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Welding

Leaving cert Engineering HL Q5

QuestionAnswer
Describe the main features of MMA Welding >Flux coated consumable electrode >Joint protected by gas from melting flux >Slag produced on top of weld >Electrode has to be changed often >Versatile process >Equipment light and portable
Describe the main features of MIG welding >Semi automatic process >Bare wire electrode fed to gun from a spool >Joint protected by inert gas (argon) >Very easy to do >Equipment big and bulky >No slag produced
Describe the main features of TIG welding >Non-consumable tungsten electrode >Filler rod added to weld by hand >Joint protected by inert gas (argon) >Very difficult and specialised >Used for Aluminium and stainless steel
Describe the main features of SAW welding >Fully automatic process set up on guide rail >Wire electrode fed from spool >Powder flux fed from hopper completely submerges the arc >excess flux sucked back into the hopper >used for straight lines eg bridges, ships, factory roofs
Describe the main features of Spot welding >Non-consumable copper electrode >Weld nugget formed between overlaping work pieces >No filler added >Very quick and easy to use >Used for sheet metals on car panels and filing cabinets
Describe the main features of Seam welding >Non-consumable copper motorised electrode rollers >Series of overlapping weld nuggets form air tight seal >No filler added >Quick and easy to use >Used to seal the edges of radiators
Describe the main features of Electro Slag welding >Fully automatic process >Used to weld very thick plate >Must be done vertically >Water cooled copper shoes enclose the weld pool >wire electrode and flux powder fed in >Weld pool rises until the whole gap is filled in
Describe three important safety features that minimise electrical hazards associated with manual metal arc welding; • MMA welding machines are protected from electrical surges. • Welding stations need to be free from dampness. • Cables and electrode holders are covered with plastic insulators. • Welding machines are earthed. • Power supplied can be adjusted to an a
Why is tungsten inert gas welding suitable for welding aluminium? Aluminium oxidises very quickly when heated. This tenacious oxide layer is overcome with the use of an inert gas, such as argon, and the cathodic action of the arc on the work-piece. Aluminium can be welded successfully in this way by TIG welding.
Explain the function of dissolved acetylene in oxy-acetylene welding If acetylene is compressed into a cylinder, it would explode under high pressure. Acetylene cylinders are packed with a porous material that is filled with acetone. The acetylene is dissolved into the acetone under pressure to prevent it from exploding.
Describe, with examples, the importance of colour coding in oxyacetylene equipment; It's important so the gasses don't get mixed up. Oxygen cylinder is black and acetylene is maroon, hoses and regulators are colour coded with oxygen as blue and acetylene as red.
Outline three safety precautions that should be observed in the preparation of equipment and materials for oxyacetylene welding; Oil & grease needs to be removed to minimise reaction with welding process Torch must be thoroughly cleaned before starting weld.Flashback arrestors need to be in place on fuel and oxygen line Correct colour coding of cylinders and hoses must be observed
Describe multi-run welds; A series of welds are run across the metals to be joined in multi-run welding. A superior weld is produced as each weld has a post heating effect on the previous run. The finished weld is stronger and more refined in structure than single run welds.
Outline two methods used to prevent porosity occurring in welds • Make sure the gas tank is not empty • Clean the material surfaces removing oil and grease • Eliminate moisture – the prime cause of weld porosity • Make sure gas flow is at correct pressure • Eliminate drafts and air
Describe the carburising flame used in oxy-acetylene welding. • Contains excess acetylene. • It has a working temperature of 3150oC. • Used to weld aluminium and alloy steel where it gives protection against oxidation. • Flame is bigger with the distinctive acetylene feather.
Describe the Oxidising flame used in oxy-acetylene welding. • Contains excess oxygen. • Has a working temperature of up to 3500°C. • Used to weld copper and brass, it would oxidise steel. • Flame appears smaller.
Describe the Neutral flame used in oxy-acetylene welding. • A balanced proportion of oxygen and acetylene. • Maximum combustion as all carbon from the acetylene is used. • Has a working temperature of up to 3300°C. • The most extensively used flame for oxy-acetylene welding.
Describe any three methods of joint protection when welding >Flux coating on the electrode in MMA welding >Inert gas pumped out of the gun in MIG/TIG welding >Arc submerged under flux powder in SAW welding >Acetylene flame
Describe three hazards associated with the use of manual metal arc welding in a school engineering room. >Other students might look at the arc and damage their eyes >Someone could trip on the wires >Appropriate ventilation >A welding apron should be worm to protect uniform
Outline the functions of the transformer, capacitor and rectifier in manual metal arc welding. A step-down transformer is used to change the mains voltage from 220V to a suitable level (80-100V) for welding The rectifier changes alternating current (AC) to direct current (DC) The capacitor is employed to provide a smooth supply of low voltage DC.
State two functions of the electrode coating in manual metal arc welding. • To generate a gas shield to protect welded joints from contamination by oxygen and nitrogen in the air. • To form a slag coating which protects the weld from oxidation and ensures a slow cooling rate for the weld • Helps to maintain the arc
Created by: todd.ciaran