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Helical Gear
Helical gears are commonly used in various applications, including automotive transmissions, industrial machinery, power generation equipment, and many other mechanical systems that require high torque transmission, smooth operation, and low noise levels.
What is a Helical Gear?
A helical gear is a type of gear that has helical teeth. It is a cylindrical-shaped gear with teeth that are cut at an angle to the face of the gear. The helical teeth are formed in a helix shape, resembling a twisted or spiraling pattern.
The helical gear’s teeth are cut at an angle to the gear’s axis, resulting in a gradual engagement and disengagement of the teeth as the gears rotate. This design feature allows for smoother and quieter operation compared to other types of gears, such as spur gears.
How to Define a Spur Gear?
- Normal Circular Pitch: The distance between similar profiles of adjacent teeth along the pitch circle or pitch line is called the circular pitch (p).
- Circular Thickness: The circumferential thickness (t) refers to the arc length on both sides of the separating gear teeth on the pitch circle.
- Helical Angle: The helix angle is formed by the transverse plane (rotation plane) at the involute tooth shape and pitch radius.
- Pitch Diameter: Pitch diameter refers to the pitch perpendicular to or at right angles to the tooth.
- Helix’s Direction: Also known as Lead, this term refers to the axial advance of the tooth throughout one rotation (as in thread pitch).
- Pitch Circle: Pitch circle is the circumference used to represent the size of gear teeth. Its distance is equal to the number of teeth multiplied by the circumferential pitch. Contrary to the tip circle and the root circle, the pitch circle is an invisible imaginary circle.
- Circle Pitch Size: The circle pitch size refers to the distance measured along the pitch circle per tooth. It is the reciprocal of the gear’s normal circular pitch.
- Transverse Pressure Angle: The transverse pressure angle is the angle between the line tangent to the tooth profile at the pitch circle and a line perpendicular to the gear’s axis. It determines the shape and strength of the gear teeth.
- Centre Distance: The centre distance is the distance between the centers of two meshing gears. It is an important parameter for correctly positioning and aligning the gears.
- Addendum (A): The addendum is the radial distance from the pitch circle to the top of the tooth. It represents the height of the tooth above the pitch circle.
- Outside Diameter: The outside diameter, also known as the outer diameter, is the diameter of the gear measured at the outermost point of the gear teeth.
- Dedendum: The dedendum is the radial distance from the pitch circle to the bottom of the tooth. It represents the depth of the tooth below the pitch circle.
- Whole Tooth Depth: The whole tooth depth is the sum of the addendum and the dedendum. It represents the total height of the tooth from the top to the bottom.
- Root Diameter: The root diameter is the diameter of the gear measured at the bottom of the tooth spaces.
- Contact Ratio: The contact ratio is the ratio of the length of the path of contact between two meshing gears to the theoretical length of the path of contact. It indicates the extent of tooth engagement and influences the smoothness of gear operation.
Types of Helical Gears
Double Helical Gear
Double helical gears are gears that combine two helical gears with opposite helical angles on the same gear shaft. It has a unique “V” shaped tooth profile, similar to the letter “W” or Z-shaped.
Herringbone Gear
A herringbone gear is a type of gear that combines two helical gears with opposite helical angles on the same gear shaft. The difference between it and a double helical gear is that the teeth are a continuous helix with no gaps in the middle.
Helical Rack and Pinion
It is a type of mechanical system used to convert rotational motion into linear motion or vice versa. It consists of two main components: a helical gear called the pinion and a long, straight rack with helical teeth.
Screw Gear
Screw gear reference bodies are rotational hyperboloids. A skew straight line is rotated around a rotational axis to produce a hyperboloid. Screw gears are made for moderate speeds and torques, such as those used in machine tool drives.
Helical Worm Gears
Helical worm gears are cylindrical objects with an external spiral thread that meshes with another gear to turn it. A worm or a screw collides with a gear in this particular gear system.
Bevel Helical Gears
they can be made to operate at other angles as well, helical bevel gearboxes are angular gearboxes in which the output shaft of the gear unit rotates 90 degrees concerning the motor’s rotor shaft.
Helical Gear
Manufacturing Process
The precision required in gear production makes the manufacturing process rather difficult. Gear manufacturing is a separate business today that depends on several historical and contemporary procedures to maintain the ideal balance between cost, quality, and operations. There are different ways in which gears can be manufactured.
Post-Manufacturing Processes
After manufacturing, the designers can apply the following surface finishing methods.
- Grinding – Grinding is a typical surface finishing technique that produces a surface with a smooth finish. It doesn’t matter if grinding is done continually or sporadically; the outcome remains the same.
- Lapping – This procedure is used for delicate gears requiring high precision. Lapping is a low- to medium-speed process that uses tiny abrasive particles to smooth a surface.
- Honing – This is another typical technique that polishes and smooths the surface. Additionally, tiny corrections can be made to the shape of the teeth.
- Shaving – This technique involves removing incredibly thin layers from the surface to create a smooth profile. Since shaving is typically expensive, it is rarely used to manufacture gears.
- Burnishing – In its simplest form, burnishing uses compression to smear a surface smoothly.
Casting
The liquid material is poured into the hollow mold in the desired shape and then hardened.
Forging
Forging is the process of heating and forming hot metal, using a press, mold, or hammer to hammer, press, or roll it into a design or shape suitable for a specific purpose.
Extrusion
Extrusion is a process in which a material undergoes plastic deformation by applying a force that causes the material to flow through a hole or mold.
Powder metallurgy
When compacted metal powders are heated to just below their melting temperatures, this process, called powder metallurgy, is used to create metal.
Gear Machining
Common cutting methods for helical gears include hobbing, shaping, broaching, and milling
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