Welding
Welding is a materials joining process which produces coalescence of materials by heating them to suitable temperatures with or without the pplication of pressure or by the application of pressure alone, and with or without the use of filler material. Welding is used for making permanent joints. It is used in the manufacture of automobile bodies, aircraft frames, railway wagons, machine frames, structural works, tanks, furniture, boilers, general repair work and ship building.
Types of welding
GAS Welding
ARC Welding
GAS WELDING
Sound weld is obtained by selecting proper size of flame, filler material and method of
moving torch
The temperature generated during the process is 33000c.
When the metal is fused, oxygen from the atmosphere and the torch combines with molten metal and forms oxides, results defective weld
Fluxes are added to the welded metal to remove oxides
Common fluxes used are made of sodium, potassium. Lithium and borax. Flux can be applied as paste, powder, liquid. solid coating or gas.
1GAS WELDING EQUIPMENT
1. Gas Cylinders Pressure
Oxygen – 125 kg/cm2 Acetylene – 16 kg/cm2
2. Regulators
Working pressure of oxygen 1 kg/cm2 Working pressure of acetylene 0.15 kg/cm2
Working pressure varies depends upon the thickness of the work pieces welded.
3. Pressure Gauges
4. Hoses
5. Welding torch
6. Check valve
7. Non return valve
2FLAMES PRODUCED DURING GAS WELDING
Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cutting operations:
(a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing flame.
Addition of more oxygen give a bright whitish cone surrounded by the transparent
blue envelope is called Neutral flame (It has a balance of fuel gas and oxygen) (32000c)
• Used for welding steels, aluminium, copper and cast iron
oxygen give a bright whitish cone surrounded by the transparent
blue envelope is called Neutral flame (It has a balance of fuel gas and oxygen) (32000c)
• Used for welding steels, Aluminium, copper and cast iron.
Oxygen is turned on, flame immediately changes into a long white inner area (Feather)
surrounded by a transparent blue envelope is called Carburizing flame (30000c)
Advantages of Gas welding.
1.Simple Equipment 2.Portable 3.Inexpensive
4.Easy for maintenance and repair
Disadvantages Of Gas welding
1.Limited power Density 2.Very low welding speed.
3.High total heat input per unit length 4.Large Heat affected Zone
5.Severe Distortion
6.Not recommended for welding reactive metals such as titanium and Zirconium.
Difference between Gas Welding and Arc Welding
GAS WELDING
1. Heat is produced by the Gas Flame
2. The Flame temperature is about 3200oC
3. Separate Filler rod introduced
4. Suggested for thin materials
5. Gas welded parts do not have much strength
6. Filler metal may not be the same parent metal
7. Brazing and soldering are done using gas
ARC WELDING
1. Heat is produced by Electric Arc
2. The temperature of Arc is about 4000oC
3. Arc Producing as well as filler rod material is the electrode.
4. Suggested for medium and thick materials
5. Arc welded parts have very high strength
6. Filler metal must be same or an alloy of the parent metal
7. Brazing and soldering can’t be carried out by electric arc.
ARC WELDING
Uses an electric arc to coalesce metals
Arc welding is the most common method of welding metals
Electricity travels from electrode to base metal to ground
1.Arc welding Equipments
• A welding generator (D.C.) or Transformer (A.C.)
• Two cables- one for work and one for electrode
• Electrode holder
• Electrode
• Protective shield
• Gloves
• Wire brush
• Chipping hammer
• Goggles
2.Electrode
Electrode is a thin rod made up of same as that of parent material. Flux is coated over the electrode to avoid oxidation. It is mostly connected to the negative polarity.
Two Basic Types of AW Electrodes
Consumable – consumed during welding process Source of filler metal in arc welding
Nonconsumable – not consumed during welding process
Filler metal must be added separately
Consumable Electrodes
Forms of consumable electrodes
• Welding rods (a.k.a. sticks) are 9 to 18 inches and 3/8 inch or less in diameter and must be changed frequently
• Weld wire can be continuously fed from spools with long
lengths of wire, avoiding frequent interruptions
In both rod and wire forms, electrode is consumed by arc and added to weld joint as filler metal.
Nonconsumable Electrodes
Made of tungsten which resists melting
Gradually depleted during welding (vaporization is principal mechanism) Any filler metal must be supplied by a separate wire fed into weld pool
3.Flux
A substance that prevents formation of oxides and other contaminants in welding, or dissolves them and facilitates removal
Provides protective atmosphere for welding Stabilizes arc
Reduces spattering
4.STEPS FOLOWED IN ARC WELDING :
• Prepare the edges to be joined and maintain the proper position
• Open the acetylene valve and ignite the gas at tip of the torch
• Hold the torch at about 45deg to the work piece plane
• Inner flame near the work piece and filler rod at about 30 – 40 deg
• Touch filler rod at the joint and control the movement according to
the flow of the material
Advantages
Most efficient way to join metals
Lowest-cost joining method
Affords lighter weight through better utilization of materials
Joins all commercial metals
Provides design flexibility
Disadvantages
• Manually applied, therefore high labor cost.
• Need high energy causing danger
• Not convenient for disassembly.
• Defects are hard to detect at joints.
Related Topics
Privacy Policy, Terms and Conditions, DMCA Policy and Compliant
Copyright © 2018-2024 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.