Weld Like a Pro. Jerry Uttrachi

Fig. 3.25. Braze welding does not melt the cast iron, and also requires heating the material to a high temperature. This essentially preheats the assembly and avoids high cooling rates. Stress on the joined area is reduced as a result, so the brittle cast iron is less likely to crack.

      The finished brazed joint is sound and wet into the cast iron. The brazing material is also very ductile. When the cast iron expands and cools as the part is heated and cooled, the brazing alloy can expand and contract as needed and does not excessively stress the cast iron. To be safe, the part is slow cooled after brazing.

       Fig. 3.26. AWS RBCuZn-C, a common flux-coated brazing alloy, was used to braze weld this simulated crack. A flux is needed to ensure good wetting of the cast iron. It removes oxides from the cast-iron surface and promotes wetting. There is sufficient coating on the rod to avoid the need for adding more.

CHAPTER 4

       TIG WELDING

      Russell Meredith applied for a patent in January 1941 for what became the invention of TIG welding. He worked for Northrup making lightweight military airplanes. The company needed an improved welding process for joining lightweight magnesium and aluminum. The focus of the patent was welding magnesium because it is 35-percent lighter than aluminum and 75-percent lighter than steel. Helium was found to provide a good protective gas shield and the patent examples mentioned the use of that gas. Northrup named the resulting process and associated products Heliarc. However, the patent claims covered welding any metal with the use of an inert gas shield. The Linde Division of the Union Carbide Corporation (UCC) that manufactured and distributed industrial gases and welding equipment purchased this basic process patent. Unlike Northrup, which built airplanes, Linde had the incentive to develop an extensive range of TIG torches and other accessories to promote the use of the process for a wide variety of applications.

       Fig. 4.1. Russell Meredith invented TIG welding while working for Northrup, a manufacturer of military airplanes, in 1941. It needed an improved welding process for joining lightweight magnesium and aluminum. Magnesium is 35-percent lighter than aluminum and 75-percent lighter than steel. The focus of his patent, shown here, was welding these materials with helium. The resulting process and associated products are called Heliarc.

Power Options

      TIG welding was initially performed with stick welding power, which was readily available at the time of its introduction. However, for welding thin materials with lower current, more precise power supplies were needed. Special power supplies were developed that were similar to stick welding power so volt amperage curves maintained a relatively constant current over the range of operating voltage. This allowed variations in arc length while still controlling the key welding parameter, current.

      DCSP Power

      A DC straight-polarity (DCSP) power configuration, also called DC electrode negative (DCEN), is used for most steel TIG welding. In DCSP TIG welding, electrons flow from the tungsten electrode through the arc to the workpiece. Balancing their negative charge, positively charged gas ions flow from the workpiece to the tungsten electrode. A large amount of energy is required to get the electrons into the work surface. This surface energy release causes heating of the workpiece and provides high weld penetration.

      DCRP Power