WO2005044534A1

WO2005044534A1 - Autoclave for composite materials

Info

Publication number: WO2005044534A1
Application number: PCT/SE2004/001471
Authority: WO
Inventors: Pontus Bergmark
Original assignee: Pontus Bergmark
Priority date: 2003-10-20
Filing date: 2004-10-14
Publication date: 2005-05-19
Also published as: WO2005044534A8; SE0302751D0; SE0302751L

Abstract

The existing invention assigns to a device and a procedure for forming of composite materials by pressure in a pressure chamber (autoclave) with a pressure means consisting of rigid particles. The device further comprises a mould tool, which comprises at least two essentially stiff parts, arranged to be brought together in that way the for forming meant material is enclosed between them and only indirectly is influenced of the by the pressure means exerted pressure via the load extension.

Description

AUTOCLAVE FOR COMPOSITE MATERIALS

Technical Field The existing innovation relates to a device and a procedure for forming of composite materials by pressure in a pressure chamber with a pressure medium consisting of solid particles .

Background Composite materials are useful in many connections, and often can supersede metals as construction material., The advantages often are low weight, high strength, dimensional stability, corrosion resistance etc. Composites can be manufactured exploiting semi manufactured products, prepreg i.e. fibres impregnated with plastic. The prepreg is soft and textile-comparable and can be cut and formed. The prepreg consists of a plastic gel with fibres e.g. epoxy with carbon fibre. For forming of such materials by melting, flowing followed by solidifying or chemical reactions (hardening) autoclaves are used. Conventional autoclaves for composite manufacturing are large gas chambers that are pressurised and heated at use. The prepreg is hereby laid up jointly with help materials on a tool that is placed in the gas autoclave that is heated and pressurised to due levels depending on the plastic material used. During the hardening the prepreg shall be compressed and the air squeezed out, with excess plastic removed form the composite . Such traditional autoclave hardening requires a requisite of different help materials, which is a drawback as the surface directed towards the help materials becomes of uneven quality, having an affect on both the appearance and the properties. One reason that the help materials are needed is that the pressure over the prepreg towards the form is uneven. This means that plastic flows to areas with lower pressures while fibres in areas with higher pressures are drained and in some areas air still is left as the local pressure is too low, giving worse strength, surface smoothness etc. The help material also is essential to apply vacuum by use of foils that are sucked towards the tool to fix the material in place and to increase the differential pressure over the prepreg. Despite the help materials the result often is far from optimal, especially for more complex structures. Conventional autoclaves also accommodate badly for large series, leading to more expensive products. The use of solid or flowing materials instead for pressure transmission gives very great advantages compared to the using of gas (air) . Granular materials do not blow up at leakage as the gas does, which can cause damage. Solid materials in addition often has better heat conduction compared to gas (air) . Autoclaves where solid or flowing materials are used as pressurising medium are known since previously. For example US 4 769 197 describes an autoclave with a pressure chamber 'and mechanical plunger where a pressure medium in the shape of * polymer particles is used to compress a composite material towards a tool on which it is arranged. Those particles '< however does not act as solid particles under pressure but as liquid, which make the pressure distribution go evenly in all ' directions inside the pressure chamber. As a consequence there are no possibilities to bring about different pressures towards different sectors of the composite materials that shall be formed. It further is essential to have a tight envelope around the composite material to make the pressure squeeze the composite material towards the tool and not in other directions. Further is in this autoclave the mechanical plunger used only to compress the polymer particles while the real pressurising then occur by to let the polymer thermally expand on heating. A drawback with such a process is however that it is relatively difficult to govern. From JP 3 112 867 it also is known to use solid particles, pulverized coal in this case as pressure medium. Also in this case the pressure medium is action directly at the composite material which is a great disadvantage as the pressure in the composite material, that is ceramic, thereby varies leading to poorer strength and poorer surface smoothness. It also is hard to create more complex geometric bodies in this type of device.

Object of the Invention Consequently, it is one object of the invention to provide a device and a process that completely or at least partially sets aside the earlier mentioned drawbacks leading to a reliable, low cost and efficient manufacturing of composites. A device gains this purpose and a procedure defined in the appended claims.

Brief Description of the Drawings The invention will be described for exemplifying purposes more in detail by means of one embodiment example and with reference to the accompany drawings, wherein: Fig 1 and 2 is one device for forming, of the invention; Fig 3 is a simple moulding tool for use in connection with one device of fig 1; Fig 4 is a product in composite material; and Fig 5 is a moulding tool for forming of the product of fig 4 in accordance with one device of the invention. Detailed Description of Preferred Embodiments In fig 1 and fig 2 is one device of the invention for forming of composite materials by pressure. The device consists in this embodiment example of a pressure chamber 1 which contains a pressure medium 2. The pressure medium here consists of solid, rigid particles as sand, used to compress a tool 3 encompassing the material for forming and itself allows some variations in thickness at the same. The pressure chamber 1 in this embodiment example consists of a box with displaceable cover 4. Placing the pressure chamber 1 in a press 5, at which the cover 4 is pressed towards the bottom of the box and at that exert a pressure against the pressure medium 2, increases the pressure in the pressure medium. The press e.g. can be a traditional mechanical-, hydraulically- or pneumatically driven press, but many other varieties certainly are possible to use in connection with the invention. The tool is divided which means that it substantially completely encompasses the material that shall be formed. In this way no direct pressure against the material will be exercised by the pressure medium, but only by the tool. In, that way the rigid and load distribution tool to give an equalization of the pressure over the composite material surface. By the pressure from the pressure medium against the tool encompassing the composite material and by raised

•temperature the material is formed that will get the ultimate ishape by melting, flowing followed by solidifying or chemical reactions (hardening) . The tool preferably comprises an inner tool, which is enclosed by the material to be formed and an outer tool that in turn encloses this material. The inner- and outer tools both can consist of several parts. The outer tool has to be constituted in that way the parts at the same have some mobility relative to the inner tool, to in this way permitting the pressure to be forwarded from the pressure medium. On this the composite material placed between the inner and outer tool, is squeezed and formed. The particles pressure against the tool is pressing in the tool parts towards each other. The space between the tool parts is protected from penetrating particles by an envelope material as tape, is placed at least over the tool gaps. The tool manages by this mutual flexibility of the tool parts, to give a pressure all over the composite surface even if any part of the composite is too thick. This make the permissible variation considerably less than with rigid tools. All surfaces for the plastic material will by this means get a smooth structure. The device further comprises heating- and cooling elements to heat respectively refrigerate the material. These elements that i.e. can comprise coils that are placed in the pressure medium, or flat-formed elements that are placed by the walls of the container. It will of course also be possible to make heat input through the walls and by means of induction. Channels in the tool and/or the walls can effectuate cooling. It also is possible to heat respectively cool the tool directly. This is especially favourable when the pressure medium comprises an essentially isolating material, i.e. a material with poor heat conduction. In this way will the heat losses be minimal. The device according to the invention further comprises a vibration unit (not shown) that will bring about vibrations in the pressure medium and by this way to compact. The device further comprises control and regulation equipment. This equipment further preferably comprises a trigger unit 6 that guides the applied pressure and heat by way of example to trig thyristors for the heating, electromagnetic contacts for cooling water, hydraulics in the press 5 and more. The trigger unit can on one hand be controlled externally by a computer 7 or in a different way stored control data where the program preferably comprises parameters for every separate process, or on the other hand in externally directly gauge measures from sensors 8. These sensors for example can be pressure sensors placed in the pressure medium 2 or on the tool 3. The computer 7 can further be used to collect data from different runs to by this way acquire a bank of experience to optimise the operation. The pressure medium can be chosen e.g. by mobility. With particles as medium it will be possible to reach very high total pressure and in addition different pressures around the tool. Further the heat conduction can have influence from the choice of medium so that heat transports from the walls to the tool. Quite the opposite - an isolating medium - sometimes can be desirable, and can likewise be gained by means of the device of the invention. In this case a medium with limited , heat conduction can be chosen and only the tool will be heated with minimum heat losses to the medium and the autoclave walls . A controlled slower heating also can be done by heating from the medium of the tool using materials encompassed the tool and adapted for this heat conduction. _r,In case heating of the tool is done instead, an isolating encompassing material can decrease the heat losses further. It further is possible to let the medium keep its great heat content and to transport it to an heat isolated container with transport back to the autoclave at next process cycle which considerably increases the process speed. The energy will in this case be retained in the process. The pressure chamber of the device needs in this case just to be slightly larger than the tool. It also will be possible to position a number of tools in same container. The pressure chamber further has been described with a movable wall for pressurising. It is of course also possible to let two or three walls to be movable to in this way exert pressures in several directions and by this also better control the desired pressure. A simple way to use the device shall now be described. The tool with encompassed prepreg is placed in the pressure chamber. A pressure is applied on the material by to prestress the tool by means of i.e. a screwed joint reinforcement or tape. Particles, preferably at raised temperature, then are filled up in the container. The device then is vibrated to compress the particles closer to the tool, and the pressure medium is pressurised by the press while sensors control the pressure distribution. By the pressures, the different parts of the tool are pressed against each other and form the material to its correct shape. The material in the tool is further heated to an appropriate process temperature under appropriate pressure. The pressure towards the tool and raised temperature forms the material and the detail gets its final form by e.g. viscous flowing and/or chemical reactions . After a advisable time under heating the tool is cooled, the pressure is released, the pressure chamber is "^''" opened, the particles are transported to an isolated container ^■for heat preservation, the tool is opened and the detail is removed from the tool . It further is possible to choose a pressure medium with such a coefficient of thermal expansion (CTE) that a given increase of the pressure also occurs by thermal expansion of at heating as a contribution to the applied pressure. The main pressure still is applied preferably mechanical. By design of the tool in accordance with the invention there are no limitations in geometry for the products to be produced at production of composites. By division of the tool in several parts and to mainly encompass the material to be formed, all surfaces gets a very even and fine structure by the shaped material, as the tool acts load equalizing and will even out the pressure that is transferred form the medium. In this way the material that shall be formed, is not affected directly by the solid particles in the pressure medium, but by the mainly rigid tool. It further is an evenly distributed pressure over the composite surface. Fig 3 is an example of a simple tool in accordance with the invention for shaping of a double curved product. This tool comprises a lower part 21, on which composite is arranged, and a higher part 22, which is moved down over the lower part. The parts at this are so constituted that a space of suitable size exists between the parts, in which the composite is situated. In this way an evenly distributed pressure towards the tool is formed when the tool is used in the device described above. Fig 4 is an example on a more complex composite product, which can be produced by means of the device according to the invention. This product comprises a square tube with openings 32 as well at the ends as along one long side. The side openings further comprise short tubes 33 joined to the main tube 31. All openings further comprise also attachment flanges 34. Fig 5 is a tool for forming of the product of Fig 4. This tool comprises partly an inner tool, which mainly encompasses the composite material; partly an outer tool that is arranged to mainly encompass the inner tool and thereby exert a pressure towards the composite material arranged in between. The inner tool in this case comprises a rod 41 for forming of the square tube and on it joined shorter parts for forming of the stub tubes at the side openings. Those shorter pieces 42 may for example be screwed tight to the rod 41. It is favourable that the inner tool at more complicated structures is divisible so it after forming can be pulled out of the complete product and be reused. It yet is conceivable to use disposable tools, which e.g. can be melting off from the finished product. In this case the inner tool must not be dividable. The outer tool in this embodiment example comprises several parts, which are joined together in such matter that they have certain mobility relative to each other, to be able to exert an even pressure towards the inner tool. The outer tool comprises a higher and lower plate 43, considered to be arranged on each side of the inner tool. For forming of the third straight long side a rod 44 is set up between the plates 43. At the ends are endplates arranged, which has, relative to the rest of the plates movable midsection 46, for forming of the joining flanges 34, and plates similar in character with movable midsections are arranged at the remaining openings 32. With forming of the stub tubes at the side openings, two parts 47 between each pair of stub tubes are arranged, at which those parts are bearing against each other with oblique surfaces. In this way those parts partly exerts a force and a pressure in towards the main rod 41 at the inner tool, and partly against the shorter pieces 42 of the inner tool by means of that the oblique surfaces are pressing the parts 47 away from each other. Finally also shorter pieces 48 are arranged at the ends, which partly are pressed towards the stub tubes from the ends, partly against the main tube from the sides. A screw union preferably puts the outer tool together or similar, at which just the inner parts are furnished with thread, at which the outer parts have some mobility between the inner parts and the screw head. Other ways to join the outer tools are yet possible, as e.g. by tape. With the device according to the invention there are many possibilities to range the pressure in a desired way. When the container has only one wall, the pressure in the direction of the movement of the wall will be much higher than in the other directions as the medium consists of solid, rigid particles. In this way the pressure in the tool can be varied in proper ways by arranging the tool in different ways relative this direction of pressure so that varying areas are projected in this direction. In most cases is yet an evenly distributed pressure preferred. When the container has walls that are movable also in one or both of the other directions, the control of the desired pressure of course is facilitated. Also the design of the tool can be used to govern the pressure for the material to be formed. The device according to the invention further can be brought in line with continuous manufacturing. Several containers can for example be used, which are pressurised by feeding forward in a pressing machine with movable sides like feeder belts. In this way new containers can be prepared and fed into the press, in the same time as finished containers comes out from the other side. The continuous manufacturing even can proceed by means of tools and pressure medium can flow through a pressure chamber, by that the tool during the time they pass the pressure chamber are exposed for pressure and heat . The invention permits that companies that earlier not have adopted composites of economical or technical reasons now can do that. Those who earlier have used composites with conventional autoclaves also with advantage can take advantage of the invention and in addition make structures that earlier not have been feasible. By means of the invention it is practicable to vary pressure and temperature within great intervals. It also is possible to apply a high and even pressure that will give an even distribution in the composite of fibres and resin. Excessive resin can be forced out to get optimal fibre content everywhere in the detail . The gaps between the different parts of the outer tool facilitates forcing aside of excess resin which eliminates the need of help materials, which in turn leads to a simple an economically favourable process. The pressure also has an influence on enclosed air or other gas that is forced out, solved or compressed. Raised pressures also improve similarity to the tool, uniformity with the tool, and uniformity in the thickness of material etc. The pressure in the device according to the invention can be chosen optimal which could mean considerable higher pressures, several ten bars higher than with conventional autoclaves, typically working in the interval from 4 to 8 bar. The heat transport in the device according to the invention further can become considerably higher than for air, alternatively lower than air at insulating medium, depending on application. The manufacturing capacity and speed increases in both cases with more effective energy application. The invention with that furnishes a cheap and simplified manufacturing compared to conventional autoclaves, and facilitates in addition to, just in one type of outfit manufacture products that earlier required a great collection of equipments. The invention also gives a considerably increased freedom in choice of geometry for the products.

Product now even can be produced that earlier not was possible with the conventional technique. Products that can be manufactured in the device according to the invention e.g. are light weight chariots for automotive, parts for electric motors, optical mirrors, springs, robot arms, parts for the boat industry as well as manufacturing of high technology products as antennas and microwave products for the aerospace industry. It also is feasible to in the device according to the invention have a pressure medium that is a combination of solid particles and gas, at which the gas spreads out between the solid particles and by that gives a further increase and levelling of the pressure. Also combinations of solid particles an vacuum can be used. The invention has been described above by means of one embodiment. Many other possible varieties of that have been brought up. It should be appreciated that numerous varieties of the invention are possible. These and other obvious varieties should be regarded to be within the scope of protection of the invention as the latter is defined in the appended claims.

Claims

1. A device for forming composite materials by pressure, comprising partly one pressure chamber with a pressure medium, at which pressure medium consists of solid particles partly a forming tool c h a r a c t e r i s e d in that the forming tool comprises at least two essentially rigid parts, adapted to be brought together in such way that the for forming meant material is enclosed between them and only indirectly influenced by the of pressure medium exerted pressure via the load spreading moulding tools.

2. A device as claimed in claim 1, c h a r a c t e r i s e d in that the tool comprises at least one inner tool and one outer tool comprising at least two parts, in that the outer tool essentially is adapted to enclose the inner tool and one around the same arranged material.

3. A device as claimed in claim 2 or 3, c h a r a c t e r i s e d in that the parts of the outer tool relative to each other is at least somewhat movable.

4. A device as claimed in claim 2 or 3, c h a r a c t e r i s e d in that the outer tool when it encloses the inner tool comprises gaps between the parts of the outer tool.

5. A device as claimed in any one of the preceding claims c h a r a c t e r i s e d in that it further comprises a control unit for control of the pressure in the pressure chamber.

6. A device as claimed in claim 5, c h a r a c t e r i^* s e d in that it further comprises to the control unit connected pressure sensors, preferably arranged at the moulding tool.

7. A device as claimed in any of the above claims, c h a r a c t e r i s e d in that it further comprises heat transferring agent for transfer of heat to the tool, and also preferably also a control unit for control of the supplied heat.

8. A device as claimed in any of the above claims c h a r a c t e r i s e d in that it further comprises a vibrating unit, for vibration and with that compacting of the pressure means .

9. A device as claimed in any of the above claims c h a r a c t e r i s e d in that the pressure means principally comprises rigid firm particles, as sand.

10. A device as claimed in any of the above claims c h a r a c t e r i s e d in that the pressure chamber comprises a container where at least one, and preferably at least two walls are movable relative to the others for applying pressure in the pressure chamber.

11. A device as claimed in any of the above claims c h a r a c t e r i s e d in that the pressure chamber comprises at least one, and preferably four movable walls as feeding belt in order to under pressure continuously carry the mould tool through for running production.

12. A procedure for forming of composite material, in a pressure chamber by exertion of a pressure against a mould tool, which pressure means consists of rigid particles c h a r a c t e r i s e d in that the for forming meant material is enclosed between the at least two essentially rigid parts of the mould tool and exerts a pressure for forming indirectly by the pressure means through the mould tool.

13. A procedure as claimed in claim 12, c h a r a c t e r i s e d in that the for forming meant material is arranged around at least one inner tool and then is encompassed by two outer tools.

14. A procedure as claimed in any claim any of claims 12 - 13, c h a r a c t e r i s e d in that also heat is supplied to the mould tool.

15. A procedure as claimed in any claim any of claims 12 - 14, c h a r a c t e r i s e d in that the pressure means after forming is conveyed our from the pressure chamber to a preferably heat preserving container before the mould tool is cooled.

16. A procedure as claimed in any claim any of claims 12 - 15, c h a r a c t e r i s e d in that the mould tool, preferably continuously, is carried through the pressure chamber under pressurising for running production.

17. A procedure as claimed in any claim any of claims

12 - 15, c h a r a c t e r i s e d in that the pressure chamber, preferably continuously is carried through a device for pressurising of the same for running production.