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(WET) HAND LAY-UP

(WET) HAND LAY-UP. COMBINING OF REINFORCING FIBER AND RESIN AT THE TIME OF PART FABRICATION. REINFORCING FIBER. E-glass, S-glass, Aramid, Carbon/Graphite

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(WET) HAND LAY-UP

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  1. (WET) HAND LAY-UP COMBINING OF REINFORCING FIBER AND RESIN AT THE TIME OF PART FABRICATION

  2. REINFORCING FIBER • E-glass, S-glass, Aramid, Carbon/Graphite • E-glass most common (process inherently produces lower "quality" composite laminate due to lack of tight resin content control and low compaction pressure) • chopped mat material • consists of randomly oriented chopped fibers or swirled continuous fibers which are held together loosely by a binder • 0.75 oz/sq ft - 3 oz/sq ft • woven fabric material form most common • available on rolls in widths from 36 in. to 60 in. typically • terminology and basic weave patterns (refs. 1, 2, and 3) • unidirectional fabric • very fine filling (stitching) yarn • biaxial fabric

  3. RESINS • polyesters • vinyl esters • epoxies

  4. MOLD/TOOL PREPARATION • procedure to some degree dependent on: • tooling material • whether tool is being used in first cycle or subsequent cycle • clean tool • scotch brite pad • wipe with a clean cloth dampened with solvent (i.e. Acetone) • mold release agents • waxes (carnuba-based) • spray releases • release films • internal releases (added to gel coat or resin system)

  5. APPLYING A MOLD RELEASE AGENT • preheat mold • apply release agent • allow period of time for release agent to "set up" (for wax) or "flash off" • buff with clean cloth • repeat application (particularly for first cycle) alternating pattern • cure

  6. THE WET LAY-UP PROCESS OFTEN BEGINS WITH A GEL COAT • typically polyester, mineral filled (clays and carbonates), pigmented (different than mold color), non-reinforced layer or coating • produces decorative, high protective, glossy, colored surface • little or no additional finishing required • can paint on, roll on, or spray on • allow gel coat to set (gel) barely tacky, but not release to the finger

  7. CUTTING THE FABRIC • cut desired pattern • tools: shears and/or utility knife

  8. WEIGHING OUT THE RESIN • weigh out resin components in specified proportions to achieve desired resin content (desired fiber volume of finished part) • epoxy curing agents expressed in parts per hundred by weight (phr) of epoxy resin or parts by weight • EPON Resin 862/EPI-CURE 3274: 100/42 • resin content expressed as percent by weight • epoxy resins typically 25% - 35% by weight (dependent on ability to wet out fiber, amount of resin bleeding out during cure, etc.) • need to account for process waste • resin bleeding out, remaining on brushes, ... • dependent on size of part (i.e. the smaller the part the greater the proportion of process waste) • draw quantity of resin components, in separate containers • thoroughly mix resin components (combine resin into curing agent container) • tools: containers, stirrers

  9. RESIN SYSTEM QUANTITIES FOR THE DEMONSTRATION PART • 16, 12 in x 12 in plies of 7781 E-glass cloth • resin system is Shell EPON Resin 862/EPI-CURE 3274 • (16 plies)(1 sq ft/ply)(1 sq yd/9 sq ft)(8.95 oz/sq yd)(1 lb/16 oz) = 0.994 lb • x/(x+0.994 lb) = 0.30 (x = lb of resin system) • x = 0.426 lb (193 gm) of resin system • EPON Resin 862 (100/(100 + 42))(0.426 lb) = 0.300 lb (136 gm) • EPI-CURE 3274 (42/(100 + 42))(0.426 lb) = 0.126 lb (57 gm) • account for process waste

  10. APPLY RESIN TO FABRIC • apply resin to fabric on mold surface or, preferably, wet out fabric with resin on separate surface and transfer to mold • resin may be sprayed, poured or brushed on, and spread with brush and/or squeegee • applying resin on mold surface prior to laying of fabric facilitates removal of entrapped air during compaction process - resin is forced up through the fabric along with the air • applying resin to fabric on separate surface prevents resin rich (female curvature) and resin starved (male curvature) areas • tools: paint brush, spray equipment, squeegee

  11. COMPACTION • resin should be applied and compacted on mold surface from the center to the outside to facilitate removal of entrapped air, visually able to see air moving • pressure can be applied with a squeegee and/or serrated roller • bridging on female contours (radii) must be avoided • tools: squeegee, serrated rollers

  12. VACUUM BAGGING SEQUENCE (VERTICAL BLEED)

  13. PEEL PLY • placed immediately on top of or under the composite laminate • removed just before bonding or painting operations to provide clean, bondable surface • woven fabric (nylon, polyester, or fiberglass) treated with nontransferable release agent

  14. SEPARATOR (RELEASE FILM) • placed on top of or under the laminate and peel ply (if used) • allows volatiles to escape from laminate and excess resin to be bled from the laminate into the bleeder plies during cure • porous or perforated • spacing of perforations or porosity of the material determines the amount of resin flow from the surface of the laminate

  15. BLEEDER • absorb excess resin from the laminate during cure (resulting in desired fiber volume) • fiberglass fabric or other absorbent materials or fabrics are used • amount of bleeder used is a function of • absorbency of material • resin content • finished part fiber volume desired

  16. BARRIER • between bleeder plies and breather • frequently nonperforated, nonadhering (release) film • resins which produce volatile by-products during cure (must be vented) use a film with small perforations and large spacing to prevent the breather from becoming clogged with resin

  17. BREATHER • on top of barrier film to allow uniform application of vacuum pressure over the laminate and removal of entrapped air or volatiles during cure • drapable, loosely woven fabric, or felt

  18. CAUL PLATES • steel, aluminum • used to maintain same heating and cooling rate as mold • more uniform application of pressure • ensure a smooth, non-wavy surface

  19. DAM • located peripherally to minimize edge bleeding • may be integral part of tool or rubber, metal bars, etc.

  20. VACUUM BAGGING • vacuum bag • used to contain any vacuum pressure applied • application of the vacuum bag extremely critical • bag perforation must be prevented • no sharp edges on tool • properly sealed on edge • no bridging (requires folds in bag) • folds must be properly made or undesirable wrinkles may occur in part • bag sealant tape • vacuum valves • vacuum hoses • vacuum source

  21. CURING • follow cure schedule recommended by resin supplier • either room temperature or elevated temperature cure resin system

  22. PREIMPREGNATED MATERIALS (PREPREGS) • reinforcements impregnated with predetermined amounts of uniformly distributed resin • processed to obtain optimum handling characteristics and reproducible cured laminate properties • thermoset and thermoplastic resin systems • reinforcing fiber • e-glass, s-glass, aramid, carbon/graphite • unidirectional tape, woven fabric

  23. HAND LAY-UP OF PREPREGS • mold preparation • ply (prepreg) cutting (and kitting) • film adhesive may be used against mold surface • ply is laid on mold using hand pressure, squeegee, and/or roller and carrier film is removed • heat gun may be used to improve tack • debulking (interim compactions) • process materials and sequence is similar to wet lay-up • cure • autoclave (applies heat and pressure) • cure cycle • temperature and pressure • ramp rates • holds

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