Gear drives(Advantages and Disadvantages)

Introduction:

Gear is the toothed wheel that transmits power and motion from one shafts to another shafts (by means of engagement between them).

      Gear drives are used in drives where constant velocity ratio is required as well as large power transmission is need of the drive. However, gear drives are costly because manufacturing process is complicated. They also require proper lubrication, cleaning, shaft alignment, space, etc.

       Advantages of Gear drives:

(a) Gear drive does not slip.

(b) It is positive drive.

(c) It is used to transmit very large power.

(d) The efficiency of transmission of gear drive is high, up-to 99%.

(e) Low velocity transmission is also possible in case of gear drives.

(f) Changing a velocity ratio can be possible by arranging different gears in mesh as in case of gear box.

(g) No requirement of tension adjustment as in case of belt drive.

       Disadvantages of Gear drives: 

(a) Gears need lubrication for smooth running.

(b) Cost of gear drive is more as compared to other drives.

(c) Manufacturing process of gears is complicated.

(d) Gear operation may be noisy.

(e) Gears require perfect alignment of the shafts.

CHAIN DRIVE (MECHANICAL ENGINEERING)

Chain drive: (Advantages and disadvantages)

Chain is a series of links connected by pin joints and mounted on sprockets for power transmission.

           The chains does not slip over sprockets. They give constant velocity ratio. It is suggested to replace belt and rope if possible to get positive drive like chain. chains are made up of metals, that is why they take less space and they can be used for longer distance between shafts.

             

The wheel with teeth, which fit into the recesses of chain is known sprocket.

Following are the advantages of chain drives:

(a) No slippage between chain and sprocket.

(b) Almost negligible stretch.

(c) Maximum heavy loads can be carried.

(d) Long operating life.

(e) Operates in hostile environments like oily,dusty, water, etc.

(f) Can be replaced easily.

(g) Chains does not require initial tension.

(h) High efficiency upto 98% can be obtained.

In spite of all these advantages, chain drives have lot of disadvantages like:
(a) High noise during operation in certain types.
(b) Wearing of link and sprockets can take place.
(c) Flexibility is limited to a single plane.
(d) Sprockets are to be replaced after service.
(e) Chain drives need housing.
(f) Proper lubrication is needed.
(g) Proper alignment of shaft is basic requirement.
(h) Not suitable for nonparallel shafts.

Chain drives are popular in various application in almost all types of industries as well as automobiles. These are used for velocity ratio less than 10:1.

Chain are classified as:
(a) Roller Chain.
(b) Duplex Chain.
(c) Block Chain.
(d) Conveyor Chain.
(e) Silent chain.

Roller Chain:
These consist of number of inner link assemblies in which adjacent pairs are connected by outer links.
An inner link has two bushes on which rollers are mounted, followed by inner plate. This complete the inner link assembly. Such number of inner link assemblies are joined together by two outer plates from two sides with two bushes atleast 19 teeth are recommended for normal application sprocket.

Duplex Chain:
Duplex chain indicates simply combination of two chains in parallel to each other. The roller chains are designed on the basis of pitch and power transmitting capacity,
           For more transmitting capacity, duplex, triplex or such chains are used.

Block Chain:
For low-speed power transmission, block chains are used. They can also be used as conveyor chains.

Conveyor Chain:
These type of chains are of hooks joints type. The sprocket is designed for smooth working of conveyor wheel. Chain is mounted on the sprocket and power is transmitted. These chains are used for material handling applications. They are designed for breaking load capacity rather than power and speed.

Silent Chain:
Silent chain offers little vibration and noise, and operates at 99% efficiency. These chains consists of a driving link, guide link and pins with joints. Silent chain drives are the best compared with roller chains because
(a) they have high power capacity,
(b) high speed,
(c) much quieter,
(d) high efficiency,
(f) more sprocket life.
Driving link is a plain link, engages sprocket teeth with less sliding and less impact.

MECHANICAL BELT DRIVES

Introduction:

Belt drives are used to transmit power from one shaft to another shaft i.e. from driver to driven. 

Mechanism of Belt drives:

Pulleys are mounted on the shafts for transmitting power. Belt is mounted on the pulleys without slip. Motion is then given to the driving pulley by using prime mover (like motor). Driving Pulley rotates and motion is transferred to driven pulley by belt. Belt tension is the important quantity which assures transmission without slip. Number of times belt tension is adjustable to maintain constant velocity ratio.

        Following three types of sections are observed in the belt:

        1. Inner face - in compression.

        2. Outer face - in tension.

        3. Neutral section line.

This parameters will decide the effective radius of pulley.

Types of Belt:

Basically, belts are of four types.

1. Flat Belt: 

Belt with rectangular in cross-section is known as flat belt. These belts are used on slightly crowned pulleys. These belts are having joint with no upper limit for center distance between two shafts.

2. Round Belt/Rope:

Rope drives are preferred for long center distance between shafts. The most important advantage is the low cost of rope/round belt. They are of circular cross-section with joint. Also there is no upper limit for distance between two centers of rope drive. Size range of rope diameter is 3 to 20 mm. Grooved pulleys are required for round belt drive.

3. Vee Belt:

Belt with trapezoidal section is known as V- belt. The grooved pulley of a V- belt is made deeper to take advantage of wedge action. They transmit more power without slip as compared to flat belt. The height of trapezoidal cross-section is ranging between 8 to 19 mm. They are used for limited center distance because their weight/unit length is more and hence belt deflects.

4. Timing belt:

Timing belts are need toothed wheels c sprockets. They are used for achieving positive belt drive. But the center distance between two pulleys is limited when timing belts are used.

MECHANICAL ENGINEERING GUIDE ALPHABET WISE

A

Abrasion Test:

It is test for hardness of metal by means of a scratch on the smooth surface of the material being tested.

Abrasive:

Minerals used in different processes like sharpening.

Absorption Dynamometer:

Absorption dynamometer is used for measuring the work done.

Accelerating Pump:

A small cylinder and piston fitted to an SI engine carburetor, and connected to the throttle so as to provide a momentarily enriched mixture when the engine is accelerated. 

Acceleration:

It is the rate of change of velocity. For constant velocity, acceleration is zero.

Accelerator:

Pedal in a motor vehicle which controls the power and speed, by acting on the throttle valve and thereby regulating the mixture of air and petrol entering the engine.

Accelerometer:

Instrument used for measuring acceleration is called accelerometer.

Actinometer:

Instrument for measuring the intensity of the solar rays.

Accumulator:

An Accumulator is an instrument that consists of a heavily weighted tank, which is raised by means of a pump , there by storing up energy to be utilized as required ,by its descent.

Accurate:

Without error within tolerances allowed, precise, correct, confirming exactly to standard.

Acetylene Gas:

When water is poured on calcium carbide, acetylene gas is resulted. Acetylene flame has high illuminating value.

Activity-on-Note (AON) Diagram:

The activity-on-node diagram is an alternative method of representing a project network, in which the jobs or activities are denoted by nodes, while the precedence relationships are represented by the arrows. AON diagram does not require any dummy activities.

Adapter:

Appliance by means of which objects of different sizes will interchange on a spindle or other fitting.

Addendum:

The radial distance between the pitch circle of a gear wheel and the tip of a tooth.

Adiabatic process:

Addiabatic process is one in which there is no flow of heat between a system and its surroundings.

Advance:
In an internal combustion engine cylinder, which the timing of the ignition is altered to cause the spark in the cylinder to pass at an earlier point, there occurs advance.