Electrophoretic coating: It refers to the coating method that uses an external electric field to directionally migrate particles such as pigments and resins suspended in the electrophoretic solution and deposit them on the substrate surface of one of the electrodes. Generally, the VOCs content of electrophoretic paint is about 3-5%. The production efficiency of electrophoresis is very high, which is basically based on assembly line! The pressure of VOCs discharge is low, but the amount of wastewater pretreated is large!
Self swimming coating: chemical reaction is the coating method for coating to be automatically deposited on the substrate surface. Metal substrate is not widely used, and it is unheard of in China.
Powder coating: usually, special electrostatic powder spraying equipment is used to spray the powder coating on the surface of the workpiece. Under the action of static electricity, the powder will be evenly adsorbed on the surface of the workpiece to form a powdery coating; The powder coating becomes the final coating with different effects and colors after being baked and leveled at high temperature!
The VOCs content of powder coating: about 0-2%. There are different opinions. One of the important reasons why some regions require VOCs treatment for powder coating lines is that some factories use low-quality raw materials to manufacture powder coatings, resulting in a very serious odor during baking. The surrounding residents complain and have to install relevant treatment facilities.
Powder coating is easy to produce dust pollution, which requires high safety and explosion-proof requirements, and high grounding requirements for workpieces and construction personnel!
The advantage of powder coating is that it basically does not produce waste water and VOCs, but its energy consumption is relatively high (baking temperature). A large amount of wastewater will be produced in the pretreatment!
Liquid painting:
Liquid coating can be divided into the following categories according to coating types:
Solvent based, water-based, UV, high solid, solvent-free and other materials.
Liquid coating can be divided into the following categories according to coating methods:
Brushing: the most traditional and simple method of painting with a brush dipped in paint
Wiping: the method of wiping by repeatedly circling with a cloth dipped in paint, which is usually used for the coating of small batches or precision instruments. The coating is very thin!
Dip coating: immerse the workpiece in the paint, take it out, and remove the excessive paint by gravity or centrifugal force. The material utilization rate is high, and the viscosity and film thickness control are the key points (somewhat similar to autophoretic paint, but not affected by the base material).
Spray coating: the coating method of spraying paint on the surface of the workpiece. The material utilization rate is high and can be recycled. Generally, the film thickness of the lower part of the workpiece is slightly higher.
Roller coating: the roller coating method on the surface of the workpiece, with high material utilization rate, is suitable for large flat workpieces. There are many manual operations in construction, home decoration, repair of large machinery and other fields. Automatic assembly lines are basically used in the coil steel and furniture industries, with very high production efficiency and precision control of film thickness.
Roll spraying: It refers to the painting method that the workpiece is installed in the roller and sprayed with a spray gun while the roller rotates. All workpieces are evenly coated with paint film and dried. It is suitable for small workpieces and parts, with slightly poor surface quality.
Spraying: the most common and widely used coating construction method
Spraying is divided into:
1、 Air spraying (within 8bar): the most popular and simplest spraying method, which can be divided into gravity type (upper pot), siphon type (lower pot), and pressure type (to be connected with a delivery pump) according to the different feeding methods. Air spraying is called finishing and finishing coating in the industry. Its main feature is fine atomization, which can obtain excellent surface effect.
Air spraying can be divided into the following categories according to the air pressure at the outlet of atomizing cap. The lower the pressure, the less the rebound, and the higher the utilization rate of paint! The specific application shall be based on the actual process requirements, and the more environmentally friendly spraying method shall be selected under the condition of meeting the process requirements.
1. Low pressure spraying HVLP (0.3-1.2 bar), the actual utilization rate of the coating is about 40%, and the particle diameter of the coating after atomization is about 10-15 μ m;
2. Medium pressure spraying (0.7-2bar), the actual utilization rate of the coating is about 30%, and the particle diameter of the coating after atomization is about 8-12 μ m;
3. High pressure spraying is also the most common (2.5-6bar). The actual utilization rate of the coating is about 20%, and the particle diameter of the coating after atomization is about 5-8 μ m;
2、 Airless spraying (80-500bar): only high-pressure pump is used to release pressure at the nozzle of the coating and produce atomization due to friction with the air. The higher the pressure, the better the atomization, and the high construction efficiency. The coating can be ejected more than 5 liters per minute. The disadvantage is that the surface quality is poor. The theoretical paint utilization rate of airless spraying is about 65%, and the actual application is based on the workpiece, material, process and construction level. It is widely used in heavy anti-corrosion fields such as heavy industry, ships, steel structures, bridges, etc. The term Caoting often used in the industry refers to heavy anti-corrosion coating.
3、 Air mixed spraying (30-200bar): combining the advantages of the atomization effect of air spraying and the spraying efficiency of airless spraying, it is usually used for processes with high film thickness and relatively high surface quality, such as furniture, engineering machinery, rail transit and other fields. In theory, the paint utilization rate of gas mixed spraying can reach more than 80%, and the actual application can be discounted by 4% to 8%. Disadvantages: the maintenance of spraying equipment is particularly important, and it is used cautiously for some enterprises with insufficient standardized management.
According to the coating characteristics, it can be divided into solvent based and water-based paint spraying, single component or two-component spraying.
According to the construction method, it can be divided into manual spraying and automatic spraying.
The above spraying methods can be divided into electrostatic spraying and non electrostatic spraying. The electrostatic spraying can improve the paint utilization rate by 10-30% compared with the non electrostatic spraying. The equipment and process change greatly, and a lot of tests need to be done.
The above categories are common in the industrial field, and we will take time to make a special introduction in the future. There is also a special kind of spraying, which is also briefly introduced here.
Interior spraying: interior spraying of workpieces, such as inner wall coating of cups, bottles, pipe fittings, shells, etc.
Thermal spraying and nitrogen spraying: by heating the paint or air, the viscosity and atomization pressure can be reduced to improve the utilization rate of materials.
Supercritical spraying: the spraying method using liquid carbon dioxide as the solvent. At present, there are only a few solvent-free spraying applications in the UV industry.
Guangzhou Tuoshen Surface Treatment Co., Ltd., the spraying manufacturer, is preferred for purchasing spraying, Guangzhou spray processing , trustworthy, welcome to inquire!
