This is a method of repairing small broken castings similar to burning on. A mould of clay or plaster of Paris is formed about the broken parts of a small casting as shown at o,

Fig. 267. - Uniting a Broken Casting.

Fig. 267. When dry, the mould holds the casting firmly. Both are supported in a box of sand, and the fracture is heated with an oxy-hydrogen or an oxy-acetylene blow pipe. At the same time a rod of metal is held in the flame so that the end melts and joins the highly heated ends of the casting. These ends are kept practically molten until enough metal has melted from the rod to join them together.

After the casting has cooled, the superfluous metal is ground away. This method of mending castings burns out the carbon of cast iron and makes the joint harder and more brittle than the iron of the casting.