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Bolting for aluminim plates

Bolting for aluminim plates

Bolting for aluminim plates

(OP)
I am using two thick aluminum (6061) plates to straighten and level a rail system inside a large vacuum chamber.  I am considering the use of stainless (300 series) steel bolts for the adjustment screws as well as the hold down bolts.  I am concerned about galling.  Do I need to use chrome plated fasteners, or can I use other techniques such as slow easy tightening to prevent galling?  I cannot use a lubricant because of the vacuum.

RE: Bolting for aluminim plates

Aluminum thread fastening is pretty much a one
shot deal, Moisture, (just humid air) causes
electrolysis between dissimilar metals.
I would recomend stainless thread inserts,
NOt heli-coils, for your application.

RE: Bolting for aluminim plates

(OP)
The SS inserts I found were 303 SS but they were passivated.  Will there be galling problems with 303SS bolts?  I need to use nonmagnetic bolting because in some situations a strong magnetic field is used in the sample area in the front of the vessel.  The vessel will be under dry conditions (vacuum) 95% of the time.   

RE: Bolting for aluminim plates

You may want to look into Xylan coating (PTFE based coating)of the fasteners.  As long as PTFE (teflon) does not outgas beyond your limitations, they should be OK.  This coating is used on many thousands of bolts, nuts, and studs in the chemical and refinery industry.

RE: Bolting for aluminim plates

Use the 300 series bolts and change the hardness of the nuts or add inserts (A286 ect.).

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