Helical Gear Design: Helical Gear Dimension and Strength

Helical Gear Design: Helical Gear Dimension and Strength - Helical gears used to move between the axes of rotation are parallel. Helix angle is the same in each gear, but the gear is shifted to the right and the other left. Involutes tooth shape is an expectation. A helix is a theoretical line or path generated on a cylindrical surface by a cutting tool which is fed length-wise at a uniform rate, while the cylinder is also rotated at a uniform rate. Initial bias intersection gear teeth are something that has become a more teeth line in the communion of the teeth.

Helical gear design includes the standard dimensions and strength. Standard dimensions are pitch diameter, outside diameter, root diameter and whole depth. The helical gear strength is the ability to withstand the deflection load and surface pressure.

Standard dimension of helical gear

Main gear dimensions are often expressed by the number of teeth (T) and the normal module (M) for the metric. Multiplying two variables leads to what is called the pitch diameter. In helical gears, the value of the pitch diameter is affected by the helix angle with the following relationship:

Note:

D = Pitch diameter (mm)

M = Normal module

T = Number of teeth

ß = Helix angle (o) 

How to determine outside diameter, root diameter, addendum, dedendum and whole depth are equal to spur gear calculation. (Read more : Spur Gear Calculation)

Helical gear strength by deflection load

Deflection load occurs due to the tangential force acting on the tooth surface. Tangential force is the force acting in the direction of rotation of the gear to a point on the pitch circle. Tangential force can be calculated by the following equation:

Note:

Ft = Tangential force (Kg)

Pe = Power estimation (Kw)

V = Velocity (m/s)

Velocity of helical gear can be calculated by the following equation:

Note:

V = Velocity (m/s)

n = Rotation speed (rpm)

D = Pitch diameter (mm)

Deflection load caused by the tangential force should not exceed a bending load per unit width on the sides of the permissible bending stress so that the wheels do not have a broken tooth. Deflection load can be calculated based on the Lewis equation, which is the basis for the gear design which is:

Note:

Fb = Deflection load per unit width (kg/mm)

Sd = Deflection stress (kg/mm2)

M = Normal module

Y = Gear factor

fv = Velocity factor

Helical gear strength by surface load

If the pressure between the surfaces of the tooth is too large, the teeth wear out rapidly. Furthermore, the tooth surface may be damaged because of the repeated fatigue load. Therefore, the pressure on the surface of the tooth or the surface load capacity must be limited. The surface pressure does not exceed the surface load per unit width. The surface load is calculated based on the Hertz theory that the decline in the equation can be obtained by the following equation.

Note:

Fs = Surface load per unit width (kg/mm)

fv = Velocity factor

Sc = Contact stress (kg/mm2)

D1 = Pitch diameter of pinion (mm)

T1 = Number of teeth of pinion

T2 = Number of teeth of gear

That is a description about Helical Gear Design: Helical Gear Dimension and Strength. If you find misconceptions in the helical gear formula, please provide the correction in the comment box.