Abstract: A process and apparatus for cutting a material using a plasma are jet provides improved uniformity along the length of cut, despite variations in cutting speed. This is achieved by pulsing the arc current and dynamically varying the pulsing. By this means the momentum of the plasma arc jet can be maintained substantially constant whilst the amount of energy delivered by the plasma arc jet is controllably varied. The pulsing can be dynamically varied in dependence on one or more of the cutting speed, the angle of ejection of a stream of molten material from the cut, the size of the droplets of the ejected material, the intensity of spectral pattern of light emitted from the plasma arc jet and material interface, and the arc voltage. The pulses can be varied by varying one or more of the pulsing frequency, the pulse duty, upper value of the pulse current, and depth of the pulses.

Abstract: A method and apparatus for detecting non-axisymmetric wear (i.e. grooving 22) of the orifice (12) of the nozzle (13) of a plasma arc torch (1) involves placement of a probe adjacent a plasma jet (21) that emerges from the nozzle (13) such that a number of electrically isolated elements (23) of the probe surround the jet (21) and measuring a voltage drop across an electrode (11) of the torch (1) and each probe element (23) to detect whether there is any deflection of the plasma jet (21). The presence of a groove (22) causes the jet (21) to deflect and is indicated by an increased voltage at the probe elements (23) towards which the jet is deflected and a decreased voltage at the opposite elements. The probe may be formed by segmenting a shield (17) of the torch.

Abstract: A method and apparatus for monitoring the condition of a plasma arc torch determines whether the nozzle (13) of the torch and an electrode (11) of the torch have suffered any erosion and distinguishes the two. The pressure of a plasma forming gas that is supplied for the torch (p.sub.1 or p.sub.n) is monitored while the torch is operating to detect erosion of the orifice (12) of the nozzle (13), and the voltage U.sub.ne between the electrode (11) and nozzle (13) is monitored, also while the torch is operating, to detect erosion of the electrode (11). A pressure, p.sub.1 or p.sub.n below a reference pressure indicative of a good (un-eroded) nozzle indicates erosion of the orifice (12), and a voltage U.sub.ne above a reference voltage indicative of a good (un-eroded) electrode indicates erosion of the electrode. The pressure measurement and U.sub.ne are compared with appropriate reference values to logically discriminate between wear of the nozzle and wear of the electrode (given that an increase in U.sub.

Abstract: An electric arc reactor having a substantially straight feed material passage extending through both the anode and the cathode. Gas is fed into the gap between the two electrodes so as to swirl about the axis of the feed passage and thereby confine the lateral extend of the arc and also confine the location at which the upstream arc root attaches to the upstream electrode. An enlargement of the passage in the gap end of the upstream electrode provides an internal sloping root attachment surface. A similar enlargement may be provided in the downstream electrode, but spaced from the gap, if the downstream electrode forms the cathode. Gas flow in a direction towards the upstream end of the feed passage is used to control the location at which an arc root attaches to the sloping surface of a passage enlargement. Magnetic means is provided to induce rotation of the arc such as to form a hollow arc column which is coaxial with the feed passage and through which feed material can pass.

Abstract: An electric arc generating device including, a first electrode and at least two further electrodes. A source of electrical power is connected to said electrodes so as to cause an arc to burn between the first electrode and one of the further electrodes. The distribution of power within the zone of the arc is controlled by repetitively changing the path of the arc. That is, one root of the arc may remain attached to the first electrode, whereas attachment of the other root is transferred between two or more of the further electrodes on a repetitive basis. The timing and extent of each change may vary according to circumstances of use. The changes in arc path are due at least in part to repetitive modification of the influence of the power source on one or more of the further electrodes, but variation of the flow rate of gas/material through the arc zone can be another controlling factor.