Weld cooling
The weld cooling system is very crucial to handle seam welding. It is key role to reduce damage to the external surface of the weld when it is heated at melting point
Elements of the weld cooling systems:
The key elements in the success of the weld cooling system are:
· ELECTRODE MATERIAL (THERMAL OR ELECTRICAL CONDUCTIVITY)
· ELECTRODE TRANSVERSE SHAPE (RADIUS PROFILE IS BEST)
· ELECTRODE CLEANLINESS (SHOULD BE DRESSED FREE FROM PICKUP OF
NONCONDUCTING COATINGS)
· ELECTRODE COOLING SYSTEM
· COOLING WATER APPLIED DIRECTLY TO THE WELD (IF APPLICABLE)
Cooling water for seam welding wheels can be either internal or external.
Internal cooling systems cool the wheel but not the weld.
- The key advantage of internal cooling is that the process is dry; the workpiece, the machine, and the operator stay dry. The cost of installing floor drains and water containment facilities is avoided.
- Neither is it necessary to remove water from inside the workpiece (as in the case of automotive fuel tanks). However, internally cooled wheels may cost more due to additional machining costs.
- Thus, operating costs for internal cooling may be higher than for external cooling. Some internal systems do not directly cool the wheel, but only the wheel shaft.
On the other hand, with external cooling, spray nozzles are aimed with some precision at the workpiece-wheel separation point. The benefits of external cooling include:
· THERMAL DAMAGE TO THE WELD SURFACE AND ANY COATINGS IS REDUCED, SO THAT WELDABILITY IS IMPROVED.
· WELD DISTORTION IS REDUCED.
· FUME EMISSION IS REDUCED.
· WHEEL CLEANLINESS IMPROVES, BECAUSE WATER IS DIRECTLY APPLIED TO THE HOTTEST POINT ON THE WHEEL, PRODUCING A QUENCH/CLEANING ACTION ON THE WHEEL SURFACE.
· WELD HARDNESS WILL INCREASE, ADDING STRENGTH TO THE WELD UNDER CERTAIN LOADING CONDITIONS SUCH AS CRUSH LOADING. (CAUTION: SOME QUENCH-SENSITIVE MATERIALS MAY NOT ALLOW EXTERNAL COOLING.)
In welding bare steel, rust-preventive water solutions are sometimes used, such as 5% borax (Na2B4O7 · 10H2O).
Metals Welded
- Most low-carbon, high-carbon, low-alloy, and stainless steels, and many coated steels above approximately 0.15% tend to form areas of hard martensite upon cooling.
- In critical applications, the welds may require postweld tempering to reduce the hardness and brittleness. In some cases, this can be done in the welding machine.
- Tempering can also be done in a furnace or by induction heating.
- Aluminum and aluminum alloys can be lap seam welded but not mash seam welded, due to their narrow plastic range.
- Nickel and nickel alloys can also be seam welded, but seam welding is not recommended for copper and high-copper alloys. Compatible combinations of dissimilar metals and alloys also can be seam welded.
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