In its simplest form, fluid bed powder coating process includes immersing a cleaned and pre-heated part into a bed of thermoplastic PE powder coating, allowing powder to melt and from a film adhering to the part and drying it in an oven. Here we break this process down and write up it in step by step for providing a clear idea of coating process to our customers.Polyethylene Powder Application includes:LDPE Powder for Metal Wire Coating,Polyetylene powder for metal fences, china polyetylene powder for fence mesh.
Step 1 Substrate cleaning
The surface of your part should be fully cleaned for avoiding soil, rust, grease, and other stains affecting the adhesion and end product performance of our powder coatings. In other words, the more cleaner the part is, the better the bond will be created. Normally, the part can be cleaned in various types as shown below:
Grit or shot blasting.
Hot alkaline cleaning and water rinsing.
Hot alkaline cleaning, rinsing, acid pickle and rinse.
Zinc or iron phosphate system.
Note: After cleaning, please do not touch the part at once as it may contaminate the surface of the part.
Step 2 Substrate pre-heating
There is no need to apply a layer of primer between the substrate and powder coating owing to inherent high adhesion strength of our thermoplastic powder. After proper cleaning process, preheat the part up to coating temperature from 270°C to 360°C in various methods such as gas, electric ovens with recirculated convected heated air, infrared heater, induction heater, radiant heater and resistance heating equipment. Normally, convection oven is the most common types that are versatile for dealing with multiple part geometries.
To ensure excellent flow and proper coating thickness, the coating temperature must be above the melting temperature of powder coatings.
Various factors that affect the preheating time and temperature should be taken in consideration such as each part's quality, configuration, size and thickness as well as heat loss when moving heated part to fluid bed.
Step 3 Fluid bed coating
After preheating, it is recommended to move the parts into the fluidized bed as soon as possible to minimize heat loss. Then keep the parts in proper motion to make sure the hidden areas that are hard to reach can be powder coated. Normally, the immersion time is about 2 - 8 seconds, but in some applications requiring thick coatings, the time can be as much as 10 - 30 seconds. Meanwhile, extremely thick coating is also available with longer dipping time.
The longer the part is immersed into the fluidized bed, the thicker the coating will form.
Normally, the motion is based on the configuration of parts and improper motion will cause a variety of problems such as pinholes and disproportion coating appearance.
Step 4 Post heating
Tilt, vibrate or use a regulated air jet to remove the excess powders immediately. And then bake the part at 180°C - 190°C for 2 to 5 minutes. Normally, the powder coating can be cured at high temperature for a short time or low temperature for a longer time. But it is recommended to choose the front curing method as higher temperatures curing are more economical due to its short dwell time in the oven.
Note: The removed excess powder coating can be reused thanks to its excellent recyclability.
Step 5 cooling
After post heating, allow the parts to be cooled below the hardening temperature of the thermoplastic powders.