Bhaskar,

I would suggest that a line passing thru the mechanism (at the angle of attack) should be at a horizontal distance from the screen C of G not exceeding 2% of the screens length. ■

Dear Shri Bhaskar,

CG of the screen when being empty and when being operating would be different. CG of the screen including material (effective CG), will go on shifting depending upon the material movement through the screen. So, whether the precision of 1 to 2% in CG location will make any difference in result?

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Author of Book : Belt Feeder Design and Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

Dear Ishwar,

I take your point, but the 2% figure has come from my practical experiance as a good safe rule.

What would your suggestion be for a tolerance?

Regards ■

Dear Bhaskar,

I do not understand when you say you modelled without deck ………

Do you mean

1.without the frame that supports the mesh?

2.without the mesh?

3.without any allowance for material on the deck?

Regards ■

Hello Mr McKenzie

You seem to be the expert wrt vibrating screen problems.

Would you be able to tell me how to design dampers for vibrating screens. I encountered problems on a job with a 30 tonne vibrating screen during shut down at about 2 Hz (the second resonance period), when it shook the whole structure. A break motor was installed, which sorted the problem, but it is very pricy and I think the correct dampers would be a lot cheaper. I do have a problem assessing the correct screen velocity at this point.

Thanks for your help

Wally ■

Gooday Wally,

I certainly don't claim to be an "expert" (just a enthusiast), but I have some notes on support spring selection which I am happy to share.

They are too lengthy to post, but if you like to send me your email address I will beam them to you. ■

If you are using two self-synchronized vibrators, then it's the same because the phase synchronization will be made so the resulting force will pass through the CG. So the important point is to know what is the through angle desired (when empty and of course when charged) ■

Wally

Screen will go for the rigid body motion and the best idea is to make the preriod when the screen is shuting down as short as possible - and the electric brake on the motor is a nice and simple option. You can use rubber bumpers that would restrict excessive motion during shut down - in lateral direction to prevent impact on the structure and vertical to prevent closing of springs. ■