Triplate transition joints

Report
Triplate transition joints
The ultimate solution to weld
aluminium to steel
By Ko Buijs
Metallurgical engineer SMT-Metals b.v.
Vacuum cladding
Production route of Triplate
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Choice of right materials and study of features
Grinding of the surfaces
Preparing of special grade explosives
Preparing vacuum chamber
Explosion welding
Flattening of the plates
Cutting into bars and special shapes
Inspection by QA-manager and independent surveyor
Transport to customer
After sales and all kind of recommendations
What happens during welding?
Explosives
Vd
Explosives
B
Vp
Aluminium plate
Cladding
S
Jet
Vp
ß
B1
Steel plate
Steel plate
Collision point
S = collision point  high pressure will locally cause super plastic
behavior of metals
Metallic bond between Al and Fe
Aluminium
atoms
Nucleus
Metal bond
Iron
atoms
Electron
clouds
Applications in the marine sector
• Cruise vessels and mega
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yachts
Offshore platforms
Fishing vessels
Ferries
Tenders and supply boats
Special ships such as
navy vessels
Vacuum cladding
Some examples
Differences with open air cladding
• Triplate is manufactured in a
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vacuum environment
Therefore we need less explosives
This will lead to a smooth interface
The result is no oxide
conglomerations in the interface
Better bending properties
Less risk of corrosion
Easy to machine
Three different interfaces
Smooth wave interface
Undulating wave interface
Turbulent wave interface
Oxide concentrations are visible
Open air cladding versus vacuum
Oxide conglomerations are visible
Small holes will initiate corrosion in due course
especially when bend
Disadvantage during bending and cutting
Limited fatigue strength
Open air cladding
Vacuum cladding
Source: http://www.fme-cwm.nl/Download/Publicaties/vm_115.pdf
Atmospheric cladded transition joints
Concentrations of oxides are visible
Open air cladding
Atmosferic clad transition joints
aluminium/steel
Side bend test
Side Bend Test 90°
Open air cladding
Vacuum clad generates no
oxide holes
Top: Atmospheric cladded
Bottom: Vacuum cladded Triplate
Hammer bend test MIL-J-24445A
Left: Atmospheric cladded
Right: Vacuum cladded Triplate
Combination hammer bend
and side bend test
Oxide holes can initiate cracks after bending
The result of crevices
Oxide conglomerations are dangerous
since they could initiate serious corrosion
in the interface steel/aluminium.
This is a result of an open air cladding.
Result of vacuum cladding. No oxide
conglomerations are visible. No crevice
or galvanic corrosion.
The strength of the interface
Tensile test
Even at bending radius 2x width
Triplate shows no cracks.
Summary of differences
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Open air cladding
Oxides with porosity
Oxides initiate fractures
Holes initiate corrosion
Side bend radius 10x
width of the strip
Variable weather
conditions
Harder to machine
(sawing and bending)
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Vacuum cladding
100% dense
Does not apply
Does not apply
Side bend radius 5x width
or even less
Does not apply since it is
inside
Easy sawing and forming
thanks to high ductility
The right set-up of Triplate
Aluminium superstructure
Triplate
transition joint
Steel plate
Steel plate
Optimum set up
Good set up
Steel plate
Acceptable set up
Transit zone shear strength in N/mm2
110
96
83
69
55
41
28
14
0
40
90
100
200
260
315
370
425
Temperature °C
Relationship between temperature and shear strength
aluminium/steel transition joints after 200 hours heat
input.
Temperature gradient during
welding
240°C
670°C
Al/Mg
Aluminium
Steel
Temperature
1550°C
Subjected to normal circumstances. It’s relevant to first
weld the aluminium plate to the transition joint
Unacceptable configurations
Steel plate
Worst possible set up
Unacceptable set up
The interface will overheat during welding. That will cause an hard
brittle interlayer.
What happens when the temperature is
too high during processing of Triplate?
Aluminium 99,5%
23Hv
6,5x
Brittle aluminium
iron crystals
760Hv
Steel 127Hv
V= 500x
1
Aluminium plate
F
F
Ideal situation
Tensile strenght min. 275 Mpa
100%
Steel plate
2
Tensile strength min. 205 Mpa
75%
F
a
F
Torque = F x a
3
Tensile strength min. 165 Mpa
60%
F
Sensitive location for notch effects
Width transition joint must be four
times the thickness of the
aluminium plate.
F
Tensile test asymmetric set-up
Triplate is not the
weakest link in the
chain
Special shapes by means of water
cutting
Full freedom of design and
digitally controlled
Triplate butt welds
• Butt welds are labour intensive
• Butt welds are expensive
• Difficult to seal it in a right way
• Avoid butt welds as much as possible
• Therefore longer lengths available (5.8 m)
Various approvals such as Lloyd’s, Veritas,
RINA, Germanische Lloyd, Det Norske
Veritas and American Bureau of Shipping
Many thanks for your attention
www.krontech.no

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