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Our 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 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. Discuss your needs with our sales staff.
Two areas of concern are heat and contamination.
Heat from friction between the lead screw and nut cannot dissipate
into the surrounding area. This is of particular
concern for motor driven stages if 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 |
| UniSlide Delrin® AF drive nuts |
0.33 |
0.02 |
0.07 |
| Delrin® thrust bearings in all UniSlide Series A15 and some Series A25 |
0.28 |
0.02 |
0.13 |
| EC 2290 epoxy |
0.12 |
0.15 |
- |
| UHMW |
0.06 |
0.01 |
0 |
| 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.
Sources of contamination include Delrin drive nuts and thrust
bearings (UniSlide Series A15 and some A25 only).
For light or medium duty, all stages can be run without lead screw and dovetail way lubrication
which precludes contamination. We apply a small amount of vacuum compatible
lubricant (Fomblin® Y VAC3) to the thrust bearings. Please call us to discuss your
application. See table below for more substitutions and modifications.
| UniSlide Assembly Material Substitutions and Modifications |
| 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 |
| Knob |
A15, MA15, A25 |
Plastic/rubber |
Aluminum knob |
None |
| 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 |
| 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 |
| BiSlide Assembly Material Substitutions and Modifications |
| Component |
Standard Material |
Substitute material |
Modification |
| Drive nut |
PET |
None |
None |
| Bearing pads |
Rulon 123 bonded with adhesive |
Rulon J bonded with epoxy |
Use 3M 2290 Epoxy. GSFC3495 |
| Lubrication on lead screw and ways |
Silicone oil |
|
Omit all oils |
| Blind Holes |
Standard fasteners |
Use cap screws with hollow shaft |
Bleeder holes |
| Limits switches |
PVC insulated wire,plastic cable clamps |
none |
Omit |
| Thrust bearings |
Pre-greased needle bearings |
Vacuum grease |
Degrease & grease with vacuum compatible lubricant |
| Surface finish |
Black anodized |
Electroless
Nickel |
Replace with raw aluminum |
| XSlide Assembly Material Substitutions and Modifications |
| Component |
Standard Material |
Substitute material |
Modification |
| Drive nut |
Delrin |
Brass, Vespel |
None |
| Bearing pads |
Rulon 123 bonded with adhesive |
Rulon J bonded with epoxy |
Use 3M 2290 Epoxy. GSFC3495 |
| Lubrication on lead screw |
Silicone oil |
|
Omit all oils |
| Blind Holes |
Standard fasteners |
Use cap screws with hollow shaft |
Bleeder holes, |
| Limits switches |
PVC insulated wire, plastic cable clamps, glue, plastic switch |
none |
Omit |
| Thrust bearings |
Pre-greased needle bearings |
Vacuum grease |
Degrease & grease with vacuum compatible lubricant |
| Surface finish |
Black anodized |
Electroless
Nickel |
Replace with raw aluminum |
Linear Encoders in a vacuum application datasheet
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