How to switch from oily paint to water-like paint from metal coating line!

According to the relevant national environmental protection requirements, industrial enterprises to achieve full emission standards. With the technical improvement of coating performance in recent years, the price of water-based coatings for metal parts has gradually decreased, and the cost of painting is only about 25% higher than that of oily paints, but the VOCs concentration of water-based coatings is lower. Under the premise of ensuring product quality, the generation and emission of VOCs can be controlled from the source to meet environmental

. Let's take an application enterprise as an example and see how they make a change.
Refitting difficulties
there are 5 main difficulties in transformation: (1) oily paint and water-based paint spraying process differences, changes, (2) the existing coating wire structure size has certain limitations, the transformation design program is difficult; (3) Renovation site, heavy workload, the need for transmission lines, leveling room, paint room, side sprayer, fire system and gas pipeline, such as transformation; According to the water-based paint work process, combined with the existing line body layout, determine the most reasonable process plan (Table 1).
Renovation Program
The original DISK spray room was converted into a paint room and preheat section
(1) to remove the DISK (automatic electrostectrical spraying equipment) spray room, converted into a paint room and preheat room (warm-up time 1.5min), through preheat to improve the surface temperature of the work parts (20 to 40 degrees C), to meet the primer spraying requirements. (2) Paint room material 1.5mm galvanized plate production, the internal use of 10 type steel skeleton painting treatment, to ensure the strength of the steel structure. Set fire doors, observation window 5.0mm tempered glass, paint room built-in explosion-proof purification lighting, the ground laid 3mm non-slip, anti-static pattern aluminum plate. (3) Paint room using the existing coating line for wind turbine supply, increase the exhaust fan and exhaust pipe, exhaust pipe using 1mm galvanizing plate, access to the existing exhaust system. In order to facilitate painting, the interior of the paint room added pure water into the drainage line, the in-water line from the previous treatment of pure water washing out, drainage line and ash chamber sink connection. (4) Paint room installation air conditioning, to prevent the winter temperature is too low, water-like paint icing. (5) The preheating device adopts the electric ceramic heating tube, uses the Fuji thermostat control, the heating temperature is 20 to 40 degrees C, the heating time is less than 10min. (6) Preheat room body galvanized plate laying 50mm insulation cotton and inner plate (density 80kg/m3), furnace body seam 400mm temperature at room temperature of 15 degrees C, to prevent heat loss and burns.
paint room, primer leveling into a flash drying furnace
(1) the existing primer leveling room and paint room transformed into a flash dry room, size 8000mm×5800mm×4000mm, flash drying temperature 50 to 80 degrees C, to meet the primer sprayed after the table dry, dry and cooling process requirements. (2) Flash dry room peripheral plate with 1.5mm galvanized plate, insulation layer 100mm, density of 80kg/m3, the internal use of 10 x type steel skeleton as a support, furnace body seam 400mm temperature at room temperature of 15 degrees C. The exhaust gas of the exhaust gas combustion unit using the existing paint curing furnace is preheated and the temperature is controllable. In addition, a gas heating device and control system have been added, and the two heating methods are used in complementary ways to save energy and meet the process temperature requirements. (3) Flash dry room import and export set heat insulation plate and air knife, air delivery using high-pressure fan, to prevent heat outside the furnace to the primer, paint spray room. The cooling section is set at the rear end, and the temperature of the workware entering the paint room drops to about 40 degrees C. (4) The hot air circulation system consists of furnace body, return air pipe, exhaust gas discharge system, bottom frame, inner frame, etc., and cycles 2 to 3 times per minute: (1) the furnace body independently sets the heating furnace, the hot air circulates through the fan; Steel connections should be minimized between the outer plate of the drying channel and the frame to reduce heat transmission. The inner plate of the furnace plate is 1mm galvanized steel plate and the outer plate is 0.8mm colored steel plate, the color is consistent with the rest of the wire body; Among them, temperature control uses two-point temperature measurement, single-point temperature control mode, set the over-temperature protection switch to protect the combustion system, in case of over-temperature or fan failure to shut down the heating system in time and issue a sound and light alarm signal, and set up a low-temperature alarm signal device. Electrical interlocks should be installed between the burner and the circulating fan to ensure proper operation. (5) Heating system structure: (1) combustion chamber according to aerodynamics, thermal engineering and other design calculations, reliable operation; The return ducts are all down to the top, and the top of the oven is covered with circulating pipes, which are cycled at the bottom of the furnace body by means of a circulating fan extraction method. The heat in the furnace is circulated through the return pipe in the furnace, stirred fully to maximize the use of heat, and (3) the burner selects a hundred products with a heat of 627600kJ. Burner and gas pipe cut-off valve connection line to set up pressure relief valve, filtration device, etc. , (4) hot air circulation fan using special high temperature resistance, low noise plug-in fan, wind volume of 360m3/h, fan built into the greenhouse body (bearing external), installation position to leave maintenance space. (6) the wind pipes are made of 1mm galvanized steel plate, external strengthening and insulation measures. Exhaust fan selection of domestic well-known brand products, exhaust pipe into the exhaust system. (7) The contents of the transformation conform to the standards of steel structure installation specifications and relevant national technical standards.
conveyor
(1) adds 21m conveyor chains and tracks in the preheating and flash dry segments to meet the water-specific paint spray heating and leveling time requirements. (2) Change the running trajectory of the transmission chain of the warm-up segment to meet the preheat conditions of the work parts. (3) The increased conveyor chain should use QXT-250 two-wheel guide suspension chain, a single lifting point load of 50 kg, hanging spacing 750mm. Track QXT-250, curved rail material 16Mn, horizontal radius of 600mm, to ensure that the work piece does not interfere when turning. (4) Add a lifting plate, C-hook, fixed fuel-saving plate, cross fork, round fuel-saving plate, oil tank and other conveyor chain accessories. (5) Adjust the drive and tightening device to ensure that the whole line runs smoothly after the chain lengthens, no crawling and obvious jitter.
conclusion
after the technical transformation of the coating line has been put into use for nearly a year, the whole line runs smoothly, the product surface spray quality to meet the process requirements. The emissions were continuously detected, with the results as: 0.72 mg/m3 of the main components of VOCs, 7.35 mg/m3 of non-methane total hydrocarbons, 0.00mg/m3 of benzene, 5.00mg/m3 of toluene, and 0.00mg/m of xylene. This shows that after the transformation of the spraying process emissions to meet GB16297-2018 "comprehensive emission standards of atmospheric pollutants" related requirements.