Importance

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Abstract

Air is flowed within an annulus fluidly connected to the load end of a pipe to be coated. A premeasured charge of powdered coating material is suspended in an injection airflow and then injected into the annulus. Spiral flow of the air and particles of coating material in the annulus is induced by successively jetting air into the annulus at selected angles to axial flow. The resulting powder cloud has spiral annular movement within the annulus toward the load end of the pipe. An optional conical deflector at the load end deflects the spiral cloud toward the wall of the pipe. The pipe is rotated counter to the tangential or circumferential component of the spiral flow. The nonaxial circumferential component of the spiral flow helps reduce the number of holidays, and insures that the coating material is deposited evenly through the length of the pipe for a uniform coating thickness. The powder cloud is much longer than the pipe. The excess coating material exiting the pipe discharge end is recycled.

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First Claim