WO2002006037A1

WO2002006037A1 - Pultrusion head to produce long fibre reinforced thermoplastic matrix profiles

Info

Publication number: WO2002006037A1
Application number: PCT/PT2001/000013
Authority: WO
Inventors: João NUNO FERREIRA DA MOTA; João PEDRO LOURENÇO GIL NUNES; António SÉRGIO DUARTE POUZADA
Original assignee: Universidade do Minho
Current assignee: Universidade do Minho
Priority date: 2000-07-14
Filing date: 2001-07-13
Publication date: 2002-01-24
Anticipated expiration: 2003-01-14
Also published as: AU2001269628A1; PT102493A

Abstract

The present patent refers to the development and fabrication of a pultrusion head (1) to produce composite profiles from thermoplastic powder coated fibre tows (2) (towpregs). Mounted in a conventional thermosetting comprosite pultrusion machine, the head (1) allows to produce continuous of long fibre reinforced thermoplastic profiles when fed with powder coated fibre tows. The head (1) is composed by three main components: a pre-heating furnace (3), a consolidation die (4) and a cooling die (12). Carbon and glass fibre reinforced 24x4x2 (mm) U-shaped profiles based on polycarbonate (PC) and polypropylene (PP) matrices, respectively, were already successfully pultruded at linear production rates varying from 0.2 to 2 m/min.

Description

DESCRIPTION

" PULTRUSION HEAD TO PRODUCE LONG FIBRE REINFORCED THERMOPLASTIC MATRIX PROFILES "

Background

Recently, the use of powder coated thermoplastic fibre tows (towpregs) opened new fields to the application of long fibre-reinforced thermoplastics [1-4]. In fact, by solving the problem of impregnating fibres with high viscosity thermoplastics these novel low-cost pre-impregnated materials can substitute with advantage conventional long fibre thermoplastic matrix prepregs.

However, the growth of long fibre reinforced thermoplastic markets still is dependent on the development of technologies and tools allowing the high rate processing of thermoplastic matrix composites in large series production machines. Nowadays, important research work is been carried on to process these materials by compression moulding, filament winding and pultrusion [5-10]. Theoretical models were also developed to simulate the processing moulding of long fibre reinforced thermoplastics, namely by pultrusion [8, 11-15].

Some pultrusion equipments and tools are patented, such as the patents next referred as EP 0712716 e EP 0814950.

Patent EP 0712716 "Process and equipment to impregnate by extrusion" refers the impregnation of fibres and tows to produce of unidirectional fibre reinforced plastics. The process (A) allows to produce fibre reinforced materials by impregnating fibre tows, which are made to pass through a wave-shaped impregnation zone, with melted thermoplastics or liquid thermosetting resins (I). The patent also claims (i) a fibre impregnation process (B) in which the fibres are made to pass through a curved impregnation zone and mixed with the thermoplastic or resin injected from its up and bottom sides; (ii) a extrusion-impregnation system for process (A), consisting on a wave-shaped impregnating channel in the direction of pultrusion; (iii) a similar system for process (B) with two misaligned entries for the melted polymer (I) located at the upper and lower parts of the impregnating channel. In both processes (A) and (B), the melting polymer feeding is made before the concave part of the impregnation zone on the fibre tow upper and bottom part. The depth of the impregnation channel can be changed during operation in order to increase or decrease in continuous the channel narrow gap in the pultrusion direction, i.e. from the fibre entry to the fibre exit. The impregnation channel has two misaligned holes in the upper and lower lateral sides to allow the melting polymer to enter. The melted material is injected through split narrow dies along the channel length.

The Patent EP 0 814 950 "Pultrusion process and equipment" is related to the development of a process and related equipment to allow to cover multifilament cables with thermoplastic resins. The process consists in a impregnation cross-head die having two holes to allow filaments to enter and exit from it. Using such die, the filaments enter from one side and are covered by a melted polymer injected from holes located in direction perpendicular to them. A pulling system allows to pull the filaments through the melted polymer existing inside the head and, then, make them to pass through different channels with successive lower diameter in order to remove the resin in excess and obtain the final dimension required to the multifilament covered cable. Brief Description of Figures

For an easy understanding the description of tools and equipments, the following schematic drawings of principle, which must be viewed as not intending to limit the scope of the invent, were attached:

Drawings: Figure 1. Schematic general diagram of the pultrusion machine. Figure 2. Consolidation die. Figure 3. Cross-section of the pultruded profile.

Figure 4. Pressurising and consolidation die used in the pultrusion-head prototype.

Figure 5. Cooling die.

Figure 6. Schematic diagram of the cooling system used. Figure 7. Dies mounted on the supporting and guidance plate. Figure 8. General view of the dies fixation system.

Detailed Description of the Invent

The developed pultrusion head 1 is an independent unit that can be easily mounted in conventional thermosetting composite pultrusion equipments to allow continuous production of long fibre reinforced thermoplastic matrix profiles. As mentioned before, the head is divided in three main zones: i) preheating zone, ii) a consolidation zone and, iii) a cooling zone

As can be seen, the ensemble of powder impregnated fibres 2 pulled from tows placed in a fibre tow holder is pre-heated by passing through a 70 x 84 mm rectangular and 625 mm length chamber of the 4,8 kW furnace 3 (Fig.l). The furnace chamber 3 is independently heated in two zones (at the chamber entrance and exit) by resistances connected to an alternate power source of 220 V and 50 Hz that are made from helical Kanthal Al wires supported on Mulit ceramic tubes protected by a Cordierite ceramic plate. In each zone, installed 2.4 kW resistances allow reaching the maximum temperature of 1000 °C inside the chamber. With such level of temperature, the system is compatible to work with any type of thermoplastic.

Rigid ceramic fibres are used for thermal isolation of furnace 3 thermal. To achieve better reflectance, the interior of the chamber was fully covered by Cordierite plates and lateral walls by rigid ceramic fibres and alumina. To facilitate the production beginning and access to the towpregs a split type design was used in the furnace to allow it being horizontally opened. For easy adaptation to different pultrusion machines, furnace 3 was also mounted on an 3kN vertical adjustable mobile table.

Temperature and power can be independently adjusted in the two chamber zones from a control panel by using a system consisting in: 2 solid state Eurotherm contactors protected by ultra-high speed cutting power fuses and 2 temperature controllers with microprocessor PID action Eurotherm 2116 connected to 2 type K thermal sensors installed inside of the pre-heating chamber.

After pre-heating, the pre-impregnated tows enter in the consolidation zone, consisting in the thermal stabilised steel die 4. Such die, responsible for the formation of the composite profile, which consists in the lower and upper part 5 and 6, respectively, presents the machined split gap 11 that allows an easy separation of the parts by using an appropriate flatten and soft tool and the four zones shown in Fig. 2: Entrance 7 b) Pressurisation 8; c) Profile consolidation 9; d) Profile stabilisation 10;

The entrance zone 7, located at the initial part of the pressurisation and consolidation die 4, presents a large aperture to facilitate the entrance of the powder-coated towpregs 2. The use of this zone allows towpregs to enter easily in the die and avoid the excessive accumulation of thermoplastic at die entrance. The entrance zone was machined with concordance radii of 5 mm and inclinations higher than 7° to facilitate an easy alignment between the furnace chamber 3 and the consolidation die 4.

The full impregnation of fibres is achieved in the pressurisation zone 8 by flow of the melted thermoplastic trough the fibre interstices. In this zone, the die is 1° convergent to allow a gradual increasing of pressure on the ensemble of towpregs. Thus, the material is compressed perpendicularly to pulling direction to allow achieving a profile without voids presenting the final thickness desired.

More complex geometrical details of the profile cross-section are formed in the profile in consolidation zone de 9. During this stage, the typical rectangular cross-section that the profile presents at the beginning of this zone suffers a smooth modified and the final desired geometry is achieved.

Finally, a constant cross-section is maintained during passage through zone 10 that allows stabilise the final pultraded profile dimensions.

Two heat transfer models proposed by Astrom et al. [11-14] and Nunes et al. [4, 8, 14] are used to design the consolidation die. Such die is opened through a horizontal split plan (Fig. 2) to allow passing the powder-coated towpregs at the process running beginning.

To reach melting temperature in the polymer at the used pulling speed, the die is also equipped with an ensemble of electric heating cartridges uniform distributed in the two parts of the die. Two controllers connected with 2 Hotset type J thermal sensors placed in two die zones allow setting the die desired temperature between 0°C and 400°C by automatic control of the electrical power feeding.

A total length of 200 mm was used in the die of the pultrusion-head prototype used to produce a 24 x 4 x 2 mm U-shaped profile (Fig.3). In this die, lengths of 40 mm and 115 mm were used in a 42 x 14 mm cross-sectional entrance and in the pressurisation zones, respectively. During the passge trough the consolidation zone having a length 40 mm, the profile cross-section varies from an initial 28 x 2 mm cross-section to the final desired U-shaped cross- section. At the end, such die presents a 5mm length in the stabilisation zone.

In the pultrusion-head prototype, ten 200 W electric cartridges were used to heat the consolidation die and obtain a total installed power of 2000 W. The cartridges were uniformly placed in each die part using a constant distance of 12 mm between them. HASCO isolating plates were used in die lateral walls to minimise heat losses to the exterior. With this system, it was possible to reach in 15 min to 20 min a maximum temperature of 400 °C in the die that could to allow using a high range of thermoplastics.

The profile obtained at the end of the consolidation die is finally solidified in the cooling zone. This zone is constituted by die 12, which has a cross-section similar to that of the final profile and that is horizontally dismountable to facilitate passing the ensemble of powder coated towpregs at the process beginning. This die is cooled by water circulation to maintain a constant temperature (Fig. 5). A small split gap 15 was machined in the die to allow using a soft tool to separate its parts 13 and 14. The pre-set cooling temperature is maintained constant by a Regloglas 17 model 90S/6/TP20/1K/RT22 thermo- regulator mounted in the water circuit having the following characteristics: Maximum temperature: 90°C; Power: 6 kW, Maximum flow: 60 1/min; Maximum pressure: 0.38 MPa.

The length of the cooling die as well as the diameter of the channels for circulation of cooling water were designed in order to maintain the desired minimum temperature. Such design the following items were taken in account: heat transported by the composite profile, heat changes with the exterior by convection, radiation and conduction and maximum heat that can be removed by the circulating water[14]. A type J model TEFl Hotset thermal sensor is used to control the cooling die. Minimum concordance radii of 5 mm and a minimum exit angle of 1° were used in the cooling die. A 5 mm ceramic plate was used between the consolidation and cooling dies to avoid unnecessary losses of energy.

The consolidation and cooling dies 4 and 12, respectively, were screwed to the support and guidance plate 18 that allow maintaining them perfectly aligned in the pultrusion machine (Fig. 7). Figure 8 shows the general aspect of the assembly of the two dies before final attachment to the conventional pultrusion machine.

A cooling die with total length of 200 mm was used in the built pultrusion head prototype. Such prototype allow producing in good conditions the 24 x 4 x 2 mm U-shaped profile shown in Fig. 3 using a PULTREX conventional pultrusion machine for thermosetting composites having maximum pulling force of 60 kN. Two types of thermoplastic powder were used as matrix: a polycarbonate (PC) from Bayer (Makrolon 2458) and a polypropylene (PP) from ICO Polymers France (Icorene 9184B P). Two types of fibres were also used: carbon fibres (C) from Amoco (Thornel T300/12/NT) and glass fibres (GF) from Owens Corning (OC 357 D).

Figure 3 schematically shows the produced PC/C profile. The pultrusion head prototype allowed producing C/PC and GF/PP profiles with good mechanical properties and fibre mass fractions between 25% and 70% using pulling speeds of 0.2 to 2 m/min

The next list present the main references related with this invent, some of them already referred in the text between brackets.

References

1. Gantt, B. (1987) "The Thermoplastic Coating of Carbon Fibers", Master Thesis, Clemson University, Clemson, U.S.A.

2. Allen, L. E., Edie, D. D., Lickfield, G. C and McCollum, J. R. (1988) "Thermoplastic Coated Carbon Fibers for Textile Preforms", Journal of Thermoplastic Composite Materials", 1, pp. 371-379.

3. Klett, J., W., (1991) "Towpregs Formation for Carbon/Carbon Composites, Master thesis, Clemson University, U.S.A.

4. Nunes, J., P. (1998) "A Study of the Processing and Properties of Sheet Molding Compounds and Unidirectional Carbon Fibre Towpregs", PhD thesis, Universidade do Minho.

5. Wilson L. M., Buckley D. J., Dickerson E. G., Johnson S. G., Taylor C. E. Covington W. E. - "Pultrusion Process Development of a Graphite Reinforced Polyetherimide Thermoplastic Composite", Journal of Thermoplastic Composite Materials, Vol. 2, July 1989.

6. Larock A. J., Hahn T. H. and Evans J. D. - "Pultrusion Processes for Thermoplastic Composites", Journal of Thermoplastic Composite Materials, Vol. 2, July 1989.

7. Astrom, B.T., Larsson, P.H. and Pipes, R.B., (1991) "Development of a Facility for Pultrusion of Thermoplastic-Matrix Composites", Composit. Manufact, 2:2, pp. 114-123.

8. Devlin J. B., Williams D. M., Quinn and Gibson A. G. - "Pultrusion of Unidirectional Composites with Thermoplastic Matrices", Composites Manufacturing, Vol. 2, n° 3 / 4, 1991.

9. Sala G. and Cutolo D. - "The Pultrusion of Powder-Impregnated Thermoplastic Composites", Composites Part A 28 A, 1997. lO. Chin-Hsing Chen and Chen-Chi M. Ma - "Pultruded Fibre-Reinforced PMMA/PU IPN Composites: Processability and Mechanical Properties", Composites Part A 28 A, 1997.

11. Astrom, B.T., (1992) "Development and Application of a Process Model for Thermoplastic Pultrusion", Composit. Manufact., 3:3, pp. 189-197.

12. Astrom, B.T. and Pipes, R.B., (1993) "A Modeling Approach to Thermoplastic Pultrusion I: Formulation of Models", Polymer Composites, 14:3.

13. Astrom, B. T. and Pipes, R. B., (1993) "A Modeling Approach to Thermoplastic Pultrusion II: Verification of Models", Polymer Composites, 14:3.

14. Mota, J. N, (1999) "Desenvolvimento de uma Cabeca de Pultrusao para

Compόsitos de Matriz Termoplastica", Master thesis, Universidade do Minho,

Guimaraes. 15.Nunes, J.P., Bernardo, C.A., Pouzada, A.S. and Edie, D.D., (1999) "Modeling of the Consolidation of Polycarbonate/carbon Fiber Towpregs", Polymer

Composites, 20:2, pp. 260-268. This invent only shall be consider limited by the following claims.

Claims

1. Pultrusion head, that mounted in conventional pultrusion machines allows the continuous processing of long fibre composite profiles from continuous powder coated pre-impregnated fibre tows (towpregs) using different types of thermoplastics and reinforcement fibres and having different fibre fractions in normal conditions and typical industrial speed production rates. Such pultrusion head is characterised by the three main zones mounted in a support structure:

- a pre-heating zone constituted by a furnace to pre-heat the thermoplastic powder coated pre-impregnated fibre tows;

- a consolidation zone constituted by a die used to consolidate the composite profile and,

- a cooling zone constituted by a die used to cool the final profile;

2. Pultrusion head, according to claim 1, that in the pre-heating zone allows to pre-heat powder coated pre-impregnated fibre tows pulled from a tow holder during the passage through a furnace chamber, which is independently heated in 2 zones (entrance and exit) by electric resistances and that can reach the maximum temperature of 1000°C.

3. Pultrusion head to produce long fibre thermoplastic matrix profiles, according to the claims mentioned before, that presents an integral furnace thermal isolation made from rigid ceramic fibres and the interior furnace chamber covered by Cordierite plates and its lateral walls covered by rigid ceramic fibres and alumina to improve reflectance. To facilitate accessing the towpregs at the beginning of production, the furnace has a split type design to allow opening the furnace chamber horizontally in two main parts and is mounted on a 3kN vertical adjustable mobile table for easy adaptation to different pultrusion machines.

4. Pultrusion head to produce long fibre thermoplastic matrix profiles, according to the claims mentioned before, characterised by having in the two zones furnace chamber the power and temperature independently controlled by solid state contactors protected by ultra-high speed cutting power fuses and 2 temperature controllers with microprocessor PID action Eurotherm 2116 connected to 2 type K thermal sensors installed inside of the pre-heating chamber.

5. Pultrusion head to produce long fibre thermoplastic matrix profiles, according to the claims mentioned before, characterised by making the pre-impregnated tows, after pre-heating, to pass to a consolidation zone constituted by a thermal stabilised steel die that as a tool responsible by the profile forming is divided in the following four zones: a) Entrance b) Pressurisation c) Profile conformation d) Profile stabilisation

The entrance, located in the initial part of the die, has a large opening to facilitate the entry of the ensemble of thermoplastic pre-impregnated tows and the die and furnace chamber alignment; in the pressurisation zone, the total impregnation of the fibres is ensured by flow of the thermoplastic powder because the 1° die convergence in this zone of the die makes the plies of the pre-impregnated tows ensemble being gradually and laterally compressed at a known speed acting perpendicular to pull direction until the final thickness and a composite profile without voids are reached; the conformation zone ensures the formation of the most complex geometrical details of the profile cross-section. In this zone, the profile section is smoothly modified until the final desired geometry is achieved.

The stabilisation zone, where the die has a constant cross-section similar to that one of the final profile, ensures the profile final stabilisation.

6. Pultrusion head to produce long fibre thermoplastic matrix profiles, according to the above mentioned claims, characterised by to ensure the solidification of the composite profile obtained at the end of the consolidation die in a cooling zone that is constituted by a die, having a cross-section similar to that one of the profile to be produced, which is horizontally dismountable along its full length to facilitate passing the ensemble of powder coated towpregs at the process beginning and that it is cooled by a closed circuit of water to maintain the temperature constant. The temperature control of this die is ensured by circulation of water through a thermo-regulator.

7. Pultrusion head to produce long fibre thermoplastic matrix profiles, according to claim 6, characterised by to have the length and diameter of the cooling die as well as the diameter and length of the cooling channels machined in such die designed in order to maintain the desired constant temperature considering the heat transported by the profile, the heat exchange with the environment (by convection, radiation and conduction) and the maximum heat that can be removed by the circulating cooling water. The cooling die has the temperature controlled by a temperature sensor and minima concordance radii and exit angle of 5 mm and 1°, respectively.

8. Pultrusion head to produce long fibre thermoplastic matrix profiles, according to the above mentioned claims, characterised for being easily adaptable to conventional pultrusion machines and by allowing to use powder coated fibre tows (towpregs) and also other conventional thermoplastic matrix pre-impregnates, such as prepregs or tapes, as raw materials to produce thermoplastic composite profiles.