JEC COMPOSITES MAGAZINE - Issue #108 - October 2016 - 29

The first polyurethane wind rotor blade made in Asia

Fig. 3: In collaboration with
HÜBERS and Chongqing Polycomp
International Corp., Covestro
succeeded in manufacturing the
first megawatt-scale PU rotor
blade in Asia, which has a length of
37.5 metres (Source: Covestro)

Larger rotor blades
with optimized design
The new PU resins offer good prerequisites for supporting the trend towards
larger rotor blades. For stability reasons, larger blades will inevitably have
thicker component sections. These
should be easy to achieve with PU infusion resins thanks to their good flow
properties, high-level mechanical properties and low exothermic behaviour
during cure. The PU resins also display
high productivity, which has a favourable impact on manufacturing costs,
particularly in view of the length of the
rotor blades.

Windnovation, a blade design company, expressed interest in optimizing the
blade design by fully utilizing the advantages of polyurethanes. The company
sees promising opportunities for rotor
blades made of polyurethane. It is looking forward to developing even more
sophisticated wind blades together
with Covestro.
PU system technology
with high output rate
HÜBERS engineered a manufacturing
system for PU vacuum infusion that, on
account of the size of the rotor blades,
is optimized for output rate and enables
uniform mould filling. The PU resins
are thoroughly degassed and pumped
into the mould without voids by a precision metering and mixing system. Fill
pressure and rate can be precisely controlled, meaning that the fill process
can be faster in the beginning to efficiently infuse the glass fibre mats, and
then slowed towards the end. The storage, conveying, vacuum infusion and
reaction of the PU resin take place in a
completely closed process.
Outlook
Cooperating with leading blade
manufacturers, glass fibre suppliers
and machinery companies, Covestro is
developing PU resins for wind blades
along the value chain. After successfully
fabricating a complete rotor blade in
Shanghai, the company is now planning to produce other prototypes with
partners to further optimize the manu-

facturing process and conduct tests on
the complete parts. Partners benefit
from the variety of facilities Covestro
operates to support customers in technology and applications development.
These facilities include, for instance,
laboratories for customer-specific
chemical development work and technical service centres for developing
processes on an industrial scale.
Furthermore, together with Saertex,
Covestro began working on an alternative to the balsa wood used in rotor blades as a lightweight core material. Saertex has since developed an
alternative - partly based on PU -
called SAERfoam™ and tested it with
Covestro. The structural core material is made from an ultra-lightweight
foam combined with 3D glass fibre
reinforcements.
Looking beyond rotor blades, Covestro's
development teams are also interested
in other components for wind turbines.
For example, the company already offers PU solutions for the pultrusion of
sections for peripheral parts, and raw
materials for coating and bonding components. Thanks to their good adhesive
properties, the PU resins show good
compatibility with known gelcoats, adhesives, repair resins, flow media, peel
plies and with different types of glass
and carbon fibres.

No108 October 2016

More information:
www.covestro.com

/ jec composites magazine

Feature Wind energy

Faster infusion and curing
The higher productivity of PU resins
stems from several factors. For instance,
the mould can be filled significantly
faster. In the case of the spar cap, infusion times ranged between only 45 and
60 minutes thanks to the much better
flow properties of the PU infusion systems. Their initial viscosity is only 50
to 100 mPas, compared to the industrial
systems commonly used that are more
in the region of 300 mPas.
The glass fibre mats are infused faster
with the PU casting resins, a noticeable improvement particularly in areas
with densely packed glass fibre mats.
Furthermore, the lower viscosity allows
longer flow paths. Shorter production
times also result from the fact that PU
resins are less reactive and therefore
harden more evenly, making the curing
process simpler and more efficient.

http://www.covestro.com

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #108 - October 2016