Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
Figure 3. Friction data for 5W30 ACEA C3 reference oil and top-treated reference oil
MoDTC at a treat-rate of 1% resulted in >50% reduction in friction but this was accompanied by a very significant increase in wear and transfer of the a-C:H15 DLC coating from the plate to the pin (figure 4).
No.110 page 2
1.2 Influence of MoDTC and PFMs on Wear Profile The 5W30 reference oil, without any top-treatment of friction modifiers showed wear on the cast iron pin (22 x 10m-18 but no observable wear on the a-C:H15 DLC plate (figure 6).
m3
/NM)
Figure 6. Pin and plate wear for cast iron - aC:H15 DLC plate reciprocating – sliding contact
PFMs when top-treated into the 5W30 ACEA C3 engine oil provided wear protection to the cast iron pin. At 1% treat-rate the wear on the cast iron pin was reduced by approximately 50% (11 x 10m-18
m3
Figure 4. Transfer of a-C:H15 DLC coating from plate to pin for MoDTC containing oils
Combinations of PFM with MoDTC resulted in the same final friction coefficient but the PFM interfered with the friction in the early stages of the test. Whilst the overall friction profile was not as good as MoDTC alone, including PFM in the formulation significantly reduced wear and eliminated the transfer of a-C:H15 DLC from the plate to the pin (figure 5).
/NM). The a-C:H15 DLC plate remained wear free as far as was observable under these test conditions.
Including MoDTC as a friction modifier in the 5W30 ACEA C3 engine oil resulted in wear taking place on the a-C:H15 DLC disc. The wear rate is a function of MoDTC concentration, with 1% producing very high levels of wear (68 x 10m-18
m3 m3 /NM) on
the a-C:H15 DLC plate and similar wear rates on the cast iron pin (20 x 10m-18 fluid.
/NM), when compared to the 5W30 reference
The inclusion of 1% PFM into the reference oil also containing 1% MoDTC prevented the transfer of a-C:H15 DLC coating from the plate to the cast iron pin. This combination also resulted in a very significant reduction in wear on both the pin (12 x 10m-18
m3 /NM) and the a-C:H15 DLC plate (7 x 10m-18 m3 /NM)
when compared to the 5W30 oil containing MoDTC. It must be noted that even with the inclusion of PFM it was not possible under these conditions to completely eliminate the wear on the a-C:H15 DLC plate due to the presence of MoDTC.
Figure 5. No transfer of coating from a-C:H15 plate to pin for PFM containing oils
34 LUBE MAGAZINE NO.139 JUNE 2017
2. Croda In-House MTM Testing (Steel disc – DLC ball) In a parallel project, the effectiveness of PFMs on two other types of DLC was investigated. The structure and composition of the two types of DLC used are summarised in table 1.
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