A comparative study of the fluidized-bed coating of cylindrical metal surfaces with various thermoplastic polymer powders

This paper reports the results of an experimental investigation into the fl uidized-bed coating of cylindrical metal specimens using two types of therm oplastic powders, Rilsan(R) PA11, a nylon-11 powder produced by Elf Atochem , France and Cotene(TM) 4612, a linear low density polyethylene powder prod uced by J.R Courtenay (New Zealand). The effects of dipping time, preheat t emperature and particle size distribution on coating thickness and surface finish were investigated. Consistent trends in coating thickness growth with dipping time were obtain ed for both nylon-11 and polyethylene powders with increases in coating thi ckness with preheat temperature. For the same preheat temperature, the lowe r melting point of polyethylene results in thicker coatings compared to tho se of nylon-11. There is a negligible change in the coating thickness for s ieved powders compared to that for unsieved powders. A pre-heat temperature s of between 240 degrees C and 300 degrees C is necessary to achieve an acc eptable surface finish with both nylon-11 and polyethylene powders. To mini mize errors in achieving the desired coating thickness, dipping times short er than 2 s are not recommended. The use of graphs of coating thickness ver sus dipping time in combination with the coating surface roughness plots pr esented in this paper enable the optimal choice of pre-heat temperature and dipping time to achieve acceptable surface finish. (C) 1999 Elsevier Scien ce S.A. All rights reserved.