Zimbabwe's leading welding and Thermal spraying specialists
Aluminium, Cast-iron, Titanium Welding
Call us: +263 712600490
TIG Welding Pvt Ltd offers a repair service for anything cast iron.
gearbox casings, etc.
Cast Iron Welding Options
Of all the everyday metals, cast iron is probably the most difficult to repair when it fractures.
The Chinese claim to have invented it centuries ago but it is only in the last century that improved production methods have given us cast iron of consistently good quality and weldability. The automotive industry is probably the biggest user of cast iron. It is ideal for engine cylinder blocks and heads because it is stable and relatively cheap. It has disadvantages:
1. It cracks. This happens when the cooling system fails and causes the combustion area to get very hot very quickly. Cast iron does not take kindly to having different temperatures in the same lump and so a crack occurs.
There are four popular ways to repair cast iron.
Said to have been invented in Ancient Egypt, this is a good solution for a range of casting problems. It is done by drilling a series of adjacent holes across a crack. The walls between the holes are broken through and a nickel lock is hammered into the resulting serrated slot. The lock is shaped to match the slot. A lock is fitted every 6mm along the crack. Between the locks the remaining crack is drilled and tapped to take nickel screws. Each screw interferes with the next one to form a continuous figure of eight. The whole is then vigorously peened and ground off. Expertly done and painted, the repair is all most invisible. The advantage of metal stitching is that it is a cold process. It can often be done in situ with minimal stripping and gives a pressure tight repair.
Disadvantages not effective on material under 4mm. thick. No use in combustion areas. The coefficient of expansion of nickel is different from cast iron so a repair in a hot area will last just as long as it takes your swipe payment to clear.
To understand cast iron welding it is necessary to know that cast iron is more like a currant cake than a plain sponge cake. The currants are lumps of iron oxide which are formed in the casting process. They are inert and cause problems with each of the welding processes. Arc welding is a fairly instant process. Filler metal is transferred across an electric arc from the end of the filler rod to the parent metal.
Popular in America, The equipment comprises a gas welding torch with a powder hopper. The method is similar to gas welding. The gas flame is used to preheat the area to be welded. When the the temperature is right a stream of powder is entrained in the flame and deposited in the weld area. The flame then fuses the powder and more powder is added and fused until the repair is complete. The result is a homogenous repair of good appearance.
The casting to be repaired is preheated and filler rods made of good quality cast iron are used to repair cast iron. The weld pool can be stirred around until the oxides and other impurities float to the surface and get flicked out. The filler rod has more graphite (carbon) and silicon than the parent metal and this dilutes the molten pool and makes a stronger joint. The cooling is slowed down to at least twelve hours to minimise stresses and hardening.
If these few words will stop just one person reaching for an arc welder to do an "easy repair" it will be worth it.
TIG Welding (Pvt) LTD