Patent GB-1350851-A (GB)
Title: Manufacture of reinforced tubing
IPC: B29C48/92
Filed: 1972-06-08
Abstract: 1350851 Extruded reinforced tube DOW CORNING CORP 8 June 1972 [10 June 1971] 26734/72 Headings B4-B5 [Also in Division F2] An extruded reinforced tubing comprises a plurality of sequentially extruded tubular cured rubber or plastics layers, e.g. silicone rubber, intermediate each pair of which is applied an abutting and preferably non-overlapping helical web reinforcement, with sequential webs preferably being wound in opposite directions. The tubular layers are each extruded from a sequential die of a plurality 24-39, Fig. 1, supplied from the same extruder 59 and between each pair of which a web is applied from a rotating reel means 26-38, the tube being formed around a mandrel extending through all of the dies 24-39 from a mounting upstream thereof. The tube is formed upon a release film 21, e.g. of polyester, polyvinyl chloride or polyethylene, which is continuously drawn from a supply 22 thereof around the mandrel in tubular form, and serves also to lead the tube at the beginning of extrusion, by attachment to a metal pulling tape 46, optionally between concave supporting rollers, and through a curing oven 41 and into a traction device 44. The mandrel, e.g. of aluminium coated with polytetrafluoroethylene, tapers in the direction of extrusion. Each reel means comprises a pair of flanges, e.g. 48, Fig. 4, axially spaced apart by a series of rollers 51 supporting a coil 28 of the reinforcing web, and each reel means is mounted for rotation, about a fixed bearing ring (55), Fig. 6 (not shown), by means of a peripheral gear ring (57) of the flange (48) engaging with a gear driven by a common, or by an individual variable speed motor, e.g. 27, Fig. 1. Each web is guided from between the flanges, between a pair of pressure pads 50, and around a roller 52 which is mounted for adjustment of its radial position and the orientation of its axis with respect to the mandrel 23. The extrusion pressure of extruder 59 is controlled from a sensor 61, and extrusion material is fed therefrom to each die by a manifold from which an outlet channel of the same length leads to each die, via a pneumatically actuated on-off valve 66, a screw threaded vernier flow control valve (65), Fig. 9 (not shown), which is adjusted manually or automatically in response to an element sensing channel pressure, and a pneumatically actuated valve 68 which is operable at the commencement of extrusion to divert extrusion material to waste. The manifold may comprise a single chamber of large capacity in comparison with the channels, but may also comprise separate passages of equal length, Fig. 8A (not shown), each connecting to a channel. Each channel supplies a semi-annular passage, from the extremities 74, Figs. 10 and 11, of which extrusion material is supplied to the midpoint of part annular die passages 76, each of which communicates at its extremities at outlets 77 at equally spaced locations with an annular die passage 78 from which the extrusion outlet 81 leads radially inwardly. For larger diameter tubing, the outlets 77 may each communicate with a further passage or sequential passages serving to discharge into the passage 78 at respectively eight or more equally spaced locations. Extrusion is commenced, e.g. upon replacement of web supplies, with the valves 68 discharging to waste, prior to connection to the dies at a desired extrusion pressure, sensed at 61, followed upon development of the full required extrusion pressure by actuation of the drawing and reel means, and this sequence may automatically be effected by a timer. The reel drive motors are synchronized with the traction device 44 to ensure abutment of the helical web turns without overlap. The tube may be continuously cured downstream of the dies or prior to curing, may be cut and preshaped, e.g. by bending, for which a stretchable reinforcement web is desirable.