Bimetalic domes

[N_Cook]

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?

 

[Steve Lusardi]

Sure you can do this, but get a few of these, as the odds of getting it right the 1st time is slim.
Steve

 

[William Sommerwerck]

How important is the overall size of the sensor?

You might find one of the sort that used to be used in kitchen appliances,
that could be inserted in a grill, waffle maker, cookpot, etc. These have
adjustable settings, which (I assume) are varied by changing the pressure on
the sensor.

 

[N_Cook]

Sure you can do this, but get a few of these, as the odds of getting it right the 1st time is slim.
Steve

According to patent
"Laser adjusted set-point of bimetallic thermal disc"
it is done at production , for precise adjustment, but no specific details
of patterns/which surface/degree of variation. I'm more interested in
adjusting otherwise useless batch made for set point of 16 degree C up to
50 or 60 degree C, with no great precision, +/- 10 deg C would be fine

 

[William Sommerwerck]

According to patent

"Laser adjusted set-point of bimetallic thermal disc"
it is done at production , for precise adjustment, but no specific details
of patterns/which surface/degree of variation. I'm more interested in
adjusting otherwise useless batch made for set point of 16 degree C up to
50 or 60 degree C, with no great precision, +/- 10 deg C would be fine

If you could find the patent for the controller I described (it's a famous
patent, from a man who patented many devices in the 50s and 60s), it might
show how this is done.

 

[N_Cook]

If you could find the patent for the controller I described (it's a famous
patent, from a man who patented many devices in the 50s and 60s), it might
show how this is done.

probably a John Taylor
http://content.yudu.com/A15ex7/Apro9/resources/8.htm
but no further forward, I'll suck some and see

 

[William Sommerwerck]

probably a John Taylor

http://content.yudu.com/A15ex7/Apro9/resources/8.htm

I'm not sure. The guy I'm thinking of is American.

 

[N_Cook]

Interesting , but no further forward. Looks as though these froststats will
remain froststats. Surprising ping and bounce as much as six inches on
change of state, the loud ping is somewhat damped when inside the casing.
Need freezer spray to change the state of these discs (hysteresis and all
that). When back to body temp I tried grinding a spot in the centre of the
concave side, no change in set temp. Tried 4 diametrical marks on the
concave side , no change in response. Tried deeper but small 8 cuts just on
the perphery, now no ping but slowly migrates from one state to the other ,
still requiring freezer spray. I wonder how they "weld" these 2 materials
together.

 

[Baron]

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 belive "Clixon" in the UK make these.

 

[Baron]

That is 'Klixon', which was a division of Texas Instruments.

Now it's a division of Sensata

<http://www.sensata.com/klixon/thermostats-thermostat.htm>

Thanks for the spelling correction and link. Its a lot of years since I
played about with them. They were very popular in water heater
circuits at one time.

 

[N_Cook]

Explosive welding.
Simple as that.
Martin

I would have thought friction welding, probably many to a spin and then
press cut to small discs

 

[Baron]

This might be the correct answer, but there are fill-metal/reducing
atmosphere/heat solutions that might do a kind of brazing for lower
cost
if you get the materials right. Explosive welding is used for US
coins
because it was possible to mimic the electromagnetic properties of
silver well enough to keep lots of vending machines in service.
I've gotta believe the requirements for a thermostat bimetal system
are loose enough to allow for alloys that don't require explosive
welds.

I was under the impression that two sheets of material were hot rolled
together and the discs just stamped out complete with the dome shape.

 

[N_Cook]

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.

The use I see them is located fairly loosely in a well in a bakelite disc
that is itself located loosely in the bakelite outer housing

 

[N_Cook]

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]

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

 

[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.)

 

[N_Cook]

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]

<[email protected]> 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.

 

[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...