In plasma welding apparatus controls are provided which regulate the rates of increasing and decreasing the welding parameters e.g., welding current, gas flow and wire feed to prevent the formations of craters in the weld at the end of a welding run. Improved welds are formed if the wire feed rate is increased prior to the start of the decrease in welding current but after the gas flow to the plasma arc has begun to decrease.
To terminate welding, the mean energy of the arc is first reduced to obtain plugging of the hole, then this energy is briefly increased before again being decreased. Application to plasma arc welding of carbon steels.
The invention relates to an apparatus to perform plasma welding, by providing a cooling water temperature detector at the inlet side of cooling water in the plasma welding torch, controlling the temperature at the inlet side of the cooling water running into the plasma welding torch at a set temperature of more than 4.degree. C. and less than 18.degree. C., starting a plasma arc when the temperature of the cooling water reaches a specified point after starting to pass the cooling water, and moving the base metals and the torch relatively upon lapse of a specified time allowed to form a keyhole after start of the plasma arc.
The invention relates to a method and an apparatus to perform plasma welding, by providing a cooling water temperature detector at the inlet side of cooling water in the plasma welding torch, controlling the temperature at the inlet side of the cooling water running into the plasma welding torch at a set temperature of more than 4.degree. C. and less than 18.degree. C., starting a plasma arc when the temperature of the cooling water reaches a specified point after starting to pass the cooling water, and moving the base metals and the torch relatively upon lapse of a specified time allowed to form a keyhole after start of the plasma arc.
A process and apparatus for reducing wear of an electrode in a plasma arc torch involves altering the gas flow in a plasma chamber surrounding the electrode immediately before and continuing after cutting of the current that sustains the arc. The altering includes closing off the gas flow upstream of the chamber, switching from a swirling flow to a radial/axial flow through the plasma chamber, reducing the arc current level in conjunction with either of the above, and venting the plasma chamber to rapidly change the gas flow and pressure in the chamber. The interval is sufficient to reduce electrode wear, but short enough that the arc remains stabilized until cut-off. In the flow stop mode, a solenoid valve is placed on an inlet tube for the plasma gas. For venting, a vent tube and another solenoid valve are added to the torch. In the flow pattern switching mode, two independent gas supply lines with control valves feed separate sets of gas inlets to the plasma chamber, one set producing a swirling flow and the other set producing a radial then axial flow.
For forming the plasma arc there is used nitrogen protoxide in the liquid state which is conducted through a valve (12) to an expansion orifice (33) which produces a cooling effect on the electrode (5,6). Applications in particular in plasma arc torch cutting.
