Clean Steel Castings: Exploring the Dynamics of Producing ...€¦ · Clean Steel Castings:...
Transcript of Clean Steel Castings: Exploring the Dynamics of Producing ...€¦ · Clean Steel Castings:...
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Clean Steel Castings: Exploring the Dynamics
of Producing Clean Steel Castings with
Modern Technology
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• Types of inclusion defects
• Cause of inclusion defects
• Effects of inclusion defects
• Defect prevention
Agenda
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Types of Inclusion Defects - The Origins of Inclusions
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• Refractory
• Slag
• Mould
• Products of De-oxidation
• Reoxidation
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• Refractory
• Slag
• Mould
Effects of Inclusion Defects - Large Defects
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Poor surface finish
Scrap
Rework
Delayed despatch
Customer rejection
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Effects of Inclusion Defects - Small Defects
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A carbon steel casting exhibiting wrinkles caused by
a solid, slightly rigid, oxide film on the liquid metal.
A Ni alloy test bar, showing a typical distribution of
bifilm cracks, opened up by the tensile test
Poor surface finish
Poor mechanical properties
Poor machinability
Customer rejection
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Casting Cleanliness is Important
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ICE3 High Speed train
Rated for 330km/hr
2008 train departed Cologne
Drive axle collapses at low speed
Cause - Fatigue failure
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Casting Cleanliness is Important
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Examples for non-metallic
inclusions found in the longitudinal
microsection (a/r-plane) close to
the crack initiation area at the
fracture
Chemical EDS analysis of the
inclusions found below the
surface of the broken axle
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Mechanisms for controlling steel cleanliness
Molten Steel preparation - Before the steel
enters the mould
• Clean and dry charge
• Clean furnace technology
• Clean ladle and metal flow technology
• De oxidation practice
As the steel enters the mould
• Metal Stream control
• Running system design
• Swirl Gates
• Turbulence control
• Filtration
• Appropriate mould technology
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Clean Ladle Technology
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• Application
– All Silica Base
– Complete Reline 7 Tonne ladle 45 minutes
– Operators value simplicity
• Operation
– 2 Tonne Ladle – 6 fills
– 5 and 7 Tonne - 3 fills
– 15 and 25 Tonne 1 fill
Insulating Board System at Akdas Turkey
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• Major Benefits
– Improvement in metal temperature control
• Reduced rate of temperature loss
• More moulds per ladle
– Improved casting cleanliness
• 27% reduction in welding rod consumption
• Reduced upgrading time
• Reduced machining costs
– Improved energy efficiency
• Avoiding ladle preheat (LPG) saved €168000 (2004)
• Other Benefits
– Ladle temperatures much lower
– No heat and noise from ladle preheaters
– No pneumatic hammers
Insulating Board System at Akdas
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Indigenous Inclusions
Origins
• Products of De-oxidation
• Products of Re-Oxidation
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Argon Purging
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Benefits
• Separation and floatation of non metal
• Alloy homogenisation
• Temperature homogenisation
Argon has very low solubility in molten steel
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De-Oxidation
Typical De-oxidants
• Silicon
• Aluminium
• Titanium
• Zirconium
• Calcium
Outcome
• All form oxides
• All form other compounds to some extent
(nitrides, sulphides etc)
• Non metallics formed will coalesce with sand
and slag to form bigger complex inclusions
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Undertaken in both furnace and ladle.
Actual practice depends on
• Alloy
• Casting Design
• Specification
• Foundry metallurgist
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Re-Oxidation
When it occurs
• Furnace Tapping
• Mould Pouring
• Running System
• Mould Filling
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• Ladle Tapping
• Ladle Pouring
• Mould Filling
Re-Oxidation
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83% of inclusions in Steel Castings
arise from re-oxidation
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How Filters Work - Flow Control
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The metal has to undertake a tortuous
path through the filter, the metal velocity is
reduced allowing time for inclusion
capture.
Energy is removed from the metal
resulting in turbulence reduction
Non Turbulent fill
enables the
production of
high surface
quality castings
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Real time X-Ray experiments
Plate size: 600x400x60mm
Casting weight: 112kg
How Filters Work - Flow Control
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Side Sprue – No Filter
How Filters Work - Flow Control
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How Filters Work - Flow Control
Side Sprue – With Filter
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How Filters Work - Inclusion Removal
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Filters remove inclusions by 3 main mechanisms
• Particle Sieving
• Deep – Bed Filtration
• Cake filtration
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How Filters Work - Inclusion Removal
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The front face of a filter after casting, showing
the “caking” effect which traps inclusions.
Sand and slag
Alumina Powder from de-oxidation
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THANK YOU FOR YOUR ATTENTION
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