Dear jishnu,

GD is the old-fashioned way for moment of inertia (Im in kg.m2)

The acceleration time (in combination with the slip and the torque transmission during the start-up) is a very important parameter for fluid couplings. It determines the heat dissipation and thereby the temperature.

For calculating the dissipated heat in the coupling, the primary Im and the secondary Im are required.

Have a nice day ■

Dear Jishnu,

The moment of inertia (Im) is given by:

The integral of d(mass)*distance^2

http://en.wikipedia.org/wiki/Momentofinertia

and

http://en.wikipedia.org/wiki/Listofmomentsofinertia

A motor manufacturer gives an Im in kg.m2 of the rotor-shaft assembly.

The system engineer of the project then uses the Im, in combination with other, reduced, moments of inertia to calculate acceleration/deceleration forces and acceleration/deceleration times.

For a fluid coupling, the engineer also accounts for coupling slip and heat dissipation during startup.

The starting torque is the driving torque from the motor during acceleration from rpm=0 to full rpm.

This starting torque is generated by electric currents and magnetic fields and is an completely different physical quantity. (kg.m)

Your question relates to:

-inertia

-acceleration or deceleration

-time

Solving these relationship’s mathematically, requires Newton’s laws.

http://en.wikipedia.org/wiki/Newton%27slawsofmotion

It takes a lot of efforts to become and to be an engineer

Success ■

Originally Posted by Teus Tuinenburg

.....

It takes a lot of efforts to become and to be an engineer

Wonderfully expressed:even without Bollywood subtitles. ■

Hello,

Following information is addressed to the readers at large and not the ‘Design engineers’ who are well versed in conveyor design.

As a rule, conveyors / bulk material handling equipment / machines have to be designed for their satisfactory performance during starting, steady running and stopping.

If a car is very good during steady running, but if its performance during starting or stopping is not satisfactory, then it will be simply labeled as a bad car.

Likewise the conveyor is designed for its satisfactory performance during starting, steady running and stopping. The conveyor / machine is subjected to inertial forces during starting and stopping. These inertial forces obviously influence the machine design and construction. Following values are needed to ascertain inertial forces:

- When analysed as a linear motion; total equivalent moving mass kg of conveyor.

- When analysed as a rotary motion; total equivalent mass moment of inertia kg(m^2) of conveyor

The conveyor designer often prefers to do such calculation as a linearly moving mass system, wherein he uses conveyor’s equivalent linear mass kg as below to find the forces:

Inertial force Newton during acceleration = Mass kg x acceleration m/(s^2)

Inertial force Newton during stoppage = Mass kg x deceleration m/(s^2)

In general, motor manufacturer is more familiar / comfortable with a rotary motion. So he needs equivalent mass moment of inertia (I) of conveyor load kg(m^2) and uses following equations of rotary motions:

Inertial torque Newton-metre during acceleration = I x Angular acceleration radian/(s^2)

Inertial torque Newton-metre during stoppage = I x Angular deceleration radian/(s^2)

Conveyor design process easily calculates conveyor equivalent linear mass or conveyor’s equivalent moment of inertia m(k^2) that is, mass multiplied by square of radius of gyration.

The G(D^2) is more a commercially used term wherein G(D^2) is equal to mass multiplied by square of diameter of gyration. The engineering textbooks and their formulae do not recognise G(D^2) value. Since diameter is 2 times the radius, the G(D^2) value is 4 times the m(k^2) value. So one has to take one-fourth of G(D^2) value to use in engineering regular formulae having m(k^2) value.

The motor manufacturer uses the m(k^2) value to calculate motor starting time duration. Less m(k^2) of conveyor means quick speed up of motor, less starting time and less heating of the motor. More m(k^2) of conveyor means slower speed up of motor, longer starting time and more heating of the motor.

In reality motor manufacturer needs these values whether it is LT motor or HT motor . However, if ‘average’ buyer is unable to give such values for motor for his simple and routine application, the motor manufacturer judges the situation and quotes for the motors. The motor manufacturer safeguards himself by way of motor specifications being mentioned by himself. If a particular motor manufacturer insists for these data all the time even for a routine requirement, then he may lose the business to his competitor. So he will not take such stand every time.

The requirement of m(k^2) value can also become must for LT motors when moving mass or m(k^2) value is proportionately large compared to the magnitude of drive power (medium-long horizontal conveyor having multiple drives and thereby LT motors). So there is no rule that such data are needed for HT motors only.

As a rule if one does not have conveyor equivalent m(k^2) value or conveyor linear moving equivalent mass value; then it simply implies that design is incomplete (because this means starting / stopping situations have not been analysed).

Please note that:

- Both the methods give same result, whether as a linear motion using linear moving mass or as a rotary motion using m(k^2) value.

- In case of conveyor, the linear moving mass or m(k^2) value, will have many values (theoretically infinite) depending upon mtph being conveyed by the conveyor. The widely used values are at zero mtph, 35% mtph, 70% mtph and 100% mtph.

- Refer design book, design manual, etc. to understand the subject and calculate the aforesaid values.

Ishwar G. Mulani

Author of Book: ‘Engineering Science And Application Design For Belt Conveyors’. Conveyor design basis ISO (thereby book is helpful to design conveyors as per national standards of most of the countries across world). New print Nov., 2012.

Author of Book: ‘Belt Feeder Design And Hopper Bin Silo’

Advisor / Consultant for Bulk Material Handling System & Issues.

Pune, India. Tel.: 0091 (0)20 25871916

Email: conveyor.ishwar.mulani@gmail.com

Website: www.conveyor.ishwarmulani.com ■

HT or LT motors till they reach their no load speed draw heavy current. This may lead to heating, a designer must understand the starting time and the current drawn during this period.

Time required to reach the no load speed will depend on inertia of rotor of motor and inertia of primary side scoop, which are directly connected to motor. ■