May I ask, can cast iron be turned?
Thread Content
The pump in our workshop has bearings whose outer rings are wearing out; the bearings are severely damaged, and the outer diameter clearance of the radial bearings is too large. The housing is made of cast iron. I plan to weld and repair it first, and then machine it to meet the installation requirements. Is it possible?
Cast iron can be turned, but it is not easy to weld as cracks may occur; it is recommended to first enlarge the inner hole and then insert a sleeve
Turning cast iron is no problem; as mentioned above, welding is more difficult. The first thing to consider is your ability to weld cast iron – if you have that capability, then everything will be fine.
Reply to 1# ljx20080513: Cast iron has good turning properties and excellent chip breaking capabilities. Unlike materials such as stainless steel, which tend to produce long chips during turning, causing issues that interfere with the machining process and requiring frequent stops for cleanup. You are probably right – the inner ring of the bearing housing should be surfaced by welding first and then turned, rather than turning the cast iron part. There are two types of welding for cast iron: cold welding and hot welding. Cold welding involves the use of specialized cast iron electrodes; it takes advantage of the good plasticity of nickel-based materials to compensate for the poor shrinkage properties of cast iron. Hot welding entails heating the entire workpiece before using ordinary carbon steel electrodes for welding. There are many articles online on repairing cast iron, which can serve as a reference
Repair by welding is a common method used for repairing ordinary cast iron parts. The cost is low, and the quality is good as well.
Reply to 4# Fish in the Desert: Yes, turning is performed after surfacing the outer layer to achieve the desired gap. Thank you for understanding
Reply to 1# ljx20080513: Plating is the best option, as it ensures high precision and prevents deformation. Welding tends to cause deformation, and cast iron has poor weldability
Turning of cast iron is not a problem, but working with white cast iron is much more difficult. When performing repair welding on cast iron, a layer of white cast iron (Fe3C) is often formed at the fusion line where the weld metal meets the base metal; this phenomenon is known as white cast. In severe cases, the entire weld cross-section can become case-hardened; the hardness of the case layer can reach up to 600 HBW, making mechanical processing extremely difficult. The reason for the formation of white cast is, on the one hand, the rapid cooling rate of the weld; in particular, the weld metal near the fusion line cools fastest ； On the other hand, improper selection of welding rods results in an insufficient content of graphitizing elements in the weld. Measures to prevent white cast iron formation: 1. Slow down the cooling rate to extend the time during which the fusion zone remains in a red-hot state, allowing graphite to fully precipitate. The specific measures are preheating the welded parts and maintaining heat for slow cooling after welding. 2. Increase the content of graphitizing elements. Carbon and silicon in cast iron are strong graphitizing elements; only when their content reaches a certain level, combined with an appropriate cooling rate, can the weld obtain a gray cast iron structure. Therefore, choosing welding materials with high carbon and silicon content is a common method to prevent the formation of case hardening. 3. Use of heterogeneous materials for welding: Welding materials based on nickel, copper, or steel are employed, so that the weld does not have a cast iron structure; this prevents the formation of white cast iron from occurring in the first place.
Cast iron has excellent machinability, but poor weldability. Different types of cast iron require different welding electrodes and welding methods, which makes it a technical challenge.