Practical description of electrostatic spraying technology

For example, when the average particle size of pure polyester powder coating cured by mixed powder coating and triglycidyl isocyanurate (TGIC) is 24μm, a coating film with a thickness of 25μm can be obtained at 100m/min. Heidenborg Digital Company applied the improved rotary electromagnetic brush technology with linear speed of 120m/min to the coating of steel, stainless steel and aluminum plate. There are several different carriers, such as conductive or insulating carriers. The electromagnetic brush technology of coating roller with fixed or rotating magnetic core has been industrialized. These systems include fixed core conductive electromagnetic brush, fixed core insulated electromagnetic brush and rotating core insulated electromagnetic brush. The last technology is also called the improved system of rotating magnetic brush. Almost all existing systems use insulated carrier particles, which can be conductive media with an insulating layer on the surface, such as iron particles coated with polytetrafluoroethylene, or simply use insulators, such as ferrite of magnetic type with high dielectric constant. The improved rotating electromagnetic brush uses magnetic ferrite as carrier, while the traditional system uses conductive carrier with insulating layer.

Generally, the improved rotary electromagnetic brush technology has a cylindrical conductive shell and a bar magnet with variable receivers at the south and north poles. The magnetic carrier on the drum forms a continuous chain in the magnetic field of the drum. This is called "fluff". When it is connected to the North Pole of Antarctica, the carrier chain is perpendicular to the colored core. Between the north and south poles, the magnetic field of the magnetic core is parallel to the colored core, and the carrier chain is basically parallel to the colored core. The outer surface of the drum or the colored core moves simultaneously with the receiver. When the magnetic core rotates, the carrier chain is lightly thrown along the movement direction of the receiver. On the contrary, in the traditional system, the "fluff" is also static because of the existence of the fixed magnetic core. The typical process conditions are as follows: it is recommended to add 1.5 PPH charging agent into powder coating, and grind it into powder, and classify it into powder with average particle size of12.9 μ m. The mixture also contains 15% strontium ferrite, and the surface of this strontium ferrite is coated with 0.3pph charging agent. After mixing in a blender for 65438 0 minutes, the surface area of the powder was 30g/m2 ... At the linear speed of 120m/min, conductive substrate, non-conductive substrate and ferromagnetic substrate were coated. For the conductive substrate, as long as there is an electric field between the roller of the electromagnetic brush and the surface of the substrate, the powder can be deposited on the grounded conductive substrate. For non-conductive substrates, corona charging of the powder itself can be used or electrodes can be embedded under or near the substrate. For substrates with rough surface and easy to retain carrier particles, such as wood and patterned plastics, powder emission can be used instead of direct contact between carrier and substrate. For this non-contact or soft-contact system, the linear speed matches the distance between the substrate and the roller. For magnetic substrates, a small amount of carriers is also necessary to eliminate the magnetic types of rollers and substrates.

The advantages of the improved rotary electromagnetic brush technology include high deposition rate, high linear velocity, flat coating and wide film thickness. The film thickness of the powder can be adjusted by the deposition voltage. Fine powder, powder with particle size less than 9μm can also be used.

TransAPP technology

TransAPP technology of Flawn Hof Company uses powder transfer technology instead of spray gun, as shown in Figure 4, which avoids the limitation of traditional powder spraying application speed and film thickness difference. In this technology, the powder is conveyed to the substrate under the conveyor belt through an endless conveyor belt. Because the powder particles are uniformly deposited on the surface of the substrate, a relatively uniform film thickness is obtained. In addition, the powder particles that are not transferred to the substrate are not wasted, but are carried to the next cycle with the transfer. This process is also suitable for nonmetallic substrates, and the highest linear velocity is 60m/min, which is suitable for near infrared curing. The traditional epoxy polyester mixed powder coating can obtain a film thickness of 70 μ m. ..