Patent GB-841968-A (GB)
Title: Method of and apparatus for lining and impregnating porous-walled conduits
IPC: B29C45/14
Filed: 1957-11-28
Abstract: 841,968. Moulding pipes. BENDIX AVIATION CORPORATION. Nov. 28, 1957 [Dec. 7, 1956], No. 37159/57. Class 87(2). [Also in Group XXVIII] A method of lining and impregnating the porous walls of a conduit having a central passage therethrough, with a sluggish fluid compound, is characterised by filling the passage in the conduit and the voids in the porous walls thereof with the compound under pressure and then forcing excess compound out of the passage and shaping the compound remaining in the passage into a smooth lining of substantially uniform thickness. In Fig. 1, the assembled but unimpregnated conduit is shown. In Fig. 2, a portion of the impregnated conduit is shown. As indicated in Fig. 1, the conduit comprises a plurality of superposed telescoped tubes or sleeves 14, 16, 18 made of braided wire. Each wire strand of the tube may be made up of about eight small wires laid side by side to simulate a flat strip. The larger diametered tubes may be braided directly on the smaller ones as a core. The end portions of the tubes 14, 16, 18 are firmly secured together by means of solder not shown. For the purpose of rendering the conduit moisture proof and at the same time to provide a smooth non-chafing inner surface on the conduit the assembled conduit is treated as described below to provide therein a lining 28 and at the same time to provide thin layers 15, 17 of the lining material respectively between adjacent layers of the metal tubes making up the wall of the conduit. A thin coating 19 of the lining material is preferably also disposed upon the outer surface of the metal tube 18. The layers 15, 18 and 19 are integrally connected to each other and to the lining 28 through the braiding of the metal tubes. Elastomers such as those having a polyvinyl-chloride base and silicone rubbers have been found suitable. One such silicone rubber or silastic compound is that sold under the name Dow Silastic 132. Another lining material which has been found suitable for use in flexible conduits for radio shielding aircraft engine ignition systems for example is a synthetic plastic material known as plastisol, i.e. a fluid dispersion of polyvinylchloride polymer in a plasticizer which may be converted by heat alone to an elastomeric vinyl compound. This material has a polyvinylchloride base with suitable plasticizers and a heat stabiliser. Suitable fillers may be used if necessary. A suitable composition consists of ten parts by weight of polyvinyl chloride such as Geon 121 four parts of Rohm and Haas Paraplex C-50 two parts of Paraplex C-60 (Appolyester) and two parts of a heat stabiliser consisting of a mixture of Paraplex C-50 and dibasic lead phthalate in equal parts "Geon" and "Paraplex" are both Registered Trade Marks. The Geon 121 should be in the form of a fine powder the plasticizers (Paraplex) are added in liquid form and the heat stabilizing mixture is added in finely powdered well mixed form. The ingredients are then mixed thoroughly preferably under vacuum. Impregnating material may be introduced into the mould by means of an injection cylinder containing an axially displaceable piston (not shown). The material is injected until it has filled the central passage in the conduit and the interstices or voids on the porous side walls of the conduit and has formed the layers 15, 17 and 19. After the conduit has been filled and the walls thereof impregnated the thrusting force remains on the piston. A mandrel 61 is then thrust to the left so as to travel through the central passage in the impregnated conduit. The excess plastic material is thrust axially through the conduit and back into the cylinder against the thrusting force on the piston. Portion 63 of the mandrel smooths the lining layer and forces out through the conduit wall any plastic material in excess of that required to form the layer 28. The impregnated conduit is transferred to an oven and baked for a suitable time and at a suitable temperature.