TIG Welding | GTAW Welding | Arc Welding Equipment’s

Tungsten Inert Gas (TIG) or Gas Tungsten Arc welding (GTAW):

It is an arc welding process wherein coalescence is produced by heating the job with an electric arc struck between a tungsten electrode and the job. The electrodes used in this process are made of either Tungsten or Thoriated Tungsten. Thoriated Tungsten electrodes run cooler than plain tungsten electrodes and maintain square arcing ends but it is more expensive.

01-TIG Welding - GTAW Welding - Non Consumable electrode inert gas welding

Shielding gas:

A Shielding gas (Argon, Helium, Nitrogen, Carbon dioxide or a mixture of gases etc.) is used to avoid atmospheric contamination of the molten weld pool. The inert gas blanket shields the entire weld area from the atmospheric attack eliminating the need for any flux. General inert gas used is Argon though Helium or a mixture of the two may also be used. A filler metal may be added if required.

01-TIG welding - hardfacing welding electrodes - TIG welding electrodes

Commercial grades (Shielding gas) used for welding are 99.9% pure. Argon is 0.38% heavier than air and about 10 times heavier than Helium. Both gases ionize when present in an electric arc. This means that the gas atoms lose some of their electrons that have a negative charge. These unbalanced gas atoms, properly called positive ions, now have a positive charge and are attracted to the negative pole in the arc.

01-TIG welding machine -  Shielding gas welding - argon shielding gas

When the arc is positive and the work is negative, these positive ions impinge upon the work and remove surface oxides or scale in the weld area. Argon is most commonly used of the shielding gases. So Argon is suitable for welding thinner material.

Whereas Helium produces a higher arc voltage than Argon. This makes it more suitable for welding heavy sections of metal that have high heat conductivity or for automatic welding operations where higher welding speeds required.

TIG Welding Polarity:

The current source may be either DC or AC depending upon application. DC straight polarity arc is used in metals other than aluminium and magnesium including copper alloys, cast iron, steel and stainless steel. It gives good heat concentration and produces welds that are deep and narrow. Welding rates are high and there is less distortion of base metal. DC reverse polarity is not generally used because it produces shallow and wide welds. AC arc is used for welding aluminium, magnesium, cast iron and a number of other metals. Penetration with AC arc is midway between the penetration produced by DC direct polarity and DC reverse polarity.

01-Tungsten electrode - TIG Process - TIG Welding Polarity

The process is most suitable for low gauge sheet metal welding and cannot compete with conventional shielded metal electrode welding for welding of heavier gauges due to the cost of inert gas.

TIG Welding Process:

A high frequency, high voltage (100 kHz to 2 MHz, 2000 volts) low amperage current supply is often used in TIG welding to initiate the arc. This is to avoid the contamination of the electrode caused when the arc is initiated by short circuiting with the work piece. When electrode tip reaches within a distance of 3 to 2 mm from the job, a spark jumps across the air gap between the electrode and the job. The air path gets ionized and arc is established.

01-TIG welding Gun - TIG Welding Torches - TIG welding Tungsten

The superimposed high frequency current causes a spark to jump the gap between the electrode and the work piece. If a high frequency source is not available the arc can be initiated by scratch starting using copper striker plate to limit electrode contamination. Tungsten inert gas welding can be done in any position. Welding speeds of the order of 400 to 1000 mm per minute have been attained by manual process. The process can also be adapted to mechanized and automatic operation.

01-Tungsten inert gas welding - arc welding equipments - TIG welding torches

Advantages:

1. No flux is used, hence there is no danger of flux entrapment when welding refrigerator and air conditioner components.

2. Because of clear visibility of the arc and the job, the operator can exercise a better control on the welding process

3. This process can weld in all positions and produces smooth and sound welds with less spatter.

4. TIG welding is very much suitable for high quality welding of thin materials (0.125mm)

5. It is a very good process for welding Nonferrous metals (Aluminum etc.) and Ferrous metals.

01-arc welding machine - TIG welding machine - arc welding equipments

Disadvantages:

1. Tungsten if it transfers to molten weld pool can contaminate. It is Hard and Brittle.

2. Filler rod end can cause weld metal contamination

3. Equipment costs are higher than that for flux shielded metal arc welding.

Submerged Arc Welding SAW | Submerged Arc Welding Deposition Rates | Submerged Arc Welding Flux Composition

Submerged arc welding: (SAW)

In submerged arc welding also known as hidden arc welding, submerged melt welding, or sub-arc welding the arc is struck between a metal electrode and the work piece under a blanket of granular flux. The welding action takes place under the flux layer without any visible arc, spatter, smoke or flash.01-submerged arc welding-hidden arc welding - submerged melt welding - Electric arc welding

Here the weld arc is shielded by granular flux, consisting of Lime, Silica, Manganese Oxide, Calcium Fluoride, and other elements.

The filler wire used may be bare or slightly copper coated. The consumable electrode is a coil of bare round wire 1.5 to 10 mm in diameter.

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Operation of Submerged Arc welding Process:

The welding action can be initiated by introducing a piece of high resistance conducting material like steel wool or carbon between the electrode and the work piece. Once the welding action has been initiated the intense heat produced by the flow of current in the high resistance path melts a path of the flux around the electrode forming a conducting pool. The molten filler displaces the liquid flux and fuses with the molten base metal forming the weld. The molten flux coating over the molten metal pool forms a blanket that eliminates spatter losses and protects the welded joint from oxidation. As welding proceeds, the molten weld metal and the liquid flux cool and solidify under a layer of unused flux. The molten flux on solidification forms a brittle slag layer which can be easily removed.

01-submerged arc welding SAW, Submerged arc welding, electric arc welding process

Unused granular flux material can be reclaimed and reused.

Characteristics of Submerged Arc welding Process:

  • Electric current is 300 to 2000A.
  • Power supply is 440 V.
  • Velocity is 5m / Min
  • The SAW process provides very high welding productivity, depositing 4 – 10 times the amount of weld metal per hour.

01-hidden arc welding, submerged melt welding, sub arc welding, submerged arc welding SAW

Advantages of Submerged Arc welding Process:

  • Thin plates can be easily welded in one pass without any edge preparation while only a slight bevelling is necessary in most other cases.
  • The quality of welds produced in submerged arc welding is very high with good toughness, ductility and uniformity of properties.
  • Submerged arc welding is most suitable for welding in the down hand or flat position although welds can be made on a straight slope.
  • Materials successfully welded by the process include low carbon steel, medium carbon steel, heat resistant steel, corrosion resistant steel, high strength steels and non ferrous metals like Monel metal, nickel and others.
  • High  speed of execution due to the use of high currents in one or more electrode wires

  • No smoke

  • The arc is concealed, enabling the operator to work without a mask and without disturbing others nearby

Limitations of Submerged Arc welding Process:

  • Solid flux submerged arc welding can be used only on alloy and non-alloy carbon steel, stainless and refractory steel
  • The use of a powder flux means that welds must be executed horizontally, unless special measures are taken
  • The process cannot weld plate less than 1.8 mm thick (due to its high penetration)
  • It is not possible to butt joint work pieces more than 16 mm thick ; thicknesses greater than 16 mm require special preparation (bevelling).

01-Submerged arc welding process, Submerged arc welding application, Submerged arc welding machine

Application of Submerged Arc welding Process:

  • Shipbuilding
  • Heavy Duty Pressure vessels
  • Off shore engineering