About Welding Machine | Electro Slag Welding ESW | Narrow Gap Welding

Electro Slag Welding | Flux Core Welding

Electro slag welding is a welding process of heavy plates in the vertical position. Wherein coalescence is produced by molten slag which melts the filler metal and the surfaces of the work. It’s an arc less process that utilizes resistance heating of the slag pool covering the molten steel.

01-electro slag narrow gap welding

Electro Slag Welding Process

Parts to be joined are positioned approximately an inch apart and an electrode (weld wire) guide tube is positioned between the parts. Copper cooling shoes are clamped to the sides, bottom and top of the joints.

01-electro slag welding - welding area enlarged

After the components are assembled power is applied and the wire is fed through the guide tube. When the wire reaches the start block there is momentary arcing which melts the granulated flux, forms the slag pool and extinguishes the arc. The process is initiated by filling the joint with the flux and starting an arc by short circuiting. The consumable guide tube directs the electrode (welding wire) and conducts the welding current to the molten slag pool. The electrical resistance of the slag pool generates heat which melts the wire, the guide tube and the edges of the two components to be joined. The temperature obtained is approximately 1800 degree Celsius at the surface and 1930 degree Celsius inside under the surface. This much heat is sufficient to fuse the edges of the work pieces and the welding electrode.

01-electro slag welding - narrow gap welding equipment

Electro Slag Welding Gap

In ESW, wires and guide tubes melted by the flux. Then the liquid metal sinks through the slag to the metal pool below and solidifies. Since the slag is less dense than liquid steel, it floats to the top and protects the metal from exposure to air. With continuing addition of weld wire the molten steel fills the gap, solidifies and fuses the two components. The weld terminated when it reaches the top of the run-out cooling shoes above the rail running surface. Unnecessary weld reinforcements removed immediately, while the weld is hot.

01-electro slag welding - vertical plate assembly

A DC current of 750 – 1000 A applied from a DC generator with flat volt-ampere. Load voltages generally range from 30 to 55 V, therefore the minimum open circuit voltage of the power source should be 60 V. Speed range of Electro slag welding are 17 to 150 mm/s.

History:

Heavy plates requires Single pass welding than multi pass welding techniques. In the early 1950’s Russian scientists announced the single pass vertical welds by the principle of electrically conductive slag. In 1959 Electro slag welding has introduced in United states.

Applications:

  • ESW often used in structural box columns and wide flanges.
  • Manufacture of large Presses and machine tools work with large heavy plates.
  • Other machinery applications include kilns, gear blanks, motor frames, press frames, turbine rings, shrink rings, crusher bodies, rebuilding metal mill rolls and rims for road rollers
  • Pressure vessels for the chemical, petroleum, marine, and power generating industries

Advantages:

  • Electro slag welding can have extremely high deposition rates, but only one single pass is required no matter how thick the work-piece is.
  • Unlike SAW or other arc welding processes, there is no angular distortion in ESW because the weld is symmetrical with respect to its axis.
  • High Welding Speed and good stress distribution across the weld.

01-electro slag welding

  • Joint preparation is often much simpler than other arc welding processes.
  • Residual stresses and distortion produced are low
  • Flux composition as compared to submerged arc welding (SAW) is very low.

01-electro slag rail welding

Disadvantages:

  • When the heat input is very high and the weld quality can be rather poor, including low toughness caused by the coarse grains in the fusion zone and the heat-affected zone.
  • In Electro slag welding, there is some tendency toward hot cracking and notch sensitivity in the heat affected zone.
  • ESW restricted to vertical position welding, because of large molten metal pools and slag.
  • It is difficult to close cylindrical welds
  • Electro slag welding tends to produce large grain sizes.
  • Submerged Arc Welding is more economical than electro slag welding for joints below 60 mm.

01-narrow gap welding - electro slag welding

Percussion Welding | Stud Welding | Capacitor Discharge Welding | Welding Technology

Percussion Welding:

Percussion or Percussive welding is similar to flash welding except that the arc is produced by the rapid discharge of stored electrical energy across an air gap between the ends of the work pieces to be welded. It belongs to a family of joining techniques generically referred to as percussion or stud welding. The weld is affected by the heat produced by the arc with pressure percussively (rapidly) applied immediately following the electric discharge.

01-percussion welding - percussive arc welding

The pieces to be welded are held in two clamps as for flash welding. One of the clamps in stationery while the other is mounted in a slide and backed up against a heavy spring. When the movable clamps is released it advances rapidly towards the fixed clamp carrying the work piece.

As the distance between the ends of the work pieces reduces to less than about 1.5 mm, then the stored electric energy causes intense arcing over the surfaces raising the temperature. As the two parts come together the arc is extinguished due to the percussion blow.

The energy required for causing the discharge may be built up either by the electrostatic method using a capacitor or by the electromagnetic method using a collapsing magnetic field linking the primary and secondary windings of an inductive device or transformer. A Protective gas shield around the weld may be provided when welds of very high quality are desired. The process is used in the butt welding of bars, rods, tubes and pipes. Theses welding machines are built for automatic operation and have pre-set controlled parameters at each stage of the cycle.

01-percussion welding process - stud welding

History of Percussion Welding:

Percussive arc welding has been around for years, but it’s only recently that technology capability and commercial demand have converged to expose some genuine component production advantages. Percussion welding has the best features of 19th century technology. It is a “heat it and beat it” method that can be readily automated using straight forward electromechanical tooling.

Welding Force:

Welding force may be applied by:

1. Pneumatic,

2. Electromagnetic,

3. Spring force or

4. Gravity (falling weights).

01-percussion welding - stud welding

Power Supplies for Percussion Welding:

(i) Low voltage (10 to 150 volts DC) / High voltage (1000 to 6000 volts DC).

(ii) Electromagnetic, Capacitive storage or Inductive storage.

(iii) Low voltage (10 to 35 volts) AC that uses a transformer to furnish the welding voltage.

01-stud welding - capacitor discharge welding

Advantages of Percussion Welding:

1. The action takes place in a very little time, usually less than 0.1 Seconds

2. It causes very little damage to material close to the weld.

3. Hardened surfaces may be welded without any danger of annealing.

4. As the heat is concentrated at the ends of the work pieces heat balance is not much of a problem.

5. Parts with different thermal conductivities or different masses can be easily welded.

Disadvantages of Percussion Welding:

1. The process cannot be used for welding heavy sections larger than 600 mm2.

2. The process is limited to butt welded joint only

Applications of Percussion Welding:

1. Welding of satellite tips to tools

2. Welding of Steel to Cast Iron

3. Welding of Zinc to Steel

4. Welding of Copper to Aluminium etc.,

5. Welding of Studs

6. Join a stranded wire directly to a component pin on axis