GB2493001A

GB2493001A - Laminate containing heater

Info

Publication number: GB2493001A
Application number: GB201112486A
Authority: GB
Inventors: Peter James Sajic
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-07-21
Filing date: 2011-07-21
Publication date: 2013-01-23
Anticipated expiration: 2031-07-21
Also published as: GB2493001B; GB201112486D0; WO2013011306A1

Abstract

A laminate item is made by providing polymer composite layers 2 and a perforated 6, resistive heater sheet layer 4, applying an electric current to the sheet 4, so as to generate heat, and thereby heat the material, so as to render the polymer layers 2 into a formable condition. The heater sheet 4 may be applied in a lay-up, or comprise electrically resistive components embedded within a polymer matrix bag 10 or sandwiched between polymer layers 2. The bag 10 is preferably a flexible film, applied (directly or indirectly) against a material to be formed. The polymer layers 2 may be resin impregnated fibre materials, containing carbon, composite, aramid, basalt or glass fibres. The formed items may be wind turbine blades, saddle trees or something in the field of orthotics. Below the forming temperature, the item may be involved in dicing.

Description

LAMINATE ITEMS

Technical Field

The present invention relates generally to laminate items, and to methods of forming S the same.

Background

It is known to employ thermoforming/stampi ng techniques wherein a pre-consol idated pre-cut thermoplastic composite sheet of constant or variable thickness is heated between banks of infrared heaters. When the material has reached its melt temperature it is transferred to a press for shaping between matched mould tools.

However, these techniques involve high heating/energy requirements and the equipment is also of high cost. Such known techniques are also only generally suitable for small parts.

An alternative technique involves positioning thermoplastic prepreg material pieces in mould tools which are heated and pressure applied via a press or autoclave/oven in order to process the material and produce the part. However, this technique requires long heating and cooling cycles, and high energy input (for example in respect of large structural components such as wing spars and turbine blades).

Summary

According to one aspect of the invention there is provided a method of forming an item from polymer layers, the method comprising providing a perforated resistive heating sheet material as a layer of the item, applying an electric current to the sheet so as to generate heat and so heat the material so as to render the polymer layers into a formable condition.

By polymer layer' we include resin impregnated fibre materials, such as carbon fibre, composite fibre, KevlarTM fibre, basalt fibre, glass fibre wherein the resin may be thermoforming or thermosetting material, is preferably polynier-based. The term includes one or more type of resin material and/or one or more type of fibre material.

The term may be viewed as including plastics composite materials. We also include layers which do not include reinforcement, eg pure polymer layers.

According to another aspect of the invention there is provided a laminate item comprising polymer layers, the item further comprising a perforated resistive heater sheet material as a layer of item, the heater sheet material arranged to receive an applied electric current so as to cause the sheet material to generate heat and so heat the polymer layers.

Brief Description of the Drawings

Various embodiments of the invention will now be described by way of example only, with reference to the following drawings in which: Figure 1 is a schematic cross-sectional view of the production of a composite plastics item, Figure 2 is a plan view of a resistive heater sheet, with an enlargement of a region of the sheet, Figure 3 is a schematic cross-sectional view of the production of a composite plastics item, and Figure 4 is a schematic cross-sectional view of the production of a composite plastics item.

Detailed Description

With reference to Figure 1 there are shown at I various components in the production of an item formed of a plastics composite matcrial, wherein each of the components forms a respective ply or lamina. The process of providing one component on top of another is termed a laying-up' process.

Outermost components 2 comprise a thermoplastic composite components. Each component comprises a plurality of layered plies, each ply comprising at least one of reinforcing fibres of carbon, glass, l(evlarTM, set within a polymer resin matrix of at least one of Polyethylene terephthalate (PET), Polyphenylene sulphide (PES), Polyctherimide (PET), Polyetheretherketone (PEEK), Polypropylene (PP), Polycarbonate (PC), Polyethylene (PE), Silicone (SI), themoplastic polyurethane (TPIJ) and Polyamide (Nylon). Inwardly located of the outer plies there are provided glass fibre (or any other insulating fabric or fibre material) insulating material layers 3, one provided to each side of a resistive heater sheet 4. The layers 3 serve to insulate the heater sheet electrically from the carbon fibre composite layers. Tt will be appreciated, however, that in other embodiments the layers 3 may be omitted from being provided on each side of the heater, such as those in which the layers are made entirely from insulating composite materials.

The resistive heater sheet 4 is shown in Figure 2, and comprises a sheet/film made of carbon fibres set and dispersed within a polymer resin matrix. The sheet 4 is of perforated form comprising an array of through-holes 6. Each hole is of approximately 1.5mm diameter, but may be in the range 1mm to 3mm, resulting in an overall solid area of 18 % relative to the overall surface area of the sheet. The thickness of the sheet 4 is in the range 0.1 to 0.15mm.

The sheet 4 comprises conductive busbars 5 (preferably of copper). Electrical wires 5a arc connected (for example by way of a soldered connection at 22) to the busbars 5 so as to enable a voltage to be applied to the sheet 4.

The polymer resin matrix of the sheet 4 is of the same type as the resin matrix of the components 2, or is of a type which is compatible with the polymer of the composite components 2.

In use, a voltage is applied to the sheet via the wires Sa and the busbar 5, so as to cause a current to flow through the carbon fibres of the sheet 4. The carbon fibres being electrically resistive, heat is thereby generated. The heat is conducted to the composite components 2 so as to thereby soften the resins of those components and render both components suitable to be formed/shaped as required by way of suitable forming surfaces.

Reference is now made to Figure 3 which shows a production process of a composite laminate item which includes the resistive heater sheet 4. The apparatus shown in Figure 3 includes a silicone vacuum bag 10, a breather 11, a release filni 12, and an underlying PTFE sheet 13, and a forming surface 19. The composite laminate item to be formed comprises the following component layers. A central resistive heater sheet 3, and working progressively outwardly, a PET resin film/fabric layer 15, a glass fabric layer 16, a further PET resin film/fabric layer 15, a heavy fabric carbon layer 17 and a lightweight carbon fabric 18.

The various layer components of the item to be formed are contained with a sealed spaced bounded by the bag 10, and sealed relative to the forming surface 19 by way of sealant tape 20.

In use, the layer components are layed-up as shown. A vacuum is then applied to the inner volume, for example of the order of 2Smmflg. A power supply connected to the wires Sa applies a current to the sheet 4. Under the weight of air pressure (which urges the component layers towards the forming surface 19) the sheet 4 generates heat which is conducted to the layers outward to the sheet, and so softening the resin of the matrices thereof The resin of at least the component layers immediately adjacent the resistive heater element, once softened and melted, is caused to flow at least partially into the through-holes of the sheet 4, and thereby bond to the sheet, and the component layer on the opposite side of the sheet 4. Similarly, the other component layers having been melted by the effect of the heat, will bond with adjacent layers.

The vacuum and power supply are applied for a predetermined time, after which the power supply is ceased and/or reduced (so as to reduce the level of heating applied) for a further time period. Thereafter the item/part has been formed and can be removed.

It will be appreciated that the resistive heater extends over substantially the entire surface area of the item. In certain circumstances it may be advantageous to use multiple resistive heater sheets, each with its own respective poser supply, in order to suitably cover the surface area.

It will also be appreciated that the polymer matrix in the heater is designed to have a melt temperature of +15-20 degress Celcius higher than the polymer matrix in the composite layers of the laminate. This is achieved by using a polymer blend in the heater matrix which consists mainly of the parent polymer and a percentage of a compatible higher melt temperature polymer blended to give a delta + high Tmelt for the heater. The heater then remains stable but plyable at the processing temp for manufacturing or forming /manipulating the composite part.

Reference is now made to Figure 4 which shows the same combination of component layers and the same forming apparatus, save that two integrally-formed electrical connectors are provided with the sheet 5, which are in the form of stud inserts attached to sheet. The stud inserts allow the formed item to be post-formed or manipulated subsequently using the resistive heater sheet.

There are numerous significant advantages to the above described embodiments.

Because only the material needs to be heated, as opposed to any associated tooling or equipment, the above manufacturing methods are highly energy efficient.

The resistive heater element becomes an integral part of the formed item, but does not in any way affect the performance or structural properties of the item (in particular given that the polymer of the sheet is matched to that of the polymer resin of the surround layers of the item.

Being an integral component of the formed item has two major advantages. One is that the item can be reformed to a different shape/configuration by tile re-application of a power supply to the sheet. Being embedded within the formed item, the item is subjected to less thermal and mechanical strain when heating. Heat is concentrated in the centre of the laminate material and therefore is evenly distributed throughout the material resulting in even heat-up rates for the product when processing the part.

Also, during cooling the composite part is the only material that needs to cool down because the tooling is insulated form the part in this process. This greatly reduces any internal stresses due to uneven heatup/cooldown rates which is quite common on existing processes were it is required to cool down associated tooling and processing equipment simultaneously. Known technology relies on external heat sources being applied to the part while processing ic radiant heat via hot air or conductive heat through heated tooling. This causes distortions on the part due to heating and cooling process.

A second important advantage is that by applying a suitable level of power to the sheet, in situ heating can be affected by conduction from the sheet to an outer layer of the item, which would be of advantage in dc-icing applications, or other applications in which a supply of heat from the item is required.

The ability of the resistive heater sheet item to generate heat is insensitive to damage such as a cut-out in the item. The sheet still retains the ability to generate heat despite the presence of a through-hole in the item.

The dense and substantially homogeneous structure of the resistive fibres in the sheet allows even heating and heat distribution over the sheet during the heating process.

The resistive heater sheet may be pre-formed into a particular shape/configuration prior to use.

Various applications of use of items formed using the resistive heater sheet are now described, and are given by way of non-limiting example. A first application is that of the manufacture of wind turbine blades. The icing-up of turbine blades can be potentially catastrophic. However, by manufacturing blades which include the resistive heater sheet, dc-icing can cffccted from within the blade itself. Similarly, nose and leading edge parts of an aircraft wing could bc manufactured to incorporate the resistive heater element, thus creating structural parts which are more efficient, lighter and more cost effective.

An application in relation to re-shaping/configuring the laminate item is that of a saddle tree. The saddle tree is made of a composite laminate which includes the resistive heater sheet and so enables the saddlc shape to be adjusted as required, so that the horse has the optimum level of comfort during its life-cycle. Another such application is in the field of orthoties in which lightweight thermoplastic carbon fibre parts can be custom shaped to suit an individual patient easily by applying internal heating to the carbon orthopaedic part. In these applications the recyclability of formed items provides resource and environmental advantages.

In an alternative manufacturing process to those described above, once the polymer resin material has been heatcd to the melt temperature, prcss mould tool parts close together, with the layer components therebetween, and so forming the item.

Claims

<claim-text>CLAIMSI. A method of forming a laminate item including polymer layers, the method comprising providing a perforated resistive heater sheet material as a layer of the item, applying an electric current to the sheet so as to generate heat and so heat the layers so as to render the polymer composite layers into a formable condition.</claim-text> <claim-text>2. The method as claimed in claim 1 in which the sheet material extends over at least a major portion of the surface area of the item.</claim-text> <claim-text>3. The method as claimed in claim 2 in which the heater sheet material extends over substantially the cntire surface area of thc itcm.</claim-text> <claim-text>4. The method as claimed in any preceding claim in which the heater sheet material is applied in a laying-up procedure.</claim-text> <claim-text>5. The method as claimed in any preceding claim in which the heater sheet material comprises an array of through-holes.</claim-text> <claim-text>6. The method as claimed in any preceding claim in which the heater sheet material comprises electrically resistive components set within a polymer matrix.</claim-text> <claim-text>7. The method as claimed in claim 6 in which the polymer matrix is of substantially the same material as the polymer of the polymer layer, or is compatible with the polymer of thc polymer layers.</claim-text> <claim-text>8. The method of any preceding claim in which the resistive heating sheet material is provided intermediate of outer layers of polymer.</claim-text> <claim-text>9. The method of any preceding claim in which the item comprises a plurality of polymer composite layers.</claim-text> <claim-text>10. The method of any preceding claim in which comprising applying a vacuum to the polymer layers.</claim-text> <claim-text>11. A laminate item comprising polymer layers, the item further comprising a perforated resistive heater sheet material as a layer of the item, the heater sheet material arranged to receive an applied electric current so as to cause the sheet material to generate heat and so heat the polymer of the layers.</claim-text> <claim-text>12. A laminate item as claimed in claim 11 in which the heater sheet material arranged to be capable of heating the item into a formable condition.</claim-text> <claim-text>13. A laminate item as claim 11 or claim 12 in which the heater sheet material arranged to be capable of heating the polymer layers to a temperature which is below that to achieve a formable condition, but sufficient to conduct heat to an external surface of the item, whilsi relaining the structural integrity of thc item.</claim-text> <claim-text>14. A laminate item as claimed in any preceding claim in which the heater sheet material comprises an array of through-holes, and the through holes covering a major portion of the surface area of the sheet material.</claim-text> <claim-text>15. A method substantially as described herein, with reference to the drawings.</claim-text> <claim-text>16. A laminate item substantially as described herein with reference to the drawings.</claim-text>