Giáo trình Anh văn chuyên ngành công nghệ hàn

int : Liê - Electrode : ự - Welding : Hàn - Welded joint: - Welding process: Q hàn - Weld: - Welding structure: - Melt (n): Sự nung - Melt (iv / tv) C - Melted (pp) - Molten (adj) - Mass: - Cool (iv / tv): - Clamp: ẹ ữ - Base metal: - Circuit: - Stream: ò - Temperature: - Bright: Sáng, sáng chói - Welding machine: Máy hàn - Amperage : dò - Voltage : - Generator : - Transformer : - Rectifier : ỉ II. GRAMMAR: Passive voice: Form: Subject (S) + Verb ( V) + Object ( O) S + ‘to be’ + V_ed (past participle) + (by.) 1. The passive tense „ ‟ „ ‟ „ ‟ ỉ ứ present, past, past perfect ...v.v ) Giáo trình Anh văn chuyên ngành công nghệ hàn 3 of an active tense voice is formed by putting the verb „ be‟ at the same tense as the active verb in front of the past participle of the active verb. The subject of the active „agent’ f T „agent’ is very often not mentioned. When it is mentioned it is preceded by „by’ and placed at the end of the clause: Ex: This plate of metal was welded by my father. 2. Passive voice at present and past tenses: S + V + O S + is / are + V_ ed Active: We build this bridge. Passive: This bridge is built. S + V ( past simple) + O S + was / were + V_ ed Active: They broke the window. Passive: The window was broken. 3. Passive voice at continuous tense requires the present continuous form of to be: S + is / am / are + V_ing + O S + is / are + being + V_ed ( past participle) Active: They are repairing the bridge. Passive: The bridge is being repaired. 4. Auxiliary + infinitive combinations are made passive by using a passive infinitive: S + should / can + V + O S + should / can + be + V_ed ( past participle) Active: You should shut these doors Passive: These doors should be shut Active: You can use the process to deposit metal to form a surface with alternative properties. Giáo trình Anh văn chuyên ngành công nghệ hàn 4 Passive: The process can also be used to deposit metal to form a surface with alternative properties. III. PRACTICE This lesson Arc welding is a method of joining two pieces of metal into one solid piece. To do this, the heat of an electric arc is concentrated on the edges of two pieces of metal to be joined. The metal melts and, while these edges are still molten, addition melted metal is added. This molten mass cools and solidifies into one solid piece. Figure 1 The electric arc is made between the work and the tip and of a small metal wire, the electrode, which is clamped in a holder and held in the hand. A gap is made in the welding circuit by holding th f d 6‟‟- ‟‟ w f the parent or base metal being welded. The electric current jumps this gap and makes an arc, which is held maintained and moved along the joint to be welded, melting the metal as it is moved. Arc welding is a manual skill requiring a steady hand, good general physical conditions, and good eyesight. The operator controls the welding arc and, therefore, the quality of the weld made. Figure 2 Giáo trình Anh văn chuyên ngành công nghệ hàn 5 Figure 3 Illustrates the action that takes place in the electric arc. It closely resembles what is actually seen during welding T “ ” is seen in the middle of the picture. This is the electric arc created by the electric current flowing through the space between the end of the electrode and the work. The temperature of this arc is about 6000 0 C, which is more than enough to melt metal. The arc is very bright, as well as very hot, and cannot be looked at with the naked eye without risking painful, though usually temporary, injury. Figure 3 The arc melts the parent, or base, metal and actually digs into it, much as the water through a nozzle on a garden hose digs into the earth. The molten metal forms a molten pool or crater and tends to flow away from the arc. As it moves away from the arc, it cools and solidifies. A slag forms on top of the weld to protect it during cooling. There are several types of welding machines include motor-generators, engine-driven generators, transformers, rectifiers, and combination transformer and rectifiers. Each type has its place and purpose. The basic function of each is the same-providing a source of controlled electric power for welding. This controlled electric power has the characteristic of high amperage at low voltage. The high amperage is required to provide sufficient heat at the arc. The voltage must be low enough to be safe for handling and yet high enough to maintain the arc. The welding machine permits the welder (welding operator) to control the amount of current he uses. This, in turn, controls the amount of heat of the arc. Some welding machine also permits the operator to select either a forceful or soft arc and to control its characteristics to suit the job. These are some standard that is used for welding 1. ASME (American Society of Mechnical Engineers), includes: - ASME Boiler& Pressure Vessel Code - ASME Code For Pressure Piping Giáo trình Anh văn chuyên ngành công nghệ hàn 6 2. AWS (American Welding Society) - AWS D1.1- Structural Welding Code - Steel 3. API (American Petroleum Institute) : - API 650 – Welded Steel Tanks For Oil Storage - API 1104 – Welding Of Pipelines And Related Facilities 4. ISO (Internaytional Standardization Organization) 5. EN (European Standard/Normal) 6. JIS – Japanese Industrial Standards IV. EXERCISE 1. Give main ideas of paragraph? 2. What is arc welding? 3. What happens in the arc? 4. What do the electrodes affect to the arc? 5. List and explain the uses of the standards? Giáo trình Anh văn chuyên ngành công nghệ hàn 7 UNIT 2: WELDED JOINT AND WELD Object: to show the types and position of welded joints I. VOCABULARY: - Welding position V trí hàn - Flat Hàn - Vertical Hàn ứ - Overhead Hàn ử - Horizontal Hàn ngang - Butt joint Liên - Corner joint Liên - Lap joint Liên - Tee joint Liên ữ T - Edge joint Liên - Butt weld hàn giáp - Fillet weld - Groove angle Góc vát - Groove weld hàn có vát mép - Spot weld - Spot hàn - Geometry - Configuration d - Preparation Sự ẩ - Surface - Weld reinforcement - Weld concavity õ - Weld width - Leg of a fillet weld - Sealing run hàn lót II. GRAMMAR: THE COMPARISON OF ADJECTIVES Shorter adjectives: form of regular comparison. Most common adjectives are short words. They form their comparatives and superlatives as shown: Adjecctive Comparative Superlative Clean Cleaner Cleanest Big Bigger Biggest Strong Stronger Strongest Long Longer Longest Giáo trình Anh văn chuyên ngành công nghệ hàn 8 Notes on the comparison of shorter adjectives Spelling of comparative and superlative forms: - Most one-syllable adjectives form their comparatives and superlatives like clean: -er and -est are added to their basic form. - Many one-syllable adjectives end with a single consonant after a single vowel-letter. This consonant doubles in the comparative and superlative, as in the case of big: bigger, biggest. - Many one-syllable adjectives end in -e, like nice or safe. These add -r and -st to the basic form: safer, safest. - Some adjectives, like dry, end in -y with a cosonant letter before it. These adjectives are usually two-syllable. In the comparative and superlative -y is replaced by i: drier, driest. Longer adjectives: Most longer adjectives combine with quantifiers „more‟ / „less‟ to form their comparatives and „ most‟ / „ least‟ to form their superlatives Ex: This joint is more beautiful than that one. This position is the most difficult job when welding a fabrication. Compound noun: Noun + Noun: Ex: Butt joint, lap joint, class room III. PRACTICE There are numerous types of welded joints and various positions in which they are welded. Figure below shows a variety of these joints as they may appear on welding jobs There are four basic welding positions: FLAT (F), VERTICAL (V), OVERHEAD (OH); HORIZONATAL (H). It is possible to weld any type of joint in any of the four positions, but whenever possible joints are placed in the flat position. Welding in the flat position is much faster and easier than any of other positions. A summary of the basic types of joints and basic types of welds is shown in figure below In a joint, the adjoining members may contact each other in several ways, as illustrated by the butt, T, corner, lap and edge joints. These general descriptions of the joint geometry, however, do not define the weld joint configuration, since it can be made in various ways. Thus, a weld butt joint can be made square, double-square, single-bevel, double-bevel, single-V, double-V, or by four other joint configurations. A T-connection can be made with a double fillet, as shown: or it may be made with a single or double- bevel or single or double J. V and U weld joints are feasible only for butt and corner welds because of the need for the preparation of both surfaces. Giáo trình Anh văn chuyên ngành công nghệ hàn 9 1. Types of joints 1.1. Butt Joint 1.2. Tee Joint 1.3. Corner Joint 1.4. Lap Joint 1.5. Edge Joint 2. Types of welds 2.1. Fillet Weld Giáo trình Anh văn chuyên ngành công nghệ hàn 10 Single Double 2.2. Square Weld Single Double 2.3. Bevel Groove Weld . Single Double 2.4. Vee Groove Weld Single Double 2.5. J Groove Weld Single Double 2.6. U Groove Weld Giáo trình Anh văn chuyên ngành công nghệ hàn 11 Single Double UNIT 3: WELDING CONSUMABLES Object: to deliver the uses and characteristics of the metal electrode I. VOCABULARY - Characteristic: - Core: Lõi - Cover: Vỏ ỏ - Shielded Metal Arc Welding (SMAW): Hàn à - Desired weld: M - Consist of: Bao - Cellulose: X - Rutile: Rutin - Dioxidizing: Ôxy hóa - Binders: - Extrusion: ù ra, é i - Tensile Strength : ự kéo - Physical properties: í í - Stabilize: Làm - Essential: ủ - DC: Dirrect current: Dòng - AC: Alternating current: Dòng - Slag removal: Gỡ Lo ỏ ỉ - Consistently: Liên ỉ - Depend on: Tùy - Filler wire: Q - Electrode wire: Dây hàn - Self-shielding Wire: Dây ự - Flux cored electrode: Dây õ - Arc welding electrode: cự - Covered electrode: Que - Electrode covering: T - Welding flux: T hàn - Shielding gas: Khí - Position: V trí - Relationship: liên quan - Designation: Sự - Characteristic: tính - Operation: Sự ành - Compound: Ghép, - Medium: Trung bình Giáo trình Anh văn chuyên ngành công nghệ hàn 12 II. GRAMMAR RELATIVE CLAUSES a. Defining relative clauses These describe the preceding noun in such a way as to distinguish it from other nouns of the same class. A clause of this kind is essential to the clear understanding of the noun. Normally relative clauses should be placed directly after their noun or pronoun: Example: The noise that the welders made woke everybody up. Relative pronouns used in defining relative clauses The format is as follows: Subject Object Possessive For things which which whose / of which That that Defining relative clauses: things b. Subject Either which or that, which is more formal: - This is the construction that / which was finished yesterday. - This is the fabrication that shows the job of my students. c. Object of a verb Which or that, or no relative at all: - The tool that / which you welded is becoming dangerous. d. Object of a preposition The formal construction is preposition + which, but is more usually to move the preposition to the end of the clause, using which or that or omitting the elative altogether: - The ladder on which the welders usually stand to join a construction. - The ladder which / that the welders usually stand on to join a construction. e. Relative adverb: where Where can replace „in/ at which‟ „w ‟ - That is the shop where (= in/ at which) students usually practise their tasks after studying theory. III. PRACTICE The first specification for mild-steel covered electrodes, AWS A5.1 was writen in 1940. As the welding industry expanded and the number of types of electrodes for welding steel increased, it became necessary to devise a system of electrode classification to avoid confusion. The system used applies to both the mild-steel A5.1 and the low-alloy steel A5.5 specification. (Figure 4 – Covered electrode) Giáo trình Anh văn chuyên ngành công nghệ hàn 13 Figure 4 Table 1 AWS numbering system a. The prefix “E” designates arc welding electrode b. The first two digits of 4-digit numbers and the first three digits of 5-digit numbers indicate minimum tensile strength E60XX 60,000 psi Tensile Strength E70XX 70,000 psi Tensile Strength E110XX 110,000 psi Tensile Strength c. The next –to- last digit indicates position EXX1X All positions EXX2X Flat position and horizontal fillets d. The last two digits together indicate the type of covering and the current to be use e. The suffix (example : EXXXX-A1) indicates the approximate alloy in the deposit -A1 ½% Mo -B1 ½% Cr, ½% Mo -B2 1-1/4%Cr, ½% Mo -B3 2-1/4%Cr, 1% Mo -C1 2-1/2%Ni -C2 3-1/4%Ni -C3 1%Ni, .35%Mo, .15%Cr -D1&D2 .25-.15%Mo, 1.25-2.00%Mn -G 50 min Ni, .30 min Cr, .20 min Mo, .10min V (only one of the listed elements is required) Giáo trình Anh văn chuyên ngành công nghệ hàn 14 Classifications of mild and low-alloy steel electrodes are based on an “E” prefix and a four or five-digit number. The fisrt two digits (or three, in a five-digit number) indicate the minimum required tensile strength in thousands of pounds per spuare inch. For example, 60=60.000 psi, 70=70.000psi, and 100=100.000psi. the next to the last digit indicates the welding position in which the electrode is capable of making satisfactory welds: 1= all position – flat, horizontal, vertical, and overhead; 2= flat and horizontal fillet welding. The last two digits indicate the type of current to be used and the type of covering on the electrode (see table 2) Originally a color identification system was developed by the National Electrical Manufacturers Association (NEMA) in conjunction with the American Welding Society to identify the electrode’s classification. This was a system of color markings applied in a specific relationship on the electrode. Table 2 – AWS A5.1-69 electrode designations for covered arc-welding electrodes Designation Current Covering type EXX10 EXX11 EXX12 DC(+) only AC or DC(+) AC or DC(-) Organic Organic Rutile EXX13 EXX14 EXX15 AC or DC(+ , -) AC or DC(+ , -) DC (+) only Rutile Rutile, iron-powder (approx 30%) Low – hydrogen EXX16 EXX18 EXX20 AC or DC(+) AC or DC(+) AC or DC(+ , -) Low – hydrogen Low – hydrogen, iron-powder (approx 25%) High iron-oxide EXX24 EXX27 EXX28 AC or DC(+ , -) AC or DC(+ , -) AC or DC(+) Rutile, iron-powder (approx 50%) Mineral, iron-powder (approx 50%) Low – hydrogen, iron-powder (approx 50%) In addition to the classifications specified by the American Welding Society, electrodes can be classsified by the characteristics of the molten metal and molten flux during the welding operation. These broad classifications are fast-freeze, fast-fill, and fill-freeze, the terms being descriptive of the operation of the electrode. Fast-freeze electrodes Fast-freeze electrodes are compounded to deposit weld metal that solidifies rapidly after being melted by arc, and are thus intended specifically for welding in the vertical and overhead positions. Giáo trình Anh văn chuyên ngành công nghệ hàn 15 Fast- freeze electrodes provide deep penetration and maximum admixture. The weld bead is flat with distinct ripples. Slag formation is light, and the arc is easy to control. Applications for fast-freeze electrodes are: 1. General-purpose fabrication and maintenance welding 2. Vertical-up and overhead plate welds requiring X-ray quality 3. Pipe welding 4. Welds to be made on galvanized, plated, painted, or unclean surfaces 5. Joints requiring deep penetration, such as square-edge butt welds 6. Sheet- metal welds, including edge, conner, and butt welds Fast-fill electrodes Fast-fill electrodes are compounded to deposit metal rapidly in the heat of the arc and are, thus, well suited to high-speed welding on horizontal surfaces. The weld metal solidifies some what slowly; therefore this type of electrode is not well suited for out- of-position welds. Arc-penetration is shallow with minimum admixture. The bead is smooth, free of ripples, flat or slightly convex. Spatter is negligible. Slag formation is heavy, and the slag peels off rapidly. Applications for fast-fill electrodes are: 1. Production weld on plate having a thickness of 3/16 or more. 2. Flat horizontal fillets, laps, and deep groove butt welds. 3. Welds on medium-carbon crack-sensitive steel when low-hydrogen electrodes are not available. (Preheat may be required) Fill-freeze electrodes Fill-freeze electrodes are compounded to provide a compromise between fast-free and fast-fill characteristics, and thus provide medium deposition rates and medium penetration. Applications for fill-free electrodes include: 1. Downhill fillet and lap welds 2. Irregular or short welds that change direction or position. 3. Sheet-metal lap or fillet welds 4. Fast-fill joints having poor fitup. 5. General-purpose welding in all position. Giáo trình Anh văn chuyên ngành công nghệ hàn 16 Table 3 Welding parameter Approximate Electrode Amperage Settings Fast Freeze Fill Freeze Fast Fill Low Hydrogen E6010 - E6011 E6013 - E7014 E7024 - E7028 E7018 Diameter of Current Setting Current Setting Current Setting Current Setting Electrode Inches(Millimeters) Amperes Amperes Amperes Amperes 3/32 in (2.4 mm) 40 - 90 75 - 105 85 - 155 70 - 140 1/8 in (3.2 mm) 75 - 130 100 - 165 100 - 175 90 - 185 5/32 in (4.0 mm) 80 - 160 135 - 225 160 - 270 140 - 230 3/16 in (4.8 mm) 110 - 225 185 - 280 220 - 330 210 - 300 7/32 in (5.6 mm) 200 - 260 235 - 340 270 - 410 230 - 380 1/4 in (6.4 mm) 220 - 325 260 - 425 315 - 520 290 - 440 Giáo trình Anh văn chuyên ngành công nghệ hàn 17 UNIT 4: WELDING TECHNOLOGY Object: To introduce general about welding technology I. VOCABULARY - Manual welding: Hàn tay - Mechanized welding : Hàn - Automated welding : Hàn ự - Fusion welding: Hàn - Arc welding: Hàn - Surfacing: Hàn ắ - Arc welding using a consumable electrode: Hàn dù ự ch - Arc welding using non-consumable electrode: Hàn qua dù ự không nóng ch - Submerged arc welding: Hàn d (Hàn h - Gas shielded arc welding: Hàn g trong môi tr í - TIG (Tungsten inert gas welding): Hàn ự w f í ự trong môi í - MIG – Metal inert gas welding: Hàn ự í - MAG – Metal active gas welding: Hàn ự í í - Self-shielded welding: Hàn ự - Pulsed arc welding: Hàn - Manual arc welding: Hàn - Automatic arc welding: Hàn ự - Robotic welding: Hàn robot - Double arc welding: Hàn - Multi-arc welding: Hàn - Twin electrode welding: Hàn 2 ự - Semi-automatic arc welding: Hàn ự - Plasma welding: Hàn plasma - Electroslag welding: Hàn ỉ - Laser welding: Hàn laze - Gas welding: Hàn khí - Resistance welding: Hàn ở - Spot welding: Hàn - Resistance seam welding: Hàn - Step-by-step welding: Hàn - Constant: Liên - Heat source: - Gap: , khe - Withdraw: Rút ủ ỏ - Spark gap: ử - Protect: Giáo trình Anh văn chuyên ngành công nghệ hàn 18 - Adjust: ỉ - Maintain: Duy trì - Stainless steel: Thép ỉ - Concentrate: T trung - Equal (to): T ân II. GRAMMAR: The passive voice with may, can, should and must S + can / may / should / must + V + O S + can / may / should / must + be + V_ed (Past participle) Active: You should shut these doors Passive: These doors should be shut Active: You can use the process to deposit metal to form a surface with alternative properties. Passive: The process can be used to deposit metal to form a surface with alternative properties. III. PRACTICE: MANUAL METAL ARC WELDING Manual metal arc (MMA) welding, also known as shielded metal arc welding (SMAW), stick welding, or electric arc welding is a constant current drooping arc process (Figure 5). In manual metal arc welding the heat source is an electric arc, which is formed between a consumable electrode and the parent plate. The arc is formed by momentarily touching the tip of the electrode onto the plate and then lifting the electrode to give a gap of 3 mm – 6 mm between the tip and the plate. When the electrode touches the plate, current commences to flow and as it is withdrawn the current continues to flow in the form of a small spark across the gap, which will cause the air in the gap to become ionised, or made conductive. As a result of this the current continues to flow even when the gap is quite large. The heat generated is sufficient to melt the parent plate and also melt the end of the electrode – the molten metal so formed is transferred as small globules across the arc into the molten pool. Giáo trình Anh văn chuyên ngành công nghệ hàn 19 Figure 5 Type of operation. Manual. Mode of Operation. Arc melts parent plate and electrode to form a weld pool that is protected by the flux cover. Operator adjusts the electrode feed rate, i.e. hand movement, to keep the arc length constant. Slag must be removed after depositing each bead. Normally the SMAW provides a small degree of penetration, requiring plate edge preparation. Butt welds in thick plate; or large fillets are deposited in a number of passes. The process can also be used to deposit metal to form a surface with alternative properties. TUNGSTEN INERT GAS WELDING Tungsten inert gas welding is a constant current drooping arc process. It is also known as TIG, gas tungsten arc welding – GTAW, wolfram inert gas – WIG, and under the trade names of argon arc and helium arc (Figure 6). Figure 6 Giáo trình Anh văn chuyên ngành công nghệ hàn 20 Type of Operation. Usually manual, but can be mechanised. Mode of Operation. An arc is maintained between the end of a tungsten electrode and the work. The electrode is not consumed and the current is controlled by the power source setting. The operator must control the arc length and also add filler metal if needed to obtain the correct weld; consequently, a high degree of skill is needed for the best results. The arc is unstable at low currents. Special provision is made for starting (high frequency or surge injection) and for welding thin materials (pulse TIG). METAL INERT GAS WELDING With a 'flat' volts/amps characteristic an attempted alteration in arc length (volts) will have little effect, hence arc length (volts) remains constant but a significant change in current will result. This is often referred to as the 'self-adjusting arc'. Metal Inert Gas (MIG) welding is a 'flat' arc process (constant voltage process). Also known as Metal Active Gas (MAG); CO2; Metal-arc Gas Shielded, flux core and GMAW (US). MIG can be used on all materials, in all positions, with high productivity and low heat input. There is no CO2 MIG welding with stainless steel. Normally DC positive though some flux cored processes uses DC negative (Figure 7). Figure 7 Type of Operation. Manual, mechanised, semi-automatic and automated (robotics). Mode of Operation. Giáo trình Anh văn chuyên ngành công nghệ hàn 21 An arc is maintained between the end of the bare wire electrode and the work piece. The wire is fed at a constant speed, selected to give the required current, and the arc length is controlled by the power source. The operator is not therefore concerned with controlling the arc length and can concentrate on depositing the weld metal in the correct manner. Hence the name 'semi-automatic' for manual operation, in which wire, gas and power are fed to a hand held gun via a flexible conduit. The process can be operated at high currents (250 - 500 A) when metal transfer is in the form of a 'spray', but, except for aluminium, this technique is confined to welding in the flat and horizontal positions. For vertical and overhead welding special low current techniques must be used, i.e. 'dip' transfer or pulsed arc. The arc and weld pool are shielded by a stream of gas. The electrode can be solid or flux cored. SUBMERGED ARC WELDING A flat arc process - (constant voltage process). It is used in beam, boom, tractor and multi-head type rigs (figure 8). Type of Operation. Mechanised, automatic or semi-automatic. Mode of Operation. An arc is maintained between the end of a bare wire electrode and the work. As the electrode is melted, it is fed into the arc by a set of rolls driven by a governed motor. Wire feed speed is automatically controlled so that it equal to the rate at which the electrode is melted, thus arc length is constant (similar to MIG/MAG - constant voltage). The arc operates under a layer of granular flux; hence „submerged arc‟. Some of the flux melts to provide a protective blanket over the weld pool. The remainder of the flux is unaffected and can be recovered and re-used, provided it is dry and not contaminated. A semi-automatic version is available in which the operator has control of a welding gun that carries a small quantity of flux in a hopper. Giáo trình Anh văn chuyên ngành công nghệ hàn 22 Figure 8 IV. PRACTICE 1. What is an inert gas? Name two. Name a widely used GMAW gas that is not inert? 2. W ‟ f G W ? 3. What is one advantage of GMAW over semiautomatic submerged-arc? Over flux- cored electrode welding? 4. Explain the principle of SMAW? 5. Explain the principle of MIG/MAG? 6. Explain the principle of TIG? 7. Explain the principle of SAW? Giáo trình Anh văn chuyên ngành công nghệ hàn 23 UNIT 5: IMPERFECTION WELDING Object: to study imperfection welding I. VOCABULARY: - Undercut: Cháy chân - Overlap: tràn - Fish eye: ắ cá - Slag inclusion: ẫ ỉ - Pit, surface pore: R - Porosity: R - Tungsten inclusion: ẫ vonfram - Burn through: Cháy xuyên ủ - Incomplete joint??: Hàn - Incomplete fusion: K - Weld crack: V ứ - Longitudinal crack: V ứ d - Transverse crack: V ứ - Underbead crack: V ứ d hàn - Toe crack: V ứ - Hot crack: V ứ - Cold crack: V ứ - Reheat crack: V ứ - Root crack: V ứ - Crater crack: V ứ - Lamellar tear: V ứ - Sub-surface: d - Notch: V í - Focal point: Tiêu - Fatigue life: Sứ ự T ỏ - Stray: - Fuse: Nóng - In service: Trong ử d ử d - Discontinuity: Gián - Diffusion: Sự án - Martensitic: Mactensit hóa già - Union: Sự liê - Adjacent: Lân - Insufficient: T ủ - Elongate: Giãn é d d - Solidification: Sự ứ ự ự ắ - nozzle: ở - Molten: Nóng Giáo trình Anh văn chuyên ngành công nghệ hàn 24 II. GRAMMAR: THE ARTICLE: A / AN AND THE. 1. The indefinite article (a/an). Indefinite article is used before a singular noun which is countable when it is mentioned for the first time and represents no particular person or thing: Example: a butt joint a lap joint a position a way 2. The use of a / an. The „a‟ is used before a word beginning with a consonant, or a vowel with a consonant sound: Example: a steel a bar of steel a joint The „an‟ is used before words beginning with a vowel ( a, e, i, o, u) or words beginning with a mute h: Example: an iron an imperfection an irregular or individual letters spoken with a vowel sound: Example: an L-plate 3. The definite article (the). The definite article is used before a noun which has become definite as a result of being mentioned in second time or afterward: Example: There is a student repairing electric in the shop. The student that you asked to help me yesterday. Or before a noun made definite by the addition of a phrase or clause: Example: The body of the weld The area of the arc strike The damage on the parent material At the end of The side of the weld Giáo trình Anh văn chuyên ngành công nghệ hàn 25 III. PRACTICE 1. Defects detected by surface inspection Defects, which can be detected by visual inspection, can be grouped under five headings. 1. Cracks. 2. Surface irregularities. 3. Contour defects. 4. Root defects. 5. Miscellaneous. 1.1. Surface cracks A crack is a linear discontinuity produced by fracture. Cracks may be longitudinal, transverse, edge, crater, centreline, fusion zone, underbead, weld metal or parent metal (Figure 9 -11). Longitudinal, in weld metal (centreline) Longitudinal, in parent plate Figure 9 Transverse Crater (star cracking) Figure 10 Giáo trình Anh văn chuyên ngành công nghệ hàn 26 Figure 11 1.2. Surface irregularities Undercut. An irregular groove at a toe of a run in the parent metal or in previously deposited weld metal. If created sub-surface it becomes a very effective slag trap in the body of the weld. Undercut is essentially a notch that in turn becomes a focal point for stress loading, thereby reducing the fatigue life of the joint. (Figure 12) Causes - current too high, voltage too high, travel speed too high, electrode too small, electrode angle. Figure 12 Overlap. An imperfection at the toe or root of a weld caused by weld metal flowing on to the surface of the parent plate without fusing to it. Causes - slow travel speed, large electrode, tilt angle, poor pre-cleaning. Giáo trình Anh văn chuyên ngành công nghệ hàn 27 Spatter. Stray globules of weld material, on parent plate outside the weld. Causes - dam