Continued from page 7
This demonstrates the flexibility of the grease; one product can be used in many areas, consolidating stock and making lubrication tasks a lot simpler.
The prototype grease was very well received by the end user, and showed significant benefits in costs, grease consumption and equipment availability.
Consumption Reduction: Figure 1
The specification target for wet roll stability was initially set at +/- 10.0% penetration change; however, this showed little differentiation between most of the benchmarked lubricants. Only the Castrol product achieved results of less than +/- 2.0% change in all three process waters, a marked improvement on existing greases and a good indication of the lubricant’s readiness for live trials.
Using the evaluation data in comparison with the performance of the previous grease, it was possible to reduce grease consumption by 50%. Further reductions are possible, but the centralised grease system is not flexible enough to further optimise grease consumption without damaging some of the critical components lubricated by the system.
The end user is happy to stay with a 50% reduction until the lubrication system is overhauled.
Significant consumption reductions are also possible as the grease no longer needs to be pumped through the lubrication system pipe work at the same rate; there is no danger of the grease blocking the pipe work leading to lubricant starvation of the bearings.
Picture 1 shows the condition of the grease inside a bearing housing before cleaning ready for inspection; no signs of hydrolisation or other issues are present.
Figure 3
Corrosion performance was benchmarked using the Rust test, ASTM D1743. This is seen as a harder test to pass compared to the more common Emcor corrosion test; considering the harsh environments of a steel plant, the Rust test is more appropriate.
All benchmarked products passed with tap water, but with process water some of the products did not perform satisfactorily.
Although the grease consumption has been significantly reduced at the start of the trial, a generous amount of grease still remains in the bearing 12 months later. This indicates excellent mechanical stability, advanced water resistance and extremely good tackiness to keep the grease in place.
Operator Acceptance: Feedback from the operators has been useful in areas where issues were previously known to occur. In the walking beam area, the plain metal bearings of the pivots used to be very noisy. This was due to metal on metal contact at high temperatures and very low speeds. After using the prototype product, no noises were heard. During the final inspection after 12 months trial, the end user confirmed that the prototype grease had prevented damage within these critical bearings, as well as halting any damage caused by using the previous grease (not all components were changed for the trial period).
High Temperature Performance: Figure 4
Summary of benchmarking tests Summarized we can say that all tested products fulfilled the initial target specification with tap water but the picture changes dramatically if process water is used. Some of the tested products (including the newly developed Castrol product) performed better than expected, so the initial specifications could be tightened to produce results that can give confidence when applying some greases to components in extreme environmental conditions.
With the laboratory based testing complete, a field trial could commence in the area of a continuous caster.
Field Trial Castrol has closely followed a trial for 12 months in the process downstream of the curved section of a six strand billet caster. This covers the extractors, straightener section, run out table to cutting torches, run out table to cooling bed, lifters, cooling bed, walking bed pivots and transfer car.
On two occasions during the trial period, pipe work for the internal cooling of the continuous caster roller bearings failed. This can be quite a common occurrence with flexible pipe work, and failures mean that bearing temperatures will rise very quickly, leading to seized bearings. This causes production quality issues, as the billet surface finish will be affected by sliding instead of rolling over the rollers.
The bearing housing and grease pipe work in the immediate vicinity will also be subjected to extreme heat; most greases will form hard deposits in this situation, requiring pipe work and bearing housing replacement as well as a bearing change. During one failure the end user reported that cooling water supply to one roller had failed for a period of between 24 and 48 hours. It was not possible to stop production, so the affected bearings had to remain in place after the cooling water system was repaired. Cast product quality was monitored, and no quality issues were reported.
At the next available maintenance opportunity, the bearings were removed from their housings and changed; however, upon further inspection they were found to be in a serviceable
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LUBE MAGAZINE NO.123 OCTOBER 2014
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