PULLEY

Pulley:

The diameters of standard pulleys are: 200, 250, 315, 400, 500, 630, 800, 1000, 1250, 1400 and 1600 mm. pulley may be straight faced or crowned. The crown serves to keep the belt centered. The height of the crown is usually 0.5% of the pulley width, but not less than 4 mm. The pulley diameter D_p depends on the number of plies of belt and may be also be determined from the formula:

D_p > K.i (mm)

Where

K = a factor depending on the number of plies (125 to 150)

i = no of plies

The compound value should be rounded off to the nearest standard size. While selecting the pulley diameter it should be ascertained that the diameter selected is larger than the minimum diameter of pulley for the particular belt selected.

The drive pulley may be lagged by rubber coating whenever necessary, to increase the coefficient of friction. The lagging thickness shall vary between 6 to 12 mm. The hardness of rubber lagging of the pulley shall be less than that of the cover rubber of the running belt.

Pulley types:

Pulleys are manufactured in a wide range of sizes, consisting of a continuous rim and two end discs fitted with hubs. In most of the conveyor pulleys intermediate stiffening discs are welded inside the rim. Other pulleys are self cleaning wing types which are used as the tail, take-up, or snub pulley where material tends to build up on the pulley face. Magnetic types of pulleys are used to remove tramp iron from the material being conveyed.

Typical welded steel pulley-Drum conveyor pulley

Spun end curve crown pulley

Spiral drum conveyor pulley

Welded steel pulley with diamond grooved lagging

Welded steel pulley with grooved Lagging

Spiral Wing Conveyor pulley

 

Power calculation for the drive unit:

The horse power required at the drive of a belt conveyor is derived from the following formula:

H.P = T_e . V

Where

T_e is the effective tension in the belt in N

V = velocity of the belt in m/s

The required effective tension T_e on the driving pulley of a belt conveyor is obtained by adding up all the resistances.

INTERVIEW QUESTIONS:GERNAL:

• Explain the Second Law of Thermodynamics.
  The entropy of the universe increases over time and moves towards a maximum value.

 

• How do you measure temperature in a Wet Bulb Thermometer?
  Wet bulb temperature is measured in a wet bulb thermometer by covering the bulb with a wick and wetting it with water. It corresponds to the dew point temperature and relative humidity.

 

• What is Bending moment?
  When a moment is applied to bend an element, a bending moment exists in the element

 

• What are the points in the Stress Strain curve for Steel?
  Proportional limit, elastic limit or yield point, ultimate stress and stress at failure.

 

• Define Reynolds number.
  Reynolds number is the ratio of inertial force and viscous force. It is a dimensionless number. It determines the type of fluid flow.

 

• What is a Newtonian fluid?
  A Newtonian fluid possesses a linear stress strain relationship curve and it passes through the origin. The fluid properties of a Newtonian fluid do not change when any force acts upon it.

 

• How many Joules is 1 BTU?
  1 BTU is equal to 1055.056 joules.

 

• What is PS?
  PS is Pferdestarke, the German unit for Horsepower.

 

• Explain Otto cycle.
  Otto cycle can be explained by a pressure volume relationship diagram. It shows the functioning cycle of a four stroke engine. The cycle starts with an intake stroke, closing the intake and moving to the compression stroke, starting of combustion, power stroke, heat exchange stroke where heat is rejected and the exhaust stroke. It was designed by Nicolas Otto, a German engineer.

 

• Explain the nomenclature of a 6203-ZZ bearing.
  6 is the type code, which shows it is a single-row ball bearing, 2 is the series, means light, 03 is the bore, which is 17 mm and ZZ is the suffix meaning double shielded bearing.

 

• What is Gear ratio?
  It is the ratio of the number of revolutions of the pinion gear to one revolution of the idler gear.

 

• What is Annealing?
  It is a process of heating a material above the re-crystallization temperature and cooling after a specific time interval. This increases the hardness and strength if the material.

 

• Define Torque.
  Torque is defined as a force applied to an object that results in rotational motion.

 

• What is Ductile-Brittle Transition Temperature?
  It is the temperature below which the tendency of a material to fracture increases rather than forming. Below this temperature the material loses its ductility. It is also called Nil Ductility Temperature.