The marine propeller is so big, how did the workers cast it at one time?

How can such a big propeller be made? Some giant ships have really big propellers. In addition to being large, there are also many small lines engraved on it, which look shiny and golden. Does anyone wonder what kind of technology this size and craftsmanship had to have?

Let's look at a few sets of pictures first. These marine propellers are indeed large, but the number of blades is significantly different. The least is like this, with only 3 blades, the usual 5 blades, then 7, and many blades. Have you found it? These paddle numbers are all odd numbers. The reason why the propeller design is so unique and regular is because the manufacturer has to consider the balance between propulsion efficiency and production cost to achieve the purpose of saving money and being easy to use.

When a marine propeller operates underwater, it rotates to cut the water flow and generate the power to propel it forward. However, when the blade rotates, it will also generate a field of low pressure on the back, which will lower the boiling point of the water flow and generate a large number of air bubbles.These air bubbles are one of the sources of ship noise and the main culprit in reducing the life of the propeller. Therefore, when manufacturers design the number of blades, there will be a set of design concepts of "reduce the rotation speed and maintain the speed".

In theory, the more blades there are, the quicker propeller slow down. But this method is not very easy to use, after all, the more blades you make, the higher the cost. The number of blades is a little less, such as 3 or 5, which is a more commonly used design. In other words, if it is a submarine that needs to improve concealment and make less noise, you can use a large number blades of propellers. If it was an ordinary ship, there would be no need to build so many blades.

In addition, in order to weaken the resonance of the single blade of the propeller, there must be another blade that is symmetrical with it across the axis, which is why the number of blades should be designed to be an odd number.

But after all, it is a theory. In real life, there are actually many marine propellers with even number of blades in use.For example, this kind of propeller with 4 blades is a further design of the manufacturer after in-depth consideration of efficiency and cost. The pattern engraving on the blades increases the friction and makes up for the small defects in the number of blades.

So after we understand the most complex design scheme, we have to look at the process of manufacturing the propeller.

First, use wood or foam material to make a model with set values. The model is sealed with sand and then solidified with carbon dioxide and special chemical materials. Then, various metal materials with strong corrosion resistance and high hardness are fused and poured into the mold, and after they are completely cooled, the rough embryo of the propeller can be obtained.Finally, it is necessary to cut and beat again to remove the rough embryo from the mold, and use the processing machine to finely polish the rough embryo, and then engrave the lines, and a brand new marine propeller is born.

The above are the basic processes of the manufacture of marine propellers. We can see that the most sophisticated and cumbersome steps are actually at the design level.

However, this is not difficult for Chinese craftsmanship. With the addition of the manufacturing technology of precision programming CNC machine tools, a high-quality propeller can be manufactured in 3 days. Therefore, although the marine propeller looks big and beautiful, it is not difficult to build.