With the wide application of aluminum profiles in the decoration industry, the surface treatment technology of aluminum profiles has also developed rapidly. Electrostatic spraying and electrophoresis painting is one of the most advanced aluminum profile treatment processes that has developed rapidly in recent years. The advantages of electrostatic spraying: energy saving, environmental protection, pollution-free, high production efficiency, easy automatic production, a variety of product colors, can meet the color individual needs of different customers. The advantages of electrophoretic coating: high surface finish, brilliant color, and the surface of the product is covered with a layer of lacquer solvent, which is more corrosion-resistant than general oxidized aluminum alloy profiles. According to the project budget, the investment in electrostatic spraying and electrophoretic spraying production lines is about the same. Generally, medium-sized aluminum profile companies have: furnace-backlog-oxidation production lines, but few companies can use both electrostatic spraying and electrophoretic painting production lines at the same time. If it is possible to produce products similar to electrophoretic paint through electrostatic spraying and oxidation coloring processes, it will reduce investment and increase equipment utilization, which is also a new technological innovation. After a year of process testing, the product was realized and can be industrialized.
1. Production process requirements
1.1 Equipment requirements
A. Aluminum alloy profile melting furnace-extrusion-oxidation coloring production line
B. Electrostatic spraying production line
C. Inspection equipment for aluminum alloy profile products, surface film thickness and coating adhesion, etc.
1.2 Process flow for the production of polished crystal aluminum profiles
Feeding of formed aluminum alloy profiles → degreasing → water washing → alkaline washing → delustering → oxidation → coloring → semi-sealing → electrostatic spraying → drying → packaging
In the production process, each process must be cleaned with water to prevent pollution and increase the use time of the bath. The key processes are: coloring → semi-sealing → electrostatic spraying. Each process is strictly controlled according to the process.
1.3 Requirements for each process
A. Degreasing: 100-150g/L (mass concentration) H2SO2: time 3-5 minutes
B. Alkaline washing: 45-85g/L (mass concentration): 5-15 minutes. If the mechanical lines on the surface of the profile are slight, the alkaline washing time can be reduced.
C. Light emission: 200-250g/LH2SO2 (mass concentration), 3-5g/LH2NO3, which neutralizes and improves the surface finish of the profile.
D. Oxidation coloring: 150-180g/LH2SO2 (mass concentration) is the oxidizing conductivity liquid, the coloring liquid is stannous salt and nickel salt, and the color material is golden champagne color.
E. Semi-sealing: a key process. The process requires sealing at room temperature, with an oxide film of 1 μm and sealing for 1 minute, but the film cannot be completely sealed here, and half of the film holes must be left to absorb the electrostatic spraying powder.
f. Electrostatic spraying: automatic spraying spray booth, the spraying agent is high-gloss transparent polyester powder, it becomes milky white, and it is covered on the surface of the profile and dried into a crystal transparent color, smooth and shiny, and the background color of the oxidized golden betel profile is set off. The color is brilliant, crystal clear, no less than electrophoretic painted aluminum products.
g. Drying and packaging: the constant temperature in the drying room is 180 degrees, and the drying time is 2 minutes. The aluminum products from the drying room are cooled to 40-50 degrees with cold air, and the quality of the products is manually inspected. It must be handled with care when packing materials to prevent bumps.
2. Product inspection
2.1 Inspection method
The test of film layer performance should be carried out after the coating has been cured for 24 hours. A. Coating thickness monitoring method:
Use a film tester to monitor the thickness of the coating.
B. Coating impact test method:
Using a punch with a diameter of 16mm, place the heavy hammer at an appropriate height and drop it freely, directly impacting the surface of the coating to produce a pit with a depth of 2.50.03mm. Observe the change of the coating.
C. Coating adhesion test method:
Draw a grid on the surface of the coating with a spacing of 2mm, and then peel it off with tape to observe whether the coating falls off.
D. Cupping test method
Use the spherical tip of the punch to advance to the sample at a constant speed of 0.2-0.1mm per second until the specified 0.750.05mm, and observe whether the coating has fallen off or separated from the profile.
2.2 Inspection equipment
A. ED-200 Eddy Current Thickness Gauge
B. Impact tester
C. Cupping tester
D. 4 times magnifying glass (for observation)
2.3 Test results
According to the national inspection standards for aluminum alloy powder coating profiles, crystal-finished aluminum profiles can fully meet the requirements for use.
Test table for crystal over-light profile products
The quality of the product did not show any quality problems during the use period. After one year of testing, the profile was placed for one year, and the surface was still smooth and transparent, and the test was level 0. There is no fading or peeling phenomenon, the film layer is thicker than the electrophoretic coating film, the cost is basically the same, and the oxidation-spraying production line is organically combined to avoid the isolated production of equipment.
The production process of crystal over-glazed aluminum profile is relatively complicated, and it is sprayed throughout the oxidized and colored scenic spots; the process must be strictly controlled in order to produce high-standard products and be accepted by customers.
Link to this article：Method for producing crystal glazing for aluminum profile by electrostatic spraying process
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