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Powder-coating is commonly used for stainless steel pipe railings. Usually, a powder coating is sprayed on the surface of the workpiece by powder spraying equipment. Under the action of static electricity, the powder is uniformly adsorbed on the surface of the workpiece in the form a powder coating;

Powder Coating: The surface of the workpiece is subjected to baking at high temperatures and leveled by various methods to form a powder coating. The spraying effect of powder spraying is superior to the conventional spraying process in terms of mechanical strength, adhesion, corrosion resistance, resistance to aging, cost-effectiveness, etc.

Powder coating uses a simple process to obtain powder-coated stainless steel products in different colors, and different powder-coating colors can be used to change the feel of stainless-steel surface. For example, the stainless-steel railing that we use commonly can be powder-coated and powder-colored.

Many coating companies encounter a common problem: After coating the stainless steel, whenever a wide tape is applied to the surface and pulled off, the coated material is torn off from the surface along with the tape, exposing the underlying stainless-steel surface. This is because of the inadequate strength of the surface adsorption force of the coating. This is one of the basic methods to test the effectiveness of spraying on any surface. In general, the following processes are required for 304 material coated:

  1. Pre-treatment:

The oil, dirt or rust is removed off the surface of the workpiece, and a “phosphoric layer” is created on the surface of the workpiece that is resistant to corrosion, and can increase the adhesion of the spray powder-coating.

The main steps of the process are oil and rust removal, phosphating, and 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 does not rust easily is formed on the original silver-white shiny surface.

  1. Electrostatic coating:

The powder coating is evenly applied on the pre-treated surface of the stainless-steel workpiece. Special workpieces (including surfaces that are prone to electrostatic shielding) is coated with a high-performance electrostatic spray machine.

Process steps: The principle of electrostatic adsorption is applied to uniformly powder-coat the surface of the workpiece. A layer of powder-coating is sprayed, and the residual fallen-off powder is recovered through a recovery system and can be reused after sieving.

3.High-Temperature curing:

The powder coating on the surface of the workpiece is heated to the specified temperature and held for the corresponding time, so that it melts, levels, and solidifies to obtain the desired surface effect of the workpiece. Process steps: The coated workpiece is pushed into the curing furnace and heated to a predetermined temperature (generally 185 degrees), and the temperature is maintained for a specified time (15 minutes); After that, the product is taken out of the oven and cooled to achieve the final product. Note: The curing furnace consists of a heating and control system (including electric heating, fuel oil, gas, coal, and other heating methods) and an insulation box.

  1. Decoration treatment:

This method is used after the electrostatic treatment to give a special appearance effect to the product, such as various wood grains, patterns, lighting, etc. Process steps: cover light; transfer and other processing methods. The electrostatic powder-coated surface is then plastic-coated by the use of a static generator that charges the plastic powder and makes it adsorb on the surface.

The surface of the product is then baked at 180~220 ℃ to melt the powder and make it adhere to the metal surface. Plastic spray products are mostly used for indoor boxes and paint films. The product shows a flat or a matte effect. The powder-coated steel mainly uses acrylic powder, polyester powder, etc. From the above-described process, it is clear that the surface roughness of the 304/316L stainless steel material determines the spraying effect, and there is a certain degree of roughness that can get a reliable surface adhesion.

The process of oil removal, rust removal, phosphating, and passivation in the pretreatment process has certain effects, but even if the effect is adequate, it is still insufficient. The reason is that oil removal, rust removal, phosphating, and passivation basically have little ability to change the surface of 304. Oil removal and rust removal are only a form of cleaning, and the main purpose of phosphating and passivation is to prevent rust, which does not change the size, color, and performance of parts. Since changing the surface roughness is naturally limited, one must look for a better method: Pickling. The pickling treatment of stainless steel can make the bright 304/316L stainless steel surface appear matte white and have a rough feel on touching, thus enabling it to be coated directly and have a better adsorption capacity.

The stainless steel pickling solution can quickly remove the rust, welding spots and stubborn black or yellow oxide scales produced during the production, forming, assembly, welding, etc. of any stainless steel parts (316L, etc.) and transform the product into silver-white stainless steel that can be used for stainless steel railings, stainless steel pressure vessels, petroleum pipelines, printing and dyeing equipment, and refrigeration equipment products. The surfaces of the parts treated with the pickling passivation effect are uniformly beautiful silver-white.

In the case of metals, manufacturers often improve the performance of the product by surface treatment of the metal. The conventionally used metal surface treatment technologies are powder-coating steel, pickling purification treatment, electrolytic polishing treatment, degreasing and rust removal treatment, chemical polishing treatment, electroplating treatment, and chemical treatment.

The characteristics of pickling are:

  1. It can be done quickly, with only about 5-15 minutes required for removal of any residual oxide scale, yellow smoke or acid mist. It is necessary to take care of the soaking time, because a short duration may yield an uneven surface.
  2. it is a simple process requiring no special operating environment, along with being non-toxic and producing little corrosion. A general plastic container can be used for this process, and the equipment is easy to configure.
  3. It does not contain hydrochloric acid, meets RoHS test requirements, and the product is environment-friendly
  4. With repeated addition of pickling accelerator, stainless steel lasts longer.