6. Conclusion
This paper shows some proposals with regard to the design and manufacturing method including the non-destructive inspection procedure of Marine propeller. The followings are summarized.
(1) The care must be taken with the evaluation of stress distribution on the blade surface in addition to the absolute value of the stress on skewed propeller by FEM.
(2) At the design of skewed propeller, it is important to locate the maximum stress at the center of the blade.
(3) To keep the integrity of propeller casting, the adoption of degassing method, application of padding to boss and control of casting speed are very effective. Namely, under the condition that the hydrogen content in molten metal is 1.0 cc/100g or below and the casting speed is higher than 0.03 sec/kg, the number of the internal defects is reduced remarkably.
(4) If the dye penetrant inspection is combined with the ultrasonic inspection, the problem on dead zone of the letter inspection can be solved.
(5) Because the size of actual defect can not be known by the ultrasonic inspection results, it should be considered that some safety factors such as defect is evaluated larger and the defect is analyzed using a disk shape having a large stress concentration factor are applied to the evaluation of internal defects in order to assure the reliability.
7. Acknowledgment
The authors would like to thank propeller shop staff for their help in the preparation of this manuscript.
8. Reference
[1] T. Koshino, Y.Ino, "Strength and Material of propeller blades", The Third Symposium on Marine Propellers, The Society of Naval Architects of Japan, (1987), p310, p322.
[2] "Manufacturing Inspection Standard for Large-Size Marine propeller", SM276, (1996), Japanese Marine Equipment Association.
