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A
few basic rules can make building a mold into a science. One
of the most important rules concerns a minimum of documentation
and regimentation. Documenting all of the materials including
dates, batch numbers, quantities of materials used and temperatures
can save many hours of guesswork when a mold runs well or
poorly in production. Regimenting
yourself to weigh chemicals accurately and consistently will
give you a good point of reference to troubleshoot any problems
that might occur with a particular mold.
When
a problem occurs, change one item at a time until you find
a solution. For example, if cure is a problem, change the
catalyst. If the problem still exists, go back to the original
catalyst and change the resin. If the problem goes away, it
had to be the resin. If you make several changes at the same
time and the problem disappears, you will not be able to determine
the cause.
Equipment
plays a leading role in producing a good mold, therefore,
keep all equipment - both spray and manual tools - in clean
working order and regiment yourself to accept nothing less.
STEPS
IN BUILDING A MOLD
There
are 6 major steps involved in building a mold. Each individual
segment should be documented and kept on file for future reference.
This information can be compiled and placed on one simplified
document. (See "Mold Birth Certificate").
These
steps are:
- Material
selection and Q.C.
- Equipment
- Gel
Coat Application
- Lamination
- Bracing/Bridging
- Documentation
Material
selection, quality control and application are the most crucial
steps when building a mold. Of course, the gel coat should
be manufactured as a tooling product.
General
characteristics of a tooling gel coat:
1.
Has a slow gel time (20-30 minutes) and a fast gel to peak
(20-30 minutes). The times are film-cure times. Add these
together and multiply times 3 for the lamination time of 120-180
minutes.
2.
Creates a peak temperature of no less than 360° F and
no more than 450° F. These temperature ranges should create
a cure cycle that will generally assure a harder surface.
3.
Releases air in 10-15 minutes at 20 mills wet in order to
assure a porosity-free layer of coating after cure.
4.
A Hegmen grind of 6.0-7.0 is a desirable reading. This means
that the largest particle sizes found within the material
itself would be 1-1/2 mill in size.
5.
One of the final steps prior to applying the tooling gel coat
is to spray a test panel with the same catalyst levels and
mils that you will apply on the master. Check the panel for
air release (porosity) by sanding the test panel. Also check
for cure, spraying and any other visual defects, etc. Porosity
is small entrapments of air. When the coating enters the gelation
stage, prior to the air completely exiting the coating, you
will see small pits on the surface or directly below the surface
as you sand. The most common causes of porosity are too fast
of a gelation cycle (lower catalyst levels to allow more air
release time) and dry spraying the material during application
of each layer (apply each layer wet).
Pour
a small sample of this mixture into a metal can lid. The gel coat
can be removed from the lid cast after 2 hours. A barcol of
15-20 should be established at this time. After 4-4.5 hours,
a barcol of 30-35 suggests that a hard and therefore high-gloss
finish will be likely. Barcol hardness is tested by an impresser
and by measuring the resistance to impression. gel coats will
read from 40-45+. Glass laminates will have a hardness of
60+.
Having
systematically selected your tooling gel coat and authenticated
the properties by our Quality Control methods, you are ready
to organize the gel coat booth and apply the tooling gel coat.
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