The propeller serves as a powerful force bearing component for propulsion. The internal requirements for strength are also high, and there should be no trachoma or bubbles. Therefore, the blades of large propellers generally cannot be formed by forging. Currently, the production method that can be used in industry is mainly high-precision casting, which involves one-time casting and mechanical polishing of the surface to meet the requirements.
In terms of industrial casting technology, copper has a low melting point, simple casting, good flowability of hot copper liquid, fewer bubbles in castings, and high smoothness; The difficulty of stainless steel casting technology is high, and poor control can easily lead to shrinkage, porosity, and crack defects. In terms of price, copper is cheaper compared to a stainless steel propeller of similar size. Therefore, the propeller material is almost monopolized by copper alloy, with nickel aluminum bronze being the most commonly used.
Due to the high melting point of stainless steel, the fire resistance of casting molds also needs to be improved. There is an empirical formula in industry that for every 100 degrees increase in casting temperature, the cost doubles. The melting point of bronze is only 800 degrees, while the melting point of stainless steel is as high as 1700 degrees, resulting in a temperature difference of 900 degrees and a casting cost increase of 7-9 times. Moreover, the cost of precision welding and hard surface polishing is included, which makes it much more expensive. So stainless steel propellers have not been widely popularized, and with the gradual popularization of stainless steel casting propellers for ships, the overall casting technology for stainless steel parts is too difficult.
