1. Study of solid lubrication with MoS2 coating in the presence
of additives
2. Space Applications Gassing under the vacuum High temperature
conditions Food and Textile industries Contamination of product 3.
Low, constant and controlled friction between the two surfaces.
Chemically stable and inert over the required temperature range.
Adhere strongly to one or both the surfaces. Sufficient resistance
to wear. Non toxic and economical. 4. Very low volatility. Chemical
inertness. Stable to radioactivity. Oxidises to molybdic oxide
(MoO3) at higher temperatures, a fair lubricant itself. Good load
carrying capacity (hexagonal layer-lattice structure). Doesnt
depend on presence of adsorbed vapors to act 5. VERTICAL SLIDE
Applies dead weight Mounts the load cell HORIZONTAL SLIDE
Scratching the specimen 3mm diameter steel ball bonded to holder
Material selected: EN8 steel of size 20 X 20 X 10mm thick Normal
Load applied: 30N Stroke length: 8mm Slider velocity: 2mm/s Test
conditions: Ambient temp. 20-35C, Humidity 50-90% Failure criteria:
Coefficient of friction > 0.2 Number of cycles v/s Friction
force plots are made for each sample 6. 1. Experiments were carried
out to study the dry friction characteristics of the rubbing
surfaces of steel specimen having roughness, Ra = 019m. The initial
coefficient of friction was around 013 and attained a value of 05
within 20 cycles. 2. Similar tests were conducted on the specimen
having Ra = 039m. The initial coefficient of friction was around
015 and attained a value of 05 within 20 cycles. RESULT: The
coefficient of friction between two steel surfaces is greater than
05 under non- lubricated conditions. TEST 1. Scratch test under dry
sliding conditions between steel specimen and steel ball 7. TEST 2.
Scratch test between MoS2 coated steel specimen and steel ball
Heating prepared specimen to around 80C (to evaporate the moisture)
Applying MoS2 by brush (2-3 coats) Heating and curing the specimen
at elevated temperature depending on composition
(additives,binders, etc.) Removing loose powder from surface
Burnishing the specimen for 15 minutes using ball tumbler Binding
Material: Sodium Silicate (Na2SiO3) 8. UNBURNISHED BURNISHED
Phosphate coating provides good base for lubrication. Being micro
porous, traps lubricant into interstices. Larger surface area for
lubricant. Excellent protection against corrosion. RESULT:
Unburnished specimen withstood 105 cycles. Burnished specimen (30
min) withstood 45 cycles. Poor adhesion between specimen and
lubricant. 9. TEST 3. Scratch test between phosphated steel
specimens coated with MoS2 and steel ball RESULT: In both the cases
above, wear rate was around 0.023 m/cycle. Unburnished specimen
withstood 250 cycles Burnished for 15 min., specimen withstood 300
cycles Zinc Phosphate base specimen Unburnished specimen withstood
190 cycles, Burnished for 15 min., specimen withstood 260 cycles.
Manganese Phosphate base specimen 10. TEST 4. Scratch test between
MoS2 coated phospated steel specimen with zirconia as an additive,
steel ball ZIRCONIA: Ceramic material which offers high resistance
to wear. Exists in both tetragonal and monoclinic crystal
structure. During scratching, metastable tetragonal converts into
monoclinic by strain induced structural transformation. More % of
tetragonal structure would give better result as lubricant RESULT:
In Mn-phosphate base, 8% zirconia as additive failed at 730 cycles,
wear rate brought down to 0.014 m/cycle. In Zn-phosphate base, 8%
zirconia as additive failed at 1400 cycles, wear rate brought down
to 0.014 m/cycle. Initial friction coefficient more than 0.1 in
each case. 11. TEST 5. Scratch test between MoS2 coated phosphated
steel specimen with zirconia and graphite as additives and steel
ballGRAPHITE: Good natural low-friction behavior when contaminated
with vapors. Good load bearing ability along with lubricating
action Reduces the friction value which was increased by additive
zirconia. RESULTS: On addition of 8% zirconia and 25%graphite;
Zn-phosphated specimen withstood 1250 cycles, with friction
crossing 0.1 after 600 cycles! Average wear rate was 0.01 m/cycle.
Mn-phosphated specimen withstood 12. Zinc Phosphate base specimen
containing zirconia 8% Zinc Phosphate base specimen containing
zirconia 8% and graphite 25% 13. TEST 6. HIGH TEMPERATURE SCRATCH
TESTS 1. Reciprocating Scratch test at 200C. Test carried for 5500
cycles Friction as low as 0.05 even after 5500 cycles. No sign of
failure, because all moisture has been evaporated. 2. Reciprocating
Scratch test after 90minutes of cooling to room temperature from
200C. Specimen withstood 3000 cycles. Sufficient time not given to
absorb moisture completely. 3. Reciprocating Scratch test after two
days of cooling to room temperature 200C. Specimen failed at 600
cycles. Result coherent with ambient conditions, as moisture had
been absorbed to saturation level. RESULT: Humidity affects the
adhesion component of friction and therefore the intercrystallite
forces, wear rate also increases as more moisture is absorbed. 14.
The addition of zirconia and graphite into the lubricant improves
its properties in terms of both friction and wear. The moisture
present in air also plays an important role in reducing friction
and wear rate. As the moisture reduces, coating performance of the
film is enhanced.
