Abstract:
Pipes having dense, watertight concrete walls are produced by vibrating a rotating mould suspended on a roller shaft as the mold is being filled, and continuing its rotation without vibration for a short time after the mold is filled. Vibration is attained by ridges or fingers which can be made effective, or not, to vibrate the mold as it is rotating. In one form, fingers on a roller shaft are slidable between ineffective positions and positions where they serially engage a smooth running surface on the mold. In other forms, a mold is movable from a position where it is supported by engagement of a ridged running surface on either the roller shaft or the mold with a cylindrical surface on the other to a position where the cylindrical surface on the mold runs on the roller shaft or on an auxiliary sleeve without vibration.