STR654 - Lecture 3b 2020.ppt
Transcript of STR654 - Lecture 3b 2020.ppt
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ١
STR654:
INSPECTION, MAINTENANCE and
REPAIR of STEEL STRUCTURES
Lecture 3b
Sherif A. Mourad
Professor of Steel Structures and Bridges
Faculty of Engineering,
Cairo University
WELDING PROCESSES
� Weldability of steel.
� Welding positions.
� Arc welding techniques.
� Other welding techniques.
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٢
Weldability of steel
Weldability is the capacity of a metal to be
welded under the fabrication conditions
imposed into a specific, suitably designed
structure and to perform satisfactorily in the
intended service.
Weldability is improved by low-carbon, fine-
grain size and restricted thickness.
Weldability of steel
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٣
Welding Positions
� Flat position� Weld metal can be deposited faster.
� Typically used for shop welds, where manipulating devices can be used to rotate the work in a flat position.
� Over head position
� Electrode diameters below 5 mm are to be utilized to avoid metal run down.
� Horizontal-vertical position.
Welding Position
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٤
Arc Welding
� Shielded Metal Arc Welding
� Submerged Arc Welding
� Gas Metal Arc Welding
� Flux Cored Arc welding
� Gas Tungsten Arc Welding
Arc Welding
� Plasma Arc Welding
� Electrogas Welding
� Electroslag Welding
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٥
Arc Welding
Shielded Metal Arc Welding
Shielded Metal arc Welding Process
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٦
Shielded Metal Arc Welding
Definition:
� Heating Source is electrical arc between the
consumable electrode and the work piece
� No Pressure is applied
Shielded Metal Arc Welding
Equipment:
� Welding power source.
� Electrode holder.
� Ground clamp.
� Welding cables & connectors.
� Accessories (chipping hammer, wire brush ,…)
� Protective equipment (helmet, glove, …)
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٧
Shielded Metal Arc Welding
� Shielding is provided by the electrode covering
� Mainly gas, very little slag→ small pool, all positions
� Mainly slag, very little gases → high amperage, high deposition rate, i.e. flat position
Shielded Metal Arc Welding
Process Advantages:� The equipment is relatively simple, not expensive and
portable
� The filler metal and the means of its protection as well as the weld metal from harmful oxidation during welding are provided by the covered electrode
� Auxiliary gas shielding or granular flux is not required
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٨
Shielded Metal Arc Welding
� The process is less sensitive to wind and draft
than the other gas shielded arc welding
processes
� It can be used in areas of limited access
� The process is suitable for most commonly used
metals and alloys
Shielded Metal Arc Welding
Process Disadvantages:
� Low deposition rate because of the limited
electrode length
� Slag removal required
� It could not be automated
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٩
Gas Metal Arc Welding
Gas Metal Arc Welding Process
Gas Metal Arc Welding
Definition:
� It uses an arc between a continuous filler metal
electrode and the weld pool
� Externally applied gas or flux cored into the wire
or both for shielding
� Without the application of pressure
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ١٠
Gas Metal Arc Welding
Advantages:
� The only consumable electrode process that welds all commercially available alloys
� No restrictions due to limited electrode length
� All positions
� High deposition rate
Gas Metal Arc Welding
� High speed of welding
� Long weld bead
� Deeper penetration
� Minimal Post weld cleaning
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ١١
Gas Metal Arc Welding
Thus the process is considered well suited for:
� High production and automated welding
applications
� Robotics use
Gas Metal Arc Welding
Limitations:
� Complex welding equipment
� More difficult in hand - to - reach places
� Air drafted
� High level of radiated heat and arc intensity
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ١٢
Gas Metal Arc Welding
Gas Metal arc Welding Terminology
Gas Metal Arc Welding
Welding ampere varies with wire feed speed (WFS)
or melting rate (MR) as follows:
WFS = aI + bLI2
� a > Constant dependent on polarity, composition
� of the electrode (for the electrode heating)
� b > Constant for electrical resistance heating
� L > Electrode extension or stick out
� I > Welding current
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ١٣
Flux Cored Arc Welding
Gas Shielded Flux Cored Arc Welding
Flux Cored Arc Welding
Self-Shielded Flux Cored Arc Welding
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ١٤
Advantages of FCAW
� High-quality weld metal deposit.
� Excellent weld appearance-smooth,
uniform welds.
� Excellent contour of horizontal fillet welds.
Advantages of FCAW
� Many steels weldable over a wide thickness
range.
� High operating factor - easily mechanized.
� High deposition rate - high current
density.
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ١٥
Advantages of FCAW
� Relatively high electrode deposit
efficiency.
� Economical engineering joint designs.
� Visible arc - easy to use.
Advantages of FCAW
� Less pre-cleaning required than GMAW.
� Reduced distortion over SMAW.
� Up to 4 times greater deposition rate than
SMAW.
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ١٦
Advantages of FCAW
� Use of self-shielded electrodes eliminates
need for flux handling or gas apparatus,
and is more tolerant to windy conditions
present in outdoor construction (see
disadvantage "6" below for gas shields).
Advantages of FCAW
� Higher tolerance for contaminants that
may cause weld cracking.
� Resistant to under-bead cracking.
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ١٧
Limitations of FCAW
� FCAW is presently limited to welding
ferrous metals and nickel base alloys.
� The process produces a slag covering
which must be removed.
Limitations of FCAW
� FCAW electrode wire is more expensive on
a weight basis than solid electrode wires,
except for some high alloy steels.
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ١٨
Limitations of FCAW
� The equipment is more expensive and
complex than that required for SMAW
however, increased productivity usually
compensates for this.
� The wire feeder and power source must be
fairly close to the point of welding.
Limitations of FCAW
� For the gas shielded version, the external
shield may be adversely affected by
breezes and drafts. Except in very high
winds this is not a problem with self-
shielded electrodes because the shield is
generated at the end of the electrode,
which is exactly where it is required.
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ١٩
Limitations of FCAW
� Equipment is more complex than that for
SMAW, so more maintenance is required.
� More smoke and fumes are generated
(compared to GMAW and SAW).
Gas Tungsten Arc welding
Gas Tungsten Arc Welding Process
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٢٠
Gas Tungsten Arc welding
Advantages
� High quality welds.
� No spatter.
� With / Without filler.
� Root pass control.
Gas Tungsten Arc welding
� Relatively inexpensive.
� Welding variables control.
� All Metals
� Independent control of heat source and filler
metal addition.
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٢١
Gas Tungsten Arc welding
Limitations
� Low deposition rates.
� More welder coordination.
� Less economic.
Gas Tungsten Arc welding
� Possible draft.
� Tungsten inclusions.
� Low tolerance for contamination.
� Coolant leakage
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٢٢
Submerged Arc welding
Submerged Arc Welding Process
Submerged Arc welding
Definition:
� Heating with an arc between a bare consumable metal electrode and the work piece.
� Arc and molten metal are submerged in a blanket of granular fusible flux on the work
� Pressure is not used
� Sometimes additional filler metal is obtained from a welding rode or metal granules
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٢٣
Submerged Arc welding
Fused fluxes:
� Raw materials are powdered, dry mixed –
melted in electric furnace - cooled - crushed
and screened for size
Submerged Arc welding
Advantages:
� Good chemical homogeneity
� not hygnoscopic, easily recycled without
chemical changes
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٢٤
Submerged Arc welding
Main disadvantage is when adding
deoxidizer or Ferro-alloys during
fabrication losses and segregation occurs
Submerged Arc welding
Bonded Fluxes:
� Raw materials are powdered, dry mixed and bonded with K or Na-Silicate.
� Then wet mix is palletized and backed at high temperature (lower than fused fluxes).
� Pellets are crushed and screened
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٢٥
Submerged Arc welding
Advantages:
� Easy additions of de oxidizers and alloying.
� Color identification.
Submerged Arc welding
Disadvantages:
� Tendency to absorb moisture.
� Possible gas evolution when molten.
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٢٦
Submerged Arc welding
Mechanically Mixed Fluxes:
� Two or more fused or bonded fluxes are mixed.
Submerged Arc welding
Advantages:
� Available commercial.
� fluxes are mixed to give any precise properties.
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٢٧
Submerged Arc welding
Disadvantages:
� Segregation during shipment, storage, feeding
and recovery.
� Inconsistency from mix to mix.
Submerged Arc welding
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٢٨
Submerged Arc welding
Plasma Arc Welding
Plasma Arc Welding
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٢٩
Electrogas Welding
Electrogas Welding With a Solid Wire Electrode
Electrogas Welding
Electrogas Welding with a Flux Cored Electrode
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٣٠
Electroslag Welding
Non-Consumable Guide Method of Electroslag Welding (Three Electrodes)
Electroslag Welding
Consumable Guide Method of Electroslag Welding
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٣١
Resistance Welding
� Resistance Spot Welding
� Resistance Seem Welding
� Resistance Projection Welding
Resistance Welding
Resistance Spot Welding
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٣٢
Resistance Welding
Basic Single Impulse Welding Cycle for Spot Welding
Resistance Welding
Enhanced Welding Cycle
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٣٣
Oxyfuel Gas Welding
Basic elements of an Oxyfuel Gas Welding Torch
Solid State Welding
� Diffusion Welding
� Friction Welding
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٣٤
Friction Welding
Friction Welding
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٣٥
Electron Beam Welding
A Simplified Representation of anElectron Beam Gun Column
Laser Beam Welding
Elements of a Typical Laser Welding System
Sherif A. Mourad - Faculty of Engineering,
Cairo University
November ٢٠٢٠
STR654 Lecture 3b ٣٦
Thermal Spraying
Cross Section of a Typical wire Flame Spray Gun