Fluidization pressure of powder feeding barrel 0.04 ~ 0.10MPa. The fluidization pressure is too high to reduce the density of powder, so that the production efficiency is reduced.
The distance from the nozzle to the workpiece is 150 ~ 300mm. If the distance from the nozzle to the workpiece is too close, the powder coating is easy to produce discharge breakdown.
Conveyor chain speed 4.5 ~ 5.5m / min. The speed of the chain is too fast, and the thickness of the powder coating is not enough.
The main equipment of 1.2.4 powder electrostatic spraying
Spray gun and electrostatic controller
In addition to the traditional built-in electrode needle, the outer ring ring is additionally arranged to make the electrostatic field more uniform to keep the thickness of the powder coating uniform. The electrostatic controller generates the required electrostatic high voltage and maintains its stability, the fluctuation range is less than 10%.
Powder feeding system
The powder feeding system is composed of a new powder barrel, a rotary screen and a powder feeding barrel. The powder coating is added to the new powder barrel, and the compressed air passes through the micropores on the fluidization plate at the bottom of the new powder barrel, and then the powder is pre fluidized. The powder particles (100 m above) are separated by the rotating screen, and the remaining powder falls to the powder feeding barrel. The powder barrel is used to supply the spray gun to the spray gun through the powder pump and the powder feeding tube.
In addition to part of the powder spray gun to the surface of the workpiece (generally 50% ~ 70%, the company is 70%), the rest of the natural settlement. A part of the powder in the process of settlement is collected by the cyclone collector of the side wall of the powder spraying chamber, and the powder particles (12 m above) are separated by the centrifugal separation principle and then sent to the rotary screen to be reused. The powder particles below 12pom are sent to the filter recovery unit, wherein the powder is compressed by the pulse compressed air to the bottom of the filter core collection bucket, and this part of the powder is cleaned regularly for sale. The clean air which separates the powder (containing the powder particle size less than 1 m, the concentration is less than 5g/m3) is discharged into the powder spraying chamber to maintain the micro negative pressure in the powder spraying chamber. The negative pressure is too big to be easy to absorb the dust and impurities outside the powder, the negative pressure is too small or the positive pressure is easy to cause the powder overflow. The powder which is settled at the bottom of the powder spraying chamber is collected and then used to enter the rotary screen through the powder pump. The mixing ratio of recycled powder and new powder is (1:3) ~ (1:1). Using the recovery system, the company's overall powder utilization reached an average of 95%.
The roof and wall panels are made of transparent polypropylene plastic material, so as to minimize the amount of powder adhesion and prevent static charge from interfering with electrostatic field. The bottom plate and base are made of stainless steel, which is easy to clean and has sufficient mechanical strength.
Air conditioner and dehumidifier. The role of the air conditioner is to keep the powder temperature below 35 degrees Celsius in order to prevent powder agglomeration; the two is through the air circulation (wind speed is less than 0.3m/s) to maintain the micro chamber pressure. The function of the dehumidifier is to keep the relative humidity of the spraying chamber is 45% ~ ~ 55%, and the humidity is too large, and the air is easy to produce the powder coating.
1.3.1 Fundamentals of powder curing
Epoxy resin, epoxy resin in the carboxyl group and the curing agent in the amine group condensation, addition reaction into large molecular network, while the release of small molecular gases (by-products). The curing process is divided into 4 stages for melting, leveling, gelation and curing. When the temperature rises to the melting point, the powder on the surface of the workpiece begins to melt and gradually forms a vortex with the internal powder until it is completely melted.
After the powder is melted, it begins to flow slowly, forming a thin and smooth layer on the surface of the workpiece. The temperature continues to rise somewhat short gel state at the gel point (after the temperature is kept constant), after the temperature continues to rise due to the chemical reaction curing powder.
1.3.2 Basic technology of powder curing
The powder curing process is 180 DEG C, bake 15min, is a normal curing. The temperature and time are the actual temperature of the work piece and the accumulated time which is not less than the temperature, not the setting temperature of the curing furnace and the walking time of the workpiece in the furnace. But the correlation between the initial equipment debugging requires the use of temperature tracker measuring the maximum workpiece, 3 surface temperature and accumulation time, and adjust the curing furnace set temperature and conveyor speed according to the measurement result (which determines the walking workpiece in the furnace time), until it meets the requirements of the curing process. So you can draw the correspondence between the two, so in a period of time (usually 2 months) only need to control the speed to ensure the curing process.
1.3.3 Main equipment for powder curing
The equipment mainly includes 3 parts: the heating burner, the circulating fan and the air pipe. The company uses the heating burner for Germany's products, using 0 ~ 35# light diesel oil. The utility model has the advantages of high heating efficiency and fuel saving. The first stage of the air supply pipe is opened at the bottom of the furnace body, and an opening is arranged at intervals of up to 600mm, with a total of three stages. This ensures that the temperature fluctuation within the range of 1 200mm workpiece is less than 5 DEG C, to prevent the workpiece from top to bottom color is too large. The return air pipe is at the top of the furnace body, so that the upper and lower temperature in the furnace body can be as uniform as possible. The furnace body is a bridge type structure, which is favorable for the preservation of hot air, and can prevent the air volume in the furnace from being reduced after the production is finished, so as to absorb the external dust and impurities.
After the curing of the workpiece, the daily inspection of the main appearance (whether or not smooth, with or without particles, shrinkage defects) and thickness (control in 55 ~ 90 m). If the initial commissioning or replacement of powder requires the use of the testing instrument and detection of the following items: appearance, gloss, color, thickness, adhesion (scribe), hardness (pencil method), impact strength, salt fog resistance (400H) and resistance (artificial accelerated aging), resistance. (1 000h)
1.5 finished product
After the completion of the classification of the goods placed in the transport vehicles, turnover box, the use of newspapers and other soft materials such as isolation, in order to prevent scratches and make the logo ready
2 Common problems and solutions of powder electrostatic spraying
2.1 Coating impurity
Common impurities are mainly derived from the particles in the dusting environment, as well as other factors caused by impurities, are summarized as follows.
(1)Impurity in curing furnace. The solution is to thoroughly clean the inner wall of the curing furnace with wet cloth and vacuum cleaner. If it is a large black particles on the need to check whether the supply air duct filter damaged, there is a timely replacement. !
(2)Dust indoor impurity. Is mainly dust, clothing fibers, abrasive and dusting system fouling equipment. The solution is to use the compressed air purge system before the start of each day, with a wet cloth and vacuum cleaner thoroughly clean the dust and dust.
(3)Suspended chain impurity. It is mainly the product of the suspended chain oil baffle and the water tray of a sling (the material is hot-dip galvanized plate). The solution is to clean up these facilities on a regular basis! }.
(4)Powder impurities. Powder additives are too many, uneven distribution of pigment, powder caused by the extrusion of powder points, etc.. The solution is to improve the quality of powder, improve powder storage and transportation methods.
(5)Pretreatment impurity. It is mainly caused by the large particle impurities and phosphating film yellow rust caused by a small piece of impurities. The utility model solves the problem that the slag in the phosphating bath and the spraying pipeline is cleaned in time, and the concentration and the proportion of the phosphating bath are controlled.
(6)Water impurity. Mainly used in the pre-treatment of water containing sand, salt content caused by excessive impurities. The solution is to increase the water filter, using pure water as the last two levels of cleaning water.
2.2 Coating shrinkage
(1)In the former, the shrinkage of the surface is caused by the addition of oil or oil, and the water is not clean. The solution is to control the concentration and proportion of the pre degreasing tank and degreasing bath, reduce the oil content of the workpiece and enhance the washing effect.
(2)Shrinkage caused by excessive oil content in water. The solution is to increase the intake filter to prevent water pump leakage.
(3)Shrinkage caused by excessive water content in compressed air. The solution is to release compressed air condensate.
(4)Shrinkage caused by damp. The solution is to improve the powder storage and transportation conditions, increase the dehumidifier to ensure the timely use of recycled powder
(5)The hanging chain oil by air blown off to the workpiece caused by shrinkage. The solution is to change the position and direction of the air outlet.
(6)Shrinkage caused by mixing powder. The solution is to change the dusting system
2.3 Coating color
(1)Color difference caused by uneven distribution of powder pigment. The solution is to improve the quality of powder, to ensure that the powder L, a, B little difference and positive and negative unity.
(2)Color difference caused by different curing temperature. The solution is to control the setting temperature and the chain speed, to maintain the consistency and stability of the curing temperature and time.
(3)Color difference caused by uneven coating thickness. The solution is to adjust the parameters of the powder injection process and ensure that the equipment is running well to ensure the uniform thickness of the coating.
2.4 Poor adhesion of coating
(1)The water treatment is not completely caused by the residual adhesion agent, phosphating residue or water bath is caused by alkali pollution. The solution is to strengthen the washing, adjust the degreasing process parameters and prevent the degreasing liquid into the water bath after phosphating.
(2)The phosphating film is yellow, or no local flooding caused by the poor adhesion of phosphating film. The solution is to adjust the concentration and proportion of phosphating bath to improve the phosphating temperature.
(3)The workpiece edge water is not dry and cause poor adhesion. The solution is to improve the drying temperature
(4)Poor adhesion of the coating caused by insufficient curing temperature. The solution is to improve the curing temperature
(5)The oil content and salt content of the deep well lead to poor adhesion. The solution is to increase the water filter, using pure water as the last 2 cleaning water.
Today is the powder electrostatic spraying technology, we hope to help