Plasmatron. Schemes, Classification

There are many methods of compression of the plasma arc torches cooling method, etc. In this article various (schematic) of the plasmatrons are identified and categorized.

When you create a torch first step is to formulate a scheme of his unit. Based on the characteristics of the process and conditions of the plasma torch system to select cooling, type of current, the plasma-forming medium, form and material of the electrode, a method for stabilizing the arc movement of the electrode spots, etc. Various schemes of plasma torches is most conveniently written in the form of classification (Figure ..) This classification is made in such a way that one of the options for each sub-section is a necessary element of a compound of the general scheme of the plasma torch of any kind.

First of all, all torches are divided into two groups by type of arc (see Fig.) arc plasma torches with the direct and indirect effects (Schemes 1 and 2). The difference between the thermal properties of both types of plasma torches and their applications have already been discussed above.

Classification criteria for torches

As the cooling system of the electrode and nozzle plasma torches are also divided into two main types: air-and water-cooled (schemes 3 and 4). The specific heat of water is much higher heat capacity of air and other gases. Therefore, the most effective and commonly used is a water cooling system, which allowed for high thermal load on the electrode and nozzle, ie, normal operation is ensured by the plasma torch at high currents and high degree of compression of the plasma arc. However, water-cooled somewhat complicates the design of plasma torch aggravate it because of the presence of water-supply hose and increases the cost of operating a plasma set. Clean water significantly affects the efficiency of heat dissipation. At high flow rates of water it is advisable to equip the installation of plasma circulating cooling system using distilled water to prevent scale formation. Air cooling system due to poor performance is used rarely, primarily for cooling maloampernyh plasma torches and hand-held plasma cutters designed for installation work in winter conditions. In these cutters operating current is typically less than a 300-400. In both systems the cooling medium is most consistently the electrode and nozzle assembly through the insulating body of the plasma torch. An important role in terms of cooling efficiency is the profile of the cavities of cooling, temperature and pressure are supplied to the torch coolant. The main task in selecting the cooling system is to maximize the intensity of the intensity of heat-walled nozzle, since the higher the heat flux, Exhaust nozzle, the steeper the temperature gradient of the gas layer between the arc column and the walls of the nozzle channel and, hence, the higher current density and power of the arc column.

Classification of torches on the methods of stabilizing the arc

Plasma torches can be categorized, and by the method of stabilization of the arc . The stabilization system of the arc, which provides compression and strong pillar of his fixation on the axis of the electrode and the plasma torch nozzle is the most important element of the plasma torch. There are three types of stabilization of the arc: gas, water, and magnetic. The simplest and most common is the stabilization of the gas in which the outer layer of cold working plasma gas, washing the walls of the arc column cools and compresses it. Thus, depending on the method of gas supply (parallel or perpendicular to the axis of the column) cement stabilization can be axial or vortex (schemes 5 and 6). The greatest reduction is achieved at the vortex of the arc to stabilize it, so this method is mainly used in plasma torches for cutting and spraying. When the axial stabilization gas flow blowing the arc column, has a calm, laminar, which provides the best conditions for the protection of heated products from the environment. Therefore, axial stabilization is used in plasma torches for welding and surfacing. Sometimes using a double stabilization of the arc (Figure 7), which combines axial gas flow through the primary and secondary vortex flow through the nozzle or vice versa. You can stabilize the arc column, washing it down with water spray (Figure 8). Formed from the steam jet is plasma-forming medium. When the water stabilization can be achieved the highest degree of compression and temperature of the arc column to 50 000 ° C. However, the presence of water vapor near the cathode region leads to an intense burning of any materials from the electrodes. In the plasma torches with water stabilization, designed for cutting, using a graphite electrode is moved automatically to the extent of its combustion. Plasma torches with water stabilization are complex structures, low reliability of the automatic feed control electrode and the complexity of the modes of excitation of the arc. Magnetic stabilization (Figure 9), which is created when a longitudinal magnetic field, compressing the arc column is less efficient than gas and water. Also, put the nozzle solenoid complicates the design of plasma torch. The advantage of the magnetic method of stabilization is the ability to control the degree of compression of the arc column, regardless of the working gas flow rate, while for the gas and water stabilization of the working gas is both a plasma-forming and stabilizing. In practice, the imposition of a longitudinal magnetic field is applied not only to stabilize the arc, but for the rotation of the anode spot on the inner walls of the nozzle to increase the resistance of the latter. For example, in the plasma torches used for the deposition of the magnetic rotation of the anode spot gas-vortex method can significantly reduce the erosion of the nozzle, and therefore contamination of the plasma jet.

See also:
Plasma Welding
Plasma Welding Introduction
Plasma Welding Technique
Microplasma Welding
Gases for plasma processing of materials
Separation of plasma jet cutting
Compression of the arc
The energy properties of the plasma arc
Rationalization of plasma welding
Plasma welding and spraying
The plasma melting and remelting
Plasmatron. Requirements for plasmatron
Plasmatron. Schemes, classification
Classification by type of electrode plasma torches
Classification of torches by the nature of the current
Structure of the plasmatron basic units