| 摘要 |
1,217,729. Coating cores by extrusion. BENTELER-WERKE A.G. 24 Sept., 1968 [29 Sept., 1967], No. 45371/68. Heading B5A. [Also in Division F2] A method of continuously providing a metal tube with a coating of foamed plastics material comprises passing the tube, while at or below ambient temperature, through an extruder cross-head 4, where at the point of application of the plastics any air and/or evolved gases are withdrawn, smoothing the surface of the coating and cooling the coated tube. Preferably the cooling is in two stages, which as shown, is by passage through a tank 11, e.g. containing water at 50-60‹ C, and through a second tank 12, e.g. containing water at 10-20‹ C. The external diameter of the coated tube is monitored by devices 10, 13, and signals generated thereby control the rate of working of tube feed device 3. The air or gases are withdrawn from cross-head 4 by means of a vacuum pump 16 via line 15. The tube may be taken from a reel 2 and straightened by feed means 3, with subsequent cutting of the coated tube, or short lengths of interconnected tubing may be fed to the cross-head. The cross-head, Fig. 3, comprises an axially adjustable mandrel 19 which controls the rate of flow of the plastics material. Ring 26 smoothes the coating and is preferably made of PTFE, and electrical resistance heaters 27 are provided. The foaming agent, e.g. azodicarbonamide, is present in an amount of 0À2-1À5 parts by weight and to the plastics and agent may be added a lightweight thermally insulating material such as asbestos or powdered diatomite, e.g. in an amount of 6-15 parts by weight. |
