common exam questions

Question 1

Give uses of the electrode coating in MMA welding?

Answer 1

1. The electrode coating prevents oxidation during welding and helps stabilize and maintain the arc.
   Other elements may also be added to the flux coating if required.
2. There are slag forming elements in the coating that help form a slag that controls cooling and shapes the weld as it cools.

Question 2

Compare multi-run and single run welds?

Answer 2

Multi runs are less brittle than single runs, as successive layers have redefined the weld metal and multi runs will tend to anneal the hard zones.
Multi run welds will build up T –joints for strength.

Question 3

Uses of slag in welding?

Answer 3

Slag performs the following functions:

1. Acts as a scavenger in removing oxides and impurities
2. Slows down the freezing rate of molten metal
3. Slows down the cooling rate of solidified weld metal
4. Controls the shape and appearance of the deposit

Question 4

Importance of edge preparation?

Answer 4

Edge preparation is very important in producing a good strong weld joint.
This will allow for good penetration and fusion of the weld pool.

Edge preparation can involve beveling, rounding, or flattening of the edges.
The type of preparation will depend on the type of joint used.

Question 5

What are slag inclusions?

Answer 5

Define: This refers to foreign matter becoming entrapped in the weld, Cause: which can be caused by welding on dirty surfaces, or contamination from the atmosphere.
Slag inclusions are caused by poor manipulation of equipment, mill scale on material or carelessness in removal of slag before next run.

Weld on clean, prepared surfaces with equipment set correctly, an appropriate filler rod, fluxes and temperatures.

Question 6

Why is welding aluminium more difficult than steel?

Answer 6

Aluminium does not change colour during heating, when the welding temperature is reached it collapses suddenly.

It conducts heat three times faster than iron and requires higher heat input than that used in welding steel.

The aluminium weld pool oxidises very rapidly which also makes welding more difficult.

Question 7

What is porosity?

Answer 7

Usual causes include gas entrapped in the weld metal, excessive moisture on the electrodes or on the metal. Use dry electrodes on dry work pieces.

Question 8

What is lack of penetration?

Answer 8

Occurs where fusion of the parent metals is not deep enough, welding current may be set too low for particular rod or work.

Select the most suitable rod (diameter), set correct temperatures on plant and remove slag carefully