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Best steel for DC electromagnet
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(Mechanical)
(OP)
18 Sep 09 11:41All,
I've read a number of threads that indicate 1018 steel annealed and 430 stainless are commonly used for solonoids.
My design problem is to pick the best material for a DC electromagnet. Would sombody please recommend a material, either one of the two I mentioned or something different?
Thank you.
(Mechanical)
18 Sep 09 12:01"Best" in terms of what? There are materials with higher permeabilities than the two you mentioned but at added cost.
(Mechanical)
(OP)
18 Sep 09 12:06BobM3,
Good point. I'm looking for high permeability so I can get the strongest flux density for a given number of turns and current. Environment is not important because the part will be encapsulated. I'm not sure about saturation though. I'd probably start with permeability as the metric then compare saturations.
(Mechanical)
(OP)
18 Sep 09 12:07Also, cost is not important but availability for prototype and research activities is.
(Mechanical)
(OP)
18 Sep 09 12:09Sorry for the jumbled thread here, the material also needs to be machinable from 2-3" bar stock.
(Materials)
19 Sep 09 17:00 Time ago, I found a very interesting technical paper about this subject. Now, I don't know if this paper is completely available ( fully !!! ) in web. However, this paper appeared in Hong Kong ( MAGIVAL, Shangay 2000,November) and it was a good tool for people who is neither metallurgists nor magnetic experts. Moreover , this paper was a usefull general info for machinability.
About your questioms, I think there is no difficulties if you explaine what you pretend in terms of:
1) magnetic properties ( Max. Permeability, Hc, Br )
2) how much is important machinability ?
3) Stainless or not ?
4) Is material easy available in stock ?
5) it is more easy to find a 3"bar stock of mild steel, Carbon or alloy steel than 430( free machined or not ) stainless grades. This depends on how many pound ( kg ) or tons you need for your design.
6) there is a lot of magnetic data available about 430 and similar grade : what do you want ?
7) Do you use the part as delivered and machined ( after turning , drilling and so on ...)or machined and annealed( stress relieved ) ? Vacuum or annealed and then machined in order to take away the stock remooving?
8) what is the final dimension ( thickness and leghth ) ?
9) Do you obtained Hollow or solid state blanks ?
10 What about magnetic testing ? Costs ? DC o AC ? How much it cost for a single sample?
Let me know if you need more info !
(Automotive)
21 Sep 09 09:4512L14 is commonly used because of the good machineability. It's magnetic properties are usually "good enough" but it all depends on how sensitive your application is to various properties.
(Mechanical)
21 Sep 09 11:42Maybe the following will get you going:
For more information, please visit Genuine Neodymium Magnet.
(Automotive)
21 Sep 09 16:33While the nickel-irons offer the highest permeability, the saturation flux density is low. I'd be surprised if you can find it in 2-3" bar stock.You will have to register but this is a link to an article on selecting soft magnetic alloys:
(Mechanical)
(OP)
23 Sep 09 12:04Thanks all
remetaper: Do you have a title for the paper? I can't locate it.
BobM3: Good link, will consider the material.
dgallup: Thanks for the 12L14 suggestion. My test house reccommended that also.
Steve
(Electrical)
24 Sep 09 12:22Use 1018 or 12L14. Roughly speaking the permiability will be about 1000 but can vary since the magnetic propertities are not controlled. Nickel [or Chrome plate] so they don't rust]. The more exotic magnetic material usually have higher saturation flux densities [not necessarilly higher permiability] at much greater cost.
(Materials)
25 Sep 09 08:43If this is a DC application who would care about the perm?Saturation is all that matters.Any low carbon steel grade with less than 0.2%C that has been annealed at 1400-1475F with a slow cool should give very nice high saturation levels.
= = = = = = = = = = = = = = = = = = = =
Plymouth Tube
(Materials)
25 Sep 09 09:29SQALB: This is the linkbut I am noting that cutting data about machinability are disappeared compared to Magival Shangay,2000. I don't know the reason why.However these links ( Cartech and Valbruna ) are useful for beginners and students giving an idea about Magnetism and the choice of right steel grade.SREID: In my opinion 1018 and 12L14 give permeability more than 1000 when annealed and slow cooled. Nevertheless, consider that Ni or Cr plating process ( after magnetic annealing)reduces permeability due to Hydrogen adsorbation. Several test of Silicon -Iron alloy confirm this problem . However a simple baking (390-400 F) after plating restores magnetic properties.EDSTAINLESS: you are right : I fully agree !
(Mechanical)
(OP)
28 Sep 09 16:04Thanks guys,
My application is A-C and I'm looking to create a high Q sensor coil. I need to machine the metal to a particular size so standard cup-core ferrite is out of the question.
(Mechanical)
(OP)
28 Sep 09 16:06EdStainless,
Actually I have two projects. One is A-C the other is D-C.
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Corrosion resistance depends on how much chromium and (sometimes) molybdenum is in the stainless steel. The higher the chromium and molybdenum, the better corrosion resistance.
The magnetism myth is because the common magnetic grades of stainless steel, 409 and 430, don't resist corrosion as well as the common non-magnetic grades, 304 and 316. You can't expect them to. Grade 409 has 11% of chromium, which is plenty for automotive muffler systems.
Grade 430 has 16% of chromium, and is mostly used indoors. Grade 304 has 18% of chromium, which makes it suitable for general purposes, including outdoor exposures. And in marine environments you need Grade 316, which has 16% chromium and also 2% of molybdenum to help it resist the attack of salt. 316 is known as marine grade.
So the common non-magnetic stainless steels have better corrosion resistance than the common magnetic grades because they have more chromium and molybdenum.
For the technically minded, in the non-magnetic grades the atoms are lined up in a crystal structure known as austenite. In the common magnetic grades the atoms are lined up in a crystal structure known as ferrite - just like in carbon steel.
So 304 and 316 are often called austenitic grades, and 409 and 430 are called ferritic grades.
It's not even true that the "non-magnetic" grades are never magnetic. As supplied, sheet and coil are non-magnetic, but when they are worked - bent, deep drawn, formed into a tube - they become magnetic. Try a fridge magnet around the bowl of your kitchen sink, which is grade 304 - you might be surprised.
The strength of the magnetism depends on how much the metal has been deformed. Even when these grades are cut (cold, by shearing) the deformation in the edge of the metal causes magnetism.
Stainless steel bolts are made by cold forging the head, and cold rolling or machining the thread. They are often quite strongly magnetic.
Cast austenitic grades are likely to crack in the casting process if they aren't formulated to be somewhat magnetic - the same applies to welds. So castings are usually magnetic, unless they have been heat treated.
Here are a pipe elbow, and a cap nut, both Grade 316, as cast.
Then there are the duplex grades of stainless steel, well known for their excellent corrosion resistance. They are all fully magnetic all the time. The best known duplex grade, 2205, resists corrosion even better than 316 because it contains 22% of chromium and 3% of molybdenum.
Austral Wright Metals stock two New Generation ferritic stainless steel grades, AWM 404GP® and 445M2. Both are magnetic, because both are ferritic. Both have at least 21% of chromium, which is more than the grade they replace, and much higher than Grade 430. AWM 404GP® replaces 304, and 445m2 replaces 316 - it contains 1% of molybdenum.
These grades offer significant advantages: corrosion resistance at least as good as the grade they replace, cost savings in the workshop because they are much easier to fabricate, and price savings because they do not contain the element used to make grades non-magnetic - nickel.
Add price stability, because the cost of nickel is volatile - over the last five years it has varied from $15,000/tonne to over $60/000/tonne. That's between A$1,200 and $4,800 on the cost of a tonne of 304 and 316.
The New Generation ferritic stainless steel grade AWM 404GP® and 445M2 are high technology, cost effective alternatives to the older grades 304 and 316. The only extra "traps for young players" in converting from the older are the need to ensure that before welding the sheet and any filler rod are grease free, and to gas shield the weld properly.
Ferritic Grades behave like carbon steel in fabrication, and many customers have told Austral Wright Metals how much they appreciate the lower shearing forces, cleaner, crisper bends, lower distortion in welding and flatter panels achieved. These cost saving features are in addition to the 3.5% more coverage per kilogramme that ferritic grades give.
AWM 404GP® and 445M2 are made by world class Asian Steel mills, who use state-of-the-art technology to produce top quality, superior steels.
Severe Marine Atmosphere, 2 years
Rain Washed
Unwashed
This graph shows that ferritic grades show superior tea staining resistance to austenitic and duplex grades of the same PRE:
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