voestalpine bohler welding URANOS NX 2200 PMC Manual De Instrucciones página 98

OPERATING INSTRUCTIONS
10. OPERATING INSTRUCTIONS
10.1 Manual Metal Arc welding (MMA)
Preparing the edges
To obtain good welding joints it is advisable to work on clean parts, free from oxidations, rust or other contaminating agents.
EN
Choosing the electrode
The diameter of the electrode to be used depends on the thickness of the material, the position, the type of joint and the type of
preparation of the piece to be welded.
Electrodes of large diameter obviously require very high currents with consequent high heat supply during the welding.
Type of coating
Rutile
Acid
Basic
Choosing the welding current
The range of welding current related to the type of electrode used is specified by the manufacturer usually on the electrode
packaging.
Striking and maintaining the arc
The electric arc is produced by scratching the electrode tip on the workpiece connected to the earth cable and, once the arc has
been struck, by rapidly withdrawing the electrode to the normal welding distance.
Generally, to improve the arc striking behaviour a higher initial current is given in order to heat suddenly the tip of the electrode
and so aid the arc establishing(Hot Start).
Once the arc has been struck, the central part of the electrode starts melting forming tiny globules which are transferred into
the molten weld pool on the workpiece surface through the arc stream.
The external coating of the electrode is being consumed and this supplies the shielding gas for the weld pool, ensuring the good
quality of the weld.
To stop droplets of molten material short-circuiting the electrode to the weld pool and extinguishing the arc if the electrode
accidentally approaches the pool too closely, it is useful to increase welding current (Arc Force) temporarily in order to break a
short circuit.
If the electrode sticks to the workpiece, the short circuit current should be reduced to the minimum (antisticking).
Removing the slag
The slag is removed by a small hammer or is brushed away if friable.
10.2 TIG welding (continuos arc)
Description
The TIG (Tungsten lnert Gas) welding process is based on the presence of an electric arc struck between a non-consumable
electrode (pure or alloyed tungsten with an approximate melting temperature of 3370 °C) and the workpiece. An inert gas
(argon) atmosphere protects the weld pool.
reason the welding power source is usually equipped with an arc striking device that generates a high frequency, high voltage
discharge between the tip of the electrode and the workpiece. Thus, thanks to the electric spark, ionizing the gas atmosphere,
the welding arc is struck without any contact between electrode and workpiece.
arc is established and the current increases to the set welding value.
To improve the quality of the filling at the end of the welding bead it is important to control carefully the down slope of the current
Property
Easy to use
High melting speed
High quality of joint
Carrying out the welding
Electrode angle depends on the number of runs. The
electrode should normally be moved in a weaving
motion with pauses at the sides of the bead to avoid
an excessive accumulation of filler material at the
centre.
94
Use
All positions
Flat
All positions