The Consumable Stack
Besides the torch or torch body a typical mechanized plasma system has upwards of seven components that make up what is commonly referred to as the consumable stack. Each manufacturer may call these items by a different name, but for purposes of this article we will use the most common names. Proper installation and maintenance of these consumables are critical for proper plasma cutting. If any of the consumable stack is incorrectly installed or worn out it can cause imprecise size, bevel or edge quality. The following is a list of a typical consumable stack and a brief description of their purpose.
Provides coolant to tip of the electrode to prevent overheating and failure. It is extremely important to use the proper sized water tube. An improper water tube can cause premature electrode failure due to overheating and electrical short circuiting.
The main purpose of the electrode is to provide power to the plasma arc, basically connecting to the negative output of the plasma power supply. Secondly the electrode conducts high voltage or high frequency (HF) energy during the initial start of the cut. This adds electricity or energy to ionize the cutting gas, creating plasma and allowing the arc to start.
Features of an Electrode
The Hafnium emitter or insert, is the most critical component. This allows for HF to start the arc. It also keeps the arc centered on the nozzle orifice.
Bore and Step are internally machined components that allow for proper coolant flow throughout the electrode to increase the life of the Hafnium emitter or insert.
Finally, the threads and shoulder ensure the proper alignment of the electrode.
Typically made from ceramic or volcanic ash, a swirl ring controls and swirls the plasma gas around the electrode and into the nozzle. This controls the point where the arc is attached to the emitter. It also controls the plasma flow through the nozzle affecting the edge angularity. Further the swirl ring insulates the nozzle from the electrode and aligns the emitter and nozzle orifice.
A swirl ring will usually swirl the gas in a clockwise rotation, but counter-clockwise swirl rings are available to assist with mirror cutting.
Nozzles are designed to constrict the gas stream flowing through the orifice in the center of the nozzle. This focuses the plasma arc which directly affects the size of the part or the kerf. A nozzle that is improper or worn out will cause the part to have improper edges and or size. The orifice should be a perfect circle and not be oval or egg shaped.
Inner Retaining Cap
The main purpose of the inner retaining cap is to hold all the internal stack up components in proper alignment. An improper or damaged inner retainer will cause the rest of the consumable stack to seat improperly. This can cause coolant leaks, gas errors and or poor cut quality.
Just like its name, a shield protects all of the other consumables from sparks and molten metal. Most shields are made of copper and also provide the proper stand off distance between the nozzle and the work piece. A damaged or improper shield can cause poor cut quality and irregular bevel issues.
Outer Retaining Cap or Shield Cap
Holds all consumables in place and in conjunction with the shield protects them from sparks and molten metal. Shield caps are made from many different materials that are designed to withstand the high temperatures associated with todays mechanized plasma cutting.
As you can see, there are many components involved with a modern mechanized plasma torch. Each consumable component is as important as the other. In order to achieve the best performance, each component must be maintained properly and changed when it begins to have excessive wear. Some parts like the water tube and swirl ring will be changed less often than others, like the electrode and nozzle. Consult your manufacturers recommendations and best practices to determine what your system requirements are.