٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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.
١ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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
٢ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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
٣ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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
٤ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
Arc Welding
Shielded Metal Arc Welding
Shielded Metal arc Welding Process
٥ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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, …)
٦ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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
٧ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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
٨ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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
٩ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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
١٠ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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
١١ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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 + bLI 2 ¢ 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
١٢ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
Flux Cored Arc Welding
Gas Shielded Flux Cored Arc Welding
Flux Cored Arc Welding
Self-Shielded Flux Cored Arc Welding
١٣ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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.
١٤ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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.
١٥ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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.
١٦ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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.
١٧ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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.
١٨ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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
١٩ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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.
٢٠ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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
٢١ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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
٢٢ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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
٢٣ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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
٢٤ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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.
٢٥ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
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.
٢٦ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
Submerged Arc welding
Disadvantages:
¢ Segregation during shipment, storage, feeding and recovery.
¢ Inconsistency from mix to mix.
Submerged Arc welding
٢٧ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
Submerged Arc welding
Plasma Arc Welding
Plasma Arc Welding
٢٨ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
Electrogas Welding
Electrogas Welding With a Solid Wire Electrode
Electrogas Welding
Electrogas Welding with a Flux Cored Electrode
٢٩ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
Electroslag Welding
Non-Consumable Guide Method of Electroslag Welding (Three Electrodes)
Electroslag Welding
Consumable Guide Method of Electroslag Welding
٣٠ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
Resistance Welding
¢ Resistance Spot Welding ¢ Resistance Seem Welding ¢ Resistance Projection Welding
Resistance Welding
Resistance Spot Welding
٣١ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
Resistance Welding
Basic Single Impulse Welding Cycle for Spot Welding
Resistance Welding
Enhanced Welding Cycle
٣٢ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
Oxyfuel Gas Welding
Basic elements of an Oxyfuel Gas Welding Torch
Solid State Welding
¢ Diffusion Welding ¢ Friction Welding
٣٣ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
Friction Welding
Friction Welding
٣٤ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
Electron Beam Welding
A Simplified Representation of an Electron Beam Gun Column
Laser Beam Welding
Elements of a Typical Laser Welding System
٣٥ STR654 Lecture 3b ٢٠٢٠ Sherif A. Mourad - Faculty of Engineering, November Cairo University
Thermal Spraying
Cross Section of a Typical wire Flame Spray Gun
٣٦ STR654 Lecture 3b