Consistency in k-factor with ASTM B994


  • Many operations professionals are familiar with the torque equation:

    T = K * db * Fp.

    This one equation tells a maintenance team how much torque to apply to a fastener to achieve proper installation. T represents torque value; Fp represents Force, or bolt tension during tightening; and db represents the fastener’s diameter. But what about that K? That’s where a maintenance team can get into trouble. The K represents all of the factors that resist the applied Force. In bolting, this is called the k-factor.

    Countless variables contribute to a fastener’s k-factor, making it impossible to control completely. But while no one can guarantee a 100% precise k-factor, it doesn’t have to remain a mystery. Bolting produced in compliance with ASTM B994 specifications can get closer than any other fastener to k-factor consistency. ASTM B994 outlines more consistent production processes, which help maintain a more consistent k-factor. While ASTM B994 cannot account for factors that occur in the field, its greater control during production — maintained through rigorous testing practices — gives a manufacturer more confidence in its process and makes it easier to set k-factor and torque values for its fasteners. When k-factor is consistent, proper fastener installation is more efficient.

    So what does ASTM B994 require manufacturers to do that results in more consistent k-factor?

    First, bolt integrity and consistency are evaluated through ongoing lab tests using samples from each production lot. ASTM B994 states requirements for manufacturing, cleaning, and preparing carbon steel bolts for the electroplating process, as well as regular chemical composition evaluations of the Nickel-Cobalt alloy. ASTM B994 also references specifications designed to determine both a fastener’s mechanical properties and the thickness of its coating. With this level of testing, a company complying with ASTM B994 SC18 Class 1 can manufacture fasteners with fewer uncontrolled production variables. Fewer uncontrolled variables produce a more consistent fastener with a more consistent k-factor.

    In addition to tightly controlled and rigorously tested production processes, a fastener company that wants to use ASTM B994 to provide k-factor consistency must take the proper steps to make sure bolts are shipped safely. One dent in a fastener’s thread can have a 30% effect on its torque value, so a company’s packaging system must be as carefully considered and tested as the fasteners themselves.

    Ultimately, ASTM B994 compliance means that a company can deliver fasteners with such a high level of chemical, mechanical, and coating consistency that they can confidently provide customers with a k-factor to aid in calculating required torque. When evaluating an ASTM B994 fastener company to determine if their bolts are right for you, ask if they comply with ASTM B994 SC18 Class 1 and if they can provide a consistent k-factor. If they can confidently stand behind their k-factor consistency, their ASTM B994 fasteners might be the right fit for your facility’s operations.

    To learn more about Doxsteel Fasteners and how we use ASTM B994 to provide k-factor consistency, contact us today.