Page 228 - Engineering Plastics Handbook

196 Engineering Plastics

Noryl EM7100: Good impact strength; easy processing; 209°F (98°C)
HDT at 264 psi (1.82 MPa)
Noryl EM7301F: 10% glass-reinforced; good polyurethane foam adhe-
sion; 252°F (122°C) HDT at 264 psi (1.82 MPa)
Noryl EM7304F: 15% glass-reinforced; enhanced polyurethane foam
adhesion; 254°F (123°C) HDT at 264 psi (1.82 MPa)
Noryl EM7430: 30% glass-reinforced; high modulus; excellent flow;
251°F (122°C) HDT at 264 psi (1.82 MPa)
Structural foam grades. These are specifically formulated as an efficient
and economical way to gain high strength and rigidity required for struc-
tural parts. Thermoplastic structural foam is a form of injection molding.
Structural foam parts have a foam core sandwiched between two dense
skins. The foam core is achieved by introducing an inert gas which acts
as a foaming agent for the molten resin. The gas is compressed in the barrel
of the molding machine. When the molten resin/gas mixture is injected into
the mold cavity as a short shot, the gas expands within the plasticized
material, helps to carry the resin throughout the mold cavity, and fills the
mold. Compressing the foam against the surfaces of the mold cavity cre-
ates the dense skin.
Structural foam is generally made in a low-pressure process where the
cavity is not completely filled with the initial injection of the mixture. This
low-pressure process features the ability to provide a large part molded
with an internal cellular structure and a tough external skin while enjoy-
ing the economics of reduced clamp tonnage.
In general, wall thickness for structural foam applications ranges from
about 0.150 to 0.500 in (3.81 to 12.7 mm) with an average thickness of 0.250
in (6.35 mm). Parts are referred to as having weight or density reduction.
This describes how much the part weight has been reduced when compared
to a solid injection-molded part. For example, a part having a 20% weight
reduction is produced by filling the mold cavity 80% full. The other 20%
of the mold cavity is filled by the expansion of the resin. Thick wall parts
achieve higher weight reductions than thin walls.
Structural foam parts have the combination of performance properties
and process features that deliver increased stiffness to weight ratio. Hence
they are suitable for metal replacement in some applications.
Modified PPE structural foam grades can maintain the strength
required for many structural parts. They are often used as an alternative
to metal. The combination of performance properties and process fea-
tures can deliver superior strength and rigidity per unit weight. Structural
foam grades offer enhanced heat insulation, improved electrical and
acoustical characteristics, excellent dimensional stability––including low
creep and water absorption, less tendency to observe sink marks on the