Coextrusion die

Details Coextrusion die Coextrusion die

1981-10-20

1983-09-13

Thurlow, Jeffery R.

Plastic article or earthenware shaping or treating: apparatus

With apparatus assembly or dismantling means or with idle part

For extrusion or injection type shaping means

264512, 264514, 264173, 2642091, 2642098, 4251311, 4251331, 425380, 425381, 425462, 425467, B29F 304

Patent

active

044039344

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to an extrusion die for the coextrusion of plastics materials in the form of a tubular film, said apparatus comprising means for separately supplying at least two extrudable materials in fluid state, a system of distribution channels connected to each supply means to form partial streams of said extrudable materials, each system of distribution channels opening into an annular collecting chamber, and an annular extrusion slot communicating with said annular collecting chamber(s).


BACKGROUND ART

In a prior art coextrusion die of the above mentioned type each extrudable material is supplied in liquid state through a centrally located supply conduit which is connected to a system of radially extending distribution channels, each system being provided in a distribution plate, and is then passed into an annular collecting chamber from which it is passed into a common annular extrusion slot.
Due to the presence of the radially extending distribution channels in the prior art coextrusion there is insufficient space for the strong clamping bolts which are required to maintain the distribution plates sufficiently tensioned to avoid leakage of extrudable materials between said plates at high extrusion pressures.
The prior art supply system for extrudable materials comprising centrally located supply conduits also suffer from the drawback that it allows no space at the centre of the die for provision of driving means when it is desired to rotate the inner and outer die parts relative to one another or for the provision of supply and discharge conduits for gaseous coolant, such as air to cool and expand the extruded tubular film. In the absence of such cooling, the production rate is considerably reduced.
The object of the invention is to provide a coextrusion die providing sufficient space for the provision of clamping bolts, means for rotating one of the die parts relative to one another and supply and discharge conduits for gaseous coolant.


DISCLOSURE OF INVENTION

According to the invention there is provided an extrusion die wherein the distribution channel system for each extrudable material comprises at least two arched channels provided in different axial planes, the ends of each arched channel being connected to the middle portion of the following arched channel and wherein the distribution channel systems are located at different distances from the centre axis of the extrusion die.
In the following the invention will be described with reference to an extrusion die for the coextrusion of three extrudable materials, wherein the arched distribution channels are circular arches and wherein the distribution channel systems are located concentrically because the use of such distribution channels and the concentric mounting of these systems are particularly advantageous as far as the manufacture of the extrusion die is concerned.
However, it should be understood that the die may comprise two or more than three distribution channel systems and that the arched distribution channels should not necessarily have the shape of circular arches and even may be composed of linear channel sections and that the distribution channel systems do not have to be concentrically mounted.
The invention is based on the discovery that by effecting the distribution of each extrudable material in a labyrinthic manner in different distances from the centre axis of the die and in different axial planes thereof, it is possible to avoid conduits for supplying extrudable materials to the die and radially extending distribution channels in the central zone of the die. Thus, the supply conduits can be connected to the end surface or exterior surface of the die and can be connected to the first arched channel of each distribution channel system through connection channels provided in the die.
Thus, the necessary clamping bolts can be inserted between the distribution channel systems and and driving means, if any, for the rotation of the inner die part as well as conduits for gaseous coolant can be mount

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