Hand layup is an open contact
molding in one-sided molds are the lowest-cost
and most common processes for making fiberglass
composite products and is the most common
method of producing composites parts in the
U.S. aircraft industry.
In a typical open mold application, the mold
is first waxed and sprayed with gel coat.
It then may be cured in a heated oven at about
120º F. In the spray-up process, after
the gel coat cures, catalyzed resin (usually
polyester or vinyl ester at 500 cps to 1000
cps viscosity) is sprayed into the mold, along
with chopped fiberglass. A chopper gun chops
roving (usually E-glass) directly into the
resin spray, so that all materials are simultaneously
applied to the mold. Using low-styrene and
suppressed-styrene resins, fillers and high-volume/low-pressure
spray guns or pressure-fed resin roller applicators
helps reduce emissions of volatile organic
compounds.
In hand lay-up processing, fiberglass (typically
E-glass) continuous strand mat and/or other
fabrics such as woven roving are manually
placed in the mold. Each ply is sprayed with
Catalyzed resin (1000 to 1500 cps) and the
resin is worked into the fiber with brushes
and rollers to wet-out and compact the laminate.
Fiber content can be increased by up to 50
percent by curing the part in a vacuum bag,
using 2 psi to 14 psi vacuum pressure and
cure temperatures under 350º F. Vacuum-assisted
resin transfer molding (VARTM) and infusion
molding systems are gaining favor with open-mold
processors wanting to cut volatile organic
compounds emissions. The applied vacuum compacts
the preform and helps the resin to penetrate
and wet-out the fiber preform. Fiber content
up to 70 percent has been reported.
Phenolic
Liquid Resin Hand Lay-Up Techniques
Those fabricators making the transition
from conventional ester and epoxy resins to phenolics
who are already experienced in hand lay-up of
structural reinforced plastics.
Materials
Options:
Resins: Any, e.g. epoxy, polyester, vinylester,
phenolic.
Fibers: Any. woven or stitched into a fabric
form.
Cores: Any
Typical
Applications:
most of aircraft composite parts, boat
hulls and decks, RV components, truck
cabs and fenders, wind-turbine blades
etc.
Spray layup
Spray-up
is an open-molding composites fabrication
process where resin and reinforcements
are sprayed onto a mold. The resin and
glass may be applied separately or simultaneously
"chopped" in a combined stream
from a chopper gun. Workers roll out the
spray-up to compact the laminate. Wood,
foam or other core material may then be
added, and a secondary spray-up layer
imbeds the core between the laminates
(sandwich construction). The part is then
cured, cooled and removed from the reusable
mold.
Spray layup
has very little application in aerospace.
This technology produces low specific
strength structures which usually do not
belong on the end product. Spray layup
is being used to join back-up structures
to composite face sheets on composite
tools. Spray layup is also in limited
use for obtaining fiberglass splash from
transfer tools.
