Patent DE-102013221178-A1 (DE)
Title: Initiating plasma arc in plasma cutting system by selectively closing valve in lead line, establishing decayable volume of gas in second segment of lead line, and initiating arc when pressure of decayable volume reaches pressure value
Inventor: MATHER JONATHAN
IPC: B23K10/00
Filed: 2013-10-18
Abstract: The method comprises providing a plasma gas supply lead line extending between a power supply and a plasma arc cutting torch, providing an in-line valve within the lead line between first and second segments of the lead line, selectively closing the in-line valve, by a controller, to capture a static volume of gas in the first segment, establishing a decayable volume of gas in the second segment, and initiating the plasma arc when a pressure of decayable volume reaches a pressure value within a predetermined range. The first segment is provided proximate to the power supply. The method comprises providing a plasma gas supply lead line extending between a power supply and a plasma arc cutting torch, providing an in-line valve within the lead line between first and second segments of the lead line, selectively closing the in-line valve, by a controller, to capture a static volume of gas in the first segment, establishing a decayable volume of gas in the second segment, and initiating the plasma arc when a pressure of decayable volume reaches a pressure value within a predetermined range. The first segment is provided proximate to the power supply, and a second segment is provided proximate to the torch. The first segment and the second segment are a part of a hose that carries a pilot gas flow and cutting gas flow. The method further comprises changing the pressure of the gas through the plasma gas supply lead line to the plasma arc cutting torch in a controlled manner to establish a gas flow rate for plasma cutting after initiation of the arc, connecting gas sources to the plasma arc cutting torch through plasma gas supply lines, controlling the in-line valve with a digital signal processor that provides an output to the in-line valve such that the in-line valve is controlled based on the output from the digital signal processor, changing one of the in-line valve or a supply valve to a first position for adjusting a flow of the gas to the plasma arc cutting torch, establishing a cutting pressure in the second segment after a transient pressure in the second segment increases to a cutting pressure level, increasing a plasma arc current to a pre-determined level, measuring a first time for the pressure in the second segment to reach a proportion of a set value for a first known length and inner diameter of the gas in the plasma gas supply lead line, measuring a second time for the pressure in the second segment to reach a proportion of a set value for a second known length and inner diameter of the plasma gas supply lead line, and calculating a length of the plasma gas supply lead line based on the difference between the second time and the first time, changing the in-line valve to a first position for increasing a flow of the gas to the plasma arc cutting torch such that a transient pressure in the second segment increases before pressure dissipation through a plasma chamber of the plasma arc cutting torch, igniting the plasma arc cutting torch when the transient pressure in the second segment reaches a value within the predetermined range, flowing the plasma gas to the plasma arc torch through the plasma gas supply line and the in-line valve within the plasma gas supply line in the first position for generating a first pressure in the segment of the plasma gas supply line between the in-line valve and the plasma arc torch, changing the in-line valve to a second position to adjust the flow of the plasma gas to the plasma arc torch and generating a second pressure that varies over time in the segment between the in-line valve and the plasma arc torch, initiating the plasma arc when the varying second pressure reaches a pressure value within a predetermined range, increasing an arc current to a pre-determined level, changing the in-line valve to a first position thereby adjusting the flow of the plasma gas to the plasma arc torch, and establishing the cutting pressure when the second pressure increases to a stable cutting pressure level. A position of the in-line valve is open and a second position of the in-line valve is closed. The difference between the second time and the first time is proportional to the difference between the amount of gas in the second known length and the first known length of the plasma gas supply lead line. Each plasma gas supply line has an in-line solenoid valve. A lower value of the predetermined range is 9 psi, and an upper value of the predetermined range is 50 psi. The plasma power supply is coupled to the torch by the lead line. Independent claims are included for: (1) a plasma cutting system; and (2) a method for operating a plasma torch system.