Polytek®'s highly regarded Poly 74-
and 75-Series Liquid Poly Urethane Mold Rubbers have been considered the
products of choice for many years by concrete precasters and GFRC manufacturers.
These products have offered a wide range of hardness (A-30 to A-80), easy
mix ratios, and the toughness and durability expected by this demanding
group of users.
New Polytek® Rubbers Stretch to the Limit
A relatively recent addition to the Poly 74-Series
product line was Poly 74-29—a soft, stretchy, 1:1-mix system with great
physical properties. Stretchy is the operative word! Poly 74-29 has an
elongation of >2300%, meaning it can be stretched 23 times its original
length (in a thin, narrow test bar) before it breaks. This is remarkable,
given that most other products in this hardness range offer elongation
two to three times less. For a rubber mold, higher elongation is better
since it means the mold can be stretched farther to remove a casting before
damage, such as tearing, occurs. Working from the assumption that higher
elongation is desirable, Polytek® set out to create firmer rubbers with
extra stretchiness. The result: new Poly 74-44 and new Poly 75-70.
New Poly 74-44:
Midrange Hardness, Superb Elongation
Poly 74-44 is a Shore A-45, 2A:1B mix ratio with
physical properties superior to other mold rubbers in its class. Amazingly,
Poly 74-44 has virtually the same elongation as its softer counterpart,
Poly 74-29. Other notable attributes of this product are its high tear
strength and high tensile strength for a rubber of this hardness.
Many customers who enjoy the "stretchiness" of
softer rubbers like 74-29 need a higher-hardness, higher abrasion-resistant,
higher-tear-strength rubber, especially for mid- to high-volume concrete
casting. A Shore A-45 rubber permits easier demolding of complex castings
than harder products, and the enormous elongation of Poly 74-44 will make
it even less susceptible to tearing. Poly 74-44 is expected to be useful
to concrete precasters and GFRC part manufacturers, as well as to plaster
casters. As with other Poly 74-Series systems, Poly 74-44 can be thickened
with Cab-O-Sil® when used as a brush-on rubber. For most molding applications
in the concrete industry, Poly 74-44 will more likely be poured, in which
case the low 3,500-cps. mixed viscosity and 20-minute working time will
be appreciated.
New Poly 75-70:
Higher Hardness and Tear Strength
Poly 75-70 is an even firmer version of Poly
74-44 with a final Shore A hardness of ~70. This system has a 1A:1B-mix
ratio, a low 3,000-cps. initial mixed viscosity, a 40-minute working time,
and very impressive physicals for tear, tensile, and elongation relative
to similar hardness mold rubbers.
Poly 75-70 is useful for high-volume concrete
casting or where additional elongation is desired in a firm rubber to
demold tight parts. Since 75-70 has a long pour time, it is ideal for
those customers creating large molds in a single pour. Like other 74 and
75-Series rubbers, Part C softener can be added to either Poly 74-44 or
Poly 75-70 to create intermediate hardness molds.
For more information on these new, high-performance
products and how they may be used to improve your concrete casting application,
please contact Polytek®'s technical support department at (610) 559-8620
or sales@polytek.com . |
