How do I determine the power handling (thermal) capabilities and impact on mechanical strength at specific power levels/temperatures?
Nichrome wire
Started by ●January 31, 2023
Reply by ●January 31, 20232023-01-31
On Tue, 31 Jan 2023 07:24:56 -0700, Don Y <blockedofcourse@foo.invalid> wrote:>How do I determine the power handling (thermal) capabilities >and impact on mechanical strength at specific power >levels/temperatures?Medium red hot is obviously OK. The problem will be the end terminations.
Reply by ●January 31, 20232023-01-31
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). The only alloy I'm aware of that gets good strength at red heat, is Inconel 750x (chrome-nickel superalloy spring material).
Reply by ●January 31, 20232023-01-31
On Tuesday, January 31, 2023 at 10:19:57 AM UTC-5, John Larkin wrote:> On Tue, 31 Jan 2023 07:24:56 -0700, Don Y > <blocked...@foo.invalid> wrote: > > >How do I determine the power handling (thermal) capabilities > >and impact on mechanical strength at specific power > >levels/temperatures? > Medium red hot is obviously OK. The problem will be the end > terminations.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.
Reply by ●January 31, 20232023-01-31
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
Reply by ●January 31, 20232023-01-31
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 :>
Reply by ●January 31, 20232023-01-31
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.
Reply by ●January 31, 20232023-01-31
onsdag den 1. februar 2023 kl. 02.06.41 UTC+1 skrev 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.the wire is spring loaded
Reply by ●January 31, 20232023-01-31
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.> 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.
Reply by ●February 1, 20232023-02-01
whit3rd <whit3rd@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. 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
