Bimetalic domes

[N_Cook]

Mark Rand <randm@internettie.co.uk> wrote in message
news:dhahf59546oirlspqcl3avhmknp3abcfl9@4ax.com...

On Mon, 9 Nov 2009 16:13:19 -0600, "William Wixon"
wwixon@frontiernet.net
wrote:




how about instead of removing material from the flat surface of the dome
to
remove material around the outside diameter? would that alter the point
at
which the dome went PING? i was just wondering if the outside edge is
constrained in a bezel, if there was more room to expand there if that
would
alter it's temperature rating?

b.w.


If there were room, one could add a preload spring to change the set
point.

Mark Rand
RTFM

I might try that , will require adding a small well for the spring

 

[Winston]

N_Cook wrote:

As used in thermal switches. Instead of in form of a bimetal strip and
continuous curving with temperature, these are 0.5 inch diameter and make a
definite flip from concave to convex at a specific temperature. About 1mm of
abrupt movement gives a very positive transition for the switch contacts.
Would it be possible to change the characteristic temperature by grinding
back a spot/ring/radii? on one face? which face? or would it just destroy
the action/activation force?

I wonder if one could paint the convex face with fingernail polish as
an etch resist and put the disc in an etching solution to thin the
concave side? Would the relatively smaller 'concave mass' shift the
trigger temperature upwards?

--Winston

--

On YouTube, all the tools have volume controls.

 

[William Sommerwerck]

As used in thermal switches. Instead of in form of a bimetal strip
and continuous curving with temperature, these are 0.5" diameter
and make a definite flip from concave to convex at a specific temperature.
About 1mm of abrupt movement gives a very positive transition for the
switch contacts. Would it be possible to change the characteristic
temperature by grinding back a spot/ring/radii? on one face? which
face? or would it just destroy the action/activation force?

Heaven knows, I don't like reinventing the wheel, but unless you can find
documentation (such as a patent) that explains in detail how these devices
work, and how a particular temperature is set, you're going to have to
experiment.

I again recommend looking for one of those interchangeable thermostats.
Perhaps ripping it apart will reveal the secret!

http://www.gopresto.com/products/products.php?stock=07211

http://www.acehardwareoutlet.com/(uahrtsrsnq0tcxf1wt3tllmg)/productDetails.aspx?SKU=998000074

http://www.advertisingcookbooks.com/si/004123.html

The Presto "Control Master" has been around at least 40 years, and Presto is
still making appliances that use it. (I don't know whether the internal
design or operating principles have changed. The probe part does appear to
be longer and narrower in the current version.)

 

[dcaster@krl.org]

On Nov 8, 8:42 am, "N_Cook" <dive...@tcp.co.uk> wrote:

As used in thermal switches. Instead of in form of a bimetal strip and
continuous curving with temperature, these are 0.5 inch diameter and make a
definite flip from concave to convex at a specific temperature. About 1mm of
abrupt movement gives a very positive transition for the switch contacts.
Would it be possible to change the characteristic temperature by grinding
back a spot/ring/radii? on one face? which face? or would it just destroy
the action/activation force?

I have been waiting for someone to suggest that the temperature at
which they switch is controlled by how domed the discs are. At least
that is my guess. Suggest you get some rubber and a ballpein hammer.
Test what the temperature is that one switches at, and then make in a
bit more domed and see if that changed the temperature at which it
switches. My guess is that more domed means more change from ambient
temperature before it switches.

Dan

 

[N_Cook]

<dcaster@krl.org> wrote in message
news:453facae-8a15-42ea-a59f-fa4c37429891@33g2000vbe.googlegroups.com...
On Nov 8, 8:42 am, "N_Cook" <dive...@tcp.co.uk> wrote:

As used in thermal switches. Instead of in form of a bimetal strip and
continuous curving with temperature, these are 0.5 inch diameter and make
a
definite flip from concave to convex at a specific temperature. About 1mm
of
abrupt movement gives a very positive transition for the switch contacts.
Would it be possible to change the characteristic temperature by grinding
back a spot/ring/radii? on one face? which face? or would it just destroy
the action/activation force?

I have been waiting for someone to suggest that the temperature at
which they switch is controlled by how domed the discs are. At least
that is my guess. Suggest you get some rubber and a ballpein hammer.
Test what the temperature is that one switches at, and then make in a
bit more domed and see if that changed the temperature at which it
switches. My guess is that more domed means more change from ambient
temperature before it switches.

Dan

I will give it a go with large ballbearing in a cup and a press. But the
full range of temp (10 to 220 deg C at least) switches all come in the same
size package and the internal spaces and activation pins are the same
dimensions including degree of doming, all that changes is the materials or
construction within the domes. Normally open for the same temp normally
closed is simply just the same dome in, the other way up

 

[Ned Simmons]

On Wed, 11 Nov 2009 08:49:44 -0000, "N_Cook" <diverse@tcp.co.uk>
wrote:

dcaster@krl.org> wrote in message
.. My guess is that more domed means more change from ambient
temperature before it switches.

Dan

I will give it a go with large ballbearing in a cup and a press.

Another thing to try is local heating and quenching in order to change
the distribution of internal stresses in the dome.

--
Ned Simmons

 

[isw]

In article <4ehlf5dnoij3gblhehjt3kvt3eap5d2f8g@4ax.com>,
Ned Simmons <news@nedsim.com> wrote:

On Wed, 11 Nov 2009 08:49:44 -0000, "N_Cook" <diverse@tcp.co.uk
wrote:

dcaster@krl.org> wrote in message
. My guess is that more domed means more change from ambient
temperature before it switches.

Dan

I will give it a go with large ballbearing in a cup and a press.

Another thing to try is local heating and quenching in order to change
the distribution of internal stresses in the dome.

It's bimetal; I don't think you want any "unexpected" stresses.

Isaac

 

[Paul Hovnanian P.E.]

N_Cook wrote:

As used in thermal switches. Instead of in form of a bimetal strip and
continuous curving with temperature, these are 0.5 inch diameter and make
a definite flip from concave to convex at a specific temperature. About
1mm of abrupt movement gives a very positive transition for the switch
contacts. Would it be possible to change the characteristic temperature by
grinding back a spot/ring/radii? on one face? which face? or would it just
destroy the action/activation force?

Pretty difficult to calibrate that change. I'd try mounting a small coil
spring so as to work with or against the direction of the snap. A setscrew
can then be used to modify the spring preload and adjust the snap point.

--
Paul Hovnanian paul@hovnanian.com
----------------------------------------------------------------------
Have gnu, will travel.

 

[steamer]

--Messed around with these ages ago. The delta-T for the flip is
inversely proportional to the radius of curvature; i.e. greater radius
translates to smaller temp changes to make it flip. I was working on what I
call a 'kinetic solar cell' which works very well in theory...

--
"Steamboat Ed" Haas : Currently broke and
Hacking the Trailing Edge! : looking for a job...
www.nmpproducts.com
---Decks a-wash in a sea of words---