WO2013011306A1 - Method for laminating items and items obtained by the method - Google Patents

Method for laminating items and items obtained by the method Download PDF

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Publication number
WO2013011306A1
WO2013011306A1 PCT/GB2012/051711 GB2012051711W WO2013011306A1 WO 2013011306 A1 WO2013011306 A1 WO 2013011306A1 GB 2012051711 W GB2012051711 W GB 2012051711W WO 2013011306 A1 WO2013011306 A1 WO 2013011306A1
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WO
WIPO (PCT)
Prior art keywords
item
polymer
sheet material
laminate
layers
Prior art date
Application number
PCT/GB2012/051711
Other languages
French (fr)
Inventor
Peter James Sajic
Original Assignee
Peter James Sajic
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Peter James Sajic filed Critical Peter James Sajic
Publication of WO2013011306A1 publication Critical patent/WO2013011306A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B37/00—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding
    • B32B37/06—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the heating method
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B37/00—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding
    • B32B37/06—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the heating method
    • B32B37/065—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the heating method resulting in the laminate being partially bonded
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C65/00—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor
    • B29C65/02—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure
    • B29C65/34—Joining or sealing of preformed parts, e.g. welding of plastics materials; Apparatus therefor by heating, with or without pressure using heated elements which remain in the joint, e.g. "verlorenes Schweisselement"
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B3/00—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar shape; Layered products comprising a layer having particular features of form
    • B32B3/26—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar shape; Layered products comprising a layer having particular features of form characterised by a particular shape of the outline of the cross-section of a continuous layer; characterised by a layer with cavities or internal voids ; characterised by an apertured layer
    • B32B3/266—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar shape; Layered products comprising a layer having particular features of form characterised by a particular shape of the outline of the cross-section of a continuous layer; characterised by a layer with cavities or internal voids ; characterised by an apertured layer characterised by an apertured layer, the apertures going through the whole thickness of the layer, e.g. expanded metal, perforated layer, slit layer regular cells B32B3/12
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B5/00—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts
    • B32B5/22—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed
    • B32B5/24—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed one layer being a fibrous or filamentary layer
    • B32B5/26—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed one layer being a fibrous or filamentary layer another layer next to it also being fibrous or filamentary
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B3/00—Ohmic-resistance heating
    • H05B3/10—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
    • H05B3/18—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor the conductor being embedded in an insulating material
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B3/00—Ohmic-resistance heating
    • H05B3/20—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater
    • H05B3/22—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater non-flexible
    • H05B3/28—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater non-flexible heating conductor embedded in insulating material
    • H05B3/286—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater non-flexible heating conductor embedded in insulating material the insulating material being an organic material, e.g. plastic
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2262/00—Composition or structural features of fibres which form a fibrous or filamentary layer or are present as additives
    • B32B2262/10—Inorganic fibres
    • B32B2262/106—Carbon fibres, e.g. graphite fibres
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2309/00—Parameters for the laminating or treatment process; Apparatus details
    • B32B2309/08—Dimensions, e.g. volume
    • B32B2309/10—Dimensions, e.g. volume linear, e.g. length, distance, width
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2309/00—Parameters for the laminating or treatment process; Apparatus details
    • B32B2309/08—Dimensions, e.g. volume
    • B32B2309/10—Dimensions, e.g. volume linear, e.g. length, distance, width
    • B32B2309/105—Thickness
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2311/00—Metals, their alloys or their compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2605/00—Vehicles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B37/00—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding
    • B32B37/10—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the pressing technique, e.g. using action of vacuum or fluid pressure
    • B32B37/1018—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the pressing technique, e.g. using action of vacuum or fluid pressure using only vacuum
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B2214/00—Aspects relating to resistive heating, induction heating and heating using microwaves, covered by groups H05B3/00, H05B6/00
    • H05B2214/02—Heaters specially designed for de-icing or protection against icing

Definitions

  • the present invention relates generally to laminate items, and to methods of forming the same.
  • thermoforming/stamping techniques wherein a pre-consolidated 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.
  • 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.
  • 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.
  • 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).
  • a method of forming an item from polymer layers 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.
  • 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 polymer-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.
  • 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.
  • a forming bag which comprises a resistive heater sheet which is embedded within a polymer matrix, or is sandwiched between polymer layers.
  • the bag is preferably of flexible sheet form and is arranged to be applied (directly or indirectly) against a material to be formed.
  • Yet another aspect of the invention relates to a method of forming an item using the forming bag of the above aspect.
  • 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
  • Figure 4 is a schematic cross-sectional view of the production of a composite plastics item
  • Figure 5 is a cross-section of a forming apparatus
  • Figure 6 is a partial view of a forming bag.
  • FIG. 1 With reference to Figure 1 there are shown at 1 various components in the production of an item formed of a plastics composite material, 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, KevlarTM, set within a polymer resin matrix of at least one of Polyethylene terephthalate (PET), Polyphenylene sulphide (PES), Polyetherimide (PEI), Polyetheretherketone (PEEK), Polypropylene (PP), Polycarbonate (PC), Polyethylene (PE), Silicone (SI), thermoplastic polyurethane (TPU) and Polyamide (Nylon).
  • PET Polyethylene terephthalate
  • PES Polyphenylene sulphide
  • PEI Polyetherimide
  • PEEK Polyetheretherketone
  • PP Polypropylene
  • PC Polycarbonate
  • PE Polyethylene
  • SI Silicone
  • TPU thermoplastic polyurethane
  • Polyamide Polyamide
  • glass fibre or any other insulating fabric or fibre material
  • the layers 3 serve to insulate the heater sheet electrically from the carbon fibre composite layers. It 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 are 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.
  • a voltage is applied to the sheet via the wires 5a 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.
  • FIG. 3 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 1 1 , a release film 12, and an underlying PTFE sheet 13, and a forming surface 19.
  • the composite laminate item to be formed comprises the following component layers.
  • 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.
  • the layer components are layered-up as shown.
  • a vacuum is then applied to the inner volume, for example of the order of 25mmHg.
  • a power supply connected to the wires 5a applies a current to the sheet 4.
  • 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 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.
  • the polymer matrix in the heater is designed to have a melt temperature of +15-20 degrees Celsius 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 pliable at the processing temp for manufacturing or forming /manipulating the composite part.
  • FIG. 4 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.
  • 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 the 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.
  • 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 de-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.
  • a first application is that of the manufacture of wind turbine blades.
  • the icing-up of turbine blades can be potentially catastrophic.
  • de-icing can effected from within the blade itself.
  • nose and leading edge parts of an aircraft wing could be 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 saddle 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 orthotics 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.
  • FIGS. 5 and 6 show use of a forming bag 50 which incorporates a resistive heater sheet 4, which is incorporated therewith.
  • the bag 50 is a laminate item which, on each side of the resistive heater sheet 4, comprises a polymer layer 51 , for example, silicone, fluoroethylene polymer, or elastomer.
  • the bag 50 may be formed by sandwiching the resistive heater 4 between the outer layers 51 applying a current to the resistive sheet and pressure to the layers 51. Thereby, the resistive heater sheet 4 will become fused (by virtue of the heater sheet bag heated the material of the outer layers so that the material melts into the through- holes of the sheet 4) with the outer layers 51 , and so form an integral item.
  • FIG. 5 shows a moulding tool 60, a composite thermoplastic material prepreg 61 , a release film 62, the forming bag 50, a vacuum outlet 63 and a breather felt (or glass fibre woven) 66.
  • the composite material 61 is placed over a forming surface 60a.
  • the release film 62 is then placed on top of the material 61 , and the forming bag 50 is then placed over the release film 62.
  • an insulation jacket 65 may be placed over the heater sheet 50.
  • the heater sheet 50 is clamped in position by way of a frame member 70. Underlying the heater sheet 50 there are provided seals 71. Air is drawn out of the space enclosed by the forming bag 50 through the vacuum outlet 63.
  • the heater sheet 50 applies pressure against the release film 62, and in turn, against the material to be shaped 61. At this time a current is caused to flow through the heater sheet 50 causing heat to be generated. The heat is conducted through to the material to be shaped 61. The material 61 is heated to a formable temperature and so in combination with the applied pressure, causes the material 61 to conform to the shape of the forming surface 60a. The current, and hence applied heat, is then switched off and the material allowed to cool quickly. Once the material has been formed to the required shape, the vacuum can be broken, the heater sheet removed, and the item formed of the material 61 removed.
  • the forming bag 50 can be re-used many times, and so is not a single-use item.
  • the resistive heater sheet 4 extends over at least a major portion of the surface area of the sheet, and preferably over the substantially the entire area of a bag 50.

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Laminated Bodies (AREA)
  • Moulding By Coating Moulds (AREA)
  • Surface Heating Bodies (AREA)

Abstract

A method of forming an item from polymer layers (2) is disclosed, the method comprising providing a perforated resistive heating sheet material (4) as a layer of the item, applying an electric current to the sheet (4) so as to generate heat and so heat the material so as to render the polymer layers (2) into a formable condition. By 'polymer layer' we include resin impregnated fibre materials, such as carbon fibre, composite fibre, Kevlar™ fibre, basalt fibre, glass fibre wherein the resin may be thermoforming or thermosetting material, is preferably polymer-based. A laminate item comprising polymer layers (2) is also disclosed, the item further comprising a perforated resistive heater sheet material (4) as a layer of item, the heater sheet material (4) arranged to receive an applied electric current so as to cause the sheet material to generate heat and so heat the polymer layers (2). A forming bag (10) is also disclosed which comprises a resistive heater sheet (4) which is embedded within a polymer matrix, or is sandwiched between polymer layers (2). The bag (10) is preferably of flexible sheet form and is arranged to be applied (directly or indirectly) against a material to be formed.

Description

METHOD FOR LAMINATING ITEMS AND ITEMS OBTAINED BY THE METHOD
Technical Field
The present invention relates generally to laminate items, and to methods of forming the same.
Background
It is known to employ thermoforming/stamping techniques wherein a pre-consolidated 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, Kevlar™ fibre, basalt fibre, glass fibre wherein the resin may be thermoforming or thermosetting material, is preferably polymer-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.
According to another aspect of the invention there is provided a forming bag which comprises a resistive heater sheet which is embedded within a polymer matrix, or is sandwiched between polymer layers. The bag is preferably of flexible sheet form and is arranged to be applied (directly or indirectly) against a material to be formed.
When an electric current is applied to the resistive heater sheet, heat is generated which is conducted through the outlying polymer of the bag, and towards the material to be formed.
Yet another aspect of the invention relates to a method of forming an item using the forming bag of the above aspect.
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,
Figure 4 is a schematic cross-sectional view of the production of a composite plastics item,
Figure 5 is a cross-section of a forming apparatus, and Figure 6 is a partial view of a forming bag. Detailed Description
With reference to Figure 1 there are shown at 1 various components in the production of an item formed of a plastics composite material, 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, Kevlar™, set within a polymer resin matrix of at least one of Polyethylene terephthalate (PET), Polyphenylene sulphide (PES), Polyetherimide (PEI), Polyetheretherketone (PEEK), Polypropylene (PP), Polycarbonate (PC), Polyethylene (PE), Silicone (SI), thermoplastic polyurethane (TPU) 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. It 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 are 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 5a 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 1 1 , a release film 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 layered-up as shown. A vacuum is then applied to the inner volume, for example of the order of 25mmHg. A power supply connected to the wires 5a 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 degrees Celsius 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 pliable 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 the 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 heat-up/cool down 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 ie 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 de-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, de-icing can effected from within the blade itself. Similarly, nose and leading edge parts of an aircraft wing could be 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 saddle 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 orthotics 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 heated to the melt temperature, press mould tool parts close together, with the layer components therebetween, and so forming the item.
Reference is made now to Figures 5 and 6 which show use of a forming bag 50 which incorporates a resistive heater sheet 4, which is incorporated therewith. The bag 50 is a laminate item which, on each side of the resistive heater sheet 4, comprises a polymer layer 51 , for example, silicone, fluoroethylene polymer, or elastomer. The bag 50 may be formed by sandwiching the resistive heater 4 between the outer layers 51 applying a current to the resistive sheet and pressure to the layers 51. Thereby, the resistive heater sheet 4 will become fused (by virtue of the heater sheet bag heated the material of the outer layers so that the material melts into the through- holes of the sheet 4) with the outer layers 51 , and so form an integral item.
Reference is now made in particular to Figure 5 which shows a moulding tool 60, a composite thermoplastic material prepreg 61 , a release film 62, the forming bag 50, a vacuum outlet 63 and a breather felt (or glass fibre woven) 66. In use the composite material 61 is placed over a forming surface 60a. The release film 62 is then placed on top of the material 61 , and the forming bag 50 is then placed over the release film 62. Optionally, an insulation jacket 65 may be placed over the heater sheet 50. The heater sheet 50 is clamped in position by way of a frame member 70. Underlying the heater sheet 50 there are provided seals 71. Air is drawn out of the space enclosed by the forming bag 50 through the vacuum outlet 63. In so doing the heater sheet 50 applies pressure against the release film 62, and in turn, against the material to be shaped 61. At this time a current is caused to flow through the heater sheet 50 causing heat to be generated. The heat is conducted through to the material to be shaped 61. The material 61 is heated to a formable temperature and so in combination with the applied pressure, causes the material 61 to conform to the shape of the forming surface 60a. The current, and hence applied heat, is then switched off and the material allowed to cool quickly. Once the material has been formed to the required shape, the vacuum can be broken, the heater sheet removed, and the item formed of the material 61 removed. Advantageously, the forming bag 50 can be re-used many times, and so is not a single-use item. The resistive heater sheet 4 extends over at least a major portion of the surface area of the sheet, and preferably over the substantially the entire area of a bag 50.

Claims

1. 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.
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.
3. The method as claimed in claim 2 in which the heater sheet material extends over substantially the entire surface area of the item.
4. The method as claimed in any preceding claim in which the heater sheet material is applied in a laying-up procedure.
5. The method as claimed in any preceding claim in which the heater sheet material comprises an array of through-holes.
6. The method as claimed in any preceding claim in which the heater sheet material comprises electrically resistive components set within a polymer matrix.
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 the polymer layers.
8. The method of any preceding claim in which the resistive heating sheet material is provided intermediate of outer layers of polymer.
9. The method of any preceding claim in which the item comprises a plurality of polymer composite layers.
10. The method of any preceding claim in which comprising applying a vacuum to the polymer layers.
1 1. 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.
12. A laminate item as claimed in claim 1 1 in which the heater sheet material arranged to be capable of heating the item into a formable condition.
13. A laminate item as claim 1 1 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, whilst retaining the structural integrity of the item.
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.
15. A laminate item as claimed in claim 1 1 which is arranged to be applied to an outward surface of an item to be formed and arranged to be releasably urged there against.
16. A laminate item as claimed in claim 1 1 or claim 15 which comprises a polymer layer on each side of the perforated resistive heater sheet material.
17. A laminate item as claimed in claim 16 in which the perforated resistive heater sheet material is embedded in a polymer matrix.
18. A laminate item as claimed in claim 1 1 which is arranged for use as a forming bag.
19. A laminate item as claimed in claim 18 which is arranged to be re-usable.
20. A laminate item as claimed in any of claims 15 to 19 which is in flexible sheet form.
21. A laminate item as claimed in any of claims 15 to 20 in which the polymer the item comprises silicone or fluoroethylene polymer.
22. A laminate item as claimed in any of claims 15 to 21 which has a thickness the range of 1.5mm to 3mm.
PCT/GB2012/051711 2011-07-21 2012-07-18 Method for laminating items and items obtained by the method WO2013011306A1 (en)

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GB1112486.4A GB2493001B (en) 2011-07-21 2011-07-21 Laminate items
GB1112486.4 2011-07-21

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DE102014012315A1 (en) * 2014-08-19 2016-02-25 Friedrich-Wilhelm Struve Tolerance compensating thin flat heating element
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USD911038S1 (en) 2019-10-11 2021-02-23 Laminaheat Holding Ltd. Heating element sheet having perforations

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