A hot-gas torch is used to direct hot air to both the joint surface and weld rod, heating the materials to their softening temperature.
[1] The hot gas torch is maneuvered in one hand to heat both the weld rod and joint surfaces in a pendulum manner in quick succession.
Use of speed welding is limited to applications of simple joint design and orientation due to the size of the nozzle and maneuverability of the system.
Gas temperature is a controlled input that should be monitored for accuracy prior to initiating the welding process.
Sufficient temperature is required to overcome a materials activation energy, resulting in a reduction of the viscosity and an increase in flowability to support diffusion across the weld interface.
Prolonged exposure to elevated temperatures exceeding material manufacturer's recommendations can result in oxidation, distortion, or molecular deterioration, which can lead to joint failure.
[1][2] Sufficient hot gas flow rate is necessary to maintain adequate, even heating of weld rod and joint surfaces.
A properly sized blower or compressor can be utilized for multiple hot gas torches if one is not integrated in the individual welding gun.
where hot gas parameters include the specific heat (cp), initial and final temperature (T1 and T2, respectively), volumetric flow rate (qv), and density (
In certain instances, the material manufacturer may recommend use of other types of hot gas such as carbon dioxide or nitrogen when a potential health and safety risk may be present under other welding conditions.
Inadequate pressure can result in weld interface porosity, poor wettability, and lack of fusion defects.
One way to reduce the presence of pores is to establish a root gap as part of the joint design through which hot gases can escape.
Pressure application can be less effective in hand welding compared to utilizing a speed tip; however both are dependent upon the skill of the operator.
To establish consistent pressure while maintaining proper alignment to the joint groove during speed tip welding, it is recommended that the welder position their grip below the hot gas gun.
Recommended weld rod angles are established for materials based on achieving proper penetration without introducing flaws or additional stresses in the joint.
Accurate positioning will result in a visible “bow wave” effect at the root, indicating diffusion across the weld interface occurred.
Improper angle can result in uneven heating and weld defects or insufficient pressure to produce a strong joint.