Marine Surveyors Lexicon


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Sandwich Panels

A sandwich panel is normally a low-density core material sandwiched between two high modulus face skins to produce a lightweight panel with exceptional stiffness. The face skins act like the flanges of an I beam carrying tensile and compressive loads. The core plays the role of the web, separating the face skins and carrying the shear loads.

Core materials provide panel thickness, with associated stiffness, at minimal weight. Stiffer panels require less support structure, simplifying structural design. Other advantages of sandwich panels include:

  • Truer, fairer and stiffer panel shapes compared with solid FRP skins or metal skins over frames.
  • Easier component handling due to increased stiffness and weight reduction.
  • Increased interior volume due to less support structure.
  • Lower VOC emissions compared with solid FRP lay-ups.
  • Significantly improved thermal and acoustic insulation.

The properties of sandwich panels can vary greatly with different skin materials and skin thickness, different core materials and core thickness. When selecting a core material, it helps to understand how the structure will be or could be stressed or compromised, as different material combinations produce quite different results.

End Grain Balsa - with its elongated vertical cell structure, provides very high compressive stiffness and resistance to crushing. It has a great capacity for handling cyclic loads, and it is possible to obtain very strong skin to core bonds. End grain balsa is cost effective, and can withstand remarkably high operating temperatures unlike many foam products.

End Grain Balsa, a highly processed ultra light wood product, imparts impressive strength and stiffness to the sandwich panel. The end grain configuration of balsa provides high resistance to crushing, and is very difficult to tear apart. End grain balsa cored panels also have the ability to handle excessive dynamic loads with high resistance to fatigue.

  • Selects - Baltek's well known grade of Rigid Sheet and Contourkore end grain balsa products. Selects grade end grain balsa with attributes of high stiffness and strength have been utilized effectively by the composites industry for almost 50 years, and offers a cost-effective approach to the benefits of sandwich construction.

Until recently, end grain balsa was excluded from some weight sensitive applications, as there were lower density foam cores available. Now, through controlled growing and careful selection, SuperLite balsa is competitive in weight, as well as offering superior performance in stiffness and strength, particularly where local crushing or bruising is a concern.

  • SuperLite premium end grain balsa allows structural weight optimization through a wide 'closely graded' density range of 5 lb/ft3 up to 16 lb/ft3 in 1-lb/ft3 increments. Each SuperLite grade has a lower density variation, producing highly consistent mechanical properties. SuperLite outperforms all conventional core materials, with the exception of aluminum honeycomb, in stiffness and strength for weight. The product of 25 years of research, genetically selected seeds are plantation grown in ideal conditions producing balsa trees with much improved consistency. Selected trees are processed in a dedicated ISO 9000-certified plant where the balsa is kiln dried, closely sorted for density and then assembled into blocks. Sheets of SuperLite are precision cut at Baltek's Northvale, New Jersey plant and further processed into various configurations.

End grain balsa core materials excel in the areas of: · Stiffness and strength for weight. · High compressive and flat wise tensile strength. · Cyclic load resistance and fatigue resistance. · Operating temperature range. · Fire resistance. · Thermal insulation. · Acoustic insulation.

  • DuraKore - specialty strip planking material for one off and prototype construction. DuraKore provides the properties of an end grain balsa core material without the need of a mold or a solid plug. Developed for custom boat construction, DuraKore will form a compound shape over or into a set of temporary transverse frames in the same way as the popular cedar strip plank building method. The frame shapes can be CNC cut to close tolerances and set up accurately using various alignment methods. DuraKore planks are made from sandwiching rigid sheets end grain balsa between two layers of 1/16 inch (1.5mm) hardwood veneer using marine grade glue. The sheets are then cut into 1ft wide planks or narrow strips, which are 8ft long. The 1ft wide planks can be scarf joined at each end to make up the length required. DuraKore strips have finger joints cut at each end to allow them to be easily assembled to the required length and are edge glued together, with a low-density gap filling epoxy adhesive, while being formed into shape over the temporary frames. They are held in place with removable fasteners while the adhesive cures. With planking complete the fasteners are removed and the surface is prepared for the application of structural fiber reinforcement. After the reinforcement layer has cured the structure is removed from the temporary framework and turned over into a receiving jig. The exposed surface is now prepared and fiber reinforcement is once again applied to the planking to complete a very effective sandwich structure. Many successful boats have been built with DuraKore, from performance racing and cruising boats to commercial fishing boats. DuraKore can also be effectively used to build a working prototype/plug in the development of new production models. DuraKore Planks fill in flat areas and can also form lightweight easy to install hull bottom stringer sections.

Structural Foams - are classified here as load carrying closed-cell plastic foam sheets that are non-friable (will not readily crumble when stressed). Many polyurethane foams supplied to the building industry for insulation purposes are friable. Structural foam sheets available include

  • AirLite - tough, high stiffness cross-linked PVC foam core material with additional density control processing.
  • AirLite/Herex® - tough, high stiffness cross-linked PVC foam core material in plain sheet form with no glue lines.
  • AirLite/Herex® ET – tough, cross linked PVC foam core material with elevated temperature resistance for use with low-temperature pre-pregs and post-cured parts.
  • Airex® R63 – very tough, resilient, and thermoformable linear PVC foam core material with exceptional impact (slamming) behavior and a non-brittle failure mode.
  • Airex® R82 - fire resistant, radar transparent, PEI thermoplastic foam core material with extreme cryogenic and elevated temperature serviceability.
  • Kapex® C51 -light weight, resilient, urethane co-polymer foam core material with short-time processing characteristics for high volume composite part production.
  • RibKore - semi flexible 'hat' sections used for local panel stiffening and bulkhead pads.

Bulker Mats - formable mats used to bulk fiberglass laminates, to reduce print through, overall weight, resin consumption, and VOC's.

  • SORIC® a new product specially designed for use in closed molding (resin infusion) processes. SORIC is both a resin transfer medium and a core material. SORIC® is an exclusive material specially developed for closed molding processes. It can be used as both an interlaminar infusion media and a core material. Brand new, SORIC® is the outcome of a 10-year development process, manufactured in a special process that creates a honeycomb pattern on the carrier sheet. This pattern allows rapid infusion of resin with an even flow front. The material is pressure stable with less than 10% thickness loss at full vacuum or 1 atm positive pressure. SORIC® will absorb significantly less resin than other infusion media materials and can result in an overall weight saving of up to 35% compared to all glass laminates. It is also conformable to complex shapes. It can be used in areas where the kerfs of solid cut and scrimmed core materials would open up and fill with large amounts of resin when infused. SORIC is compatible with all types of resins and can be used in conjunction with other solid core materials. It is compatible with all kinds of manufacturing processes including, Vacuum infusion, RTM, press molding, pre-pregs, filament winding and pultrusion. SORIC is not meant for use as a print-blocker in hand lay-up applications.

  • COREMAT® a random oriented, non-continuous polyester non-woven fabric and microspheres for greater conformability. Coremat® is a microsphere filled, random laid, chopped fiber polyester fabric with excellent conformability, which is used as a laminate bulking and print-control mat. Laminate thickness can be quickly increased with reduced resin usage (an average of 20%) resulting in overall weight savings of 18 to 30% compared with an all-glass lay up. Gel coat appearance is enhanced through the print blocking abilities of Coremat®, which also provides high impact damage tolerance with twice the insulation value of all-glass laminates. Labor saving with faster laminate thickness building and reduced VOC emissions are also realized with Coremat®. Coremat can be used where other core materials must be deleted to segregate from fasteners, cut-outs and through-hole fittings. It will provide a high degree of screw holding capability.

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