Que5.4. Write short note on position of weld. Answer 1. The position of weld is indicated by an arrow and a reference line. For Example i. When the weld symbols is below the reference line the weld is made on the same side of the joint as the arrow head, i.e., the arrow side 5.4.1( i). ii. When the weld symbol is above the reference line, the weld is made on the other side of the common contrary the arrow headFig.5.4.1( ii). iii. When the weld symbol is on both sides of the reference line, the welding is to be carried out on both sides of the commonFig.5.4.1( iii). iv. When resistance welds are to be indicated, the arrow shall point towards the centre line along which the welds are to be made. Que5.5. Explain how a good joint design can be named? Answer For selection of good common design weldment should have following considerations 1. Adequately designed to meet the willed service for the needed life. 2. Fabricated with specified accoutrements and in agreement with the design generalities. 3. Handled and maintained duly. 4. The design of a weldment should be harmonious with sound engineering practices. 5. factors of acceptable size should be specified to insure that stresses from awaited service loads aren’t inordinate. 6. The willed service should be precisely anatomized to determine whether cyclic lading might affect in fatigue failure in largely stressed-out members. 7. Environment conditions leading to brittle fracture, creep, and erosion of welds should be considered in the design. Que5.6. Define cracking of weld. Explain briskly cracking and cold cracking. List the rules that must be followed to avoid cracking. Answer Cracking of Weld 1. Cracking is a weld disfigurement that may appear on the weld face or under the weld blob. 2. The cracking in the material is due to inadequate strength or rigidity at the applicable stage to tolerate the welding stresses which exceed the fracture stresses. 3. Cracking may do in weld essence, heat affected zone( HAZ) or in both. Hot Cracking 1. Cracking occurs at a high temperature just below the freezing point is known as hot cracking. 2. Hot cracking is told by the sulphur and carbon content of mild sword weld essence because sulphur tends to form a emulsion iron sulphide( FeS) which can form a low melting point eutectic of Fe/ FeS and insulate to form a network at the grain boundaries of the sword and it remains liquid after the essence has firmed . 3. There’s no cohesion between the grains and the weld essence which may tear piecemeal under contractional stresses. 4. Hot crack may be nonstop or spastic. It frequently extends from the weld root and may not extend to the face of the weld. Cold Cracking 1. Cold cracking is generally observed at room temperature. 2. Cold cracking occurs in both weld essence and conterminous base essence. 3. Causes of cold cracking are as follows Essence fineness combined with a tensile stress exceeding the fracture stress. ii. common restraint and high thermal inflexibility. iii. Presence of hydrogen in the weld essence. Rules which must be followed to avoid cracking in welded joints 1. By keeping the weld essence and base essence ductile after welding because ductile ingredients are suitable to distort plastically before the cracking. 2. By perfecting the strength or rigidity of material so that it can tolerate the welding stresses at applicable stages of welding. 3. Maintaining the proper welding speed and proper bow length. 4. Maintaining the proper current viscosity. 5. junking or restriction of the contaminations similar as S and high C or Ni content because they form low freezing point liquid flicks. 6. precluding the martensite conformation in welding of sword during cooling. 6. By using correct welding fashion or use of padding essence having same rate of compression as that of the parent essence. 7. By precluding the martensite conformation in the weld region, cracking can be avoided. Que5.7. Describe the colorful blights in welding and its causes and remedies. OR Explain any five welding blights along with the causes and remedies. AKTU 2017- 18, Marks 10 Advance Welding 5 – 9 H( ME- Sem- 5) Answer colorful blights in welding and its causes and remedies are as follows Deficient Penetration 1. Deficient penetration occurs when the depth of the welded joint is inadequate. 2. Penetration is defined as the distance from base plate’s top face to the maximum extent of the weld nugget. Base essence Base essence Base essence Weld blob Fillet weld Base essence Root Root 5.7.1.( a) Deficient penetration at the root of a butt weld. b) Deficient penetration at the root of a fillet weld. a)( b) Causes of Deficient Penetration 1. indecorous joints. 2. Too large root face. 3. lower bow current and faster bow trip speed. 4. Too large electrode periphery and longer bow length. Remedies of Deficient Penetration 1. adding the heat input. 2. Reducing the trip speed during the welding. 3. Changing the common design. 4. icing that the shells to be joined fit duly. ii. Addition 1. Eliminations may be in the form of sediment or any other foreign material, which doesn’t get a chance to float on the face of the solidifying weld essence and therefore gets entangled inside the same. 2. Eliminations lower the strength of the joint and make it weaker. Causes of Addition 1. Too high or too low bow current. 2. Long bow and too large electrode periphery. 3. Insufficient dicing and drawing of former passes in multipass welding. 4. incorrectly placed method welds. 5. Too small included angle of the joint. Remedies of Addition 1. drawing the weld blob face before the coming subcaste is deposited, by means of a line encounter. 2. furnishing sufficient shielding gas. 3. Redesigning the joint so as to permit sufficient space for proper manipulation of the billabong
of molten weld essence. iii. Porosity and Blowholes 1. Porosity is a group of small voids and blowholes are comparatively bigger insulated holes or depressions. 2. They’re substantially generated due to the entangled feasts. 5.7.3. Porosity. Causes of Porosity and Blowholes 1. Use of indecorous electrode and longer bow. 2. Faster bow trip pets. 3. Too low and too high bow currents. 4. sick job face i.e., presence of scale, rust, oil painting and greaseetc., on the face of the job. 5. Due to the gas ruse during solidification of weld. Remedies of Porosity and Blowholes 1. Proper selection of electrodes and padding essence. 2. bettered welding ways similar as preheating of the weld area or an increase in the rate of heat input. 3. Proper cleaning and the forestallment of pollutants from entering the weld zone. 4. Reduced welding pets, to allow time for gas to escape. iv. Spatter 1. Spatters are the small essence patches which are thrown out of the bow during welding and get deposited on the base essence around the weld blob along its length. Causes of Spatter 1. inordinate bow current. 2. Use of longer bow. 3. Use of damp electrodes. 4. Electrodes being carpeted with indecorous flux constituents. 5. Arc blow making the bow willful . Remedies of Spatter 1. Use proper bow current to weld. 2. Use proper bow length. 3. Use fresh electrodes. 4. Use of AC power to reduce bow blow. Undercut 1. Undercut is a kind of weld disfigurement which forms a groove in the parent essence along the sides of the weld blob. 2. Groove reduces the consistence of the plate and also reduces the strength of the weld. Undercut 5.7.5. Undercut. Causes of Undercut 1. Wrong manipulation and inclination of electrode and inordinate weaving. 2. Too large electrode compasses. 3. Advanced current. 4. Longer bow. 5. Faster bow trip speed. Remedies of Undercut 1. Use proper bow current. 2. Use proper electrode. 3. Weaving should be proper and as per demand. 4. Use proper bow trip speed. vi. Hot Tear 1. In this welding disfigurement the deposited essence being hot, starts developing crack from the near edge so that after it has been solidified the crack increases. 2. Hot tearing, also known as solidification cracking is due to tearing of the grain boundaries of weld essence before complete solidification has taken place and essence is still in plastic state. Causes of Hot Tear 1. indecorous selection of electrode material. 2. Welding current isn’t proper. 3. indecorous electrode consistence. Remedies of Hot Tear 1. elect proper electrode material. 2. Welding current should be optimum as per the demand. 3. Electrode consistence should be optimum and according to the base essence to be welded.
