Anglicky v odborných předmětech "Support of teaching technical subjects in English “

1. Anglicky v odborných předmětech"Support ofteachingtechnicalsubjects in English“ Tutorial: Engineeringtechnology Topic: Problems with welding arc – causes and defects´ remove Preparedby: Ing. Josef Martinák st. Projekt Anglicky v odborných předmětech, CZ.1.07/1.3.09/04.0002 je spolufinancován Evropským sociálním fondem a státním rozpočtem České republiky.

2. Big spatter • Precautions: • To decrease welded flow • To reduce arc length • To control right polarity • According to electrode type • To clean, and dry welded place • Causes: • Too big welding flow • Too long arc • Humidity or dirt on welded edges

3. Difficult arc ignition • Precautions: • To increase welded flow • No-load voltage of welding source is low for used electrode types • To clean grounding brace surface • To dust off or grind off electrode tip gently and to ignite arc by contact • Causes: • Too low welding flow • Ignition voltage is low • Ignition electrode tip covers ground electrodes

4. Cold joints • Causes: • Low welding flow • Wrong electrode leading • Too high welding speed • Small electrode diameter

5. Fissures in crater • Precautions: • To fill crater at welding finish • Causes: • Too quick welding shut down (starting fissure in crater cavity is caused by shrinkage at welded metal solidification)

6. Root defects • Causes: • Moving welding speed is high • Used electrode diameter is too thick • Space between welded materials is too small • Wrong electrode leading • Precautions: • To decrease welding speed • To choose smaller electrode diameter for root weld • To use right gap between welded parts (e.g. By grinding) • Correct welding technique

7. Cracks in welded joints • Precautions: • To choose welded material • To decrease cooling speed by correct preheating • To use dried alkaline electrodes • Causes: • Basic material with higher carbon, manganese or other alloyed elements content • Quick cooling in thermally influenced area of basic material • Damp electrodes • ( hydrogenembrittlement)

8. Crystallizing cracks • Causes: • Wrong electrode type • Basic material with high carbon and sulphur content • Wrong weld geometry • Weld – mainly root layers and tack welds – if not sized sufficiently taking into consideration possible shrinking effect • Precautions: • To use electrodes with alkaline coat whose welded metal is more resistant to crack’s development • To use correct electrode material with goodweldability • To prevent wide spaces among components and to ensure right root penetration

9. Pores • Precautions: • To re-dry of electrodes according to manufacturer’s instructions or use new ones • To remove paint impurities and corrosive products of welded surfaces, to remove iron scales and to dry humidity on welded surfaces • Causes: • Humidity of wrongly stored electrodes • Impurities or protective paint on welded edges

10. Arc blowing • Causes: • Electric arc blowing due to magnetic fields • Appearance mostly at direct flow welding • It is shown on weldment edges and in limited space • Precautions: • To fix ground clamp at the place of weld commencement (welding to proceed from grounding clamp) • To use alternative current where possible • To change electrode angle. If possible, to keep the shortest arc length.

11. Slag inclusions • Causes: • Slag overtake the welding arc • Imperfect slag removal between individual runs • Convex run’s shape makes ´slags´ pockets’ • Wrong welding run’s sequence • Removal: • To increase welding speed or to extend electrode position angle • Accurate slag removal by grinding, if it is necessary • Use right technique of welding runs placing • To choose right welding process

12. Questions and revision • Describe causes of big spatter.

13. Literature • DILLINGER, Josef. A KOL. Moderní strojírenství pro školu i praxi. 1. Praha: Europa-Sobotáles, 2007. ISBN 978-80-86706-19-1. • M. HLUCHÝ, J. KOLOUCH, R. PAŇÁK. Strojírenská technologie II Translation: • www.seznam.cz • www.slovnik.cz • JANATA, Petr. Handy slovník technický anglicko-český a česko-anglický. Plzeň: Nakladatelství Fraus, 2000. ISBN 80-7238-075-3 • Lingea LEXIKON 5, Technický slovník anglicko-český a česko-anglický. 2010.