It consists of a porous separator and a container that divides the container into upper and lower portions.
The working process is such that compressed air is introduced into the container portion below the partition, and the compressed air is passed through the porous partition to suspend the upper powder from the air flow and roll over in the upper container to assume a "boiling" state. The preheated workpiece passes through the "boiling" powder zone to achieve the coating effect. The preheating temperature of the workpiece may be slightly higher than the melting temperature of the powder.
In recent years, the fluidized bed process has been improved, and combined with electrostatic powder to form electrostatic fluidized bed powder coating, has been widely used.
To get a good effect on the coating, you should pay attention to the following aspects:
The structural form of the fluidized bed is simple, the internal smoothness avoids dead angles, and it is better to provide a vibration device; the porous separator in the fluidized bed should have a certain pore size and air density distribution; the size of the powder particles passes through 50~150 mesh. / mesh screen hole is good, the shape is close to the spherical shape is ideal; the water content of the powder coating is required to be as low as possible to avoid fluidization and coating bubbles; the flow rate and flow rate of the compressed air must be adjusted until the powder coating is stably fluidized, so as not to overflow At the same time, the compressed air should be purified and dried.
Flame Spraying In an oxyacetylene flame, the powder is passed through a high temperature zone of the lance at a speed of about 50 m/s, heated to a molten or semi-molten state, and sprayed onto the preheated surface to the desired thickness. The powder flame spraying process is relatively simple and can be used for the coating of the rail surface and the mechanical wear repair work.
The hot-fusion method is a process between a flame spraying and a fluidized bed. The process is to preheat the workpiece to a temperature above the melting temperature of the powder, and then spray the powder with a spray gun to melt the coating into a coating.
Electrostatic powder coating This is one of the fastest growing construction processes in powder coating.
Fundamental:
A high-voltage corona discharge electric field is formed between the spray gun and the workpiece. When the powder particles are ejected from the spray nozzle through the discharge zone, a large amount of electrons are added to become negatively charged particles, and under the action of electrostatic attraction, Adsorbed onto a positively charged workpiece. When the powder adheres to a certain thickness, the phenomenon of "same-sex repelling" occurs, and the powder can no longer be adsorbed, so that the thickness of the powder layer of each part is uniform, and then the layer is leveled by the heating and baking to form a uniform film. Layer; powder electrostatic spraying process, the typical powder electrostatic spraying process is as follows: upper part → degreasing → cleaning → rust removal → cleaning → phosphating → cleaning → passivation → powder electrostatic spraying → curing → cooling → lower parts; The main factor in the quality of electrostatic spraying.
In the final electrostatic spraying, in addition to the quality of the surface pretreatment of the workpiece, there are spraying time, spray gun form, spray voltage, powder spray amount, powder conductivity, powder particle size, powder particle size, powder and air mixture. Speed ​​gradients, etc.
The resistivity of the powder:
The resistivity of the powder is preferably 1010 to 1016 ohm/cm, and the resistivity is too low to cause the powder to be dispersed, and the resistivity is too high, which may affect the thickness of the coating.
Powdering amount:
At the beginning of spraying, the amount of powder spray has a certain influence on the film thickness. Generally, the amount of powder sprayed is small and the deposition rate is high. The amount of dust spray is generally controlled in the range of 50 g / min to 1000 g / min.
Speed ​​and gradient of powder and air mixture:
The velocity gradient is the ratio of the velocity of the powder-air mixture at the exit of the gun to the spray distance. During a certain spray time, the film thickness will decrease as the spray gradient increases.
Spray distance:
The spraying distance is a main parameter for rejecting the film thickness. It is generally controlled at 10~25 cm from the workpiece, which is determined by the spray gun form.
Spraying time:
Several parameters such as spraying time, spraying voltage, spraying distance, and spraying amount are mutually affected. When the spraying time increases and the spraying distance is large, the influence of the spraying voltage on the film thickness limit value is reduced. As the powdering time increases, the effect of the amount of dusting on the growth rate of the film thickness is significantly reduced.
Water dispersion powder coating:
The water-dispersible powder coating is a stable dispersion of the powder coating and the aqueous medium. It has the advantages of both water-based coating and powder coating. All conventional means including dip, brush, spray and electrostatic coating can be used in the process.
Powder electrophoresis coating:
It is a product of both integrated powder coating and current coating, which combines the two characteristics. The basic principle is that the powder particles (generally required to be 40 μm or less) are dispersed in an aqueous solution containing an electrophoresis resin, the aqueous electrophoresis resin is used as a carrier, and the powder particles are used as a film-forming substance to charge the powder particles in a DC electric field. Electrophoretic deposition into a film. It is suitable for the construction of complex shapes
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Welding Neck Flanges are easy to recognize at the long tapered hub, that goes gradually over to the wall thickness from a pipe or fitting.
The long tapered hub provides an important reinforcement for use in several applications involving high pressure, sub-zero and / or elevated temperatures. The smooth transition fromFlange thickness to pipe or fitting wall thickness effected by the taper is extremely beneficial, under conditions of repeated bending, caused by line expansion or other variable forces.
These Welding Neck Flange are bored to match the inside diameter of the mating pipe or fitting so there will be no restriction of product flow. This prevents turbulence at the joint and reduces erosion. They also provide excellent stress distribution through the tapered hub and are easilyradiographedfor flaw detection.
This Welding Neck Flange will be welded to a pipe or fitting with a single full penetration, V weld (Buttweld).
Welding Neck Flange
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