Industrial machines demand a steady flow of power to execute various tasks. Most machinery in industrial settings operates using mechanical power, primarily in the form of rotational torque. To generate this mechanical energy, a prime mover is needed, which converts one form of energy into mechanical energy. For example, an electric motor transforms electrical energy into mechanical energy. The mechanical power transmission system is responsible for guiding this power from the prime mover to the designated parts of the machine. This system mainly comprises four types of drives, with additional mechanical components to ensure seamless power transmission. These include the gear drive, belt drive, chain drive, and rope drive, each with unique advantages.

With competitive pricing and timely delivery, Kexin earnestly hopes to be your supplier and partner.

A gear drive is a type of rigid mechanical drive suited for short-distance power transfer. It ensures slip-free power transmission (positive drive), even under heavy loads. Based on the arrangement of the shaft and the teeth profiles, gear drives can be classified into four types: spur gears, helical gears, bevel gears, and worm gears. The spur gear, which features straight teeth parallel to the gear axis, can only be used for parallel shaft power transmission. In contrast, the teeth of the helical gear are cut at an angle to the gear axis, making them suitable for parallel shafts but with a twist—the teeth are helical. Bevel gears can have either straight or spiral teeth and are used for interacting shafts, while worm gears are designed for perpendicular non-intersecting shafts.

Although helical gears have their advantages over spur gears, they exert an axial thrust load on the bearing, which poses limitations on power transmission. To counteract this issue, the herringbone gear or double helical gear was developed. In a herringbone gear, the teeth are machined into two halves with mirrored helices, effectively canceling out the thrust forces from each half. Consequently, it allows for the transmission of significantly higher power without major issues. Below is a detailed comparison of helical and herringbone gears:

Table: Helical Gear vs. Herringbone Gear

Teeth Configuration: Helical gear teeth are shaped in a helix on the pitch cylinder, either left-hand or right-hand. Mating helical gears must have opposite helix orientations. Conversely, a herringbone gear incorporates both left-hand and right-hand helix teeth within the same gear unit. Other factors like pitch circle diameter, module, tooth count, and helix angle remain consistent in both halves of a herringbone gear.

Thrust Force Concerns: Despite providing smoother load distribution, reduced vibration, and greater load capacity, helical gears generate detrimental thrust loads. This causes the need for strong bearings capable of handling both radial and axial loads. Herringbone gears, however, cancel out these thrust forces, needing only radial force handling by the bearings.

Helix Angle: Thrust force increases with the helix angle, yet higher angles can reduce vibration and tooth wear and increase load capacity. Helical gears typically have a helix angle of about 20–25° to manage thrust forces. In contrast, herringbone gears can support helix angles up to 45° due to the absence of thrust forces.

For more insights on Herringbone Gears, feel free to contact us for expert advice.

Bearing Requirements: Bearing the load from driver and driven shafts usually requires rolling contact bearings, which also mitigate vibration and load, transmitting them to the ground via the frame. Bearings like deep groove ball bearings, angular contact bearings, and tapered roller bearings can handle radial and axial loads, making them suitable for helical gears. On the other hand, cylindrical roller bearings, which only need to handle heavy radial loads, are ideal for herringbone gear assemblies.

Power Transmission Capacity: Mechanical drives vary in their power transmission capabilities based on their design, material, and other features. While helical gears offer higher transmission capabilities than spur gears, they are not generally used for heavy-duty applications due to thrust load and bearing constraints. Herringbone gears are preferred for high-power applications, such as in herringbone planetary gear trains in coal cutters, Aerospace Gear Components, wind turbines, and more.

Fabrication Complexity: While cutting helical teeth on cylindrical gear blanks is straightforward, herringbone gears present more challenges. The junction between left and right halves needs to be cut with extreme precision to avoid overstepping. Specialized hobbing tools designed with grooves that match the herringbone gear's shape are necessary. This requires precise locational and angular alignment.

This article aims to provide a clear comparison between helical and herringbone gears. For further understanding, refer to the following textbooks:

1. Design of Machine Elements by V. B. Bhandari (Fourth edition; McGraw Hill Education).
2. Machine Design by R. L. Norton (Fifth edition; Pearson Education).
3. A Textbook of Machine Design by R. S. Khurmi and J. K. Gupta (S. Chand; 2014).

Determining the Best Angle for Herringbone Gears

The optimal angle for herringbone gears has been a topic of much discussion among engineers and designers. Generally, a helix angle of 30 degrees is considered ideal for most applications. For example, the combined angle of two helical gears, each with a 15-degree angle (15° + 15° = 30°), forms a functional herringbone gear. This helix angle provides a balance between reducing vibration and tooth wear while increasing load capacity.

In practical scenarios, deviations may occur. For instance, in 3D printed components like the Reprap Extruder gear, angles observed can be much steeper, around 50 degrees. These angles might not always be suitable for all applications and need adjustments based on specific requirements.

For additional details, check out Aerospace Gear Components for more insights.