nonmagnetic/electrically nonconductive/low outgassing

[Trix4kids]

Hi,

I was looking for the right materials for a rack/pinion design to open a door. Here are some constraints.
Temp=160F
Pressure=10^-6Torr
all parts must be low outgassing, nonmagnetic and electrically nonconductive.

I thought of using aluminum for the door/rack/pinion since it is nonmagnetic. I then planned on using a class II anodize on the aluminum to make it nonconductive. However the anodizing will cause high outgassing which is not allowed. I am unsure exactly what other nonmetals would work under these conditions. I do know of nylon gears, however I understand nylon becomes brittle at high temperatures.

Any suggestions would be GREATLY appreciated.

Frank

 

[NickE]

Maybe teflon (not sure bout the out gassing/volatiles thou) other plastics, maybe even bakelite or other filled phenolic, or even an aramid strengthened epoxy. These should all give you your temperature performance. I'm not too sure bout outgassing since Ive only worried with SEM samples and we usually coated the non-metallics under vaccumn helping to remove the volatiles etc before being put into the airlock of the scope.

Can you "bake out" your parts after production, hold at 200F and subject to the low pressure for a few days?

nick

 

[Maui]

Why not use a ceramic coating on a 300 series stainless steel? It would be non-magnetic, non-conductive, and would not outgas. And, if designed properly, it would have the mechanical strength for your application.


Maui

 

[TVP]

The concern with nylon at high temperature is more related to the limiting pressure on the gear surface, since the strength/stiffness decreases with temperature. I am not a plastic gear expert, but there are a number of heat-stabilized nylons available that should be able to perform adequately at ~ 70 C (160 F). I would discuss this further with someone from DuPont, Bayer, DSM, etc.

 

[Trix4kids]

Maui,
Do you know what that would cost and what companies can do that? I was thinking of using Delrin, though I am unsure if it can handle the low pressure. I am almost positive it is low outgassing.

 

[Trix4kids]

I have found some gears made from DURACON (M25-44). Does anyone know if they will survive the temp and press and if they are low outgassing?

 

[TVP]

Duracon is another type of acetal/POM similar to Delrin or Celcon. Nylon has better heat resistance than acetal.

 

[Trix4kids]

Is there a way to make a C1018 steel gear rack nonmagnetic? I have tested aluminum in the chamber and the fact that it is conductive has not affected the process. Therefore, the material I am looking for no longer has to be electrically nonconductive, only nonmagnetic.

 

[123Cat]

Macor the machinable ceramic ,,, although it is brittle
Or Pyrofolite , easy to machine, then baked hard

123cat

 

[123Cat]

Then its 304SS Trix
123Cat

 

[RichLeimbach]

If the material does not have to be non-conductive anymore, just non-magnetic, why not use a non-magnetic stainless steel (maybe 304) ?

 

[Trix4kids]

Thanks guys. Now I am looking for 304 stainless or aluminum gears with a max height of 3/8" for the rack but none of the gear companies have responded. I received a quote from rush gears for close to $2000 for a 6ft length using aluminum!!

 

[Trix4kids]

Anyone know if a 3/8x3/8x40" brass rack will outgass at T=160F and P=10^-6Torr

 

[EnglishMuffin]

Once upon a time when I worked in the vacuum field, we used to have things electroless nickel plated to prevent outgassing. That way you can just use standard components and have them plated. But I don't know how well it stands up from a wear perspective.

 

[Trix4kids]

Unfortunately, the budget of this project won't allow the high prices of electroless nickel plating. But I did think of that option. That size brass rack was quoted at $250 for plating.

 

[EnglishMuffin]

Well, it still might be cost effective if by so doing you can use off the shelf stuff. Just a thought.

 

[Trix4kids]

Thanks. You have a point.

 

[kenvlach]

Trix4kids,
Agree with choice of either 304 SS or an Al alloy. EN plating would provide wear & galling resistance.

Advise getting more competitive bids on the EN plating. If no masking and an easy-to-plate substrate (i.e., not free-machining leaded crap), 0.001" of mid-phos EN runs $0.10/sq. inch in my area. [However, your job would be a minimum lot charge of $75]. Surcharges for lengths more than 5 ft and for baking (advisable for gearing).

Lots of machine shops are looking for work. $2000 is outrageous unless there is some geometry I don't understand. What do you mean by a 3/8" high x 6 ft long gear (or is this the rack?).

 

[Trix4kids]

Yes that is the rack with a thickness of 3/8" and length of 6'. I have searched hard for aluminum and nonmagnetic stainless racks but they are all custom jobs with high pricing. Mcmaster does sell the size but only in brass and magnetic stainless. The brass rack is about $50.

 

[hacksaw]

anodized Al is fine for 10(-6) torr, but it has to be done right.

the cheap/quick anodizing processes produce a thick and porous film, but the modern solutions leave a uniform hard film that is abs. okay.

304 ss is non-magnetic until you machine it otherwise cold work.

you can reduce the need for non conductive materials if you incorporate insulating bushings or washers in your design