voestalpine Böhler Welding

Coating of stick electrodes

4th Apr 2017

Tasks of the coating:

  • Ionization of the air path (stable arc)
  • Protecting the arc and the welding bath from unwanted contact with air (O2, N2 )
  • Slag formation on the surface (slow cooling, minimizing pore formation)
  • Metallurgical effect on the weld metal due to de-oxidation and binding of impurities such as sulfur and phosphorus
  • Alloying of elements to compensate for burn-off
  • Increasing the deposition rate and recovery by adding iron powder Recovery: The ratio of molten weld metal to molten core stick and percent of weight.

Recovery: The ratio of molten weld metal to molten core stick and percent of weight
 

Coating thickness
It’s all in the thickness… As the coating thickness increases the metal droplet transfer becomes finer the suitability for gap bridging and out of position welding lessens the seam appearance improves, i.e. the weld seam is more finely rippled and smoother the penetration of the weld increases.

Coating types
According to the European Norm DIN EN ISO 2560, there are a total of eight different types of coated stick electrodes for arc welding of unalloyed steels and fine-grained steel.
The four main types are named after their main components:

  • C (Cellulose) cellulose electrodes
  • A (Acid) acid electrodes (Today however, acid electrodes can hardly be found anymore and have been almost completely replaced by rutile electrodes.)
  • R (Rutile) rutile electrodes
  • B (Basic) basic electrodes

 

Cellulose-coated stick electrodes

Due to the high level of cellulose in the coating, they have excellent properties for out-of-position welding, but poor properties for horizontal welding. They are therefore mainly used for vertical-down welding on large pipes.

Rutile-coated stick electrodes

These electrodes are very popular due to their good welding properties. The welding arc is stable and calm and is easy to reignite, the seams are finely rippled, and most of the slag comes off by itself. Rutile-coated electrodes have sufficient toughness properties, but are only suitable for out-of-position welding to a limited extent (high-alloy). BÖHLER electrodes for under water welding are a special type namely rutile acid (RA). They have a special sealing to protect against the water.

Basic-coated stick electrodes

The main advantages of basic electrodes are the outstanding toughness properties of the weld metal and its resistance to hot and cold cracks. Basic-coated electrodes have a coarse droplet material transfer, can be used to weld in all positions and have somewhat coarsely rippled seams. The slag can be relatively easily removed, but not as easily as with rutile-coated electrodes.

TIP: The coating material should be selected based on what you want to weld. Always clarify this before starting to weld.

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Stick electrodes coating