<\/figure>\n\n\n\nThe plasma arc cutting utilizes direct current, with the electrode connected to the negative terminal, and work-piece to the positive terminal (that is DCEN polarity). The hot ionized column of plasma issues from the constricting nozzle at a high speed. In the transferred arc mode, the arc is struck between the electrode placed inside the nozzle and the work-piece.<\/p>\n\n\n\n
However, the arc is made possible by a pilot arc that is struck first between the electrode and the constricting nozzle. The nozzle is connected to the ground terminal, and the pilot arc is initiated by a high-frequency generator connected to the electrode. This arc is maintained for a while, till the orifice gas blows through the orifice and establishes a low resistance path for striking the arc between electrode and work-piece.<\/p>\n\n\n\n
When the main arc is struck, system controls open the relay of pilot arc so that unnecessary heating of the constricting nozzle is avoided.<\/p>\n\n\n\n
Very high temperatures of the order of 18000\u00b0F to 25000\u00b0F (10000\u00b0C to 14000\u00b0C) are generated during the plasma arc cutting operation. Hence an active supply of cooling water needs to be circulated in the nozzle. The nozzle is made of a copper alloy. This enables cooling rapidly.<\/p>\n\n\n\n
The latest developments in plasma arc cutting permit several variations of the process to cater to different applications. Some of the variations are discussed below:<\/p>\n\n\n\n
Dual flow plasma cutting<\/h2>\n\n\n\n In this variation, a blanket of shielding gas is provided around the plasma. This gas is supplied through the shielding gas nozzle which lies outside to constricting nozzle.<\/p>\n\n\n\n
The gas supplied through the orifice of the constricting nozzle is generally nitrogen. The choice of the secondary shielding gas depends on the material to be cut. For aluminium it is an argon-hydrogen mixture, while for mild steels and stainless steel \u2013 carbon dioxide gas may be used.<\/p>\n\n\n\n
Using the secondary shielding gas enables slightly higher speeds for mild steel. However, for some metals, the quality of the cut is not up to the mark.<\/p>\n\n\n\n <\/figure>\n\n\n\nWater shield plasma cutting<\/h2>\n\n\n\n This variation is same as the dual flow plasma arc cutting described above, except that water is used instead of the shielding gas. This improves the life of nozzle, however cut sharpness and speed show not much improvement.<\/p>\n\n\n\n
Water injection plasma cutting<\/h2>\n\n\n\n In this variation of the plasma arc cutting, a symmetrical water jet impinges concurrent to the main arc around the constricting nozzle. The water blanket provides shielding to the plasma from the atmospheric gases, and further constricts the plasma stream.<\/p>\n\n\n\n
The end of the nozzle beyond the water blanket is made of ceramic material, so that a double arc is not struck.<\/p>\n\n\n\n
This water constricted plasma produces a narrow sharply defined cut. Higher speeds than the conventional plasma arc cutting can be deployed.<\/p>\n\n\n\n
When the orifice gas and shielding water are injected at a tangent, the plasma gas emerging from the nozzle has a swirling motion. This produces a sharp corner on one of the parts and a bevel on the other part. This type of behaviour is advantageous sometimes, when a bevel is desired on one of the parts.<\/p>\n\n\n\n <\/figure>\n\n\n\nWhen high current is required to be done, the torch is mounted on a mechanically driven carriage rather than hand held. When high currents are used, a water spray surrounding the plasma performs the function of reducing smoke and noise emanating from the cutting operation.<\/p>\n\n\n\n
Sometimes, worktables that have water in contact with the underside of the metal being are also used. The water on the underside reduces smoke and noise.<\/p>\n\n\n\n
Other Aspects Of Plasma Arc Cutting Equipment<\/h2>\n\n\n\n The plasma arc cutting can be used to cut metals in all positions. The torch used in the process, as described in above paragraphs, is not of the same design as the plasma arc welding torch, but is of a different design. PAC can also be used for piercing holes, and for gounging metal.<\/p>\n\n\n\n
The metals that are generally cut using plasma arc cutting are aluminium and stainless steel, although it can also be used for cutting copper alloys, carbon steel, and nickel alloys.<\/p>\n\n\n\n
The control console comes equipped with special controls for regulating the plasma gas flow rate and the shielding gas flow rate. A water flow switch is provided to keep tabs on the level of cooling water in circulation. If the level falls below a certain level, the switch turns the operation off.<\/p>\n\n\n\n
In automatic operation, the PAC torch fits inside an automatic flame cutting machine which guides the movement of the torch.<\/p>\n\n\n\n
The cutting action generates a good amount of gases. So the cutting work should be done in an area having adequate ventilation. Also, lot of noise gets generated during cutting. Hence ear protection should be worn, especially when working with equipment using high electrical power.<\/p>\n\n\n\n
The cutting operator should wear ear protection. The normal protective clothing must also be worn to protect the operator from the sparks. Other personnel protective equipment such as helmet, gloves are also necessary for safety. The filter glass used in the helmet should be of shade 9 rating.<\/p>\n\n\n\n
Applications<\/h2>\n\n\n\n Plasma arc cutting produces sharp cuts of high quality. It is generally used for cutting of stainless steel, aluminium, and carbon steel. Cutting operations towards both production work and maintenance work can be undertaken with PAC. It is used for bevelling a plate in preparation for fit up in a welding joint, or for stack cutting, for shape cutting, or for piercing holes, plasma gouging<\/a>, etc.<\/p>\n\n\n\nThe stack cutting done with a plasma arc cutting torch is more efficient than that with an oxyacetylene torch.<\/p>\n\n\n\n
So this was about plasma arc cutting in brief. Please leave your thoughts in the comments section below.<\/a><\/p>\n\n\n\n