What are the existing methods for measuring blade thickness of marine propellers?

The existing measurement method for blade thickness is usually to draw a line on the pressure surface and suction surface of the blade at the same time according to the blade radius, and give the thickness process value on each award according to the distance from each radius reference line of the blade to the pressure surface and suction surface given in the type value table. As shown in Figure 4, the blade section thickness of the radius is d1, d2...... Di, d10. In the specific measurement, the workers use the caliper to measure the thickness and then use the steel ruler to compare and read the value. Because the propeller is a space curve in the blade, the caliper cannot accurately locate the S point on the extension plane of the blade cylinder section perpendicular to the direction of the pressure surface pitch line, and the measurement accuracy is not high. In addition, the workers also have errors when comparing the steel ruler readings, Therefore, this thickness measurement method is greatly affected by the experience and feel of the measuring personnel. The measurement of blade thickness with accuracy of Class II and III can basically meet the requirements, but it can not meet the needs of design and manufacturing of blade thickness with accuracy of Class S and I, especially for S and blade, in order to avoid linear discontinuity, it is specified that the deviation measured continuously from local pitch and thickness should not be greater than half of the range covered by positive and negative tolerances, The measuring accuracy of calipers can not meet the requirements at all.
Axial measurement of blade thickness
In order to avoid using the caliper, which is a measurement method with large error, it is necessary to measure the blade surface coordinates on the suction surface and the pressure surface at the same time, and then calculate the blade thickness value through conversion. However, the domestic propeller manufacturers have not yet used a three-coordinate measuring instrument in production. If two measurements are made on the pitch gauge, the positioning error of two installations cannot be avoided. Therefore, it is necessary to install the pitch measuring needle at both ends of the pitch gauge at the same time, After converting the design thickness of the blade, take a certain radius section of the blade, and the interface is at an angle with the horizontal plane φ， angle φ That is, the pitch angle of the blade on the radius, measured up and down at the same time, and the line between the two measuring points is parallel to the axial direction. On the expanded plane of the cylindrical section with the radius of the measuring point, the line is still straight and at 90 ° with the theoretical pitch line- φ Angle, as shown in Figure 4. Use the pitch gauge to measure the design thickness point value of the pressure surface and suction surface according to the angle value of the design thickness point of the pressure surface and suction surface given by the process.