Source of “Soft” Iron?

[Dean Godfrey-CookeParticipant @deangodfrey-cooke74440]

Hi All

A project I'm working on requires some small soft iron parts, they need to be soft iron as they'll be part of a magnet and need to lose any magnetism they get.

I'm really struggling to find a supplier, I only need about 10mmx200mm, ideally flat bar.

Does anyone know where I might be able to buy/salvage this from?

 

Cheers

Edited By Dean Godfrey-Cooke on 13/12/2012 13:33:08

Edited By Dean Godfrey-Cooke on 13/12/2012 13:33:24

[Dean Godfrey-CookeParticipant @deangodfrey-cooke74440]

For magnetic purposes

[AndyfParticipant @andyf]

My first thought was that you might dismantle a scrap transformer and use the laminations, but it would need to be a substantial one to provide strips 200mm long.

Less destructively, the metal strapping used around crates etc might work; I have just tried stroking a piece with a magnet, and it didn't want to pick up any swarf afterwards. If you have any, you could try the same test.

In either case, you would have to glue (epoxy or similar) the layers together to build up the thickness required, or maybe use brass, copper or aluminium rivets.

Andy

[Dean Godfrey-CookeParticipant @deangodfrey-cooke74440]

Hi Andy

Thanks for the quick response. The strips only really need to be 10x10mm. Do you think the laminations would work well?

Cheers

[AndyfParticipant @andyf]

I should think so, Dean.After all, laminations work well in transformers. Wouldn't cost much to try it out, if you have a scrap transformer or some strapping lying around.

You mentioned soft iron, but if rigidity wouldn't be a problem, you could try cast iron.

Andy

[Brian WoodParticipant @brianwood45127]

Hello Dean,

I have a transformer lamination to which you are welcome. Overall dims. are 170mm long by 39mm wide, with two punched out slots leaving a 95mm undamaged section between them at 39mm wide. Thickness is 0.80mm. It is a little rusty here and there, but it is not heavy damage.

Transformer laminations are ideal for your needs requiring the rapid build up and collapse of magnetic fields where any residual magnetism would severely limit magnetic field strength and nullify the operation. If you PM me with your address I'll post it.

Kind regard

Brian

[Dean Godfrey-CookeParticipant @deangodfrey-cooke74440]

Hi Andy

I think Cast is too hard from a magnetic point of view, it would accept a magnetic field but not lose it once the field was removed.

And Brian, you have PM, thanks very much!

I'm hoping to make a couple of Eletro-permanent magnets for a device I'm working on, may even end up using them to mount things on the lathe.

I'll let you know how it goes once I've got the bits together.

[AndyfParticipant @andyf]

Hi Dean,

You might be right about the cast iron, but the base of my dial indicator stand seems to be CI and displays no magnetism when its internal magnets are swirched to "off". Nor do any CI machine parts after the stand is detached from them.

But Brian's laminations sound ideal, and are sure to work.

Andy

[Swarf, Mostly!Participant @swarfmostly]

Hi there, Dean,

I suggest that you cultivate your local Amateur Radio club and see if any of their members have any P.O. 3000 relays in their 'might come in handy' box. The bobbin core and yoke are made of soft iron.

This source won't fulfil your 200 mm requirement – that seems a bit long, did you mis-type?

P.O. 3000 relays (try a Google) aren't used as much since telephone exchanges went digital though I guess the less exotic versions are still used in some control & switching applications. My Google search before writing this post threw up several hits from firms who are still manufacturing them though, for cannibalisation, eBay is probably a more cost-effective source.

Best regards,

Swarf, Mostly!

[Dean Godfrey-CookeParticipant @deangodfrey-cooke74440]

Hi Swarf

200m was in total, I only really need 10mmx10mm per bar, 2 per magnet, 10 magnets 😀

I'll have a look for those relays, could do with some testing to see what works best.

Andy, I didn't think about the dial indicator stands, I assume the switch just flips over one magnet to break the magnetic circuit, manually doing what I'm planning electronically. I may have some CI I can chop up so I'll add it to the test.

Cheers all

[Dean Godfrey-CookeParticipant @deangodfrey-cooke74440]

Swarf, did you mean GPO3000 relays?

[Speedy Builder5Participant @speedybuilder5]

Just for info, in the early 70's, we had big disc drives 2.5 Mb yep biguns !!!!! The voice coils which moved the read heads in and out had a pair of magnetic bricks about 4"x3 x 1 and a voice coil about 2" dia. That sat on a soft iron solid bar 2" dia x 5" long. I never thought about saving th iron bits, but used the magnets to retrieve lost iron on the canal system up and down the country.

[Les Jones 1Participant @lesjones1]

Hi Speedy Builder5,
Those disk drives sound like Dec RK05's Your comment made me think that some of the metal from the magnet assembly of loudspeakers may be "soft iron" The type with a ferrite magnet is probably the best. I have dismantled many loudspeakers but never noticed if the metal around the magnet retained any magnetism.
Dean, One thing you have not mentioned is how thick the metal needs to be.

Les.

[Swarf, Mostly!Participant @swarfmostly]

Hi there, Dean,

Yes, the 3000 pattern relay was extensively used in telephone exchange equipment of the generation developed when the GPO (aka 'General Post Office&#39 was responsible for telephones as well as the Royal Mail. They were available with a wide range of contacts and coil resistances. There was also a smaller type, the pattern 600.

There was an apocryphal story that the evening before the telephone activities split from the GPO to become British Telecomm, it still hadn't been decided how the Royal Mail were going to pay their phone bills or how British Telecomm were going to stamp their letters! Probably not true but it makes a good story!

Regarding loudspeakers, keep a lookout for the really old fashined 'wound field' types where the field winding provided the magnetic bias for the loudspeaker (instead of a permanent magnet) and also acted as the smoothing choke (aka 'inductor&#39 for the high tension supply. I remember that some of those had a serious lump of soft iron.

Do be careful though, iron (& steel) components of that era, both loudspeakers and relays, were often cadmium-plated. Cad plate was the default anti-rust treatment in the electronics industry. (A typical plating shop cad-plating bath would have an anode consisting of a metal basket containing lumps of metallic cadmium that started out the size of tennis balls.) If cad-plated components are stored in humid conditions, they can develop a surface coating of a white powdery cadmium compound that is dangerous if ingested – now wash your hands, please!

Best regards,

Swarf, Mostly!

[I.M. OUTAHEREParticipant @i-m-outahere]

Hi Dean,

Try a motorcycle wrecker or junk yard as the ignition coils and generator coils have laminated cores .

You may get a burnt out unit for free or near to it .

Also any small I/C spark ignition engine like edge trimmers and lawn mowers have magneto coils so you could try them as well .

Ian.

[Anonymous]

Transformer laminations are normally silicon steel. The addition of silicon reduces the remnance of the steel, but does not eliminate it. If the steel had zero remanance then the B-H curve would go through zero in each direction and the area under it would be zero, which would imply zero hysteresis losses. Steel is actually a misnomer as the material contains almost no carbon.

So transformer laminations will be much better than mild steel or soft iron, but is not perfect.

Regards,

Andrew

[Dean Godfrey-CookeParticipant @deangodfrey-cooke74440]

Wow, you guys really know your coils!

Les, the width isn't too important at the minute, I figure I can stick a few thin layers together or grind down something thicker. I'm aiming for about 4-5mm.

I've read that some loudspeakers use soft iron for shielding, even today, not sure if there's some electrical goods grave-yard I could head to, would be a gold-mine for me. Could do with some old CRTs to nick the enamelled wire from too 😀

Ian, I binned some coils from a GPZ550 not that long ago, that's why I hate throwing things away! (Can you guess who made me do it?)

Andrew, what do you reckon has the most narrow hysteresis loop then – that's readily available?

Thanks again for all the responses guys.

[Anonymous]

Dean,

Ah, readily available, that's the catch. You may find the following link giving magnetic properties of materials useful, although it's a bit weak on remnance:

**LINK**

The material RM4550 is available from the following (search under nickel iron alloys), although I'll bet it is not cheap:

**LINK**

I assume that your application is DC or low frequency, in which case some silicon steel transformer laminations are probably as good as it is going to get. When I was looking for silicon steel a few years ago I failed to find any companies prepared to sell small quantities.

Regards,

Andrew

 

Edited By Andrew Johnston on 14/12/2012 11:41:05

[jason udallParticipant @jasonudall57142]

Also if dc then won't need to insulate laminations and or consider eddy current losses. ( hence lay of laminations) otherwise ( ac etc) might neeed to think about section of metal…

Will watch with intrest.

[Billy MillsParticipant @billymills]

Don't waste time with scan coils, the turns are glued together with a very good adhesive, you might be able to get the wire to part eventually but it might be minus enamel. There were two processes used in the winding, hot enamel sprayed on during winding and a second adhesive overcoat on the wires, after winding a current was used to hot melt the windings into one mass. If you try to reuse the second type you will have one hell of a mess. Scan coils were never loose wound they were always laquered up because they would buzz like hell otherwise.

Loudspeakers with wound magnets were a very nice source of wire 50 years ago. They were made when the perminance and strength of regular magnets was poor- this was before WW2. Any radio that has survived since 1939 is probably worth far more as a radio than as a scrapper! You might find a few 50 feet down in a landfill but only some speakers had wound magnets, the enamel is getting on for 80 years old and those old enamels were not that great.

Invest in some new wire, the Scientific Wire Company is a very good source for many different kinds of wire.

Billy

[Ian S CParticipant @iansc]

If you can find some genuine wrought iron, give that a go, its fairly pure iron, with very little carbon. Ian S C

[NJHParticipant @njh]

Hi Dean

 

Here is the data sheet for the PO 3000 type RELAY

You will see that component parts are available separately – further investigation required for the costs though!

[ Any ex-BT telephone exchange maintenance Technical Officer, from the golden years of telephony, will probably have nightmares and dangerous flashbacks caused by looking at the above link! ]

Norman

Edited By NJH on 15/12/2012 12:54:12

[Billy MillsParticipant @billymills]

You can get electromagnets for holding doors closed or fire doors open. The door closing types are rectangular blocks that mount to the door frame and a striker plate that screws to the door. When given 12V at about 1/2A they produce up to 600 lbs of "pull". They tend to be 12 or 24V DC. Used for card or fob secured access-0 they work very well.

The "hold fire door open" types are around 3" diameter and are often 240V AC.

New they are around £40 each but have a look on ebay. CPC have a few types, SR07634 is their part number for the first type.

Regards,

Billy.

[Author]

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