Application of powder electrostectrectrectration coating process in protective equipment

Abstract: This paper introduces the process of static coating of powder in protective equipment, including equipment composition, process flow, factors affecting the quality of coating, quality testing of coating, common problems and solutions.
keywords: protective equipment; powder static coating; pre-treatment; curing; troubleshooting
0 foreword
The author's company's protective equipment is widely used in homes, commercial places and other places, but also some used in underground or semi-subterranean forework, not only for appearance decoration and economy has higher requirements, but also for corrosion resistance and self-weight requirements. In order to improve the appearance quality, prevent surface corrosion, enhance market competitiveness, the use of aluminum alloy as the base material for protective equipment, and safe and environmental protection, cost-effective, energy-saving, coating performance excellent powder electrostitive coating process for surface treatment .
1 equipment composition
powder electrostitive coating equipment mainly includes high-voltage generator, spray gun, powder supply system, powder room, curing device, recycling device, conveyor system, auxiliary system and so on.
1.1 High-voltage generator
high-voltage generator is the key to powder electrostectrective spraying, it makes the charged powder particles and the work piece between the power difference, in the high voltage action ordered the powder adsorption on the work piece and form a paint film. Voltage directly affects the amount of powder attachment, generally controlled at 60 to 80kV, too high easy to cause powder rebound and edge hemp point, too low powder rate is low.
1.2 Spray Gun
Is the main equipment for powder electrostitectrecturization, which uses voltage to atomize and diffuse negatively charged powder particles and attach them to positive work pieces. The powder rate is mainly determined by the distance, angle, nozzle model, powder rate, etc. between the gun head and the work piece. Different nozzles should be selected according to different work pieces to achieve a uniform atomization effect.
1.3 powder supply system the
supply system consists of an air pressure pump, a powder supply barrel and a pipe. The new powder in the powder barrel is piped into the spray gun under air pressure, which directly affects the amount of powder, which in turn affects the thickness of the coating. Uniform and stable powder is a strong guarantee of uniform coating, air pressure is generally controlled at 0.30 to 0.45MPa.
1.4 powder room
powder room is the key equipment to ensure the quality of coating, powder room must maintain air flow balance, adequate lighting, the inner wall using easy-to-clean PP board, and the use of vacuum cleaner to clean, to maintain the dust content of the powder room, so that it is lower than the explosion limit (10g/m3).
1.5 curing device
curing device using a fuel heater, in conjunction with the circulating fan, to maintain a uniform temperature, to ensure that the sprayed work parts at (180±5) degrees C of temperature even curing 20min.
1.6 Recycling device
using a large cyclone secondary recovery device, the spray gun sprayed out did not go up to the work part of the powder is the air flow generated by the centrifuge fan into the large cyclone separator, the larger powder particles are separated, into the collection box, these powders filtered by vibration filter and recycled into the powder tank recycling.
1.7 conveyor system
using a hanging conveyor chain to send the work piece directly to the powder chamber, after spraying directly to the curing furnace, according to different requirements to adjust the chain speed, generally 4.5 to 5.5m/min, to ensure curing time and spray quality.
1.8 Auxiliary system
the auxiliary system has an air compressor and an oil-water separator. Air compressor is the only facility to produce compressed air, in order to make the coating evenly atomized, to ensure a good coating, but also must be equipped with oil and water separators, in order to meet the output compressed air very clean requirements.
2 Process Description
2.1 Process
Chemical de-oiling→ flowing hot water washing→ flowing cold water washing→ alkali erosion→ flowing hot water washing→ flowing cold water washing→→ Chemical light → flow cold water washing→ flow cold water washing→ drying→ electrostitive powder coating→ curing→ cooling→ classification inspection→ into storage.
2.2 pre-treatment
treatment quality is not easy to cause coating film shedding, shrink holes, stains and other defects. In order to improve the binding force between the metal substate and the coating, pre-treatment is carried out.
Since the parts to be coated are aluminum products, in order to remove dust, oil, metal oxides, minor scratches and other defects, the following pre-treatment is required: chemical de-oiling→ flowing hot water wash (60 to 70 degrees C, 1 to 2min, the same below → flow cold water washing (room temperature, 1 to 2min, the same between 1 and 2min) →bly corrosion→ flowing hot water washing→ flowing cold water washing →chemical lighting→ flowing cold water washing → flowing cold water washing→ drying. The following is a 1m3 slot as the standard, indicating the groove composition and operating conditions of each operation.
2.2.1 Chemical de-oiling
105 cleansing agent 5 to 8mL/L
sodium carbonate (Na2CO3) 20 to 40g/L
phosphate tripodium (Na3PO4.12H2) O) 20 to 40g/L
temperature 60 to 80c
time 7 to 10min
2.2.2 alkaline erosion
naOH) 10 to 20g/L
temperature 60 to 80 degrees C
5 to 15min
2.2.3 Chemical light
nitric acid (HNO3) 300 to 400mL/L
room temperature
10 to 20 s
2.3 electrostitive spraying
electrostectrical spraying is a kind of electrostitive action, so that the powder is evenly adsorbed to the surface of the work piece, forming a powder coating surface treatment method, it has good corrosion decoration, high paint utilization rate, safety and efficiency advantages, has been widely used in various industries.
2.3.1 Precautions when spraying
(1) Before spraying, check whether the spray gun powder is smooth, whether there is a leak, static sprayer ground must be good.
(2) electrostitive powder coating is loaded into a vibrational automatic sieve, filtered into the powder supply barrel under clean air pressure.
(3) for large servings, long-distance spraying, voltage of 60 to 80kV, for re-injection or when static shielding is more serious, low voltage should be used, generally 30 to 50kV.
(4) atomized air pressure is generally adjusted to 0.30 to 0.45MPa.
(5) the gun is generally 150 to 300mm away from the work piece, while working to maintain the spray gun and the work piece plane vertical, before and after the movement rate of 0.1m/s, uniform speed up and down re-spraying.
(6) For places where spraying is not required, cover it with workwear.
(7) to ensure that the powder barrel is insulated from the ground, the powder deposited on the gun and the arm of the gun should be cleaned in a timely manner.
(8) often replace the powder supply tube.
(9) sprayed work parts in a timely manner to check the appearance of the work surface whether there is leakage or uneven spraying. If so, wipe off with a microfibre towel or blow off the powder from the work piece with clean compressed air and re-spray it.
2.3.2 The curing of the powder coating
puts the sprayed work parts in the oven, heats them to a predetermined temperature (180 to 200 degrees C), and keeps them warm for the corresponding time (10 to 20min), so that the powder melts, levels, cures and cools them naturally. Note:
touch the spray site and the violent vibration workwork before baking (1) by hand.
(2) oven seal insulation, and the use of a hot air circulation system, so that the internal air flow to each other, to ensure uniform temperature.
(3) after each shift to use a vacuum cleaner to clean the oven, to ensure that the oven is clean, and dedicated to baking.
2.3.3 Appearance Quality Check
After cooling according to the following appearance quality requirements for 100% inspection:
(1) coating film should be flat, smooth, no significant color difference.
(2) no leakage is allowed.
(3) does not allow obvious orange peel, pinholes, shrink holes, scratches, bruises and other phenomena.
2.3.4 Factors that affect the quality of coating
In addition to pre-treatment, factors affecting coating quality include powder resistivity, gun movement rate, spray voltage, spray distance, powder amount, spray time, etc.
2.3.4.1 Powder resistivity
The resistivity is too low, the charged particles on the work piece are prone to loss of charge; The ideal powder resistivity is 1010 to 1016 s/cm.
2.3.4.2 Gun movement rate
The gun movement should be uniform, the rate is generally controlled at about 0.1m/s, the upper and lower spacing does not leave a neutral, to avoid the appearance of spray and leakage.
2.3.4.3 Spray voltage
voltage has a greater impact on the powder rate, generally controlled at 60 to 80kV. When the voltage is too low, the powder rate is low, the amount of powder attachment after the voltage is higher than 90kV is also reduced, and it is easy to cause defects such as pinholes and shrink holes.
2.3.4.4 spray distance
spray distance mainly affects film thickness, generally controlled at 150 to 300mm. Increased distance can affect film thickness and efficiency, and shorter distances make it easy to discharge through the coating.
2.3.4.5 powder spray
the amount of powder mainly affects film thickness and deposition rate, generally controlled at 50 to 200g/min, when the amount of powder spray is small, the deposition efficiency is higher.
2.3.4.6 Spray time
The spray time and spray voltage, spray distance, powder amount and other parameters affect each other. When the spraying distance is large and the spray time is extended, the effect of spray voltage on the film thickness limit is reduced, and with the extension of spray time, the effect of the spray amount on the film thickness growth rate is significantly reduced.
3 coating performance detection
3.1 salt spray resistance
using (50±5) g/L, pH 6.5 to 7.2 sodium chloride solution, at (35±2) degrees C temperature conditions for the work parts first 24h spray, then dry 24h, 2 cycles a total of 96h. After the test, the quality of the coating film was observed, and the foaming and rusting degree of the coating met the level 2 stipulated in Articles 4.5 and 4.6 of GB/T1766-2008 "Rating Methods for the Aging of Color paint and varnish coatings".
3.2 coating thickness
a special thickness gauge is used to measure 5 points above 10mm apart on the work piece, taking an average. The coating thickness is required to be between 50 and 100 m.
3.3 Adhesion
Test coating adhesion in accordance with GB/T9286-1995 "Scratch Test of Color paint and varnish paint film", requiring at least 2 levels.
3.4 Impact Resistance
tested according to GB/T1732-1993 Paint Film Impact Resistance Determination Method, which is qualified without cracks after a high impact of 1kg at a height of 50cm.
4 Common problems and solutions
common problems and solutions to powder electrostectrecture coatings can be found in Table 1.
5 conclusion
after many tests, groping, the company's aluminum alloy substrate protection equipment powder electrostitectrative coating process is stable. 3 years of practice has proved that the pass rate of more than 95%, in order to ensure the quality of products and enhance its market competitiveness has made a certain contribution.