Multi-Gas Plasma Arc Torch Gas Transition Method
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Solution Overview
Problem
Multi-gas plasma arc torches experience poor cut quality due to the time required to replace pre-flow gas with plasma gas, resulting in excessive dross, wide kerf width, and large cut surface angles, particularly at low current processes, small nozzle orifice sizes, high pre-flow pressures, or low plasma pressures.
Innovation Solution
A method involving the directed pre-flow gas within the plasma arc torch, switching to a plasma gas, and adjusting gas pressure to preferred values during cutting or marking operations, with options to generate the pilot arc before or after switching to the plasma gas and incorporating a time delay for optimal arc transfer and gas replacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pre-flow gas is used to initiate pilot arc, then arc ignition is reliable, but cut quality deteriorates due to slow gas replacement
Solution Approach 1:
The patent introduces a pre-flow gas passage that delivers pre-flow gas to the plasma gas inlet before the main plasma gas flow begins. This preliminary action ensures the pilot arc can be reliably ignited with the less reactive pre-flow gas, while the system is already prepared for the rapid transition to plasma gas, thus resolving the contradiction between reliable ignition and fast gas replacement.
Solution Approach 2:
The gas delivery system is segmented into separate pre-flow gas and plasma gas pathways. The pre-flow gas flows through a dedicated pre-flow passage to the inlet, while plasma gas flows through the main plasma gas passage. This segmentation allows independent control of each gas flow, enabling the pre-flow gas to be quickly displaced by plasma gas without compromising pilot arc stability during the transition.
2Stability of the object's composition
If pre-flow pressure is increased to improve pilot arc stability, then arc stability improves, but gas replacement time increases
Solution Approach 1:
The patent employs dynamic control of gas pressures and flows during the transition from pre-flow to plasma gas. The pre-flow gas pressure can be maintained at a higher level for pilot arc stability, while the plasma gas flow is dynamically increased to rapidly displace the pre-flow gas. This dynamic adjustment allows the system to maintain stability when needed while achieving fast replacement when the transition occurs.
3Manufacturing precision
If nozzle orifice size is reduced for low current processes, then cutting precision improves, but gas replacement becomes slower
Solution Approach 1:
The patent provides different gas flow paths and pressure controls for different regions of the torch system. The pre-flow gas and plasma gas can be delivered with different pressures and flow rates optimized for their specific functions. This local optimization allows the small orifice to maintain precise cutting while the upstream gas delivery system compensates for the slower replacement rate by creating a more efficient displacement flow.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method reduces the time delay in transitioning from pre-flow to cutting stage, improving cut quality by ensuring complete gas replacement and optimal operating parameters are met sooner, especially beneficial for low amperage and small orifice plasma arc torches.
Implementation Method 1
directing a pre-flow gas within the plasma arc torch, switching to a plasma gas that is different from the pre-flow gas
Implementation Method 2
changing the pressure of the plasma gas to a value that is preferred during the cutting or marking operation
Implementation Method 3
a pilot arc is created in the gap between the electrode and the tip, often referred to as the plasma arc chamber, wherein the pilot arc heats and ionizes the gas
Implementation Method 4
the pilot arc heats and ionizes the gas. The ionized gas is blown out of the torch and appears as a plasma stream
Data Source
AI summary
A method of starting a multi-gas plasma arc torch for cutting a workpiece is provided that includes directing a pre-flow gas within the plasma arc torch and switching the pre-flow gas to a plasma gas before a pilot arc is transferred to the workpiece. The plasma gas is supplied initially at a first gas pressure when the pre-flow gas is switched to the plasma gas. The gas pressure is switched to a second gas pressure that is different than the first gas pressure after the pilot arc is transferred. The method provides a smooth transition from the pre-flow gas to the plasma gas and reduces the time delay in replacing the pre-flow gas with the plasma gas in the plasma arc torch, thereby improving cut or marking quality.