To increase torque, an electric motor must necessarily rotate slowly. And as a rule, roller mills don't go fast. So 5 rpm may be a little too low, but we're on the right track. Especially since the rollers are also almost 300 mm in diameter
I have a garden shredder at home. The roll must be in the range of 120 in diameter and 100 mm in length. I think it shouldn't exceed 20 rpm.
Now that you have all the calculation on Excel, all you have to do is adapt the geometry of your rolls to return to more acceptable values. I'm attaching the example I tried to make to see what it can look like.
On the other hand, for the teeth, the S235 is perhaps a little soft and may mark itself in the long run. Maybe we need to consider a harder steel. A cheap solution would possibly be to take them in a keyed bar. That's for sure, you're made to work in shear.
Afterwards, to go further, I think we have to change our philosophy altogether. For example, switching to inclined teeth to have a smaller contact surface and therefore reduce the grinding effort.
One last thought: given the rotational speed and torque, I think a flywheel is illusory. To have a significant kinetic energy, you would need an enormous mass. So a very large footprint.
It may even force you to start empty (which will never be the case on a block) because you'll already have to launch this XXL steering wheel.
calcul_puissance_moteur_v3.xlsx
Yes the teeth will be made of reinforced steel tkt not.
For the philosophy, and the geometry of the rollers, no matter how hard I try to convince my boss, he wants them like that. He asks that we do a test, if it's not conclusive, we change.
for he says that we already have parts with this geometry and he wants to make do with what he has.
What worries me is my pine nuts. Because for the original diameter, it is equal to my center distance. But for the number of teeth I need the module. and this module, according to the formula I have quoted to you before, is absurd.
In fact I don't know if I should choose my tangential effort according to the torque that the chosen motor will give me, or take the grinding effort directly.
Honestly, I think that the shredding effort is too great. 300 kN to grind a horn???!!!
300 kN is indeed a lot but it is consistent with the dimensions of the roll (over 500 mm it will grind several horns at the same time). Afterwards, just as we consider the void between the horns to caculate the crushed volume per turn, you can perhaps apply the same coeff on the surface of the tooth. This will reduce the amount of shredding effort required.
As for the sprockets, I'm not too familiar with the subject. On the other hand, if it's probably a diameter problem, you may have to consider a chain transmission for example. This will allow for smaller diameter pinions, and therefore a lower tangential force for the same torque.
Indeed, I have to apply this coefficient.
But I think it's more my compression stress that is too great, 30 Mpa.
I don't remember where I got it, but it's for a bone.
For a horn we must not exceed 10 Mpa??
If only I could have the exact value?!!!
To get the true value, you would have to do a few tests:
- cut pieces of horn of known cross-section
- Load with different weights until crushed
- repeat the operation on several samples to determine an average resistance
Thinking back to this question of knowing the limit in compression, I wonder if we are not on the wrong track. Shouldn't we rather consider the shear resistance? We started talking about the limit in compression and as I didn't necessarily imagine the system in this way I stayed on it. But now I still have a lot of doubts.
The shear strength of a material is often much lower than that of tension/compression (crushing a sheet of paper doesn't make sense, but it's easy to cut it with a chisel).
The problem is to determine the sheared surface. Would you be able to determine a kind of average diameter of a horn?
To tell you, that's really what I told myself about shear, because compression is when the forces are opposite and on the same axis.
Yes I can determine the average diameter of the horn, except that there are hooves too. So what should I base my measurements on?
I found this on the net:
"The shear strength varies according to the authors from 7 to 11 kgf/mm2 for cortical bone and from 0.10 to 0.5 kgf/mm2 for cancellous bone . Basically, cortical bone is 20 times stronger in shear than cancellous bone."
Do you think I can use the one for cancellous bone? It must be > to that of a horn right?
Edit:
The principle is that the tooth exerts pressure on the horn (or hoof) in relation to the other roller to grind it. It then undergoes compression I think. Because the case I have (see roller image) I don't think the horn undergoes shearing.
Hello
For shear, my thought is to say that the role of the teeth on the roller is equivalent to that of the teeth on a machine tool cutter for example. The effectiveness of the tooth comes from the shear and not from the compression exerted on the material.
On the other hand, in a screed, for example, the shear always includes a compressive aspect (the faces of the axis are supported in the hole in the screed) but the effect is less in relation to the shear force in the section.
The compression will be really effective between the 2 rolls. But in this case, the torque of the motor no longer intervenes, since there is no longer any effort to oppose the advancement of the tooth.
For measurements, it may be necessary to consider horns and hooves separately. Once you have an average diameter for each type, from this value and the length of the roll, you know how many can fit side by side at most. By deduction, you have a maximum shear surface (which has a fairly low chance of presenting itself so it leaves room for operation).
As for the question of resistance, probably the bone is harder than the horn. But that's really not my field.
I understand your point of view.
Since horns have a larger diameter than hooves, I will size according to theirs.
After I think the best solution would be to equip the motor with a variator and experiment what power would be adequate.
I wanted to put a figure on everything by calculations but there are too many hypotheses.
You helped me a lot, thank you very much.
I'll attach the final result and the performances if we weren't mistaken;).
Peace!
Hello
I do believe that a good trial will be more effective than a long calculation. I would have liked to be able to be affirmative but it is true that I am not really used to this type of special machines.
As I said before, I think you have to start with a fairly large engine (22 kW doesn't shock me for this kind of machine). The dimmer is a good idea. By servoing in speed, you will be able to measure the torque consumed (via the measurement of the intensity in general).
Good luck for the future. You can possibly send me a message even if it didn't work (even if I hope the opposite...)
Hello
I'm attaching the image of the first floor that went into production.
I take it to the lower level with the knives.
1.jpg