CA1183667A

CA1183667A - Device for producing cellular structures of thermoplastic material

Info

Publication number: CA1183667A
Application number: CA000389059A
Authority: CA
Inventors: Robert E. Lhommeau; Guy R. Ducruy
Original assignee: INDUMAT SA
Current assignee: INDUMAT SA
Priority date: 1980-10-30
Filing date: 1981-10-29
Publication date: 1985-03-12
Also published as: DE3142876C2; IT1140016B; GB2086304B; GB2086304A; NL183017C; JPS57105322A; FR2493219A1; US4478563A; DE3142876A1; NL8104865A; JPS6220886B2; FR2493219B1; BE890899A; IT8124769A0; LU83716A1

Abstract

ABSTRACT OF THE DISCLOSURE

The present invention concerns manufacture of cellular structures of thermoplastics material. In particular the invention concerns apparatus for use in the production of cellular structures of thermoplastics material comprising a supply and injection stage (b) for supplying the thermoplastics material (12), a die stage (e) throughwhich the thermoplastics material supplied by the supply and injection stage is extruded to form the cellular structure (15), and a cooling stage (d) supplied in use with cooling fluid (4) for cooling the extruded thermoplastics material, the different stages being located one above the other and the apparatus further comprising a plurality of regularly spaced cylinders (7), each cylinder (7) having a lower part (10) of lesser diameter provided with heating means (11) and an upper part (8) of greater diameter, the bodies of the cylinders extending through the supply and injection stage and the upper parts thereof forming said die stage. The invention is particularly applicable to the manufacture of cellular structures of large dimensions for buildings.

Description

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BACKGROUND~ OF THE INVENTION
The present invention concerns a device for producing cellular structures of thermoplastic material.
The cellular structures to which the invention relates ma~
be defined, in a general manner, in the following way:
they are structures formed by cells or chambers which are cylindrical, parallel, contiguous and separated by thin or thick walls. The term cylindrical should be in-terpreted as generally accepted, the form of the cells thus being defined by the surface described by a straight line or generatrix being displaced parallel to itself whilst following a closed curve referred to as a directrix. The shape of the directrix may be round, oval, elliptical or polygonal, for example.
The directrix form especially aimed at is the hexagon, the cellular structure thus defined then being of the honeycomb type.
DISCUSSION OF THE PRIOR ART
Structures of the aforesaid kind and produced from thermoplastic materials are already known. ~s a rule, they are obtained by processes of two kinds. The first process consists in staxting from a sheet of plastics material and using heat-moulding. A process of this kind cannot be applied in cont:inuous manner, it requires a sizeable plant and substantial modifications must be made to change the form of the structure produced Moreover, in accordance with a process of this nature~ the height of the cylindrical cells produced is affected by limitations.
The second process consists in injecting a soft-ened thermoplastic material into a closed mould, the product setting thanks to a cooling operation on the walls of the mould which follows the injection stage. This second technique cannot, by definition, be applied except piece-by-piece and it is thus impossible to envisage a continuous application. Furthermore, in accordance with this second process a complex plant is necessary if it is wished to ,,,,, , ~ .

obtain cellular structures having thin walls and large dimensions.
Finally prior art devices are known for the production of the said cellular structures which allow continuous production and which commonly comprise a plastics material feed stage, a die stage for extrusion of the plastics material, and a cooling stage for the cellular pro-duct obtained and which is supplied with a cooling fluid;
the different stages being situated one above another and the die stage being formed by evenly spaced apart cylindri-cal elements. Devices of this kind are described in par-ticular in the following patents:
- USA Patent No. 3,616,018 - USA Patent No. 3,825,641 - French Patent No. 78 33678 - French Patent No. 74 30736 - USA Patent No. 3,792,951 - USA Patent No. 3,038,202 The clevices described and illustrated in these patents render it possible to produce cellular structures of the said kind, but have the disadvantage that the dimensions of the obtainable produces are still extremely limited, meaning that the number of cells which may be produced at the same time remains very small.
As a matter of fact, to obtain appropriate prac-tical results in the case of elements of large size, it is essential that the supply of thermoplastic material should be perfectly uniform in respect of temperature and pressure.
It is equally necessary that the cooling action should be performed right at the outlet from the extrusion stage and this in uniform and homogenous manner for each of the individual cells.
None of the prior art devices cited in the fore-going allow an operation of this nature, and the dimensions of the products obtainable remain very small.

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In accordance with the USA Patent No. 3,616,018 for example, the extrusion device (see Figure 4) comprises a single feed 2 for the totality of the individual cells which are to be produced, and the extruded product is then cooled in a separate device comprising external cooling plates 4 (Figure 1). Moreover, at the level of the extru-sion device 1, air is fed into a common chamber 16 and from the latter via longitudinal passages 13 situated in each tubular element 14 forming the extruder.
It is clearly apparent that, in this case, the supply of thermoplastic material is not homogenous through-out the dimensions of the extruder; analogously, the tempera-ture and pressure of the air fed from the chamber 16 and through the ducts 13 also varies from one tubular element 14 to another, so that it is impossible to envisage the production of elements of large dimensions.
Analogously, the operation of cooling by means of

2 separate device causes the same results and moreover raises the risk of a deformation of the structure obtained between the extruder and the cooling device.
To eliminate the last disadvantages, the USA
Patent No. 3,825,641 makes use of a forming device at the outlet of the extrusion head, which is intended to guide the product obtained during its cooling to assure the stability of its geometrical configuration.
The device described in the French Patent No.
78 33678 has the same disadvantages.
In the device according to the French Patent No.
74 30736, so-called calibrating devices are incorporated to assure the geometrical stability of the extruded product during its cooling.
Finally, a device is described in the USA Patent No. 3,039,2G2, which comprises an extrusion head, cooling means and separate calibrating or sizing means, and in which the heating and cooling operations are provided simulta-6~

neously for the totality of the individual cells produced, that is to say in an inhomo~enous manner.
OBJEC~5 OF-THE INVENTION
Considering the empty spaces they contain and the multiple walls defining them, the cellular structures of the typP described in the foregoing have considerable heat and noise insulation qualities and mechanical properties which are of interest. As a result, such cellular structures are sough~ after for building purposes, for example for forming vertical or horizontal walls in particular, and rnay replace expanded, sandwiched and composite materials which are already known and in use.
The present invention has as its object a device of the kind described in the foregoing and which renders it possible to eliminate the prior art disadvantages already set out, by allowing the production of cellular structures of large dimensions, by which is meant elements comprising a very great number of individual cells.
SUMMARY OF THE INVENTION
~n accordance with the invention, the said c~lindrical elements comprise a lower portion of smaller diameter e~uipped with heating means which delimits the said supply stage, and an upper top portion of a greater diameter forming the said die stage.
Thanks to the structure in accordance with the invention, the supply of thermoplastic material at the level of the cylindrical elements forming the extrusion head is perfectly uniform in temperature and pressure, since each of the cylindrical elements includes its own heating means.
Furthermore the cooling fluid of the said cooling stage is conveyed through the said cylindrical elements. In this manner, each cell-like element produced is cooled separately and immediately upon its emergence from the cylindrical elements, meaning from the extrusion head, so that a uniform overall cooling action is obtained for the product as a whole.

, :~1133~7 Furthermore, the cooling fluid thus assures retention of the geometrical configuration of the individual cells at the outlet of the cylindrical extrusion elements, thereby averting the necessity for forming or si~ing means as described in the prior ~rtO
The device preferably comprises passages for supplying the said cooling fluid, which are situated within said cylindrical elements and are separated from the internal surface of these by a layer of A heat insulating material. In this manner a heating action on the cooling fluid is prevented during its passage through the cylindrical elements.
The said top portions of the cylindrical elements are advantageously capped by a dome traversed by the said supply ducts, the said topiportions being formed from a heat insulating material and the said domes being,produced from a heat insulating material. These steps allow of an addi-tional improvement of the instantaneous cooling action at the level of the outflow extrernity of the cylindrical elements.
According to a particularly advantageous embodi-ment, the said top portions and the said domes are formed from polytetrafluoroethylene.
The device in accordance with the invention may -in known manner - include a device for withdrawing extruded material and which pulls the latter in the direction of extrusion. In this case, the withdrawal or extraction device may comprise endless driving belts equipped with protube~ances which co-operate with the periphery o~ the product made, the speed o~ the said belts being positively controlled as a function of the delivery of the die stage.
If a continuous production is to be performed, th~ device may comprise a severing device which is of the cutting wire type and is carried by a carriage displaceable in the direction of extrusion so that the product may be cut to lengths without stopping the extruding operation.
Finally, in accordance with another advantageous embodiment the said cooling fluid may have a higher density than that of the thermoplastic material extruded, which eases and speeds up the advance of the extruded product at the level of the cooling stage. In the said cooling stage, the cooling fluid is preferably in direct contact with the said top portions and the dome of each of the cylindric~l ~I-~o~b~ r.~ _~oli~ ~

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then sets in immediately following the extrusion ~tage and the risk o~ a deformation of the geometrical configuration of the individual cells is reduced com-plementarily.
Accordingly, the invention is broadly claimed herein as a device for upwardly extruding a multiple tube structure from a thermoplastic matexial comprising: an extrusion die comprised of a plurality of reguIarly spaced cylinders having upper ends defining extrusion orifices therebetween; means mounting said cylinders in upright regularly spaced relation to each other so that there are spaces.between adjacent cylinders, each cylinder having a lower portion of smaller diameter than the upper end; heating means associated with the lower portion of each cylinder, said upper ends being of a greater dimension than the lower portion and of a heat insulating mate:rial; supply means for injecting fluid thermoplastic material to a bottom region of each space between the adjacent cylinders; a liquid cooling bath above and in direct contact with the upper ends of the cylinders; a cooling liquid passage extending through each cylinder in thermally insulated relation to the cylinder; means for supplying liquid to said cooling bath through said passages extending through each cylinder;
traction means in said cooling bath for pulling extruded multiple tube structure solidified by said bath upwardly through the bath, and cutting means in said liquid cooling bath for cutting the solidified multiple tube structure.
BRIEF DESCRIPTION OF THE D~AWINGS
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Other features and advantages of the invention will emerge upon perusing the following description, whilst referring to the accompanying drawinys which were given solely by way of non-limiting examples, in which.
Figure 1 is a diagrammatical-overall view of one emhodiment according to the present invention for the production of cellular structures of large dimensions, Figure 2 is a diagrammatical outer view of a cylinder forming the die stage and passing through the plastics material inje~tion stage, Figure 3 is a diagrammatical plan view of the tops of the said cylinders/
Figure 4 is a view in cross-section of cell-like structures of hexagonal section in the plane at right angles to the generatrix of the cells, Figure 5 is a view in perspective of a part of the cellular structure according to Figure 4 and after parting off along two mutually parallel planes, Figure 6 is an outer view of a modiied form of the said cylinders, Figure 7 is a view in longitudinal cross-section of ihe cylinder of Figure 6 along a plane passing through its axis, Figure 8, second sheet of drawings, is a view from above of the cylinder of Figure 6.
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DETAILED DESCRIPTION OF A PP~EFERRED EMBODIMENT
Referring now to the accompanying drawings Figure 1 shows a diagrammatical cross-sectional view of a plant for the production of celluIar structures.
For the purpose of clearness, the plane of Figure 1 will be assumed vertical.
The description and drawings specifically relate to the production of a cellular structure whereof the cells have a -/---/

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unifoxm hexagonal cross-section; however it will be fully appreciated that the present invention encompasses all other cross-sectional forms and in particular circular, oval, elliptical or polygonal forms of regular or irregular nature in general.
As seen from the bottom to the top, the plant shown in Figure 1 comprises five stages which are the following:
- a stage a for the supply of a cooling fluid which comprises a tank 1 fed with cooling fluid via a pipe 2 con-nected either to a source of fluid or to the outlet of a cooling fluid recycling circuit. The fluid passes through the second and third stages of the plan-t, being ducted to the fourth and cooling stage d by means of small-bore pipes

3. The cooling fluid 4 travels upwards from below/ from the tank 1, that is to say according to the arrow f. An insula-tion is incorporated along the trajectory through the second and third stages b and c of the pipes 3; this will be described in greater detai3 hereinafter - a stage _ for supplying thermoplastic material, the latter being injected in the fluid condition at the base of the stage _ via an injection tube 5. The thermoplastic material utilised is at a temperature of the order of 240C.
This may for example be polypropylene. The base of the second stage b is formed by a partition 6 traversed by the cylinders 7 which also pass through the stage _ as a whole and whereof the tops 8 form the third and so-called die stage c. At their centre, the cylinders 7 have a cavity 9 traversed by the cooling fluid pipes 3. The insulation between these pipes 3 and the wall 10 of the cylinders 7 is formed in this case by air. The wall 10 of the cylinder 7 is thick and provides heating, the heating action being produced by a network 11 formed either by electrical resist-ances or by heating fluid passages. The thermoplastic material 12 is consequently kept in the fluidstate thanks to its contact with the walls 10 of the cylinders 7, a temperature sensor 13 allowing temperature of the thermo-plastic material 12 to be controlled by acting on the heating system of the walls 10 of the cylinders 7. This wall may, for example, be kept at an even temperature of the order of 250C. The outer shape of each cylinder 7 has a flare at the top of the cylinder, at the upper sec-tion of the second stage b, in the direction towards the passage orifices of the die stage c for the purpose of easing the displacement and advance of the thermoplastic material 12. Two cylinders 7 which allow production of a section of a cellular structure comprising a central cell and incomplete peripheral cells, are illustrated in unbroken lines in Figure l;as is shown in dotted lines, the dimen-sions of the plant and the number of cylinders 7 may beincreased at will ir. such manner as to produce complete panels of cellular structure, that is to say structures comprising a substantial number of cells.
- The die stage c is thin, insulating and comprises the tops 8 of the cylinders 7. In the example illustrated, these tops have a uniform hexagonal outline; each is capped by a dome 14. The traversal of the die stage c by the cooling fluid pipes 3 also provides insulation as stated in the foregoing, this is by the actual material of the die stage c, that is to say c,f the tops 8 of the cylinders 7, these being produced from a plastics material, for example such as PTFE (or polytetrafluoroethylene) or PFA [poly~
fluoroalkoxy). The pipes 3 pass through the respective centres of the tops 8 of the cylinders 7. The gaps left between the tops 8 of the cylinders 7 determine the cross-section of the cellular structure formed, which in the case illustrated in Figure 5 is a structure in which the cells have a regular hexagonal cross-section which renders it po~sible to obtain a honeycomb structure.
- A cooling stage d in which the cellular structure ..... : ~

obtained, and denoted as a whole by the reference 15, is cooled by the cooling fluid 4 coming from the first s~age a. The cooling of the thermoplastics matexial issuing fr~m the die stage c occurs comparativel~ quickly, and the struc-ture is practically rigid as early as the space situatedclose to the domes 14 of the cylinders 7. During produc-tion~ the structure as a whole develops in the direction of the arrow g. This development of the structure 15 in the direction towards the outlet of the plant is promoted b~ the archimedian thrust exercised by the cooling fluid of the stage d. To enhance this action, a cooling fluid will prefer-ably be selected which has a high density, and which is in any event higher than the density of the plastics material forming the structure 15. The withdrawal of the structure 15 in the direction of the arrow g is moreover performed by traction elements 16 situated at the level of the cooling stage d and exerting a light traction along ~ and at the same time a grip on the periphery of the structure 15. The traction ~lements 16 are formed by endless flexible belts 17 eyuipped with protuberances coming into engagement with the structure 15, these belts being received by rollers 18 and 19 of which at least one is rotated by a drive motor 20.
Given that, during production, the base of the cellular structure, that is to say its volume situated close to the die stage c is still in the softened statel the traction elements 16 should not exert an e~cessive force on the structure 15 which could cause rips or at least degradations.
To avert problems of this ~ind, the motor 20 is positively controlled, and the speed of rotation it imparts to the roller 19 depends on the deli~ery of the die stage c.
- A fifth and final stage e for severing the struc-ture 15 is situated in the upper portion of the plant. The severing of the structure 15 is performed within the actual cooling fluid. It is performed by means of a cutting wire ~1 equipped with protuberances which is displaced sideways :~ _ g _ , 6~,~

in such manner as to part the structure 15 in a plane at right angles to the axis of its cells. The wire 21 is borne by a carriage 22 comprising driving means which are not shown. Since the severing of the structure 15 occurs continuously, that is to say whils~ this structure develops along the arrow g, the parting acting occurs on the run and, to this end, a motor 23 draws the carriage 22 along g at the same speed as tha~ at which the structure 15 is fed forward. After each cutting operation, the wire 21 is returned downwards in such manner as to cut and deliver another slice of the structure 15. As wire 21 is within the cooling fluid the latter acts as a lubricant during the cutting operation and renders it possible to obtain slabs or cellular structures 15 having perfectly cut edges free of burring. The cooling fluid filling the cooling stage d and the cutting stage e is discharged from the plant via a pipe 24, at wh:ich time it may purely and simply be dis-charged or recycled in the direction towards the pipe 2 supplying the bottom tank 1 after having had its optimum temperature restored and above all having been freed of the impurities it contains which originate in particular from the cutting operation by means of the wire 21.
The plant described herein may operate either : continuously, that is to say may continuously deliver the structure 15 which is out off in stage e, or may opexate intermittently and deliver a particular quantity of struc-ture 15.
A c~linder 7 corresponding to those appearing in the plane of Figure 1 but lacking the dome 14, is illus-trated in Figure 2. This shows the pipe 3 passing throughit from end to end, its hexagonal top 8 whereof the outer geometrical outline in conjunction with the tops 8 of the other cylinders 7 determines the cross-section of the cells of the structure 15, its flared external top portion 25 ea$ing the passage of the plastics material in the fluid 36t~

state through the passage orifices of the die stage c.
Three similar cylinders 7 are illustrated in plan view in Figure 3~ The space 26 delimited b~tween kheir three tops 8 renders it possible to obtain a structure corresponding to that shown in perspective in Figure 5 and whereof the cross-section in shown in Figure 4.
A modified form of the cylinder 7 shown in Figure 2 is shown in Figures 6 and ?. This cylinder has a hemi~
spherical upper dome 14, a hexagonal top 8 and, again, the internal pipe 3 for ~raversal by the cooling fluid situated at the centre of the passage 9 providing an insulation by means of the very barrel 10 of the cylinder. The insulating nature of the top 8 forming the die stage c of the plant renders it possible to prevent heat exchanges by conduction between the barrel 10 of the cylinder and the cooling pipes 3. The pipes 3 open at the upper part of the cylinder ~ in the centre of the top dome 14.
Other plastics materials than polypropylene may be utilised to produce a cellular structure similar to the structure 15.
A ceLlular structure corresponding to that obtained by the process of-the invention may be applied to produce beams, self-supporting insulating panels, or load carrying floors intended for the building industry.
A structure of this kind may be used to replace the known expanded cellular products, to produce sandwiched or compcsite materials, providing perfect insulation and allowing of their application within the sphere of self-supporting structures by virtue of their mechanical proper-ties. The cellular structure of the invention may equally be applied to produce filters, drains, hermetic caissons and elements usable in the sphere of heating by solar power or in that of vibration dampers~ A material of this kind may advantageously replace the honeycomb structures produced from aluminium.

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~ 7 The plastics material utilised may or may not be loaded and it is possible to make use of all additives known at present to endow the same with particular physical or mechanical properties.
Once it has been obtained in the form of beams or slabs, the product of the invention may be heat-moulded in such manner as to assume an external shape corresponding to that required for its application. Its two opposed surfaces may be equipped with an additional coating, for example of glass fibres.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Device for upwardly extruding a multiple tube structure from a thermoplastic material comprising:
an extrusion die comprised of a plurality of regularly spaced cylinders having upper ends defining extrusion orifices therebetween; means mounting said cylinders in upright regularly spaced relation to each other so that there are spaces between adjacent cylinders, each cylinder having a lower portion of smaller diameter than the upper end; heating means associated with the lower portion of each cylinder, said upper ends being of a greater dimension than the lower portion and of a heat insulating material;
supply means for injecting fluid thermoplastic material to a bottom region of each space between the adjacent cylinders; a liquid cooling bath above and in direct contact with the upper ends of the cylinders; a cooling liquid passage extending through each cylinder in thermally insulated relation to the cylinder; means for supplying liquid to said cooling bath through said passages extending through each cylinder; traction means in said cooling bath for pulling extruded multiple tube structure solidified by said bath upwardly through the bath, and cutting means in said liquid cooling bath for cutting the solidified multiple tube structure.

2. Device according to claim 1, wherein the upper ends of said cylinders are capped by domes of heat insulation material.

3. Device according to claim 2, wherein said domes are of polytetraflubroethylene.

4. Device according to claim 1, wherein the upper ends of the cylinders comprise a thermoplastic material with a melting point much higher than the temperature of the extruded material.

5. Device according to claim 1, wherein said traction means comprise endless driving belts having protuberances engaging the periphery of the extruded material, and means for controlling the speed of the belts as a function of the rate of extrusion of the multiple tube structure.

6. Device according to claim 1, wherein said cutting means comprises a severing device carried by a carriage which is movable in the direction of extrusion to cut the extruded material without stopping the extrusion.

7. Device according to claim 6, wherein said severing device comprises a cutting wire.

8. Device according to claim 1, wherein the cooling liquid bath comprises a liquid of a density greater than the extruded thermoplastic material.