General information regarding sandwich structure with pvc foam core

Realizzazione imbarcazione con sistema di infusione sottovuoto WorKing27.
Fonte originale: http://www.youtube.com/watch?v=fQiza2SmxYw

The sandwich panel is composed of two resistant external layers called "skins" and a connective central element called "core", a light and incompressible material. The sandwich construction is a lightweight and extremely rigid structure.

Consequently, when this structure is subjected to bending stress, one of the skins is stressed to traction and the other to compression. The skins oppose a high resistance to these stresses, acting as inextensible and incompressible materials. As the skins are spaced apart from pvc foam core, an incompressible material, we obtain a structure with a rigidity and a lightness higher than the traditional structures (e.g. laminate).

The structural sandwich is also defined by its performance in relation with the shear strength and the shear modulus, stiffness combined with the capacity of flexion, the non-deformation ...

The main features of the sandwich structure are:

  • the resistance, given by the skins
  • the lightness, given by the core
  • the very low water absorption, almost equal to 0, given by the core
  • the insulating power, given by the core 
  • the good fire resistance, given by the core 

This short list sets out that the components characteristics interact one with another in the construction of the composite material and, in order to obtain a sandwich panel of excellent quality, the strength and modulus of the skins, the thickness and the nature of the core, capacities and loads must be carefully balanced.

At last, the above list shows that the properties of the structural sandwich panel are closely linked to the quality of the core.

For this reason, for producing high quality sandwich structures and consequently high performance finished products, YDRA Marine recommends to use its PVC foam core panels characterized by cross-linked closed-cell rigid/semi-rigid Pvc foam, because specific for the sectors of marine, aeronautic, automotive, wind energy, sport and many other industrial applications...

For making the sandwich structure, the pvc foam core is subjected to the process of infusion, with lamination or molding with the system One Off, or to the process of thermoforming.

The infusion lamination or Vacuum infusion process:
The lamination by infusion uses the technology of vacuum pressure to drive the resin within the laminate. The materials are placed dry in the mold, closed by a thermoplastic bag, with high deformability and hermetically fixed to the flanges, inside which the vacuum is applied. This removes the entrapped air between the layers and the resin flows smoothly, sucked between the fibers by means of the network charge.

The manual lamination:
The method of manual lamination consists of the use of a mold, previously processed with gelcoat, in which are laid layers of composite fabrics impregnated with liquid epoxy resins and vinyl esters. The structure is then reinforced with PVC foam core and the subsequent covering with fabrics, the so-called sandwich.

The thermoforming:
Thermoforming is a process of shaping flat PVC foam core sheet which includes 2 stages: softening the sheet by heating (within the temperature limit allowed by the core material), followed by forming it in the mold cavity.

The advantages of thermoforming process are:

  • to create complex structure like 3 dimensional shape
  •  to obtain lighter sandwich structure thanks to the reduced use of adhesive and resins.