STT - Surface Tension TransferTM

Description of equipment

Welding source STT II is a unique welding source for GMAW (MIG/MAG) welding, whose name is derived from the principle of control of the entire welding cycle: Surface – Tension – Transfer. The STT source is the only one provided with the controlled weld metal transfer to the weld pool in predefined parameters, which control the STT source according to the actual arc parameters measured in given moment. This unique control system of the entire welding cycle is bringing its perfect regulation in the real time, through direct feedback, electric arc – control of parameters on the arc.

How is the STT II source working?

The unique control of entire welding cycle is in the scanning of voltage parameters on the arc and evaluation of measured values, so that the source instantaneously reacts on all phases of the spray metal transfer to the weld pool according to real situation on the arc. The source is working with direct feedback of the welding parameters control. In principle the STT source can be described in the following way: when welding in the short-circuitting area, changing of the short-circuitting phase and burning phase on the arc occur. The source is capable, through its unique scanning of the parameters on the arc, to recognize the coming of the individual phases and in the real time will adjust the welding parameters.
At the beginning of the short-circuitting phase the STT source will limit the welding current for 10 A.
At the beginning of the phase of arc restriking the source will limit the welding current for cca 50A. Control of the welding current is independent on the operator and is proceeding automatically.
In fig. 1, there is seen characteristic flow of voltage and welding current with the standard source with flat characteristics ( source with constant voltage – CV) and the source STT II in relation to one cycle of the weld metal transfer to weld pool.

Fig. 1

Advantages and possibilities of STT II source

The above stated principle of STT II activity is given by a set of circuits, which control entire process and control, for example, the circuit of easy welding, which continuously compares real values on arc with the reference values stored in memory and with the values of preceeding cycles evaluates situation and in the real time performs proper interference into welding parameters. Then , there is here a unique circuit called „dV/dt detector“, which identifies the phase closely before the ending of short-circuit.

STT source is a welding source GMAW (MIG/MAG), which works neither with constant current characteristics, CC nor with constant voltage characteristics CV. It is a source with a wide range of welding parameters control, where wire feed speed and welding current are controlled independently.

Welding parameters are being set according to the real need of all phases of welding cycle.

Advantages arising from the principle of STT source

  • heat input in weld is minimal
    • root deformation is thus decreased
    • area influenced by heat is smaller
  • minimal spatter up to 90% lower than with conventional sources GMAW (MIG/MAG)
    • weld cleaning is minimal
    • area around weld is clean
  • size of weld pool is the same in any position and situation of welding, for example, at the end of a thin sheet, in weld root, the weld pool is not increasing
    • operator need not be afraid of sagging
    • even less experienced operator is capable of welding weld roots,even in thin sheets up to 0,6mm and in downward vertical position!!!
  • process is flexible
    • STT source will also easily manage a wide gap between materials to be welded, for example sheets 3 mm, gap 12mm!!!
  • perfectly controlled process
    • when welding thin sheets, weld roots etc. Replaces existing technology of welding with non-consumable electrode GTAW (TIG), with several times higher productivity and better welding results
  • for welding unalloyed and low-alloyed steels
    • enables use of shielding by CO2 gas, at high quality of weld
    • saves welding costs
  • enables choice of larger wires
    • saves costs for filling material
  • weld appearance is excellent
    • no grinding is needed!!!
  • STT source is easy to use
    • training of attendance is short
    • user will use the advantages of STT source „from the first day“
  • harmful fumes are lowered to minimum
    • environmental pollution is low
  • enables welding of common unalloyed and low-alloyed steels, high-alloyed steels
    and electroplated steels
    • universal source for a wide spectrum of users
    • enables application of technology of soldering by electric arc, for example
      thin sheets of car bodies
    • higher soldering speed with lower heating of parts being soldered
    • various shielding gases can be used, including pure argon and helium for stainless steels
    • user has a choice according his possibilities and price
  • application of hard-facing
    • due to low heat input to weld pool, only minimal mixing with base material occurs and build-up weld has in many cases required properties already in 1st layer and does not suffer from breaks
Fig. 2 - Traditional source (left) - Welding with STT II (right)

Controls of STT source

Description of control panel

Practical use of STT II

Practical use of STT II

Technical specification of INVERTEC® STT® II

Name Code for order Feeding
Output current and voltage Input current at loading Range of output currents Weight
208 230 460
K1525-1 208/230/460
3 phase
225A/29V/60% 33 30 19 Top current
Bottom current
53 kg 589x336x620

Assembly of STT source including feeder

Feeder LN-742
Source STT II is, as standard,delivered with feeder LN-742. The source and feeder are situated on truck K 10262-1. No. of order PSTT2-7-2A. The unit must be provided with interconnecting cable 2-30m. No. of order K 10 268 XM PG.
Feeder LN-742, No. of order K617-1 can be provided with guide rolls for wire diameter from 0,6 to 1,2mm, for unalloyed welding wires, low-alloyed wires and high-alloyed wires. Feeder LN-742 is provided with a standard euro plug for connection of welding guns. The user has a choice according to his requirements.

Recommended equipment

Remote control for bottom and top current.
10-pin connector, cable 7,6m.
No. of order K942-1.


CZ WELD s.r.o., Pod brizkami 800, 530 02 Pardubice, Czech Republic, tel./fax: +420 466 303 210,