Cold rolling oil
The purpose of cold rolling oils in the cold rolling of metal strip is manyfold. For example, lubrication and cooling of the entire system such as strip and (work) rolls. Also flushing particles away and control friction are key in the cold rolling process. Therefore, the composition and viscosity of the cold rolling oil are designed for optimal balance and often customized for the required process conditions. A regular underestimated challenge is the maintenance of the cold rolling oil during usage and preserve its properties.
Development
Generally, cold rolling oils are developed to meet customers’ requirements. The composition is based upon well-chosen base oil(s) to meet the viscosity requirements and selection of the desired additives at the designed concentrations. Additives such as lubricity and extreme pressure molecules give the cold rolling oil its tribology performance, while other additives are present as well to create a stable, long lasting cold rolling oil.
Cold rolling oil in use
Now the next challenge for the cold rolling oil starts. Whereas the fresh cold rolling oil is in perfect shape to perform optimal in the cold rolling mill, it is also subjected to change over time. It is very likely that the properties of the cold rolling oil may change during its usage. Obviously, we should limit any change, so its performance remains constant.
What happens during rolling with the oil? First of all, in the rolling process itself small metal particles are generated. Formation of particles depends on the severity of the rolling conditions, alloy type, surface roughness and the oil quality. In practice metal particles with various sizes are generated. Large particles may have negative effect on the surface quality and their presence should be avoided. The oil quality has influence on the generation of large particles and the filtration system is extremely important to remove large particles from the oil. The same comment is true for the somewhat smaller particles, however smaller particles have less risk to generate surface defects. Besides the particles that can be filtered out rather easily, also very small particles are generated. These very small particles behave as being dissolved and cannot be filtered out on mesh size. As these very small particles are usually sensible to oxidation, they behave as quite polar substances. This means that it is possible to filter these out of the oil with special activated filter aid that adsorbs polar substances. In this case, also the level of some additives could be affected and monitoring these additives by routine analyses is recommended. Considering the particle formation, it should be clear that the filtration performance is key in oil quality and rolling performance.
In addition, also other types of contamination to the cold rolling oil may happen. For example, we could discuss hydraulic oil leakage at the cold rolling mill. Initially, some hydraulic oil leakage may not be the first topic to think about as an issue. Although hydraulic oil leakage is quite common to happen, most people are not aware of the consequences. However, considering cold rolling oil as an essential and constructive part of the cold rolling process, the question may arise how to keep it in good shape. As hydraulic oil differs significantly from cold rolling oil, contamination of the cold rolling oil with hydraulic oil does changes the composition and performance of the cold rolling oil.
Hydraulic oil leakage
Hydraulic oil typically has much higher viscosity and thus viscosity increase of the cold rolling oil is the first indication of contamination with hydraulic oil. Q8Oils offers also lower viscosity alternatives of the cold rolling oil as top up possibility in order to correct for the viscosity increase. The viscosity can be adjusted back to the desired level, but on molecular level the distribution of base oil molecular sizes has changed. This may affect emissions and the behaviour of the oil in the oil wiping system, cleaning, degreasing and annealing steps.
Additives in hydraulic oil are different and enter the cold rolling oil due to hydraulic oil leakage. Unfortunately, it is quite impossible to remove these additives from the cold rolling oil so they remain as contamination. Also by hydraulic oil leakage, the cold rolling oil additives are diluted resulting in decreased performance. This can be corrected with top up of an cold rolling oil alternative with higher additive levels, or by adding the additives as such to the cold rolling oil. Q8Oils supports and offers both solutions to maintain the cold rolling oil quality.
Routine analyses
As described, the maintenance of the cold rolling oil is very important. A very useful tool is the QRAS program (Q8Oils Routine Analyses System), where Q8Oils supports their customers to frequently (e.g. monthly) collect oil samples from the cold rolling oil in use to monitor its quality by means of properties and contamination. Changes in the cold rolling oil are observed at an early stage and possible scenarios and/or actions can be discussed to maintain the desired cold rolling oil properties.
Sustainability
Nowadays, the term sustainability is used in many ways. Generally, sustainability is all about the preservation of resources. In the cold rolling process this can be about energy reduction, re-use of materials and especially for cold rolling oils themselves to keep these in good condition and prevent that cold rolling oil itself ends up as waste unnecessarily. In this article, options to maintain the cold rolling oil performance is discussed.
Remarks
Q8Oils work closely together with customers to improve their cold rolling process with customized oil compositions. An important part of improvements is the correct understanding of the cold rolling mills, the operation parameters and other steps in the entire process. Optimization and maintenance of the cold rolling oil for each cold rolling mill separately may give the best performance and productivity.
For more information, please contact our Rolling Team at Q8Oils.
