Spiral bevel gears are among the most commonly used types in shaft reciprocating drive applications. In this article, Nam Phuong Viet will provide the most general information about this type of gear. As well as notes when choosing spiral bevel gears for your application.
What is a spiral bevel gear?
Spiral bevel gears, also known as helical bevel gears, are bevel gears with teeth machined in a spiral pattern on a truncated cone shaft. Depending on the design drawing or the role used as a driving or passive gear the core can be hollow or solid.
This design provides high transmission efficiency, reduces noise and makes the transmission system operate more smoothly.
Spiral bevel gears are commonly used for transmission systems that require durability and precision such as automotive, aerospace, and other machinery systems that require stable transmission.
Structure and operating principle of helical bevel gears
In terms of structure, spiral bevel gears have a conical design with the following identifying characteristics:
- Gear cone: Teeth cut diagonally at a certain helical angle, help the teeth to mesh slowly when moving, reducing impact and helping the gear operate more smoothly.
- Gear shaft: Usually machined smaller than the cone, the shaft length depends on the design. The shaft core has 2 types: solid shaft and hollow shaft, depending on the application.
The working principle of spiral bevel gears
Helical bevel gears operate on the principle of transmitting power between two non-parallel shafts (usually at a 90-degree angle). When one gear rotates, the force from the helical teeth is transferred to the opposing gear, causing it to rotate in the desired direction. The helical teeth of the gears make sliding contact rather than slamming against each other as in straight bevel gears, resulting in smoother and quieter motion.
Advantages and disadvantages of spiral bevel gears
Advantages of helical bevel gears
- Smooth movement with low noise
- The helical tooth structure allows for even force distribution on the tooth surface, thereby increasing the load capacity.
- High transmission efficiency, low energy loss
- The ability to change the direction of transmission gives the machine systems high flexibility in terms of space and structure.
Disadvantages of helical bevel gears
- High manufacturing costs due to high precision requirements and complex machining steps.
- Difficulty in maintenance and replacement, especially in large and complex systems.
- Sensitive to assembly errors
- There is a limit to the rotation speed because when the rotation speed is too fast, the centrifugal force will reduce the durability of the gear.
In general, spiral bevel gears have many advantages but also have certain disadvantages. Therefore, when choosing gears for your transmission system, you should consider based on the system characteristics and specific usage goals.
Applications of helical bevel gears in industries
Thanks to its superior technical characteristics, spiral bevel gears are currently being chosen by many businesses. Especially in systems that require durability and stable operation under high-load conditions.
Some notable applications include:
- Automotive gearboxes and differentials
- Aircraft gearboxes and transmission systems
- Heavy equipment such as excavators, diggers and cranes
- Industrial reduction gearboxes
- Wind turbine systems
- Hydropower and thermal power plants
- Manufacturing and machine building
- Automated production lines
Technical parameters to note when choosing spiral bevel gears
Tooth step
- Is the distance along the generating line of the cone surface divided between two corresponding points on two consecutive teeth.
- To determine the correct tooth pitch, readers can refer to the technical standard documents TCVN 12133:2017 on Bevel gears – Accuracy system; TCVN 4143:1985 on Bevel gear transmission – Terminology, symbols, and definitions.
The diameter of the gear ring and the length of the tooth
- The pitch diameter is the diameter of the imaginary circle on the pitch cone where the teeth of the two gears mesh. This geometric parameter determines the transmission ratio of the transmission.
- Pitch diameter at the largest diameter of the pitch cone: d = m * z. Where: d is the pitch diameter, m is the number of modules, and z is the number of teeth.
- The tooth length is determined perpendicular to the generator line of the pitch cone. This geometric parameter affects the load-bearing capacity and fatigue strength of the teeth.
The angle of inclination or helix of the tooth
- The helix angle is the angle between the tangent line of the tooth helix at any point and the generating line of the pitch cone at that point.
- The helix angle is determined based on the working speed, output torque, manufacturing material and working conditions.
- The normal helix angle range is usually between 15° and 30°. However, in some special cases, the helix angle can be larger or smaller.
Gear manufacturing materials
- Commonly used materials: Carbon steel with carbon content from 0.3% to 0.6%; Alloy steel SCM415, SCM435, 20CrMo, 42CrMo; Stainless steel; Cast iron; Brass; Aluminum; Composite materials.
- When choosing materials to manufacture spiral bevel gears, it is necessary to pay attention to technical parameters such as hardness, fatigue strength, wear resistance, corrosion resistance, and machinability.
Hardness of tooth surface
- Hardness is affected by the manufacturing material, processing method (quenching, high frequency quenching, grinding) and coating (nitride, carbide). Methods for determining tooth surface hardness: Rockwell, Brinell, Vickers. Or you can bring the product to Quatest centres for testing.
Gear ratio
- The gear ratio of a spiral bevel gear is calculated in the same way as other gears.
- The gear ratio determines the number of teeth on the gear and the output torque.
Load capacity and torque
- Influencing factors: Manufacturing material, tooth shape, gear size, working conditions, machining method.
- Types of loads to consider: Load along the generating path, radial load, combined load.
CO, CQ certificate
- For spiral bevel gears imported from abroad, both CO and CQ certificates are required.
- For domestically produced spiral bevel gears, only CQ certificates are required.
Conclusion
Spiral bevel gears are an important component in many industrial transmission systems. With their unique helical tooth design and superior load-carrying capabilities, spiral bevel gears are effective in a wide range of applications, from automotive and aerospace to heavy industry and power generation.
However, to ensure the performance and service life of the gear, it is very important to choose the right specifications, from the tooth pitch angle, and manufacturing material to accuracy and load capacity.
Understanding the influencing factors and applications of spiral bevel gears will help engineers and manufacturers optimize system design, increase performance and minimize costs incurred due to failure or maintenance.
And finally, if you find this content useful, please share it with Nam Phuong Viet. Nam Phuong Viet also hopes to receive your support for the Apex Dynamics gearboxes products using spiral bevel gears that we are distributing.
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