Gas Welding Flame

Question 1

How many zones are in the welding flame?

Answer 1

there are two zones; the primary combustion zone and the secondary combustion zone

Question 2

What happens in the primary combustion zone?

Answer 2

Oxygen is sucked in from the weld pool and is burned with carbon monoxide and hydrogen, giving off carbon dioxide and water vapour (C2+H2+O2→2CO+H2).

This is the zone of most heat where the welding takes place.

Question 3

Give the chemical equation for the primary combustion zone

Answer 3

(C2+H2+O2→2CO+H2).

Question 4

What happens in the secondary combustion zone?

Answer 4

In the secondary combustion zone, oxygen is sucked in from the weld pool and is burned with carbon monoxide and hydrogen, giving off carbon dioxide and water vapour (CO+H2+O2→CO2+H2O).
This zone pre-heats the joint edges and prevents oxidization.

Question 5

Give the chemical equation for the secondary combustion zone of gas welding

Answer 5

(CO+H2+O2→CO2+H2O)

Question 5

Give the chemical equation for the secondary combustion zone of gas welding

Answer 5

(CO+H2+O2→CO2+H2O)

Question 6

Name the three different ratios of flame

Answer 6

neutral flame, oxidising flame, carburising flame

Question 7

Answer the following questions in terms of a neutral flame:

1. What is the ratio of acetylene to oxygen?
2. How often is it used?
3. What materials is it used on?

Answer 7

Neutral Flame:

1. Equal mix,
2. Most commonly used welding flame.
3. Used for welding steel, stainless steel and cast iron.

Question 8

Answer the following questions in terms of an oxidising flame:

1. What is the ratio of acetylene to oxygen?
2. What materials is it used on? Why?
3. What type of flame does it act as for steels?

Answer 8

Oxidising Flame:

1. excess oxygen
2. Used for welding brass as it prevents fuming and loss of zinc.
3. Also acts as a decarburising flame for steels.

Question 9

Answer the following questions in terms of a carburising flame:

1. What is the ratio of acetylene to oxygen?
2. What is it used in?
3. When being used for said purpose (2.), why is it used for this?

Answer 9

Carburising Flame:

1. excess acetylene
2. Used in special welding
3. to ensure good protection against oxidisation.

Question 10

Explain what must be labelled for a diagram of a neutral flame

Answer 10

Drawn: a flame shape coming from
Label: maximum temperature zone, unburnt gas, primary combustion cone, secondary combustion envelope,

Question 11

Explain what must be labelled for a diagram of a carburising flame

Answer 11

Label: inner cone, feather, envelope

Question 12

Explain what must be drawn and labelled for a diagram of an oxidising flame

Answer 12

inner cone

Question 13

At what temperature does a neutral flame burn?

Answer 13

3100 degrees C

Question 14

At what temperature does an oxidising flame burn?

Answer 14

3250 degrees C

Question 15

At what temperature does a carburising flame burn?

Answer 15

2950 degrees C

Question 16

What observations are made on the neutral flame?

Answer 16

There is a small rounded core white flame.
No acetylene feather part of flame.
No chemical effect on the metal.

Question 17

What observations are made on the oxidisng flame?

Answer 17

Narrow pointed inner white-blue flame.
Not used for steel as it will oxidise it.
Used to weld copper, brass, bronze.
Also used in brazing.

Question 18

What observations are made on the carburising flame?

Answer 18

Flame has an ‘acetylene feather’ - a large inner light-green-blue flame.
Good oxidization protection.
Welding alloy steels and aluminium