vacuum heat treatment

A hydroplane racing team located in Cinnaminson, NJ had three propeller blades heat treated to ensure parts were free of scale and keep the blades from shearing apart. The propellers will now withstand the RPM and torque conditions of racing without failing. Also, the hardening will protect the blades from impact with potential debris in the water.

This case study/press release from the heat treater, Metlab, goes into detail to describe the propellers and how heat treatment changed the material.

A modern unlimited hydroplane is the world’s fastest racing boat, capable of speeds greater than 200 mph. These boats represent the product of over 100 years of evolution in race boat design and materials with the most powerful engines, most advanced construction techniques, and the best safety systems available in boat racing today. A typical unlimited hydroplane can weigh a minimum of 6,750 pounds.

All unlimited hydroplanes are a “three-point” design, meaning they are designed only to touch the water at three points when racing – at the rear of the two front sponsons (the projections of the hull in front of the driver cockpit) and the propeller at the rear of the boat. Most of the unlimited class boats are powered by Chinook helicopter Lycoming T55 L7 turboprop engines, generating up to 3,000 HP.

Metlab, which is known for offering a wide variety of thermal processing solutions, had the opportunity to heat treat a series of propellers for a hydroplane racing team located in Cinnaminson, NJ.

The propellers must meet strict design criteria imposed by the Union Internationale Motonautique (or “UIM,” headquartered in Europe), not only for propellers but for the entire boat design. The propellers are typically 16″ in diameter and have three blades. Different pitch propellers are chosen for use based on course length, conditions, and starting position. It is not uncommon for a racing propeller to cost more than $15,000.

The propeller creates the distinctive “rooster tail” behind the boat, raising literally tons of water into the air for up to 300 feet behind the boat. They are made from several different materials, but the steel of choice is 17-4 PH stainless steel chosen for its mechanical properties and corrosion resistance. The propeller must support a significant portion of the boat’s weight while rotating up to 14,000 RPM.

Three propeller blades were heat treated for the client to the H-900 condition (900°F/ hours at heat). They were age hardened in a vacuum furnace to ensure parts were free of scale. The high tensile strength (200 KSI) produced by the heat treatment keeps the blades from shearing apart; the excellent ductility associated with the heat-treated material allows the propellers to withstand the RPM and torque conditions without failing. And a hardness of HRC 40 protects the blades from impact with potential debris in the water. 17-4 PH stainless steel properly heat treated also benefits from increasing torsional fatigue strength, a common cause of propeller failure.

Metlab provides heat treating solutions for highly technical parts and components. Consult with a metallurgical specialist at Metlab about your specifications and heat treating requirements.