Nichrome wire

[Don Y]

How do I determine the power handling (thermal) capabilities
and impact on mechanical strength at specific power
levels/temperatures?

[John Larkin]

Medium red hot is obviously OK. The problem will be the end
terminations.

[whit3rd]

Strength? It stretches, if you have it hot and under stress.
That doesn't make for good mechanical strength (and
is why stove elements are kanthal/ceramic swaged tube over
the heating element).

The only alloy I'm aware of that gets good strength at red heat,
is Inconel 750x (chrome-nickel superalloy spring material).

[Fred Bloggs]

It melts at 1400oC so you want to stay clear of that.

Tensile strength is 100,000 psi for annealed, 200,000 psi for hard drawn. Yield strength is 50,000 psi. There's a slight temperature dependence to those numbers, buried in a materials handbook somewhere, the manufacturers don't really say outright. Generally the wire snaps at 30% elongation. Whoever manufactured the wire almost certainly has a chart which shows about a half dozen reference temperatures resulting from a half dozen different currents, and all that repeated for every single gauge of wire they make. Heater OEMs do just fine with that data.

[Phil Hobbs]

On 2023-01-31 14:04, whit3rd wrote:
> On Tuesday, January 31, 2023 at 6:25:07 AM UTC-8, Don Y wrote:
>> How do I determine the power handling (thermal) capabilities
>> and impact on mechanical strength at specific power
>> levels/temperatures?
>
> Strength? It stretches, if you have it hot and under stress.
> That doesn't make for good mechanical strength (and
> is why stove elements are kanthal/ceramic swaged tube over
> the heating element).

Of course it's nice not to short your cooking pots to 240VAC, too. ;)

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

[Don Y]

On 1/31/2023 12:04 PM, whit3rd wrote:
> On Tuesday, January 31, 2023 at 6:25:07 AM UTC-8, Don Y wrote:
>> How do I determine the power handling (thermal) capabilities
>> and impact on mechanical strength at specific power
>> levels/temperatures?
>
> Strength? It stretches, if you have it hot and under stress.
> That doesn't make for good mechanical strength (and
> is why stove elements are kanthal/ceramic swaged tube over
> the heating element).

But its used in other places, beyond "calrods". ISTR toasters
having "supported" wires. And, I think my pizzelle maker
is similarly constructed. The mechanical loads in each case
are static and largely limited to just supporting itself.

I'm not sure what the heating elements in "glass cooktops"
look like "under the glass"...

> The only alloy I'm aware of that gets good strength at red heat,
> is Inconel 750x (chrome-nickel superalloy spring material).

I've not indicated that it needs to glow cherry red.
Rather, I want to know how much power I can dissipate
(in a given product) and what the mechanical consequences
at that power level (temperature rise) are likely to be.

I recall having a pair of electric *socks* as a kid. Powered
by D cells. Definitely not cherry red :>

[whit3rd]

On Tuesday, January 31, 2023 at 4:30:48 PM UTC-8, Don Y wrote:

> I recall having a pair of electric *socks* as a kid. Powered
> by D cells. Definitely not cherry red :>

Maybe Nitinol? The flexibility (elastic range) is more important than other mechanical
properties. For a hot-wire cutter, my experimenting with NiCr was dominated
by the way the taut wire didn't hold its length.

I suspect the familiar wave-surface foam slabs are cut with a straight (wire? knife?)
as the foam was fed from a pair of very bumpy rollers.

[Lasse Langwadt Christensen]

the wire is spring loaded

[Don Y]

On 1/31/2023 6:06 PM, whit3rd wrote:
> On Tuesday, January 31, 2023 at 4:30:48 PM UTC-8, Don Y wrote:
>
>> I recall having a pair of electric *socks* as a kid. Powered
>> by D cells. Definitely not cherry red :>
>
> Maybe Nitinol? The flexibility (elastic range) is more important than other mechanical
> properties. For a hot-wire cutter, my experimenting with NiCr was dominated
> by the way the taut wire didn't hold its length.

I saw a guy cutting "foam" (no idea how to describe WHAT type of foam)
with what looked like a "bow" (as in bow-and-arrow) made out of what
I assumed was nichrome. The frame of the bow had enough springiness
to keep the wire taut.

But, I don't know what sort of mechanical load the wire "sees" as
it melts that stuff.

[Liz Tuddenham]

If you don't mind the increased power dissipation and poorer cut
definition, you could use a thicker wire. An adjustable mounting, that
allows you to shorten the length of wire in use, will reduce the
stresses when cutting thinner material.

There ought not to be too much side load on a hot cutting wire unless
the machine is being over-worked, but if the force is mainly from one
direction, substituting a nichrome ribbon for the wire might give more
resistance to bending in that direction.

Rather than starting from the resistance of the wire, try looking for a
material that has the necessary hot strength/flexibility and then cut a
narrow strip of it from some sheet. Match the electrical supply to the
material, rather than the other way around.

--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

[Jasen Betts]

On 2023-02-01, Liz Tuddenham <l...@poppyrecords.invalid.invalid> wrote:
> whit3rd <whi...@gmail.com> wrote:
>
>> On Tuesday, January 31, 2023 at 4:30:48 PM UTC-8, Don Y wrote:
>>
>> > I recall having a pair of electric *socks* as a kid. Powered
>> > by D cells. Definitely not cherry red :>
>>
>> Maybe Nitinol? The flexibility (elastic range) is more important than
>> other mechanical properties. For a hot-wire cutter, my experimenting
>> with NiCr was dominated by the way the taut wire didn't hold its length.
>>
>> I suspect the familiar wave-surface foam slabs are cut with a straight
>> (wire? knife?) as the foam was fed from a pair of very bumpy rollers.
>
> If you don't mind the increased power dissipation and poorer cut
> definition, you could use a thicker wire. An adjustable mounting, that
> allows you to shorten the length of wire in use, will reduce the
> stresses when cutting thinner material.

Cutting foam is interesting the faster you go the cooler the wire gets.
but if you stop the wire inside the foam gets hotter than the wire
that's in free air (because it's insulated). I expect that there's
a cutting speed where the wire temperature is near uniform,

> There ought not to be too much side load on a hot cutting wire unless
> the machine is being over-worked, but if the force is mainly from one
> direction, substituting a nichrome ribbon for the wire might give more
> resistance to bending in that direction.

Yes, but the wire only needs to emit heat in one direction and the
ribbon is not facing that direction.

> Rather than starting from the resistance of the wire, try looking for a
> material that has the necessary hot strength/flexibility and then cut a
> narrow strip of it from some sheet. Match the electrical supply to the
> material, rather than the other way around.

I've experimented with stainless steel in the past, but the thermal
coefficient of resistance has the wrong sign leading to hot spots
forming where the wire is doing the least work. nichrome at-least has
a flat coefficient.

--
Jasen.
pǝsɹǝʌǝɹ sʇɥƃᴉɹ ll∀

[Don Y]

Or, only apply the material in applications for which it is
suited! That's the point of my question.

[John Larkin]

On Wed, 1 Feb 2023 09:57:21 -0000 (UTC), Jasen Betts
<use...@revmaps.no-ip.org> wrote:

>On 2023-02-01, Liz Tuddenham <l...@poppyrecords.invalid.invalid> wrote:
>> whit3rd <whi...@gmail.com> wrote:
>>
>>> On Tuesday, January 31, 2023 at 4:30:48 PM UTC-8, Don Y wrote:
>>>
>>> > I recall having a pair of electric *socks* as a kid. Powered
>>> > by D cells. Definitely not cherry red :>
>>>
>>> Maybe Nitinol? The flexibility (elastic range) is more important than
>>> other mechanical properties. For a hot-wire cutter, my experimenting
>>> with NiCr was dominated by the way the taut wire didn't hold its length.
>>>
>>> I suspect the familiar wave-surface foam slabs are cut with a straight
>>> (wire? knife?) as the foam was fed from a pair of very bumpy rollers.
>>
>> If you don't mind the increased power dissipation and poorer cut
>> definition, you could use a thicker wire. An adjustable mounting, that
>> allows you to shorten the length of wire in use, will reduce the
>> stresses when cutting thinner material.
>
>Cutting foam is interesting the faster you go the cooler the wire gets.
>but if you stop the wire inside the foam gets hotter than the wire
>that's in free air (because it's insulated). I expect that there's
>a cutting speed where the wire temperature is near uniform,

Given a wire with a decent tempco, one could servo the temperature.

>
>> There ought not to be too much side load on a hot cutting wire unless
>> the machine is being over-worked, but if the force is mainly from one
>> direction, substituting a nichrome ribbon for the wire might give more
>> resistance to bending in that direction.
>
>Yes, but the wire only needs to emit heat in one direction and the
>ribbon is not facing that direction.
>
>> Rather than starting from the resistance of the wire, try looking for a
>> material that has the necessary hot strength/flexibility and then cut a
>> narrow strip of it from some sheet. Match the electrical supply to the
>> material, rather than the other way around.
>
>I've experimented with stainless steel in the past, but the thermal
>coefficient of resistance has the wrong sign leading to hot spots
>forming where the wire is doing the least work. nichrome at-least has
>a flat coefficient.

Constant current drive would do that to some extent. Constant voltage,
the opposite. 304 has a pretty low positive tempco, about 850 ppm.
Most metals are more like 4000.

[Fred Bloggs]

On Tuesday, January 31, 2023 at 8:58:31 PM UTC-5, Don Y wrote:

>
> But, I don't know what sort of mechanical load the wire "sees" as
> it melts that stuff.

That's because you're just an anonymous troll who doesn't know the first thing about science, engineering, or applied analysis.

[Don Y]

Yeah, in "cutting" applications you tend to end up with a
"blade" that is longer than your longest cut will ever be.
So, parts of the "blade" see different thermal loads.

I'd imagine an industrial supplier would have their process
set *to* the material they are making (they are unlikely to
use a single cutter to address an unconstrained number of
different sizes/applications.

And, if you are using the wire just as a heat source, you
likely don't have that sort of variation in "loads".

[Clifford Heath]

Never mind, Don. It looks like Fred's been playing in the mirror again.

[Liz Tuddenham]

It sounds as though you need a composite wire: something like copper,
with a large +ve temp coefficient, to carry the current and someting
less conductive like nichrome or similar to give hot strength.

As you presumably only need short lengths, there would be no need to
search for a continous manufacturered product, you could make wires like
this yourself in short lengths using a home-made batch creeler. For
preliminary experiments you could hold one end of the wire bundle in a
bench vice and the other end in a small hand drill; then turn the drill
to twist the bundle. I expect the 'lay' will go all wrong, but it will
give you a test piece that will prove the concept.

I have put a sketch of a possible way of making these wires more
professionally at:
<http://www.poppyrecords.co.uk/other/Creeler.gif>

You make a couple of tools as shown in the upper drawing, with a hollow
stem for gripping in the vice or the drill chuck, and a disc with holes.
Thread the copper wire through the central hole and 6 nichrome wires
through the outer holes. When the chuck is rotated, the nichrome wires
should wrap evenly around the central copper one but the whole assembly
will shorten as they take up a helical shape. To prevent this buckling
the copper wire, the latter is tensioned as shown in the lower drawing.

Hope this helps.

[Don Y]

Or, adjusted by the user based on observations of the "current stretch":

<https://hotwirefoamfactory.com/4-Foot-Compound-Bow-Cutter.html>

[legg]

On Tue, 31 Jan 2023 17:30:35 -0700, Don Y
<blocked...@foo.invalid> wrote:

<snip>

>I'm not sure what the heating elements in "glass cooktops"
>look like "under the glass"...
>

It will depend on the mfr. some are visibly simple coils
laid in a former.

Have 'repaired' a few with zig-zag ribbons imbedded in
filled insulator forms. These are brittle and very difficult
to make a secure electromechanical joint at any point of
failure. They're not meant to be fooled around with.

A compression flat-fit, forcing-plates secured by offset
screws with split washers, seemed to work. Don't know how
long they lasted. Owner a fanatic for repair of esoteric
brands.

Glass cooktops are a joke, provoking the worst aspects
of the electric stove top cooking w/r to delays, heat tranfer
and loss.

RL

[Don Y]

On 2/3/2023 1:21 PM, legg wrote:
> On Tue, 31 Jan 2023 17:30:35 -0700, Don Y
> <blocked...@foo.invalid> wrote:
>
> <snip>
>> I'm not sure what the heating elements in "glass cooktops"
>> look like "under the glass"...
>
> It will depend on the mfr. some are visibly simple coils
> laid in a former.
>
> Have 'repaired' a few with zig-zag ribbons imbedded in
> filled insulator forms. These are brittle and very difficult
> to make a secure electromechanical joint at any point of
> failure. They're not meant to be fooled around with.
>
> A compression flat-fit, forcing-plates secured by offset
> screws with split washers, seemed to work. Don't know how
> long they lasted. Owner a fanatic for repair of esoteric
> brands.

Buy a spare appliance "for parts". :>

> Glass cooktops are a joke, provoking the worst aspects
> of the electric stove top cooking w/r to delays, heat tranfer
> and loss.

As well as maintenance. And, appearance (they show way too much
dirt, dust, fingerprints, stains, etc. -- perhaps as an
incentive for you to clean them often?)

However, they seem to be the most readily offered varieties
(induction and radiant).

I've lobbied for gas simply because it is easier to keep clean.
OTOH, I find electric better for REALLY slow cooking; it's
near impossible for me to make a 16 qt pot of red sauce on
a gas stove without the bottom layer of content getting scorched.

[Clive Arthur]

On 03/02/2023 20:21, legg wrote:

<snip>

> Glass cooktops are a joke, provoking the worst aspects
> of the electric stove top cooking w/r to delays, heat tranfer
> and loss.
>
> RL

But induction is the bee's knees. I'd never go back to gas, and the
only thing I miss is using the flame to char peppers.

--
Cheers
Clive

[Jan Panteltje]

On a sunny day (Fri, 3 Feb 2023 23:32:41 +0000) it happened Clive Arthur
<cl...@nowaytoday.co.uk> wrote in <trk5iq$1l09j$1...@dont-email.me>:

It depends:
I have one induction cookplate that gives me a big headache when using it.
Probably RF radiation, so I no longer use it.
My Chinese induction experiments work fine though:
http://panteltje.com/pub/induction_heater_quadcopter_power_dummy_load_test_IMG_6102.JPG
http://panteltje.com/pub/melting_solder_in_an_metal_olive_bottle_cap_IMG_5191.JPG
http://panteltje.com/pub/carbon_crucible_zero_load_IMG_5429.JPG

[Joe Gwinn]

My wife would find that crippling.

But more generally, some European friends of mine have an induction
cook top. It is fast to boil water, but it nonetheless is very
frustrating to cook with, because it has only ten distinct power
levels, so one cannot get the power level just right.

There are some makes and models that have more like one hundred
levels, which is enough to be stepless in practice. But most have at
most ten levels, and the product brochures are ambiguous here.

So, if no specific number of power levels is clearly stated in plain
words, most likely it's no more than ten, so move on.

For a cook top in one's possession, one can measure the distinct power
levels by measuring the AC power consumption as one slowly adjusts the
cooking power level while heating a big pot of water.

Joe Gwinn

[Clive Arthur]

Ours, a mid range AEG, has half steps from half to 9 so about 18 levels,
plus a 'power boost' which is frighteningly quick. I really like it,
you can dry-fry chopped onion really slowly and get a large pot of spuds
on the go really quickly. It's so much easier to clean than gas and
only gets hot where a hot pan sits.

We did have to lose some of our very old pans though, but they didn't go
to waste.

After using other types for years, we came across these in holiday
rental accommodation, and were so impressed we decided to change.

--
Cheers
Clive

[Liz Tuddenham]

Just as an aside, telephone drop wires are made of copper-coated high
tensile steel, so they might be worth investigating.

[Don Y]

We didn't like the induction cooktops when we were shopping.
It seems their (practical) claim to fame is how quickly they
heat up. But, aside from bringing a pot of water to boil,
they're not going to significantly change the overall cooking
time.

Pancakes, yesterday. Roughly two minutes per skillet-full.
I suspect I could cook on a higher heat setting but will
that cut the time down to... 90 seconds? And, what would
the consequences be for the flapjacks? Will the sausages
be ready?

If I bring a pot of water to temperature instantly (!), will
that meaningfully change the amount of time it takes for the
contents to cook? (why not use a microwave oven for all
food prep?)

I routinely (4-6 wks) make a 16 qt pot of red sauce. It
takes ~12 hours to cook -- so the flavors mellow. The
biggest problem is making sure the pot doesn't get *too*
hot (the thermal gradient through a foot of sauce is pretty
high) and burn to the bottom of the pan. I can't use a gas
stove for this (can't get the flame low enough as it always
leaves a small hot spot). And, electric is a juggling act
to see how close to "OFF" you can set the control!

[The induction cooktops seemed to have a few fixed settings
instead of an infinitely variable dial. Some models also had
interactions between burners; "if the power drawn by burners
1&2 -- or 3&4 -- exceeds a threshold..."]

We've been more focused on the oven portion wrt baking.
If you can cut a sheet of cookies down to 8 minutes from
12 -- and make 6 (or more) sheets in a batch, then you can
*actually* speed things up.

[OTOH, reducing this to much less than 8 minutes will likely
mean you don't have the cookies off the last sheet and the
*next* sheet ready to go before the current sheet demands
attention!]

[Don Y]

I don't have a need/application. Rather, trying to understand how
the material can be used, if a potential need *does* arise.

[legg]

On Sat, 04 Feb 2023 10:56:40 -0500, Joe Gwinn <joeg...@comcast.net>
wrote:

>On Fri, 3 Feb 2023 23:32:41 +0000, Clive Arthur
><cl...@nowaytoday.co.uk> wrote:
>
>>On 03/02/2023 20:21, legg wrote:
>>
>><snip>
>>
>>> Glass cooktops are a joke, provoking the worst aspects
>>> of the electric stove top cooking w/r to delays, heat tranfer
>>> and loss.
>>>
>>> RL
>>
>>But induction is the bee's knees. I'd never go back to gas, and the
>>only thing I miss is using the flame to char peppers.
>
>My wife would find that crippling.
>
>But more generally, some European friends of mine have an induction
>cook top. It is fast to boil water, but it nonetheless is very
>frustrating to cook with, because it has only ten distinct power
>levels, so one cannot get the power level just right.
>
>There are some makes and models that have more like one hundred
>levels, which is enough to be stepless in practice. But most have at
>most ten levels, and the product brochures are ambiguous here.
>
>So, if no specific number of power levels is clearly stated in plain
>words, most likely it's no more than ten, so move on.

Should be able to get different coupling levels by moving the
container off-centre or off-surface.

Choice of container will also be included in the learning curve.
A 'simmering' vessel might just be a poor heater, or sitting on
an intervening dinner plate.

>
>For a cook top in one's possession, one can measure the distinct power
>levels by measuring the AC power consumption as one slowly adjusts the
>cooking power level while heating a big pot of water.
>
>Joe Gwinn

RL

[Joe Gwinn]

On Sat, 4 Feb 2023 16:21:48 +0000, Clive Arthur

What I found that matched your description is AEG model IKB64431XB.
The other AEG models found so far have nine non-zero power modes, plus
bower boost. This implication is that nine levels was not enough, so
they provided half-steps in between. Maybe that's sufficient.

>We did have to lose some of our very old pans though, but they didn't go
>to waste.

I have some induction-ready pans, but it would be painful to replace
all the old non-magnetic pots. For instance, pure copper pans.
Fortunately, boring old cast iron does work on induction, econ though
cast iron cookware was invented long before electricity was a thing.

>After using other types for years, we came across these in holiday
>rental accommodation, and were so impressed we decided to change.

My European friends served that purpose, as they complained of being
unable to adjust the heat level and being forced to constantly
readjust the level.

I do have a free-standing induction hob (Nuwave PIC Gold, model
30211-BR, designed in US, made in China) that claims about 100 power
levels, and this seems to be true, and I can see the power AC power
consumption levels changing as one would expect. I don't know if I
can tell 50 levels from 100 levels by measuring AC power, but it
certainly has many more than 9 non-zero levels.


The other issue is that with all-electric, one is SOL if no power. But
if non-electronic, a gas stove will still work. With electronically
controlled stoves, the key question to ask is if anything will work if
no power. Nowadays, a common pattern is that some of the stovetop
burners will work in the dark, but the fancy stuff will not.

Joe Gwinn

[Jasen Betts]

On 2023-02-04, Joe Gwinn <joeg...@comcast.net> wrote:
> On Sat, 4 Feb 2023 16:21:48 +0000, Clive Arthur
>

> The other issue is that with all-electric, one is SOL if no power. But
> if non-electronic, a gas stove will still work. With electronically
> controlled stoves, the key question to ask is if anything will work if
> no power. Nowadays, a common pattern is that some of the stovetop
> burners will work in the dark, but the fancy stuff will not.
>

A small disaster that takes out the electricty supply will likely be
fixed before anyone starves to death or even looses their freezer
and as it's small you can drive (or walk) to the edge of it and buy
cooked food.

A large disaster will likely take out the natural gas pumps too, like
in "Texas 2021"

[Don Y]

On 2/4/2023 3:05 PM, Jasen Betts wrote:
> On 2023-02-04, Joe Gwinn <joeg...@comcast.net> wrote:
>> On Sat, 4 Feb 2023 16:21:48 +0000, Clive Arthur
>>
>> The other issue is that with all-electric, one is SOL if no power. But
>> if non-electronic, a gas stove will still work. With electronically
>> controlled stoves, the key question to ask is if anything will work if
>> no power. Nowadays, a common pattern is that some of the stovetop
>> burners will work in the dark, but the fancy stuff will not.
>
> A small disaster that takes out the electricty supply will likely be
> fixed before anyone starves to death or even looses their freezer
> and as it's small you can drive (or walk) to the edge of it and buy
> cooked food.

You can also keep a bag of charcoal and grill, outdoors (even if you
live in cold places).

The real pisser is folks with heat pumps during a power outage...
no hot water, no heat, no ACbrrr, no lites, no TV, no internet, etc.
"All electric" homes have serious downsides!

> A large disaster will likely take out the natural gas pumps too, like
> in "Texas 2021"

We had an unnaturally cold spell several years ago (10?).
There was insufficient gas pressure to meet the demands of
all of the homes craving heat.

Your furnace would light; then shutdown because the flame
wouldn't get hot enough, quick enough. Lather, rinse, repeat.

The temporary fix was to shut off the gas supply to parts of
town so the other parts had enough pressure to run their
appliances.

[Phil Hobbs]

You folks don't have real weather, though. Round here we get the
occasional storm that would make an Orkneyman or Shetlander shudder.

Gas heat, gas cooktop, gasoline generator, Good Medicine.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

[Jan Panteltje]

On a sunny day (Sun, 5 Feb 2023 14:46:38 -0500) it happened Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote in
<99d86a08-66dc-7e57...@electrooptical.net>:

>On 2023-02-04 01:21, Jan Panteltje wrote:
>> On a sunny day (Fri, 3 Feb 2023 23:32:41 +0000) it happened Clive Arthur
>> <cl...@nowaytoday.co.uk> wrote in <trk5iq$1l09j$1...@dont-email.me>:
>>
>>> On 03/02/2023 20:21, legg wrote:
>>>
>>> <snip>
>>>
>>>> Glass cooktops are a joke, provoking the worst aspects
>>>> of the electric stove top cooking w/r to delays, heat tranfer
>>>> and loss.
>>>>
>>>> RL
>>>
>>> But induction is the bee's knees. I'd never go back to gas, and the
>>> only thing I miss is using the flame t