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| Pourable
Polyurethane Mold Rubber |
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Fast
72-40 RTV Liquid Rubber
Features
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- Low
viscosity
- Pour
or brush-on
- Non-staining
- Color
mix indicator
- Economical
- Variable
hardness
- Long
work time
- Odor
free
- Rapid
cure
- Good
flow and bubble release
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Description
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Fast
72-40 Rubber consists of liquid Part A and Part B, which cures
at room temperature to a versatile mold rubber after mixing
in correct ratio. It may be poured or thickened and applied
by trowel or brush, to achieve high quality, flexible molds.
These molds are particularly useful for creating wax or plaster
casts. They are outstanding for casting resins and concrete
when combined with release agents or barrier coats such as
PVA. .
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Model
Preparation
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Fast
72-40 rubber may be subject to cure inhibition by particular
surface contaminants and may adhere to certain surfaces. Multiple
coats of paste wax or potters soap are superior sealers for
plaster. Fast 72-40 bonds powerfully to shellac-coated surfaces
so they should always be coated with a release agent. Ease 2300
Release Agent should be used to coat non-porous surfaces and
models sealed as indicated above. Plastics such as styrene and
coatings such as lacquer may be softened using Fast 72-40 and
have to be coated with a barrier such as PVA Solution |
Mixing
and Curing
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Stir
separate components prior to use. The mix ratio of ten parts
of A to one hundred parts of B by weight is imperative. An error
of 5% in the weight of either component can affect the physical
properties of the cured rubber and an error of 15% can result
in a soft, poorly cured compound. Before demolding, allow curing
for more than 8 hours at room temperature, 77°F ((25°C).). |
Flow
Control
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Cab-O-Sil
M-5 can be added for several viscosities in the mixed uncured
rubber. Part D is a liquid thickener that is also available
to thicken Fast 72-40. One part D added to 100 parts B results
in a light cream texture and two parts D results in a grease-like
texture. Part D must be stirred completely into Part B before
Part A is added. One additional part of A must be added for
each part of D that is used. Use of corrosive Part D entails
careful weighing and care. |
Using
the Mold
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A release
agent must be used when casting epoxy, urethane and polyester
resins. A barrier coat, like PVA-Solution (top coated with a
release agent), may be required with some resins. |
Softer
Molds
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To create
rubbers as soft as Shore A-6, a liquid softener, such as Part
C, can be added. Prior to combining with Part A, Part C should
be weighed and mixed completely with the correct amount of Fast
72-40 Part B. Each 20 parts of Part C combined with 100 parts
total A and B will reduce the hardness approximately 10 to 15
Shore A points. |
Storage
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Cured
molds eventually soften over time. Mixing components in the
correct mix ratios and storing molds in a dark, cool, dry area
contribute to long mold life. Fast 72-40 molds should not soften
significantly for 2-4 years with proper care. Molds should be
discarded before they become too soft to handle. Exposure to
sunlight, standing water or ground moisture will cause fast
corrosion of the rubber. Do not store molds outdoors. |
Physical Properties: |
|
Fast 72-40 |
Mix ratio, by weight |
10A to 100B |
Hardness, Shore A |
40 |
Pour time |
30 min. |
Color |
Ivory (brown A, white B) |
Viscosity, mixed |
4,000 cps. |
Cubic inches/pound |
20.0 |
Shrinkage during cure |
Nil |
Packaging: |
|
Containers |
Size |
Net lbs. |
Product |
Weight/lbs. |
A |
B |
A |
B |
Fast 72-40
Mix Ratio
1A to 10B |
9.9 |
1 pt. |
1 gal. |
0.9 |
9.0 |
49.5 |
1/2 gal. |
5 gal. |
4.5 |
45.0 |
495.0 |
5 gal. |
55 gal. |
45.0 |
450.0 |
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Ease 2300 Release Agent: 14 oz. can, case of 12 cans
Fast Part 72C Softener: 1 pt. (1.0 lb.), 1 gal. (9.0 lbs.), 5 gals. (45.0 lbs.)
Fast Part 72D Thickener: (Includes extra Part A)
1 pt. each A & D (2.0 lbs.), 1/2 gal.
each A-& D (9.0 lbs.), 5 gals. each A & D (90.0 lbs.)
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