| 摘要 |
Tubular articles, particularly barrels of hypodermic syringes, of glass or other thermoplastic material, are provided with a matt surface in the bore, and are subsequently brought to the correct bore dimensions by heating on a mandrel, the matt surface being preserved. The matt surface is stated to give better sealing with a piston than a smooth bore. The bore of a tubular blank is roughened mechanically, e.g. by lapping or sand-blasting, or chemically, the resulting bore diameter permitting the blank to be placed over a mandrel which preferably has a coefficient of expansion greater than the blank. The heat applied expands the mandrel and blank differentially, the blank being so stretched that when the mandrel and blank are cooled, the latter is of the required bore size and may easily be removed from the mandrel. Alternatively, the blank, when softened by heat, may be pressed on to the mandrel by fluid pressure, such as external air pressure, by internal vacuum or by mechanically rolling the outer surface of the blank whilst the blank and mandrel revolve. The blank may be formed at one end with a nozzle for the needle, and at the other end with an outwardly directed flange, before the matt surface is produced by lapping. The stretching of the blank may be effected in stages on two or more mandrels. |
