Plasma Cutters (for cutting torches)

The plasma torch (torch or a plasma torch to cut) - a device for forming plasma cutting, connected to the power source.

Plasma torches (torch) ESAB PT-27, Hypertherm T80 manual plasma cutting and P3-400VA for mechanized cutting

The main components of the plasma torch:

• electrode with the electrode;
• nozzle, forming a plasma arc or plasma jet;
• arc chamber for plasma formation;
• insulator separating the electrode and nozzle units;
• of gas and water supply.

Many cutters also has a twist knot, which provides a vortex (tangential) flow of plasma-forming gas in the arc chamber to compress and stabilize the arc.

Manual plasma cutter apparatus MULTIPLAZ-15000 

The design of plasma torch TD-300 for mechanized cutting

The main types of plasma torches
The design concept of a plasma torch and the design of its elements depend on the working environment, the method of its submission to the arc chamber, the arc ignition and cooling systems. The main types of plasma torches (torches):

• for inert (argon, helium) and reducing (nitrogen, hydrogen) gases;
• for oxidizing gases - containing oxygen;
• double flow - for inert, reducing and oxidizing environments;
• with the gas-liquid stabilization of arc.

Plasma torches with water and a magnetic arc stabilization have limited application.

The simplest are the torches for inert (neutral) and reducing gases.

Insulated nozzle and cathodic sites form an arc chamber forming a channel. In the end face of the camera is placed tungsten cathode, stabilized by oxides of lanthanum, yttrium, thorium, or any other impurities that increase the emission properties and resistance against the tungsten interactions at high temperatures with active gases (oxygen, air, etc.). The cathode is worn under the influence of heat released in the cathode region of the arc.

The cathodes are usually made of tungsten in the form of rods with a diameter of 3-6 mm and a length of 50-150 mm, or short cylindrical inserts with a diameter of 2-3 mm and a length of 5-6 mm. In plasma cutters with tungsten cathode rod, held in a clamp or chuck, work environment is usually fed coaxial cathode. Working part of the cathode rod sharpened to fix the arc cathode spot. Due to the coaxial (axial) gas arc can be stretched to greater length at a lower operating voltage, which is important for manual plasma cutting and cutting of thick metal.

Widespread machine and hand-held plasma cutter with gilzovymi cathodes.

Insert a refractory material pressed into a channel-liners katoderzhatelya of copper or another heat-conducting metal. Shank sleeves intensively cooled by air or water, which improves the cooling of the cathode and increase the life of the cathode insert. Butt gilzovyh cathodes are usually flat. The arc is stabilized by a swirling flow of gas. Vortex captures the arc cathode region in the center of the butt paste. The active arc spot to form a paste wears gradually deepening of the cavity. The diameter and depth of the cavity depend on the intensity of the heat input to the cathode and the cooling heat-transfer medium.

Gilzovye cathodes are widely used in plasma cutters that use as a working medium compressed air. The cathode paste of refractory metals - zirconium and hafnium - at high temperatures form a stable arc based on a film of refractory oxides and nitrides, which protects the metal from pure evaporation. These cathodes are called film or plenkozaschitnymi. The existence of the cathode spot due to the high emissivity and low electrical resistance of films of oxides and nitrides at high temperatures. Regular wear of cathode spots is due to the evaporation of oxide-nitride melt, and a one-time, more substantial - with the ignition of the arc due to the destruction of the film by thermal shock.

Plasma cutters with film cathodes are also used for cutting in oxygen. At the same cathode resistance is somewhat lower.

For a vortex (tangential) feed gas in the plasma arc chamber plasma torch used zavihritelnye device. In the simplest case, the functions performed swirler body of the plasma torch, and the working gas is fed into the arc chamber through the derived tangential to its walls. Effective use of rings or washers zavihritelnyh of heat-resistant ceramic, placed in front of the nozzle. Their disadvantage is the low strength of ceramics. As the rotator itself can act nozzle. Rational design of swirler, made ​​in the form of a screw thread on the outer surface of the electrode, which is set firmly in the socket body of the plasma torch.

When cutting in oxidizing environments also use plasma torches with hollow (hollow) cylindrical cathode made ​​of copper , heavily water-cooled. The plasma torch has a system of vortex stabilization of the arc. The cathode is distributed - under the influence of the vortex cathode spot moves rapidly to the inner surface of the cylindrical cathode, without destroying it.

Two-flow plasma torches equipped with two coaxial nozzles - internal and external (protective cap). Gas flowing into the inner nozzle, conventionally called the primary, in the outer - a secondary or supplementary. Primary and secondary gases may have a different structure, function and flow. As the electrodes are used as tungsten and plenkozaschitnye cathodes.

In the double-flow plasma torches with rod tungsten cathode primary gas (nitrogen or argon) is fed into the inner nozzle protects the tungsten electrode from oxidation. In the outer nozzle enters the working oxidizing gas - air or oxygen. The working part of the cathode can be placed in the cavity under the internal nozzle or between nozzles. In the first scheme, the plasma becomes mainly a protective gas and oxidizing gas is used mainly to stabilize the arc. In the second case it is possible to obtain a plasma stream with a high oxygen content.

Plenkozaschitnye cathodes, for example, used plasma cutters Hypertherm (series HSD, HT, HPR, and others). At the same protection (optional), the gas provides the following functions:

• plasma torch protection against splashes of molten metal during the punching of holes;
• prevents the formation of a "double" of the arc;
• additional compression of the arc, which increases the specific energy density, makes the cut thinner and reduces melting at acute angles;
• promotes the formation of almost perpendicular to the cut with a sharp upper edge without melting, and absent or small burr from the bottom.

Quite common to gas-liquid plasma cutter arc stabilization . They are forming a system is usually similar to the inert or reducing gas, an active gas-or double plasma torches, with the difference that the nozzle assembly has a system of canals to supply water to the compressed arc column. In order to stabilize the arc and gas-liquid two-phase flow is used, which is administered primarily by double-beam pattern of the plasma torch. The amount of water that stabilizes the arc set such that the water is completely evaporated. In gas-liquid stabilization of arc increases the concentration of energy in the arc column and increase its cutting properties. Due to the fluid in the nozzle forming conditions improve cooling. When cutting with the use of water-air stabilize the steel edge is less saturated with nitrogen than with air-plasma cutting.

In addition to the plasma torches with gas-liquid stabilization of arc using plasma torches with water spray and liquid-gas cooling system . In the cutters with the water spray system with water channels around the pole of the arc formed by a water jacket. The water cools the edge of the treated metal, which minimizes the heat-affected zone. The level of noise, the selection of aerosol and radiation for cutting.

The nozzle of the plasma torch is designed to form the cutting arc. The shape and size of the nozzle channel parameters and determine the properties of the arc. With a decrease in its diameter and increasing the length of the flow rate increased the plasma concentration of energy in the arc, its power and cutting ability. The longer retained the shape and size of the nozzle, the longer its life.

The nozzle is the most heat-stressed part of the plasma torch. To channel between the walls of the nozzle and the plasma flow in the column of a powerful arc (with a temperature of 10000-20000 ° C and above) present a layer of relatively cool gas, current and gas flow rate is selected according to the diameter and length of the nozzle. The best material for the manufacture of nozzles - high-purity copper having a high thermal conductivity and relatively low cost. In most cases, cooling nozzle, a system of water channels. When cutting thin arcs cooled torch nozzle can be a gas.

See also:
manual plasma cutting apparatus
plasma cutting machines
plasma cutting
plasma cutting
plasma welding technology