Process and apparatus for producing curved hollow bodies of thermoplastic material

A process for producing elongated curved hollow bodies at least partially comprising thermoplastic material wherein

• firstly a preform is extruded from an extrusion head of an system,
• the preform is engaged by a gripping means which is movable in space,
• the preform is moved by the gripping means into the region of a guide stencil arranged above the mold cavity of a mold portion of a divided blow molding mold for receiving the preform, the blow molding mold being so arranged that the mold cavity surface for carrying the preform includes a horizontal component at least on part of its longitudinal extent,
• the preform is introduced into the stencil by a downward movement of the gripping means and by a movement thereof following the configuration of the guide stencil, the guide stencil having first and second wall portions disposed at a spacing from each other and the spacing thereof increasing in an upward direction, the spacing at the bottom of the guide stencil approximately corresponding to the maximum width of the mold cavity whereby the preform is guided by the guide stencil towards the mold cavity in a definitive orientation relative thereto, the preform passing into the mold cavity through a lower opening in said guide stencil towards which said preform is guided by said wall portions,
• the blow molding mold is closed, and
• the preform in the closed blow molding mold is pressed by an increased internal pressure in the preform against the wall of the mold cacity thereby to form the hollow body therefrom,
• wherein the preform is pressed into the mold cavity by an additional means acting thereon from above through the guide stencil.

An extrusion blow molding apparatus for the production of elongate curved hollow bodies which at least partially comprise thermoplastic material, including

• an extrusion system including an extrusion head,
• a blow molding mold which is divided at least into first and second mold portions and having a mold cavity which corresponds to the desired shape of the hollow body to be produced and which when receiving the tubular preform to be inserted into the mold cavity of a mold portion is so arranged that the mold cavity surface that carries the preform includes at least one portion longitudinally extending in the same horizontal plane
• a guide stencil for the preform, the guide stencil extending above the blow molding mold along the length of the mold cavity of the mold portion which is in the preform-receiving position,
• said guide stencil including first and second spaced-apart wall portions which transversely with respect to the longitudinal configuration of the mold cavity are at a spacing which increases in an upward direction, wherein an open topside has a greater transverse dimension than an open underside, the open underside of the guide stencil at least approximately corresponds to the maximum transverse dimension of the mold cavity,
• a gripping means adapted to engage the preform from the extrusion head and introduce it into the guide stencil and movable in space in order to follow the configuration of the open topside of the guide stencil when inserting the preform, and
• means for moving the guide stencil between an operative position in which it is above the mold cavity and a position in which it is outside the region of movement of the blow molding mold portions upon closing movement thereof.

An extrusion blow molding apparatus for the production of elongate curved hollow bodies which at least partially comprise thermoplastic material, including

• an extrusion system including an extrusion head,
• a blow molding mold which is divided at least into first and second mold portions and having a mold cavity which corresponds to the desired shape of the hollow body to be produced and which when receiving the tubular preform to be inserted into the mold cavity of a mold portion is so arranged that the mold cavity surface that carries the preform includes at least two portions longitudinally extending in different planes,
• a guide stencil for the preform, the guide stencil extending above the blow molding mold along the whole length of the mold cavity of the mold portion which is in the preform-receiving position,
• said guide stencil including first and second spaced-apart wall portions which transversely with respect to the longitudinal configuration of the mold cavity are at a spacing which decreases in an downward direction, wherein an open topside has a greater transverse dimension than an open underside, the open underside of the guide stencil at least approximately corresponds to the transverse dimension of the preform,
• a gripping means adapted to engage the preform from the extrusion head and introduce it into the guide stencil and movable in space in order to follow the configuration of the open topside of the guide stencil when inserting the preform, and
• means for moving the guide stencil between an operative position in which it is above the mold cavity and a position in which it is outside the region of movement of the blow molding mold portions upon closing movement thereof.