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Askold Horns
Askold Horns

Counter-Strike 1.6 Download Clean Edition -

Cast iron is made up of iron and carbon in different proportions, with additional elements such as manganese, silicon, chromium, nickel, copper, molybdenum, etc. to enhance specific properties. In addition, it may contain significantly higher levels of sulphur and phosphorus as impurities making it difficult to weld without cracking. The different grades of cast iron include grey iron, white iron, ductile (nodular) iron, and malleable iron with widely varying weldability. All categories of cast iron except white iron are considered as weldable, although the welding can be significantly more difficult compared with carbon steel welding. However, it can be difficult to tell the difference between these different types of cast iron without detailed metallurgical analysis. Despite this, cast iron is a durable, wear resistant metal that has been used for centuries.

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As mentioned above, cast iron can be difficult to weld because of its specific composition, but it is not impossible if you use the correct welding technique to avoid weld cracks. This involves careful heating and cooling, often including pre-heat, the correct choice of welding rods, and allowing the part to cool slowly.

Cast iron has poor ductility hence it could crack due to thermal stresses when rapidly heated or cooled. The susceptibility to cracking depends on the cast iron type/category. This means it is required to understand which type of alloy you are working with:

It is important to clean the cast iron before welding, removing all surface materials, such as paint, grease and oil, paying particular attention to the area of the weld. The casting skin may be removed through grinding. It is essential that the cleaned surface is wiped with mineral spirits to remove the residual surface graphite prior to the welding. Slowly preheating the weld area for a short time will help remove any moisture trapped in the weld zone of the base material.

Localised heating, such as the one encountered during welding, results in restricted expansion as the HAZ is contained by the surrounding cooler metal. The thermal gradient will determine the resulting stress. Ductile metals like steel is able to relieve the stress by stretching, but because cast irons have poor ductility they are liable to crack instead. Pre-heating reduces the thermal gradient between the HAZ and the surrounding casting body, minimising the residual stresses caused by welding. Pre-heating cast iron before welding slows the cooling rate of the weld and the surrounding area. Where possible, heat the entire casting. Typical minimum pre-heat temperatures are from 100-400C, depending on the type of the cast iron and the allowable HAZ hardness . Any pre-heating should be done slowly and uniformly.

The two main electrode types for manual metal arc welding are iron based and nickel based. Iron based electrode will produce weld metal with high carbon martensite, hence generally limited to minor repair of casting and when colour matching is required. Nickel alloy electrodes are the most commonly used, offering a more ductile weld metal. Nickel electrodes can also help to reduce the pre-heating and HAZ cracking by providing a lower strength weld metal.

TIG welding can provide a clean weld on cast iron, but not generally preferred due to its highly localised heating characteristics.. As with all TIG welding, the quality of the finished weld is largely determined by the skill of the welder.

As with other techniques, cleaning the surface is important with braze welding. A flux can be used to prevent oxides forming, promoting wetting, cleaning the surface and allowing the filler to flow over the base metal.

Less expensive than 99% rods, these are also machinable and are frequently used for thick section repairs. A lower co-efficient expansion means that these produce fewer fusion line cracks than the 99% rod. These ferro-nickel rods are ideal for welding cast iron to steel.

Steel rods provide the cheapest option of the three and are best for minor repairs and filling. Steel electrodes produce hard welds, which require extra grinding to finish and are not machineable. However, despite these drawbacks, steel rods provide colour matching and can better tolerate castings that are not completely clean than the nickel rods.

As a weld cools and contracts, it causes residual stress to build, leading to cracking. The chances of cracking can be reduced through the application of compressive stress. Compressive stress is applied by peening (using a ball peen hammer to deliver moderate strikes), which deforms the weld bead while still soft. However, peening should only be used with relatively ductile weld metal, that is on welds produced with nickel consumables.

Allowing cast iron to cool down too rapidly can lead to cracking. The cooling process can be slowed down by using insulating materials or the periodic application of heat. Some methods include placing the workpiece in an insulating blanket, placing it into dry sand, or even putting it over a wood fire oven and allowing the metal to cool as the fire dies down.

It is possible to weld cast iron, but it needs to be done using the correct techniques and with care to avoid cracking. Most welding methods require the surface of the material to be cleaned and cast iron benefits from pre and post-weld heating as well as careful cooling.

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