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Basics 4: Cleaning Materials and Components for Vacuum Use

Last update February 16, 2001

Introduction
Reference:
B.S. Halliday Cleaning Materials and Components for Vacuum Use Vacuum /volume 37/ numbers 8/9/pages 587 to 591/1987

This article is a pale imitation of the B.S. Halliday paper and mainly concerns the cleaning of a properly designed vacuum system that has been dismantled for cleaning. You did make a sketch of where all the pieces go before taking it apart,didn't you?

Oils,greases,flux residue,and assorted crud will evolve or desorb gases into the vacuum system degrading system performance to the point of unusability in some cases. Mechanical and chemical cleaning will be required,methods will depend upon the degree of vacuum required .

Solvents

Good housekeeping is essential at all times: A clean work area, proper ventilation /protection from toxic or corrosive vapours, correct storage of solvents,and adequate training to handle the chemicals involved are absolute necessities. Solvents must be kept clean and used solvents stored safely for re-cycling. Be sure solvents used are compatible with materials in the vacuum system and that all rubber o-rings,gaskets,etc. have been removed and that replacements are on hand.

Trichloroethane and trichloroethylene are sometimes used for some types of vapour degreasing operations. Freshly machined aluminum can react violently with either solvent so they should never be used without expert advice. Cole-Parmer have a very handy chemical compatibility engine on their web page which may be useful in this sort of situation.

Acetone and Toluene are solvents commonly used for the cleaning of vacuum system parts. Both are toxic and highly flammable. Neoprene gloves and a fume cabinet are de-rigeur for either one and MSDS sheets should not be taken lightly. Vermont Safety Information Resources,Inc. have MSDS and other safety data available.

If you are in a dry,prairie winter climate such as ours, some precautions against static electricity discharges should also be taken.

Non toxic solvents have come on the market in recent years - some of them are also non-flammable and are highly recommended as an alternative to Acetone for degreasing. We have had pretty good luck here with LPS Precision Clean, a product available through local electronics jobbers,for initial de-greasing followed by a soap and water rinse.

The local Cardinal Industrial Electronics people recently sent me a sample of Chemtronics Pow-R-Wash, a non flammable brush clean system intended as an Electrical and Electronics cleaner. I filled an old,oil soaked Pirani gauge tube with Pow-R-Wash and let it soak overnight,then rinsed and dried the gauge. Oil deposits came off the glass easily, so this stuff may be worth a try. Pow-R-Wash evaporates quite rapidly and the manufacturer claims it leaves no residue.

The Kurt J. Lesker Company have also sold non toxic vacuum system solvents in the past.

Envirosense Environmentally preferred products link

One important thing to remember with all solvents is that they require some time to work, a quick slosh will usually lead to disappointing results.

Cleaning Procedures:

Follow the steps in the order below to the degree of vacuum required. Drying should ideally be done in a vacuum furnace, otherwise a flow of clean, warm air from a heat gun may be used in most cases.

Getting Started

Procedures in this section are mainly for stuff that has come through a machine-shop procedure or for baked on crud on something like a diffusion pump.

Removal of gross contamination:cutting oils,flux,etc. Scraping,brushing and wiping,and grease removal. Abrasive blasting followed by a water rinse.

O RINGS

O rings should be cleaned by simply wiping with a lint free,disposable industrial wiping tissue. If there is any doubt about the condition of an o ring,replacement is probably your best option. Never use volatile solvents on O rings-the rubber will absorb the solvent and it will outgas into your system as well as deteriorate the o ring material. O ring grooves and mating surfaces may be cleaned with acetone or other solvents but be sure to wipe them clean and inspect them carefully before re-assembly.

An O RING SIZE CHART is included here as an aid to finding the correct size of replacement O ring. Make sure the O ring compounds resistant to all the media with which it will come in contact and is rated for the expected temperature range. The "Parker O-ring Sizes and Compound Reference Guide" ORD 5703 is a good source of information that you should be able to obtain locally.

New O rings may be lubricated with a thin film of vacuum grease or in some cases water. The idea here is to just make them slippery enough to move into position.

Have a look at the Orbiter Manufacturing and Assembly page for some really fancy O ring problems and solutions.

Rough Vacuum (A to 10e-03 mbar)

Simple degrease with solvent rinse,swabbing,or immersion.
For rough vacuum a tap water rinse followed by drying and installation may be done at this point.Otherwise skip the rinse and continue to the next step.

Medium Vacuum (10e-03 to 10e-06 mbar)

Vapour degrease (If you have one),otherwise a clean solvent rinse.
For Medium vacuum a tap water rinse ,then a di water rise followed by drying and installation may be done at this point.For higher vacuum skip the rinses and continue.

High Vacuum (10E-06 to 10E-08 mbar)

Electro polish. (If required)
Detergent/soak cleaner immersion with ultrasonic agitation.
Tap water rinse.
Deionized water rinse.
Dry
Install. For ultra-high vacuum skip the 200 degree C. bake and continue.
Bake out at 200 degrees C. in vacuum.

Ultra High Vacuum (Below 10e-08 Mbar)

Bake out in Situ at 200-400 Degrees C. under vacuum.
Glow Discharge Clean. (Only once!)
Operational Use may cause further outgassing.
Some more up to date data can be found in the Glow Discharge/Plasma Cleaning Links

Copy from Basic Vacuum Technology Resources

 

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