Metal locking tie, doe they hold up?

[Joerg]

Folks,

Had a nice clamp for mounting some square ferrites but it's too big, ran
out of space. Lasse had suggested metal type straps a while ago. Found this:

http://media.digikey.com/photos/Panduit Corp Photos/MLT...CP.jpg
http://www.panduit.com/groups/MPM-NL/documents/PartDrawing/086914.pdf

Is anyone familiar with these? Do they really hold forever? Is the
tongue just pulled through and then left alone like with cable ties, or
does it have to be bent over?

Not sure how one you exert so much force on the tongue but I guess that
needs a serious pair of pliers. Which kind of ruins the rounded edges
that I could really use for St.Elmo's fire avoidance

 

[Joerg]

I don't think you should bend them

would something like this make you sleep better?
http://www.absolutesource.com/products/specialty-cable-ties/stainless-steel/ladder/

That might be better but they don't have datasheets, and the 6" is out
of stock :-(

using copperwire and soldering an option?

If it was for prototyping, sure. I'd use the aluminum fence ties I have
left over from building our fence

I'll just try the Panduit ties and if they don't work it just has to be
good old lacing cord.

 

[Rich Grise]

http://www.absolutesource.com/products/specialty-cable-ties/stainless-steel/ladder/

That might be better but they don't have datasheets, and the 6" is out
of stock :-(


If it was for prototyping, sure. I'd use the aluminum fence ties I have
left over from building our fence

I'll just try the Panduit ties and if they don't work it just has to be
good old lacing cord.

If you intend to use more than, say, a dozen of these, you should get a
ty-wrap gun:
http://shop.ebay.com/sis.html?_nkw=Panduit+GS2B+tie+wrap+gun+MS90387+1+ty+wrap

Cheers!
Rich

 

[Joerg]

Not sure if it will really work for what you are trying but
look at the security ties used for truck cargo. Here is one type
Uline carries:

http://www.uline.com/BL_2303/Metal-Truck-Seals?keywords=Security Ties

Also check out the 3M VHB tapes. They might do what you need.

The seem to operate on a similar principle as the Panduit ties. The
Panduit ties have the advantage of rounded corners which is nice.

http://www.uline.com/Grp_240/3M-VHB-Tapes

Anything with glue would not pass muster with agencies, and with me

 

[Joerg]

If you intend to use more than, say, a dozen of these, you should get a
ty-wrap gun:
http://shop.ebay.com/sis.html?_nkw=Panduit+GS2B+tie+wrap+gun+MS90387+1+ty+wrap

Oh, they'd do that one of these days. But this is a start-up so we want
to try to live with the least amount of capex Dollars possible.

 

[Rich Grise]

http://shop.ebay.com/sis.html?_nkw=Panduit+GS2B+tie+wrap+gun+MS90387+1+ty+wrap

Oh, they'd do that one of these days. But this is a start-up so we want
to try to live with the least amount of capex Dollars possible.

For whatever it's worth, I've done them with a flush-cut dikes and my
fingers - I hold the flat side of the dikes against the shoulders of
that little block, and pull the loose end until I cinch it up. So far,
I haven't needed more than finger-tight to cinch up the bundle, then,
of course, just clip off the end with the dikes.

Cheers!
Rich

 

[Joerg]

For whatever it's worth, I've done them with a flush-cut dikes and my
fingers - I hold the flat side of the dikes against the shoulders of
that little block, and pull the loose end until I cinch it up. So far,
I haven't needed more than finger-tight to cinch up the bundle, then,
of course, just clip off the end with the dikes.

Yeah, I think so as well. In this case they'll have to use gloves, no
skin oils allowed. Can't clip off though because that leaves sharp edges
... corona ... bzzzt .. hissssss ...

 

[Joerg]

I was thinking something like 2mm wire (isolated if you like) pre-bent
into a U, across
the core through holes on each side of side of it, bent on the back
and soldered

It's tough to hold tension that way. For a small component you don't
have to hold tension because it's inherently and rigidly connected to
the pins with which it hangs on to the board. The ferrite doesn't have
that. Unfortunately ferrite manufacturers remain blissfully
disinterested in how their cores are supposed to be fastened. They could
even make an extra buck here, but they don't seem to care.

if four pads can can hold a pcb mount transformer, why not a core ?

They can't. I have seen designs like that and had to tell the clients
the sad news that a re-layout was required because we couldn't safely
drill holes for a couple of screws. The heavy forces from the
transformer core turned the solder into mush if a unit was transported a
lot (depending on the area, road conditions, and so on).

Sometimes one can use pot cores for which there are holders. But you
can't get large ones easily in 43-material and also I've seen pot cores
fall apart upon shock and vibration.

 

[Rich Webb]

It's tough to hold tension that way. For a small component you don't
have to hold tension because it's inherently and rigidly connected to
the pins with which it hangs on to the board. The ferrite doesn't have
that. Unfortunately ferrite manufacturers remain blissfully
disinterested in how their cores are supposed to be fastened. They could
even make an extra buck here, but they don't seem to care.



They can't. I have seen designs like that and had to tell the clients
the sad news that a re-layout was required because we couldn't safely
drill holes for a couple of screws. The heavy forces from the
transformer core turned the solder into mush if a unit was transported a
lot (depending on the area, road conditions, and so on).

Sometimes one can use pot cores for which there are holders. But you
can't get large ones easily in 43-material and also I've seen pot cores
fall apart upon shock and vibration.

Dang, just give in and use lacing cord. Explain to the young-uns that it
is a cool new binding technique. ;-)

 

[Joerg]

Dang, just give in and use lacing cord. Explain to the young-uns that it
is a cool new binding technique. ;-)

Yeah, I'll likely have them send me two boards for testing. Then I'll do
the 2nd one with lacing cord and tell'em "This here board is how them
real fellahs do it".

 

[Joerg]

You can get special tools to install these things:

http://www.panduit.com/Products/Pro...lcabletiespermid&N=5000001+338&Nu=P_RollupKey

Yes, but not right now. Start-up companies try to avoid that sort of
expense early on.

 

[Rich Grise]

Yeah, I think so as well. In this case they'll have to use gloves, no
skin oils allowed. Can't clip off though because that leaves sharp edges
.. corona ... bzzzt .. hissssss ...

I can't understand why you're using a metal tie at corona-type voltages.
=:-O

Thanks,
Rich

 

[Joerg]

I can't understand why you're using a metal tie at corona-type voltages.
=:-O

Because it has to make darn sure it'll hold. The high voltage is only
there in a fault situation. It will work, I've designed this stuff many
times before and there's always metal in there somewhere. But in the
past I got away with toroids which are very easy to mount. Not this time.

 

[legg]

The seem to operate on a similar principle as the Panduit ties. The
Panduit ties have the advantage of rounded corners which is nice.



Anything with glue would not pass muster with agencies, and with me

It would not be an agency issue, if it functioned. The VHB material is
a listed adhesive system with UL under QOQW2.MH17478. You'd have to
review it's suitability re temperature and flamability.

Lacing tape/cord has temperature, flamability and environmental issues
as well.

You should also run some kind of testing with any potential metalic
solution. HF transformers don't like close ferrous metal - even
diamagnetic materials may induce heating effects you're not counting
on. Anything forming a conductive loop may also have more than just a
passive effect.

Working solutions in higher-powered equipment used adhesives and
mechanical clamps with integral not-conductive elements.

RL

 

[Joerg]

It would not be an agency issue, if it functioned. The VHB material is
a listed adhesive system with UL under QOQW2.MH17478. You'd have to
review it's suitability re temperature and flamability.

They'd want endurance tests and that can get old. I'd rather not rely on
glues here.

Lacing tape/cord has temperature, flamability and environmental issues
as well.

Sure, but there is a major advantage: Aerospace certifications already
exist and that usually makes a very compelling case in front of a
notified body.

You should also run some kind of testing with any potential metalic
solution. HF transformers don't like close ferrous metal - even
diamagnetic materials may induce heating effects you're not counting
on. Anything forming a conductive loop may also have more than just a
passive effect.

That's what I'll have to try but IME it hasn't mattered too much. The
loops go around the outside of the ferrite core, outside the magnetic
loop. I have shielded such cores in the past where the shield was total,
and cradled them closely. There was only some minor capacitive loading
with toroids (expected) but not with multi-aperture cores.

Working solutions in higher-powered equipment used adhesives and
mechanical clamps with integral not-conductive elements.

No adhesives. I'd be ok with a (serious) non-conductive clamp but they
don't seem to exist. Plastic tie-wrap are not so great because the can
dry out and then snap. Too flimsy. I took apart an older machine earlier
this year and at least half the tie-wraps had snapped and fallen onto
the bottom panel, leaving some harnesses dangling a bit.

 

[Joerg]

I'd be reluctant (hah! No magnetic terminlogy joke implied!) to use a
metal strap to hold a ferrite core to a PC board.

Electromagnetically making a single shorted turn (which is what your
metal strap will be) may or may not be relevant to you.

Usually not, at least I've never seen that.

Mechanical shock resistance (i.e. don't break the core if somebody
drops the box) would be my big worry.

Got to muffle that anyhow because the board can flex a bit upon impact.
I was planning on neoprene or stuff like that. Between strap, board and
core.

Not sure if you have a square rod, or a square transformer core, or a
square ferrite ring, but look inside some consumer type equipment at
how rods and transformers are attached to PCB's. I've seen everything
from wax (e.g. old portable transistor radios with rods) to molded
plastic holders (these seem *VERY* ideal to me in terms of both
standoff and mechanical shock absorption) to plastic transformer
housings being used.

Even with e.g. molded chokes you have to realize that the high density
of the ferrite material requires a lot of mechanical thought with
regards to mounting.

It's a double-hole core but a big old fat one. Rather squarish, about
1.2" by 1.2" and 0.6" thick. The windings run only through the holes,
not along the outside of the core.

Yes, ferrite is iffy. That's why I plan to cushion it with something
like neoprene. You can buy it in sheets everywhere and cut it with scissors.

 

[Cydrome Leader]

Folks,

Had a nice clamp for mounting some square ferrites but it's too big, ran
out of space. Lasse had suggested metal type straps a while ago. Found this:

http://media.digikey.com/photos/Panduit Corp Photos/MLT...CP.jpg
http://www.panduit.com/groups/MPM-NL/documents/PartDrawing/086914.pdf

Is anyone familiar with these? Do they really hold forever? Is the
tongue just pulled through and then left alone like with cable ties, or
does it have to be bent over?

those lock with a ball bearing that wedges in the ramp. they will hold
forever. there's no need to fold the end back.

they're fairly stiff so tightening one on ferrite with square edges is
asking to chip the edges off.

 

[Joerg]

those lock with a ball bearing that wedges in the ramp. they will hold
forever. there's no need to fold the end back.

Thanks, that's good to know.

they're fairly stiff so tightening one on ferrite with square edges is
asking to chip the edges off.

I plan to protect them with neoprene. Need that anyhow for buffer
because the steel straps don't have much compliance.

But how stiff can they really be if the thickness of the 304 stainless
steel is only .010"? I have shaped a hose clamps around square objects
with my fingers and those are much thicker.

 

[Joerg]

snip

weren't you going to wrap it in neopren anyway?

Yes, but you'd still have to apply tension and solder joints really do
not like that at all. Solder has a tendency to creep under pressure or
tension.

if you have access to a mill or even just a tablesaw and a drill press
it wouldn't take many minutes to cut a 1.2"x0.6" slot in a piece of
20mm acetal or something like that, cut it into 1.2" long pieces and
drill some holes for screws

Sure, but my clients usually prefer a part number and a price over a
custom part that needs SOPs, ECOs and all that "fun stuff"

Seriously, I've already got two (unavoidable) custom parts on there.
With the whole bureaucratic paper trail.

 

[josephkk]

Usually not, at least I've never seen that.



Got to muffle that anyhow because the board can flex a bit upon impact.
I was planning on neoprene or stuff like that. Between strap, board and
core.



It's a double-hole core but a big old fat one. Rather squarish, about
1.2" by 1.2" and 0.6" thick. The windings run only through the holes,
not along the outside of the core.

Yes, ferrite is iffy. That's why I plan to cushion it with something
like neoprene. You can buy it in sheets everywhere and cut it with scissors.

If i thought the product was made in a size small enough for your needs i
would suggest SS banding like is sometimes used to attach signs and other
equipment to signal poles and the like. It is a lot like steel shipping
strapping. There are thermo welded plastic versions also.

?-)