Joseph L. Purnhagen is Global Commercial Manager of Metal Processing Additives at The Lubrizol Corporation.
Suppliers of water-based synthetic and semi-synthetic metal-stamping and forming lubricants create formulations that help maximize lubricant service life, cool better and provide a healthier work place while reducing friction and preventing tooling and part material from sticking together. These sophisticated forming fluids present different formulating challenges and require a different set of performance additives to produce these expanded benefits.
Traditional oil-based metal-stamping lubricants excel at providing a long service life and with minimal maintenance requirements. In this fluid type, lubricant formulators are primarily concerned with additive solubility in the base oil, and achieving the right balance of different additives to meet the performance requirements of the given application. But water-based metal-forming lubricants are different. By introducing performance additives into a water-based mix, suppliers of metal stamping lubricants create formulations that help maximize lubricant service life, cool better, and provide a healthier work place while reducing friction and preventing tooling and part material from sticking together. However, water-based (emulsion) metal-forming fluids present a much greater design challenge. The presence of water creates an ideal breeding ground for microbes, and control of metal corrosion is more difficult in a water-based system. Performance additives used in metal-stamping lubricants include lubricity enhancers, extreme-pressure (anti-weld) agents, corrosion inhibitors, emulsifiers and biocides. Achieving long service life from water-based metal-stamping lubricants is not as simple as the introduction of a single ‘silver bullet’ type of additive, but a result of careful consideration of the entire performance additive system and the interaction or synergies between the various components. The additives that deliver the primary functions of the fluid for stamping and forming operations—lubrication and corrosion protection—will cease to perform properly if the overall system in which they are delivered becomes unstable.
Emulsifier additives are the key components that allow for a lubricant to mix with water, and retain a stable mixture over an extended period of service. Various types of emulsifier additives are used in soluble-oil (milky appearance) and semi-synthetic (translucent appearance) metal-stamping-fluid formulations. These additives provide the ability to create stable emulsion of materials that are inherently insoluble in water, such as petroleum oils, esters, vegetable oils and synthetic base stocks. In modern lubricant formulations, a carefully balanced ratio of several different emulsifier chemistries is used to achieve the ideal performance for a particular application. The emulsifier system must be durable enough to maintain consistency through the demanding service conditions in a stamping press, including high pressures and introduction of metal content to the emulsion. In addition to their emulsifying properties, these additives can contribute supplemental corrosion inhibition and lubricity to the finished metal-stamping fluid, offering formulators tools that provide multiple functions simultaneously. Newer product developments in emulsifier chemistry include a focus on achieving multi-functional performance and reducing the emulsion foaming tendency.
The uncontrolled growth of microbes (bacteria and/or fungi) is one of the most common sources of emulsion degradation and subsequent low fluid service life. Water-based metal-stamping-fluid emulsions contain an ideal breeding ground for microbes to thrive: water, organic food sources from oils and other performance chemistries, and typically a slightly elevated temperature from the service conditions. To keep microbial growth in check, biocidal additives are introduced to the metal-stamping lubricant, either in the fluid concentrate or as supplemental tank-side additions. When applied properly, including biocide product selection and consideration of the correct treat-rate concentration, biocides effectively control the growth of microbes, promote a longer fluid service life and reduce microbial health risks.
All biocidal products and suppliers are not equal. The selection process must include knowledge of the compatibility with the overall lubricant formulation. For emulsions, biocides with solubility properties in both oil and water can show superior long-term stability and deliver the best overall performance profile. In addition, suppliers of quality metal-stamping fluids generally include some degree of service or training so that biocides are used safely and effectively with their particular products. The results of uncontrolled microbial growth can include product performance degradation, emulsion instability, loss of corrosion protection, foul odors, and irritation or illness for shopfloor workers.
Stability Required for Long Lubricant Life
Metal-stamping lubricants are applied to facilitate a higher level of productivity for stampers. To maintain this productivity over an extended fluid service life, the stability of the emulsion system must be durable and predictable. The best lubricity enhancers and anti-weld additives will not perform if the emulsion system they are delivered in is falling apart. Lubricant designers and suppliers strive to maximize the long-term durability of their products through a combination of robust emulsifier chemistries, effective anti-microbial programs and service programs for fluid maintenance at the shopfloor.
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