MESHING TEETH COME IN CONTRACT SUDDENLY. MESHING TEETH COME IN C...

5. Meshing teeth come in contract suddenly.

Design of Power Transmission System

S K Mondal’s

Chapter 3

Which of the statements given above are correct?

(a) 1, 3, 4 and 5 (b) 1,2, 3 and 4

(c) 1, 2 and 3

(d) 2, 4 and 5

IES-54Ans. (c)

IES-55. Assertion

(A):

The Lewis equation for design of gear tooth predicts the static load

capacity of a cantilever beam of uniform strength.

Reason

(R):

According to law of gears interchangeability is possible only when

gears have same pressure angle and same module. [IES-2008]

(a) Both A and R are true and R is the correct explanation of A

(b) Both A and R are true but R is NOT the correct explanation of A

(c) A is true but R is false

(d) A is false but R is true

IES-55Ans. (b) The beam strength of gear teeth is determined from an equation (known as

Lewis equation) and the load carrying ability of the toothed gears as determined by

this equation gives satisfactory results. In the investigation, Lewis assumed that as

the load is being transmitted from one gear to another, it is all given and taken by

one tooth, because it is not always safe to assume that the load is distributed among

several teeth.

Notes: (i) The Lewis equation is applied only to the weaker of the two wheels (i.e. pinion or

gear).

(ii) When both the pinion and the gear are made of the same material, then pinion is

the weaker.

(iii) When the pinion and the gear are made of different materials, then the product of

(

σ

w

×

y or

) (

σ

o

×

y

)

is the deciding factor. The Lewis equation is used to that wheel

for which

(

σ

w

×

y or

) (

σ

o

×

y

)

is less.

IES-56. In the formulation of Lewis equation for toothed gearing, it is assumed

that tangential tooth load F

t

, acts on the

[IES-1998]

(a) Pitch point

(b) tip of the tooth

(c) Root of the tooth

(d) whole face of the tooth

IES-56Ans. (b)

IES-57. Assertion

(A): The Lewis equation for gear tooth with involute profile predicts the

static load capacity of cantilever beam of uniform strength.

[IES-1994]

Reason

(R): For a pair of meshing gears with involute tooth profile, the pressure

angle and module must be the same to satisfy the condition of inter-changeability.

(a) Both A and R are individually true and R is the correct explanation of A

(b) Both A and R are individually true but R is not the correct explanation of A

IES-57Ans. (c) For a pair of meshing gears with involute tooth profile, the pressure angle and

module must be the same to satisfy the condition of inter-changeability it is not

correct. Due to law of gearing.

IES-58. The dynamic load on a gear is due to

[IES-2002]