AGMA 923-C22: Metallurgical Specifications For Gearing

Steel gears in a machine, adhering to AGMA 923-C22.

The great Greek mechanic Archimedes invented gears in 300 BCE. The Roman world found plenty of use for gears, especially in heavy duty machines like mills and irrigation wheels, where power was transmitted. The other application for them was in small-scale water-clocks, calendrical instruments, and automata—self-operating machines like bell strikers in mechanical clocks. Since Ancient Rome, gearing has evolved and become more complex, which is why AGMA 923-C22: Metallurgical Specifications For Steel and Cast Iron Gearing specifies metallurgical characteristics in modern gearing.

What Is a Gear and How Do Gears Work?

A gear is a component in a rotating circular (sometimes conical or square) machine that consists of a toothed wheel attached to a rotating shaft. It is used to transfer motion, torque, and power between machine components. Since gears slot together, when one is turned, the other one also turns. If they are different sizes, they can increase the power of a turning force. This is because the smaller wheel turns quicker but with less force, and on the contrary, the bigger wheel turns slower with more force. Various mechanical devices like bicycles, washing machines, winches, cars, and electric screwdrivers use gears.

Manufactured metal gearbox in a car, adhering to AGMA 923-C22.

The AGMA 923-C22 Standard for Steel Gearing

AGMA 923-C22 provides test procedures and metallurgical characteristics for steel and cast iron gearing. The various characteristics—raw material, heat treatment, post heat treat processing, and associated inspections—are typically evaluated during the manufacturing sequence. Here are the specific characteristics the standard looks at in its test methods:

  • Banding
  • Carbon
  • Chemistry
  • Hardness
  • Hardenability
  • Decarburization
  • Effective Case Depth
  • Grain Size
  • Intergranular Oxides
  • Magnetic Particle
  • Mechanical Testing
  • Metallography
  • Microstructure
  • Nodularity
  • Nodule Count
  • Nonmetallic Inclusions
  • Reduction Ratio
  • Surface carbon
  • Surface Temper
  • Ultrasonic Inspection

The metallurgical requirements in the standard are intended to assure the quality of the gear teeth. AGMA 923-C22 defines three different metallurgical quality grades. Grade 1, Grade 2, and Grade 3 gearing are produced by different heat treatment processes and have different ratings. It is important to note that within the scope of this standard, gear design and rating, case depth, allowable stress numbers, and quality control sampling plans are not included.

What Are the Types of Gears?

There are various types of gears depending on what task they need to perform. Tasks range from changing the speed or force of rotation, changing the axis of rotation, transferring power between a motor and other moving elements. Here are the types of gears:

  • Bevel
  • Gear Rack
  • Helical
  • Hypoid
  • Miter
  • Screw
  • Spiral Bevel
  • Spur
  • Worm

AGMA 923-C22: Metallurgical Specifications For Steel and Cast Iron Gearing is available on the ANSI Webstore.

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