Monday, February 26, 2018

Sandwich structure, FRM process of FRP

Panels composed of a light weight core material like honey comb, foamed plastic etc. to which relatively thin, dense, high strength faces or skins are adhered to produce material with lower and lower density and higher and higher stiffness.
Honey comb:
Manufactured product consisting of sheet metal or a resin impregnated sheet material (paper, fibrous glass etc.) which has been formed into hexagonal shaped cells.
a.       It is a method of preparing a sandwich structure.
b.      An open cell urethane foam is impregnated with a controlled amount of epoxy or other structural resins.
c.       Dry glass fabric or mat facing sheets are placed on either side of the foam and the assembly is placed in a mould.
d.      As the mould closes the dry glass is pressed by the foam against the mould surface and the air from the foam is escaped through the dry glass.
e.       When the mould is closed, the resin escapes from the foam and saturates the facing sheets.
f.       After curing, the laminate with considerably low density (than FRP) results.
g.      Advantages: The physical properties are superior to SMC parts and lower pressures than SMC parts is used.
h.      Capital investment for large presses is less, hence saving is considerable.
i.        Process cannot be used for parts with sharp curves, ribs or bosses.
j.        Fabrication of automobile body parts is made by FRM
Sandwich structures are also made by using an integrally woven 3-dimensional structure, with the facing attached to the core during the weaving operation.
Additional compression and bending strength can be obtained by placing foam or PP inserts between the webs. The woven structure can ne impregnated before or after the inserts are in place. However, curing is done after the inserts are placed. The foam inserts are usually not removed to get additional strength while PP inserts are removed to minimize the weight with the hollow core.

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