Preheating Applications in Welding

March 16, 2018 ·
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Red-D-Arc Welderentals

Importance of Preheating in Welding – Equipment Options

Why preheat?

Preheating reduces the risk of cracking in weld metal and heat-affected zone (HAZ) by:

Lowering the cooling rate of the weld – prevents formation of brittle weld metal/HAZ, allows more time for hydrogen to escape the molten weld.
Removing moisture (hydrogen source) from the part.
Reducing shrinkage by lowering the temperature differential.

Preheat or not?

The requirement and level of preheating for steel is determined by the relevant welding code and is dependent on the weld heat input, chemical composition of steel (carbon equivalent), thicknesses, diffusible hydrogen etc. Non-ferrous materials generally require preheat because of their high thermal conductivity.

“Induction heating delivers the most consistent and fastest results”

Preheating can be carried out using the following methods:

Applying direct flame – surface of the part heated and then heat conducted through the part, open flame.
Placing the part in a furnace – uniform heating of complete part if sufficient time provided in furnace, limitations of use due to the size of the furnace.
Electric blankets – surface of the part heated and then heat conducted through the part.
Induction heating using blankets – heat generated by electromagnetic currents within the material.

Out of the above methods, induction heating delivers the most consistent and fastest results and allows for the precise temperature control. It is also the safest and most energy efficient method.

The temperature is measured on the workpiece using thermocouples, temperature crayons or infrared pyrometers. The measuring positions are specified by the relevant welding code and are typically dependent on the thickness and geometry of the joint.

Red-D-Arc’s range of induction heating equipment includes air cooled and water cooled induction heating systems with heat applied via blankets and rolling inductors (for moving parts). These systems feature the ability to accurately monitor, control and record temperature. The required accessories including blankets, cables, thermocouples and recorders are also available for rental.

Visit our induction heating equipment page to find out more.

Red-D-Arc Welderentals

Red-D-Arc Welderentals™ an Airgas company rents and leases welders, welding positioners, welding-related equipment, and electric power generators – anywhere in the world. Our rental welders, positioners and specialty products have been engineered and built to provide Extreme-Duty™ performance and reliability in even the harshest environments, and are available through over 70 Red-D-Arc Service Centers, strategically located throughout the United States, Canada, the United Kingdom, France, and the Netherlands, as well as through strategic alliances in the Middle East, Spain, Italy, Croatia, and the Caribbean. From our rental fleet of over 60,000 welders, 3,700 weld positioners, and 3,700 electric-power generators, we can supply you with the equipment you need – where you need it – when you need it.