Plastic article or earthenware shaping or treating: apparatus – Means feeding fluent stock from plural sources to common... – Extrusion shaping means
Patent
1998-02-13
1999-10-26
Pyon, Harold
Plastic article or earthenware shaping or treating: apparatus
Means feeding fluent stock from plural sources to common...
Extrusion shaping means
4253824, 425462, 425465, B29C 4706, B29C 4714
Patent
active
059717360
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a device for joining at least two material flows in a laminar coextrusion machine.
2. Description of Related Art
Extrusion machines are used to transform plastic raw material into a sheet that can then be worked.
The plastic materials known at this time have specific characteristics.
Also, there is no single plastic material which combines all the characteristics desired for a particular use.
For example, some materials have good mechanical strength while others are resistant to external factors, such as ultraviolet rays, and still others are particularly suitable for working at high or low temperatures.
In order to obtain an object having the desired characteristics, it is known to produce multilayered products by means of a process known as coextrusion.
There are two types of coextrusion, one called "manifold" coextrusion which consists of using, for each material, an extruder and as many extrusion heads as there are layers to be constituted.
These heads converge on an extrusion die where the layers are joined.
With this type of coextrusion, each material is handled separately along its entire path, which makes it possible to use extremely different materials with widely varied melting points, but operation is very complex and the material very expensive.
The other coextrusion process, which is the one to which the invention relates, is the process known as laminar extrusion.
In this process, the joining of the layers takes place in a channel disposed upstream from a single extrusion head in a tool called an extrusion box.
For this reason, the different layers must move at the same speed and continuously in order to prevent any shear.
It is therefore necessary to obtain a laminar flow in each layer.
In order to obtain and maintain this laminar flow, it is necessary to reduce the causes of disturbances, that is mainly, the losses of pressure that result in changes in the cross-section of the channels for transporting the flows and in their directions.
A laminar coextrusion unit of this type comprises: layers of different materials to be joined, issuing from the extruders into a so-called global flow, this device also being called a distribution box, and global flow.
This joining device essentially comprises a main channel into which opens, for each material flow, a so-called supply channel connecting each end to the main channel.
In the first coextrusion systems, the flow of a first viscous material was introduced into this extrusion box in the form of a cylindrical rod which constituted the core of the product, and the other flows conformed to the circular cross-section of the flow up to its outlet, where all of the flows were then transformed into a planar sheet with the aid of a geometric transformation means.
This geometric transformation means was essentially comprised of a so-called geometric transformation channel of rectangular cross-section which was perpendicular to the axis of movement of the rod downstream from the main channel and wherein the cross-section of this geometric transformation channel increased in at least one of the two dimensions of its cross-section, and in the direction of movement of the flow, until the desired cross-section was obtained.
This geometric transformation on output is not easy to obtain given that this is a multi-component product with different viscosities and properties.
Thus, it was difficult to conform to the different tolerances of each layer.
In order to eliminate the problems of the geometric transformation of a multi-layer rod, it is known to preform each layer before they are joined, and for this reason, the above-mentioned geometric transformation means is placed in the path of each extruder flow and upstream from the point at which these flows are joined (U.S. Pat. No. 5,137,675).
Thus, extrusion devices become extremely complicated when it is necessary to equip the extruders with a multiplicity of parts designed to be removable for cleaning.
The devices are even more compl
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Extrusion de Basse Normandie-Exbanor S.A.
Kerins John C.
Leyson Joseph
Pyon Harold
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