Lube-Tech
rotational speed, the centrifugal force can now be precisely determined, at which acceleration force the drops are moving. At that point the adhesion force must be overcome respectively.
To allow for easy comparative evaluation of series tests independent of the mass of the drops, the so called transition factor is calculated, which is the normal acceleration when drops start to move, divided by the specific gravity: transit an = an/g.
The movement of the drops can be determined optically. If olephobic coatings with high concentration are tested, the droplets move in total (Figure 6), the red dots represent the initial position of the drops. If uncoated surfaces are tested, the droplets leave traces of smaller drops (Figure 7).
PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
No.117 page 4 Test Plan and Results
The test plan for the comparative assessment comprised three base oils used as lubricants in fine mechanics, a polyalphaolefin (surface tension =30 mN/m), an ester oil (=32 mN/m), and a silicone oil (=21 mN/m). The materials used are glass with
surface roughnesses “smooth” (Ra 0,04µm, Rz 0,45µm) and “rough” (Ra 0,91µm, Rz 7,91µm), a polyamide 66, a polybutylenetherephtalate and a polyacetale.
In addition, the influence of an oleophobic surface coating in varying concentrations (10-high, 50-medium high, 200-medium, 500-low) as used in forlife lubricated fine precision components on the adhesiveness of the lubricants has been tested. Drop volumes varied from 0.2 to 1.5µl (Figure 8).
Figure 8. Varying drop volumes for adhesion tests
Figure 6. Transition point of droplets on oleophobic surfaces
Figure 9. Influence of surface roughness on transit factor Figure 7. Transition point of droplets on non-coated surfaces
The influence of surface roughness and concentration of oleophobic layers on the transit factor of silicone oil on glass is given in Figure 9.
LUBE MAGAZINE NO.146 AUGUST 2018 33
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64
