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Technology for repairing slag inclusion defect of copper propeller

Views: 29     Author: Site Editor     Publish Time: 2020-04-20      Origin: Site

Repair technology of copper propeller with slag inclusion defect by Argon Arc welding
Marine propeller, also called propeller, is an important casting of marine power plant and an important equipment to ensure the safety of navigation. The propeller running in sea water bears huge alternating load, which requires high mechanical property, high corrosion fatigue degree and excellent cavitation corrosion resistance. The propeller made by Longye Propeller Company of Zhoushan is made of copper alloy and is mainly used in the manufacture of large, high-speed ship propellers. The defects of the anti-fatigue and anti-cavitation erosion are casting, high processing requirements, and welding problems such as difficult fusion, porosity, hot crack, low-grade welding deformation, etc. . The Argon Arc welding is used to repair the slag inclusion of propeller.
Defect description
The Copper Alloy has narrow crystallization range and large volume shrinkage, and it also contains active elements AL, MN, FE and Ni which have strong affinity with oxygen. During the casting process, the high temperature copper water enters the dry insufficient propeller cement sand mold and the casting system, the surface layer of the mold massive adsorbed water-based crystal water precipitates rapidly to become the water vapor, the oxidation slag is produced when the water vapor interacts with the alloying elements. More than half of the defects were found at the lower 0.5R-0.8R side of the blade, and because of the protective oxide film covering the entire surface of the liquid copper during casting, which then entered the blade, the surface area continues to expand. However, when the copper liquid rises to the highest point of the propeller mold, that is, 0.3R-0.5R leading edge, due to the large reduction of the horizontal section of the Blade and the change of the copper liquid flow direction towards the upper part of the propeller shell and riser, a large number of secondary oxide slag accumulated and the removal resistance increased, resulting in a sharp increase of the secondary oxide slag in the region.
Selection of welding materials
Welding material should be selected according to the propeller material with similar performance grade.
Preweld preparation
Use sanding machine to polish the defect, remove the defect completely until good parent material appears. Processing out of the appropriate welding groove, groove should be smooth without burr. Then uses the acetone, the steel brush and so on to clean up the repair spot and both sides 20mm scope oil pollution, the oxide, moisture and so on other magazines. The electrode is dried at 200 °C and kept for 1 ~ 2 hours. Due to the high thermal conductivity of copper, the heat is easy to lose during welding, so preheating is necessary before welding. On the other hand, preheating can also improve the distribution of welding stress and reduce the risk of stress corrosion cracking. The preheating temperature shall not be lower than 150 °c, the temperature between layers shall not exceed 300 °C, and the preheating range shall not be less than 100 mm from each direction of the welding area.
Welding parameters and operation
Argon arc welding is used to repair the defect of propeller in our factory. The diameter of welding wire is 7mm.
Post Weld treatment
Because copper alloys are very sensitive to stress corrosion, stress relief heat treatment must be done after welding. For very small welds, the local stress relief treatment can be carried out by using a flexible gas distance or an electric heating wire heater to heat the welds locally to the annealing temperature. The number of minutes of heat preservation is greater than the number of millimeters of the thickness of the section, then cover the cooling with asbestos cloth. After the post-weld heat treatment completely cooled, carrying out coloring inspection, until its inspection results did not find cracks, pores and other defects, quality to meet the requirements, otherwise to repair welding. Finally, Static Balance Test, calibration, pitch measurement, thickness measurement, grinding, polishing.
Using Argon Arc welding to repair the marine propeller, adopting reasonable welding process parameters can repair the slag inclusion defects of the propeller, ensure the mechanical properties of the propeller materials, and improve the service life of the propeller, ensure the safe navigation of the ship.


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