Deposition of Powder Coatings on Heated Ware

When a polymer powder material is brought into contact with metal ware heated above the polymer melting point, the processes of deposition, holding powder particles on the ware surface and formation of a solid polymer layer can be joined together. 

A diagram of a polymer inhibited coat formation on a heated article is presented in Fig. 3.22. As soon as polymer particles come into contact with the article surface, they stick to it, warm up and melt. The first stage of this process, consisting of the formation of a monolayer of particles on the article surface, is completed in 1-2 seconds. It is expedient to incorporate contact inhibitor particles into the powder composition so as not to impair 

Depending on the method of bringing polymer particles into contact with the article we discriminate between coating application in a fluidized bed, blasting with a gas-polymer mixture and bringing into contact with the powder in a loosely poured or compacted state. 

Coating application in a fluidized bed can be carried out by a vortex, vibrovortical or vibration method. These methods are based on powder fluidizing, i.e. conversion of the powder layer into a pseudo-liquid (boiling bed) under the effect of vibration or up-flow gas streams sufficient to keep the powder particles in a suspended state. 

The vortical method of coating deposition consists of immersion of the heated article in the fluidized bed of the polymer powder formed by blowing a gas flow through the porous bottom of a vessel containing the powder (Fig. 3.23). Under certain parameters of the gas flow, the immovable layer of powder particles poured into the vessel to the level Ho expands up to the level H. The particles acquire mobility and transfer into the airborne state. The criterion for this change is a constant value of the gas pressure differential in the powder bed volume [52]. 

---