Thermal Dynamics Corporation

Raymond G Wilkins

Fred A Rogers

Bruce O Hatch

David A Tatham

John A Boisvert

Dennis J Solley

William Wakefield

David J Nelson

Plasma cutting apparatus (10) for use in cutting a material (M). A torch (12) cuts the material. A control unit (14) controls the cutting operation performed by the torch and includes a control module (16) in which the control unit is housed. At least one power unit (18) supplies power to the cutting torch, the application of this power being controlled by the control unit. Each power unit includes a power module (24) in which the power unit is housed. A cooling unit (54) for cooling the torch is also available. The cooling unit includes a cooling module (56). The control module, power module(s), and coolant module are removably stackable one on top of the other.

Modular, stackable plasma cutting apparatus

An electrode used in a plasma-arc torch has ridges formed on the side surface thereof for initiating a pilot arc. The required voltage for initiating a pilot arc is substantially reduced by employing this type of electrode. The ridges have much smaller radii of curvature which substantially enhance the local electric field strength responsible for creating the pilot arc discharge. The ridges are oriented substantially along the flow lines of the plasma gas so as to create the least disturbance. In one embodiment with spiral gas flow, this results in helically oriented ridges. In another embodiment with straight gas flow, the ridges are parallel to the longitudinal axis of the electrode.

Ridged electrode

The present invention minimizes shock hazard in using a touch start plasma torch. The resistance between the torch tip and the workpiece is compared to a predetermined value set by estimating the resistance between a person's hand to ground under the most unfavorable conditions. In the preferred embodiment, such comparison is performed by supplying an AC voltage to a resistor in series with a torch tip, the resistor having a resistance equal to the predetermined value. The peak voltage at a point in the circuit connection between the resistor and torch tip is sensed and if such peak is less than half of the peak voltage of the AC voltage supplied to the resistor and torch tip, the resistance between the torch tip and ground is less than the predetermined value and a control signal will be generated. A relay will switch on the power supply supplying high voltage between the cathode and the workpiece only when it receives the control signal indicating that the resistance between the torch tip and ground is below the predetermined value.

Torch operation interlock device

A plasma torch system is provided which creates a pilot arc having high instantaneous power and low average power. The pilot arc ignition circuit reduces the pilot arc duty cycle by pulsing on the pilot arc and then extinguishing it. A plasma torch disclosed also reduces RF noise in the line by eliminating the additional spark gap typically used in the power supply circuit and by placing the triggering circuit on or adjacent the torch handle.

Plasma torch starting circuit

A plasma torch circuit includes a control for initially setting the torch at a desired height above a workpiece during the time the non-transferred arc exists between the torch cathode and the torch tip. Measurement is made of the voltage between the cathode and the workpiece, and that voltage is compared to an input for controlling torch height. During transferred arc operation, a reference is initially created by storing the cathode-to-workpiece voltage occurring immediately after the transferred arc is turned on, and using the latter stored voltage as a reference for torch height maintenance.

Growing community of inventors

Hanover, NH, United States of America

Raymond G Wilkins