Gear Hobbing

Gear Hobbing

There are many types of equipment used in the drilling and processing of oil and gas, and they are important for the survival and effective functioning of the oil industry. Many of these instruments, such as oil field pump equipment that use horizontal and vertical pumps, require a geared device. 

 

These devices can change the speed, torque, and direction of a power source through the teeth of the gears. The device preserves the input power and simply trades off forces against movement to obtain a desired amplification in the output force, creating a mechanical advantage. To produce these cogwheels or gears, specific machining is needed to cut the teeth into the workpiece, this machining process is referred to as hobbing.  

 

Hobbing is a machining process for cutting gears, splines, and sprockets. It is the most widely used gear cutting process for creating spur and helical gears, and more gears are cut by hobbing than any other process. A special type of milling machine, the hob, uses a cutting tool used to cut the teeth into the workpiece. It is cylindrical in shape with helical cutting teeth. These teeth have grooves that run the length of the hob, which aid in cutting and chip removal. The cross-sectional shape of the hob teeth are almost the same shape as teeth of a rack gear that would be used with the finished product. There are slight changes to the shape for generating purposes, such as extending the hob’s tooth length to create a clearance in the gear’s roots. This manufacturing technique is one of the fundamental processes of gear manufacturing and is both accurate and inexpensive

The Defining Dimensions of a Hob Used for Machining an Involute Gear.

Hob Machine Dimensions

Based on diagram on from Degarmo’s Materials and Processes in Manufacturing (9th ed.) (2003); by: E. Paul DeGarmo, J. T. Black, Ronald A. Kohser

Types of Gears

Spur Gears

Spur Gears, the most common and efficient type of gear, is used when the application of transmitting power and uniform rotary motion from one parallel shaft to another is required. This gear is also known as a straight gear.

Helical Gears

Helical gears, a type of cylindrical gear, have teeth that are set on an angle to the gear axis. The features and benefits are similar to spur gears but can be a better option when higher velocities are needed. They have greater tooth strength, a higher load carrying capacity, and a smoother and quieter operation due to their higher face contact ratio.

Gear Pumps

Gear pumps are one of the most common types of pumps for hydraulic fluid power  applications. They are positive displacement pumps, meaning they pump a constant amount of fluid in each revolution.

Types of Shafts and Splines

Parallel key splines

Parallel key splines have equally spaced, straight-sided grooves that are parallel in both the radial and axial directionsThis type of spline is similar to a keyway drive, with the exception that the keys are integral to the shaft and equally spaced around the circumference. The outside diameter of the shaft and major diameter of the internal spline or the minor diameter of the internal spline and the minor diameter of the shaft. 

Involute Splines

Involute splines also have equally spaced teeth, but the teeth are involute and usually not as tall. The involute form and the lowered height increase strength by decreasing stress concentration as well as the possibility of cracks due to fatigue. Involute splines come in several varieties: Flat root side fit, fillet root side fit, and major diameter fit. 

 

Crowned Splines

Crowned splines are usually involute splines whose teeth are crowned or curved to compensate for angular misalignment. Usually, the tooth has a symmetrical crown about the centerline of the spline face-width. At this centerline the tooth thickness is at its maximum. Moving toward the ends the tooth thickness gradually decreases, with the thinnest sections occurring at each end face. 

Serrated Splines

Serrated splines have teeth of the male detail are in the form of an included angle, with the female serration having spaces of the same included angle. Serrations are generally used on smaller diameter drives, where an involute form would not add strength. This shape allows for more teeth on a smaller shaft circumference and providing greater contact area.

Helical Splines

Helical splines have equally spaced teeth that form a helix around the shaft. The helix enables better load sharing of rotational torque along the length of the shaft and is therefore used in applications of high torque. 

We are a unique specialty Metals Service Center specializing in quality High-Quality Alloy and Nickel Alloy metal products and are the experts in Pump Shaft Quality (PSQ) long bar products. See the full list of specialty alloys and capabilities Double Eagle Alloys offer and let one of our experienced team members assist you.

Sources: