OTHER HAND LAYUP TECHNIQUES IN FRP

1.      VACUUM BAG MOULDING:

a.       It is the simplest method of pressurizing the lay-up and always result in a higher quality hand lay-up laminate than that made by contact moulding.

b.      A form-fitting bag is used on the outer surface of the part. The bag material must be heat resistant and should not affect or be affected by the resin.

c.       Film material suitable for bag manufacturing include Cellophane, PP, Nylon, and Fluorocarbons. Neoprene, Silicone, Butyl rubbers are also used.

d.      The bag is tailored to the part to minimize the wrinkles.

e.       Vacuum is drawn to pressurize the lay-up up to atmospheric pressure. Hence higher reinforcement loading is obtained in the finished part with higher density and increased physical properties.

f.       A better surface is obtained on the side away from the mould.

g.      Heat curing is more readily done because the resin content is lower and the pressure inhibits the flow of resin.

h.      A bleeder (breather) sheet is incorporated in the lay-up so as to rub out the part and eliminate air bubbles and excess resin.

i.        A vacuum pump; associated resin traps to prevent pump damage; special bags; breather sheet and vacuum lines are the equipment required, in the process, in addition to that required for contact moulding.

2.      PRESSURE BAG MOULDING:

a.       Uses a tailored rubber bag as the contact and vacuum moulding.

b.      Tooling is considerably stronger and is made to resist pressures from 5-50 psi or higher.

c.       Parts are considerably more dense and contains higher reinforcement content.

d.      The process is mainly applicable to female moulds, because bags used on male moulds tend to pucker and developed folds.

e.       The technique is combinely used with vacuum so as to remove most of the entrapped air.

3.      AUTOCLAVE MOULDING:

It is very similar to the pressure bag moulding.

The major difference and advantage of the process are:

a.       Cure is carried out in the autoclave hence the tooling required is not very pressure resistant. Although pressures as high as 100 psi can be used.

b.      A simple Kirksite or Aluminum tool is ideal because it is only in compression.

c.       Parts are dense and exhibits excellent physical properties.

The major disadvantages of the process are: 

a.       Cost of installing an autoclave.

b.      Limitations imposed by the size of the autoclave on part sizes.

Improvement brought about by the additional pressure do not undo the poor resin distribution or bad placement of the fibrous reinforcement etc.