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How to repair marine screw

Views: 21     Author: Site Editor     Publish Time: 2020-04-20      Origin: Site

Propeller repair propeller is an important ship equipment, because the propeller is located underwater, so its maintenance and repair rely on regular docking maintenance. Most ship propellers are mainly made of metal materials. In the course of use, many defects of propellers mainly occur on the blades for various reasons. The common defects are corrosion, crack, fracture and deformation, etc. , and some of the defects will also cause the ship in navigation anomalies. The ship in dock repair or row repair, the propeller should be careful appearance inspection, check whether there are cracks, Sawtooth, defects found should be repaired in a timely manner. When the damage can not be repaired in place, the propeller should be removed for repair and the contact surface of the taper hole should be checked. In order to meet the requirements of the repaired propeller, the Blade Pitch, blade thickness and blade diameter should be measured when the propeller is repaired by bending correction, broken edge repair and large area welding repair. The static balance test should be carried out when the propeller is repaired by repairing the broken edge and large area surfacing welding. The repair methods of propeller can be divided into three parts: Surface Polish, crack repair, notch and fault block repair, serious erosion area surfacing, bending, deformation correction, blade edge repair. Among them, the welding repair of propeller is the most critical project. The documents to be submitted after the repair of the propeller are: "inspection report, Material Test Report, schematic diagram of repair area of welding materials, composition and mechanical properties, as well as other problems to be explained. " Not all the cracks in the blades can be repaired, but there are strict rules. The principle of Blade crack repair is to repair the crack on the blade part larger than 0.7 r and the crack on the blade part between 0.4 r and 0.7 r, the length of which does not exceed 1 / 4 of the blade width 3 The short cracks in the root of propeller blades with diameter D ≤2m shall not exceed 1 / 8 of the blade width, and the short cracks in the hub of propeller blades with Diameter d ≤1.2 m shall not exceed the thickness of the hub. The propeller should be renewed when there is a serious crack that causes the blade to be broken. If the propeller has been repaired or welded for a long time, and the material properties have changed, it is easy to produce embrittlement and crack, and it is difficult to ensure the quality after repair, the propeller should be replaced. Propeller cracks should generally be repaired by welding, and the cracks should be chiseled to the end point before welding. Under certain conditions, drilling the crack-stopping hole is allowed as a temporary repair measure. When a deep and penetrating crack occurs on the blade, a stop hole shall be drilled at both ends of the crack before repair. The diameter of the crack shall be 0.2 times the maximum thickness of the blade at the crack, I. E. D 0.2 t, then weld the groove according to the thickness of the blade where the crack is, because the thickness is 20-30mm, so open the x Groove, and then weld repair. In order to reduce the thermal stress produced during welding, the pre-heating temperature should be 200-300 °C. The copper propeller is repaired by gas welding with copper welding wire. If the copper 227 Phosphor Bronze Welding Rod is used to weld the ferromanganese brass propeller, the practice proves very good. As long as the current is adjusted properly and the preheating is sufficient, the welding rod droplets can be well fused with the propeller when welding. After welding, evenly heat the whole blade to about 200 °C, cover it with asbestos cloth, in order to eliminate or reduce the welding residual stress, sprinkle dry sand on it, in order to keep warm and cool it slowly. Because the crack location of the blade thickness is more than 20 mm, can also be repaired with the wave key. Cracks are found beyond 0.4 r and within 0.15 blade width from blade edge, and the length of the cracks does not exceed three times the thickness of the blade. The quantity is not more than two, only need to drill stop crack hole, do not need to weld. After the propeller is welded and repaired, the surface must be flattened and polished to remove the defects such as slag inclusion and porosity, and the appearance of new cracks must be carefully checked.

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