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  Engineering Info

UniSlides patented dovetail bearings give it certain advantages over other designs. They have been used in a myriad number of environments from outer space to vacuum chambers. The necessity for modification depends upon the so-called hardness of the vacuum and other specific requirements. Velmex can supply assemblies that are free of grease and oils. However, for critical applications the assemblies should be cycled in an outgassing chamber to remove residual contamination.

Two areas of concern are heat and contamination. Heat from friction between the lead screw and nut cannot dissipate into the surrounding area. With motor driven units, this is of particular concern when the lead screw RPMs are high and the unit is in continuous operation. Substituting with a brass or Vespel drive nut may be necessary. In addition, motor induced heat can also be a problem.

Outgassing Data

Material % TML % CVCM % WVR
Rulon 123® (bearing pads) 0.00 0.00 0.01
Delrin® drive nuts 0.33 0.02 0.07
Delrin® thrust bearings in all Series A15 and some Series A25 0.28 0.02 0.13
EC 2290 epoxy 0.12 0.15 -
Vespel ® drive nuts 1.09 0.00 0.38
* Data from NASA Reference Publication 1124, rev. 3, 1993, Outgassing Data for Selecting Spacecraft Material.

Contamination is another issue. The table above lists outgassing characteristics of Rulon PTFE (data sheet) and Delrin. Rulon bearing pads are attached with a thin layer adhesive which is oven cured for 90 minutes at 325 degrees Fahrenheit. The amount of material used is small and the bake out helps to minimize outgassing.

Other sources of contamination include Delrin drive nuts and
thrust bearings (Series A15 and some A25 only). For light or medium duty, UniSlides can be run without lubrication which precludes contamination. We can also apply any vacuum compatible lubricants which you supply to us. Please call us to discuss your application. See table below for more substitutions and modifications.

 

Velmex Material Substitutions and Modifications to Reduce Contamination
Component UniSlide Series Standard Material Substitute material Modification
         
Drive nut All Delrin Brass, Vespel Substitute
         
Bearing pads A60 Rulon PTFE bonded with adhesive UHMW, Vespel Secured with screws, not adhesive. Show me
Bearing pads All Rulon 123 bonded with adhesive Rulon J bonded with epoxy Use 3M 2290 Epoxy. GSFC3495
Lubrication on lead screw and ways All Lithium grease Vacuum compatible lubricant Omit all grease. Substitute your lube
Blind Holes All Standard fasteners   Bleeder holes, Use cap screws with hollow shaft
Scales Graduated knob and Scale and Vernier Models Normally fixed with adhesive Fasten with screws Omit adhesive
Thrust bearings A15, MA15, some A25 Delrin none Use A25 Series with SS Ball bearing
Thrust bearings All except the above Pre-greased Radial, Steel BB   Degrease radial ball bearings
         
Knob A15, MA15, A25 Plastic/rubber Aluminum knob None
Engraved Knobs Graduated Wax filler in engraved lines and numbers -- Omit
Surface finish All None Electroless Nickel None
  All None Black None
Motor All Motor Driven Standard Motors Vacuum compatible motors None

 

 

 
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