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KOM

Unit-4

GEAR

Q1) What are the parameters we should consider in gear selection process?

A1) Gear Selection Considerations

Gears are employed in a variety of mechanical devices, and, consequently, several different types and designs are available. The suitability of each type of gear and its exact design for a motion or power transmission application is dependent on the specifications and requirements of the application. Some of the principal factors which may be considered when designing and choosing a gear include:

1) Operational and environmental conditions

2) Dimensional restrictions

3) Transmission requirements

4) Design standards

5) Costs

Q2) Explain Gear Terminology

A2) Gear Terminology

Gear terminology is the various terms to study the gear which is being discussed below and figure 1 show the various terms used in gear terminology.

Figure.1. Gear Terminology

Pitch Circle: It is an imaginary circle which transmits the same motion by pure rolling as the transmitted by the gears in mesh.

Pitch Circle Diameter: Diameter of pitch circle is known as the pitch circle diameter.

Circular pitch: Circular pitch is the distance of a point on one tooth to the corresponding point on the adjacent tooth along the pitch circle. It is denoted by the p.

t = number of teeth.

d = pitch circle diameter.

Diametric Pitch: Diametric pitch of a gear is the number of teeth per unit length of pitch circle diameter in inches. It is denoted by P.

Module: it is the ratio of pitch circle diameter in mm to the number of teeth on the gear. it is denoted by m.

Q3) Explain Velocity ratio

A3) Velocity ratio: It is the ratio of angular velocity of driven gear to the angular velocity of driving gear. It is denoted by VR.

Let N be the rpm, w be the angular velocity and T be the number of teeth on gear. While subscript 1 and 2 are used for the driving and driven gears respectively.

Q4) Explain Gear Ratio

A4) Gear ratio is the ratio of number of teeth on driven gear to the number of teeth on driving gear. it is denoted by G.

T= number of teeth on driven gear.

t = number of teeth on driving gear.

Q5) what is Involute Gear Profile

A5) Involute Gear Profile

Involute profile is obtained by the locus of a point on a straight line when it rolls about a circumference of a circle without slipping. The circle about which the straight-line rolls is known as the base circle. Figure 2 shows the generation of involute profile in which the line BD is rolling about the base circle with center O and the path ABC shows the involute profile traced by the line.

Figure 2 Involute profile

Q6) what is Cycloidal Profile

A6) Cycloidal profile is obtained by the locus of a point on the circumference of a circle when it rolls on a straight line without slipping. Gear tooth are made by two kind of cycloidal profiles. Face of gear tooth have epicycloid profile while flank have hypocycloid profile. Figure 3 shows the cycloidal profile of gear teeth.

Epicycloid profile is obtained by the locus of a point on the circumference of a circle when it rolls on the circumference of another circle without slipping, while hypocycloid profile is obtained by the locus of a point the circumference of a circle when it rolls inside the circumference of another circle.

Figure 3 Cycloidal Profile of gear teeth

Q7) Explain Path of contact?

A7) In order to calculate the path of contact of gear considers the figure 4 which shows the two gears in contact. In which smaller gear is termed as the pinion while lager gear is known as the wheel.

Figure 4 Two gears in contact

Path of contact is given by the line CD shown in the figure 4. In the given figure:

R = radius of pitch circle for the wheel

r = radius of pitch circle for pinion

R a = radius of addendum circle for wheel

r a = radius of addendum circle for pinion

Q8) what are the different materials used to manufacture the gears?

A8) Materials used to manufacture gears:

Tempered steel is one of the most common materials for different types of gears, and aluminium is also common. Other materials used are:

High strength steels

Forged stainless steels

Copper-based alloys

Cast or forged aluminium alloys

Cast iron or grey cast iron

Magnesium alloys

Q9) what are the applications and utilities of gears?

A9) Applications & Utilities of Gears

The different types of gears are present in many sectors, such as:

The agricultural sector, in which they play a key role in carrying out mechanized tasks, such as sowing, ploughing or irrigation, as well as in the tractors themselves.

In the automotive field, their function is usually to act as transmitters of forces and to regulate speed.

As for naval vehicles, gears operate on fishing boats, submarines, workboats or yachts.

In the generation of wind power, gears increase the speed of generators, a function that is also used by cement manufacturing industries. Roller mills are used for the transport of slabs and for wire rolling mills.

In addition, there are four applications of gears that are particularly emblematic, and which are implemented in countless sectors and fields:

Q10) Describe all the characteristics of gears?

A10) Characteristics of Gears by Type

“A” indicates advantageous characteristics and “D” indicates disadvantageous characteristics
Type of Gear	Characteristics
Spur	Most common type of gear Circular gear body Straight teeth cut or inserted parallel to the gear’s shaft Used for parallel axes configuration Mated with spur gears, internal gears, or gear racks High precision and efficiency (A) Easy to manufacture (A) Does not produce thrust force (A) Capable of handling high speed and high loads (A) Gear teeth experience high stress due to tooth design (D) Noise production during high speeds (D)
Helical	Circular gear body Teeth twisted at an angle around gear body Used for parallel axes configuration Available in right-hand and left-hand designs Available in single and double helical designs Gradual tooth engagement and less impact loading (A) Quieter, smoother operation (A) Capable of handling greater loads (A) Lower efficiency (D) Higher design complexity, greater cost of manufacturing (D) Single helical design products thrust force (D), double helical does not (A)
Bevel	Cone-shaped gear body Used for intersecting axes configuration Available in straight, spiral, and Zerol® bevel tooth designs Straight: simplest bevel gear design and easiest to manufacture (A); high impact, noise level, and stress (D) Spiral: gradual tooth engagement and less impact loading, noise, and vibration (A); higher design complexity and greater cost of manufacturing (D) Zerol®: Quieter and smoother than straight bevel, able to rotate in both directions unlike spiral bevel (A)
Worm	Pair comprised of a circular gear and a screw-shaped gear Used for non-parallel, non-intersecting axes configuration Large gear ratios and gear reduction (A) Quiet, smooth operation (A) Self-locking mechanism (A) Low transmission efficiency (D) Large amounts of friction (D)
Rack and Pinion	Pair comprised of a gear rack and cylindrical gear Used for parallel axes configuration Rack mated with spur or helical gear Converts rotational motion to linear motion or vice versa Simple design, easy to manufacture (A) Capable of handling greater loads (A) Transmission cannot continue infinitely in one direction (D) Large amount of backlash between mated teeth (D) Gear teeth experience high friction and stress due to tooth design (D)

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