Method and apparatus for producing a finned tube from synthetic plastics material

A method for forming a finned tube from a synthetic plastic material, comprising

• continuously extruding said synthetic plastic material in molten form around a fixed axially extending core while simultaneously forming an axially moving exterior moulding chamber thereabout and continuously moving said moulding chamber in an axial direction of production away from the point of extrusion, said moulding chamber having radially extending fin forming vented slots therein and a plurality of radially extending conveyor grooves each having an upstream conveying surface disposed at substantially a right angle with regard to the direction of production and a flank shallow pitched in the direction of production,
• forcing molten plastic into said vented mould recesses to completely form in sequence a series of radially extending fins one after another, an upstream fin being formed only after its immediate downstream adjacent fin has been completely formed,
• forcing molten plastic into said conveyor grooves to form a series of raised portions having a height equal to about 0.12-0.16 times the minimum wall thickness of said tube being formed, and
• advancing said tube in the direction of extrusion as it is being formed by movement of said moulding chamber in the direction of extrusion while maintaining frictional interengagement between said conveyor grooves of said moulding chamber and said raised portions of said tube.

An apparatus for carrying out a method for producing a finned tube from synthetic plastics material, the tube being provided with raised portions (63) of height equal to about 0.12-0.16 times the minimum wall thickness of said tube, said raised portions having conveyor faces (64) trailing in a direction of production (4), with pairs of encircling half moulds (2, 2', 2a) which supplement each other on a moulding line (9) to form a mould which moves in a direction of production (4), the half moulds (2, 2', 2a) comprising, defining an outside of a moulding chamber (27), a mould recess (28) formed alternately by portions (60) for moulding an outside wall of the tube and vented mould recesses (61) for completely forming the fins, with, preceding the moulding chamber (27) in the direction of production (4) a nozzle (25) with a nozzle gap (37) and with a core (36) adjacent the nozzle gap (37) and defining an inside of the moulding chamber (27) and widening out in the direction of production (4) towards the moulding recess (28), forming a draught (43), with, immediately adjacent the nozzle gap (37) and constructed between the draught (43) of the core (36) and the moulding recess (28) an expansion space (38) with, preceding the expansion space (38) and constructed between the moulding recess (28) and the nozzle (25), a safety gap (34) and with a cooling core (55) on a downstream side of the moulding core (36) in the direction of production (4), wherein the portions (60) for moulding the outside wall of the tube are provided with conveyor grooves (62) of size to form said raised portions (63), said conveyor grooves (62) being provided with a conveying surface (64) on a rearward side and at substantially a right angle with regard to the direction of production (4), said conveyor grooves (62) having flanks (65) which are shallow pitched in the direction of production.