Li ce ns ed C op y A ki n K ok sa l, B ec ht el L td , 1 2 D ec em be r 20 02 , U nc on tr ol le d C op y, ( c) B S I BRITISH STANDARD BS EN 26848 1991 ISO 6848 1984 Specification for Tungsten electro[.]
British Standard Licensed Copy: Akin Koksal, Bechtel Ltd, 12 December 2002, Uncontrolled Copy, (c) BSI A single copy of this British Standard is licensed to Akin Koksal 12 December 2002 This is an uncontrolled copy Ensure use of the most current version of this document by searching British Standards Online at bsonline.techindex.co.uk BRITISH STANDARD Specification for Licensed Copy: Akin Koksal, Bechtel Ltd, 12 December 2002, Uncontrolled Copy, (c) BSI Tungsten electrodes for inert gas shielded arc welding and for plasma cutting and welding This European Standard EN 26848:1991 has the status of a British Standard BS EN 26848:1991 ISO 6848:1984 BS EN 26848:1991 Cooperating organizations Licensed Copy: Akin Koksal, Bechtel Ltd, 12 December 2002, Uncontrolled Copy, (c) BSI The European Committee for Standardization, under whose supervision this European Standard was prepared, comprises the national standards organizations of the following Western European countries This British Standard was published under the authority of the Standards Board and comes into effect on 28 June 1991 © BSI 07-1999 The following BSI references relate to the work on this standard: Committee reference WEE/39 Draft for comment 83/71681 DC ISBN 580 19758 Austria Oesterreichisches Normungsinstitut Belgium Institut belge de normalisation Denmark Dansk Standardiseringsraad Finland Suomen Standardisoimisliito, r.y France Association franỗaise de normalisation Germany Deutsches Institut für Normung e.V Greece Hellenic Organization for Standardization Iceland Technological Institute of Iceland Ireland National Standards Authority of Ireland Italy Ente Nazionale Italiano di Unificazione Luxemburg Inspection du Travail et des Mines Netherlands Nederlands Normalisatie-instituut Norway Norges Standardiseringsforbund Portugal Instituto Portugs da Qualidade Spain Asociación Espola de Normalización y Certificación Sweden Standardiseringskommissionen i Sverige Switzerland Association suisse de normalisation United Kingdom British Standards Institution Amendments issued since publication Amd No Date Comments BS EN 26848:1991 Contents Licensed Copy: Akin Koksal, Bechtel Ltd, 12 December 2002, Uncontrolled Copy, (c) BSI Page Cooperating organizations Inside front cover National foreword ii Foreword Introduction Scope and field of application Definition 3 Composition Designation Marking Technical delivery conditions Annex A Conditions of use Table — Codification, composition and identification colour Table — Suitability of current supply type Table — Recommended current ranges depending on the electrode diameter National appendix NA Inside back cover © BSI 07-1999 i BS EN 26848:1991 National foreword This British Standard has been prepared under the direction of the Welding Standards Policy Committee It is the English language version of EN 26848:1991, “Tungsten electrodes for inert gas shielded arc welding and for plasma cutting and welding — Codification” published by the European Committee for Standardization (CEN) It supersedes BS 6678:1986 which is withdrawn EN 26848:1991 is identical with ISO 6848:1984 published by the International Organization for Standardization (ISO) A British Standard does not purport to include all the necessary provisions of a contract Users of British Standards are responsible for their correct application Licensed Copy: Akin Koksal, Bechtel Ltd, 12 December 2002, Uncontrolled Copy, (c) BSI Compliance with a British Standard does not of itself confer immunity from legal obligations Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, the EN title page, pages to 6, an inside back cover and a back cover This standard has been updated (see copyright date) and may have had amendments incorporated This will be indicated in the amendment table on the inside front cover ii © BSI 07-1999 EUROPEAN STANDARD EN 26848 NORME EUROPÉENNE March 1991 EUROPÄISCHE NORM UDC 621.791.754/.755.037:621.791.947.55 Descriptors: Arc welding, gas shielded welding, plasma arc welding, arc cutting, welding electrodes, tungsten, chemical composition, colour, codification, marking English version Tungsten electrodes for inert gas shielded arc welding and for plasma cutting and welding — Codification Licensed Copy: Akin Koksal, Bechtel Ltd, 12 December 2002, Uncontrolled Copy, (c) BSI (ISO 6848:1984) Electrodes de tungstène pour soudage l’arc en atmosphère inerte et pour soudage et coupage plasma — Codification (ISO 6848:1984) Wolframelektroden für Wolfram-Schutzgasschweißen und für Plasmaschneiden und -schweißen — Kurzzeichen (ISO 6848:1984) This European Standard was accepted by CEN on March 1991 and is identical to the ISO standard as referred to CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CEN member This European Standard exists in three official versions (English, French, German) A version in any other language made by translation under the responsibility of a the member into its own language and notified to the Central Secretariat has the same status as the official versions CEN members are the national standards bodies of Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxemburg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom CEN European Committee for Standardization Comité Européen de Normalisation Europäisches Komitee für Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels © CEN 1991 Copyright reserved to all CEN members Ref No EN 26848:1991 E EN 26848:1991 Foreword In 1989, ISO 6848:1984 was submitted to the CEN P.Q.-procedure CEN/TC 121 decided to submit ISO 6848:1984 without modifications to Formal Vote As the International Standard ISO 6848:1984 was accepted by CEN as a European Standard, the following countries are bound to implement this European Standard: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxemburg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom Licensed Copy: Akin Koksal, Bechtel Ltd, 12 December 2002, Uncontrolled Copy, (c) BSI Endorsement notice The text of the International Standard ISO 6848:1984 was approved by CEN as a European Standard without any modification © BSI 07-1999 EN 26848:1991 Licensed Copy: Akin Koksal, Bechtel Ltd, 12 December 2002, Uncontrolled Copy, (c) BSI Introduction In inert gas shielded arc welding and in plasma cutting and welding, it is essential that the electrode be carefully selected Its nature, diameter, surface condition and the type of current used greatly influence work quality and arc stability Owing to the development of arc temperatures in the order of 000 °C, it is necessary to use a metal with an extremely high melting point for the manufacture of an electrode which is non-consumable by definition Tungsten meets this requirement and, in addition, provides the advantage of a high thermionic emission; it is therefore a prime material for making such electrodes Certain substances, added during manufacture of the electrodes, promote the electron emission The most common substances are: thoria (ThO2), zirconia (ZrO2), lanthanum oxide (LaO2) and cerium oxide (CeO2), the amounts of which range from 0,3 to % depending on the element These dopes are responsible for increasing the usable life of the electrodes because of their higher electron emission, better arc starting and arc stability Adding these oxides reduces the risk of tungsten contaminating the welds Given similar diameters, electrodes containing oxides can take a higher current than pure tungsten ones; lower diameter electrodes therefore may be used The effect of oxide additions is also more noticeable with large diameter electrodes because of the greater size of the tip covered with a layer of emissive substance Scope and field of application This International Standard lays down requirements for tungsten electrodes for inert gas shielded arc welding, and for plasma cutting and welding Definition tungsten electrode current-carrying bare tungsten rod, with or without oxide additive, serving as anode or cathode for the generation of an electric arc Composition Tungsten electrodes may contain oxide additives to improve the emission characteristics The chemical composition of these electrodes shall be in accordance with the requirements given in Table Designation The codification of tungsten electrodes is based on their chemical composition in accordance with Table 1: a) the first letter indicates the primary element; b) the second letter indicates the oxide additive (the letter selected is the initial of the element name); the following number is the mean oxide content multiplied by 10 Table — Codification, composition and identification colour Composition Codification Oxide additive % (m/m) WP WT WT 10 WT 20 WT 30 WT 40 WZ WZ WL 10 WC 20 — 0,35 to 0,55 0,80 to 1,20 1,70 to 2,20 2,80 to 3,20 3,80 to 4,20 0,15 to 0,50 0,70 to 0,90 0,90 to 1,20 1,80 to 2,20 a nature ThO2 ThO2 ThO2 ThO2 ThO2 ZrO2 ZrO2 LaO2 CeO2 Impurities Tungsten % (m/m) % (m/m) # 0,20 # 0,20 # 0,20 # 0,20 # 0,20 # 0,20 # 0,20 # 0,20 # 0,20 # 0,20 99,8 balance balance balance balance balance balance balance balance balance Identification colourb green blue yellow red violet orange brown white black grey a The oxide additives are generally finely dispersed in the tungsten matrix, but the so-called composite electrodes are made up of a pure tungsten core with an oxide coating This type of electrode combines the qualities of pure tungsten with those of the tungsten containing oxides, but have the disadvantage that they cannot be tapered b The composite electrodes shall be identified by a second, pink ring © BSI 07-1999 Licensed Copy: Akin Koksal, Bechtel Ltd, 12 December 2002, Uncontrolled Copy, (c) BSI EN 26848:1991 Marking 6.4 Electrode quality In accordance with Table 1, tungsten electrodes shall be marked on the basis of their chemical composition, with one (or possibly, as in the case of composite electrodes, two) colour ring(s) at one end of the electrode The width of each ring shall be mm or more Technical delivery conditions The electrode shall show neither surface defects (micro-fissures, cracks, scale, etc.) nor internal defects (porosity, inclusions, etc.) The electrode surface shall be free of oil, grease or other impurities The smooth and clean surface condition required may be achieved by dressing The electrode tips in particular shall be perfectly dressed and free of burrs 6.1 Diameter 6.5 Marking of boxes or unit packages The diameter, expressed in millimetres, shall be selected from the following range: 0,5 – 1,0 – 1,6 – – 2,5 – 3, – – – 6,3 – – 10 The tolerances on the standard sizes are as follows: a) for diameters < 2,5 mm: ± 0,05 mm b) for diameters $ 2,5 mm: ± 0,1 mm The following information shall either be printed directly on each box or unit package or appear on a glued-on label: a) name of manufacturer or supplier; b) diameter of the electrodes; c) length of the electrodes; d) symbols for the chemical composition in accordance with Table 1; e) colour identification in accordance with Table 6.2 Length The length, expressed in millimetres, shall be selected from the following range: 50 – 75 – 150 – 175 with a tolerance of ± mm 6.3 Straightness Straightness plays an important role in plasma cutting This is why the electrodes used for this purpose shall not deviate from the straight by more than ± 0,5 mm over their length They shall be measured along a generatrix 6.6 Packing Tungsten electrodes shall be packed so that their surfaces are protected from all damage or stain when they are properly transported and stored © BSI 07-1999 EN 26848:1991 Annex A Conditions of use A.1 Influence of the type of current The electric arc may be supplied with either direct current or alternating current Licensed Copy: Akin Koksal, Bechtel Ltd, 12 December 2002, Uncontrolled Copy, (c) BSI NOTE Table indicates which type of current is more suitable to the type of metal or alloy to be welded A.1.1 Direct current supply The arc behaviour is different depending on whether the electrode is connected to the positive or negative terminal of the power source With the electrode positive, there is a greater output of heat at the electrode and less penetration of the work than with negative polarity The current-carrying capacity of an electrode of a given size will therefore be lower with positive polarity than with negative polarity A.1.2 Alternating current supply With this type of supply, the current changes direction each half-cycle: the electrode is in turn anode and cathode A.2 Amperage The electrode size should be selected so that the current value is high enough for the arc to cover the whole area of the electrode tip, which is then heated up to a temperature approaching its melting temperature If the current is too low for the electrode size selected, the arc is erratic and unstable, and tungsten particles may be ejected If, however, the current is too high, it will cause the electrode to overheat and its tip to melt; drops of molten tungsten will fall into the weld, and the arc will become erratic and unstable NOTE Table gives the recommended current ranges, depending on the type of supply and electrode diameter A high current value provides, in addition to a perfectly stable arc, a better concentration of heat, but this value is limited depending on the conditions of use However, an adequate degree of taper of the electrode tip permits improvement of these conditions, for example the degree of taper of the electrode with d.c negative polarity should be chosen according to the current used A more obtuse angle is recommended at higher currents for a given electrode diameter A.3 Further remarks The choice of an electrode type and size and of the welding current is influenced by the type and thickness of the parent metal to be welded or cut The capacity of tungsten electrodes to carry current is dependent upon a number of other factors, in particular, type and polarity of the current, the shielding gas used, the type of equipment used (gas or water cooled), the extension of the electrode beyond the nozzle and the welding position employed An electrode of a given size will have its greatest current-carrying capacity with direct current, electrode negative; less with alternating current, and still less with direct current, electrode positive Table lists some typical current values that may be used with argon shielding However, the other factors mentioned above should be carefully considered before selecting an electrode for a specific application Table — Suitability of current supply type Direct current Type of metal or alloy to be welded Electrode negative (–) Alternating current Electrode positive (+) Aluminium (thickness # 2,5 mm) 2 Aluminium (thickness > 2,5 mm) and its alloys Magnesium and its alloys Carbon steels and low alloy steels 3 Stainless steels 3 Copper 3 Bronze Aluminium bronze Silicon bronze 3 Nickel and its alloys Titanium NOTE The numbers indicate, as a guide only, the suitability of the current: = type of supply giving the best results; = type of supply giving good results; = type of supply not recommended or impossible © BSI 07-1999 EN 26848:1991 Table — Recommended current ranges depending on the electrode diameter Direct current A Electrode diameter Electrode positive (+) Pure tungsten Tungsten with oxide additives 0,5 to 20 to 20 1,0 10 to 75 10 to 75 1,6 40 to 130 60 to 150 10 to 20 75 to 180 100 to 200 2,5 130 to 230 3,2 mm Licensed Copy: Akin Koksal, Bechtel Ltd, 12 December 2002, Uncontrolled Copy, (c) BSI Electrode negative (–) Pure tungsten Tungsten with oxide additives Alternating current A Pure tungsten 15 to 15 15 to 55 15 to 70 10 to 20 45 to 90 60 to 125 15 to 25 15 to 25 65 to 125 85 to 160 170 to 250 17 to 30 17 to 30 80 to 140 120 to 210 160 to 310 225 to 330 20 to 35 20 to 35 150 to 190 150 to 250 275 to 450 350 to 480 35 to 50 35 to 50 180 to 260 240 to 350 400 to 625 500 to 675 50 to 70 50 to 70 240 to 350 330 to 460 6,3 550 to 875 650 to 950 65 to 100 65 to 100 300 to 450 430 to 575 to Tungsten with oxide additives 650 to 830 10 © BSI 07-1999 BS EN 26848:1991 National appendix NA Licensed Copy: Akin Koksal, Bechtel Ltd, 12 December 2002, Uncontrolled Copy, (c) BSI The United Kingdom participation in the preparation of this European Standard was entrusted by the Welding Standards Policy Committee (WEE/-) to Technical Committee WEE/39, upon which the following bodies were represented: Aluminium Federation Associated Offices Technical Committee Association of Welding Distributors British Association for Brazing and Soldering British Compressed Gases Association British Constructional Steelwork Association Ltd British Railways Board British Steel Industry Electricity Supply Industry in United Kingdom Engineering Equipment and Materials Users’ Association Magnesium Industry Council Power Generation Contractors’ Association (BEAMA Ltd.) Process Plant Association Welding Manufacturers’ Association (BEAMA Ltd.) 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