thanks for your answers,

I think i use the worst scenario

regards,

Harm van der Pol ■

Dear B. J. Jacob,

I agree with that

But how can i determine the spring stiffness when I use fiberglass leafsprings?

If i would drive the system with the same frequency as the natural frequency of the system, it will also result in a verry high spring stiffness i think.

System:

mass of trough incl. transport material = 250 kg.

frequency = 20 Hz.

Amplitude = 5mm (stroke = 10mm).

The systems needs to frequent start/stop.

Should it be a motor with unbalance weights or could i use a elektro motor with positive crank arm?

regards,

Harm van der Pol

Student Fontys University Eindhoven (Holland) ■

Greetings Harm

I agree that assuming the head load to be hydrostatic will pose problems for the operation of the feeder, especially when applying leaf springs.

The constant value referred to by Designer results from the effect we call "bridging" of the particles above a certain height.

We use a relatively simple approximation of the head load, explained in the attachment.

If you need further info, please contact me, or view our site at www.schenck.co.za.

Best wishes and good luck

Attachments

feeder head load (ZIP)

■

Thank you for your reply.

It is realy simple, but helpfull!.

Can you also tell me something about the springs?

regards Harm van der Pol ■

Hi again Harm

Unfortunately my experience of leaf spring applications is limited to high frequency (50Hz) and small stroke (2s=1.6mm). I have not come accross your requirements before, but here are my thoughts on it:

The combination of 10mm stroke and 20Hz frequency will result in G-forces of about 8G (8 x earth's gravitational force). I agree with Gary that your feeder pan may not be able to withstand these forces.

Further, the use of unbalanced vibrator motors may limit the requirement of frequent starts and stops, and will also not furnish an instantaneous stoppage when power is cut, limiting accuracy of feed batches (assuming that this is what you want to achieve).

The most common electromagnetic drive is a resonance application of a two-mass system which means that the vibrations imposed on the first mass (connected to the structure via coil springs or rubber buffers) at a frequency very close to the natural frequency of the system, induces through natural frequency resonance, a secondary vibration into the second mass which is connected to the first mass via leaf springs or some other type of spring. The combination of stiffness and mass of the two-mass system results in the natural frequency, and in general, the stiffer the spring between the two masses, the higher the natural frequency.

Thus, as leaf springs are added between the two masses, the natural frequency increases and the primary vibration frequency must be increased to "catch up" with the higher natural frequency to achieve resonance. This is a very complicated business, but lacking a method of determining what the stiffness of the springs are (maybe somebody can help here?!) it may be necessary to build the feeder with a "base quantity" of leaf springs, and adding ore removing springs to "tune" the feeder when testing it. The addition of springs can be done by simply sandwiching spacer plates between the leaf springs (spacers must not be the same length as the leaf springs, but only serve to seperate the leafs at their connection points).

Bear in mind that with an ampluitude which you are aiming for, the spacers must be thick enough to still separate the springs when they are bent to their maximum deflection. Also bear in mind that if a spring is added to one side of the feeder, it must be mirrored on the other side to ensure that the total stiffness of the spring systems on both sides is symmetrical alon the longitudinal axis of the pan.

One could actually write a thesis about the subject, and I believe someone has done that, but I hope this helps to make things at least as clear as mud!

Good luck! ■

Dear Dirk,

from experience I know manufactures as Key Technologies and KMG Systems creating vibrating conveyors with frequencys of 25Hz and amplitudes of 3-4mm.

Sow maybe i would work with 20 Hz and stroke=10mm

but thanks for your reply

regards Harm ■