Pre-weld and post-weld heat treating is critical for many welding operations. Without proper thermal manipulation, welds and heat affected zones can have mechanical properties that are undesirable. Worse yet, inadequate heat treatment can result in cracks and devastating weld failures. While temperature and time are the primary concerns when heat treating a weld, the heating method should also be considered diligently when selecting a process. Induction heating is one of the most popular types of heat treating methods, and rightfully so. The benefits of induction heating are many, and Red-D-Arc has the equipment you need to successfully implement an induction heat treating operation for your projects.
What is Induction Heating?
Induction heating is a heat treating process that, when used properly, can alter the mechanical properties of a weld and its adjacent base metal in a way that meets the demands of the application in which the weld is being used. Induction heating relies on the science of electromagnetism to heat the part. Induction coils are placed around the material being heat treated, and alternating current is fed through them. This alternating current going through the induction coils creates a rapidly alternating magnetic field.
The eddy currents that occur as a result of this heat the material surrounded by the coils. Magnetic materials are even more easily heated by the alternating magnetic fields.
Importance of Preheating in Welding – Equipment Options
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.
Scheduled for completion in July 2016, U.S. Bank Stadium, the new home of the Minnesota Vikings, is a fixed roof structure that will be nearly 30 stories tall at its highest point. During construction, the base plates of some of the structural support columns needed to be pre-heated to 400o prior to welding. Traditional heating by flame proved to be difficult. It was determined that induction heating was the right solution to safely and efficiently heat the steel to an exact temperature. Induction heating is the preferred method to address challenges associated with the pre-heating of structural steel because it provides a safe and accurate method of heating the metal to a precise temperature.
Red-D-Arc offers Miller ProHeat 35 Induction Heating Systems (IHS) available for rent, lease and sale. This highly efficient technology uses non-contact heating to induce heat electromagnetically rather than using a heating element in contact with the part.
UPDATE: This project was completed ahead of schedule.