HELICAL GEARS PPT

Question 1

has teeth in form of helix around the gear.

run more quietly than spur gears and maybe operated at pitch line velocities of up to 50 m/s and over.

may be of single helical type or double helical type.

Answer 1

Helical gears

Question 1

may be right handed on one gear and left handed on the other.

Answer 1

helixes

Question 2

The teeth of helical gears with parallel axis have _________, as in spur gearing.

This provides gradual engagement and continuous contact of the engaging teeth.

Answer 2

line contact

Question 3

mean low tooth loads, which in turn promote quietness (smooth operation) and high efficiency of transmission.

Answer 3

High pitch line velocities

Question 4

In case of ______________ there is some axial thrust between the teeth, which is a disadvantage.

Answer 4

single helical gears

Question 5

In order to eliminate this axial thrust, __________________ (i.e.
herringbone gears) are used.

It is equivalent to two single helical gears, in which equal and opposite thrusts are provided on each gear and the resulting axial thrust is zero.

Answer 5

double helical gears

Question 6

a constant angle made by the helices with the axis of rotation.

Answer 6

Helix angle

Question 7

(or simply circular pitch). It is the circular pitch in the plane of rotation or the diametral plane and is denoted by Pc.

Answer 7

Transverse Circular pitch

Question 8

(or simply normal pitch). It is the distance between similar faces of adjacent teeth along a helix on the pitch cylinders normal to the teeth. It is denoted by PN.

It may also be defined as the circular pitch in the normal plane which is a plane perpendicular to the teeth.

PN=PCcosa

Answer 8

Normal Circular pitch

Question 9

in the normal direction is different from the ________________ ϕ in the direction of rotation because of angularity of the teeth. They are related by the equation

Answer 9

Pressure angle

Question 10

The tooth displacement (i.e. the advancement of one end of tooth over the other end) or overlap should be at least
equal to the circular pitch, such that

Answer 10

Face Width of Helical Gears

Question 11

has two components :
one is tangential component (WT) and the other axial component (WA).

Answer 11

normal tooth load (WN)

Question 12

As the helix angle increases, then the tooth overlap increases and at the same time, the end thrust also increases, which is undesirable.

It is usually recommended that the overlap should be 115 percent of the circular pitch.

Answer 12

Axial or end thrust load

Question 13

The maximum face width may be taken as 12.5 m to 20
m, where m is the _______.

Answer 13

module

Question 14

In single helical gears, the helix angle ranges from

Answer 14

20° to 35°

Question 15

While for double helical gears, it may be made up to

Answer 15

45°

Question 16

may be defined as the number of teeth that can be generated on the surface of a cylinder having a radius equal to the radius of curvature at a point at the tip of the minor axis of an ellipse obtained by taking a section of the gear in the normal plane.

Answer 16

Formative or Equivalent Number of Teeth for Helical Gears

Question 17

Though the proportions for helical gears are not standardised, yet the following are recommended by
American Gear Manufacturer’s Association (AGMA).

• Pressure angle in the plane of rotation,

Answer 17

ϕ = 15° to 25°

Question 18

Though the proportions for helical gears are not standardised, yet the following are recommended by
American Gear Manufacturer’s Association (AGMA).

• Helix angle,

Answer 18

α = 20° to 45°

Question 19

Though the proportions for helical gears are not standardised, yet the following are recommended by
American Gear Manufacturer’s Association (AGMA).

• Addendum =

Answer 19

0.8 m (Maximum)

Question 20

Though the proportions for helical gears are not standardised, yet the following are recommended by
American Gear Manufacturer’s Association (AGMA).

Dedendum =

Answer 20

1 m (Minimum)

Question 21

Though the proportions for helical gears are not standardised, yet the following are recommended by
American Gear Manufacturer’s Association (AGMA).

Minimum total depth =

Answer 21

1.8 m

Question 22

Though the proportions for helical gears are not standardised, yet the following are recommended by
American Gear Manufacturer’s Association (AGMA).

Minimum clearance =

Answer 22

0.2 m

Question 23

Though the proportions for helical gears are not standardised, yet the following are recommended by
American Gear Manufacturer’s Association (AGMA).

Thickness of tooth =

Answer 23

1.5708 m

Question 24

In helical gears, the contact between mating teeth is gradual, starting at one end and moving along the teeth so that at any instant the line of contact runs diagonally across the teeth.

Answer 24

Strength of Helical Gears