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BRAND:

DAMELIN

PROGRAMME:

NATED MECHANICAL ENGINEERING N6

MODULE:

MECHANICAL DRAWING AND DESIGN N6

WEEK NUMBER/DATE:

3 / 17/8/2020

TOPIC:

PULLEYS AND GEARWHEEL DESIGN (SESSION 1)

LECTURER NAME:

ADEBOLA ADEYEMI

LESSON OBJECTIVES

Upon completion of this module, as a learner, you must be able to:  Describe the hub and boss  Describe the thickness of gear wheels and pulleys.  Describe the parts of gearwheel and pulleys with the empirical formulas.

SUPPORTING MATERIAL PRESCRIBED TEXT BOOK : LORENZO MARASCHIN

VIDEO LENGTH

60 MINUTES OR MORE

3.1  

Introduction Pulleys are used to transmit power from one shaft to another with the help of belt or rope running over them. Pulleys are made from cast iron, cast steel, wrought iron or aluminium.

The main parts of pulley are;

1. Hub or boss 2. Rim 3. Arms or rim

3.1.1

Hub or Boss

• • • •

It is the central hollow cylindrical portion of pulley. The size of bore on hub is corresponds to the diameter of the shaft. It is mounted on shaft. A keyway is provided to fasten the pulley to the shaft with the help of a key.

3.1.2

dBOSS=2dSHAFT

Hub or boss dimensions

Where d=diameter LengthBOSS=1.5 x dSHAFT LengthBOSS=LKEY Where L=length of key

3.1.3

Gearwheel Arm



It is joining member of the hub and the rib of pulley.



It may be straight or curved.



It’s cross section may be circular or elliptical.



Pulleys with smaller diameter are provided with a rib, which is like a circular disc joining hub and rim.

3.1.4

Number of Arms or rib

The following table gives a rough guide of arms needed by any pulley

Number of arms PCD in mm

Number of arms

175-500

4

525-750

5

775-1500

6

The following formulae can be used:

𝐷

𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑎𝑟𝑚𝑠 = 1.5 + 4 Where D=pulley or gearwheel diameter in metres

3.1.5

  

Rim

It is the periphery of the pulley on which the belt runs. The outer face of the rim is made slightly convex which is called crowning. This keep belts at centre when pulley is misaligned.

3.2

3.2.1

Rim thickness for gear wheels and pulleys

Gear wheels

Rim thickness = 0.5 x Circular pitch

3.2.2

Pulleys

Rim thickness(t) =(0.01D + 3)mm

3.2.3

Width of Pulleys

B=pulley width b=belt width



The width of the pulley is given by the following formula Width of pulley=Belt width x 1.05 B=b x 1.05

3.2.4

  

Crown on flat belt pulley

Flat surface belt is not suitable if the belt is required to run smoothly. Flat surface belt tend to slip of the edges of the pulley easily. To prevent this the pulley is made convex

The height of the crowning depends on the size of pulley diameter (D) as follows: h=Crown h=2mm (D up to 250mm) h=2.5mm (D between 250-400mm) h=3mm (D more than 400mm)

Bending Moments on Pulleys

3.3

(𝑇 −𝑇 )x 𝐿

1ARM

= No1 of2arms𝐸

•

L =

•

L =

BM

E

E

(𝐷𝑝𝑢𝑙𝑙𝑒𝑦+𝑡)−𝑑 𝑏𝑜𝑠𝑠 2

𝑃𝐶𝐷−𝑑 𝑏𝑜𝑠𝑠 2

for flat belt

for V-belt

If no information of the shaft or boss is given then: (𝐷𝑝𝑢𝑙𝑙𝑒𝑦+𝑡) 2 E

L =



If the belt thickness is not given then: •

L = E

(𝐷𝑝𝑢𝑙𝑙𝑒𝑦) 2

3.4

Bending Moments on gearwheels

  

The larger gear of the two meshing gears must be used to find the arm dimensions. It is because it is the one experiencing larger bending moment induced in the arms. The following formulae can be used to calculate the value of LE.



𝐸 BM1ARM = No𝑇of arms



LE =

𝐹 x𝐿

𝑃𝐶𝐷−𝑑𝐵𝑂𝑆𝑆 2

If no information of the shaft or boss is given then:



LE =

𝑃𝐶𝐷 2

BRAND:

DAMELIN

PROGRAMME:

NATED MECHANICAL ENGINEERING N6

MODULE:

MECHANICAL DRAWING AND DESIGN N6

WEEK NUMBER/DATE:

3 / 21/8/2020 (NEXT CLASS)

TOPIC:

PULLEYS AND GEARWHEEL DESIGN (SESSION 2)

LECTURER NAME:

ADEBOLA ADEYEMI

LESSON OBJECTIVES



Design a gearwheel using the correct formulae to do calculations.

SUPPORTING MATERIAL PRESCRIBED TEXT BOOK : LORENZO MARASCHIN

VIDEO LENGTH

60 MINUTES OR MORE

THANK YOU FOR YOUR ATTENTION!...