Development of friction coefficient controller for E-coat (KTL) 2018-36-0200
Global competitiveness increase in the past decades has been a crucial factor for the technological advance and industrial automotive development. Possibility of reducing costs, concentrate knowledge and increase in manufacturing efficiency has lead to development of global automotive platforms. In this scenario, the supply chain needs for adaptations that allow evolution at the same fastness imposed by original equipment manufacturer (OEM). Such demands reflect directly on the fasters market requiring lighter and stronger products. Stronger products are obtained by increasing corrosion resistance and lowering friction coefficient, in order to increase the clamp load and, consequently, reduce the weight without reducing performance. However, increasing corrosion resistance causes, generally, an increase in friction coefficient and, consequently, a decrease in clamp load. To minimize such effects, the surface coating industry has been developing, over the years, friction controllers that provide a higher corrosion resistance and better control of friction coefficient. Currently, there are products that exceed 1.000 hours of resistance to salt spray (salt spray tests according to ASTM B-117) and have friction coefficient from 0.08 to 0.12 (tests performed according to ISO 16047). However, these surface treatments are not commonly applicable due to higher costs. This impact is even more significant when we deal with larger, and hence heavier, parts such as U-bolt. An alternative to these surface treatments would be E-coat (KTL). Generally, fasters coated with KTL show high corrosion resistance, friction coefficient and friction deviation that makes their application technically unfeasible. Due to this characteristic, the KTL fasteners usually specify in the thread the phosphate and oiled coating. That is, even with fastener body presenting high corrosion resistance, the thread has low corrosion resistance in order to meet the friction coefficient specification. The present work aimed to develop a friction controller solution for fasteners coated with KTL that meets 480 hours of salt spray resistance (minimum zinc flake specification), including the thread, and present a friction coefficient of 0.08 to 0.16 (phosphate and oiled reference).