As the thickness of the workpiece increases to 0.750 inches, the arc current is set at the power supply to be in the high current mode, which mode exceeds about 75 amperes. The torch can be operated with the nozzle in contact with and being dragged along the workpiece. Thus, with approximately 40 amperes of arc current, which is considered the low current mode of operation, a metal plate of 0.40 can be cut efficiently by the moving plasma torch. The relationship between the arc current supplied to the torch and the thickness of the metal being cut is generally set so that the ratio of the arc current amperes divided by 100 equals the thickness of the plate which can be cut. In practice, an maintains the nozzle at least about 0.100-0.125 inches from the metal workpiece being cut by the moving plasma torch as the torch is operated in a high current mode. With this high current flow necessary to sustain a focused arc plasma sufficiently powerful to cut a relatively thick workpiece, the nozzle itself must be maintained above the conductive workpiece so that the nozzle does not contact the workpiece and allow the arc to attach to the nozzle. However, when cutting thick metal, the plasma torch is operated in a high current mode wherein the power supply is set at a current level over 75 amperes. The low current causes a lower energy and, thus, does not substantially overheat the nozzle. The low current mode of operation, with a current in the general neighborhood of 40 amperes, does not cause substantial nozzle damage even when the conductive nozzle is dragged along the conductive metal workpiece with the arc extending through the nozzle opening. The torch is operated in a low current mode which maintains a current in the range of about 35-50 amperes, which is at a set point sufficient to sustain a stable arc and to obtain realistic traveling speeds and cutting quality. The swirling gas is focused in the nozzle chamber where it can be ionized and discharged through the small orifice or outlet of the nozzle.ĭuring cutting of relatively thin metal workpieces, the nozzle of the plasma torch is often dragged directly over and in contact with the metal. A vortex action of the plasma gas passing through the annular chamber in the nozzle is caused by forcing the gas through a plurality of holes leading to the gas passageway. The plasma cutting process creates ionized gases within the annular chamber between the nozzle and electrode which establishes and maintains the plasma arc column due to the energy provided by the power supply connected between the nozzle and electrode and between the nozzle and the workpiece. The material being cut is conductive and has a variety of thicknesses. Electrical energy established by a voltage differential between the electrode and nozzle creates an arc in the nozzle for ionizing the gas before it passes from the outlet of the nozzle toward the workpiece, normally metal. These plasma cutting torches involve an electrode within a cylindrical cavity of a nozzle having an outlet through which the plasma column issues after being established in the annular passageway between the electrode and nozzle. Both of these prior patents are incorporated by reference herein for background information applicable to the present invention and so that details of the plasma torch technology need not be repeated.īACKGROUND OF INVENTION Plasma arc torches are employed for cutting metal of various thicknesses. One of these circuits is illustrated in Blankenship U.S.Īnother electrical protection circuit is illustrated in Dallavale U.S. Since plasma arc torches involve electrical current, a variety of protection circuits are employed. This type of nozzle is shown in Blankenship U.S. These designs employ a nozzle with a generally cylindrical cavity receiving a generally cylindrical electrode with a power supply providing current for establishing an arc between the electrode and nozzle. INCORPORATION BY REFERENCE A large variety of plasma torch designs has been used in the past. The present invention relates to the art of plasma torches of the type including an electrode within a cavity of a nozzle and employing electric energy for establishing an arc between the electrode and nozzle to maintain a plasma issuing from the nozzle, and more particularly, to a system, method and circuit for protecting the nozzle of the plasma torch. The polar and tropical worlds: a description of man and nature in.
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