I need to make an insulator that is subject to electrical arcing. The
100 year old originals appear to be machined from an asbestos compound
of some kind. I don't have any asbestos and I don't want to machine
asbestos anyway.
I've made an insulator from epoxy resin with loads of chopped
fibreglass in it. It's the middle one he
http://i40.tinypic.com/md35du.jpg

Asbestos panels fit into the slots.

Unfortunately I have discovered that I can set the epoxy alight after
a few seconds using a blowtorch, and that is no good. There is likely
to be arcing and bits of molten copper flying around nearby.

What else could I make the insulator from? I doubt that Formica would
catch alight very quickly so I could machine it from that.
Or maybe concrete reinforced with fibreglass.
Or pottery.
Any other ideas?

On 8 Apr, 13:22, Matty F wrote:
I need to make an insulator that is subject to electrical arcing.
What else could I make the insulator from?
Any other ideas?

How about machinable glass-ceramic? Look up Macor.

Although it is flammable, perspex can also be good in this type of
application, because it does not suffer from surface tracking.
(Rather than carbonising, the surface layer just evaporates.)

John

On Apr 9, 12:33 am, John Walliker wrote:
On 8 Apr, 13:22, Matty F wrote:

I need to make an insulator that is subject to electrical arcing.
What else could I make the insulator from?
Any other ideas?

How about machinable glass-ceramic? Look up Macor.

That looks ideal thanks. There's even a warehouse a few miles away
selling it.

Although it is flammable, perspex can also be good in this type of
application, because it does not suffer from surface tracking.
(Rather than carbonising, the surface layer just evaporates.)

I'd rather not have anything that could feed a fire. Most of what's in
the picture that isn't metal is asbestos.

Matty F wrote:
I need to make an insulator that is subject to electrical arcing. The
100 year old originals appear to be machined from an asbestos compound
of some kind. I don't have any asbestos and I don't want to machine
asbestos anyway.
I've made an insulator from epoxy resin with loads of chopped
fibreglass in it. It's the middle one he
http://i40.tinypic.com/md35du.jpg

Asbestos panels fit into the slots.

Unfortunately I have discovered that I can set the epoxy alight after
a few seconds using a blowtorch, and that is no good. There is likely
to be arcing and bits of molten copper flying around nearby.

What else could I make the insulator from? I doubt that Formica would
catch alight very quickly so I could machine it from that.
Or maybe concrete reinforced with fibreglass.
Or pottery.
Any other ideas?
What is the machine?

On Apr 9, 12:40 am, Matty F wrote:
On Apr 9, 12:33 am, John Walliker wrote:

How about machinable glass-ceramic? Look up Macor.

That looks ideal thanks. There's even a warehouse a few miles away
selling it.

Macor is very expensive. 25x25x100mm is about GBP175 and they don't
have a bigger size.
If I used clay and fibreglass I could use the mould that I made for
the epoxy, then I won't even need to machine it.

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember Matty F
saying something like:


What else could I make the insulator from?

Find what one of these is flame-retardent.
http://en.wikipedia.org/wiki/Engineering_plastic

On Apr 9, 1:06 am, James Salisbury nntp.dsl.pipex.com wrote:
Matty F wrote:
I need to make an insulator that is subject to electrical arcing. The
100 year old originals appear to be machined from an asbestos compound
of some kind. I don't have any asbestos and I don't want to machine
asbestos anyway.
I've made an insulator from epoxy resin with loads of chopped
fibreglass in it. It's the middle one he
http://i40.tinypic.com/md35du.jpg

Asbestos panels fit into the slots.

Unfortunately I have discovered that I can set the epoxy alight after
a few seconds using a blowtorch, and that is no good. There is likely
to be arcing and bits of molten copper flying around nearby.

What else could I make the insulator from? I doubt that Formica would
catch alight very quickly so I could machine it from that.
Or maybe concrete reinforced with fibreglass.
Or pottery.
Any other ideas?

What is the machine?

It's a motor controller for a tram.

Here's one I prepared earlier!
http://i43.tinypic.com/n21jj4.jpg

Here's what that one looked like when I was given the job of putting
it together:
http://i43.tinypic.com/2w3ns7k.jpg

Start by sorting out all the bits:
http://i50.tinypic.com/34o3lfk.jpg

Matty F wrote:
I need to make an insulator that is subject to electrical arcing. The
100 year old originals appear to be machined from an asbestos compound
of some kind. I don't have any asbestos and I don't want to machine
asbestos anyway.
I've made an insulator from epoxy resin with loads of chopped
fibreglass in it. It's the middle one he
http://i40.tinypic.com/md35du.jpg

Asbestos panels fit into the slots.

Unfortunately I have discovered that I can set the epoxy alight after
a few seconds using a blowtorch, and that is no good. There is likely
to be arcing and bits of molten copper flying around nearby.

What else could I make the insulator from? I doubt that Formica would
catch alight very quickly so I could machine it from that.
Or maybe concrete reinforced with fibreglass.
Or pottery.
Any other ideas?

I would think you need to mould a ceramic material (clay?) and have it
fired and glazed like HT insulators.
Don

Matty F wrote:

I need to make an insulator that is subject to electrical arcing.

I've made an insulator from epoxy resin with loads of chopped
fibreglass in it.

Unfortunately I have discovered that I can set the epoxy alight after
a few seconds using a blowtorch, and that is no good. There is likely
to be arcing and bits of molten copper flying around nearby.

What else could I make the insulator from? I doubt that Formica would
catch alight very quickly so I could machine it from that.

I don't know about price or availability, but back when I had to
do this sort of thing professionally, Arclex is one of the
materials we used:
http://www.tenmat.com/Content/Arclex

Now that the mental mist is clearing, this may be the one we used
to line some tube train fuse boxes, and the machine shop went
through lots of tungsten-tipped tools trying to cut holes in it.

Nomex is quite popular

http://www.presspahn.com/Products/Nomex/Nomex.htm

Duratec looks interesting

http://www.promat.co.uk/UserFiles/fi...es/duratec.pdf

Chris
--
Chris J Dixon Nottingham UK


Have dancing shoes, will ceilidh.

Matty F wrote:
I need to make an insulator that is subject to electrical arcing. The
100 year old originals appear to be machined from an asbestos compound
of some kind. I don't have any asbestos and I don't want to machine
asbestos anyway.
I've made an insulator from epoxy resin with loads of chopped
fibreglass in it. It's the middle one he
http://i40.tinypic.com/md35du.jpg

Asbestos panels fit into the slots.

Unfortunately I have discovered that I can set the epoxy alight after
a few seconds using a blowtorch, and that is no good. There is likely
to be arcing and bits of molten copper flying around nearby.

What else could I make the insulator from? I doubt that Formica would
catch alight very quickly so I could machine it from that.
Or maybe concrete reinforced with fibreglass.
Or pottery.
Any other ideas?

Masterboard/multiboard. Its a gyspum and glass fibre composite IIRC.

Masterboard/multiboard. Its a gyspum and glass fibre composite IIRC.

I was just going to say that! I suspect that Aquapanel might be fire
resistant too. You can buy blocks of compressed vermiculite for making
brazing hearths, etc but they probably don't have the mechanical strength.

On 8 Apr, 13:22, Matty F wrote:
I need to make an insulator that is subject to electrical arcing.

Tufnol. The basic stuff is linen fabric with phenolic. Easy to
machine, well behaved. Tufnol themselves in the UK are also helpful
with advice.

2F/14 is the "electrical" grade, but this is mostly about permittivity
at frequencies far above trams care about. For general use they offer
many grades. If you need better self-extinguishing or low-fume
performance against fire, then they have other grades with glass fibre
reinforcement and epoxy.

Epoxy can be self-extinguishing, but you need good layup technique and
a vacuum rig to cure it. It's about getting a much better mat/resin
ratio.

100 years ago, it was probably slate. AFAIK manufactured asbestos
boards weren't good enough until the 1920s, owing to lack of suitable
resins. Personally I'd use offcuts of Marinite, which is industrial
switchgear panelling. Trespa works too.

"Matty F" wrote in message
...
On Apr 9, 12:40 am, Matty F wrote:
On Apr 9, 12:33 am, John Walliker wrote:

How about machinable glass-ceramic? Look up Macor.

That looks ideal thanks. There's even a warehouse a few miles away
selling it.

Macor is very expensive. 25x25x100mm is about GBP175 and they don't
have a bigger size.
If I used clay and fibreglass I could use the mould that I made for
the epoxy, then I won't even need to machine it.


Concrete moulds well but I don't know how well it resists arcing even when
dried out.

Matty F wrote:
I need to make an insulator that is subject to electrical arcing. The
100 year old originals appear to be machined from an asbestos compound
of some kind. I don't have any asbestos and I don't want to machine
asbestos anyway.
I've made an insulator from epoxy resin with loads of chopped
fibreglass in it. It's the middle one he
http://i40.tinypic.com/md35du.jpg

Asbestos panels fit into the slots.

Unfortunately I have discovered that I can set the epoxy alight after
a few seconds using a blowtorch, and that is no good. There is likely
to be arcing and bits of molten copper flying around nearby.

What else could I make the insulator from? I doubt that Formica would
catch alight very quickly so I could machine it from that.
Or maybe concrete reinforced with fibreglass.
Or pottery.
Any other ideas?

Don't personally know but it may be worthwhile asking a Tesla coil
enthusiast such as http://www.richieburnett.co.uk/tesla.shtml

On Apr 9, 5:17 am, Andy Dingley wrote:
On 8 Apr, 13:22, Matty F wrote:

I need to make an insulator that is subject to electrical arcing.

Tufnol. The basic stuff is linen fabric with phenolic. Easy to
machine, well behaved. Tufnol themselves in the UK are also helpful
with advice.

2F/14 is the "electrical" grade, but this is mostly about permittivity
at frequencies far above trams care about. For general use they offer
many grades. If you need better self-extinguishing or low-fume
performance against fire, then they have other grades with glass fibre
reinforcement and epoxy.

Epoxy can be self-extinguishing, but you need good layup technique and
a vacuum rig to cure it. It's about getting a much better mat/resin
ratio.

I suspect that I didn't get the mixture exact enough. It's a 1:5 ratio
which is hard to measure accurately in small quantities.
I've used epoxy before and it seemed reasonably fire resistant.

100 years ago, it was probably slate. AFAIK manufactured asbestos
boards weren't good enough until the 1920s, owing to lack of suitable
resins. Personally I'd use offcuts of Marinite, which is industrial
switchgear panelling. Trespa works too.

We have a box of similar material. It wasn't thick enough but I
imagine I could epoxy a couple of bits together and machine it.
I'll test what we have for fire resistance.
I'm in New Zealand so don't have easy access to odd materials.

On 8 Apr, 21:56, "Dave" wrote:

Don't personally know but it may be worthwhile asking a Tesla coil
enthusiast such ashttp://www.richieburnett.co.uk/tesla.shtml

Maybe for spark gap supports, but coilers usually care a lot about
permittivity and little about fire hazards. Mine's largely
polypropylene.