Vacuum Consumables. Introduction

Transcription

1 Vacuum Consumables Introduction The Airtech range of vacuum consumables has been designed for use in a wide range of vacuum bag processes. Such processes include autoclave / prepreg curing, wet resin / vacuum assisted curing, low temperature oven / prepreg processes and infusion processes. Gurit has selected a specific range of Airtech products which are particularly suitable for working with Gurit epoxy prepreg and laminating systems where they are regularly used for the curing of large composite structures at temperatures up to 150 C. The diagram below shows a simple vacuum stack indicating the products that are typically used for vacuum bag curing of composite components in low temperature ovens and high temperature autoclaves. To Vacuum Pump To Vacuum Gauge Vacuum Bagging Film Breather/Bleeder Fabric Sealant Tape Peel Ply Release Film (Perforated) Release Coated Mould Laminate Vac Cons

2 Infusion processes such as SPRINT, SCRIMP, RIFT, VARTM use less consumable products, compared to other processes, as indicated by the following diagram. These products are normally expected to operate at temperatures below 50 C. Airtech have developed a range of high quality, low cost products suitable for these processes which meet the general philosophy of infusion methods, i.e. low cost affordable manufacturing. Gurit s Guide to Composites, contains more detailed information on the range of composite manufacturing processes. Resin Infusion Processes - SCRIMP, RIFT, VARTM etc. Sealant Tape Resin drawn across and through reinforcements by vacuum Vacuum Bag To Vacuum Pump Resin Peel Ply and/or Resin Distribution Fabric Reinforcement Stack Mould Tool Resin Film Infusion products such as SPRINT use a relatively simple vacuum bag system. But due to the higher temperatures used to meet the film it is some times necessary to use different products to those used above in Resin Infusion Processing. The following pages explain the function and characteristics of each of the consumable products illustrated, and provide information on the Airtech range available from Gurit. Additional details are available directly from Airtech Advanced Materials Group. To contact Airtech tel: (UK) (Mainland Europe) (USA & rest of world) Resin Film Infusion (RFI) - SPRINT Sealant Tape Oven or autoclave used to apply heat to melt and cure the film To Vacuum Pump Vacuum Bag Dry Reinforcement Stack Mould Tool Pre-Catalysed Resin in Sheet Form 2 Vac Cons

3 Peel Plies Peel Plies are woven fabrics that are generally applied as the last material in the composite laminate sequence. They are designed to be peeled from the surface following cure to leave a textured surface, which is clean and contaminant free. This surface is then ideally prepared for secondary bonding, filling or painting and does not usually require any further mechanical abrasion. This is particularly beneficial when using aramid fibre ( e.g. Twaron / Kevlar ) as the reinforcement material. The textured surface left on the laminate is an imprint of the weave of the peel ply and therefore fine weaves will impart a finely textured surface. Peel plies are usually made from polyamide ( nylon ) or polyester fibres. Polyamide fabrics are more commonly used, though polyester fabrics must be used with phenol-based resin systems. Most peel plies have heat sealed edges ( apart from full width products ) to prevent any selvedge impression on the laminate. Red warp ( 0 ) tracers are also woven into some products to help indicate their presence on the laminate. In some cases it may be possible for the fabric to be supplied dyed for the same purpose. When using peel ply it is important to remember that they will absorb some resin from the laminate. Particular care must therefore be taken when using low resin content materials such as prepregs, in the manufacture of thin laminates, since excessive resin may otherwise be extracted. Prepregged peel plies are available to overcome this issue, or the use of a finely woven peel ply, which will absorb less resin, may also help in these instances. Peel plies are manufactured under controlled conditions. It is important to store peel plies in a cool and dry environment, ensuring the fabric is kept clean and free from possible contamination. Product Description Stitch Ply A Fibre nylon 6-6 Colour white, with red tracer yarns every 25mm Weave plain Warp (ends / cm) 19 Warp (fibre / dtex) 235 Weft (ends / cm) 15 Weft (fibre/ dtex) 235 Max use temperature ( C) 185 Total Area (wt / g/m 2 ) 82 Vac Cons

4 Release Films Release Films are used to separate and release the laminate from the vacuum stack following the cure of the composite component. Airtech Release films are supplied both as perforated and unperforated to allow resin and volatiles to bleed out of the laminate. The latter are manufactured using hot needle perforating which ensures that the holes do not close up during consolidation and ensure a high quality perforation pattern. For a fixed cure cycle, the amount of resin that will bleed out of the laminate is determined by the flow characteristics of the resin system, the cure pressure and temperature, and by the spacing and size of the perforations. For instance the smaller the hole, or the wider the spacing between holes, the lower the amount of resin, which will bleed out of the laminate. The selection of a release film should be based on the resin system being used, the temperature and pressure of the cure cycle, the shape of the component to be cured and the amount of resin bleed that is required. For example, release films that have higher elongations, will be more suitable for complex curvatures, though tailoring the film is recommended to ensure no bridging of the film occurs. It is important to remember that the mechanical performance of a film is dramatically affected by the presence of the perforations. Gurit recommends that prior testing is carried out before final use to ensure the film s handling and release characteristics are adequate for the chosen resin system and cure conditions. Some release films are supplied coloured for easy identification and to ensure joints can be accurately positioned on large components. Excessive overlaps with perforated film should be avoided since this will affect the local bleed of the resin. Rolls of release film should be stored and handled in clean and dry conditions to prevent any contamination onto the final composite component. The film should also be removed from the laminate following adequate cooling to ensure easy removal of the film. Product Description WL3600 Film Type PP Film thickness (mm) Maximum use temperature ( C) 120 Colour Clear Perforations available non-p,p,p3 & P90 Explanation of Perforated Pitch: Perforation Reference Nominal Hole Size (h) Pitch (x) (mm) Pitch (y) (mm) Bleed Characteristics P High P Medium y y 2 x x 2 ø = h Roll Direction P Low 4 Vac Cons

5 Vacuum Bagging Films Vacuum Bagging Films are used to seal the whole of the composite laminate, including the other vacuum consumables, to the tooling surface. A vacuum is then applied in order to apply atmospheric pressure to the component. This pressure can be increased in an autoclave, or maintained for a standard, one-atmosphere cure cycle at the chosen cure temperature. Many films can be used for this purpose, but nylon Airtech films are commonly used, due to their good temperature resistance, cost effectiveness, ease of use and low air permeability (necessary to achieve a good quality laminate and vacuum integrity). Nylon films are susceptible to variations in humidity, since moisture is used as a natural plasticiser. Therefore, it is recommended, especially in dry environments to condition the film before use. Components, particularly with complex geometries, must be vacuum bagged with plenty of tucks to give depth to the film. Failure to make contact with the laminate over tight corners is called bridging. This may lead to a resin rich, local area (caused by an unequal consolidation pressure), or in the worst case, may lead to complete failure of the vacuum film. Care must be taken when handling and storing vacuum bagging films to prevent damage. A surface puncture in a roll of film, may affect many metres, which will then have to be cut off and scrapped. Airtech individually package roll s of film in a tough cardboard outer tube, to provide sufficient protection to the film. If you require further information on vacuum bagging techniques, please contact the Technical Service department or Airtech Advanced Materials Group directly. Product Description Film Type WL7400 PA6 Film thickness (mm) 0.05 Maximum use temperature ( C) 205 Elongation (longitudinal) % 375 Elongation (transverse) % 400 Colour Manufacture Method Green Tint blown tube Vac Cons

6 Sealant Tape Sealant tapes are used to provide an integral seal between the tool surface and the vacuum bag. The Airtech range of sealant tapes are manufactured from a blend of synthetic rubbers combined with inert fillers, plasticisers and tackifiers. These provide the optimum combination of properties required for sealing against a variety of tool surfaces, such as composite, metal or glass and for the subsequent curing of the composite. The tackiness of the tape has been designed to ensure that the tape can be easily laid onto the tool surface, with sufficient reserve to enable removal if re-positioning is required. The tack and adhesion characteristics of the Airtech sealant tapes are also designed to allow a shock -type release of the bagging film, with the tapes cohesive properties designed to minimise the residue of the tape remaining on the tool. Tapes that are used for elevated temperature cure cycles exhibit increased cohesion, reduced flow and a clean release, due to a cross linking mechanism which takes place within the tape, during the cure cycle. Therefore, these tapes are given shelf lives to guarantee their performance. Product Description AT90 AT140 Dimensions (mm) 12 x 3 12 x 3 Roll length (m) 15m 15m Colour black White Max use temperature ( C) Shelf life (months) n/a n/a Tackiness medium high 6 Vac Cons

7 Flash / Release / Shrink Tapes Flash tapes are typically used within a vacuum stack to locate and secure vacuum consumable materials as the component is being bagged, and throughout the component s cure cycle. This is particularly important on components being built with vertical, inclined or even overhanging surfaces. Flash tapes can also be used in their traditional role to mask off areas to be painted, degreased or to prevent surface damage. The Airtech tapes are supplied with a single sided pressure sensitive adhesive. Some tapes have release qualities which allow parts to be flashed yet ensuring easy removal of an epoxy component. These tapes may also be useful for quick tool repairs where a released surface is important. Shrink tapes are used to consolidate a component during an elevated temperature cure. Shrink tapes are typically used on round sectioned components, since they are easy to wrap and a uniform pressure is applied by the tape. When heated the polyester tape shrinks in the lengthwise direction only, inducing pressure which acts on the underlying part. There is an optimum temperature for maximum shrink force, though this force can be increased by using more layers of tape. Airtech shrink tapes are supplied with a release coating to ensure the component does not bond to the tape. Product Description Flashbreaker 1 A575RC Use flashtape shrinktape Film type polyester polyester Adhesive type silicone n/a Maximum use temperature ( C) Minimum shrink temperature ( C) n/a 93 Optimal Shrink temperature ( C) n/a 150 Maximum shrink pressure (MPa) n/a 17.2 Colour blue clear Release coating n/a TFE Vac Cons

8 Self Adhesive Mould Release Materials Self adhesive mould release materials are popular for the coating of moulds, as an effective alternative to the use of release wax or liquids. Such products are often used on one-off wooden moulds in the production of custom racing yachts and spars. These materials are often PTFE ( e.g. Teflon ) coated glass-fibre fabrics or can be skived grades, which are more popular for compound curvatures. Airtech self adhesive materials are supplied with release backers in a roll format. These products should be applied to dry and contaminant free surfaces, which are free of grease / solvent and are not pre-released. Air should not be entrapped under the material when applied, since this may cause the material to lift during the cure cycle. Product Description Base fabric material Coating material Adhesive Tooltec A007 glass PTFE Silicone Maximum use temperature ( C) 200 Thickness without adhesive (mm) Vac Cons

9 Breather / Bleeder Fabrics & Infusion Meshes The breather fabric performs two functions during the cure cycle. The first, as the name suggests, is to allow the vacuum stack to breathe. This breathing function ensures that the air sealed under the vacuum bag can be easily extracted. It also provides a path for the flow of any entrapped air, or volatiles, from within the laminate during the cure cycle. The second function, in combination with the perforated release film, is to absorb any excess resin that is bled from the laminate. Where a separate layer of breather fabric is used for this secondary function, it is often known as a bleeder. In most simple vacuum bag processes, one layer of fabric acts as both a bleeder and a breather. Airtech s range of breather fabrics are all manufactured from polyester fibres which are needle punched to form the non-woven, feltlike fabric. There are no chemical binders used in these products. The tex of the fibre, the fibre length and the punching density have all been optimised to create breather fabrics with optimum characteristics. All the breather/bleeder fabrics have been designed to produce good elongation in all directions, so that they can be draped easily over complex curvatures. This helps to minimise any bridging situations which may otherwise tend to occur. The selection of a breather fabric should be based on the curing pressure, the amount of bleed required, the size of the component and the location of the vacuum port(s). A breather can be used in combination with another breather, or in multiple layers where increased thickness is required. Narrow strips of breather are commonly laid around the tool periphery, under the vacuum fittings or over sharp corners to provide an increase in air flow. Infusion meshes are used to transport the resin across the top of the reinforcement stack. They can also be used as a breather when performing debulk operations. Product Description Econoweave 44W Econoweave 1010W Breatherflow 20 Knitflow 40 Type non-woven non-woven bi-planar mesh knitted mesh Fibre Polyester Polyester polypropylene polythyene Colour white white clear green / yellow 1 Nominal thickness (mm) Weight (g/m 2 ) Max use temperature ( C) Vac Cons

10 Vacuum Fittings Vacuum fittings are used to plumb the whole of the bagged composite component to the vacuum pump. This therefore allows a vacuum to be applied and maintained to the material for either a debulk operation or for a final cure. These Airtech group of fittings essentially consist of a breach unit (through bag connector); a quick release coupling (plug and socket); and a reinforced hose capable of holding a negative pressure. Product Description VV401C AQD500S AQD500P VG20 Econo Flo 3 Use thru-bag connector vacuum socket vacuum plug vacuum gauge vacuum hose Thread (bsp) 1/4 1/4 1/4 1/4 1/4 Seal silicon viton viton n/a n/a Dimensions 75mm base m Max use temperature ( C) Vac Cons

11 Notice All advice, instruction or recommendation is given in good faith but Gurit AG (the company) only warrants that advice in writing is given with reasonable skill and care. No further duty or responsibility is accepted by the Company. All advice is given subject to the terms and conditions of sale (the Conditions) which are available on request from the Company or may be viewed at the Company s Website: The Company strongly recommends that Customers make test panels and conduct appropriate testing of any goods or materials supplied by the Company to ensure that they are suitable for the Customer s planned application. Such testing should include testing under conditions as close as possible to those to which the final component may be subjected. The Company specifically excludes any warranty of fitness for purpose of the goods other than as set out in writing by the Company. The Company reserves the right to change specifications and prices without notice and Customers should satisfy themselves that information relied on by the Customer is that which is currently published by the Company on its website. Any queries may be addressed to the Technical Services Department. Gurit are continuously reviewing and updating literature. Please ensure that you have the current version, by contacting Gurit Marketing Communications or your sales contact and quoting the revision number in the bottom right-hand corner of this page. E gurit@gurit.com W 11 Vac Cons