Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Reshaping running or indefinite-length work
Patent
1996-11-22
1998-10-06
Silbaugh, Jan H.
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Reshaping running or indefinite-length work
2642094, 2642095, 425325, 425384, 425392, B29C 4790
Patent
active
058172700
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for manufacturing biaxially oriented tubing from thermoplastic material, comprising forcing the tube over a mandrel at an orientation temperature of the plastic material, which mandrel comprises an expansion part which produces expansion in the circumferential direction of the tube, the forcing over the mandrel being achieved by exerting a pushing force on the tube upstream of the expansion part of the mandrel by means of pushing means acting upon the outside of the tube, and by exerting a pulling force on the tube downstream of the mandrel. In the context of the present invention the term tube also relates to hose-type products.
BACKGROUND OF THE INVENTION
The present invention also relates to a device for manufacturing biaxially oriented tubing from thermoplastic material, comprising a mandrel over which the tube is forced at an orientation temperature of the plastic material, which mandrel comprises an expansion part which produces expansion in the circumferential direction of the tube, while the device for forcing the tube over the mandrel comprises pushing means which are placed upstream of the expansion part of the mandrel and, by acting upon the outside of the tube, can exert a pushing force on the tube, and also comprises pulling means placed downstream of the mandrel, for exerting a pulling force on the tube.
The object of biaxial orientation of the plastic material of a tube, also known as biaxially stretching a tube, is to improve the properties of the tube through orientation of the molecules of the plastic material of the tube in two mutually perpendicular directions. In the case of a certain known method the biaxial orientation is produced by forcing the tube over a mandrel, as a result of which the tube is deformed. Upstream of the mandrel the tube is brought to a suitable orientation temperature. In practice, a temperature distribution which is within a suitable range for biaxial orientation of the molecules of the plastic material of the tube is present inside the tube wall.
In the case of the known method an axial pulling force is exerted on the tube downstream of the mandrel. The solid mandrel comprises a conical expansion part which produces the increase in the dimensions in the circumferential direction of the tube. The fact that the tube passes over this expansion part essentially determines the orientation of the plastic material in the circumferential direction of the tube. The axial pulling force essentially determines the orientation in the axial direction. The biaxial orientation obtained is fixed (frozen) by cooling down the tube.
A method and device of the type mentioned in the preamble is known from EP-A-0 563 721. This publication describes how a tube with a cylindrical tube wall is manufactured in a continuous process by means of an extruder. Viewed in the direction of movement of the tube, a solid, undeformable mandrel with a conical expansion part is situated downstream of the extruder. The tube is forced over the mandrel at an orientation temperature which is suitable for the plastic material concerned, through a pulling force being exerted on the tube downstream of the mandrel. Upstream of the expansion part of the mandrel a pushing force is also exerted on the tube, i.e. a thrusting force in the direction of the expansion part of the mandrel. The additional pushing force permits a reduction of the pulling force exerted on the tube--which is limited in practice by the tear strength of the viscous plastic material of the tube--and a greater degree of biaxial orientation.
The pushing force is achieved by means of a so-called corrugator. The corrugator shown comprises two chains with hingedly coupled blocks, each of which is moved along a corresponding closed track. The two closed tracks have an active part in which the tube to be oriented is enclosed by the facing tube contact faces of the blocks of the two chains. An essentially cylindrical run-on part of the mandrel is situated in the interior of the tu
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patent: 3296661 (1967-01-01), Moustier
patent: 3856905 (1974-12-01), Dawson
patent: 5096634 (1992-03-01), Tsadares et al.
patent: 5449487 (1995-09-01), Jarvenkyla
patent: 5460771 (1995-10-01), Mitchell et al.
Prenger Jan Hendrik
Schuurman Johan
Visscher Jan
Eashoo Mark
Silbaugh Jan H.
Wavin B.V.
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