Oshkosh Truck Corporation and Pierce Manufacturing Improve Safety, Simplify Assembly, and Cut Service Costs with Spiralock Thread Form Innovation

         Oshkosh Truck Corporation, a top U.S. manufacturer of heavy-duty military and commercial trucks, prides itself in manufacturing a top quality product that can perform under the most extreme weather and terrain conditions. The constant shock and vibration that the vehicles are are subjected to requires reliable locking in the threaded joints. It is critical that axles, frames, and chassis are securely fastened because failure in the field creates serious issues for military personnel due to difficulties with getting and replacing parts. Furthermore, lack of reliable fastening systems may lead to injury or loss of human life.
         On chassis and non-permanent fixtures, Oshkosh engineers were using prevailing torque locknuts and anaerobic compounds (adhesives), which were not very effective in preventing vibration loosening.  Additionally, warranty and service costs on the heavy-duty vehicles were rising.  These concerns prompted Oshkosh to find a more reliable, cost-effective fastening method.
         Oshkosh turned to Madison Heights, Mich.-based Spiralock Corp., designer and manufacturer of an innovative self-locking thread form technology.  The secret to Spiralock’s thread form is a 30º wedge ramp cut at the root of the female thread.  Under clamp load, the crests of the threads on any standard bolt are drawn tightly against the wedge ramp.  This causes thread contact forces to be applied at approximately 60º from the bolt axis, rather than 30º away as in a standard thread form.  The mechanical advantage – the angular relationship between the unique wedge ramp and the male thread – restricts bolt or screw movement.
         A key Spiralock benefit over conventional locking methods is that the male fastener can be loosened and retightened as many times as necessary without any loss in locking force, thus reducing maintenance costs.  The thread form works with standard male fasteners and eliminates the need for add-on locking components such as lock washers, thread adhesives, crimping or inserts, to name a few.
         Spiralock’s 30º wedge ramp cut at the root of the female thread also eliminates common stripping or shearing problems because the design distributes the clamp load much more evenly over the threads, which improves safety. Testing of Spiralock nuts and taps in critical Oshkosh threaded joints resulted in an end to the loosening problems as well as documented cost savings.  By eliminating the use of anaerobic compounds from the tapped holes, Oshkosh was able to simplify the assembly process, reduce harm to the environment and employees, and reduce costs associated with the purchase and use of the thread-locking compounds.  Eliminating service and warranty issues related to fastened joints provided additional cost savings to Oshkosh.
         Oshkosh’s subsidiary Pierce Manufacturing, a leading U.S. manufacturer of custom firefighting apparatus, also found itself in search of a fastening solution.  Because in life-saving situations, the integrity and reliability of both emergency equipment and human effort are crucial, Pierce spares no effort to “deliver the utmost in performance, safety and reliability to firefighters, emergency crews and communities they serve.”  Pierce takes pride in building customer trust through their service mark “One-Source Solutions”, an integrated approach to all processes from the planning stages, through manufacturing, to support services.
         When loosening striker bolts on fire truck doors caused rattling problems, Pierce engineers relentlessly searched for a solution.  A series of standard locking nuts were tested but without satisfactory results until Spiralock self-locking thread form technology came into the picture.  An Oshkosh Truck engineer recommended testing a Spiralock nut on the door striker bolts.  The loosening problem was solved. 
         The application initially used one model of truck but quickly advanced to five different models, which now all use Spiralock nuts.   “The Spiralock resolution brought us valuable savings in manpower, time and money,” reports Rich Demski, the Chassis Product Manager at Pierce Manufacturing.   With an estimated average cost reduction of $5 per door ($20 per truck), Spiralock technology saves Pierce Manufacturing roughly $20,000 annually in parts, labor and repair costs.
         In extensive laboratory tests, Spiralock threads have demonstrated superior resistance to vibration loosening.  These tests compared three types of female thread forms: a standard nut; a prevailing torque locknut; and a nut tapped with a Spiralock thread form, under controlled conditions.
         During vibration testing, the standard nut lost its preload (tension) clamping force almost immediately and the prevailing-torque locknut lost 70% of its preload clamping force.  The Spiralock nut, however, maintained its preload clamping force for the entire 120-second test period.  Additional tests verified these results and demonstrated that the Spiralock thread, unlike the others, can be loosened and retightened many times with no appreciable loss of holding power.  This can substantially reduce maintenance costs.
        Switching to a Spiralock nut allowed Pierce to eliminate a weld-on cage nut on fire truck door latches.  Spiralock engineers went a step further and designed a custom nut that prevented slippage during assembly.  This brought further improvements in the production area.  What was once a two-man operation became a one-man task. “Working with Spiralock engineers was a great experience,” adds Peter Chard, Pierce’s Senior Manufacturing Engineer.  “We came looking for a nut to eliminate rattling and loosening and we got one that eased assembly as well.   We ended up with a better design and happier customers.”