This is my first post to this list. Let's see if it works.

I have a vacuum chamber, which pulls needed vacuum for aluminizing,
so I am now at stage of needing to get electrodes into the stainless
steel chamber. James Learch already offered some ideas, and I was
hoping to see if there were others as well. I would be happy to
know of specific electrodes used and how they were inserted into
the chamber.

Along same line, anyone know if Tungsten is really required? Can I
now instead use something like Kanthal wire or perhaps a car cigarette
lighter heating element, etc? This seems more convenient.

I'll now wait and see if this gets distributed to the members.

Dominic-Luc Webb

Greetings

I have NO experience with vacuum coating - but I would think that your
car cigarette lighter element would more likely be a nichrome type of
wire. From the Kanthal website it is rated to 1450 degrees C and
nichrome may be rated higher (but I doubt it) whereas tungsten is rated
at over 3400 degrees C - I know which one I would be using!

Darald

Tungsten is strong for its thickness, but generally is very, very
thin, as in light bulbs. However, the nichrome and kanthal wires
are commonly much thick so are quite strong. Reduced form of
aluminum goes to melts at slightly above 500 degrees. It is
not clear to me that the temperature ratings you mention are
the determining factor in choice. I rather like the strength of
highly re-usable things like car cigarette lighters and kanthal
wires.

Perhaps there are specific tungsten electrodes one would suggest?

Perhaps someone knows there is in fact a reason to not use these
other options?


Dominic-Luc Webb

On Monday, December 8, 2003, at 07:31 AM, Dominic-Luc Webb wrote:

Tungsten is strong for its thickness, but generally is very, very
thin, as in light bulbs.

Try TIG welding electrodes.

However, the nichrome and kanthal wires
are commonly much thick so are quite strong. Reduced form of
aluminum goes to melts at slightly above 500 degrees. It is
not clear to me that the temperature ratings you mention are
the determining factor in choice. I rather like the strength of
highly re-usable things like car cigarette lighters and kanthal
wires.

Perhaps there are specific tungsten electrodes one would suggest?

Perhaps someone knows there is in fact a reason to not use these
other options?

The issue is whether one wishes to evaporate pure aluminum, or also
evaporate aluminum and some of your heating element with it, contaminating
your mirror coating. Tungsten's extremely low vapor pressure even at
high temperatures makes this very unlikely. The same cannot be said
for Nichrome. I don't know what is in Kanthal and I'm too lazy to
Google for it, but I do know you don't want to sputter your mirror
with nickel (an ingredient of nichrome).

On Mon, 8 Dec 2003, Gomez wrote:

Try TIG welding electrodes.

Not knowing welding, are all TIG electrodes tungsten, or should
I ask for a specific type?

Dominic-Luc Webb

--- In VacuumX@..., Dominic-Luc Webb <dlwebb@c...> wrote:

On Mon, 8 Dec 2003, Gomez wrote:

Try TIG welding electrodes.

Not knowing welding, are all TIG electrodes tungsten, or should
I ask for a specific type?

I think that if have decided to wind your own W filaments - you
would be better off buying wire from www.smallparts.com as recently
posted.

Now about welding rods. Your welding supplier will carry all sorts
of TIG welding electrodes. Typically the pure tungsten rods will
have a green end (paint), and are used for TIG welding aluminum.
Other types are 2% thoriated as well as types including other rare
earch alloying ingredients. These ingredients increase electron
emission during the welding proces, but are probably not wanted for
evaporation.

Last time I bought abox of 0.020 inch rods price was about $12 for
10 rods. 6 inches long. As someone has pointed out they are
brittle unless properly warmed.

I would think that bulk wire purchased from smallparts would't have
this problem (but I could be wrong).

Lesker.com carries all sizes and shapes of pre-spiraled tungsten
filaments.
-Bill

Dominic-Luc Webb

On Monday, December 8, 2003, at 11:29 AM, Dominic-Luc Webb wrote:

On Mon, 8 Dec 2003, Gomez wrote:

Try TIG welding electrodes.

Not knowing welding, are all TIG electrodes tungsten, or should
I ask for a specific type?

So far as I know, they are all Tungsten. Some are alloyed with a small amount of Thorium, which makes the arc easier to start. I assume we don't want that.

开云体育

Greetings

I have NO experience with vacuum coating - but I would think that your
car cigarette lighter element would more likely be a nichrome type of
wire. From the Kanthal website it is rated to 1450 degrees C and
nichrome may be rated higher (but I doubt it) whereas tungsten is rated
at over 3400 degrees C - I know which one I would be using!

Darald


On Mon, 2003-12-08 at 03:38, Dominic-Luc Webb wrote:
> This is my first post to this list. Let's see if it works.
>
> I have a vacuum chamber, which pulls needed vacuum for aluminizing,
> so I am now at stage of needing to get electrodes into the stainless
> steel chamber. James Learch already offered some ideas, and I was
> hoping to see if there were others as well. I would be happy to
> know of specific electrodes used and how they were inserted into
> the chamber.
>
> Along same line, anyone know if Tungsten is really required? Can I
> now instead use something like Kanthal wire or perhaps a car cigarette
> lighter heating element, etc? This seems more convenient.
>
> I'll now wait and see if this gets distributed to the members.
>
> Dominic-Luc Webb
>
>
>
>
>
> To unsubscribe from this group, send an email to:
> VacuumX-unsubscribe@...
>
>?
>
> Your use of Yahoo! Groups is subject to
>
>



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On Mon, 8 Dec 2003, Gomez wrote:

Not knowing welding, are all TIG electrodes tungsten, or should
I ask for a specific type?

So far as I know, they are all Tungsten. Some are alloyed with a
small amount of Thorium, which makes the arc easier to start. I assume
we don't want that.

OK, I looked around on the Net and did some quick learning about TIG
electrodes. As one member already suggested, green does appear the
best choice, being essentially pure tungsten (99.97%). This type has
letter symbol designations such W, WP, YWP and EWP, but all are color
coded green. Other types have small traces of La, Th, Zr or Ce and
have their respective character designations indicate the added metal,
like EWCe or EWLa, etc. Even these are 97-99.3 tungsten.

Interestingly, while TIG electrodes seem to be more expensive over here
in Sweden (5 USD each), they are a lot longer, typically 300 mm, about
12" US units.

Here is the link to a place that has a decent-looking table of codes
and compositions for TIG electrodes:




Dominic-Luc Webb