### ME2352 DESIGN OF TRANSMISSION SYSTEM Two Marks Questions With Answers 2014

Anna University, Chennai

Design of Transmission Systems (ME2352) TWO MARKS Module 1

1. What is a power drive? Mention their types.

The power drive is a set of machine members employed to transmit power or energy produced in one machine to another machine. Their main *types (1) Mechanical, (2) Hydraulic, (3) Pneumatic and (4) Electrical drives.

2. What is meant by mechanical drives? Classify them.

The drives which transmit power by means of contact forces are called as mechanical drives. They can be classified based on

(a) Way of power transmission.

(i) Friction drives [e.g. Belt drives, Rope drives] (ii) Toothed drives [e.g... Gear drives, Chain drives]

(b) Centre distance between power shafts

(i) Long distance drives (e.g. Belt drives, chain drives, rope drives) (ii) Short distance drives (e.g. Gear drives)

(c) Intermediate link between driving and driven members. (i) No intermediate link (e.g. Gear drives)

(ii) With intermediate link (e.g. Belt, rope drives, chain drives)

3. State the -Law of Belting'

The law of belting states that the centerline of the belt when it approaches the pulley must lie in the mid plane of that pulley which should be perpendicular to the axis of the pulley. Otherwise the belt will run off the pulley.

4. Explain the term crowning of pulleys. Pulleys are provided a slight conical shapes (or), convex shapes in their rim's r surface in order to prevent the belt from running off the pulley due centrifugal force. This is known as crowning, of pulley. Usually the crowning height t may be 1/96 of pulley face width.

5. Briefiy explain about friction and its applications

Friction is said to be a resisting force that is developed between two relatively -moving surfaces. For some machines, this frictional force may be an unwanted force and hence it is to be reduced to the maximum level for some other machines. Bearings brakes, clutches are the good examples.

6. What are the types of belts? (a) Flat Belts

(b) V Belts.

(ii) Multiple V belt. (iii) Ribbed Belt. (c) Toothed or Timing

(d), Round, Belts.

.7. State the materials for belts.

Leather, cotton fabrics, rubber, animal's hair, silk, rayon, woolen etc

8. Indicate some merits and demerits of belt-drive; Merits

1. Belt drives are used for long distance power transmission.

2, their operations are smooth and flexible.

3. Simple in design and their manufacturing cost is lower. Demerits,.

1. They need large space.

2. Loss of power due to friction is more.

9. By what materials, belt-pulleys are made? Belt-pulleys are made of cast-iron or steel

10. What is meant by the ply of belt?

Flat belts are made of thin strips and laminated one over the other in order to get thick belt. These thin strips or sheets are called as plies of belt. Usually flat belts are made of 11 ply, 4 ply, 5 ply, 6 ply and 8 ply belt etc And 4 ply belt is thicker ham 3 ply belt and so-on.

11. Mention the different types of joints employed for joining flat-belts. (I) Cemented joints (ii) Laced joints (iii) Crest joints. (iv)Hinged joints

12. What conditions should be followed when flat belt drive is installed?

1. The axes of power transmitting shafts should be parallel.

2. It should have, optimum center distance between the shafts'.

3. The tight-side of the drive should be at the bottom side of the pulley.

13. What is belt rating?

Flat-belts are made of different sizes such as 3 ply, 4 ply and V - belts are made of different grades such as A, B, C, D and E grade belts. Belt rating is defined as the power transmitting capacity of unit size flat belt or a particular grade single V belt.

14. Specify the application of round belt. Round-belt is applied, in sewing machine.

15. Specify the purpose of crowning of bets.

To prevent slipping from pulley due to centrifugal force

16. What factors should be considered during the selection of a belt drive?

a) Amount of power to be transmitted. b) Peripheral and angular speeds. c) Speed ratio. A) Efficiency. e) Centre distance between staffs f) Space available. g) Working environment.

17. Explain creep in belts.

Since the tensions produced by the belt on the two sides of the pulley are not equal, the belt moves with a very negligible velocity, due to the difference of two tensions. This slow movement of the belt over the pulley is known as creep of belt and it is generally neglected."

18. How is a V-belt designated?

V-belt is designated by a grade letter followed by its inside length in code number, year of coding. For example, D 3048: IS 2494: 1964. M belts are designated by the grade letter and inside length only such D - 3048. Sometimes, the inside length may be denoted in inches as D -

19. In what ways, timing belts are superior to ordinary V-belts?

Since the timing belts possess toothed shape in their -inner side, engagement with toothed pulley will provide positive drive without, belt-slip where as in the case of ordinary V-belts, chances of slip are and hence positive drive is not possible at all times. Hence toothed belts (I timing belts) are superior to ordinary V-belts.

20. What purpose does the housing of gear-box serve?

Gear-box -housing or casing is used as container inside which, the gears, shafts, bearings and other components are "mounted.' Also it prevents the entry of dust inside the housing and reduces noise of operation. That is, the housing Safe-guard the inner components.

21. What is the function of spacers in a gear-box?(6r) What are spacers as applied to a gear-box?

Spacers are sleeve like components, which are mounted, in shafts in-between gears and bearings or one gear and another gear in order to maintain the distance between them so as to avoid interruption between them.

22. Flill in the blanks of the following.

(a) The number of gears employed in a gear-box is kept to the minimum by arranging the. Speed of the spindle is ........................... series.

(b) In a gear- box, -for a set of gears, if the centre distance and module are same, then the sum of teeth of engaging pair will be.....

Answers

a) Geometric series.

b) Equal.

23. What are the types of ropes?

They are two type namely a) Fiber ropes

b) Wire ropes.

24. In what ways wire ropes are superior to fiber ropes?

a) Wire ropes are stronger, more durable than fiber ropes. b) Wire ropes can withstand' shock loads.

c) Their 'efficiency in high.

d) They can be operated for Very long centre distance even up to 1000 m. Hence wire-ropes are superior in most of occasions.

25. How are wire-ropes classified?

(a) Based on nup4ber of strands and wires..

i) 6x7 ii) 6 x 19 iii) 6 x 37 iv) 8 x 19 ropes. (b) Based on the direction of wire I a with respect to strands in twisting.

i) Cross lay ropes.

ii) Parallel-lay ropes.

iii) Compound lay ropes.

26. How is wire-ropes designated?

A wire-rope is designated by the number of strands and the number of wires in each strand. For example, a wire rope having six strands, and each strand containing nineteen wires can be denoted as 6 x 19rope.

27. What are the various stresses induced in wire ropes?

i. Direct tensile load due to load and self-weight of the rope. ii. Bending stress when the rope winds round the drum.

iii. Stresses due to changes in starting and stopping etc.

28. Write the features of a chain drive.

A chain drive is a flexible mechanical drive which may be considered to be intermediate between belt drive and gear drive in that it has features common to both, Chains are suitable for long as well as short center distance drives and give a more compact, drive than is possible with belts. Chain drives are similar to belt drives in which the chains, are operated between toothed wheels called as sprockets.

29. Mention the applications of chain drives.

Chain drives are employed in transportation machineries like motor-cycle, bi-cycles, automobiles and technological machineries, like agricultural machines, crushes etc.

30. What are the advantages of chain drives? Chain drives

1. Are having more power transmitting capacity.

2. Have higher efficiency and compact size.

3- Exert -less load on shafts since no initial tension is applied on the sprocket shafts.

4. Require easy maintenance

31. Specify some drawbacks of chain drives.

1. The design of chain drive is more complicated. 2. The operation is noisy and production cost is high. 3.

They require more accurate assembly bf shafts than for belts.

32. Indicate the types of chains.

a) Driving chains b) Hauling chains c) Loading chains.

6. What are the kinds of driving chains?

MODULE 2

1. Mention some applications of gear drives.

Gear drives are employed in many fields such as from smaller instruments to the heaviest and most powerful machismos, crushers etc. Some of the common a p p l i c a t i o n s o f g e a r s a r e i n h o i s t i n g machineries, rolling mill, machine tools such as lat machines, etc.

2. Why are gear drives superior to belt drives or chain drives? the advantages of gear drives?

1. The gear drives possess high load carrying capacity, high compact layout.

2. They can transmit power from very small values to several kilowatts.

3. How are gears classified? Gears are classified based on (a) Axes of gear shafts as

i) Parallel – e.g. spur, helical, herring-bone gears. ii) Intersecting – e.g. Bevel gears. iii) Non- parallel and non-intersecting – e.g. - worm, gears, Skew gears.

(b) Profile of gear tooth

I) Involutes gears. ii) Cycloidal gears. (c) Position of teeth on wheel rim.

D Tooth parallel to axis of gear – e.g. Spur gears. ii) Tooth inclined to axis of gear – e.g. Helical gears. (d) Pressure angle

i) Gears with 201 pressure angle. ii) Gears with 14 1/20 pressure angle.

4. Illustrate the materials for making gears'.

1. Ferrous metals such as carbon steels, alloy steels of nickel, chromium and vanadium.

2. Cast-iron of different grades.

3. Non-ferrous metals such as brass, bronze, etc.

4. Non-metals like Phenolic resins nylon, Bakelite etc.

Among them steel with proper heat treatment is extensively, employed in many of 'the engineering applications.

5. Specify the types of gears-failures.

a) Tooth breakage. b) Pitting of tooth surface. c) Abrasive- wears. d) Seizing of teeth etc.

6. At what occasions non-metallic gears are employed.

.Non-metallic gears are employed 'where we require silent operation and low power transmission. For example, in instruments like pressure gauge and so on.

7. Fill in the blanks of the following

a) In a gear pair, the smaller gear is, called as. . . . . . . . . . . . . . . . . . . . . . . . . . . . . and the bigger is called as ....................................................................................

b) When the gear and pinion are made of different materials, their design based on.........

Answers

a) Pinion, wheel or gear. b) Weaker material.

8. What is meant by spur-gear?

Spur-gear is the gear in which teeth are cut at the circumference of a slab called as gear-blank such that the teeth are parallel to gear-axis.

9. Define the following terms.

a) Tip circle or addendum circle is the circle which coincides crests or tops of all teeth.

b) Root circle or addendum circle is the circle which coincides with. roots or bottoms of all teeth.

c) Pitch circle is the imaginary circle in which the pair of gears rolls one over the other. This circle can be visible when the pair of gears fast rotating. This will lie between tip circle and root circle.'

10. How are the following terms defined?

a) Pressure angle (a) is the angle making by the line of action common- tangent to the pitch circles of mating pars.

b) Module m is the ratio of pitch circle diameter to the number d of gear teeth, and is usually represented in millimeters.

11. Define the following terms.

a) Back lash is the difference between tooth thickness and the space into 'which it meshes, measured along the pitch circle. If we assume the tooth thickness as t, and space width as t2 then backlash = t2 – t1

b) Gear ratio (i) is the ratio of number of teeth of larger gear to that of smaller gear. At is also defined as the ratio of high speed to the low speed in a gear drive.

Usually, the gear ratio should always be greater than one.

12. Fill in the blanks of the following.

a) The difference between tip circle radius and pitch circle -radius is.......

b) The difference between pitch circle radius and root circle radius is......................

Answers

a) Addendum, b) dedendum.

13. What factors influence backlash?

The factors like errors in tooth thickness, pitch, tooth spacing, mounting misalignment, etc influence the backlash.

14. What preliminary design considerations should be, adopted, When selecting gear drive?

All kinds of gears cannot be useful for all kinds of work. Hence following factors should be considered for selecting a specific type of gear drive.

i) The amount of. power to be transmitted. ii) Space availability.

iii) Amount of gear ratio for single step.

Iv) Causes for gear failures and their preventing methods. v) Proper material

vi) Life of gears required, usually 10,000 hours.

15. What is interference in gears? How can you overcome it?

Gear profile usually starts, from base circle and ends with tip teeth are made in such a way that their contact is along the pro the top surface of teeth is made, flat, the tip of the teeth of one gear dig I into the bottom flank of mating gear. This action is called interference.

16. On what basis gear cutters are selected?

Gear cutters are selected based on the following conditions.

1) Properties of materials for work piece and tools.

2) Cost of production.

3) Structure of gears such as spur gear, helical gears and so on.

4) Module of the gear.

17. How do gears fail?

.Gears may fail due to tooth breakage by overload and misalignment of shafts. b) Corrosion of teeth by improper lubricants. c) Tooth wear because of insufficient lubrication. d) Interference because of no under-cut.

18. Fill in the blanks of the following.

a) The size of gears are usually specified by their ......... b) the commonly used gear tooth-profile is

.........

Answers

a) Outer diameter, module, number-of teeth. b) Involutes profile.

19. What is working depth of a gear-tooth?

Working depth of gear is the radial distance between addendum circle and clearance circle. It is equal to two times, the addendum value.

20. What stresses are induced in gear tooth?

1. Surface compressive stress.

2. Bending stress.

21. What is meant by a corrected gear?

In normal gear, there may be an undercut between base circle and root circle which weakens the teeth. This undercutting can be avoided by making some modifications on the gear profile. This modification is addendum modification or profile correction or profile shift. The gear, which has this correction, is called as corrected gear.

22. Write short notes on backlash of gears.

Backlash can be defined as the play between a mating pair of gear assembled condition.

23. What are the effects of little backlash and. excessive backlash on gears

Too little backlash may lead to over loading, overheating and ultimately seizure resulting eventual failure of the system. On the excessive backlash may cause, non uniform - transmission of motion. Backlash may also cause noise and impact loads.

24, Define form factor?

Form factor is a constant, employed in the design of gear which, design t h e shape and the number of teeth.

25. Why dedendum Value is more than addendum value?

In order to get clearance between the teeth of one gear and bottom surface of mating gear so as to avoid interference, dedendum is having more value than addendum.

81. Specify the machine tools used for producing spur gears.

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26. What is a helical gear?

A helical gear is a cylindrical gear similar to spur-gear except that the teeth are cut at an angle, known as helix angle 'to the axis of the gear shaft, whereas in spur-gear, teeth are cut parallel to the axis.

27. In what ways helical gears are differed from spur gears-

 1. Spur gears Teeth are cut parallel to the axis. Helical gears Teeth are cut inclined to the axis. 2. 3. Entire width of tooth is simultaneously engaged with full Width of mating gear. Rough and noisy operation Gradual engagement is obtained since their teeth are inclined to Axis. Smooth and silent operation. 4. Less power is transmitted. More power can be transmitted.

28. What are the advantages of helical gears? Helical gears

I) transmit more power. ii) Provide smooth and soundless operation. Iii) used for high speed and high velocity ratio processes.

29. What is helix angle? How this angle differentiate helical gear from

Helix angle -is the angle between the axis of the gear and the through tooth face. For helical gear, teeth are cut at an inclined axis, specified as’ helix angle and its value ranges from 80to25' the case of spur gear, tooth-are cut parallel to the axis, the spur gear is zero.

30. Fill in the blanks of the following:

a) Double helical gears are otherwise called as .......... b) Crossed helical gears are known as........

Answers

a) Herring bone gears. b) Skew gears.

31. What is a herringbone gears?

A herring bone gear is made of two single helical gears attached other hence called as double helical gear in which the teeth of be set in the opposite direction to the teeth of another gear arrangement the axial thrust produced in one gear will be null’, thrust produced in another gear, and the resultant thrust is improves the life of the gear. Sometimes, a single cylindrical block is ova-ployod for making, herring bone, Gear.

32. Write any two applications of a skew gear-drive. (or) Where do we, use skew gears?

The skew gears or crossed helical gears are employed in instruments, distributor drive of automobile engine etc, where small loads are applied.

1. What is a bevel gear?

Bevel gear is the type of gear for which the teeth are cut on conical surface in contrast with spur and helical gears for which the teeth are cut on cylindrical surfaces. The structure of bevel gear is similar to and uniformly truncated frustum of a cone.

2. When do we use bevel gears?

When the power is to be transmitted in an angular, direction, i.e., between the shafts whose axes intersecting at an angle, bevel gears are employed.

3. How are bevel gears classified? Bevel gears are classified in two ways

1. Based on the shape of teeth. a) Straight bevel gears.

b) Spiral bevel gears

4. Based on the included angle between the shaft axes, called as shaft angle a) External gears < 900)

b) Internal gears > 90*)

c) Crown gears =90

5. What’s a crown gear?

A crown gear is a type of bevel gear whose shaft angle is 90 degree and angle of pinion is not equal to the pitch angle of gear. Let Shaft angle

6. What is the specific feature of miter gear?

Miter gear is the special type of crown gear in-t which the shaft,, 900 and the pitch angles of pinion and gear are equal and each angle to 45'.

7. Fill in the blanks of the following

a) Bevel gears having shaft, Angle of, 90" are known as........

.b) when the spiral angle of a. Bevel gear is zero, it is called as...

Answers

a) Crown gears. b) Zerol bevel gear.

8. Define the following terms

a) Cone distance or pitch cone radius. b) Face angle.

a) Cone distance or pitch cone radius is the slant length of pitch cone, i.e., distance between the apex and the extreme point of tooth of bevel gear.

b) Face angle is the angle subtended by the face of the teeth at the cone centre. It is equal to the pitch angle plus addendum angle. It is also called as tip angle.

9. In which gear-drive, self-locking is available? Self locking is available in worm-gear drive.

10. When do we use worm-gears?

When we require transmitting power between nonparallel and non-intersecting shafts and very high velocity ratio, of about 100, worm gears, can be employed. Also worm-gears provide self-locking facility.

11. Write some applications of worm gear drive.

Worm gear, drive find wide applications like milling machine indexing head, table fan, steering rod of automobile and so on.

12. What are the merits and demerits of worm gear drive; Merits

1) Used for very high velocity ratio of about 100

2) Smooth and noiseless operation.

3) Self-locking facility is available. Demerits

1) Low efficiency.

2) More heat will be produced and hence this drive can be operated inside an oil reservoir or extra cooling fan is required in order to dissipate the heat from the drive.

3) Low power transmission.

1. What purpose does the housing of gear-box serve?

Gear-box -housing or casing is used as container inside which, the gears, shafts, bearings and other components are "mounted.' Also it prevents the entry of dust inside the housing and reduces noise of operation. That is, the housing Safe-guard the inner components.

2. What is the function of spacers in a gear-box? (6r) what are spacers as applied to a gear-box?

Spacers are sleeve like components, which are mounted, in shafts in-between gears and bearings or one gear and another gear in order to maintain the distance between them so as to avoid interruption between them.

3. Fill in the blanks of the following.

(a) The number of gears employed in a gear-box is kept to the minimum by arranging the. Speed of the spindle is. . . . . . . . . . . . . . . . . . . . . . . . . . Series

(b) In a gear- box, -for a set of gears, if the centre distance and module are same, then the sum of teeth of engaging pair will be.....

Answers

a) Geometric series.

b) Equal.

4. What is a speed diagram? (Or) What is the structural diagram-of -&.gear-box?

Speed diagram or structural diagram is the graphical representation different speeds of output shaft, motor shaft and intermediate shafts.

5. For what purpose we are using gear-box?

Since the gear-box is provided with number of gears of different size arranged is different forms, we can get number of output speeds by operated motor at single speed.

6. Name the types of speed reducers. a) Single reduction speed reduces. b) Multi reduction speed reducers.

7. What does the ray-diagram of gear-box indicate?

The ray-diagram or kinematic arrangement of a gear box indicates arrangement of various gears in various shafts of the gear box in order to obtain the different output speeds from the single speed of the motor.

8. What is step ratio?

Step ratio is the ratio of one speed of the shaft to its previous lower speed since the spindle speeds are arranged in geometric progression, the ratios adjacent speeds (i.e., step ratios) are constant.

If Nr is; the maximum speed and N, is the minimum speed, then,

Nr (r-1)

= (Step ratio)

Nr-1

1. What is cam?

Cam is a rotating mechanical member used for transmitting desired motion to a

Follower by direct contact

2. Classification of cam?

(i) According to cam shape

(ii) According to follower movement

(iii) According to manner of constraint of the follower

3. Classify cam based on a shape?

 (i) Wedge cam (ii) Radial cams (iii) spiral cams (IV) drum cams (v) Spherical cams

4. Classification of follower?

(i) According to follower shape

(ii) According to motion of follower

5. What is roller follower?

In place of a knife edge roller is provided at the contacting end of the follower

6. Spherical follower?

In the contacting end of the follower is of spherical shape.

7. Angle of ascend?

The angle of rotation of the cam from the position when the follower begins to rise till it reaches its

Highest points it is denoted by Î¸

8. Angle of descend?

The angle through which the cam rotates during the time the follower returns to the initial position. It is denoted by Î¸ r.

9. Angle of dwell?

It is the angle through which the cam rotates while the follower remains stationary at the highest or the lowest.

10. Angle of action?

The total angle moved by the cam during its rotation between the beginning o f rise and the end of return of the follower

11. What is radial or disc cams?

In radial cams the follower reciprocates or oscillates in a direction perpendicular to the cam axis. The cams are all radial rams. In actual practice, radial cams are widely used due to their simplicity and compactness.

12. What is dwell?

The zero displacement or the absence of motion of the follower during the motion of the cam is called dwell.

13. What is classification of followers according to follower shape? (i) Knife edge follower

(ii) Roller follower

(iii) Mushroom or flat faced follower and

(iv) Spherical faced or curved shoe follower

14. What is classification of follower according to the motion of the follower? (i) Reciprocating or translating follower

(ii) Oscillating or rotating follower

15. What is classification of followers according to the path of motion? (i) Radial follower and

(ii) Offset follower

16. What are the motions of the follower?

The follower can have any of the following four types of motions

(i) Uniform velocity

(ii) Simple harmonic motion

(iii) Uniform acceleration and retardation

(iv) cycloidal motion.

17. What is the application of cam?

Closing and opening of inlet and exit value operating in IC engine.

18. What are the necessary elements of a cam mechanism? (i) Cam-The driving member is known as the cam

(ii) Follower-The driven member is known as the follower. (iii) Frame-It supports the cam and guider the follower.

19. What is translating angle?

The wedge is replaced by a flat plate with a groove. The plate cam moves back and forth imparting a translator or motion to the follower. Thus these cams are also known as translating cams.

20. Write the formula for maximum velocity?

Vo (max) = 2Ï‰s

Î¸ o

V r (max)=

2Ï‰ s Î¸ o

21. What is a clutch and where it is used?

Clutch is machine, component used as temporary coupling: and is used mainly in automobiles for engaging and disengaging the driving shaft where periodical engagement is required.

22. What s meant by positive clutch?

Which transmits power from driving shaft to the driven shaft by jaws or teeth is called positive clutch. No slipping is there.

23. By what means, power is transmitted by clutches? In clutches, power transmission is achieved through

(a) Interlocking (b) Friction (c) Wedging

24. Why are cone clutches better than disc clutches?

Since the cone discs are having large frictional areas and they can transmit a larger torque than disc clutches with, the same oil diameter and actuating force and hence cone clutches are preferred over disk clutches. But usually cone clutches are mainly used in low peripheral applications.

25. What factors should be considered when designing friction clutches?

(a)The friction materials for the clutch should have high co- efficient of friction and-they should not be affected by moisture and oil.

(b) May be light in weight.

(c) The design is in such a way that the engagement should be made without shock and fast disengagement without drag.

26. Why should the generated heat be dissipated in clutch operation?

In order to save the friction plates and materials from melting by the heat produced during operation, the generated heat should be dissipated.

27. Name the two theories applied for the design of friction clutches.

1. Unif6rm Pressure theory

2. Uniform wear theory

28 .In what ways, the clutches are different from brakes?

The clutch used to engage the driving and driven members and keep them moving (i.e., rotating) together, where as brakes are employed to stop a moving member or reduce its speed.

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