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Old 5th Jul 2019, 8:03 pm   #1
G6Tanuki
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Default Removing plastic jacket from 'moulded' ferrite EMI chokes.

Following a bit of a clearout, a boxful of old VGA and DVI cables have been sent to the bin, but on the way I took time to cut off the moulded ferrite EMI-chokes from them.

Does anyone have suggestions about how best to remove the moulded hard-plastic encaspulation so I can re-use them? Trying to slice it off using a Stanley-knife is not easy and would probably mean I end up needing a trip to A&E!

Would heating them to maybe 150C to soften the plastic be OK? Or would it do bad things to the characteristics of the ferrite? (I've seen permanent changes in the magnetic characteristics of ferrite-cored baluns after they've been 'cooked' through antenna failures and resultant crazy SWR causing heating).

Can't think of any sorts of generally-available chemicals that might dissolve the plastic [you can't easily buy Aqua Regia or Hydrofluoric Acid these days....]
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Old 6th Jul 2019, 2:41 am   #2
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Default Re: Removing plastic jacket from 'moulded' ferrite EMI chokes.

Careful use of a heat gun/paint stripper (not sure what you call them in the UK, I've heard both) would be my first port of call.

You will only want to heat enough to soften it so a sharp knife will cut through it.

Or a hacksaw blade cutting longitudinally along the casing on the mold lines, but I think that is going to get fiddly.
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Old 7th Jul 2019, 12:16 pm   #3
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Default Re: Removing plastic jacket from 'moulded' ferrite EMI chokes.

You could try the opposite route and put the choke in a deep freeze, then attack it with a hammer. You may break the ferrite though.
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Old 11th Jul 2019, 10:52 am   #4
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Default Re: Removing plastic jacket from 'moulded' ferrite EMI chokes.

Circular saw attachment for a Dremel or equivalent and careful how deep you cut?
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Old 11th Jul 2019, 11:08 am   #5
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Default Re: Removing plastic jacket from 'moulded' ferrite EMI chokes.

I usually cut the ends off next to the ferrite then use a screwdriver to push the wires through and ream the edges with a stanley knife and use them as is!

Only thing with reusing them is you don't usually know what ferrite material is used so I wouldn't use them for baluns or anything like that. Fine for RFC / suppression though. You can get a whole box of ferrite cores for not much more than a tenner from RS these days from Fair Rite so there's not much point skimping on that side of things.
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Old 2nd Oct 2019, 1:32 pm   #6
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Default Re: Removing plastic jacket from 'moulded' ferrite EMI chokes.

As a followup to this, here's the method I found best:

1] Put the kettle on and make yourself a really hot cup of tea.

2] Put the unused boiling-water in a mug and add the ferrites.

3] Drink some of the tea while the water warms/softens the plastic round the ferrites.

4] Fish out one of the ferrites and use side-cutters to nibble away the plastic from one end of the ferrite.

5] Put the nibbled ferrite back into the cup of hot water and drink more tea.

6] Fish the ferrite out again and use the side-cutters to cut a coarse spiral round the outside of the cylindrical part of the ferrite so it can be peeled back.

7] Put it back into the cup of hot water. Drink more tea.

8] Fish the ferrite out again, and then push the ferrite out of the remains of the plastic jacket.

9] Drink any remaining tea.


So far I've done a good dozen using this method and have not cracked any of the cores. Now, if only there was an easy/quick way to assess the exact magnetisation characteristics. I need some tubular ferrites for making 'copper tube transformers' for a solid-state linear-amp.
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Old 2nd Oct 2019, 3:46 pm   #7
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Default Re: Removing plastic jacket from 'moulded' ferrite EMI chokes.

Whilst it probably won't help in your RF transformer application:
When I come across unknown ferrite tubes or rings I temporarily wind them with 10 turns of wire, measure the inductance, and attach a label with the result (or write it with a white pen).
If they are a few 100's of microhenries, they are useful for RF suppression on audio signal wires etc - see pictures.
Of course, this doesn't give any indication of the saturation characteristics etc
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Old 3rd Oct 2019, 7:31 am   #8
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Default Re: Removing plastic jacket from 'moulded' ferrite EMI chokes.

Just usually use a knife, but not a Stanley, I use an Opinel for most knife work it's body/handle is less clunky than a Stanley and more easily gripped and thus easier to control, see pic. Using my thumb as the anvil, this way you have a lot of control over the knife, no slips, no cuts. My thumb is pretty calloused so the knife if did make contact would do no damage.

Andy.
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Old 3rd Oct 2019, 10:23 am   #9
Steve G4WCS
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Default Re: Removing plastic jacket from 'moulded' ferrite EMI chokes.

So far I've done a good dozen using this method and have not cracked any of the cores. Now, if only there was an easy/quick way to assess the exact magnetisation characteristics. I need some tubular ferrites for making 'copper tube transformers' for a solid-state linear-amp.[/QUOTE]


What Mr Bungle said.

I would buy new stock to ensure I was using the right material.

I just googled "type 43" ferrite and the cores are readily available, Farnell CPC have them for 30 odd pence each if they are the right size for your application

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Old 3rd Oct 2019, 12:08 pm   #10
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Default Re: Removing plastic jacket from 'moulded' ferrite EMI chokes.

Re: post 8 & its photo. When I was at school and attending woodwork classes, we were always firmly told "Keep all parts of your body behind the cutting edge!" I've never forgotten that - and it's served me well for many years.

Al.
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