CA2032257A1

CA2032257A1 - Extrusion die for the production of hollow-chamber panels

Info

Publication number: CA2032257A1
Application number: CA002032257A
Authority: CA
Inventors: Hans Lorenz; Heinz Gross
Original assignee: Roehm GmbH Chemische Fabrik
Current assignee: Roehm GmbH Darmstadt
Priority date: 1989-12-23
Filing date: 1990-12-14
Publication date: 1991-06-24
Also published as: EP0435078B1; ES2070257T3; DK0435078T3; DE8915137U1; EP0435078A1; DE59008479D1; ATE118400T1; JPH04135824A

Abstract

ABSTRACT
A new extrusion die for the production of hollow-chamber panels, contains two parallel slits (1), formed by lips (4, 5), for the extrusion of two parallel plane outside walls of a hollow-chamber panel and a core piece (2), which is placed between slits (1) and in which a multiplicity of cross-slits (3) are cut for the extrusion of webs and according to the invention one of the two lips (4, 5), which form slit (1), is designed flexibly and flexible lips (4, 5) can be adjusted by a multiplicity of control elements (7) which are independent of one another. By the new extrusion die, hollow-chamber panels with increased crosswise rigidity can be produced, since thickness variations of the outside walls, which would affect-the crosswise rigidity, can be reduced.

Description

2~32257 DESCRIPTION
~xtrusion d_e for the production of hollow-chamber panels . The invention relates to an extrusion die for the production of hollow-chamber panels from thermoplastic, for example, from poly(methyl methacrylate), polycarbonate or pol~vinyl chloride.
Known extrusion dies for this purpose contain according to DE-A 15 04 800 two slits 1, formed by lips 4, 5, running in a straight line and parallel over the width of the extrusion die, for the extrusion of two parallel plane outside walls of the hollow-chamber panel and a core piece 2, which is placed between slits 1 and in which a multiplicity of cross-slits 3 are cut, which come out into slits 1 and serve for extrusion of webs which connect the outside walls of the extruded hollow chamber to one another. Preferahly cross-slits 3 are placed at right angles to slits 1.
The hollow-chamber panels produced with such extrusion dies, which are also identified as web panels or web double panels, have achieved a significant place in construction. Often rectangularly limited sections of such hollow-chamber panels are laid horizontally or slightly inclined so that their lateral edges, running in the extrusion direction, rest on a suitable substructure and the intervening surface of the section is freely supported. This assumes a sufficient crosswise rigidity, which, besides its own weight, optionally must take into account additional live loads such as wind pressure or snow load. To guarantee its crosswise rigidity at a width of 1 to 1.2 m, a 2 0 3 2 ~ ~ 7 wei~ht per unit area of at least 4.7 kg/m2 is prescribed in the building permit for hollow-chamber panels made of PM~A. This regulation starts from the assumption that a like crosswise rigidity at a lower weight per unit area could not be achieved.
It sets a bottom limit to the requirement of plastics for the production of hollow-chamber panels.
Object and achievement The object of the invention is to provide an improved extrusion die with which hollow-chamber panels can be produced of like crosswise rigidity at lower weight per unit area or higher crosswise rigidity at the same weight per unit area.
With the known generic type extrusion dies the outside walls of the hollow-chamber panels are produced by rigid lips. The feed of the thermoplastic molding compound within the extrusion die to the lips is generally controlled by a choke bar, which for design reasons has considerable rigidity, but is adjustable to a limited extent to guarantee a uniform delivery of molding compound over the entire width of the extrusion die. Differences in the flow resistance of the molding compound between the center and ends of the extrusion die can be largely equalized by the choke bar so that the thicknesses of the outside walls are basically the same over the entire width of the extruded hollow-chamber panels.
It has now been found that the crosswise rigidity of the extruded hollow-chamber panel can be improved if for their production an extrusion die of the generic type is used, in which 3 ~0~22L~7 one of the two lips 4, 5, which form slit 1, is designed flexibly and the flexible lips 4, 5 can be adjusted by a multiplicity of control elements 7 which are independent of one another. During extrusion flexible lips 4, 5 can be adjusted with great accuracy to the required thickness of outside walls.
The crosswise rigidity of the hollow-chamber panel depends decisively on that of the outslde walls. It is again affected by the thickness variations of the outside walls. I~ was determined that the crosswise rigidity of a plastic panel of uneven thickness is not greater than tha~ of a completely even panel which is as thick at the thinnest spots of the uneven panel.
The material, which is contained in the thickness variations of the uneven panel, is lost for the crosswise rigidity.
By the adjustable flexible lips according to the invention present in the extrusion die the thickness of the outside walls can be adjusted to the required thickness substantially more accurately then with usual extrusion dies, which have rigid lips.
The crosswise rigidity of the hollow-chamber panel thus extruded corresponds substantially to the required thickness and is not reduced by thickness minima, which unavoidably occur with the usual extrusion dies. The thickness variations of usually produced extrudates is due to melt throughput variations over the width of the extrusion die, which can have a series of causes.
These include defects in the design or embodiment of the manifold, temperature differences in the molding compound melt or 4 203~2~7 in the die body or deviations from the originall~ provided operating point of the die.
~ 'ith the specified requirement on the crosswise rigidity the required thickness of the outside walls can be di~ensioned as low as the thickness minimum of a usual hollow-cham~er panel with uneven outside walls of correspondingly higher required thickness. With the use of usual extrusion dies with rigid lips thickness variations up to ~ 20%, at times up to ~0%, on the outside walls occur; they cannot be avoided either by an elaborate temperature control or by a fine control of the choke bar adjustment. By the extrusion die according to the lnvention the thickness variations can be reduced to + 5~. As a result, the required *hickness can be reduced by up to 15~. In view of the weight of the webs, a reduction of weight per unit area of the hollow-chamber panel up to 10% with constant crosswise rigidity results. A particular advantage of the extrusion die according to the invention resides in the fact that a choke bar can be completely dispensed with, since the molding compound flow can be controlled soley by the flexible lips.
Embodiment of the invention A suitable configuration of the extrusion die according to the invention is seen in figure 1, which shcws a cross section through the die.
Extrusion die 10 contains an intake channel 11 for the thermGplastic molding compound~ which can be connected to an extruder. Intake channel 11 inside the die is divided into two 2 ~ ~ 2 2 ~ 7 feed channels 12, from which the molding compound reaches the manifolds 13 placed crosswise over the entire die width. ~rom there the molten molding compound goes into slits 1 on both sides of core piece 2. One part of the molding compound flows out of slits 1 into cross~ise slits 3, which are cut into core piece 2, and, on leaving the crosswise slits, forms the webs of the hollow-chamber panel. On lips ~/5 the molding compound leaves in the form of the outside walls of the hollow-chamber panel. The thermoplastic hollow extrudate is cooled below the softening temperature in a vacuum forming channel (not shown), which is placed tight behind extrusion die 10 and thus obtains its final configuration.
According to the invention one each of the two lips 4, 5, which form slit 1, is designed flexible. For this purpose, lip 4 is placed on the end of a tongue 14 extending over the die width, a tongue whose length and thickness are dimensioned so that lip 4 can be pushed into slit 1 by control elements 7, as a result of which its inside width is reduced. Such an arrangement is identified in technical language as "flexlip" and is used otherwise only in the extrusion of thin sheets.
The elastic bending clearance of the flexlip under the action of control elements 7 is on the order of O.O1 to 0.5 mm.
In the extrusion of thin sheets the molding compound flow of the extruded sheet web can be reduced locally, for example, by up to 50% by a flexlip. But the outside walls of an extruded hollow-chamber panel are substantially -thicker, e.g., 0.5 to 3 mm.

6 20322~7 Consequently, the effect of the flexlip on the thickness of the extruded web is relatively much smaller; it is on the order of 30~ at most.
Suitably the ex*rusion die according to the invention is designed symme*rical to core piece 2 so that both slits 1 can be adjusted in the same way. For the adjustment of the slit width it is sufficient if one each of lips 4/5, which form slit 1, is designed flexible. Preferably it is outside lips 4.
The exposed external sides of extrusion die 10 as well as the exposed sides of ton~ues 14 can be provided with thermal 1nsulations-or heating jackets to guarantee a uniform temperature control.
Screw bolts can be used as control elements 7, which can be adjusted by head 15. The closer control elements 7 are placed next to one another, the finer the slot thickness can be adjusted. The center-to-center distances of the control elements can be, e.g., 8 to 40 mm. Preferably short screw bolts 16 are used for rough adjustment, while for fine adjustment electrical expansion pins or piezotranslators can be used, which can be placed coaxially to screw bolts 16. They can be connected by a control unit to thickness measuring sensors, which measure the thickness of the outside walls in the relevant area of the extruded hollow-chamber panel and indicate a corresponding measured quantity to the control unit. For the thickness measurement, for example, an absorption measurement in a spectral range, in which the extruded molding compound absorbs a radiation 7 2~22~7 as a function of the layer thickness, is suitable. In this way, a setpoint for the provided thickness of the outside walls of the hollow-chamber panel, which is input in the control element, is automatically compared with the measured actual value and is converted in a suitable control quantity for the adjustment of the electrical expansion pins or piezotranslators.

Claims

1. Extrusion die for the production of hollow-chamber panels, containing two slits (1), formed by lips (4, 5), running in a straight line and parallel over the width of the extrusion die, for the extrusion of two parallel plane outside walls of the hollow-chamber panel and a core piece (2), which is placed between slits (1) and in which a multiplicity of cross-slits (3) are cut, which come out into slits (1) and serve for extrusion of webs which connect the outside walls of the extruded hollow chambers to one another, characterized in that in each case one of the two lips (4, 5), which form slit (1), is designed flexibly and in that flexible lips (4, 5) can be adjusted by a multiplicity of control elements (7) which are independent of one another.

2. Extrusion die according to claim 1, wherein crosswise slits (3) are placed at right angles to slits (1).

3. Extrusion die according to claim 1 or 2, wherein it contains electrically heated expansion pins or piezotranslators as control elements (7).

4. Extrusion die according to claim 3, wherein the electrically heated expansion pins or piezotranslators are connected by a control unit to thickness measuring sensors, which measure the thickness of the outside walls in the relevant area of the extruded hollow chamber panel.