Welding cast iron can be challenging due to its brittle nature and susceptibility to cracking. There are several common welding methods available, including manual arc welding, gas welding, CO₂ shielded welding, and manual electroslag welding. Among these, manual arc welding is further divided into hot welding, semi-hot welding, and cold welding. Gas welding also has different approaches such as hot welding, heating and reducing welding, and non-preheating welding. The choice of method depends on factors like the size and thickness of the casting, the condition of the damaged area, the structural complexity, and post-weld requirements—such as whether machining, tightness, strength, or color matching is needed.
In many cases, automotive and tractor cylinder blocks suffer from cracks, holes, or deformation that require repair through welding. These components are typically made from materials like HT21-4 or HT15-32, which have poor weldability due to their high carbon content. Combined with the thin and uneven walls of the cylinder structure, welding can easily lead to cracking, making the repair process quite difficult. Considering practical production conditions, efficiency, and cost-effectiveness, manual arc cold welding is often preferred.
To illustrate this process, two real-world examples are presented below.
**Case 1: Dongfeng Windmill Cylinder**
During an overhaul, a portion of the cylinder surface was damaged by impact. To repair it, we replaced the damaged section with low-carbon steel plate and used manual arc cold welding. A 3.2mm diameter cast 308 electrode was used with a welding current of 100A. The welding was done in short segments, with intermittent and dispersed techniques to minimize stress buildup.
Since the defect was on the surface without requiring deep processing, using the original block would increase internal stress and reduce the crack resistance of the filler metal. Therefore, we first cleaned the area thoroughly, then preheated the low-carbon steel plate. Only a half-side groove was opened around the casting. We used both cast 308 and 506 carbon steel electrodes for cross-use, ensuring quality while keeping costs low. Each weld segment was no longer than 20mm. After each weld, we immediately tapped the weld with a small hammer to relieve stress, reduce cracking, and improve density. Any minor porosity or slag could be minimized through this process without affecting the tensile strength of the weld.
After cooling to a safe temperature, we brushed off the slag and repeated the process until the repair was complete.
**Case 2: Forklift Cylinder with Cracks**
A forklift cylinder had developed a 50mm-long crack after freezing in winter due to lack of antifreeze. The middle part of the crack was slightly raised by about 5mm.
To address this, we first flattened the crack using pressure iron and sealed the ends. Given the long length and high rigidity of the crack, we used a 3.2mm cast 308 electrode with a beveled edge from a sanding wheel. Each weld was kept between 10–15mm long. After welding, we tapped the weld with a small hammer, brushed it clean, and allowed it to cool to approximately 600°C before proceeding to the next section.
Finally, we reinforced the weld with three 30x50mm steel plates, 3mm thick, to ensure the crack was fully sealed and the structure was stable.
Practical experience has shown that the above methods are effective and reliable for repairing cast iron components, especially cylinder blocks. These techniques offer a feasible solution that can be widely adopted in industrial settings.
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