PURPOSE: To raise the shear adhesion strength between a plastic layer and a concrete layer provided on the surface of the plastic layer by forming an uneven surface on the molten plastic layer covered on a steel pipe by spraying the atomized particles of water onto the surface of the molten plastic layer.
CONSTITUTION: A molten hot plastic material is coated on the surface of a steel pipe and then before the molten plastic coat 1 is hardened, atomized water particles 2 is sprayed from a spray nozzle onto the molten plastic coat, whereupon large numbers of fine water droplets 3 adhered to the surface of the molten plastic coat 1 coalesce producing large water droplets 3' and by the cooling action of the coalescence, convexed portions 4 are formed on the molten plastic coat below the droplets 3'. At a time when the size of the convexted portions 4 is increased to about 0.5mmW3.0mm, the grown water droplets 3' are removed by air or laminar water flow and then the plastic coat is forcibly cooled with water.
ADACHI TAKEO
NAKAGAWA TOKIO
SAITOU RIYOUJI
OOMORI KATSUMI
