IX.3. PRIMEROS DATOS DE LOS EDIFICIOS AL SUR DE LA PUERTA DE CARTEIA
IX.3.1. Introducción y objetivos
chloride can decompose into phosgene gas—a poison gas—when exposed to ultraviolet radiation. Keep cutting areas ventilated, and keep chlorinated solvents away from the cutting area.
Operators should be sure to read and understand the Material Safety Data Sheet of any solvent in use.
Table 3
Recommended Shade Densities for Plasma Arc Cutting Filter Lenses(1)
Current Range (A) Minimum Shade Comfortable Shade(2)
Less than 300 8 9
300 to 400 9 12
>400 10 14
Notes:
(1) Adapted from ANSI Z49.1, Safety in Welding, Cutting and Allied Processes. See Section 2 for information in obtaining this document.
Also see AWS F2.2, Lens Shade Selector Chart.
(2) As a rule of thumb start with the shade that is too dark to see the cutting zone. Then go to a lighter shade which gives a sufficient view of the cutting zone without going below the minimum.
A1. Introduction
The AWS Board of Directors has adopted a policy whereby all official interpretations of AWS standards will be handled in a formal manner. Under that policy, all interpretations are made by the committee that is respon-sible for the standard. Official communication concern-ing an interpretation is through the AWS staff member who works with that committee. The policy requires that all requests for an interpretation be submitted in writing.
Such requests will be handled as expeditiously as possi-ble but due to the complexity of the work and the proce-dures that must be followed, some interpretations may require considerable time.
A2. Procedure
All inquiries must be directed to:
Managing Director, Technical Services American Welding Society
550 N.W. LeJeune Road Miami, FL 33126
All inquiries must contain the name, address, and af-filiation of the inquirer, and they must provide enough in-formation for the committee to fully understand the point of concern in the inquiry. Where that point is not clearly defined, the inquiry will be returned for clarification. For efficient handling, all inquiries should be typewritten and should also be in the format used here.
A2.1 Scope. Each inquiry must address one single provi-sion of the standard, unless the point of the inquiry involves two or more interrelated provisions. That provision must be identified in the Scope of the inquiry, along with
the edition of the standard that contains the provisions or that the Inquirer is addressing.
A2.2 Purpose of the Inquiry. The purpose of the inquiry must be stated in this portion of the inquiry. The purpose can be either to obtain an interpretation of a standard re-quirement, or to request the revision of a particular provi-sion in the standard.
A2.3 Content of the Inquiry. The inquiry should be concise, yet complete, to enable the committee to quickly and fully understand the point of the inquiry. Sketches should be used when appropriate and all paragraphs, fig-ures, and tables (or the Annex), which bear on the in-quiry must be cited. If the point of the inin-quiry is to obtain a revision of the standard, the inquiry must provide tech-nical justification for that revision.
A2.4 Proposed Reply. The inquirer should, as a pro-posed reply, state an interpretation of the provision that is the point of the inquiry, or the wording for a proposed re-vision, if that is what inquirer seeks.
A3. Interpretation of Provisions of the Standard
Interpretations of provisions of the standard are made by the relevant AWS Technical Committee. The secre-tary of the committee refers all inquiries to the chairman of the particular subcommittee that has jurisdiction over the portion of the standard addressed by the inquiry. The subcommittee reviews the inquiry and the proposed reply to determine what the response to the inquiry should be.
Following the subcommittee’s development of the re-sponse, the inquiry and the response are presented to the entire committee for review and approval. Upon approval
Annex A
Guidelines for Preparation of Technical Inquiries for AWS Technical Committees
(This Annex is not a part of AWS C5.2-2001, Recommended Practices for Plasma Arc Cutting and Gouging, but is included for information purposes only.)
by the committee, the interpretation will be an official in-terpretation of the Society, and the secretary will transmit the response to the inquirer and to the Welding Journal for publication.
A4. Publication of Interpretations
All official interpretations will appear in the Welding Journal.
A5. Telephone Inquiries
Telephone inquiries to AWS Headquarters concerning AWS standards should be limited to questions of a gen-eral nature or to matters directly related to the use of the standard. The Board of Directors’ policy requires that all AWS staff members respond to a telephone request for an official interpretation of any AWS standard with the information that such an interpretation can be obtained
only through a written request. The Headquarters staff cannot provide consulting services. The staff can, how-ever, refer a caller to any of those consultants whose names are on file at AWS Headquarters.
A6. The AWS Technical Committee
The activities of AWS Technical Committees in regard to interpretations, are limited strictly to the interpretation of provisions of standards prepared by the committee or to consideration of revisions to existing provisions on the basis of new data or technology. Neither the committee nor the staff is in a position to offer interpretive or con-sulting services on: (1) specific engineering problems; or (2) requirements of standards applied to fabrications out-side the scope of the document or points not specifically covered by the standard. In such cases, the inquirer should seek assistance from a competent engineer experi-enced in the particular field of interest.
Both the plasma arc cutting process and the gas tung-sten arc welding process, from which it derived, share some terminology. However, due to the greater complex-ity and recent developments in plasma arc cutting new terms have come into common usage. Familiarity with these terms will provide a common language for opera-tors, service personnel, and management, and will also help readers make useful comparisons between the sys-tems available. Refer to AWS A3.0, Standard Welding Terms and Definitions, for a complete list of terms used in this document. A term preceded by an asterisk is not currently defined in AWS A3.0 or is a variation of the A3.0 definition.
*arc length, plasma arc cutting. The distance from the electrode to the attachment point on the workpiece.
*backlash. A mechanical situation where a reversal of driving motion does not result in the immediate rever-sal of the driven assembly. Excessive backlash is generally caused by damaged, worn or poorly manu-factured parts.
*ball transfer. A ball bearing assembly used to reduce the friction experienced by an object that must slide over or under another object. Ball transfers are com-monly used in work tables.
*ballscrew. A mechanical drive system component resembling a threaded rod which is used to convert rotary motion to straight line motion.
*bevel cutting. A plasma arc cutting technique that uses a tilted torch to produce an angle on the edge of parts being cut.
*chopper. A high-performance plasma arc power source design using power semiconductor switching techniques.
*computer numeric control (CNC). Microprocessor-based electronic machine control used to coordinate and manage the cutting machine functions.
*consumables, plasma arc cutting. Torch parts that are eroded or otherwise worn during normal cutting or gouging operations, such as electrodes, nozzles, shields, caps and swirl rings.
*coordinate drive. Machine motion system where movements are electronically controlled. Axis motion can be executed independently as with point to point positioning or can be synchronized as with contour cutting.
*current density, plasma arc cutting. A measure of the degree of arc constriction achieved with a plasma arc torch. Units are Amperes/in.2 or mm2.
*cut angle/bevel angle, plasma arc cutting. The angle formed between the cut surface and a theoretical plane perpendicular to the plate surface. Plasma arc cutting tends to remove more metal from the top than from the bottom, producing a cut angle.
*cycle time. The total amount of time needed to process a part, including the time needed for material handling and other noncutting activities.
*diagnostics. Messages issued by a control which indi-cate faults and aid in troubleshooting.
*direct numeric control (DNC). The practice of creating and maintaining part programs in one location and down-loading them to the cutting machine location when needed.
double arcing. A condition in which the welding or cut-ting arc of a plasma arc torch does not pass through the constricting orifice but transfers to the inside sur-face of the nozzle. A secondary arc is simultaneously
Annex B
Terms and Definitions
(This Annex is not a part of AWS C5.2-2001, Recommended Practices for Plasma Arc Cutting and Gouging, but is included for information purposes only.)
established between the outside surface of the nozzle and the workpiece.
*drag, plasma arc cutting. The offset distance between the entrance and exit points of the gas stream on the plate being cut, measured on the cut edge.
*drag angle, plasma arc cutting. The angle between the impinging jet stream centerline and a direction perpen-dicular to the plate surface.
*drive. A term used to describe any system of compo-nents used to produce machine motion, including such components as motors, ballscrews, servo amplifiers, etc.
*dross, plasma arc cutting. Resolidified molten metal and oxides adhering to the top or bottom edge during thermal cutting.
*duty cycle, plasma arc cutting. A power source specifi-cation describing the percentage of time a system can be operated at a given current level. Based on a ten minute cycle.
*electrode, plasma arc cutting. The plasma arc torch part from which arc current is emitted.
*feedback. A signal used by a controller to monitor the events being controlled and modify output commands.
*fumes. Airborne solid particulate matter generated by the welding process. Fume particles are usually sub-micron in size, and thus tend to remain airborne and drift with the air currents.
*hafnium. The metal used most commonly for the elec-trode emitter for air or oxygen plasma gases.
*heat-affected zone, plasma arc cutting. The region on the edge of the plasma cut where the heat of the arc has changed the properties of the material. Generally a hardening of the material is the primary concern.
*high-frequency discharge. High-voltage power sup-plied to the plasma torch, which breaks down the air gap between the nozzle and electrode in order to ini-tiate the plasma stream.
*inverter power source. A high-performance plasma power source design which takes advantage of advanced power semiconductor circuitry to reduce the size and weight of the transformer and, hence, the overall size of the power source.
*kerf, plasma arc cutting. The void left by the linear removal of material by any kind of cutting process (saw, plasma arc, oxyfuel gas, etc.)
*manual data input (MDI). A CNC operating mode in which the operator may enter part program informa-tion or short commands.
*nesting. The creation of an array of parts on a plate, generally arranged to minimize the amount of scrap after cutting.
*nibbling. A method of producing parts using a punch press to rapidly punch the outline of the desired shape.
*nontransferred arc. An arc established between the electrode and the constricting nozzle of the plasma arc torch. The workpiece is not in the electrical circuit.
*nozzle, plasma arc cutting. A “consumable” torch part containing a hole, or orifice, through which the arc passes.
*nozzle diameter, orifice diameter. The diameter of the nozzle through which the plasma arc passes.
*off-line. Not under machine control. Operations such as guidance programming are developed before produc-tion time.
*open circuit voltage, plasma arc cutting. The voltage present at the electrode in the brief internal before the torch ignites and whenever the arc is extinguished with the power source still active.
*overshoot. A condition where a controlled variable such as standoff or workpiece position will briefly exceed or hunt around its commanded value.
oxyfuel gas cutting (OFC). A group of oxygen cutting processes that uses heat from an oxyfuel gas flame.
*pantograph. A mechanism which follows a template to reproduce the shape of the template to scale.
*photo optical tracing. A shape-cutting technique in which the cutting machine takes its motion control information from a photoelectric sensor that scans a drawing of the desired shape during the cutting process.
*piercing. A method of starting a plasma arc cut in which the arc plunges into and through the workpiece before cutting begins.
pilot arc. A low current arc between the electrode and the constricting nozzle of the plasma arc torch to ionize the gas and facilitate the start of the welding arc.
*pilot hole. On a punch/plasma press, a punched hole at the edge of which the plasma arc cut is started.
*plasma, arc plasma in AWS A3.0. A gas that has been heated by an arc to at least a partially ionized condi-tion, enabling it to conduct an electric current.
*plasma arc cutting (PAC). An arc cutting process that uses a constricted arc and removes the molten metal in a high-velocity jet of ionized gas issuing from the constricting orifice. Plasma arc cutting is a direct cur-rent electrode negative (DCEN) process.
*plasma gas/cutting gas/orifice gas. A gas directed into the torch to surround the electrode, which becomes ionized by the arc to form a plasma, and issues from the torch nozzle as the plasma jet.
*plenum chamber. The space between the electrode and the inside wall of the constricting nozzle of the plasma arc torch.
*proximity probe. Electronic inductive proximity sensors capable of detecting the location of the workpiece, often used for initial height sensing.
*punched tape. A method of storing and transporting part programs in which characters are recorded on the paper or Mylar tape using standardized patterns of punched holes. Programs generated off-line are loaded into the machine controller using a tape reader.
Punched tape for data storage is being phased out in favor of disks and DNC.
*rack & pinion. A mechanical drive system used to con-vert rotary motion to straight line motion. These units consist of a relatively small round pinion gear which engages a length of toothed rectangular bar.
*SCR power source. A type of power source that uses a semiconductor device known as the silicon-controlled rectifier in the main power circuit.
*secondary gas/shielding gas, plasma arc cutting.
Unlike the plasma gas, the secondary gas does not
pass through the orifice of the nozzle. It passes around the nozzle and forms a shield around the arc.
*servo system. Electronic machine tool positioning system.
*shape library. A CNC feature that provides a collection of commonly used shapes for part programs, which can be scaled, rotated and translated as necessary to create the desired cut-part shapes.
*standoff/torch-to-work distance, plasma arc cutting.
The distance between the outer most portion of the torch and the work surface.
*thoriated tungsten. A metal used as the plasma cutting electrode emitter for a non-oxidizing plasma gas, such as nitrogen.
transferred arc. A plasma arc established between the electrode of the plasma arc torch and the workpiece.
*turret. An assembly which holds punching tools on a punch press. The turret rotates to select different tools.
*ultraviolet light. Short wavelength light emitted during arc cutting and welding processes that is harmful to the eyes and skin.
*vortex. An intense swirling gas similar to a tornado.
Most plasma arc cutting systems develop a vortex of some extent in the nozzle during cutting.
*workclamp. An assembly used to hold the workpiece, generally using hydraulic pressure for clamping force.
*workpiece, plasma arc cutting. The piece of material to be cut or gouged.
*zirconium. An element used in some electrodes as a plasma arc cutting electrode emitter. Although similar to hafnium, zirconium provides a shorter service life.
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(2) American Machinist, “Technology Trends,” July 1993, p. 22.
(3) ASM Handbook, Vol. 6, 1993, pp. 1166–1171.
(4) AWS Welding Handbook, Vol. 2, 8th Edition, 1994, pp. 482–489.
(5) Colt, J. D., “Longlife® Oxygen Plasma Arc Cut-ting,” Hypertherm Inc., Hanover, NH, 1994.
(6) DIN 2310 – Teil 4 (German) Thermal Cutting;
Plasma Arc Cutting, Principles of Process, Terms, Quality, Dimensional Tolerances, September 1987.
(7) Engblom, G. and Falck K., Welding in the World, Vol. 28, No. 11/12, pp. 204–215, 1990.
(8) Fernicola, R. C., Welding Journal, “New Oxygen Plasma Arc Process Rivals Laser Cutting,” June 1994, pp. 65–69.
(9) Handal M. D., Kathleen, The American Red Cross First Aid and Safety Handbook, Little Brown & Co.
ISBN: 0316736465
(10) Harris, Ian, “Plasma Arc Cutting of Bridge Steels,” Edison Welding Institute, 1997.
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(12) Lindberg, B., Welding & Metal Fabrication, April 1990, p. 166.
(13) Linde Publication: “Plasma Cutting Fundamen-tals,” reprinted in Australian Welding Journal, Winter 1987, pp. 5–8.
(14) Manohar, M., Snyder, J. P. II, “Dross Formation During Plasma Arc Cutting of Steel,” Welding Journal, November 1994.
(15) G. Pilot et al, “Measurements of Secondary Emis-sions from Plasma Arc and Laser Cutting in Standard Experiments,” Decommissioning of Nuclear Installations, ISBN:1-85166-523-4, Elsevier Applied Sciences, 1989.
(16) Plasma-Arc Cutting and Welding, PAC and PAW, Welding Design and Fabrication, 65(6), pp. 23–56, June 1992.
(17) Trainor, R. S., “Fume Emissions Testing for Plasma Arc Cutting,” Hypertherm Inc., Etna Road, Ha-nover NH, 1998.
(18) Wu, Y., Hackett, C., Eickhoff, S., “The Effects of Plasma Arc Cutting on Mild Steel,” Hypertherm Inc.
1997.
(19) Physik und Technologie des Plasmastrahls in der Schweiss-, Schneid und Spritztechnik: Vortrèage d. 3.
Kolloquiums Physik u. Technologie d. Plasmastrahls in d. Schweiss-, Schneid u. Spritztechnik in Aachen am 20.
u. 21. Mèarz 1975.
Annex C
Selected Reading List
(This Annex is not a part of AWS C5.2:2001, Recommended Practices for Plasma Arc Cutting and Gouging, but is included for information purposes only.)
AWS List of Documents on Arc Welding and Cutting
AWS Designation Title
C5.1 Recommended Practices for Plasma Arc Welding
C5.2 Recommended Practices for Plasma Arc Cutting and Gouging C5.3 Recommended Practices for Air Carbon Arc Gouging and Cutting C5.4 Recommended Practices for Stud Welding
C5.5 Recommended Practices for Gas Tungsten Arc Welding C5.6 Recommended Practices for Gas Metal Arc Welding C5.7 Recommended Practices for Electrogas Welding
C5.10 Recommended Practices for Shielding Gases for Welding and Plasma Arc Cutting
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