White rubbery power tranny insulators

[N Cook]

Not mica and not the grey plastic-like stuff, anyone familiar.?
They are on a Kustom 6160A mixer amp, USA Kustom , not Custom, under TOP66
trannies.
They have shrunk on the upper section (hottest ?) to the point of very
nearly shrinking under the tranny bodies and the uncovered parts are
ruffled, showing the heated area has shrunk significantly, even split
possibly, not taken apart yet, although check out cold ok.
No other over-temperature indications.
I will replace with mica but is this usual for these, I've not come across
white , relatively thick rubbery ones before.
Almost look like thin slabs of slicone bath sealant.

 

[default]

Not mica and not the grey plastic-like stuff, anyone familiar.?
They are on a Kustom 6160A mixer amp, USA Kustom , not Custom, under TOP66
trannies.
They have shrunk on the upper section (hottest ?) to the point of very
nearly shrinking under the tranny bodies and the uncovered parts are
ruffled, showing the heated area has shrunk significantly, even split
possibly, not taken apart yet, although check out cold ok.
No other over-temperature indications.
I will replace with mica but is this usual for these, I've not come across
white , relatively thick rubbery ones before.
Almost look like thin slabs of slicone bath sealant.

They are probably silicone rubber with some fiberglass imbedded to
make them puncture resistant.

Silicone takes high temperatures very well, never saw one that
deteriorated with heat - yet.

 

[Chris Jones]

Not mica and not the grey plastic-like stuff, anyone familiar.?
They are on a Kustom 6160A mixer amp, USA Kustom , not Custom, under TOP66
trannies.
They have shrunk on the upper section (hottest ?) to the point of very
nearly shrinking under the tranny bodies and the uncovered parts are
ruffled, showing the heated area has shrunk significantly, even split
possibly, not taken apart yet, although check out cold ok.
No other over-temperature indications.
I will replace with mica but is this usual for these, I've not come across
white , relatively thick rubbery ones before.
Almost look like thin slabs of slicone bath sealant.

Like this?
http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=681120
I have never had trouble with them shrinking.

Chris

 

[Eeyore]

Not mica and not the grey plastic-like stuff, anyone familiar.?
They are on a Kustom 6160A mixer amp, USA Kustom , not Custom, under TOP66
trannies.
They have shrunk on the upper section (hottest ?) to the point of very
nearly shrinking under the tranny bodies and the uncovered parts are
ruffled, showing the heated area has shrunk significantly, even split
possibly, not taken apart yet, although check out cold ok.
No other over-temperature indications.
I will replace with mica but is this usual for these, I've not come across
white , relatively thick rubbery ones before.
Almost look like thin slabs of slicone bath sealant.

You can get the synthetic insulators in many colours including white, (rust) red
and green.

The white (and green) ones tend to be high performance (low thermal resistance)
so you may be degrading performance with a typical mica washer.

Graham

 

[Eeyore]

Like this?
http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=681120
I have never had trouble with them shrinking.

Likewise.

The 'ruffling' merely means the washer has been subjected to some serious
mounting pressure. The nice thing abot these flexible washers is the 'conform'
i.e. mould themselves to surfaces underpressure which enhances the heat
transfer.

Graham

 

[N Cook]

Like this?
http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=681120
I have never had trouble with them shrinking.

Chris

Probably the same

This picture shows one
http://home.graffiti.net/diverse:graffiti.net/insulator.jpg
the part at "A" has almost shrunk under the tranny.
None of the material looks heat damaged as its all the same tone of white.

 

[Eeyore]

This picture shows one
http://home.graffiti.net/diverse:graffiti.net/insulator.jpg
the part at "A" has almost shrunk under the tranny.
None of the material looks heat damaged as its all the same tone of white.

It's NOT shrinkage ! The pad has simply conformed to the surface.

Graham

 

[N Cook]

white.

It's NOT shrinkage ! The pad has simply conformed to the surface.

Graham

The trannies are flat-backed as is the heatsink, no convexity/concavity.
Assuming the pads were rectangular to start with, the tops of each of the 4
trannies are now 6 to 8mm narrower than the bottoms. The ruffling is on the
outer edge, the original dimension. If the material had been squashed then
the ruffling would be on the inner exposed edges.
Will probably take apart today after on-load powered-up testing

 

[N Cook]

I'm getting a bit confused on the thermal characteristics.
Thermal conductivity of this silicone material in W/(m*K) at 3.5 is about 10
times better than mica at 0.35, silicone grease about 0.2 .
At least I know its the minimum amount of grease to be used, it annoys me
coming across amps with great dollops of the stuff all around that gets on
your clothing.

But the thickness at 0.4 mm is about 6 times thicker than the 0.07mm mica
washers I would use. What is the final relative de-merit of using mica
instead of white silicone pads ?

 

[N Cook]

followup: see thread

"Mica versus Silicone pad insulators"