Finishes are put on glass fabrics to allow a strong bond between the
resin and the glass. If you take a sheet of glass and put resin on it,
let it cure then try to peel it off it will easily come off, or chip
off. Finishes like Volan or Silane act as intermediaries between the
resin and the glass. Volan has been around a lot longer than the Silanes
but I think is still one of the best finishes. Volan is generally the
softest finish with the exception of some Silanes. Volan is a chrome
based finish that complexes with the silicon dioxide in the glass and
leaves one group to bond to the resin. Silane is a molecule that, like
carbon, has four groups (bonds) with three of them bonding to the
silicon dioxide in the glass leaving one group to bond to the resin.
Some of the reasons for using Silanes instead of Volan are 1 - doesn't
leave a green tint like Volan which is preferable for surf boards. 2 -
forms a little stronger bond and generally considered more moisture
resistant. 3 - better for the environment.
When cloth is woven it has an oily starch type material on it to make
the glass yarn slide a little easier to prevent breakage. After weaving
is complete the cloth is heat cleaned to remove any of this material
then the finish is added. There's a lot to know about Finishes and you
want to be sure you're getting cloth that is proper for the resin and
application you're doing.
The thread count and weave of the fabric can make a lot of difference in
the the handling of the cloth as well. Some weaves are tighter than
others and are not suitable for complex curves. The satin weaves will
take complex curves better but are a little tougher getting the bubbles
out. Satin weaves are also effected by the type of finish. This is
probably because the yarn is closer together and allows cross bonding of
the finish more than in plain weaves. For example, there's a tremendous
difference in the way a satin weave like 7781 will be if it's finish in
Volan or in a Silane. Some Silanes are pretty good while some can be
pretty stiff and good for flat panels only. We sell the stiffer material
for a good bit less than the softer material. Unidirectional fabrics are
for composites where you need the strength in one direction like in a
wing. Or, you need it to conform in one direction more as would be the
case for composites tubes. Some of the unidirectional fiberglass styles
include 1557, 1543, 3743, 7715, 7721 and 2515.
Silane - is a type
of finish on fiberglass cloth based on silicone. It has four bonds like
carbon. Three of the bonds are methoxy groups. When they are reacted
with silicone dioxide, in the glass of the glass fibers, they give up an
alcohol group forming silicone-oxygen-silicone bonds. The remaining bond
of the original four is an organic compound that is compatible with a
variety of different types of epoxy, polyester, phenolic, and other
thermo-set resins. There are many different finish numbers for basically
similar types of Silanes. Most Silanes are suitable for epoxy resins.
There are exceptions, for example CS-316 is a Silane that is for
Volan - is the chrome based finish that's been around for years.
It is good for any resin. Cloth finished in Volan is generally softer
than cloth finished in Silanes. Fiberglass cloth that's finished in
Volan may be written as "Volan" on the box or as 504 (BGF), F3, F16, F43
and other numbers if made by Hexcel. The differences may be %
concentration of the chrome itself.
Greige - This is in the loom state and has no finish per se
except that it still has the oily PVA on it that was on the yarn so the
yarn would slip preventing fiber breakage during weaving. Many rubber
coaters use fiberglass in the greige for their coating applications.
Other info on Fiberglass
You can get some idea by the count - threads per inch. Warp is length
wise down the cloth and fill is side to side. If you laid a ruler on the
cloth and counted the threads in one inch that's the number you'd get.
The lighter weight fabrics like 104,
107, 1080, 2112,
2113, 2313 are the ones
that have been used in model planes for years, with 106 being the most
common to use with epoxy over balsa skins. For molding R/C fuselages
softer materials like 1522 3.7 oz, 7533 6 oz type materials are easier
to use than tighter weaves.
A lot of the fabrics were first used primarily in the circuit board
industry and because of this more is available at cheaper prices. Some
materials that are easier to laminate are more expensive because of the
higher demand and lower production.
S-2 glass - S glass (primarily S-2 glass) is generally considered to be
about 20% stronger than e-glass. S-Glass is 64-66% Silicone Dioxide
compare to E-Glass at 52-56%. S-Glass has no Calcium Oxide where E-glass
has 16-25%. S-Glass has more Aluminum Oxide at 24-26% where E-Glass is
12-16%. S-Glass has no Boron where E-glass is 5-10%. S-Glass does have
9-11% Magnesium Oxide where E-glass very little. The price of S-Glass is
higher than E-Glass. The reason for this that was given to me some years
back is that S-Glass is processed at a higher temperature than E-glass.
It burns through the oven liners faster and this replacement cost is the
reason for the higher price. Most of the materials on this site are
E-glass with the exception of styles like 6533, 6781, and
17645 which are S-2 glass and are noted accordingly.
Some methods for applying resins.
Squeegee - When I do big layups like long 4' wide or wider panels
I work fast pouring the resin down the center and to to the sides. I
make big long strokes from the center out and longways up and down the
panel. I move my whole body and not so much my arm independently. Once I
get the cloth wet out out or at least exposed to the resin I then go back
and work the resin in the cloth harder getting the ideal fiber to resin
ratio desired. Using more than one batch of resin I try to get any area
completely wet out before mixing a new batch.
In other words I don't leave some of the cloth coated on the top with
resin not soaking through. In hot weather
the resin could start gelling on the top and make it harder for the
fresh batch to soak in. After completely wetting out an area using the
squeegie you can do a test by slowly pulling the squeegie and if you
still have a wave of resin you need to squeegie a little more.
Brush - Use a brush in certain areas only. Don't use a brush for
big layups. I normally only use a brush when I'm stippling. I'm sure
there's many experts out there that can describe stippling better than I
can but I'm going to do my best. Stippling is a combination of a little
bit of brushing to deliver the resin to the right place then jabbing
with the bristles to force the resin and cloth in where it's supposed to
go followed with some brushing to
smooth everything out. This is done in corners, tight contours, taping,
but never on flat layups.
Rollers - I personally don't use rollers a whole lot myself and
always thought they were more for chopped strand mat. Since I don't use
chopped strand mat in anything I don't use rollers. I have used rollers
some and they can be useful just not that much for the things I've done.
Resin Infusion - This is where you seal off dry reinforcement
using peel ply, an absorbent layer and an outer sealing layer and apply
a vacuum which sucks in catalyzed resin from the opposite end of the
setup. The idea is to get a vacuum bagged type layup with less work. I
have done very little resin infusion and am not the expert in this area.
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