Please enable JavaScript.

Coggle requires JavaScript to display documents.

WELDING, WELDING TOOL EQUIPMENT, TYPES, Excessive, 1. (USES), 2.…

- - - - When acetylene is mixed with oxygen in correct proportion in the welding torch and ignited, the flame is produced which is sufficiently hot to melt and join the parent metal. A filler rod is generally added to build up the seam for greater strength.
    - - 1. High Pressure oxy-acetylene welding:-Acetylene is supplied from acetylene cylinder in compressed form.
        2. Low pressure oxy-acetylene welding:-In this acetylene gas is supplied from generator at low pressure. In the generator calcium carbide is added in the chamber in which water is already present. Acetylene starts forming and collected from top of water and used for further welding.
        CaC2+ 2 H2O → C2H2+ Ca(OH)2
    - - Stage 1
        2C2H2 + 2O2 = 4CO + 2H2
        Stage 2
        4CO + 2H2 + 3O2 = 4CO2 + 2H2O
        Stage 3
        2C2H2 + 5 O2= 4CO2 + 2H20 (vapour) + 1284.57 k J / mol
    - - 1. Oxygen Gas Cylinders- coloured Black or Blue
        2. Acetylene Gas Cylinders-coloured Red Pressure
        Oxygen –125 kg/cm2
        Acetylene –16 kg/cm2
        3. Regulators
        4. Pressure Gauges
        5. Hoses
        6. Welding torch
        7. Check valve
        8. Non return valve
        9. Gas lighter
        10. Protective clothing
- - - - 2. OXIDIZING FLAME
      - 1. NEUTRAL FLAME
      - 3. CARBURIZING FLAME
- - - - Equipments
        
        1. A welding generator (D.C.) or Transformer (A.C.)
        2. Two cables-one for work and one for electrode
        3. Electrode holder
        4. Electrode
        5. Protective shield
        6. Gloves
        7. Wire brush
        8. Chipping hammer
        9. Goggles
        
        ELECTRODES
        
        ▪Filler rods are used in arc welding are called electrodes.
        ▪Metallic wires having same composition as the metal to be weld.
        ▪Coated uniformly with a protective coating called flux. e.g. titanium oxide, potassium oxide, cellulose, iron or manganese, Ferro silicates, carbonates, gums, clays, asbestos etc...
      - TYPES
        
        1. Shielded Metal Arc Welding (SMAW): “Stick welding”
        
        •Arc temperature is nearly 5500°C
        •The electrode is also the filler rod
        •Only for steel
        •Strong welds if done properly (but often not)
        •Very high heat input: good for thick parts, bad for grain growth and distortion
        
        2. Gas Metal Arc Welding (GMAW):
        "MIG" (Metal-Inert-Gas)
        
        1. Complex mechanism but simple to perform and easy to automate.
        2. The electrode is also the filler rod, fed continuously from a spool.
        It melts in the arc.
        3. For steel or aluminum.
        4. Low skill level can achieve good weld.
        5. Medium heat input: distortion and grain growth are significant
        
        ADVANTAGES
        
        •Continuous weld may be produced (no interruptions);
        •High level of operators skill is not required;
        •Slag removal is not required (no slag);
        
        DISADVANTAGES
        
        •Expensive and non-portable equipment is required;
        •Outdoor application are limited because of effect of wind, dispersing the shielding gas.
        
        3.Gas Tungsten Arc Welding (GTAW):
        “TIG” (Tungsten-Inert-Gas)
        
        •The electrode is tungsten (not consumed)
        •The filler rod is separate and fed manually
        •High skill level required to achieve good weld
        •Difficult to automate
        •Low heat input and small weld bead:
        distortion and grain growth are minimized
        
        ADVANTAGES
        
        •Weld composition is close to that of the parent metal;
        •High quality weld structure
        •Slag removal is not required (no slag);
        
        DISADVANTAGES
        
        •Low welding rate;
        •Relatively expensive;
        •Requreshigh level of operators skill.
        
        4. SUBMERGED ARC WELDING (CAW)
        
        Submerged Arc Welding is a welding process, which utilizes a bare consumable metallic electrode producing an arc between itself and the work piece within a granular shielding flux applied around the weld.
        Since the electrode is submerged into the flux, the arc is invisible. The flux is partially melts and forms a slag protecting the weld pool from oxidation and other atmospheric contaminations.
        
        ADVANTAGES
        
        •Very high welding rate;
        •The process is suitable for automation;
        •High quality weld structure
        
        DISADVANTAGES
        
        •Weld may contain slag inclusions;
        •Limited applications of the process -mostly for welding horizontally located plates.
        
        Resistance Spot Welding (RSW):
        
        ELECTROSLAG WELDING
        
        • Electroslag welding is an uphill welding process. Uphill welding process is a process in which weld joints are made in the vertical direction and the plates to be welded are held vertically.
        • It works on the common principle of heat generation due to arc and electric resistance.
        • At the starting, arc is produced between the welding electrode and base metal, which tends to melt filler metal.
        • This filler metal will fill the cavity to some extent. Now the current passes through this extended surface, and heat is generated due to electric resistance.
        • This heat further tends to melt filler metal, which is continuously fed from the roller. Filler wire is fed through the roller continuously. This wire is fed through a tube that directs its flow.
        • This filler wire melts and fills the weld and makes a strong joint.
        
        ADVANTAGES
        
        •Cooling rate is very low so there is no problem of cold cracking
        .•There is no problem of slag inclusion or porosity in electro slag welding
        •The process is semi-automatic and faster
        •Heavier section can be welded in single pass
        •High productivity can be achieved
        •Low cost for joint preparation
        
        DISADVANTAGES
        
        •Too high heat input to base
        •High temperature of welding needs cooling arrangement
        •Slow rate of cooling give columnar grain in weld
        
        Resistance Spot Welding (RSW): “SPOT WELDING”
- - - - Isolating welding zone from ambient air. e.g. organic matter like wood pulp
    - - china clay, felspar, manganese, & titanium ores
    - - ferro silicon,ferro titanium,ferro manganese reduces oxides.
    - - Ionized the zone b/w electrode and part to be weld and ensuring stable burning.
    - - so that covering should have proper binding with bare electrode.
- - - - 5. CRACKS
        
        Cause:
        low ductility of weld, solidification shrinkage
        
        Prevention:
        when finishing move back the electrode to fill up the crack, increase crater fill time by power source.
        
        it is discontinuity in the metal that significantly reduces strength.
      - 7. UNDERFILL
        
        Cause:
        improper welding techniques
        
        Repair:
        simply weld to fill.
        May require preparation by grinding.
        
        Prevention:
        apply proper welding techniques for the weld type and position.
        Use stripper beads before the cover pass.
        
        depression in weld below adjacent base metal surface.
      - 8. SPATTER
        
        Cause:
        high are power, damp electrodes
        
        Prevention:
        Reduce are power, reduce are length, use dry electrodes
        
        Repair:
        remove by mechanical process
        
        small particles of metal that attach themselves to the surface
      - 4. INCOMPLETE FUSION
        
        Repair:
        remove and reweld, being careful to completely remove the defective area.
        
        Prevention:
        Eliminate the potential
        
        Cause:
        Low amperage ,fast travel speed, short are gap, lack of preheat, electrode too small, unclean base metal
        
        A weld in which fusion has not occurred throughout entire section of joint
      - 3. POROSITY
        
        In this defect, air bubbles or gases are present in the weld zone.
        
        Cause:
        Inclusion of atmospheric gases, sulfur in weld metal, or surface contaminants
        
        Prevention:
        Slower speed to allow gases time to escape
      - 9. INCOMPLETE PENETRATION
        
        Cause:
        Low amperage, low preheat, tight root opening, fast travel speed, short arc length
        
        Prevention:
        Correct the contributing factors.
        
        Incomplete penetration happens when your filler metal and base metal aren’t joined properly, and the result is a gap or a crack of some sort.
        
        Repair:
        Back gauge and back weld
      - 2. UNDERCUT
        
        Undercutting is an extremely common welding defect. It happens when your base metal is burned away at one of the toes of a weld.
        A portion of the base metal is melted away.
        
        Cause:
        High amperage, wrong electrode angle, long arc length, electrode is too large for the base metal.
        
        Prevention:
        Clean metal before welding
        
        Repair:
        Weld with a smaller electrode, sometimes must be low hydrogen with preheat
      - 1. SLAG INCULSION
        
        Slag is the waste material created, and bits of this solid material can become incorporated into the weld.
        Bits of flux and rust can be counted as slag.
        
        Cause:
        Low amperage, improper techniques, slow travel rate
        
        Prevention:
        Increase amperage, increase travel rate
        
        Repair:
        Remove by grinding or other mechanical processes
      - 6. OVERLAP
        
        weld metal spills beyond joint onto part surface but no fusion occurs.
        
        Cause:
        improper welding technique, steep electrode angle, fast travel speed
        
        Prevention:
        overlap is a contour problem proper.
        Proper welding technique will prevent this problem.
      - 13.ARC BLOW
        
        Arc deflection as a result of magnetic effects into the opposite direction of the earth lead clamp.
        Arc deflection as a result of magnetic effects in the direction of heavy part of work piece especially at corners and edges.
        
        Remedies:
        1. Use AC electrodes where possible.
        2. Try welding away from earth clamp connection.
        Try splitting the earth clamp and correct to both side of the joint.
- - - - •Produce gas or liquid tight joints.
        •Several parallel seams can be produced.
        •Overlap can be less than spot welding.
    - - •Cost of equipments is high.
        •Welding can be done only along straight line.
        •Difficult to weld thickness greater than 3mm.
- - - - •Making of projections is an extra operation.
        •All projection should be of same height.
        .•Metal which cannot support projection, cannot be weld.
    - - •Used for welding refrigerator condensor
    - - •It is possible to weld more than one spot at a given time.
        •Life of electrode is much longer than spot welding electrode.
        •The uniformity and appearance of weld is better as compared to spot welding.
- - - - •In wire drawing Industries
        •For producing butt joint in tubes, pipes & rods etc.
    - - •It consumes less welding current.
        •Process is cheap.
        •Process is fast.
        •It offers 100% strength factor.
        •Preparation of weld surface is not required.