"Super High Strength" Solenoid?
"Super High Strength" Solenoid?
(OP)
Ok, new to the forum here - long time browser, first time poster... Anyhow - I'm an ME, so I'm not too familiar with magnetics, but I've been working on developing something and have hit a wall. All I'm trying to figure out is; just how 'powerful' can a solenoid realistically be made? By this I mean a standard 'plunger' type solenoid. The thing I've been trying to determine is how can I calculate the resultant force exerted on the plunger given a particular geometry, current and material(s)? I understand that this is a multi-faceted analytical situation, but is there any fairly simple methods by which to determine this? More specifically, I'm trying to decipher the feasibility of creating a solenoid that can exert a force of about 15000 lbf on a plunger of approximately 3" in diameter over a relatively short distance. Is this even plausible? I've heard solenoids can be made very strong, but have found none even close on the market. Is this because this is far too much to expect, or that few uses have been found for such a thing? I know electric motors can easily be made to produce such forces, so why not solenoids? And, if it is near impossible to do such a thing using a solenoid device, is a linear motor a better candidate as far as method goes?
Thanks in advance for your replies!
Bruce J.
Thanks in advance for your replies!
Bruce J.





RE: "Super High Strength" Solenoid?
Hi jensenb001
Try these links for starters
http://www.vias.org/kimberlyee/ee_09_10.html
http://
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desertfox
RE: "Super High Strength" Solenoid?
BTW - I have educated myself a-bit on this subject prior to posting. I've read C.R.Underhills old 'textbook' on electromagnetics and solenoids, but still gotten little applicable fomulae. I've also tried a couple of free trial versions of magnetic FEA programs (MagNet and Quickfield) but have been unable to get data that I am confident in (most likely due to my inexperience in setting boundary conditions for such systems).
RE: "Super High Strength" Solenoid?
Thanks for the response, they only way forward I can see is to break the plunger movement down into steps, so you then calculate the force between the moving and fixed poles for each discrete step, starting with the plunger fully out and the pole gap decreasing each step by a uniform amount.
So you would need to calculate Reluctance, inductance and permeability for each step as you move the pole along and finally theres leakage of the magnetic field which you also need to consider,I have some old books here, I will look through them and post again.
desertfox
RE: "Super High Strength" Solenoid?
RE: "Super High Strength" Solenoid?
RE: "Super High Strength" Solenoid?
Energy density is w = 0.5 * B^2 / mu0
Stored energy is W = w*Volume = 0.5 * B^2 / mu0 * (Area*g) where g is gap distance
Force = dW/dg = 0.5 * B^2 / mu0 * Area
Force/Area = 0.5 * B^2/mu0
Using SI units, mu0 = 4*pi*1e-7
Force/Area = (0.5/ 4*pi*E-7) B^2 ~ 400,000 B^2 [SI units]
If we assume B= 1T, then we have 400 kPa pressure, which is about or about 4 atmospheres. If B = sqrt(2) T = 1.4 T, then you'd have about 8 atmospheres.
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(2B)+(2B)' ?
RE: "Super High Strength" Solenoid?
isrealkk - I do understand that saturation plays a role, though I am planning on this device only operating for a very short time and over a very short distance (millimeters or less)- is saturation time dependent? Is the information you provided a sort of 'rule of thumb' or is there a resource that I can find that delineates this? I'd like to learn as much as possible so I can see if there are any avenues by which to circumvent these physical limitations.
Also, I've heard that once a solenoid has drawn the core all the way in - thereby reducing the reluctance of the system as a whole to it's lowest (where it 'likes' to be), it can be 'held' there with tremendous force. Given this it would go to reason that if I place the core just off-center, a large force would be exerted to get it to this position - surely more so than if the plunger were far from the ideal (centered) position... Is this correct reasoning? What is the main limitation to a solenoid being as strong as an electric motor? What is the weak link here and can it be overcome? Thanks!
RE: "Super High Strength" Solenoid?
To me, M22 is laminated steel used for large motors. I got this plot from free software FEMM, which also has a large variety of other materials loaded in.
I don't think you will get to 7T using steel regardless of how much excitation you apply. It would have to be some exotic material, nothing like I have heard of for industrial equipment.
You might want to search the forum for ideas.
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(2B)+(2B)' ?
RE: "Super High Strength" Solenoid?
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(2B)+(2B)' ?
RE: "Super High Strength" Solenoid?
An induction motor (rotary or linear) operates on the principle of current induced in the moveable part and it is the interaction of field from induced current and applied field which causes force or torque. Solenoid does not operate on the same principle (interaction of field from induced current with applied field).
Already covered... saturation of iron is going to limit possible solenoid force for a given size plunger.
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(2B)+(2B)' ?
RE: "Super High Strength" Solenoid?
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(2B)+(2B)' ?
RE: "Super High Strength" Solenoid?
Also, would the situation change if I were to place a coil on/within the plunger and excite that, as with the armature of an electric motor - essentially creating a cylindrical linear motor. Would saturation still be the limiting factor? It seems like it would play a smaller role. I'd then be generating force due to opposing magnetic fields rather than simply providing a path for a reduction of reluctance. Where/how might I calculate the resulting forces? I do apologize for being vague about the purpose of the device, but it is necessary. Thanks!
RE: "Super High Strength" Solenoid?
The reason us that the force depends on difference in energy density (w = 0.5*B*H) between iron and air. B is roughly the same in iron as air. We have assumed that the energy density in iron was negligible (Hiron<<Hair) when operating at or below saturation. However as we get out to the right of the curve far beyond excitation, Hiron is no longer negligible. Very far to the right the slope of the iron B vs H curve becomes approximately mu0 and at this point as we increase applied excitation, Hiron increases the same amount as Hair and energy density in iron increases as much as in air, so there is no associated increase in force derived from the excitation increase.
Yes, that's my understanding also, based on use of iron-core devices.
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(2B)+(2B)' ?
RE: "Super High Strength" Solenoid?
RE: "Super High Strength" Solenoid?
Compositepro - No, I understand that concept as a whole, just worded differently I suppose...
RE: "Super High Strength" Solenoid?
There are apparently linear actuators that can get higher force than solenoids, again using principles closer to what we associate with motors.
A reference on these devices, see "LINEAR ELECTRIC ACTUATORS AND GENERATORS" by Boldea and Nasar ISBN 0-521^8017-5
For free general electromagnetics and electric machinery, , google MIT OpenCourseware and find the courses on electromagnetics and electric machinery
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(2B)+(2B)' ?
RE: "Super High Strength" Solenoid?
RE: "Super High Strength" Solenoid?
Linear motors can be readily stacked in series, and a concentric hydraulic force multiplier might be packaged into it to trade off stroke for force.
If the linear motor was flooded, that would also be a bonus for cooling if the duty cycle is fairly short.
RE: "Super High Strength" Solenoid?
http://www.exlar.com/
RE: "Super High Strength" Solenoid?
RE: "Super High Strength" Solenoid?
Jensenb, search for a (commercially failed) product of Joseph Lucas (inventor of darkness) called a "Helenoid". Basically, it's a short stroke solenoid with a helical gap, capable of fairly high forces and speeds within a relatively small envelope.
Mike Halloran
Pembroke Pines, FL, USA
RE: "Super High Strength" Solenoid?