Views: 38 Author: Site Editor Publish Time: 2018-09-20 Origin: Site
Due to the long-term use of Aluminum propellers, the collision of floating objects, the hitting of reefs or the rolling of steel cables will deform the blades and often cause blockages and cracks. After the blade is deformed, the light will cause the pitch to be inaccurate with the normal, resulting in unusable. The heavy one will distort the local position of the blade or create bending and curling near the leading edge and beside the blade tip other than about 2/3R. The former requires a measurement of the pitch; the latter is often more obvious. After the blade is deformed, it will cause the hull to vibrate, and the tail shaft and the tail bearing are easy to wear. Often encountered in propeller repair is the repair of blade bending.
Correction methods for blade bending usually include cold correction and hot correction.
Cold correction refers to correction at a heating temperature of 205 ° C or less. Cold correction applies to tips with blade tips and blade edges less than 30 mm thick. When the bending is small and the section is thin, the hammer hitting load correction can be used, otherwise the static pressure of the top pressure should be used for correction.
Hot correction is suitable for all situations, mainly for correction of blade bending or large area. Both dynamic and static load correction methods are available. The recommended hot correction temperature should refer to the preheating temperature of the weld repair. The heating temperature should pass through the entire section thickness of the correction and be maintained until the correction is terminated.
The lower support should be installed at the correction site to avoid transferring the load to other blade sections. Apply a rigid metal pad for pressure correction. The size of the heating portion during blade correction should be greater than the 100-150 mm portion that must be corrected, and 50-75 mm from each aspect of the defective portion. The magnitude of the corrective force is determined by considering the physical-mechanical properties of the material in both cold and hot states. After heat correction, measures must be taken to reduce the cooling rate of the blade by covering the asbestos cloth with a blade.
Correction method of blade deformation
(1) Heavy hammer tapping method. First place the propeller flat on the plate with the pressure facing up. First, determine the size to be corrected for each blade, that is, the height of the leading edge and the edge to the plate on each radius, and then tap gently with a hammer. The hammer is made of soft copper to make the hammer head so that the surface of the blade is not damaged when it is knocked. Because the deformation is serious, it is heated and beaten. Always measure the height of the leading edge and the edge to the plate during the correction process, and check for cracks until the surface is smooth and meets the requirements.
Find the propeller blades without deformation. With this blade as the standard, draw the radius lines on the blades, and draw the corresponding radius lines on the deformed blades. When correcting the blades, make the leading and trailing edges to the flat plate. The height is equal to the height of each point in the standard corresponding position.
If there is a small bend in the local position of the blade, the deformation can be heated first, and then tapped from the front with a small hammer.
(2) Correction on a press. Large and medium propellers can deform the blades on the press. Lift the propeller through a trolley and lift the crane to adjust the position.
(3) Correction with a platen on the plate. When correcting, the distance from the bolt to the point of application should be installed to be about 1/3 of the total length of the pressure plate. Slowly tighten the nut and apply pressure to the deformation of the blade through the pressure plate to gradually restore the original shape. It is also possible to change the jack at the place of the horn and correct it with a jack.
Large propellers are relatively heavy. If it is difficult to tilt the blades, the plate can be tilted for correction. If the blade is thicker and thicker, it should be corrected on the plate.
(4) Multi-plate correction. Multi-plate correction is also called row correction. The two blades are used to correct the bending of the blade in situ. It clamps the pressure plate on the curved blade and then corrects it with a jack.
When the blade is bent more, it is locally heated at the bend of the sweat sheet, and then the nut is tightened slowly (the jack can also be used) to gradually restore the blade to its original shape.
This platen method can only correct the bending deformation of the blade. It cannot be used to correct the distortion.
(5) Corrected with a fork-shaped pry bar (or jig). For the deformation of the small propeller blades and the local deformation of the medium propeller blades, the fork-shaped pry bar can be used for correction. When correcting, fix the propeller on the flat plate, make the blade deformation record, insert the fork-shaped crowbar into the blade correction part, slowly shake the crowbar, and measure the edge and the leading edge of the blade at each radius to the plate at any time. Height until the blade returns to its original shape.
There are many ways to correct the deformation of the blade. It should be selected according to different deformation conditions and equipment conditions, or several methods can be combined. For the corrected propeller, the allowable difference in diameter and pitch is determined by the allowable deviation of the size and geometric parameters of the marine propeller.