he smoothness of a compositesurface depends on several differentfactors, such as the type of

reinforcement used, the choice of resin, themanufacturing method and the curingparameters, including temperature, pressureand curing-cycle variations. Surfacedistortions often appear after a certain timeas the composite is being exposed tounintended post-cure. In the case studydescribed herein, all parameters except thereinforcement structure were kept constantin order to analyze the influence of thereinforcement.

Surface smoothness ofcompositesIn the manufacture of composite parts, thecomposite surface often displays a sort oforange-peel pattern which usuallyintensifies as the surface is being painted,especially in black. A variety of fillers,gelcoat systems and curing cycles were

Case Study: Composite surfacesmoothness improvement

Oxeon the fastestgrowing company in Sweden

Oxeon has beenacknowledged as the fastestgrowing company in Sweden2010 and has been awarded

the Gazelle price“Supergasell” by Swedish

financial newspaper “DagensIndustri”. The “Supergasell”

is an annual award thatrecognizes the company that

has shown the mostexceptional growth and

created new employmentopportunities.

developed and investigated to reduce thesedefects. The large-pattern print-throughcreated by bulky reinforcements can beminimized by the use of surface plies withlow areal weight and a very fine weavepattern, reducing fibre crimp and theassociated waviness. However, print-through remains largely visible.

Practical case studyIn 2009, Håkan Sundelin, from the well-known Finnish luxury composite sailboatmanufacturer Baltic Yachts, mentioned thefact, during a discussion with Oxeon, thattheir up-to-200-foot-long hulls sometimesdisplayed visible surface defects in the formof print-through. According to Mr.Sundelin, these surface defects oftendeveloped within 6-12 months, as the boatswere being assembled. To minimize theproblem, various reinforcement structuresand materials have been tested as the outersurface layer. The solution with the bestresults so far has been a 200-gsm glasswoven roving fabric, and the second best a200-gsm carbon-fibre woven roving cloth. Baltic and Oxeon initiated a joint testprogramme, for which Oxeon supplied its100-gsm TeXtreme® Spread Tow Fabric.Panels made with the original layupstacking sequence using TeXtreme® and thetwo above-mentioned materials as surfacelayers were produced and stored in theassembly hall for six months to study thevisual differences.

Spread Tow Fabrics could be a valuable solution to improve thesurface smoothness of composites, reducing print-through and visual defects. These reinforcements could reduce the use of extrafillers, padding and thick gelcoats, leading to weight and laboursavings. Here is a case study describing how the Finnish companyBaltic Yachts successfully improved their composite hulls through the use of Spread Tow Fabrics.

TOxeon AB,

Norrby Långgata 45, SE-504 35 Borås, Sweden

Phone: +46 33 20 59 70Fax: +46 33 20 59 79

contact@oxeon.sewww.oxeon.se

Applicatio

ns

Original publication in JCM No63 March 2011 / jec composites magazine 21

FREDRIK OHLSSON, PRODUCT MANAGER MATERIALS,

OXEON AB

By

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During the inspection thatfollowed, Håkan Sundelinclearly observed thedifferences between thedifferent panels. While the hullsections with the traditionalwoven yarn fabrics displayeduneven surfaces andimperfections, the test samplesproduced with TeXtreme®looked much smoother.

“We had been trying to optimizeour manufacturing parametersfor a long time, but had still notmet an acceptable level ofsurface finish, mainly due toprint-through. The resultsobtained when using TeXtreme®as the surface ply showeddramatic improvements,” saysHåkan Sundelin.

Measurements andanalysisThe OptiTopo test developedby Innventia AB (formerlySTFI) was used to quantifythe differences in surfacesmoothness, especially print-through. This test uses acamera and two light sourcesto optically detect thetopography of a given surface.The tests can be conducted ona max. 30 x 30 mm area, whichwas considered representativeof all surface materialstructures.

The results shown in Fig. 1represent the surfacetopography of the differentpanels measured and displayedas height variations [µm].

Benefits of Spread TowFabricsOxeon produces and marketsTeXtreme® Spread Tow Fabricfrom HS, IM and HM carbonfibres in a wide range of arealweights starting at 76 gsm. Spread Tow Fabrics areproduced with virtually no in-

plane or out-of-plane fibre crimpand have relatively longer fibrefloats, resulting in fewerinterlacing points whencompared to traditional wovenyarn fabrics. Through this unique structure,the resin-rich valleys/pits arerelatively fewer and insignificantin size, as can be seen in Fig.2. In addition to its unique abilityto improve surface smoothness,TeXtreme® also improvesmechanical performance andsaves significant weight, as thefibres are oriented relativelystraighter and the fabricstructure consumes less resin,which reduces matrix deadweight.

ConclusionTeXtreme® Spread Tow Fabrichas been shown to improve thesurface smoothness ofcomposites, resulting in reducedprint-through. The present case study showsthat Finnish manufacturer BalticYachts was able to improve thesurface smoothness of itscomposite sailboat hulls byswitching to Spread Tow Fabricsfor surface ply. The surface smoothnessimprovements weredemonstrated by an OptiTopolaboratory test.

More information: www.oxeon.se

Fig 1: OptiTopo results on variations of surface plies. Upper left: 200-gsm glass roving fabric, upper right: 200-gsm carbon-fibre woven roving cloth. Lower left: 100-gsm TeXtreme®, lower right: 2 layers of 100-gsm TeXtreme®. Colour scale in µm

Fig 2: Spread Tow Fabrics (STF) reduce print-through problemsthrough their unique structure compared to standard carbonreinforcements

22 jec composites magazine / Original publication in JCM No63 March 2011

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