Why thermoplastic powder does not bubble in fluidized bed?

LDPE powder coating

Why thermoplastic powder does not bubble when boiled up in fluidized bed?

There may be several reasons for this issue:

The Quality Of Thermoplastic Powder

If the particle size is inconsistent, there is excessive water content, impurities or aggregates present, it will affect the fluidity and suspension of the powder . Consequently, it becomes difficult for the powder to generate bubbles or maintain stability in the fluidized bed.

Air Pressure And Airflow

Insufficient or excessive air pressure and flow disrupts the suspension state and dispersion of the powder, resulting in uneven bubbling or lack thereof in the fluidized bed.

Fluidized-Bed Equipment

Poor design of the fluidized-bed orifice plate such as improper aperture size or low/high porosity along with an uneven surface or dirt accumulation on the plate hinder proper distribution and penetration of air within the system causing incomplete bubbling of powder in the fluidized bed.

Preheating Temperature of Workpieces

If temperatures are too low or high it affects adhesion properties and curing speed of powder coatings leading to difficulties in generating bubbles that quickly disappear after foaming occurs within a fluidized bed. 

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