| 摘要 |
<p>An iron or steel pipe or tube, while heated, and containing a quantity of bitumen in a fluid state in the bottom, is maintained substantially horizontal, and rotated slowly, e.g. by rollers to lap or spread the bitumen in successive layers into a uniform coating. The speed of rotation is insufficient to subject bitumen to any appreciable centrifugal force. The bitumen may be introduced into the tube before, during, or after heating, e.g. by dipping, end rings being employed, if desired, to retain a sufficient quantity. After the initial setting of the bitumen, the end rings may be removed, and the rotation of the tube may be continued while a cooling medium, e.g. a water spray, is applied to the exterior until the bitumen solidifies. Heating means such as a gas torch may be passed through the tube to soften temporarily, and so smooth, the surface of the bitumen coating. A small quantity of a filler such as slate dust or kieselguhr may be added to the bitumen. According to the Provisional Specification the tube may be coated in the cold state.</p> |
