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 Post subject: Hello
PostPosted: Mon Jan 07, 2019 5:51 am 
recent arrival

Joined: Mon Sep 24, 2018 4:43 am
Posts: 2
Although there's a plethora of data that allows a vacuum practitioner to model a vacuum system's expected performance in terms of pumpdown, ultimate vacuum, and total outgassing rate, there's still a point where practical anarchy exists. Since all the various data sets that have been so carefully measured are only useful within envelopes of specific parameters that can be defined, we still have to consider that every practical vacuum system will have points in its history where those parameters cannot be related clearly to the conditions within the system.

Those points are several; a new system, a newly cleaned system, or a system taken out of storage, and many others. Chambers, under these stages must be considered to be in an "unconditioned" state that will require that they be placed into a "conditioned" state before their performance parameters can hope to match those in the literature.

When the entire system is conditioned, the gas load encountered by the high vacuum pump will be within the parameters found in the literature for the materials' outgassing rates. This, then, is the goal that needs to be achieved in order to place a system into operation for its intended application. There are many techniques that can help us achieve that goal.

Elastomer O-rings are a good example. New Viton O-rings are loaded with water that was synthesized internally during manufacture and other components of varying degrees of volatility such as solvents, mold release agents, and unreacted monomers. These can be removed from the O-rings before installation by the simple expedient of a 150[degrees] C vacuum bake. This should be a standard procedure for new O-rings and older ones that have been exposed to contaminants. Even though they will acquire further water vapor during subsequent air exposure, you can consider them to be conditioned to a standard performance state.

To bake or not to bake

Methods of dealing with the surface and subsurface contamination of the chamber material will depend upon the ultimate vacuum required, the application, and the system itself. Bakeout of the chamber to volatilize water and hydrocarbon residues would be an obvious expectation. If the chamber is a bakeable, metal-gasketed ultrahigh vacuum (UHV) system, baking the system, especially into the roughing pump, would be standard procedure.

Flushing the chamber with hot gas, such as nitrogen ([N.sub.2]) can be effective in removing surface contaminants. If the [N.sub.2] is passed through a clean gas heater (commercially available) and allowed to flow slowly through the chamber for maybe 1/4-1/2 hour, contaminants will be entrained in the flow and carried out through a small exhaust port into the air. Time and temperature parameters need to be worked out for each system. This technique, though effective to some extent, is only a partial solution for high vacuum systems.

Internal light bulb techniques

Drawbacks to this technique are avoiding cold spots and driving volatilized hydrocarbons into the high vacuum pump along with temperature limitations in O-ring systems.

In the end

Since any new or newly cleaned vacuum chamber will require conditioning before being put into routine operation, there are a number of choices of effective techniques to speed the process. The technique or techniques chosen will depend upon the system, its condition, and the process to be carried out, so careful consideration of technique and needs is required for a successful result.
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Last edited by sage12 on Fri Mar 08, 2019 1:22 pm, edited 1 time in total.

 Post subject: Re: Hello
PostPosted: Mon Jan 07, 2019 8:27 am 
lord high faltbotmeister
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Joined: Thu Sep 06, 2007 8:05 am
Posts: 880
Location: atlanta, georgia
Welcome sage12, glad to have you on board. Sounds like you will be able to lend a unique perspective to the group, looking forward to it!
Now you just need to get yourself a folder or two, or three.


"There is nothing--absolutely nothing--half so much worth doing as simply messing around in boats"

1988 A1 Expedition
2010 carbon Klepper Quattro
BSD sail rig, 24' mizzen + 36' main
39' jib
Torqeedo outboard
1938 Sachs-Fichtel seitenbordmotor

 Post subject: Re: Hello
PostPosted: Mon Jan 07, 2019 11:04 am 

Joined: Mon Jul 10, 2017 3:08 pm
Posts: 227
Welcome aboard, Looking forward to hearing more.

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