Application and Features of Common Coatings for Workpiece Painting

【China Aluminum Industry Network】Different coating methods have different application effects. The following are the main types of coating methods and application features:

Electrophoretic coating: A coating method in which particles such as a pigment and a resin suspended in an electrophoretic fluid are transferred in a directed manner and applied to the surface of one of the electrodes by an applied electric field. The VOCs content of the electrophoretic paint is usually about 3-5%. The efficiency of electrophoresis production is very high, basically the main line is the assembly line! VOCs discharge less pressure, but the volume of wastewater from the pre-treatment is large!

Self-swimming coating: The use of chemical reaction is the coating method of coating deposited on the surface of the substrate automatically. The metal substrate is used, and the application is not too extensive. Domestically owning such technology has not been heard.

Powder coating: The electrostatic powder spraying equipment is usually used to spray the powder coating on the surface of the workpiece. Under the electrostatic action, the powder will be evenly adsorbed on the surface of the workpiece to form a powder coating; the powder coating is baked at high temperature. Leveling and curing, become the final coating of different effects, colors, etc.!

The content of VOCs in powder coating is about 0-2%, and there are different opinions. An important reason for the requirement of VOCs for powder coating lines in some regions is that some factories use powder coatings made of poor quality raw materials to cause bad odors during baking. Seriously, complaints from neighboring residents had to be installed to install related facilities.

Powder coating is prone to dust pollution, and the safety and explosion-proof requirements are relatively high. The grounding requirements for workpieces and construction workers are high!

The advantage of powder coating is that it does not generate wastewater and VOCs, but the energy consumption is relatively high (baking temperature). Pre-treatment will have a lot of waste water produced!

Liquid coating:

Liquid coating is divided into the following types according to the type of coating:

Solvent-based, waterborne, UV, high solids, solvent-free materials.

Liquid coating can be divided into the following categories according to the coating method:

Brushing: The method of coating with brush and paint, which is a simpler construction method than traditional

Wiping: The method of rubbing and painting with rags of enamel paint is often used for the coating of small batches or precision instruments. The coating is very thin!

Dipping: The method of immersing a workpiece in a paint, removing it, and removing excess paint by gravity or centrifugal force, with high material utilization, viscosity and film thickness control is a priority (somewhat similar to self-swimming paint, but not affected by the substrate).

Dripping: The coating method of spraying the paint on the surface of the workpiece has high material utilization rate and can be recycled. Usually, the film thickness of the lower part of the workpiece will be slightly higher.

Roller coating: The use of roller coating method on the surface of the workpiece, high material utilization, suitable for large flat workpieces. The use of manual operations in fields such as construction, home improvement, and repair of large-scale machinery. In coil steel and furniture industry, automation lines are basically used. The production efficiency is very high, and the precision of film thickness control is also very high.

Roller spray: The workpiece is installed in the drum, the drum is rotated while sprayed with a spray gun, and all parts are evenly coated with a paint film and dried. Applicable to small parts and parts, surface quality is slightly worse.

Spraying: The more common and widely used coating construction method

Spraying is divided into:

First, the air spray (within 8bar): more popular and simpler spraying method, according to the different feeding methods, it is divided into gravity type (upper pot), siphon type (lower pot), pressure feeding type (to be connected to the transfer pump ). The air spray industry is known as Finishing, finishing coating, the main feature is fine atomization, can obtain excellent surface effect.

Air spray according to the atomization cap outlet air pressure can be divided into the following categories, the lower the pressure the less the rebound, the higher the utilization of the coating! Specific applications need to be based on the actual process requirements, in the case of meeting the requirements of the process to choose a more environmentally friendly spray method.

1. Low-pressure spraying HVLP (0.3-1.2bar), the actual utilization rate of the coating is about 40%, and the particle diameter after the coating is atomized is about 10-15μm;

2. Medium-pressure spray (0.7--2bar), the actual utilization rate of the coating is about 30%, and the diameter of the particles after the coating is atomized is about 8-12μm;

3. High-pressure spraying is also more common (2.5-6bar), the actual utilization rate of the coating is about 20%, and the diameter of the particles after the coating is atomized is about 5-8μm;

Second, airless spray (80-500bar): Only use the high pressure pump to release pressure from the nozzle at the nozzle and generate atomization with air. The higher the pressure, the better the atomization, and the construction efficiency is very high. Every minute The paint spit out can reach more than 5 liters, the disadvantage is poor surface quality. The theoretical utilization rate of airless spray is about 65%, and the practical application is based on 4-80% off of the workpiece, material, process and construction level. It is widely used in the heavy anti-corrosion field of heavy industry, ships, steel structures, and bridges. Cauting, which we often refer to in the industry, is heavy anti-corrosion coating.

Third, mixed gas spraying (30-200bar): combines the advantages of both the atomization effect of air spraying and the spraying efficiency of airless spraying, and is usually used in processes with higher film thickness and relatively higher surface quality, such as furniture. There are many applications in fields such as construction machinery, rail transit and so on. The utilization rate of paint in the theory of mixed gas spraying can reach more than 80%, and the actual application can reach 4-8 fold. Disadvantages: It is particularly important to maintain the spraying equipment, and it is prudent for some enterprises that are not well-regulated.

According to the characteristics of the coating can be divided into solvent-based and water-based paint spraying, single-component or two-component spraying.

According to construction methods can be divided into hand spray and automatic spray.

The above spraying methods can be further divided into electrostatic spraying and non-electrostatic spraying. The electrostatic spraying can improve the utilization of the coating by 10-30% compared with non-static spraying, and the equipment and process vary greatly, and a large amount of tests are required.

The above categories are relatively common in the industrial field. We will take the time to do thematic presentation later. There is also a special type of spray, here is a brief introduction.

Inner cavity spraying: spraying the inner cavity of the workpiece, such as cups, bottles, tubes, shells, etc.

Thermal spray, nitrogen spray: By heating the paint or air has reached a spray method to reduce viscosity, reduce the atomization pressure, improve material utilization.

Supercritical Spraying: Spraying methods using liquid carbon dioxide as the solvent, there is currently only a small amount of solventless spray application in the UV industry.

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