The arc plasma forms as a result of the electrical heating of any gas to a very high temperature so that its atoms are ionized and conduct electricity.

The plasma arc torch consists of an electrode surrounded by a constricting nozzle which forms a plenum chamber around the electrode. The plasma gas flows through this chamber and is heated and ionized by an electric current between the electrode and the nozzle or the work. The heating causes the gas to expand greatly and exit a small orifice at the end of the nozzle at big b velocity. A pilot arc or high-frequency spark is required to start the main arc.

The plasma gas exits from the nozzle at very high speeds and temperatures; up to 16,000°C (30 000°F) and 6000 m/s (20 000 ft/s). The energy of the arc is concentrated in a small area and thereby produces very rapid beating of the workpiece it impinges.

There are two forms of plasma arc torch operation: transferred arc and non-transferred arc. In the transferred arc mode, the arc current flows between the electrode and the work. This mode of operation is used for welding and cutting. In the non-transferred arc version, the current flows from the electrode to the torch nozzle. The arc within the nozzle heats the plasma gas which exits the nozzle at high speed. This mode of operation is used for plasma spraying powder, where no electrical connection is made with the work. The extreme heat of the arc is absorbed partly by the water cooled nozzle and partly by the plasma gas on ionization.

When the ionized gas strikes the workpiece, it gives up its energy to supply heat to the workpiece as it returns to the normal gaseous state.

PLASMA ARC CUTTING (PAC)

An arc cutting process that uses a constricted arc and removes the molten metal with a high velocity jet of ionized gas issuing from the constricting orifice.

Plasma arc cutting produces fast, high-quality cuts that often require no further finishing. It accomplishes this by passing an electric current through a column of gas, causing it to ionize and become plasma. The resulting plasma produces temperatures up to 16000°C (30000°F). This causes the gas to expand and results in high-velocity flow through the torch orifice. When this high-temperature plasma arc stream strikes a workpiece, it melts the metal rapidly, and the high-velocity jet blows it away. The process makes clean cuts and forms little or no dross or slag on most metals, requires no preheat, and produces a minimum heat-affected zone, with little or no distortion.

While oxyfuel gas cutting is limited to metals which combine with oxygen at elevated temperatures, plasma arc cutting is not limited to this chemical reaction: it is only limited to materials which are electrical conductors.

Historical Background

PAC was invented in the mid 1950s and became commercially successful shortly after its introduction to industry. The ability of the process to sever any electrically conductive material made it especially attractive for cutting nonferrous metals that could not be cut by the oxyfuel cutting (OFC) process. It was initially used for cutting stainless steel and aluminum. As the cutting process was developed, it was found that it had advantages over other cutting processes for cutting carbon steel as well as nonferrous metals .

Advantages and Limitations

Advantages. When compared to mechanical cutting processes, the amount of force required to hold the workpiece in place and move the torch (or vice versa) is much lower with the “non-contact” plasma arc cutting process. Compared to OFC, the plasma cutting process operates at a much higher energy level, resulting in faster cutting speed. In addition to its higher speed, PAC has the advantage of instant start-up without requiring preheat. Instantaneous starting is particularly advantageous for applications involving interrupted cutting, such as severing mesh.

Limitations. There are notable limitations to PAC. When compared to most mechanical cutting means, PAC introduces hazards such as fire, electric shock, intense light, fumes and gases, and noise levels that may not be present with mechanical processes. It is also difficult to control PAC as precisely as some mechanical processes for close tolerance work. When compared to OFC, the PAC equipment tends to be more expensive, requires a fairly large amount of electric power, and introduces electrical shock hazards.

El arco de plasma se forma como resultado del calentamiento eléctrico de cualquier gas a una temperatura muy alta de manera que sus átomos sean ionizados y conduzcan electricidad.

La antorcha de arco de plasma consiste en un electrodo rodeado por una boquilla constreñida que forma una cámara del pleno alrededor del electrodo. El gas de plasma atraviesa este compartimiento y es calentado y ionizado por una corriente eléctrica entre el electrodo y la boquilla o el elemento de trabajo. La calefacción hace que el gas se expanda fuertemente y salga por un pequeño orificio en el extremo de la boquilla a gran velocidad. Un arco piloto o una chispa de alta frecuencia se requieren para encender el arco principal. El gas de plasma sale de la boquilla a velocidades y temperaturas muy elevadas; hasta 16.000°C (30 000°F) y 6000 m/s (20 000 ft/s). La energía del arco se concentra en un área pequeña de tal modo que produce un choque muy rápido sobre el objeto en el que incide.

Hay dos formas de operación de la antorcha del arco de plasma: arco transferido y arco no-transferido. En el modo de arco transferido, la corriente del arco fluye entre el electrodo y el objeto de trabajo. Este modo de operación se utiliza para la soldadura y el corte. En la versión de arco no-transferida, la corriente fluye del electrodo a la boquilla de la antorcha. El arco dentro de la boquilla calienta el gas del plasma que sale de la boquilla a alta velocidad. Este modo de operación se utiliza para la proyección con plasma de polvo, donde no se hace ninguna conexión eléctrica con el objeto de trabajo. El calor extremo del arco es absorbido en parte por la boquilla refrigerada por agua y en parte por el gas de plasma en la ionización.

Cuando el gas ionizado pega sobre el objeto, entrega su energía para suministrar calor al objeto de trabajo a medida que vuelve al estado gaseoso normal.

CORTE CON ARCO DE PLASMA (PAC)

Es un proceso de corte con arco de plasma que utiliza un arco constreñido o estrechado y quita el metal fundido con un chorro de alta velocidad del gas ionizado que proveniente del orificio constreñido.

El corte al arco de plasma produce cortes rápidos, de alta calidad que a menudo no requieren ningún otro acabado. Se logra esto pasando una corriente eléctrica a través de una columna de gas, haciéndola ionizar y convertirse en plasma. El plasma resultante produce temperaturas de hasta 16000°C (30000°F). Esto hace que el gas se expanda y resulte un chorro de alta velocidad que atraviesa el orificio de la antorcha. Cuando esta corriente de alta temperatura del arco de plasma incide sobre un objeto, derrite el metal rápidamente, y el chorro de alta velocidad lo barre limpiándolo. El proceso hace cortes limpios y forma poca o ninguna escoria de metal o restos de metal fundido en la mayoría de los metales, no requiere ningún precalentamiento, y produce una zona afectada por el calor mínima, con poco o nada de distorsión.

Mientras que el corte de gas del combustible oxigenado se limita a los metales que se combinan con oxígeno a temperaturas elevadas, el corte al arco de plasma no se limita a esta reacción química: se limita solamente a los materiales que son conductores eléctricos.

Antecedentes históricos

El corte con arco de plasma fue inventado a mediados de los años cincuenta y llegó a ser comercialmente exitoso poco después de su introducción en la industria. La capacidad del proceso de separar cualquier material eléctricamente conductor lo hizo especialmente atractivo para el corte de metales no ferrosos que no se podrían cortar por el proceso del corte con combustible oxigenado (OFC). Fue utilizado inicialmente para corte del acero inoxidable y el aluminio. A medida que el proceso de corte fue desarrollado, se determinó que tenía ventajas sobre otros procesos de corte para cortar el acero al carbón así como los metales no ferrosos.

Ventajas y limitaciones

Ventajas. Cuando se compara con los procesos mecánicos de corte, la fuerza requerida para sostener el objeto en el lugar y para mover la antorcha (o viceversa) es mucho más baja que con el proceso “sin contacto” de corte al arco de plasma. Comparado con el corte con combustible oxigenado, el proceso de corte de plasma funciona con un nivel de energía mucho más alta, dando por resultado una velocidad de corte más rápida. Además de su velocidad más alta, el corte con arco de plasma tiene la ventaja del arranque inmediato sin requerir precalentamiento. El arranque instantáneo es particularmente ventajoso para aplicaciones que requieren un corte interrumpido, tal como separación de partes.

Limitaciones. Hay limitaciones notables en el corte con arco de plasma. Cuando se compara con mayoría de los medios mecánicos de corte, el corte con arco de plasma introduce peligros tales como el fuego, descarga eléctrica, niveles intensos de luz, humos y gas, y ruidos que puedan no estar presentes con procesos mecánicos. Es también difícil controlar el corte con arco de plasma tan precisamente como algunos procesos mecánicos por poca tolerancia de trabajo. Cuando se compara con el corte con combustible oxigenado, el equipo de corte con arco de plasma tiende a ser más costoso, requiere bastante más cantidad de energía eléctrica, e introduce peligros de descargas eléctricas.

Fig. 1 - Plasma arc torch teminology - Terminología de antorcha de plasma

Fig. 2 - Basic plasma arc cutting circuitry - Circuito básico de corte de plasma

« Previous 1 2 3 4 5 Next »

FREE SHIPPING Hobart Air Force 500i Plasma Cutter with MVP $1,299.99 The Hobart Air Force 500i plasma cutter features a multivoltage plug (MVP) that allows user to connect to common 120V or 230V power receptacles without tools. U.S.A. Cutting Thickness (in.): up to 5/8, Volts: 115/230, Amps: 27, Duty Cycle: 35% @ 27 Amps, Pilot Arc: Yes, Plasma Gas Flow/Pressure: 4.5 CFM @ 60 PSI, Clamp Cable Length (ft.): 16.5, Power Cord (ft.): 10, Cart: No, Dimensions L x W x H (in.): 14.25 x 8.25 x 11.25 Ergonomic trigger safety, more efficient air consumption and economically priced consumables [Read more] Store: Northern Tool and Equipment Brand: Hobart FREE SHIPPING Hobart Air Force 700i Plasma Cutter $1,499.99 The Hobart Air Force 700i plasma cutter can cut mild steel up to 7/8in. It provides a lightweight, powerful inverter design and an ergonomic trigger safety, with more efficient air consumption and economically priced consumables. U.S.A. Cutting Thickness (in.): up to 7/8, Volts: 230, Amps: 40, Duty Cycle: 60% @ 40 Amps, Pilot Arc: Yes, Plasma Gas Flow/Pressure: 6.0 CFM @ 75 PSI, Clamp Cable Length (ft.): 16.5, Power Cord (ft.): 10, Cart: No, Dimensions L x W x H (in.): 14.25 x 8.25 x 11.25 [Read more] Store: Northern Tool and Equipment Brand: Hobart Northern Industrial Angled Welding/Plasma Cart $79.99 Portable MIG/Plasma cart is designed to hold portable MIG welders and plasma cutters. Low center of gravity and slanted top shelf provide easy access to weld controls. Bottom shelf stores helmet, gloves, welding tools and consumables Rear shelf holds shielding gas cylinders up to 7 1/2in. dia. Cart includes front casters and rear wheels for easy mobility [Read more] Store: Northern Tool and Equipment Brand: Northern Industrial Welders Northern Industrial Replacement Nozzles for Plasma Cutter (Item# 164610) 3-Pk., Model# 2.20.04.902 $7.99 Northern Industrial replacement nozzles work with the Northern Industrial Plasma Cutter Model 375, Item# 164610. [Read more] Store: Northern Tool and Equipment Brand: Northern Industrial Welders Thermadyne Plasma Cutting Tip 80 Amp, Model# 80X19-3 $7.99 Thermal Dynamics 80 Amp drag cutting tips. Fits Cutmaster True Series 82. NOTE: Customer must order a minimum of 5 tips. U.S.A. [Read more] Store: Northern Tool and Equipment Brand: Thermal Dynamics Thermadyne Plasma Cutter Electrode, Model# 80X23-3 $9.99 Thermal Dynamics plasma cutting electrode. Fits Cutmaster True Series 82. NOTE: Customer must order a minimum of 5 tips. U.S.A. [Read more] Store: Northern Tool and Equipment Brand: Thermal Dynamics Applications of Laser-Plasma Interactions $111.00 <PRecent advances in the development of lasers with more energy, power, and brightness have opened up new possibilities for exciting applications. <STRONGApplications of LaserPlasma Interactions</STRONGreviews the current status of high power laser applications. </P<PThe book first explores the science and technology behind the ignition and burn of imploded fusion fuel, before describing novel particle accelerators. It then focuses on applications of high power x-ray sources and the development of x-ray lasers. The book also discusses how ultrahigh power lasers are used in nuclear and elementary particle physics applications as well as how the high power density of laserplasma interactions is used to study matter under extreme conditions. The final chapters deal with femtosecond lasers, presenting applications in materials processing and nanoparticles.</P<P</P<PWith contributions from a distinguished team of researchers, this work illustrates the many applications of high power lasers, highlighting their important roles in energy, biology, nanotechnology, and more.</P [Read more] Store: A1Books Advances In Plasma-grown Hydrogenated Films $251.44 Physics of Thin Films is one of the longest running continuing series in thin film science, consisting of 25 volumes since 1963... [Read more] Store: Indigo Books & Music (CA) Blood Plasma - A Medical Dictionary, Bibliography, and Annotated Research Guide to Internet References $48.95 This is a 3-in-1 reference book. It gives a complete medical dictionary covering hundreds of terms and expressions relating to blood plasma. It also gives extensive lists of bibliographic citations. Finally, it provides information to users on how to update their knowledge using various Internet resources. The book is designed for physicians, medical students preparing for Board examinations, medical researchers, and patients who want to become familiar with research dedicated to blood plasma. If your time is valuable, this book is for you. First, you will not waste time searching the Internet while missing a lot of relevant information. Second, the book also saves you time indexing and defining entries. Finally, you will not waste time and money printing hundreds of web pages. [Read more] Store: eBooks.com Frontiers in Dusty Plasmas $208.00 Around the time of the first "Earth Day, " on April 22, 1970, the academic world joined in a virtual explosion of societal interest in a topic that inherently lies in the confluence between "social problems" and "public policy" -- the ways in which humans use and abuse the natural environment. In the worlds of social movement organizations and policy, that newfound interest showed up in dramatic growth of environmental organizations and a stream of powerful new environmental laws. In the academic world, echoes of the explosion showed up in equally dramatic growth of interdisciplinary "environmental" programs with an explicit focus on the fact that "environmental problems" are inherently social problems as well. Over the past decade, a growing body of research has shown that equity issues need to receive greater attention in academia -- not just among activists, and not just as the focus of courses on environmental ethics, but as topics that deserve careful academic study and that in many ways are at the core of what we call "environmental" problems. As David Orr (1992) noted, "the symptoms of environmental deterioration are in the domain of the natural sciences, but the causes lie in the realm of the social sciences and humanities.". This volume is intended to call this research to attention, but also to encourage its further expansion; far from being the kind of topic that ought to be relegated to a small pigeonhole, issues of equity and inequality deserve to be absolutely central to the study of connections between humans and the habitat that we share with all other life on earth. Research in Social Problems and Public Policy is now available online at ScienceDirect full-text online from volume 8 onwards. [Read more] Store: eBooks.com Fundamentals of Plasma Physics $68.00 This rigorous explanation of plasmas is relevant to diverse plasma applications. More thorough than previous texts, it exploits new powerful techniques to develop deeper insights into plasma behavior. Written for advanced students, it explores a host of essential and advanced topics while emphasizing the fundamentals that apply to all plasmas. [Read more] Store: eBooks.com Glow Discharge Plasmas in Analytical Spectroscopy $280.00 This multi-author, edited volume includes chapters which deal with both basic and highly complex applications. Glow discharge devices are now being used in very novel ways for the analysis of liquids and gases, including molecular species detection and identification, an area that was beyond the perceived scope of applicability just ten years ago. It is expected that the next decade will see a growth in the interest and application of glow discharge devices far surpassing the expectations of the last century. [Read more] Store: eBooks.com Hadrons and Quark-Gluon Plasma $46.00 This book provides an accessible introduction to the rapidly expanding field of hadronic interactions and the quark-gluon plasma. Covering the basics as well as more advanced material, it is ideal for graduate students as well as researchers already working in this and related fields. [Read more] Store: eBooks.com High Density Plasma Sources $180.00 A description of the design, physics and performance of high density plasma sources used in plasma processing. [Read more] Store: eBooks.com - Lincoln Electric P20 Plasma Cutter, Model# K2820-1 $989.99 This Lincoln Electric 20 Plasma Cutter provides professional-grade results in a lightweight, portable plasma cutting system that can be carried anywhere with little effort. It can cut materials up to 1/4in. and operates on standard 115V household power. It is an ideal choice for the farm, HVAC, auto body shop, contractor, sheet metal fabricator or homeowner anyone who needs to cut metal. Cutting Thickness (in.): 1/4, Volts: 115, Amps: 20, Duty Cycle: 40% @ 20 Amps, Pilot Arc: Yes, Plasma Gas Flow/Pressure: 3.5 CFM @ 65 PSI, Clamp Cable Length (ft.): 9 1/2, Power Cord (ft.): 8, Cart: No, Dimensions L x W x H (in.): 16 x 6 1/2 x 12 1/2 Cuts up to 3/8in. mild steel and also cuts stainless steel and aluminum Uses standard compressed air, requiring 3.5 CFM @ 65 PSI Built-in air pressure regulator Includes cutting torch assembly with 9.5-ft. reach Saddle hooks for convenient storage [Read more] Store: Northern Tool and Equipment Brand: Lincoln Electric Northern Industrial Replacement Torch Cover for Plasma Cutter (Item# 164610), Model# 2.20.04.901 $16.99 The Northern Industrial replacement torch cover works with the Northern Industrial Plasma Cutter Model 375, Item# 164610. [Read more] Store: Northern Tool and Equipment Brand: Northern Industrial Welders Northern Industrial Replacement Electrodes-Tips for Plasma Cutter (Item# 164610) - 3-Pk., Model# 2.20.06.301 $10.99 Northern Industrial replacement electrodes-tips work with the Northern Industrial Plasma Cutter Model 375, Item# 164610. [Read more] Store: Northern Tool and Equipment Brand: Northern Industrial Welders - Thermadyne Plasma Cutter - 80 Amp, Model# SY106701111 $2,499.99 Lightweight and portable, the Cutmaster True Series 82 is easy to move from location to location, Connect to an air compressor and this easy-to-use system is ready to cut. U.S.A. Cutting Thickness (in.): Up to 1 1/2, depending on material, Amps: 80 Equipped with the patented 1Torch Recommended cut: 3/4in. Maximum cut: 1 1/2in. [Read more] Store: Northern Tool and Equipment Brand: Thermal Dynamics Hobart Airforce 700i Plasma Cutter Tip and Electrode Kit $13.99 This Hobart tip and electrode kit is designed specifically for use with the Hobart Airforce 700i Plasma Cutter. Includes 2 tips and 2 electrodes Works With: Hobart Airforce 700i [Read more] Store: Northern Tool and Equipment Brand: Hobart Northern Industrial Replacement Diffusers for Plasma Cutter (Item# 164610) - 3-Pk., Model# 2.07.42.010 $16.99 Northern Industrial replacement diffusers work with the Northern Industrial Plasma Cutter Model 375, Item# 164610. [Read more] Store: Northern Tool and Equipment Brand: Northern Industrial Welders Northern Industrial Plasma 375 Cutter $699.99 The Northern Industrial Plasma Cutter is a lightweight unit that features powerful inverter technology for smooth cutting. Handles almost any project you can thrown at it, from mild steel to copper, brass, stainless and aluminum up to 3/8in. Cutting Thickness (in.): Up to 3/8 (.375), depending on material, Volts: 230, Amps: 15-40, Duty Cycle: 35% at 40 Amps, Plasma Gas Flow/Pressure: 4.5 CFM @ 60 PSI required, Clamp Cable Length (ft.): 10, Cart: No Cuts electrically conductive material Cuts 3/8in. mild steel, 1/4in. aluminum, 1/4in. stainless steel, 1/4in. galvanized metal, 1/8in. copper and 1/8in. brass Uses shop air no special gases required Pilot arc feature for cutting fence and expanded metal Troubleshooting indicator lights Built-in air pressure gauge and pressure adjustment control NEMA 6-50P plug [Read more] Store: Northern Tool and Equipment Brand: Northern Industrial Welders - Hobart AirForce- 250CI Plasma Cutter - 12 Amps $799.99 The new AirForce 250CI plasma cutter with built-in air compressor features a new lightweight inverter design that is both lightweight and powerful. Built-in compressor for total portability and low system cost. Cuts mild steel up to 1/4in. thick using standard household current. New HP-25 torch is more comfortable, efficient and economical. U.S.A. Cutting Thickness (in.): Up to 1/4, depending on material, Volts: 115VAC, Amps: 20, Duty Cycle: 35% at 12 Amps, 110 Volts DC, Pilot Arc: Yes, Plasma Gas Flow/Pressure: Preset with built-in compressor, Clamp Cable Length (ft.): 16.4, Power Cord (ft.): 7, Cart: No, Dimensions L x W x H (in.): 7 1/2 x 13 x 10 New lightweight, powerful inverter design New HP-25 torch is more efficient and comfortable Built-in piston-driven air compressor Cuts mild steel up to 1/8in. @ 10in. per minute; 1/4in. mild steel @ 3in. per minute Also cuts stainless steel, aluminum, brass and copper Cable management strap secures torch and cables to make transportation easy and convenient Thermal overload protections Pilot arc start ensures constant arc start and minimizes tip burnout Post-Flow Cooling cools torch after cut to extend life of consumable tips and electrodes Fan-on-demand system runs only when needed Diagnostic LED lights indicate system status 5/3/1 Industrial Warranty 5 year warranty on transformers, stabilizers, reactors, rectifiers, rotors, stators and brushes 3 year warranty on drive systems, PC boards, solenoid valves, switches and controls 1 year warranty on MIG guns, plasma torches, relays, contactor, triggers, regulator, accessories, spool guns, battery, field options and running gear. (90 days for industrial use.) Normal wear items such as drive rolls, contact tips, nozzle, gas diffuser, plasma torch tips and electrodes and weld cables are not covered under warranty. Engine warranty is provided by the engine manufacturer. [Read more] Store: Northern Tool and Equipment Brand: Hobart Hobart Replacement Swirl Ring, Retaining Cup and O-Ring for Airforce 700i Plasma Cutter $19.99 This Hobart kit is designed specifically for use with the Airforce 700i Plasma Cutter. It includes a replacement swirl ring, retaining cup and O-ring. Works With: Hobart Airforce 700i [Read more] Store: Northern Tool and Equipment Brand: Hobart The Official Patient's Sourcebook on Plasma Cell Neoplasms $28.95 This book has been created for patients who have decided to make education and research an integral part of the treatment process. Although it also gives information useful to doctors, caregivers and other health professionals, it tells patients where and how to look for information covering virtually all topics related to plasma cell neoplasms (also Cancer multiple myeloma; Hyperglobulinemic Purpura; Kahler Disease; Macroglobulinemia; Macroglobulinemia primary; Malignant plasmacytoma), from the essentials to the most advanced areas of research. The title of this book includes the word official. This reflects the fact that the sourcebook draws from public, academic, government, and peer-reviewed research. Selected readings from various agencies are reproduced to give you some of the latest official information available to date on plasma cell neoplasms. Given patients' increasing sophistication in using the Internet, abundant references to reliable Internet-based resources are provided throughout this sourcebook. Where possible, guidance is provided on how to obtain free-of-charge, primary research results as well as more detailed information via the Internet. E-book and electronic versions of this sourcebook are fully interactive with each of the Internet sites mentioned (clicking on a hyperlink automatically opens your browser to the site indicated). Hard-copy users of this sourcebook can type cited Web addresses directly into their browsers to obtain access to the corresponding sites. In addition to extensive references accessible via the Internet, chapters include glossaries of technical or uncommon terms. [Read more] Store: eBooks.com

« Previous 1 2 3 4 5 Next »

Principles of Operation

The arc is constricted by passing it through an orifice downstream of the electrode. The basic terminology and the arrangement of the parts of a plasma cutting torch are shown in Figure 1. As plasma gas passes through the arc, it is heated rapidly to a high temperature, expands, and is accelerated as it passes through the constricting orifice toward the workpiece. The intensity and velocity of the plasma is determined by several variables including the type of gas, its pressure, the flow pattern, the electric current, the size and shape of the orifice, and the distance to the workpiece. Plasma arc cutting circuitry is shown in Figure 2. The process operates on direct current, straight polarity. The orifice directs the super-heated plasma stream from the electrode toward the workpiece. When the arc melts the workpiece, the high velocity jet blows away the molten metal to form the kerf, or cut. The cutting arc attaches to or “transfers” to the workpiece, and is referred to as a transferred arc.

The gases used for plasma arc cutting include nitrogen, argon, air, oxygen, and mixtures of nitrogen/hydrogen and argon/hydrogen.

The most common pilot arc starting technique is to strike a high-frequency spark between the electrode and the torch tip. A pilot arc is established across the resulting ionized path. When the torch is close enough to the workpiece so the plume or flame of the pilot arc touches the workpiece, an electrically conductive path from the electrode to the workpiece is established. The cutting arc will follow this path to the workpiece.

Equipment

Torches.

The plasma cutting process is used with either a hand-held torch or a mechanically-mounted torch. There are several types and sizes of each, depending on the thickness of metal to be cut. Some torches can be dragged along in direct contact with the workpiece, while others require that a standoff be maintained between the tip of the torch and workpiece.

Certain plasma arc torch parts must be considered to be consumable. The tip and electrode are the most vulnerable to wear during cutting, and cutting performance deteriorates as they wear. The timely replacement of consumable parts is required to achieve good quality cuts.

Power Supplies.

Plasma arc cutting requires a constant current or drooping volt-ampere characteristic, relatively high-voltage, direct-current power supply.

To achieve satisfactory arc starting performance, the open circuit voltage of the power supply is generally about twice the operating voltage of the torch. Operating voltages will range from 50 or 60 volts to over 200 volts so PAC power supplies will have open circuit voltages ranging from about 150 to over 400 volts.

Newer types of plasma cutting power supplies include electronic phase control and various types of “switch mode,” or inverter, power supplies. The switch mode power supplies utilize high-speed, high current semiconductors to control the output. They can either regulate the output of a standard DC power supply, the so-called “chopper” power supply, or they can be incorporated in an inverter-type power supply.

As new types of semiconductors become commercially available, it can be expected that improved versions of this type of power supply will appear.

Switch mode supplies have the advantage of higher efficiency and smaller size, and are attractive for applications where portability and efficiency are important considerations.

Motion Equipment.

A variety of motion equipment is available for use with mechanized plasma cutting torches. This equipment can range from straight-line tractors to numerically-controlled or direct computer controlled cutting machines with parts nesting capabilities, etc. Plasma cutting equipment can also be adapted to robotic actuators for cutting other than flat plates.

Environmental Controls.

The plasma cutting process is inherently a noisy and fume-generating process. Several different devices and techniques are available to control and contain the hazards. One commonly used approach to reduce noise and fume emissions is to cut over a water table and surround the arc with a water shroud. This method requires a cutting table filled with water up to the work-supporting surface, a water shroud attachment for the torch, and a recirculating pump to draw water from the cutting table and pump it through the shroud. In this case, a relatively high 55 to 75 Wmin (15 to 20 gpm) water flow is used.

Another method, underwater plasma cutting, is also in common use. With this method, the working end of the torch and the plate to be cut are submerged under approximately 75 mm (3 in.) of water. While the torch is underwater but not cutting, a constant flow of compressed

air is maintained through the torch to keep water out.

The primary requirements in water table design are adequate strength for supporting the work, sufficient scrap capacity to hold the dross or slag resulting from cutting, procedure for removing the slag, and ability to maintain the water level in contact with the work. When the table is used for underwater cutting, it is necessary to provide a means of rapidly raising and lowering the water level. This can be accomplished by pumping the water in and out of a holding tank, or by displacing it with air in an enclosure under the surface of the water.

A cutting table for mechanized or hand plasma cutting is usually equipped with a down-draft exhaust system. This is vented to the outdoors in some cases, although fume removal or filtering devices may be required to meet air pollution regulations.

Teoría de operación

El arco es constreñido pasándolo a través de un orificio en dirección hacia el electrodo. La terminología básica y la distribución de las partes de un soplete cortador de plasma se muestran en la figura 1. A medida que el gas de plasma pasa a través del arco, se calienta rápidamente a una temperatura alta, se expande, y se acelera mientras pasa a través del orificio constreñido hacia el objeto. La intensidad y la velocidad del plasma está determinada por varias variables incluyendo el tipo de gas, su presión, el patrón de flujo, la corriente eléctrica, el tamaño y la forma del orificio, y la distancia al objeto. El trazado de circuito de corte al arco de plasma se muestra en la figura 2. El proceso funciona con corriente continua, de polaridad directa. El orificio dirige la corriente sobrecalentada de plasma desde el electrodo hacia el objeto de trabajo. Cuando el arco funde al objeto, el chorro de alta velocidad arrastra el metal fundido para formar el kerf o ancho de corte. El arco de corte se fija o “transfiere” al objeto de trabajo, y se conoce como arco transferido.

Los gases usados para el corte con arco de plasma incluyen el nitrógeno, argón, aire, oxígeno, y mezclas de nitrógeno/hidrógeno y de argón/ hidrógeno.

La técnica de encendido de arco piloto más común es producir una chispa de alta frecuencia entre el electrodo y la extremidad de la antorcha. Un arco piloto se establece a través de la trayectoria ionizada resultante. Cuando la antorcha está bastante cercana al objeto de manera que el penacho o la llama del arco experimental toquen el mismo, se establece una trayectoria eléctricamente conductora del electrodo hacia objeto de trabajo. El arco del corte seguirá esta trayectoria al objeto.

Equipo

Antorchas

El proceso de corte de plasma se utiliza tanto con una antorcha de mano como con una antorcha de montaje mecánico. Hay varios tipos y tamaños de cada una, dependiendo del espesor del metal que se cortará. Algunas antorchas se pueden arrastrar a lo largo en contacto directo con el objeto de trabajo, mientras que otras requieren que un aislamiento sea mantenido entre la extremidad de la antorcha y el objeto.

Ciertas piezas de la antorcha de arco de plasma se deben considerar como insumos consumibles. La extremidad y el electrodo son los más vulnerables al desgaste durante el corte, y la operación de corte los deteriora mientras se usan. El reemplazo oportuno de piezas consumibles se requiere para alcanzar cortes de buena calidad.

Fuentes de alimentación.

El corte con arco de plasma requiere una fuente de alimentación de corriente constante o características de voltio amperios filtrados y estables, relativamente alto voltaje, y corriente continua.

Para alcanzar un desempeño de disparo de arco satisfactorio, el circuito abierto de voltaje de la fuente de alimentación es generalmente dos veces más el voltaje de funcionamiento de la antorcha. Los voltajes de funcionamiento se extenderán desde 50 a 60 voltios hasta encima de los 200 voltios de manera que las fuentes de alimentación de PAC tendrán voltajes del circuito abierto desde aproximadamente 150 hasta más de 400 voltios.

Los nuevos modelos de fuentes de alimentación de corte de plasma incluyen control de fase electrónico y varios tipos de fuentes de alimentación tipo fuente conmutada o inversor. Las fuentes de alimentación conmutadas utilizan semiconductores de alta velocidad y de gran intensidad para controlar la salida. Pueden tanto regular la salida de una fuente de corriente continua estándar, la fuente de alimentación conocida como fuente con interruptor chopper, o pueden ser incorporadas en una fuente de alimentación tipo inversor.

A medida que nuevos tipos de semiconductores llegan a estar disponibles comercialmente, se puede esperar que versiones mejoradas de este tipo de fuente de alimentación aparezcan.

Las fuentes del modo conmutado tienen la ventaja de mayor eficiencia y de un tamaño más pequeño, y son atractivas para los usos donde la portabilidad y la eficacia son consideraciones importantes.

Equipo de movimiento.

Una variedad el equipo de movimiento está disponible para su uso con los sopletes cortadores mecanizados de plasma. Este equipo puede extenderse desde tractores rectilíneos a máquinas cortadoras de control numérico o controlado directamente por ordenador con sistema jerarquizado de piezas. El equipo de corte de plasma se puede también adaptar a actuadores robóticos para cortar otras placas planas.

Controles del medio ambiente.

El proceso de corte de plasma es intrínsecamente un proceso ruidoso y de generador de humo. Diversos dispositivos y técnicas están disponibles para controlar y contener los peligros. Un acercamiento de uso general para reducir emisiones de ruido y de humo es cortar sobre una tabla de agua y rodear el arco con una cubierta de agua. Este método requiere una tabla de corte llena de agua hasta la superficie de soporte del trabajo, un accesorio para cubierta de agua para la antorcha, y una bomba de recirculación para extraer el agua de la tabla de corte y para bombearla a través de la cubierta de agua. En este caso, un caudal de agua relativamente alto de 55 a 75 Wpm (15 a 20 gpmm) se utiliza.

Otro método, el corte subacuático de plasma, es también de uso común. Con este método, el extremo de trabajo de la antorcha y la placa que se cortará se sumergen bajo aproximadamente 75 milímetros (3 pulgadas) de agua. Mientras que la antorcha está bajo el agua pero sin cortar, un flujo constante de aire comprimido se mantiene a través de la antorcha para expulsar el agua.

Los requisitos fundamentales en el diseño de la tabla de agua son una fuerza adecuada para soportar el trabajo, suficiente capacidad de desecho para retener la escoria o metal fundido resultante del corte, procedimiento para quitar la escoria, y capacidad para mantener el nivel del agua en contacto con el objeto de trabajo. Cuando la tabla se utiliza para corte subacuático, es necesario proporcionar medios de levantar y de bajar rápidamente el nivel del agua. Esto puede ser logrado bombeando el agua dentro y fuera de un tanque intermedio, o desplazándola con aire en un recinto bajo la superficie del agua.

Una tabla de corte para el corte mecanizado o manual de plasma está equipada generalmente con un dispositivo de escape de tiro descendente. Este se expulsa al aire libre en algunos casos, aunque los dispositivos de extracción de humo o de filtración pueden requerir ajustarse a regulaciones de contaminación atmosférica.