On the friction and wear performance of boric acid lubricant combinations in extended duration operations
Department of Mechanical Engineering, University of Pittsburgh
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B]4.4. Transmission fluid with boric acid[/B]
Based on the poor results of the boric acid experiments, the solid lubricant material was physically dissolved without the use of dispersant (5% weight) with the transmission fluid to establish its potential use as an additive in liquid lubricants.
As shown in Figs. 5 and 6, this lubricant combination was found to provide the excellent friction and wear properties as the friction actually decreased over a significant portion of the testing period.
Specifically, as depicted in Fig. 6, the transmission fluid and boric acid had an initial coefficient of friction of 0.08.
This coefficient value gradually decreased to a value of 0.062 at the completion of the sliding experiments, which was 40% less than that obtained in the transmission fluid only experiments.
The comparatively higher initial coefficient of friction values for the transmission fluid and boric acid combination were most likely due to the fact that the boric acid crystals were not evenly distributed within the transmission fluid at the start of experiments.
As shown in Fig. 6, however, it appears that the boric acid became evenly disbursed within the fluid after approximately 100 m of sliding.
Once evenly distributed, the lubricant combination was able to provide a continuous hydrodynamic lift and a low shear resistance within the contact interface to function as an excellent lubricant.
Unlike the independent transmission fluid and boric acid cases, the complimentary properties of the lubricant combination allowed it to withstand significant degradation over time.
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Considering the dispersion of the boric acid crystals, the surface tension properties of the transmission fluid help constrain the boric acid powder so that it did not move outside of the contact region.
Likewise, the addition of the solid boric acid particulates into the fluid increased its viscosity, which decreased its displacement outside of the contact interface, reducing its degradation over time.
Hence, placing the boric acid within the transmission fluid allows the system to gain the beneficial properties of both lubricants over the entire testing period.
Along with having the lowest frictional values, the combined boric acid and transmission fluid case also had the best wear resistance of the initial lubricants tested.
In both the profile of the wear track of the disk (Table 1) and the measured wear volume
of pin (Fig. 5 and Table 2), the lubricant combination demonstrated excellent wear behavior.
Considering the profile of the disk wear track, the average (0.162 m) and RMS (0.222 m) surface roughness profile values were the lowest recorded in the
experiments.
This demonstrates that the wear track generated in the presence of the combined lubricant was the most uniform among all the samples tested.
As illustrated in Fig. 9, the low roughness values indicate as the disk asperities were plastically deformed and rounded rather than being sheared-off to form valleys. Considering the wear on the pin, both Fig. 5 and Table 2 indicate that excellent wear resistance was achieved by the combined lubricant.
In fact, the measured wear rate at the completion of the experiments was three times less than that of the transmission fluid alone.
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Lots of pictures and graphs to be seen here.
My findings after adding BA to gearboxes:
It worked extremely well.
A, difficult to describe, smoothness due to less vibration and less resistance to gear changing could be felt.
HOWEVER:
Gearboxes rely on syncromeshes (friction clutches) between each gear to get them spinning at the same rate before the gear is engaged, so that they don't grate when the gear is engaged.
These syncromeshes became way less effective due to the dramatic reduction in friction they rely on.
This meant that I had to hold the gear lever against that initial resistance one feels just before the the gear slips into place for much longer.
I put too much in the 1st gearbox I treated, making it close to unusable.
Draining and replacing the gear oil had no, to very little effect.
We opened the gearbox and used valve grinding paste on the syncros.
Then a thorough clean with cloths and a wash out with diesel and much hand turning of the gearbox in each gear.
This fixed it while retaining the said 'smoothness'.
Subsequent gearboxes were treated with way less BA.
IIRC around 2 teaspoons full of powder dissolved in very little water so that around one teaspoon of powder remained undissolved.
Differentials:
Differentials react very well to adding around the same dose as mentioned above IIRC, with a complete cancellation of diff whine in one case.
It took way longer to kick in. A day or 3 IIRC, vs 10 km in engines.
Limited slip differentials, that again rely on friction to limit slip, became waaay less limited...