Composite materials Hexion
Hot topic
Evolving fire
performance requirements
can be met through the
use of phenolic resins
I n a continuing drive to improve passenger train safety,
fire specifications are getting increasingly stringent.
Meanwhile, the rail industry is becoming more global,
with OEMs operating in multiple regions either through expansion
or strategic partnerships. Hexion reports that European norms are
becoming the de-facto fire performance standards as they are
among the strictest, and using them as a guide allows OEMs to
harmonize processes across their production locations and meet
standardised performance specifications.
Unsaturated polyesters are often used in fibre-reinforced
composites for mass transit and marine applications. “They
generally require high levels of flame-retardant additives as well
as an intumescent gel coat that acts as a char barrier to protect
the underlying polyester structure,” says Ramesh Pisipati, global
business development director at Hexion. “Flame performance
can be dependent on the integrity of this gel coat.”
process to get the same part-to-part additive distribution, for
uniform fire performance. “However, the high filler loading required
to achieve target fire performance can present difficulties in resin
transfer moulding and vacuum infusion processes,” he says.
“Fire resistance may also be impacted by surface finishes.”
An alternative
Hexion says phenolic resins are finding increasing use in fibrereinforced
composites as an alternative to unsaturated polyesters;
residual monomer content.
“Being intrinsically fire-resistant,
phenolic resins offer a better safety
margin without the need for flameretardant
additives or gel coats,”
says Pisipati. “This allows them to
be used for even fine weave cloths
for thin parts. In addition, the
back face of a component made
with phenolics has the same fire
resistance as the front face. In
the past, phenolic parts required
additional surface preparation –
Railway Interiors International ANNUAL SHOWCASE 2019 74
HL3 applications
The company reports that phenolics have been used
The use of prepregs can also eliminate the need to
the company attributes this to their fire, smoke and toxicity
(FST) properties, ease of processing and low
filling in pin holes and then painting.”
The company recently introduced
a phenolic gel coat that it says decreases
post-moulding surface preparation, saving approximately 30%
of production time. “Post-curing of phenolic parts is essential
to maximize physical properties and achieve the desired
dimensional stability,” says Pisipati.
predominantly in HL3 applications and have many
years of proven fire performance at competitive cost.
“In addition, they provide lightweighting benefits versus
highly filled polyesters and aluminium,” says Pisipati.
work with liquid raw materials. In this process, a fabric
impregnated with resin and a catalyst is placed in a
heated mould and formed/cured in place to produce the
part. “While this has been widely used for epoxy systems,
phenolic prepregs are becoming more popular as a means to
Pisipati adds that it is also imperative to manage the fabrication
LEFT: A door post cover for
a Hitachi Class 800 train
ABOVE: A battery box for a Chevy
Volt, hot-press moulded by Hexion
using a phenolic SMC formulation
provided by FTI Group
BELOW: A seatback, hot-press
moulded using a phenolic prepreg
supplied by FTI Group
RIGHT: A wash table wall
manufactured by Qantos, using
an RTM process, for Thameslink’s
Siemens Desiro