Most boat propellers made out of aluminum and stainless steel are produced in a similar way using a one piece cast system.
The manufacturing process starts out with melting down wax pellets, then the melted wax is injected into a master mold that makes a propeller shaped out of the wax once the wax cools down and hardens. A cylinder extension called the pour cup is also made the same way and is attached to the front of the wax propeller. This wax propeller can now be used as a pattern to make metal props.
This pour cup and propeller combination is then washed and rinsed to remove any oily substance. The wax prop is dipped into a vat filled with a non stick solution that is left on and coats the prop. Then the prop is submerged into a tank filled with water and silica sand. The prop is then put into a ceramic based mixture several times, after each time the prop is coated with sand. The prop is then dried with the use of fans.This process builds up a thick and hardened shell around the wax prop.
The wax propeller is now put into an oven where the wax is melted away leaving just the ceramic shell. The shells are fired in another oven to strengthen them. A worker takes the shell out of the oven and another worker pours melted liquid metal into the ceramic shell through the pour cup. Once the metal has cooled and hardened the ceramic shell is knocked away from the now formed metal propeller. The pour cup is then cut of the propeller. The propeller edges are ground down with a grinding wheel to smooth them and the rest of the prop is also ground down to get rid of any imperfections. The prop is then put into a bin filled with little vibrating polishers. This produces a shiny mirror type finish to the propeller. The production process is over now and the prop is inspected using a laser that checks for design conformity. If it passes it is boxed and sent out for sale.