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MD2 > SPUR GEARS PPT > Flashcards

SPUR GEARS PPT Flashcards

1
Q

In precision machines, in which a definite velocity ratio is of importance (as in watch mechanism), the only positive drive is by

A

gears or toothed wheels

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2
Q

A __________ is also provided, when the distance between the driver and the follower is very small.

A

gear drive

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3
Q

According to the position of axes of the shafts.
* The axes of the two shafts between which the motion is to be transmitted, may be

A

(a) Parallel,
(b) Intersecting, and
(c) Non-intersecting and non-parallel.

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4
Q

These gears are called ___________ and the arrangement is
known as bevel gearing.

A

bevel gears

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5
Q

The bevel gears, like spur gears may also have their teeth
inclined to the face of the bevel, in which case they are known
as

A

helical bevel gears

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6
Q

The gears, according to the peripheral velocity of the gears, may be classified as :

A

(a) Low velocity,
(b) Medium velocity, and
(c) High velocity.

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7
Q

The gears having velocity less than 3 m/s are termed as

A

low velocity gears

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8
Q

Gears having velocity between 3 and 15 m/s are known as

A

medium velocity gears

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9
Q

If the velocity of gears is more than 15 m/s, then these are called

A

high speed gears

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10
Q

The gears, according to the type of gearing, may be classified as:

A

(a) External gearing,
(b) Internal gearing, and
(c) Rack and pinion

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11
Q

In ____________, the gears of the two shafts mesh externally with each other

A

external gearing

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12
Q

The larger of these two wheels is called __________ and the smaller wheel is called pinion.

A

spur wheel or gear

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13
Q

The larger of these two wheels is called spur wheel or gear and the smaller wheel is called ________.

A

pinion

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14
Q

In _____________, the gears of the two shafts mesh internally with each other as shown.

A

internal gearing

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15
Q

The larger of these two wheels is called ____________ and
the smaller wheel is called pinion. In an internal gearing, the motion of the wheels is always the same.

A

annular wheel

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16
Q

The straight line gear is called _______ and the circular wheel is
called _______.

A

rack and pinion

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17
Q

The teeth on the gear surface may be

A

(a) Straight,
(b) Inclined, and
(c) Curved.

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18
Q

are toothed wheels whose teeth are straight and parallel to the shaft axis. They are used to transmit motion and power between parallel shafts

A

Spur Gears

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19
Q

It is an imaginary circle which by pure rolling action, would give the same motion as the actual gear.

A

Pitch circle

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20
Q

It is the diameter of the pitch circle. The size of the gear is usually specified by the ____________. It is also called as pitch diameter.

A

Pitch circle diameter

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21
Q

It is a common point of contact between two pitch circles.

A

Pitch point

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22
Q

It is the angle between the common normal to two gear teeth at the point of contact and the common tangent at the pitch point. It is usually denoted by ϕ. The standard pressure angles are 14 1/2° and 20°.

A

Pressure angle or angle of obliquity

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23
Q

It is the radial distance of a tooth from the pitch circle to the top of the tooth.

A

Addendum

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24
Q

It is the radial distance of a tooth from the pitch circle to the bottom of the tooth.

A

Dedendum

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25
Q

It is the circle drawn through the top of the teeth and is
concentric with the pitch circle.

A

Addendum circle

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26
Q

It is the circle drawn through the bottom of the teeth. It is
also called root circle.

A

Dedendum circle

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27
Q

It is the distance measured on the circumference of the pitch
circle from a point of one tooth to the corresponding point on the next tooth.

A

Circular pitch

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28
Q

It is the ratio of number of teeth to the pitch circle diameter. It is denoted by Pd.

A

Diametral pitch

29
Q

It is the ratio of the pitch circle diameter to the number of teeth. It is usually denoted by m. Mathematically, Module, m = D / T

The recommended series of modules are 1, 1.25, 1.5, 2, 2.5,
3, 4, 5, 6, 8, 10, 12, 16, 20, 25, 32, 40 and 50.

A

Module

30
Q

It is the radial distance equal to the difference between the dedendum and addendum, in a meshing gear.

A

Clearance

31
Q

It is the radial distance between the addendum and the dedendum circle of a gear. It is equal to the sum of the addendum and dedendum.

A

Whole depth or Total Depth

32
Q

It is radial distance from the addendum circle to the clearance circle. It is equal to the sum of the addendum of the two meshing gears.

A

Working depth

33
Q

It is the width of the tooth measured along the pitch circle.

A

Tooth thickness

34
Q

It is the width of space between the two adjacent teeth measured along the pitch circle.

A

Tooth space

35
Q

It is the difference between the tooth space and the tooth thickness, as measured on the pitch circle.

A

Backlash

36
Q

It is surface of the tooth above the pitch surface.

A

Face of the tooth

37
Q

It is the surface of the top of the tooth.

A

Top land

38
Q

It is the surface of the tooth below the pitch surface.

A

Flank of the tooth

39
Q

It is the width of the gear tooth measured parallel to its axis.

A

Face width

40
Q

It is the curve formed by the face and flank of the tooth.

A

Profile

41
Q

It is the radius that connects the root circle to the profile of the
tooth.

A

Fillet radius

42
Q

It is the path traced by the point of contact of two teeth from the beginning to the end of engagement.

A

Path of contact

43
Q

It is the length of the common normal cut-off by the addendum circles of the wheel and pinion

A

Length of the path of contact

44
Q

It is the path traced by a point on the pitch circle from the beginning to the end of engagement of a given pair of teeth. The ____________ consists of two parts, i.e.

A

Arc of contact

45
Q

It is the portion of the path of contact from the beginning of
the engagement to the pitch point.

A

Arc of approach

46
Q

It is the portion of the path of contact from the pitch point to the end of the engagement of a pair of teeth.

A

Arc of recess

47
Q

It is the ratio of the length of arc of contact to the circular pitch i.e. number of pairs of teeth in contact.

A

Contact ratio

48
Q

the common normal at the point of contact between a pair of teeth must always pass through the pitch point.

This is fundamental condition which must be satisfied while
designing the profiles for the teeth of gear wheels.

A

law of gearing

49
Q

is the curve traced by a point on the circumference of a circle which rolls without slipping on a fixed straight line.

A

cycloid

50
Q

When a circle rolls without slipping on the outside of a fixed circle, the curve traced by a point on the circumference of a circle

A

epicycloid

51
Q

On the other hand, if a circle rolls without slipping on the inside of a fixed circle, then the curve traced by a point on the circumference of a circle

A

hypocycloid

52
Q

was one of the first regular profiles used for gear teeth.

A

cycloidal form

53
Q

An involute of a circle is a plane curve generated by a point on a tangent, which rolls on the circle without slipping or by a point on a taut string

A

Involute Teeth

54
Q

Used for general purpose gears. It is stronger but has no
interchangeability. The tooth profile of this system has cycloidal curves at the top and bottom and involute curve at the middle portion.

A

14 1/2° Composite system

55
Q

The tip of tooth on the pinion will then undercut the tooth on the wheel at the root and remove part of the involute profile of tooth on the wheel.

This effect is known as ____________ and occurs when the teeth are being cut.

A

interference

56
Q

The material used for the manufacture of gears depends upon the strength and service conditions like wear, noise etc.

A

Gear Materials

57
Q

The gears may be manufactured from metallic or non-metallic materials. The metallic gears with cut teeth are commercially obtainable in

A

cast iron, steel and bronze

58
Q

The __________ materials like wood, rawhide, compressed paper and synthetic resins like nylon are used for gears, especially for reducing noise.

A

nonmetallic

59
Q

The _______ is widely used for the manufacture of gears due to its good wearing properties, excellent machinability and ease of producing complicated shapes by casting method.

The ________ gears with cut teeth may be employed, where smooth action is not important.

A

cast iron

60
Q

The ______ is used for high strength gears and ______ may be plain carbon steel or alloy steel.

The ________ gears are usually heat treated in order to combine properly the toughness and tooth hardness.

A

steel

61
Q

The _____________ is widely used for worm gears in order to reduce wear of the worms which will be excessive with cast iron or steel.

A

phosphor bronze

62
Q

______________ assumed that as the load is being transmitted from one gear to another, it is all given and taken by one tooth.

A

Lewis Equation

63
Q

The permissible working stress (Sw) in the Lewis equation depends upon the material for which an allowable static stress (So) may be determined.

A

Permissible Working Stress for Gear Teeth in the Lewis Equation

64
Q

The ___________________ is the stress at the elastic limit of the material. It is also called the basic stress

A

allowable static stress

65
Q

Every gear tooth acts as a cantilever. If the total repetitive dynamic load acting on the gear tooth is greater than the beam strength of the gear tooth, then the gear tooth will fail in bending, i.e. the gear tooth with break. In order to avoid such failure, the module and face width of the gear is adjusted so that the beam strength is greater than the dynamic load.

A

Bending failure

66
Q

It is the surface fatigue failure which occurs due to many repetition of Hertz contact stresses. The failure occurs when the surface contact stresses are higher than the endurance limit of the material. The failure starts with the formation of pits which continue to grow resulting in the rupture of the tooth surface.

In order to avoid the ________, the dynamic load between the gear tooth should be less than the wear strength of the gear tooth.

A

Pitting

67
Q

The excessive heat is generated when there is an excessive surface pressure, high speed or supply of lubricant fails. It is a stick-slip phenomenon in which alternate shearing and welding takes place rapidly at high spots.

This type of failure can be avoided by properly designing the parameters such as speed, pressure and proper flow of the lubricant, so that the temperature at the rubbing faces is within the permissible limits.

A

Scoring

68
Q

The foreign particles in the lubricants such as dirt, dust or burr enter between the tooth and damage the form of tooth.
This type of failure can be avoided by providing filters for the lubricating oil or by using high viscosity lubricant oil which enables the formation of thicker oil film and hence permits easy passage of such particles without damaging the gear surface.

A

Abrasive wear

69
Q

The corrosion of the tooth surfaces is mainly caused due to the presence of corrosive elements such as additives present in the lubricating oils.

In order to avoid this type of wear, proper anti-corrosive additives should be used.

A

Corrosive wear

MD2 (22 decks)

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