Porcelain thermally conductive insulators ?

[N_Cook]

1.8mm slabs of porcelain under TO220 devices.

(This is continuation of Ampeg BA600-115, can of worms.
I've got mains back on it and is in working order , now to try with high
power.)

This is my educated guess as to what happened at manufacture as absent but
distinctive 20mm long bolt not found around here. The 4 output devices
should be held to the heatsink via a cross-bar over all 4 of them and 2
bolts thru it into the heatsink. The insulators are ceramic and the 2
central ones, butted up together , do not clear the retaining bolts on their
outer edges. After graunching the thread the assembler decided to leave it
out and trust to luck one off-centre bolt would hold.
Coming to reassembly I found a 3mm screw for replacement but it would not
hold, as tapped thread is stripped, so I tapped that one hole out to 4mm.
Tried grinding a clearance notch on the side of one pad but got nowhere as
ceramic.
Not only that but I had no trouble holding the slab in fingers while trying
to grind a slot , it was barely getting warm - good thermal insulator or
small grinding wheel not generating heat as not cutting into the material ?
So ,lateral thinking, decided to grind down the screw thread where it
interferes with the ceramic , on one bolt.
I wonder if this was a one off at manufacture or a whole batch like this,
all that was needed was shift a tapped hole 1mm, plenty of room there for
that. Or one ceramic pad 1 or 2 mm narrower.

ps
anyone use "chain mail glove" for small part in-hand grinding? At 80GBP and
upwards unlikely , firstly on cost, second need fingers for gripping items.
As an experiment wound some kevlar (ex fibre optic leads) around finger of
old glove and held in place with hot melt string. Simulated
grabbing/skittering of Dremmel and grinding disc into this on a piece of
dowel. It did not penetrate to the dowel, I expected the kevlar to snag and
stall the motor but cut clean through.

 

[Baron]

N_Cook Inscribed thus:

1.8mm slabs of porcelain under TO220 devices.

I would check that ! Its more likely that they are Beryllium_oxide !

Tried grinding a clearance notch on the side of one
pad but got nowhere as ceramic.
Not only that but I had no trouble holding the slab in fingers while
trying to grind a slot, it was barely getting warm - good thermal
insulator or small grinding wheel not generating heat as not cutting
into the material ?

The dust from grinding or abrading Beryllium_oxide is highly toxic !

 

[Barry]

1.8mm slabs of porcelain under TO220 devices.

(This is continuation of Ampeg BA600-115, can of worms.
I've got mains back on it and is in working order , now
to try with high power.)

This is my educated guess as to what happened at manufacture as absent
but
distinctive 20mm long bolt not found around here. The 4 output devices
should be held to the heatsink via a cross-bar over all 4 of them and
2
bolts thru it into the heatsink. The insulators are ceramic and the 2
central ones, butted up together , do not clear the retaining bolts on
their
outer edges. After graunching the thread the assembler decided to leave
it
out and trust to luck one off-centre bolt would hold.
Coming to reassembly I found a 3mm screw for replacement but it would
not
hold, as tapped thread is stripped, so I tapped that one hole out to
4mm.
WARNING

Tried grinding a clearance notch on the side of one pad but got nowhere
as
ceramic.
WARNING

Not only that but I had no trouble holding the slab in fingers while
trying
to grind a slot , it was barely getting warm - good thermal insulator
or
small grinding wheel not generating heat as not cutting into the
material ?
So ,lateral thinking, decided to grind down the screw thread where it
interferes with the ceramic , on one bolt.

{snip}

Those ceramic insulators are made from beryllia (berylium oxide), a
ceramic that has a higher heat conductivity than aluminum. You should
be _extremely_ careful in handling them. Quoting from the Wikipedia
article: "Like all berylium compounds, BeO is carcinogenic and may
cause chronic beryllium disease. Once fired into solid form, it is
safe to handle as long as it is not subjected to any machining that
generates dust." Likewise the American Beryllia site says: "Exposure
to fine, airborne beryllium oxide powder or dust in sufficiently
large concentrations, may cause a lung disease in a small number
of hypersensitive people."

Grinding a beryllia insulator is considered exceptionally dangerous.
Please read the MSDS at
http://www.AmericanBeryllia.com/lit/Beryllium_Oxide_MSDS.pdf.

I once needed some microwave windows made of beryllia. I was going
to order beryllia blanks, have the edges sputtered in gold, and braze
them into 316 stainless waveguide sections. I called the engineers
at National Beryllia (now American Beryllia) to discuss this application.
In short order, they convinced me that they should manufacture the
windows as there was a chance that the differential thermal expansion
between the beryllia and the stainless steel waveguide could potentially
shatter the ceramic and release beryllia powder. After learning the
cost, I went with sapphire windows instead.

Some people are hypersensitive to beryllium compounds. If you are
not in the hospital yet, consider yourself _very_ lucky. A small
percentage of the population is so hypersensitive that the small
amount of dust you created could be lethal.

Dr. Barry L. Ornitz WA4VZQ [my_ham_call at live.com]

 

[N_Cook]

N_Cook Inscribed thus:


I would check that ! Its more likely that they are Beryllium_oxide !


The dust from grinding or abrading Beryllium_oxide is highly toxic !

Unfortunately it would not grind. I assume it was not heating up because the
grinding disc was just running over the surface without even rubbing , let
alone grinding, so no dust, still the flat edge . Does BeO have that sort of
translucent appearance of porcelain? I've managed to grind small sections of
the ceramic used is high temperature "chock block" connectors, that has a
normal solid white appearance. But given its use here then presumably BeO.
It was the slightly milky/translucent porcelain-like appearance that
convinced me.

 

[Grant]

Unfortunately it would not grind. I assume it was not heating up because the
grinding disc was just running over the surface without even rubbing , let
alone grinding, so no dust, still the flat edge . Does BeO have that sort of
translucent appearance of porcelain? I've managed to grind small sections of
the ceramic used is high temperature "chock block" connectors, that has a
normal solid white appearance. But given its use here then presumably BeO.
It was the slightly milky/translucent porcelain-like appearance that
convinced me.

Only BeO I've seen was pink, and I'd not try to grind it, toxic!

Safe if not shattered.

Grant.

 

[N_Cook]

Only BeO I've seen was pink, and I'd not try to grind it, toxic!

Safe if not shattered.

Grant.

I've seen pink TO3, presumably BeO, insulators before but they did not have
this transclucent like appearance.

 

[Baron]

N_Cook Inscribed thus:

Unfortunately it would not grind. I assume it was not heating up
because the grinding disc was just running over the surface without
even rubbing , let alone grinding, so no dust, still the flat edge.
Does BeO have that sort of translucent appearance of porcelain?

The surface tends to have the appearance of good quality photocopy
paper, very smooth with a barely visible grain. A bit like ferrite
beads.

I've managed to grind small sections of the ceramic used is high
temperature "chock block" connectors, that has a normal solid white
appearance. But given its use here then presumably BeO.
It was the slightly milky/translucent porcelain-like appearance that
convinced me.

Both Aluminum oxide and Beryllium oxide are extremely hard materials. I
belive that the pink dye was used later to specifically identify
Beryllium. So its a good chance that the white insulators that you
have are Aluminum oxide. Even so its not a good idea to try to grind
them.

Ceramics are also used to machine metals, including some that are so
tough that only ceramic cutters can be used on them.

 

[Barry]

Both Aluminum oxide and Beryllium oxide are extremely hard materials.
I
belive that the pink dye was used later to specifically identify
Beryllium. So its a good chance that the white insulators that you
have are Aluminum oxide. Even so its not a good idea to try to grind
them.

Beryllia is white, the same as alumina. There is no standard on coloring
beryllia insulators for use as heat transfer links. No dye is used as
the beryllia is sintered (fired) at very high temperatures. Instead a
colored inorganic metal oxide is added in small amounts. Beryllia has
about seven to ten times the thermal conductivity of alumina, so if the
links were used with high power parts, they are probably beryllia.
Beryllia has about one third better thermal conductivity than aluminum
nitride in the 25 to 300 C temperature range. Only diamond and cubic
boron nitride are better thermal conductors (but at an exceptionally high
cost).

Until you know for sure what these insulators are made of, treat them as
beryllia. I.e., do not grind or crush them.

73, Dr. Barry L. Ornitz WA4VZQ

 

[N_Cook]

N_Cook Inscribed thus:


The surface tends to have the appearance of good quality photocopy
paper, very smooth with a barely visible grain. A bit like ferrite
beads.


Both Aluminum oxide and Beryllium oxide are extremely hard materials. I
belive that the pink dye was used later to specifically identify
Beryllium. So its a good chance that the white insulators that you
have are Aluminum oxide. Even so its not a good idea to try to grind
them.

Ceramics are also used to machine metals, including some that are so
tough that only ceramic cutters can be used on them.

The next time I come across one I'll try passing a laser beam or bright
light through it to see if any light passes through. It was that
translucency appearance, like porcelain , that I noticed.

 

[N_Cook]

I had to get inside that amp again, yet another PbF problem from next to
zero insertion force speaker connector at the PA 4 removal & inserts by me
was enough , only 6 months old.
The slabs pass red laser pointer light, but then on checking but so does the
ceramic of high temp "choc block".
These slabs are more trnasmissive and scatter the light throughout the slab
not just the entry and exit area of the chock block.

 

[Baron]

N_Cook Inscribed thus:

I had to get inside that amp again, yet another PbF problem from next
to zero insertion force speaker connector at the PA 4 removal &
inserts by me was enough , only 6 months old.
The slabs pass red laser pointer light, but then on checking but so
does the ceramic of high temp "choc block".
These slabs are more trnasmissive and scatter the light throughout the
slab not just the entry and exit area of the chock block.

Mmm ! Interesting. I have a small quantity of boxed TO3 BeO
insulators. I'll have to get one out and see.

 

[josephkk]

N_Cook Inscribed thus:


I would check that ! Its more likely that they are Beryllium_oxide !


The dust from grinding or abrading Beryllium_oxide is highly toxic !

BeO is very expensive. I would be very surprised to find any in such
application.

 

[N_Cook]

N_Cook Inscribed thus:


I would check that ! Its more likely that they are Beryllium_oxide !


The dust from grinding or abrading Beryllium_oxide is highly toxic !

BeO is very expensive. I would be very surprised to find any in such
application.


++++


These were not made for the job. They have a hole for either TO220 or TOP66
maybe size transistors . So too wide for this use and the hole is not used
.. The layout does not mean they have to be 1.8mm thick , any thickness from
mica up could have been accommodated. Normally you would go for the thinnest
of insulators.

 

[N_Cook]

N_Cook Inscribed thus:


Mmm ! Interesting. I have a small quantity of boxed TO3 BeO
insulators. I'll have to get one out and see.

It maybe a function of thickness, these being 1.8mm thick slabs rather than
wafers

 

[Baron]

josephkk Inscribed thus:

BeO is very expensive. I would be very surprised to find any in such
application.

I wonder how much 12 dozen TO3 BeO insulators would be worth ?

 

[Baron]

N_Cook Inscribed thus:

It maybe a function of thickness, these being 1.8mm thick slabs rather
than wafers

I cracked open a box of TO3 BeO insulators this afternoon...
I was very surprised ! I tried shining a red laser pointer through one.
Its weird but they do seem to glow but no direct light through it.

Putting one against a small hole in a cardboard box and viewing the sun
shows nothing, no light, nothing. Most odd !

 

[N_Cook]

N_Cook Inscribed thus:


I cracked open a box of TO3 BeO insulators this afternoon...
I was very surprised ! I tried shining a red laser pointer through one.
Its weird but they do seem to glow but no direct light through it.

Putting one against a small hole in a cardboard box and viewing the sun
shows nothing, no light, nothing. Most odd !

Thast was the same here complete scarttering with no obvious bright spot
directly opposite the entry point. Chock block ceramic was just the
adjascent bright spot , much attenuated in comparison to the porcelain or
vitrified BeO slab

 

[josephkk]

josephkk Inscribed thus:


I wonder how much 12 dozen TO3 BeO insulators would be worth ?

The last time i saw a price they were over US $1 each, but that was over
30 years ago and for military use. Between the now rabid regulation and
the expected cost i would be rather surprised to find them in commercial
instrument amplifiers. Of course with Chinese manufacture such bets may
be knocked into a cocked hat.

 

[Baron]

josephkk Inscribed thus:

The last time i saw a price they were over US $1 each, but that was
over 30 years ago and for military use. Between the now rabid
regulation and the expected cost i would be rather surprised to find
them in commercial instrument amplifiers. Of course with Chinese
manufacture such bets may be knocked into a cocked hat.

You mentioned "military use", the original packing had "Marconi" on the
label ! I've had them for more than 20 years. They came as part of an
auction lot. If I recall, a subcontracting company that went bust when
Marconi was taken over.

 

[N_Cook]

josephkk Inscribed thus:


I wonder how much 12 dozen TO3 BeO insulators would be worth ?

The last time i saw a price they were over US $1 each, but that was over
30 years ago and for military use. Between the now rabid regulation and
the expected cost i would be rather surprised to find them in commercial
instrument amplifiers. Of course with Chinese manufacture such bets may
be knocked into a cocked hat.

++++

I'm assuming boards soldered up in China but assembled into the cab in USA.
So these insulators would likely be fitted in the USA. They obviously were
not made for the job, wrong cross-section area, unnecessarily thick, hole
not used - perhaps they just had them laying around. That grey silipad could
have been used with FET legs preformed to accommodate.