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20 CHAPTER 3 Findings and Applications Findings of Industry Survey sodium stearate in the rest. Other plants use sodium soaps in all die boxes. Information regarding strand manufacture and the appro- High-carbon wire and high-speed lines result in greater priate test methods was solicited directly from manufacturers heat and require lubricant formulation with a higher soft- of lubricants used to manufacture PC strand and from PC ening point and a high fat content. (High fat content equals strand manufacturers. 60% for calcium-based lubricants and 75% for sodium- based lubricants.) Some formulations use a blend of fats Lubricant Manufacturers (hydrotallow and stearic acid) to achieve certain melting (softening) points. Some specific information gained from representatives of In general, calcium soaps melt at a lower temperature than the lubricant manufacturing industry included the following: do sodium soaps. Additives in lubricants can include lime, sodium carbon- A wide range of lubricants is used in U.S. strand manu- ate, sodium phosphate, sodium sulfate, antioxidants, and facturing operations. One supplier suggests at least six of borax. their products are used throughout the country in strand production. Strand Manufacturers Lubricants are often a blend of multiple soaps, including sodium and calcium stearates, and can include fillers such Some specific information gained from representatives of as lime. the strand manufacturing industry included the following: The type (formulation) of lubricant recommended by the lubricant manufacturer is dependent on the type of metal Induction furnaces are typically used during the stabiliza- pretreatments and the condition of the metal surface. tion process after the wires have been stranded. The strand Rod or wire can be either mechanically or chemically cleaned surface temperature is typically measured with in-line in- (acid pickled). Mechanical descaling can be performed frared sensors and is in the range of 700-785F as the strand using shot blasting, reverse bending, or wire brushing. leaves the furnace. The strand remains at approximately Chemical cleaning was considered superior to mechanical this temperature for 2-10 sec, until the steel is quenched in descaling by lubricant manufacturers. Subsequent pretreat- a water bath. Although there may be some limited washing ments include borax and lime. action as the strand passes through the bath water, which Wire that is only marginally cleaned (retained scale) requires is circulated through filters and a heat exchanger, no other a lubricant with a heavy residue. cleaning methods were reported. Additional cleaning meth- Products are formulated with different melting points. ods used by some plants may be proprietary. Twenty or more different sodium soaps are available, as Problems in the quality of raw materials used in the strand well as different sources of fatty acid, such as stearic acid. production process are identified when a significant change One-to-three different products can be used in line for in drawing performance, such as reduced die life or an in- manufacturing prestressing strand. crease in energy demand, is observed. It is common for Calcium salts of fatty acids are often used in the first set of adjustments in the drawing process to be necessary since dies. Some plants use calcium soaps in three die boxes and lubrication performance is highly temperature-dependent