The immersed components of hydroelectric power plants are permanently in contact with the water stream and their wear occurs by corrosion, erosion and cavitation. This damage is usually repaired by welding: the procedure is fast and reduces plant downtime. Adopting proper weld procedures are crucial for blade performance and to establish a protocol the following experiment was devised: rectangular samples 600x200x15mm were obtained from a discarded blade used in a hydroelectric power plant and in the median region a 3mm deep groove was milled to simulate erosion damage. The damage was repaired by welding using MIG, WIG, MMAW and oxyacetylene techniques using 136L as filler on cold and preheated at 400�C base materials. Specimens from the welded ensembles were obtained and prepared accordingly for corrosion testing. Post corrosion testing studies using the light microscope and scanning electron microscope were performed in order to determine surface damage. At first glance results appear contradictory: the corrosion test results revealed best behavior for MIG weld repairs, on the cold sample, while the corrosion features measured on the exposed area revealed that oxyacetylene welding would be best. Complementary methods are required and currently employed to establish optimum welding procedure parameters for water turbine blade repairs.
Flame straightening is a technology process used to eliminate deformations. This method relies on local heating of the material to correct geometry or damaged parts. In the local automobile services its main use is for repairs of less critical deformed components. The maximum temperature and thermal gradient, heating time, cooling rate and number of heating cycles affect the mechanical properties since local heating can alter material microstructure. The aim of this research was to determine the mechanical characteristics of thin steel plates repaired by local heating associated with plastic deformation (similar to hot working) and cold straightening (similar to local cold working) for automotive side and door panels made of structural steel. Thin sheet plates, 0.9mm thickness, were deformed by impact and repaired by local heating using the flame and induction heating then plastically deformed while hot as well as straightened without heating. The heat repaired samples were studied by light microscopy to determine microstructure change and samples were tensile tested to determine their mechanical characteristics. Local excessive grain growth generates anisotropy, the assembly behaves as a composite material with regions that show significant plastic deformations while others little or no deformations at al. Without procedures adjusted to each material repairs involving heating are to be avoided, cold working should be employed when replacement is not possible.
Straightening of impact damaged car panels is a common practice when damaged area is small to medium. Common car panel straightening methods are hammering, heating and welding pins and pulling on the material using a device called a spot weld puller, so that the straightened metal sheet may have, as a consequence, its microstructure, stress and strain state altered. The aim of this research was to find how the above methods alter the corrosion behavior of the alloy used for car panel manufacture. Samples from similar damaged car panels were obtained, straightened, tested and compared to a sample from an original panel. Testing implied microstructure characterization, surface wetting investigation and corrosion testing. It was concluded that when straightening is carried out by hammering and using the spot weld puller the worst corrosion behavior is to be expected.
The aim of this research was to determine the influence of the metallic materials characteristics on the dynamics of a car crash. Another important aspect is that the metallic parts are sometimes repaired after minor accidents and this fact influence strongly the mechanical characteristics and their influence on the dynamics of a car crash. In this paper, we analyze the mechanical characteristics of thin steel plates repaired by local heating associated with plastic deformation (similar to hot working) and cold straightening (similar to local cold working) for automotive side and door panels made of structural steel. Thin sheet plates, 0.9mm thickness, were deformed by impact and repaired by local heating using the flame and induction heating then plastically deformed while hot as well as straightened without heating. The heat repaired samples were studied by light microscopy to determine microstructure change and samples were tensile tested to determine their mechanical characteristics. Local excessive grain growth generates anisotropy, the assembly behaves as a composite material with regions that show significant plastic deformations while others little or no deformations at all. Without procedures adjusted to each material repairs involving heating are to be avoided, cold working should be employed when replacement is not possible.
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