Non-Ferrous Hot Rolling Lubrication: The Next Generation

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1 2013 STLE Annual Meeting & Exhibition May 5-9, 2013 Detroit Marriott at the Renaissance Center Detroit, Michigan, USA Non-Ferrous Hot Rolling Lubrication: The Next Generation Non-Ferrous Metals Robert L. Blithe Houghton International Valley Forge, PA ABSTRACT: Non-Ferrous rolling lubricants have traditionally been designed from a common platform of chemistries. Historically this chemical platform has produced properties that compromise some of the intended performance aspects. This presentation will review the historical perspective of Non-Ferrous rolling oils, as well as offer some insight into positive attributes that new chemistries have delivered. By making use of chemical technology, next generation rolling lubricants can be developed that provide improvements in emulsion consistency, improvements in lubrication properties and performance, and improvements to metal surface finishes. INTRODUCTION: Non-ferrous hot rolling lubricants have traditionally been designed from a common or similar platform of chemistry components that have worked effectively for many years. Over the years, the nature of non-ferrous hot rolling emulsion chemistry components may have changed but the basic purpose and control aspects of soluble-oil emulsion systems for hot rolling non-ferrous metal alloys has not been altered that much. One of the primary purposes for utilizing a soluble-oil emulsion product in non-ferrous rolling applications is to provide transport of water-insoluble components to the work surface, or rollbite, in a uniform, consistent, and cost effective manner. The water phase of the emulsion provides cooling for the mill equipment, most notably the work rolls and back-up rolls, while the stability characteristics of the emulsion helps control the quench effect on the metal strip or slab being rolled. The various properties of the water-insoluble components within the emulsion are what help reduce roll forces, minimize work roll wear, and provide the desired metal finish or surface quality.

2 DISCUSSION: Several different factors control the various properties and performance aspects of non-ferrous rolling emulsions, and the balance of these factors determines the lubrication properties of the rolling emulsion. 1. Chemical Factors these are the purely chemical aspects and attributes of the chemical compounds used in the rolling oil: the choice of emulsifying agents used in the emulsifier package, the oil concentration of the emulsion, the choice of waterinsoluble lubricating agents. 2. Physical Factors these relate to the various mechanical aspects of the specific rolling process and equipment: the metal alloy(s) being processed, the emulsion system pumps and spray nozzles, the rolling mill equipment itself. 3. Physico-Chemical Factors these are physical factors whose properties can be altered to cause a change in chemical component behavior: emulsion temperature, emulsion system size and volume turn-over rate, filtration and skimming equipment. Non-ferrous rolling products have undergone changes over the years, progressing from simple mixtures of simple molecules to complex mixtures of simple molecules. In many respects, it has been much easier to control these simple molecule emulsion systems and they tend to be more predictable in their behavior. The future of non-ferrous rolling lubricant development is moving towards the utilization of simple mixtures of multi-functional molecules, which represents an innovative approach to emulsion control and the development of new or different control models. Many of the early non-ferrous hot rolling emulsions were based upon simple soluble-oil chemistry products which produced very stable emulsion systems, where many of the chemical components were derived from natural products. These soluble-oil emulsions tended to contain a high percentage of emulsifying agents, and they were usually alkali-soap based systems. The oil droplet particle size distributions for these emulsions tended to fall below 1 micron, and usually were below 0.5 micron, but while many of these products produced nice stable emulsions they would not be characterized as providing good rolling lubrication properties. The next generation(s) of non-ferrous hot rolling products progressed to using anionic soap chemistry emulsions based upon alkanolamine soaps as the principle emulsifier component employed to control the meta-stable rolling emulsion to the desired characteristics, various nonionic co-emulsifier components were utilized in small quantities to help provide the proper emulsion control. These products tended to rely upon natural fats, oils, and fatty carboxylic acid components for both the emulsifying components and the lubrication agents; shifting the emulsion particle size distribution was the control mechanism employed to alter the overall lubrication properties of the meta-stable emulsion. Over time synthetic lubrication components replaced the natural fats and oils, which resulted in better emulsion control and more consistent lubrication properties, but the basic product technology was still an anionic alkanolamine soap chemistry emulsion which required control of the emulsion particle size distribution in order to maintain the desired lubrication properties.

3 One of the biggest emulsion control issues with the anionic alkanolamine soap chemistry technologies involved the formation of metallic soaps from aluminum debris and the carboxylic acids present within the emulsion. Fatty carboxylic acids, most notably oleic acid, were proven lubricating agents for aluminum rolling operations, but the fatty acids will react to form metallic soap complexes. The variation in emulsion metallic soap content over time contributed to changes in emulsion stability, shifts in emulsion particle size distribution, roll-bite viscosity changes, and changes in lubrication properties. One of the consequences of high metallic soap levels, or high ash levels, was an out of control emulsion condition which required significant or frequent partial dumps, with add-back of fresh rolling oil, in order to regain emulsion control. This partial dump pattern was a never ending cycle, and continually repeated itself. To help combat the emulsion issues that resulted from metallic soap formation, anionic product chemistries with minimal amounts of free carboxylic acid were developed. These product chemistries still relied upon anionic alkanolamine soap emulsification systems with various nonionic co-emulsifier components, but the product technology was still a particle size controlled emulsion system. To enhance the lubrication properties while using a minimal amount of carboxylic acid, lubricating ester levels were increased and new lubrication agents were utilized. Many new types of lubricating agents for use in non-ferrous rolling products have been developed under the Green Technology initiatives; these lubricating agents utilize natural or renewable component technology. But as with previously developed technology systems, many of the emulsion systems were built upon anionic alkanolamine soap technologies which relied upon particle size shifts to control both emulsion stability and emulsion lubrication properties. The new vegetable oil derived or modified chemistries represented an improvement over natural fats and oils, but the emulsion systems could be difficult to control. NEW TECHNOLOGY DEVELOPMENT: New rolling oil technology has been developed that is not based upon carboxylic acid technology or anionic soap technology, which minimizes the amount of metallic soap formation that occurs within a rolling emulsion, making metallic soaps and their negative attributes a non-issue. The removal of the anionic alkanolamine soap emulsifier component required the development of new emulsification packages, part of an innovative rolling oil development program. This new rolling technology delivers consistent lubrication properties while maintaining the desired metal quench characteristics, and provides a clean and uniform metal surface finish at high emulsion temperature conditions as well as low emulsion temperature conditions. One of the challenges in the development of new emulsification technology for rolling processes involved providing all of the positive attributes that anionic soap technology provided without relying upon carboxylic acid or carboxylate ion chemistry components as the principle component of the new emulsifier package. In this new type of emulsification system, particle size becomes independent of performance and particle size distribution becomes a secondary factor in emulsion control. Emulsion lubrication properties become a function of the energy within a process operation, a condition where thermal separation rate becomes independent of emulsion particle size or particle size shifts. A very stable emulsion can provide good lubrication properties for rolling operations, something that was not easily achieved with anionic soap chemistry emulsion systems.

4 The use of a new emulsion control mechanism presents a dilemma for many people who have worked with traditional anionic chemistry emulsion systems for many years, they will have to learn new particle size behavior and emulsion control mechanisms. Since particle size distribution could be controlled independently from lubrication properties, emulsion stability could now be managed differently than when anionic emulsifying agents were utilized as the primary emulsification component. Particle size analysis captures emulsion oil droplet size information for a specific emulsion condition or specific point in time, and particle size will change the longer the emulsion sample sits under a static environment without shear stress. Particle size distribution does not always provide information relevant to emulsion stability. Simple forms of emulsion stability index (ESI) testing have been utilized to track changes in emulsion characteristics, but the ESI tests do not tell the whole story for many of the meta-stable emulsion systems used in non-ferrous rolling applications and is not an effective mechanism for comparing emulsion characteristics of old technology products with new technology products. New analysis techniques are available that measure the changes in optical density of an emulsion over time, across an entire static emulsion sample, providing a more detailed understanding of emulsion stability characteristics. The use of a Turbiscan instrument, available from Formulaction, to measure light transmission and reflection properties of an emulsion sample over time can provide a more detailed understanding of the change that occurs within an emulsion sample, and is a companion analysis to emulsion particle size distribution analysis. Emulsion stability monitoring can provide information on the rate of clarification that occurs in the bottom portion of a sample, the rate of creaming that occurs in the top portion of a sample, and may provide information on the oil separation that occurs at the very top. Kinetic calculations can be performed on the desired sections of the emulsion samples, allowing for the direct comparison of change in different emulsion samples. RESULTS: In the following information example, the particle size distribution profiles (graph 2) for two different product emulsion samples appear to be nearly identical when processed under identical shear conditions. The corresponding emulsion stability comparison (graph 1) for the same emulsion samples shows a difference in the stability characteristics, and the creaming affect that occurred in the top portion of each emulsion sample. The emulsion stability testing was completed by monitoring the changes in the backscattered light across the upper portion of the emulsion sample, and focusing on the changes that occurred within the top 10 mm of each sample. A uniform volume for each emulsion sample was held in a static state condition at 30 C for a 24 hour period, each sample was tested every hour. The emulsion stability aspects were compared by looking at the change in the observed phase thickness in the top 10 mm of each emulsion, Delta H(t), versus time.

5 Graph Particle Size Distribution Volume (%) Particle Size (µm) Red line - 2% concentration Green line - 2% concentration Graph 2