This document summarizes the key characteristics and differences between spur gears and helical gears. It discusses how spur gears have straight teeth parallel to the axes, while helical gears have teeth that are curved and helically shaped. Helical gears operate more smoothly and quietly compared to spur gears due to the gradual contact of the teeth. However, helical gears also induce axial thrust on the bearings. The document provides examples of applications for each gear type and concludes with the authors thanking the reader.

1. Guided by;
Prof. HRT
Spur Gear and Helical Gear
G.H Patel College of Engineering and
Technology
By:
150110119124 ( Mitul )
150110119125 ( Deep )
150110119126 ( Sharvil )
150110119127 ( Vishvak )
150110119128 ( Festus )
(2C19)Mechanical Engineering

2. SPUR
GEAR

3. Characteristics of Spur Gear
• Spur gears have straight teeth parallel to the axes and thus are not
subjected to axial thrust due to tooth load.
• At the time engagement of the to gear of the two gears, the contact
extends across the entire width on line parallel to the axes of rotation.
• This result is sudden application of the load, high impact stresses and
excessive noise at a high speed.
• The gears have external teeth on the out surface of the cylinders, the
shafts rotates in the opposite direction.

4. • In an internal spur gear, the teeth are formed on the inner surface of
an annulus ring.
• An internal gear can mesh with an internal pinion ( small gear ) only
and the two shafts rotates in the direction

5. External Spur Gear Internal Spur Gear

6. Force on spur gear teeth
• Fᵗ = Transmitted force
• Fᵑ = Normal force or separating force
• F ͬ=Resultant force
• θ = Pressure angle
• Fᵑ = Fᵗ tanθ
• F ͬ = Fᵗ/cosθ

7. • Power = T n / 63000
• Torque, T = Fᵗ r and r= Dᵨ / 2
• Combining the above we can write
Fᵗ = 2T / Dᵨ

8. • Metal cutting machines
• Power plants
• Marine engines
• Mechanical clocks and watches
• Fuel pumps
• Washing Machines
• Gear motors and gear pumps
• Rack and pinion mechanisms
• Material handling equipments
• Automobile gear boxes
• Steel mills
• Rolling mills
Application of Spur Gear

9. HELICAL GEARS

11. HELICAL GEARS CONT....
In HELICAL GEARS the teeth are inclined to the axis
of a gear. They can be left-handed or right-handed
depending on the direction in which helix slopes.
In HELICAL GEARS the teeth gears, the teeth are
curved, each being helical in shape. 2 mating gears
have the same helix angle, but teeth of opposite
hands.
Are used in transmitting torques between parallel or
non parallel shafts, they are not as noisy as spur gears.

12. Terms related to helical gears
1. Helix Angle- It is the angle at which the teeth are inclined to the axis
of gear. It is also known as Spiral Angle.
2. Circular Pitch- It is the distance between the corresponding points
on adjacent teeth measured on the pitch circle. It is also known as
Transverse Circular Pitch.
3. Normal Circular Pitch(Normal Pitch)- It is the shortest distance
measured along the normal to the to the helix between
corresponding points on the adjacent teeth. The normal circular
pitch of two mating gears must be same.

13. Why Helical Gears???
The angled teeth more gradually than the Spur Gear teeth, causing
them to run more Smoothly and Quietly. With the parallel Helical
Gears, each pair of teeth first make contact at a single point at one
side of the Gear wheel.
A moving curve of contact than grows gradually across the tooth
face to a maximum than recedes until the teeth break contact at a
single point on the opposite side.
Also Spur Gears WHINE at high speeds. So Helical Gears are
preferred instead of Spur Gears in high speed applications.

14. Applications
Helical Gears are used in high speed applications. Speed is
considered high when the Pitch Line Velocity exceeds 25m/s.
Large Power Transmission
Also recommended for very high Load as in Automobile Gear
boxes, etc.

15. Disadvantages
The disadvantage of Helical Gears is that they induce axial thrust in
one direction on the Bearings.
The thrust is usually an end thrust due to action of a force
component along the Gear Axis. The bearings and the assemblies
mounting the Helical Gears must be able to withstand the thrust
load.
As stated the thrust is along the axis of the Gear, so it is often
accommodated by appropriate thrust bearings, and a greater degree
of sliding friction between the meshing teeth – often addressed with
the additives in the lubricant.

16. THANK YOU!