New Ideas, Methods and Materials for Improving Blade Repairs

#WindWebinar

New Ideas, Methods and Materials for Improving

Blade Repairs

#WindWebinar

q  This webinar will be available afterwards at www.windpowerengineering.com & email

q  Q&A at the end of the presentation q  Hashtag for this webinar: #WindWebinar

Before We Start

#WindWebinar

Paul Dvorak Moderator

Windpower Engineering & Development

Tony Gray Key Account Manager

-Wind Energy Sika Corp.

Lou Dorworth Direct Services

Division Manager Abaris Training Resources Inc.

New Ideas, Methods and Materials for Improving Blade Repairs

Meet your presenters…

Introduc)on •  Turbine blade damage requires the applica)on of

simple but func)onal repairs given the physical difficulty of the task

•  The most common opera)onal damage is from surface impact and rain/dust erosion

•  Other damage from bird strike, lightning strike, other

object impact, and/or the propaga)on of manufacturing anomalies

•  The repair methods and materials need to be simple but effec)ve in order to maintain the blade’s structural integrity and future opera)onal effec)veness

Types of Damage & Common Repairs

•  Erosion damage (without major fiber damage) –  Abrade, clean, fill & fair with suitable epoxy or polyurethane filler

•  Minor scratches or dings affec)ng surface ply –  Abrade, to remove paint around damage down to the laminate surface, fill scratch or ding with filler paste &

apply 1-‐layer of fine glass fabric with epoxy

•  Damage into or beyond outer ply of laminate –  Remove and replace damaged plies or apply a bonded doubler repair

•  Damage into sandwich core structure –  Remove & replace damaged core and structural plies in damaged skin or apply doubler repair

•  Damage through structure –  Remove damage through structure and repair from both sides (if accessible) using repair plies or doublers

•  Op)on: Repair from one side using “no backside access” techniques

Note: all repair types are “zone dependent” requiring aerodynamic/aeroelas)c considera)ons

Cri)cal Aerodynamic Areas Aerodynamic Loading of Wind Turbine Blades

Laminar Flow and Boundary Layer

Note the change in laminar flow as angle of aZack (blade pitch) changes in model at right

Blade Repair Zones

1

2

34

Repairs to turbine blades require considera)on of aerodynamic and aeroelas)c loads on the structure – repair design and approach

may be adjusted to meet zone requirements

Blade Repair Zones Zone 1. For both for aerodynamic and structural purposes; the blade leading must be maintained for the

laminar boundary layer. Zone 1 is from the 20% to 100% span length and to 25%-‐30% of the local chordline. Zone 1 will always require a flush repair.

Zone 2. For aeroelas)c purposes; do not add significant weight to this zone of the blade, so as to maintain

mass balance. Not a major structural region of the blade, however the repair needs to be an aeroelas;c semi-‐structural repair.

Zone 3. Primarily for aeroelas)c purposes; the repair does not necessarily need to be flush for airflow

aerodynamics, but it must not add significant weight behind the shear center. However, trailing edge repairs are typically flush for aeroelas;c requirements.

Zone 4. Not required to be aerodynamically smooth, but may need to be a semi-‐structural or structural

repair based on the severity of the damage and the proximity of the damage to the main load bearing region of Zone 4 (i.e. spar cap). Because of the large enclosed area of the blade in Zone 4 the torsional rigidity is much higher than loca)ons in Zone 3 and aeroelas)c requirements are not necessarily cri)cal. (Note: significant damage to Zone 4 training edge may need a flush semi-‐structural repair.)

Leading Edge Erosion •  Most common type of damage

to most cri)cal part of the aerodynamic airfoil –  May or may not require structural

ply replacement •  Common approach is to repair is

to fill and fair back to smooth aerodynamic surface –  Abrasion of damage and

surrounding area prior to fill & fair with epoxy or polyurethane paste

Stepped Removal & Repair •  Each damaged layer is removed in

“steps” so as to provide a landing for each replacement layer in the repair.

–  Usually bulk mul)-‐axial material; repaired bulk ply for bulk ply.

•  Step removal almost always results in damage to underlying structure

•  Each bulk repair ply then overlaps the corresponding exposed layer in the structure.

–  Faying surfaces do not match axial orienta)on requirements

Typical Stepped Repair Loads are distributed through the repair via

a lap joint into the underlying layers

The resul)ng repair sits above the surface

Copyright © Abaris Training 2015

Filler Ply

Typical Stepped Repair Shear stress distribu)on in a stepped repair

Note peak stress concentra)ons at edges of each step-‐lap within the repair

Copyright © Abaris Training 2015

Filler Ply

Tapered-‐Scarf Repairs •  A tapered-‐scarf angle is machined

through the composite structure so as to expose each layer along a gently-‐angled slope.

•  Each repair ply then lays over the corresponding exposed layer along the tapered angle. –  Recommend mul)ple

unidirec)onal materials for replacement of each mul)-‐axial bulk ply

One Tri-‐axial = Three Unidirec)onal

Typical Tapered-‐Scarf Repair Loads are transferred directly through the edges of each

unidirec)onal element of the mul)-‐axial layer, in plane, on axis, in shear, matching that of the underlying structure

The resul)ng repair is flush with the surface

Typical Tapered-‐Scarf Repair Uniform shear stress distribu)on through a tapered scarf

joint

Trailing Edge Scarf Repair

Damage Damage removal & scarf

Final repair

Vacuum Bagging & Curing the Patch

•  Vacuum bag with bleeder & breather layers –  Facilitates compac)on of the repair plies

•  Heat blanket with thermocouples and process controller –  Used to accurately control

cure temperature

Typical Heat Blanket Layup Scheme

Breather/Insula;on

Vacuum Bag

- Apply a minimum of 22 in Hg vacuum and maintain throughout cure cycle

*Heat at 1-5°F/Min

*Cool at <5°F/Min

*Hold at 150°F ± 10°F x 60-70 mins

* Temp based upon lagging thermocouple

Typical Cure Cycle Recipe Based on two-‐part amine cured epoxy resin chemistry

Post-‐Repair Finishing

Gel Coat

Filler Paste

Care is taken to prevent sanding into underlying repair plies

CHOOSING THE RIGHT MATERIALS FOR BLADE REPAIRS TONY GRAY KEY ACCOUNT MANAGER – WIND ENERGY [email protected]

(574) 361-‐8424

24 |

SIKA CORPORATION A LITTLE ABOUT US… §  Sika is a world leader in construc)on chemicals

§  Speciality chemical products in automo)ve & industrial markets

8/18/15 | Sika Industry -‐ Inven)ng the Future

25

§  Factors in Making a High Quality Repair

§  High Quality Repairs in Less Time

TOPICS

25

26

KEY FACTORS IN MAKING A HIGH QUALITY REPAIR

Mixing and application

Curing and finishing

Suitable product

Environmental conditions!

Substrates & Surface Preparation

27

SUITABLE PRODUCT

�  Critical damage in main body of blade

�  Half way or entirely through 1st ply of fibreglass

Structural Damages Surface Damages �  Non-structural damage of surface �  Less than half way through 1st ply

of fibreglass

Ø  2C laminating resin + suitable glass fibre fabric

Ø  2C surface filler

Polyester resin & filler – Polyester blades only! Epoxy & Urethane – Good for all blade types

28


Suitable product


29

ENVIRONMENTAL CONDITIONS

Temperature… Humidity… �  High influence on 2C products �  Moderate influence on 2C products

High temperatures… à  shorten pot life & cure times

(quicker sanding, grinding etc.)

Refer to the Product Data Sheet for Application Temperature & Humidly Range Typical Repair Products:

→  Applica)on temperature: 18C (64F) – 25C (77F) → Max humidity – 70% RH

30



Suitable product



31

MIXING & APPLICATION

Wrong mixing may lead to… �  Too Short application time �  No or insufficient curing �  Too long curing time �  Bad end properties (e.g. soft or brittle material)

Correct mixing ensures… �  Sufficient application time �  Correct curing speed and

homogeneous and full curing �  Good end properties after curing & durability

L J

32




Suitable product



August 18, 2015 33

CURING & FINISHING

Curing behavior - Resins �  To reach OEM durability a resin repair

must be post cured. �  Post curing raises the Tg of the resin.

Takes the resin from a glassy (brittle) state to a flexible (rubbery) state.

�  Tg should always be higher than operating temperature of the blade

�  Typical OEM spec is 75°C – 80°C (167°F - 176°F)

Curing behavior - Fillers �  Some fillers need multiple coats to build

thickness. �  Application temperature has a large

affect on the open time & sanding time. �  Not all fillers sand the same.

34




Suitable product



August 18, 2015 35

HIGH QUALITY REPAIR IN LESS TIME �  Buy your products from a name that you can trust �  Chose the wind repair products that:

1.   Give the largest temperature & humidity applica;on window

2.   Cure fast 3.   Are easy to mix

36

HIGH QUALITY REPAIR IN LESS TIME TEMP & HUMIDITY APPLICATION WINDOW

Sika Specialty Wind Repair Products

§  Specialized products for up tower blade repair

§  Applica)on temperature 5C (40F) – 35C (95F)

§  Max humidity – 80% RH

Currently available repair season

Extended repair season

Average min & max temp (Northern US)

Commonly Used Wind Repair Products

§  General purpose made for shop environment.

§  Applica)on temperature 18C (64F) – 25C (77F)

§  Max humidity – 70% RH

37

HIGH QUALITY REPAIR IN LESS TIME CURING FAST


§  Resin has long post cure )mes depending on resin type used

§  Mul)ple applica)ons of filler must be made to build thickness and fill pin holes

§  Filler sand )mes can be lengthy depending on type used, especially at cold temperatures


§  Resin has fast post cure )mes. Post cure in as liZle as 30 minutes to reach OEM spec Tg

§  Thixotropic filler materials that builds thick layers with a smooth finish in one applica)on.

§  Filler sand )mes of 35 minutes or less down to 5C (40F)

August 18, 2015 38

HIGH QUALITY REPAIR IN LESS TIME EASY TO MIX


§  Cans of A & B components that must be mixed onsite to reach correct ra)o ()me consuming & error prone)


§  Ready to go A/B foil packs (Resin)

§  Side by side or coaxial cartridges with sta)c mixer (Fillers)

§  Cartridges save material by only dispensing what is required & can be used on mul)ple repairs

§  Tendency to mix more than is required – causes excess waste

August 18, 2015 39

SIKA SPECIALTY WIND BLADE REPAIR PRODUCTS

Epoxy Repair Resin Polyurethane Fillers

Sikadur® Blade Repair Kits

Sikaforce® 7800 Red & Blue

Hybrid UV Resistant Sealant

#WindWebinar

Paul Dvorak Managing Editor Windpower Engineering & Development [email protected]

New Ideas, Methods and Materials for Improving Blade Repairs

Lou Dorworth Direct Services Division Manager Abaris Training Resources Inc. [email protected]

Questions?

Tony Gray Key Account Manager – Wind Sika Corp. [email protected]

#WindWebinar

Thank You q  This webinar will be available at

www.windpowerengineering.com & email

q  Tweet with hashtag #WindWebinar

q  Connect with Windpower Engineering & Development

q  Discuss this on EngineeringExchange.com