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in the segment of this article, I am going to describe the Types & Classification of gear with gear drive and gear train along with gear terminology and their advantages and much more.
So, Stick with me and let me roll into the mainstream.
It will be great if we start with the Gear definition first.
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Let’s roll into the mainstream…
What is Gear?
A gear is a rotating machine part having cut teeth that mesh with another toothed part in order to transmit torque.
A gear is a toothed wheel that is used on machines, workshop mechanisms, etc. to transmit power between two shafts situated at small distances.
There are many methods to transmit power between two shafts such as belt drive, rope drive, chain drive, etc.
In belt drive and rope drive, slip occurs during power transmission due to which there is a loss of velocity-ratio and transmitted power. This loss is overcome by the use of toothed wheels called gears.
Classification of Gear-
The gears may be classified as:
- According to the position of the axis of the shafts.
- According to the type of gearing.
- According to the position of teeth on the gear surface.
- According to the peripheral velocity of the gears.
1. Types of Gear: According to the position of the axis of the shafts-
According to the position of the axis of the shafts, There are four types of gear and they are-
- Spur Gear
- Helical Gear
- Rack and Pinion Gear
- Worm and Worm Gear
- Hypoid Gear
- Bevel Gear
Let’s look at these different types of gears one by one-
I. Spur Gear-
Spur gears are mounted on two parallel shafts, one is the driver, and the other is driven. The teeth on the spur gear are parallel to axis of shaft.
These gears are used on gear trains of machine tools, clutches, couplings, etc.
II. Helical Gear-
Helical gears are used for connecting coplanar and parallel shafts. These gears have helical teeth cut on their periphery, one helical gear mesh with the other helical gear.
The meshing teeth of gears have opposite helixes.
Types of Helical Gear-
There are two types of helical gears:
- Single helical gear
- Double helical gear
i. Single Helical Gear-
Single helical gears are used for low speeds and loads. They produce less noise as compared to spur gear. During their operation, an axial load is produced which is undesirable.
ii. Double Helical Gear-
In order to reduce axial loads on shafts double helical gears are used. These gears are used in automobile gearboxes, steam turbines, and gas turbines for the reduction of speed.
III. Rack and Pinion-
Rack and pinion is a mechanism to convert the rotary motion of the pinion into the reciprocating motion of the rack.
The teeth of the rotating pinion mesh with a rack move it in a straight-line motion.
Rack and pinion assembly is used reciprocating on the lathe to provide longitudinal motion of a saddle. It is also used to provide reciprocating motion of the planner table.
IV. Worm and Worm Gear-
These gears are used for non-parallel and non-intersecting shafts. Shafts at 90° are generally connected with this type of gear.
The worm contains threads in a helix form and meshes with the teeth of the worm gear or wheel. In this pair, the worm is the driver, and the worm wheel is the driven element.
It is used to transmit low power at a high-velocity ratio.
V. Hypoid Gear-
This type of gear connects two shafts that are situated in different planes and do not intersect with each other. The shape of these gears is like that of spiral gear. They are also known as cross-helical gears.
VI. Bevel Gear-
When two shafts intersect at the right angle the motion of the driver shaft is transmitted to the driven shaft with the help of bevel gears.
In bevel gear assembly the smaller bevel gear (driver) meshes with the larger bevel gear (driven) for reduction of its speed.
Both gears are mounted on shafts situated in the same plane but intersecting at the right angle.
The shape of bevel gears is that of the frustum of a cone whose vertex is the cut point of the shaft axis.
Classification of Bevel Gear-
Bevel gears can be classified as-
- On the basis of teeth
- On the basis of the angle between the axis of shafts
i. On the basis of teeth-
On the basis of teeth, bevel gears may be straight teeth or spiral teeth.
ii. On the basis of the angle between the axis of shafts-
The bevel gears may be inclined at an angle less than 90° or inclined at 90°.
Other Types of Bevel Gear-
There are two other types of bevel gear-
- Crown Gear
- Internal Bevel Gear
i. Crown Gear-
The crown gear is like a rack and pinion in comparison to a pair of spur gears.
ii. Internal Bevel Gear-
These gears have teeth cut towards the inside of the cone of gear, thus the pitch of teeth is reduced from the outside towards the inside of the cone of gear.
2. Types of Gear: According to the types of Gearing-
There are two types of gearing according to this type-
- External gearing
- Internal gearing
I. External Gearing-
In external gearing two gears mesh each other externally. The tooths are made on their external surface.
In this system, gears rotate in opposite directions.
II. Internal Gearing-
In internal gearing, a bigger wheel, generally called annular gear has internal teeth and a smaller wheel, known as pinion has external teeth.
3. Types of Gear: According to the position of teeth on the gear surface-
There are three types of gear according to this position of teeth on the surface of the gear-
The position of teeth on the gear may be straight, inclined, or curved. They are known as spur gear, helical gear, and spiral gear respectively.
4. Types of Gear: According to the peripheral velocity of the gears-
There are three types of gears according to their velocity-
- Low-Velocity Gears
- Medium Velocity Gears
- High-Velocity Gears
The peripheral velocity of the gears may be categorized as low velocity, medium velocity, and high velocity.
I. Low-Velocity Gears-
Low-velocity gears are those whose periphery velocity is 3m/s or less than 3m/s. Helical Gear can be an example of low-velocity gear.
II. Medium-Velocity Gears-
Medium-velocity gears are those whose periphery velocity ranges from ‘3m/s’ to ’15m/s’.
III. High-Velocity Gears-
High-velocity gears are those whose periphery velocity ranges from 15m/s and above.
Terminology of Gear-
The technical terms related to gears are given below-
It is an imaginary circle dividing the total height of the tooth into two unequal parts. The upper bigger part is called the addendum and the lower smaller part is called the dedendum.
The pitch circle, if rotated, will produce the same speed as the actual gear.
Pitch circle diameter:
This is the diameter of pitch circle. It is denoted by letter D. It is important diameter of gears. All the calculations of gears are done on the basis of this diameter.
Circular Pitch (C.P.):
It is the arc distance measured around the pitch circle from the flank of one tooth to a similar flank in the next tooth.
It is expressed as the number of teeth per inch of the pitch circle diameter (P.C.D.).
It is defined as the length of the pitch circle diameter per tooth.
This is the radial distance from the pitch circle to the tip of the tooth. Its value is equal to one module.
This is the radial distance from the pitch circle to the bottom of the tooth space.
This is the radial distance from the tip of a tooth to the bottom of a mating tooth space when the teeth are symmetrically engaged.
Its standard value is 0.157 m.
This is the arc distance measured along the pitch circle from its intercept with one flank to its intercept with the other flank of the same tooth.
The face of Tooth:
It is that part of the tooth surface which is above the pitch surface.
The flank of Tooth:
It is that part of the tooth surface which is lying below the pitch surface.
This is the diameter of the blank from which the gear is cut. It is equal to P.CD plus twice the addendum.
The teeth of a pair of gears in mesh, contact each other along the common tangent to their base circles. The angle between the line of action and the common tangent to the pitch circles is known as the pressure angle.
The total depth of teeth:
This is the radial distance between the addendum and the dedendum circles of gear.
The total depth of teeth = Addendum + Dedendum
In gear drive, two shafts are connected to each other by means of gears. Each shaft has a gear fitted o d on it and meshes with the gear fitted on the other shaft.
The two gears have cut teeth of similar size and shape. They are mounted on the shafts with the help of keys.
The geared center contains a hole drilled equally to the size of the shaft on which it is to fit.
Advantages and Limitations of Gear Drive-
Here are some of the advantages and disadvantages of gear drive-
Advantages of Gear Drive-
- Constant velocity ratio.
- Transmission of power at low speeds also.
- Transmission of power between shafts situated very near to each other.
- High efficiency (about 99%).
- Easy transmission of power at a minimum and maximum limits.
- Installation in low space areas
- Compact in nature.
- Easy and accurate power transmission for angular shafts in comparison to other types of drives
- Involves less wear and tear and maintenance costs.
- A better and long service life.
- Reliable drive.
Disadvantages of Gear Drive-
In spite of so many advantages, gear drive involves some limitations and drawbacks:
- 1. Gear manufacturing is a costly technique and needs special equipment.
- Lubrication is required in gear drive operation.
- Due to incorrect alignment or defective teeth, a lot of noise and vibrations are produced.
Application of Gears-
Here are some of the major applications of gear or gear drive-
- In Lifts and Elevators
- Power Plants
- Aerospace Industry
- Automobile Industry
- In Pump system
Power and speed are transmitted from one shaft to other through a number of gears meshing with each other. The combination of such meshing gears is known as a gear train.
The gear train is used to reduce or increase speed from one shaft to another shaft in the required ratio.
The application of gear trains is found in automobile engines, machine tools, mechanisms of watches, toys, etc in which speed and torque have to be reduced or increased.
Types of Gear Train-
Gear trains may be classified according to the required velocity ratio, the combination of gears and relative position of shafts.
Main types of gear trains are:
- Simple gear train
- Compound gear train
- Epicyclic gear train
- Reverted gear train
They are described below:
1. Simple Gear Train-
A simple gear train uses two gears which may be of different sizes. If one of these gears is attached to a motor or a crank then it is called the driver gear.
The gear that is turned by the driver gear is called the driven gear.
2. Compound Gear Train-
When more than one meshing gear is mounted on a shaft then the gear train is called a compound gear train.
Compound gear trains involve several pairs of meshing gears. They are used where large speed changes are required or to get different outputs moving at different speeds.
Advantages of Compound Gear Train-
The advantages of compound gear train in comparison to simple gear train are:
- Higher values of velocity ratio can be obtained.
- Space occupied is limited, so the cost is also less.
- Two gears are mounted on the same shaft, so different types of gears can be used.
- The load is distributed on the gear wheels, so smaller teeth and the pitch of teeth can be used.
- The system is compact and easy to maintain.
This is the end of the Types & classification of gear. I hope you enjoyed being here and got your desired knowledge.
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Abhishek Tiwary is a blogger by passion and a Quality Engineer by profession. He completed his B.Tech degree in the year 2017. Now working in a reputed firm. He loves to share his knowledge with others.