Unit 003: Principles of welding
Handout 1 – Heat sources required for fusion welding
The following basic notes have been produced for learners and tutors and if required could be extend.
To make a fused joint the heat source must be capable of creating localized fusion in a controlled manner. Basic requirements for the production of a fully fused joint: Temperature should be `significantly above the melting point of the parent plate – too small a difference in temperature means the heat just flows away from the joint, thus making it difficult to reach melting point and keep a molten zone. Heat should be concentrated into a small area if the weld metal is to be constrained. There must be adequate heating capacity, the amount of heat required will depend upon the physical properties of the metal and the joint configuration. The heat source must be able to be regulated to suit the joint and to remain constant during the welding operation. Heat input – success of any welding operation depends upon the heat input to the joint. To achieve melting, the rate at which heat is applied must be greater than the rate at which it flows into the parent plate. Thermal conductivity of the parent plate is a most important consideration when choosing a welding condition. To combat the problem of thermal conductivity, pre-heating can be applied (will be dealt with at a later stage). Another consideration is the cross-sectional area of the conductor, ie thickness of plate and joint configuration. Joints usually containing two or more members, and each member provides a pathway for heat flow, eg a ‘T’ joint has three possible heat paths and so will cool faster than a butt joint which has two. To summarize – parameters involved with effective melting of the parent metal during welding are: metal thickness
thermal conductivity of the material
temperature of the parent plate prior...
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