Patent Publication Number: US-2009220296-A1

Title: Partially threaded bolt for use with a self-threading fastener and method of use

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a partially threaded fastener nut for use with self-threading fasteners, and more particularly to such a fastener nut which has a partially threaded cavity for use with a self-threading fastener that contains a collecting, retaining, and compacting recess for material cut by the self-threading fastener. 
     2. Problems in the Art 
     There is an unmet need to provide a bolt and nut system which has increased vibration resistance over existing products available today. Vibration heavy applications include military applications such as artillery and tanks and also includes civilian applications such as elevators, roller coasters, and mills to name a few non-limiting examples. 
     SUMMARY OF THE INVENTION 
     According to the invention, there is provided a partially threaded fastener nut for complementary use with a self-threading fastener that can collect, retain, and compact cutting material. The nut is hardened on the hex faces and on the ends while the interior of the nut is typically unhardened but can be partially hardened or hardened to a lesser degree than the self-threading fastener. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a self threading fastener that collects cuttings in a fastener cavity and a typical hex nut. 
         FIG. 2  depicts a side cutaway profile of the fastener and nut of  FIG. 1  demonstrating that the nut is partially threaded. 
         FIG. 3  depicts a view of the fastener of  FIG. 1  engaged with the nut of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As is well known in the art, the nut  10  may be made of hardenable steel. The nut  10  is fabricated with the steel in its soft state and thereafter is heat treated. Threads  9  can be cut before or after heat treating depending on the grade of nut  10  desired. The exterior surface  5  and ends  7  of the nut  10  should have a hardness of from about Rockwell Hardness Scale C (“RHC”) 48 to about RHC 55 to a depth of from about 0.008 to about 0.012 inch. The interior surface  1  of the nut  10  should have a hardness of from about RHC 32 to about RHC 39. The hardness is determined by a micro-hardness test (ASTM E-384) performed on the layer present at 0.002 inches from the exterior surface  5 . 
     Fundamentally, the inner surface  1  of the nut  10  should be softer (less hard) than the self-threading fastener  100 . This permits the fastener  100  to cut more easily through the interior surface  1  of nut  10 . Some of the material cut from the nut, the cuttings  50 , by the self threading fastener  100  is retained in a cavity  101  of the self threading fastener  100  where the cuttings  50  are collected, retained and compacted. 
     The interior diameter  3  of the bore  4  along the unthreaded interior surface  1  of the nut  10  is slightly smaller than the fastener diameter  109  across the fastener threads  103 . 
     The inner surface  1  of the nut  10  may also be lined with a different metal or alloy that is softer than the steel of the fastener  100  and which will form the cuttings  50  which heat weld with the threads  9  in the nut  10  cut by said fastener  100  so as to help lock the fastener  100  and nut  10  together for a more stable arrangement. 
     It has been found that the nut  10  can be hardened on its exterior surface  5  and ends  7  while masking the interior surface  1  of the nut  10  so as to prevent carburization during heat treatment. The interior surface  1  of the nut  10  can also be coated in copper as the masking agent which will result in the copper being available for cutting and collection by the self threading fastener  100  as it cuts its way through the nut  10  both through the copper and through the underlying steel. The use of masking agents to prevent the carburization of steel during the hardening process is well known in the art and will not be discussed in detail. CONDURSAL, available from The Duffy Company of Palatine, Ill., is ideally utilized as a masking agent because it is environmentally friendly. Other types of masking agents such as copper sulfate and petroleum based agents (to name a few non-limiting examples) can also be utilized depending on the specific needs of the metal fabricator during the hardening process. 
     It will be apparent from the Figures that the fastener  100  is intended to engage a leading thread  2  of the nut  10 , preferably in a clockwise rotation. A counterclockwise threading is also possible. 
     Modifications may be made in the invention without departing from the spirit of it.