Gear makers often use bronze alloys because the material can be more durable than steel in many applications. However, bronze is much more expensive than steel, and much of the material ends up as chips on shop floors during manufacturing.
To lower cost, weight, and to make a shaft integral to a gear without using a key, gear blanking company Accurate Specialties Inc. (ASI) has experienced increased interest in its composite blank systems – gear blanks that use cast iron hubs mated to a bronze outer ring cast in place (see image above). ASI provides a near-net finish, then gear makers cut the bronze ring into teeth, leaving the less-expensive hub metal untouched, says Steve Friedrich, sales manager for the Waukesha, Wisconsin-based foundry.
Bronze shrinks slightly more quickly than iron or steel as it cools, so when ASI employees pour a bronze outer ring onto a cast-iron shaft, the ring mechanically fixes itself to the hub as it cools, preventing rotation of the two pieces under load. Engineers design features in the iron hub circumference to increase that mechanical resistance to rotation. Friedrich adds that a lot of engineering know-how goes into the process to ensure that the compressive load created by the shrinking bronze doesn’t crack the iron or steel hub.
ASI is working on new applications to lower weight and material costs, Friedrich says, such as coating an aluminum rotor with thin bronze layer using a thermal spray process – an application that could remove a heavy bronze brake rotor from a utility reel trailer tension brake application.
Accurate Specialties Inc.