What is powder coating

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Plastic spraying is a surface treatment method in which plastic powder is sprayed on parts. Plastic spraying is the electrostatic powder spray coating that we often talk about, and its treatment process is a more commonly used decorative technology of metal surface treatment since the 1980s. Compared with ordinary spray paint surface treatment, this technology has the advantages of advanced technology, energy saving, high efficiency, safety and reliability, beautiful color and so on. Therefore, it is often used in the field of light industry and home decoration. Its working principle lies in charging plastic powder through high-voltage electrostatic equipment, spraying paint on the surface of the workpiece under the action of an electric field, and the powder will be uniformly adsorbed on the surface of the workpiece to form a powder coating; Leveling and curing after high temperature baking, the plastic particles will melt into a dense final protective coating with different effects; firmly adhere to the surface of the workpiece. [1]
Chinese name: spraying plastics, foreign name: spraying plastics, electrostatic spray property. A surface treatment method defines the use of an electrostatic generator to charge plastic powder at 180 ~ 220 ℃.
table of Contents
1 Definition
2 Electrostatic spraying
▪ Advantage
▪ Process principle
▪ Process flow
3 Inspection Standards for Plastic Spray Products
definition
The plastic powder is charged through a high-voltage electrostatic device. Under the action of an electric field, the coating is sprayed on the surface of the workpiece, and the powder is evenly adsorbed on the surface of the workpiece to form a powdery coating. After the powdery coating is baked at high temperature, Leveling and curing, the plastic particles will melt into a dense final protective coating with different effects; firmly adhere to the surface of the workpiece, [1] plastic sprayed products are mostly used for indoor use, the paint film is flat or matte effect. The spray powder is mainly acrylic powder, polyester powder, etc.
Electrostatic spray
Electrostatic spray
Electrostatic spraying
Advantage
No thin material is needed, and the construction has no pollution to the environment and is non-toxic to human body. The coating has excellent appearance quality, strong adhesion and mechanical strength; the spraying construction has a short curing time; the coating has a much higher resistance to corrosion and abrasion; no primer is needed; Simple construction, low technical requirements for workers; cost is lower than spray painting process; some construction occasions have explicitly proposed that electrostatic spraying process must be used for processing; the flow phenomenon common in spray painting process does not occur during electrostatic dust spraying.
Process principle
The corona discharge phenomenon is used to make the powder coating adhere to the workpiece. The process is as follows: The powder coating is sent to the spray gun by the powder supply system by compressed air gas. The high voltage generated by the high-voltage electrostatic generator is added to the front end of the spray gun. Due to the corona discharge, a dense charge is generated near the powder. When sprayed, charged paint particles are formed. It is attracted to the opposite polarity of the workpiece by the electrostatic force. As the powder sprayed increases, the charge builds up more. When it reaches a certain thickness, it will generate static electricity. The repulsive effect does not continue to adsorb, so that the entire workpiece gets a powder coating of a certain thickness, and then the powder is melted, leveled, and solidified by heating, that is, a hard coating film is formed on the surface of the workpiece.
Process flow
1. Pre-treatment:
Purpose: to remove the oil stain, dust, rust on the surface of the workpiece, and to form a “phosphoric layer” on the surface of the workpiece that is resistant to corrosion and can increase the adhesion of the spray coating.
Main process steps: oil removal, rust removal, phosphating, passivation. After the pre-treatment of the workpiece, not only the surface is free of oil, rust and dust, but also a uniform and rough gray phosphate film that is not easy to rust is formed on the original silver-white shiny surface, which can prevent rust and increase the spray coating Of adhesion.
2. Electrostatic spraying
Purpose: uniformly spray the powder coating on the surface of the workpiece. Special workpieces (including locations prone to electrostatic shielding) should be sprayed with a high-performance electrostatic spray machine.
Process steps:
Using electrostatic adsorption principle, uniformly spray a layer of powder coating on the surface of the workpiece;
The fallen powder is recovered by the recovery system and can be reused after sieving.
3.High temperature curing
Purpose: To heat the powder coating on the surface of the workpiece to the specified temperature and keep it for a corresponding time, to melt, level and solidify, so as to obtain the desired surface effect of the workpiece.
Process steps: The sprayed workpiece is pushed into a curing furnace, heated to a predetermined temperature (generally 185 degrees), and maintained for a corresponding period of time (15 minutes); the furnace is taken out and cooled to obtain the finished product. Generally, different workpieces have different heating temperature and holding time.
Note: heating and control system (including electric heating, fuel oil, gas, coal burning and other heating methods) + insulation box = curing furnace.
4.Baking cooling
Out-of-bath cooling is a process of cooling the result of the spraying process and returning it to normal temperature.
5. Decoration treatment
Purpose: to make the workpiece after electrostatic spraying achieve a special appearance effect, such as various wood grains, patterns, and gloss.
Process steps: masking; transfer and other processing processes.
Inspection standards for sprayed products
1. Purpose
To ensure the standardization of the inspection of plastic spray products, to achieve uniform and effective quality control of the products.
2. area
This standard applies to inspection and on-site quality control and inspection of sprayed products.
Standard requirements for spraying products of hardware tools:
1. Inspection methods for trial-manufactured plastic spray products
New products or newly modified spray products are submitted for the first time for inspection. Inspection and confirmation by technical department and inspection department. Check that the structure of the sprayed product meets the design requirements; the external silk screen of the sprayed product meets the design requirements, including the position, color, size, and clarity of the silk screen.
Structural aspects of sprayed products
1.1 Basic requirements for the structure of plastic sprayed products: The size and assembly of plastic sprayed products shall comply with the requirements of drawings, and meet the corresponding technical requirements and national standards.
1.2 Structural inspection method of spray-molded products: After the spray-molded products are submitted for inspection, one set of corresponding semi-finished products is tested to verify that the structure of the products is correct and that the spray-molded products are required to be easily installed. The semi-finished product for trial installation requires that the installation hole position is not shifted, and the screw installation can be fastened in place without being skewed: the position, height, and clearance of the device exposed outside the spray-painted product must be suitable; The upper and lower covers of the spray-molded product are tightly matched, which is convenient for installation and removal; the rivet sleeve in the spray-molded product is not allowed to loosen or even fall off. If the test is qualified, the next process inspection can be continued. If one test fails, the second product should be tested again. If the same problem occurs, the product shall be treated as failed.
1.3 Appearance of sprayed products
Appearance is visually inspected with normal or corrected vision.
1.3.1 Spray color: The spray color should be consistent with the selected sample or swatch. The surface color of the sprayed product is uniform, and there is no obvious color difference by visual inspection.
1.3.2 Thickness of sprayed layer: The thickness of sprayed layer should meet the design and use requirements, uniform sprayed thickness and strong adhesion.
1.3.3 Product cleaning: The visible surface parts inside and outside of the product should be clean without any stains, oil stains and other dirt that affect the appearance, and no white traces are allowed after finger scratching.
1.3.4 External silk screen inspection requirements for plastic sprayed products
Check that the silkscreen content and color of the sprayed products meet the requirements of the design drawings. The silkscreen is clear, and no defects such as misprints, missing prints, color mismatches, unrecognizable or defective large silkscreen disconnections are allowed.
1.3.5 Inspection requirements for appearance defects of plastic sprayed products
1.3.5.1 Water leakage and rust: Plastic sprayed products are not allowed to leak. Inspection of plastic sprayed products must be done by waterproof test first. Take 2% of each batch of sprayed products for waterproof test, put toilet paper in the bottom of the box, then install the screws and tighten the sprayed products, seal the plug holes with tape, and seal the top, front, and back of the sprayed products. Rinse under the faucet for 20 minutes, then wipe the surface of the sprayed product dry. After inspecting the sprayed product, check whether the toilet paper is wet, and it is acceptable if it is not wet. After the waterproof test, all products are opened, and the bottom of the box is placed under strong light for light transmission inspection. The four corners of the bottom of the box are not allowed to have light transmission, and cracks, lack of welding, and holes are not allowed. The chamfer is smooth, and no nicks, cracks, or deformations are allowed. The waterproof rubber pad is of a suitable size and does not allow aging, unevenness and damage. The material of the rubber pad must be consistent with the sample.
The surface of the sprayed product must not have rust. The thickness of the surface of the sprayed product must be uniform, and the sprayed product must not fall off, which will cause the sprayed product to rust.
1.3.5.2 Damage and deformation: The surface of the sprayed product must not be damaged or deformed, and the surface should be flat and free of corner warping and bending.
1.3.5.3 Scratches: Scratches caused by friction are not allowed.
1.3.5.4 Particles: The surface of the spray-molded product must not have small pieces of plastic powder, silk screen ink dots, bumps, protruding marks or flow marks. Dispersion and a small amount of particles are allowed.
1.3.5.5 Dimples: There must be no dimples on the surface of the spray-molded product. Dispersions and trace amounts are allowed.
1.3.5.6 Scratches: There should be no scratches on the surface of the spray-painted products, let alone scratches that are too deep, not leaking out of the bottom plate; there should be no scratches on the surface of the spray-painted products. Only scattered and trace amounts are allowed.
1.3.5.7 Gap: Plastic-sprayed products must be waterproof and require gaps.
2. Processing of test results:
Structural inspection of plastic sprayed products. If two test units fail to pass the test, they are judged to be batch unqualified. If the visual inspection qualified rate of plastic sprayed products is greater than or equal to 95%, the unqualified products will be returned for rework. <95%, it is judged as batch failure. If the batch of sprayed products is unqualified, fill in the non-conformity report and submit it to the Quality Control Center.