In this article we are going to study about  following Topics:

• Types of Gears
• Usage of Gears in various Application fields
• Types of Gear manufacturing Process
• Types of Raw materials used in Gear manufacturing
• Gear material selection process in Design?
• Gear matrial Specifications, properties and its heat treatment methods.
• Raw material inspection activities

Types of Gears:

1. Spur Gear: This gear has parallel teeth around the cylindrical circumference

2. Helical: These have slanted tooth traces that make more contact with one another and take a helix shape     
   
                                                        
3. Herringborne 
4. Internal Gears                                              
5. Bevel Gears (Straight/Spiral)           

2. Worm & Worm wheel: This comprises two mating parts. Worm shaft which is having screw shape and the worm wheel which is constructed from soft material to reduce friction   

7. Rack & Pinion: This combines a pinion (Circular gear and a rack (Linear gear). Rack and pinion convert rotational motion into a linear motion.          

Usage of Gears in Various application fields

• Agricultural equipment
• Automobile Transmission
• Cement plants
• Steel plants
• Sugar plants
• Paper plants
• Defence & Aero space
• High speed turbines
• Mining & Earth moving equipment
• Marine
• Cranes, Lifts, conveyors
• Wind mills

Types of Gear Manufacturing Processes:

• Casting –Any degree of complexity and size can be produced. Used applications like toys, small appliances, hand tools etc. Not possible to use high load carrying capacities
• Forging – Steel billets heated and hammered into die to form desired shape. Produces near net gears, reducing material cost, superior strength. Specialized tooling and process knowledge required to achieve AGMA8-9 Level gears. Used in agricultural, material handling equipment
• Cold drawing & Extrusion- A bar is drawn or pushed through a series of dies to achieve the final shape with desired tooth form. Used for mass production of spur gears. Used for watches, electric clocks, small motors etc
• Powder metallurgy & Sintering: Alloy powders mixed, compacted into a die, and sintered/heated in an atmosphere-controlled furnace for the particles to bond. Material utilization is 100%. Raw material cost is high. Used in household appliances, automotive components etc
• Fine Blanking: A sheet of metal is pressed between two dies to form a desired shape. Mainly used for bevel gears. 2 to 20kg weight gears production only possible. Used for automotive, appliance, medical equipment
• Machining: Gears will be manufactured with very accuracies by using various high precision gear manufacturing machines likes gear hobbing, Gear shaping, Gear grinding with various types of heat treatment process

Types of Raw Materials used in Gear manufacturing:

• Cast iron: These gears withstand repeated and sustained wear, making the metal ideal for precision gear manufacturing. The casting method can easily produce complex gear shapes
• Steel: Steel alloy gears are high strength because they are typically heat treated for enhanced toughness and hard ness, especially in the teeth. Carbon steel, is used to produce spur, helical, bevel, worm, and gear racks. Alloy steels to be selected based on the applications and load carrying capacity. Design engineers will select specific raw materials, heat treatment process to achieve the rating of gears. Accordingly, right selection of raw materials to be selected.
• Bronze: The copper alloys include aluminium bronze and phosphor bronze. These non-magnetic gears are best for corrosive environments. This material used for worm wheels

Gear Material selection process in Design:

If we need to identify the best material for gears, following points to be addressed

1. What is the application, environment condition for the proposed gears?
2. The application is hot or cold condition?
3. Whether the application is high speed?
4. Do these gears need to continually self-lubricated?
5. Which is important, ductility or hardness?
6. How much wear these gears receive and what period will the wear occur?
7. Are oxidization, Corrosion, or magnetic fields an issue?

Gear Material specification, properties, and heat treatment methods:

• Medium carbon steels are commonly used for gear manufacturing. The applications where high strength and toughness are needed requires these materials.
• Medium carbon steels has a carbon content ranging from 0.3% to 0.6%.
• Due to increased carbon content, these are stronger and harder than low carbon steels.
• These are having less ductile and more difficult to form and weld
• They often require heat treatment such as quenching, tempering. Since manganese contents between 0.30% to 0.60% it is possible to achieve the desired mechanical properties.
• Case hardened steels EN36C, EN353, SAE 8620H, 16MnCr5, 20MnCr5, 18CrNiMo7-6. : This material having Chrome-Nickel-Moly carburising steel generally supplied annealed to HB 229max. Carburised and heat treated it develops a hard wear resistant case to HRC 60-63 and a tough strong core with a typical tensile strength range of 900=1300MPa.
• These are all case hardened steels. This materials needs to do Gas carburising and hardening to get higher surface hardness with good case depth. In the above materials we can maintain  surface hardness value 58-62 hrc core hardness 28-32-40 hrc depending Upon material.These gears will be supplied case hardened and Profile ground
• Carbon steel for surface hardening C45, C60E, EN8 : These materials are used for output shafts of gear boxes with normalished condition
• Direct Hardening Alloy steels EN19, EN24, 42CrNiMo6 : These materials are used for gears with through hardening as well as surface hardening. In the above materials we can maintain  hardness value  as below by doing hardening and Tempering. These gears can be supplied with cut finish as well as profile grinding finish

  En 24 (upto 450 BHN)

   En 19 (upto 350BHN)

  En 9/C60E (up to 280BHN)

we can achieve higher hardness of 58 -62Hrc by doing gas Nitriding, sursulf Nitriding  with case depth of 0.5mm and lesser.We can achieve higher case depth by doing Induction Hardening.

Properties of medium-carbon steel

Each grade has its own properties that distinguishes it from other medium-carbon steel grades. The table below gives you a range of values for medium-carbon-steel properties.

Raw material Inspection methods:

• To ensure raw material originality it is better to get mill test certificates for the steels used for gear manufacturing.
• In case of high-speed application gears, integrated test bars to be received from mills. So that we can ensure the chemical/mechanical properties of original material
• In raw material stage, chemical composition to be verified. This can be verified by wet analysis method or Spectrometer.
• Test bars to be checked for UTS, Elongation to ensure mechanical properties
• Charpy test to be done to check impact strength
• To check any cracks ultrasonic testing to be conducted. By doing this any catastrophic failures can be avoided after final machining
• After heat treatment process gears can be checked for cracks by using magnaflux testers.
• Hardness values to be verified by using hardness testers
• To check grinding cracks, Nital etching test to be conducted
• During heat treatment, each heat test piece to be verified to check the exact case depth

Conclusion: 

In this article we have articulated about types of gears, applications, gear manufacturing process, different types of materials used for gear manufacturing. We have explained about types of heat treatment process and raw material properties and raw material inspection process methods. If we are following all these parameters clearly without any lapse gears will perform better.