It is known to prepare polyurethane plastic packing rings or disks for scrapers and other such bodies for sliding through pipelines, wherein the crosslinking material is cast in a mold which matches as closely as possible the intended final shape, which in the concrete case is the shape of the packing ring or disk. When these plastic packing rings or disks are used as parts of scrapers and other such bodies for sliding through pipelines, the marginal portions of the packing ring or disk are exposed to severe friction, and they constitute a weak point in meeting the stringent requirements relating to the tight fit of these friction surfaces. In the case of scrapers in pipelines, especially in off-shore petroleum drilling operations, however, pipeline lengths of 50 km, 100 km and more have to be traversed in a single draft, which creates extremely stringent requirements to be met by the packing rings and disks. A short useful life in these scraper disks and packing rings thus not only increases reconditioning costs and involves undesirably great material costs, but in some special applications it leads even to the breakdown of the scraper. If the friction resistance at the sliding surfaces is too high, then the amount of power required to move the sliding body is disadvantageous in many applications.
USPTO Backgrounds
USPTO Backgrounds