PROCEDURE POR MkLTPACRING GLASS
FIBRE REINFOflCED POLYESTEt S1I]EIP MODEL$.
DELFT SI4IFEUILDING LABonAToR;
REPORT No 68
Ir. J.J. van d.en BOL3OU.
A glass fibre reinforced polyester model is formed inside a female mould. This female mould, also made of reinforced polyester is moulded to a master model.
This modal is made of paraffin-wax or balsa wood, in
the conventional way, and corresponds with the lines. drawing. However there are small differences witha nor-mally used model, for
instance,
themodel is made without
sheer. The sheerline is sc'atohed in the surface aM ap-pears as a Line line in the female mould and the final
reinforced, plastic model. Also the attachment of the
ap-pendages should be considered beforehand.It is essential that the surface of the model is
perfectly smooth, for every imperfection would become
apparent in the f inisbed product. 8peclal attention should
be paid. to the small sbririltholes which
often are present in the parafíin-.wax surface. In. most eases a smallperoen-tage of polyethyleen of low molecular weight mixed with the paraffin is a good remedy (see appendix for used
materials and recipes).. For several operations it is
preferable that the model can be turned. In that case a wooden model, which can be bolted or screwed on a
horizon-tal board is used.
A wooden model should be given several coats of var-nish and the surface should be waxed before applying the release agent.
The female mould is made in two halves. The model is placed upside down on
a flat
horizontal board and another-2-board is placed vertica].ly along the contours of keel,
steii
azd stern, in such a way, that one side of the board
coincides with the plane of symmetry of the model (Lig.1)
The board should be supported effectively.
The free eide of the model is coated with a release
agent that is applied with a brush and which forms a thin
impermeable film. (see appendix). This film should be
allowed todry for at least one hour.
The first coat is the gelooat, a layer of resin con..
taming no reinforcing Libree. The gelcoat should be brush..
ed on liberaly for if this film is too thin the surface
will show a "weavy" appearance due to shrinkage of the
subseQuent layers.
The second coat conaist
of a sheet of woven glass
fibre cloth, thoroughly wetted with resin. Care is taken
that
O air is inclosed. This coat should. not be applied
before the gelcoatis allowed to cure, although as a
general rule there is no objocion,on applying subaequent
layers before the resin has cuned. (see appendix for
formation about the used materials)4
The third coat consieta of a sheet of chopped atrand
mat and. resin.
For the flat sides of the mould a sandwich conetruot
ion is used. The core of the sandwich consista of a sheet
of hard lastc foam (polyvin4oblorid) 1 cm. thick. This
sheet is glued on with rean or pressed on the still wet
mat, and: covered with a fresh layer of chôpped strand mat.
After the first halve of the female mould. baa cured
the vertical board can be removed.
The second halve is made in the same way, but in this
case the vertical flange of the finished part forme the
boundary of the fresh laminate, instead of the vertical
board.
-ef ore the release agent is applied some small bolts
with cylindrical heads are inserted in the flange, their beads sticking out on the side of the second part of the mould to act as dowels (see fig. 3).'
When the two halves are finished, they should be stiffened by some frames made o! reinforced polyester
sheet (fig.
3 ).J
In general it is advisable to allow the moulding to mature for at least two weeks before removing the model.
By that time the resin should be fully polymerised and. stable.
After the maturing time the mould can be released. The construction of the model happens in essentially the same way (fig. 4 ) o although the choice of the etrengthe.. ning material will be different, according to the uses to
be made of the model.
When the room inside the model is of primary
import-ance a sandwichoonstx'uotjon of p.v.c foam with two layers of woven cloth on each side, Is chosen, so framescan be
eliminated.
When a low model weight is the first consideration the model is made of two layera of cloth and inside frames on a spacing of approximately 40 cm. are built in.
Models which will be used for the measurements of longitudinal bending moments are constructed of two or three layers of a unidirectional woven cloth, in auch a way that the local stiffnes. is sufficient and the
longi-tudinal stiffness corresponds approximately wih that of
the ship (the criterium is theO period of the two-node,
vibration).
Resistance strain gagea are incorporated in the ekin between the layera.
Colours can be added in the gelcoat.
After the model is released from the
mould
the sheeris
out along the scratched line.
Deck or stringerplates
frames etc. are builtim
after the model is replaced in tbemould.
-4.-AU Xlat parts (decka, bulkheads,
ramea floors) ar
out from sheet which is available from several firnis. These
part e are
glued. in
the hull by means of a lining of glass
fibre rovine and. resin. A putty of chopped f±bres and resin
also can be used.
-5-APPENDIX
A.1 Polyester resin,
Cryatic 189 medium vtacoait. Manufactured. by Scott Bader & Co. Ltd.
WollastonWellinboroug1i-Northwnpt onshire
England.
This resin can be used at room temperature but preer-ably not below 200 C. A lower temperatura affects the
aetti.nE time and may reéult in an undercured product,
unless a high catalystand accelerator content ia
used..
The resin is mixed with a catalyst and a accelerator
which are supplied by the factory-. We howaver use the
following chemicals z
Catalyst Butanox,
(50% Methyl ethylketone peroxide in d.imethyl phtalate)
Made by
Xoury & v.d.
LaMe.
Deventer Netherlands,
Accelerator Cobal.tnaphtanate 6% Cobalt Made by Noury & v.d. Lande.
The accelerator should be mired
thoz'ouBh3.y with the
resin before the catalyst is added.
Table I ShOWS tim approximate setting time in minutes at 200 C. as a function of the accelerator-and catal
contents.
In practice the amounts of catalyst
ana accelerator axe
taken equal and range fron 0,5
to 1,0 cc. on 100 grana
of resin.
B. pelease aRent.
Qlyvinylalc oho1,
1,
25 gr. MOWiÓ1 N. 3018.
8upplied by
'a.bwarke Hoechst A.G.
Frankfurt'
(M)Germany
0,5 gr. Manoxol 0.T. (sodium&tootyl aulphoaucoinate),
wetting agent1
Made by:
Hardman & Holden Ltd.
Miles P].attixi, Manchester 10.
tigland,
60 gr.
naturateci alcohol 96%.
200 gr. distilled wate.
cc. Butanox
toi loo gr.
0oba1t
Resin
napt.
tor 100 gr.Resin
05
0,6
1,0
1,2
1,'4.0,25
135
90
40
28
22
18
lO0
'+420
12
8
2,00
25
18
92
is solved tu 3. and then 2. is added
4. is boated to 70°C. and also added
Nie result should be filtered.
O.
Pol7ethjleen used in the paraffin-wax mixture.
Polysthyleen AC - 6
35 %
Made by:
Allied. Chemical & Dye Corporation
£1.0 Rector etreet
Newyork. 6 N.Y.
U.s.A.
D.
Elastic foan
Draka Viriycel
HA - 040 - 01
Made by LV. Hollundache DraadE
en Kabelfabriek
Amsterdam - Netherlands.
E,
Glass fibre reinforoent.
All glass fibre used in models is "ailane" finished
Piniab. 136. Code numbers refer to Pibergias of Owens
Corning Corporation.
Other manufacturers may use different code numbers
or indications,
I
Chopped strand Mat.
Weight
1+ - 2 oz. per square fQot.
Mat of 1f oz, works more easilye
Cloths.
Square-wovefabrics, Weight about 10 oz. per
square yard. Thickness about 0,015",
Woven Roving,
is a coarse square woven fabric
of untwisted strands. It is sometimes used
beoauee of its groat strength in comparison
with normal cloths. Weight approximately 26
oz.
per square yard.
I. Unidirectional Íabrioa.
Code number 13,
5.
Rovinp.
Continuous stranda wound with rie twist.
Used 'or linings, putty etc.
The
Polyester flandbook" edited by Scott Bader'
& Co,
PUTTY VERTICAL BOARD PARAFFIN..WAX OR WOODEN MODEL HORIZONTAL BOARD SUPPOR T
r
/
-1
dA
FIG. ir
r 4 .' prfA
C EL C OATFIRST ANO SECOND LAYER
FIG. 2 FOAM CORE
FINALCOAT