Medium carbon or alloy steel grades designed for cold formed threaded fasteners in property classes such as 8.8, 9.8, 10.9 and 12.9 require a surface conversion process to create a thin, adherent coating that will facilitate deformation and ensure high product quality. Traditional zinc phosphating and reactive soap processes, although well established in metal pre-treatment for cold deformation applications, are associated with a number of potential drawbacks, including high acidity, high energy consumption and phosphate sludge. Moreover, they can involve numerous individual steps, from initial degreasing and pickling, to activation, phosphating and soaping, with frequent intermediate rinsing.
In contrast, Bonderite L-FM FL has been developed to provide a flexible, one-step process with better cost performance and a much smaller water footprint. The product is a non-reactive, water-based polymeric coating that enables a sustainable surface conversion process. Since the coating adheres to the surface physically without any reaction, the only aqueous evaporates are produced in the subsequent drying step prior to cold deformation.
As a single-step process, Bonderite L-FM FL eliminates all rinsing steps, which saves water and offers reduced energy demand with appropriately lower CO₂ emissions. Furthermore, when the cold formed screws are de-phosphatised for final heat treatment, the polymeric coating is easier to remove, says Henkel, which permits the use of a de-phosphating cleaner in much lower concentration. Overall productivity is also said to be enhanced by the lubricity and pressure resistance of Bonderite L-FM FL in comparison with traditional zinc phosphating processes, which results in longer extrusion die life.