BH curve variance of AISI 1215 2

[exeng]

I'm trying to find out what kind of tolerance/consistency you could expect to get from one lot/cast of steel to the next. I'm working with AISI 1215 to produce a proportional linear solenoid and I am having trouble maintaining a narrow spread on the force output performance.
I know that dimensional variance will have a significant effect but am unsure how the BH curve tolerance will impact it.
Also what effect if any would the grain size or any other metalurgical property have on the BH curve.

 

[MagMike]

Both the grain size and metallurgical properties will have large effects in your application, especially since the material is probably not being saturated.

As mentioned here before (by EdStainless), structural steels are not processed with magnetic properties in mind. To improve consistency, you'll need to specify a heat treatment to optimize the magnetic properties.

How narrow is your spread on the force output performance?

Trying to control the chemical composition will help too, but that is more difficult because then you'll be required to buy an entire casting.

 

[exeng]

Thanks MagMike,
I've been getting a spread of around +/- 5% up until my last batch of prototypeing at which stage I got a spread of around +/-10% at the maximum field intensity.
You are right in saying that the materials aren't fully saturated at least in-so-far as not all the components are.
What magnitude would the effects be on consistency do you think if the components were annealed ?
What do you think I should be able to achieve from a consistency point of view ?

 

[EdStainless]

Even with anneal I would be surprised if you could do better than +/-5%.
If you are working below sat, then permiability is critical, and minor chemistry variations will have a large impact.

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Rust never sleeps
Neither should your protection

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[MagMike]

exeng,

I think you've been lucky that the spread within a batch was only +/-5%. I'm only guessing, but I suspect the permeability could vary +/-40% unless steps were taken to carefully control the material.

I agree with EdStainless, +/-5% from lot-to-lot is the best one could hope for, even if everything is controlled. You'll have to work closely with your supplier to achieve that.

 

[dgallup]

No one makes 1215 with controlled magnetic properties. You need to go to one of the electrical irons if you need better consistency. It is still hard to get really consistent magnetic response. Most precision solenoids use some form of adjustment to make up for dimensional and material variability.

 

[exeng]

Thanks all for the input.
What kind of adjustment would be the norm ?
Something like a matched coil winding or feedback through an LVDT perhaps? What other options would be pratical ?

For precision solenoids I'm finding it difficult to find any literature quoting manufacturers normal/precision spread. Does anyone know where to find any of this kind of detail?

 

[EdStainless]

The one that I liked best was a company that tested each assembly in a reference coil, and then machined grooves the OD to get the desired response. By trial and error they had figured out a formula to machine by. This does mean that all of your units will operate at the bottom end of the range.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[exeng]

Thanks all for the advise.
Could anyone recommend some good reference manuals/books for this field ?

 

[EdStainless]

For the basics, Ferromagnetism by Bozorth. It was first printed in 1951. Check out Alibris.com you can get a good used one for about $100.


= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[dgallup]

Most electro-magnetic fuel injectors have an adjustable spring load that compensates for the magnetic and fluidic tolerances. A few companies like Delphi actually fine tune the airgap and/or stroke while flowing the injector. I think that is one reason they are in bankruptcy.

 

[TStaples]

Exeng,

Another good text is "Electro-Magnetic Devices", by Herbert C. Roters. (i.e. of "Roter's Method" fame.) It was first published in 1941 and is currently out of print. You can find them used however.

Some of the period information is quite humorous (i.e. the terrible magnet wire insulations of that era,) but the basics are all there.

-Tony Staples

http://www.tscombustion.com