qualitätsanforderungen an kritische verbindungselemente einer...
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Ach, nur eine Schraube!
Nur eine Schraube?Qualitätsanforderungen an kritische Qualitätsanforderungen an kritische
Verbindungselemente einer WEA
Meinert Hansen, 21. WINDENERGIETAGE 13.-15.11.2012
Hexagon bolts(M8-M64) according to standards including ISO 4014/17 and DIN 931/33 or customer specification
Studs: M16-52
Rods: M16-52
DIN912: M16-M48
Nacelle fasteners
DIN912: M16-M48
Quality 8.8, 10.9, 12.9
Surface treatment: HDG, Zinc flake
Wide range of studding (M16-64) according to standards or customer specification
Quality: 10.9
Surface treatment: HDG, Zinc Flake
Blade bolt kits
TÜV approved construction bolts for the tower: EN 14399 (DIN 6914/15/16) range from M12-M64
Quality 10.9
Surface treatment: HDG
Tower flange bolts
Treaded rods for foundation in range from M16-52.
Quality 8.8
Length: Up to 6000 mm
Surface treatment: Black or with HDG
Foundation kits
Delivered with plastic shrink tube on part of rod that goes into concrete – we even supply complete kits including anchor rings, all packed in containers ready for site-delivery
What is good quality?
• Why is consumers willing to pay 25% more for an Audi than they will pay for a Skoda with similar specifications?
• The difference is INSIDE!
12/11/2012 7
Quality = Full control in every step
Hot forging & robot handling
Machining&
Threading
Quenching &
Tempering
Raw material & supplier
control
Cleaning &Surface
treatment
Packaging &
Distribution
Final quality verification
12/11/2012 8
Raw material inspection
• Own material standards is always used
• Material certificate from steel mill
• Alloy composition verified with spectrograph
• Dimensional inspection• Dimensional inspection
• Identification tag verification against documentation from supplier
• After approval is the material registered in ERP-system and released for production
12/11/2012 9
Robot assisted hot forging
• Product drawings on every item
• Repeatability
• 100 % reliability
• Temperature control
• Over temperature is scrapped
• Low temperature may be reheated once
• Dimension control by operator
• Calibrated tools
• Documented process data
12/11/2012 10
Machining and threading
• SPC and MPC control
• Automatic SPC control in
new machines – data
storage
• In line dimension control by • In line dimension control by
operator
• Calibrated inspection tools
• Only use of upper 75% of
thread tolerance to ensure
tight connections
12/11/2012 11
Quenching and tempering
• Quenching and tempering-temperature is 100% registered and documented for each steel batch
• Data kept for minimum 20 years
• Temperatures are set according to type of bolt, dimension and property classtype of bolt, dimension and property class
• A hardening test from every steel batch is made prior to heat treatment of whole steel batch
• Vertical quenching to ensure straightness on long bolts
• More than 30 years of historical data
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Cleaning and surface treatment
• Mechanical cleaning introduced for all 10.9 products above M27
• No pickling means no adding of hydrogen during the process
• Temperature controlled Hot • Temperature controlled Hot Dip Galvanizing process
• Process is semi automatic and controlled by operator
• Zinc layer verified by operator
• New line fully PLC-controlled including optical inspection
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Final quality verification• The final test is a verification
of the process stability
• All process data stored
• Every batch has 100%
traceability and are marked
with a unique batch no.with a unique batch no.
• All batches are inspected
according to product
specifications and customer
requirements
• Issue of 3.1 or 3.2
certificates acc. to EN 10204
12/11/2012 14
According to ISO 898-1:2009:Additional material requirement for bolts with d≥16mm:Impact strength test at -20°C, min. 27 Joule.
Low temperature ductility
12/11/2012 15
Typical DF-values for 8.8 exceeds 80 Joule at -20°C
Typical DF-values for 10.9 exceeds 30 Joule at -20°C
Hardening capability exceeds 6 sigma!
CTQ 2: Tensile Strength
Rm [N/mm²]
1000,000
1050,000
1100,000
1150,000
1200,000
Dat a
4 Sigma LCL
4 Sigma UCL
Target
LSL
USL
Brinell Hardness [HB]
280,000
290,000
300,000
310,000
320,000
330,000
340,000
350,000
360,000
370,000
Dat a
4 Sigma LCL
4 Sigma UCL
Target
LSL
USL
Ultimate tensile
strenghtHardness
12.11.2012
950,000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
# of pa r t s
270,000
280,000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
# of pa r t s
CTQ 1: proof stress
Rp 0.2 [N/mm²]
0,000
200,000
400,000
600,000
800,000
1000,000
1200,000
1400,000
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49
# of parts
data
poin
ts
Data
4 Sigma LCL
4 Sigma UCL
Target
LSL
USL
Yield
strength
Packaging and distribution
• Manual packing of large bolts
• 100 % visual inspection
• Control of straightness and surface quality
• Bolts packed according to customer requirements:customer requirements:– O-rings
– Nuts and washers
– Protection sleeves
• Zero-failure products!
12/11/2012 17
What is hydrogen embrittlement?
Hydrogen may lead to brittle fracture in high strength bolts
– Hexagon head screws and bolts in 10.9 or 12.9 qualities – above 320 HV
– Case hardened thread forming screws and chipboard screws are also sensible
– Caused by absorption of atomic hydrogen in the steel
– Hydrogen is highly mobile and travels toward areas with the highest stress concentration
The fracture occurs where the deformation is high
– The hydrogen enters at minor cracks and surface discontinuities
– In the transition zone between head and shaft– In the transition zone between head and shaft
– In the transition from the thread run-out to the shaft
– Most commonly seen on dimensions smaller than 5 mm or larger than 30 mm.
Characteristically indications of hydrogen embrittlement
– There is usually no elongation of the bolt material after fracture
– The fracture occurs during mounting or within 24 hours
– The failure load level is usually lower than the yield strength
– It happens suddenly without any advance warning
The dark areas are brittle areas where the fracture has initiated
Where does the hydrogen come from?
Raw material
– Through the hot rolling of bars folds and inclusions in the material must be avoided
– Temperature control during rolling
– Homogeneous structure in the raw materials ensures consistent quality of the final products.
– Impurities in the raw material – especially sulphides,
ProcessingProcessing
– Temperature control during hot forging
– Pressure and lubricant control
– Controlled temperature and time during hardening and tempering
– The pickling process is typically made in 8-16% hydrochloric acid
– Inhibitors are used to minimise the formation of hydrogen.
– Post baking at 200-230°C for min. 4 hours to reduce the hydrogen level
The amount of hydrogen from the process is cumulative!
What actions are taken at Dokka Fasteners?
External processes– Investigations made with Det Norske Veritas in Høvik in 2004 showed that the concentration
of hydrogen was higher in the centre of broken bolts larger than M30 than the material close to the surface even though the bolts where hot dip galvanised.
– De-gassing is performed in the furnace at the steel mill prior to the hot rolling of bar or
– Baking is done at the steel mill after hot rolling of the bars at 650°C in 32 hours prior to processing at Dokka Fasteners
Internal processesInternal processes– Equipment for structural analysis of steel bars has recently been installed in our laboratory
– Batch level inspection to validate grain size, homogeneity and impurities.
– The forging temperature is verified individually prior to forging
– The entire heat treatment process is computer controlled and all data is collected as documentation
– Mechanical cleaning prior to hot dip galvanizing eliminates the largest contributor of hydrogen
– Pre-loading test randomly performed on finished products according to ISO 15330