Method of making self-locking threaded elements

Abstract

Method of making a self-locking threaded element, e.g. a screw including a strongly adhered convexly curved plastic body on its threaded surface allowing smooth assembly and giving strong frictional engagement between the element and a mating threaded surface. In the method, a stream of fine particles of heat-softenable plastic is directed against a threaded surface portion of a heated metallic element. Contacting particles are caught on the heated surface and fused by heat from the element to form a continuous plastic body which is then hardened by cooling.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is: 
     
       1. The method of providing a threaded portion of an article with a self-locking element comprising an adhered body of normally hard, tough, resilient thermoplastic resin, said method including the steps of heating the threaded portion to a temperature above the softening point of said resin, thereafter directing a stream of fine particles of said thermoplastic resin to a selected area of said threaded portion while said threaded portion is at a temperature above said softening point, catching resin particles from said stream by softening them and causing them to adhere to said threaded portion by heat from the surface of said threaded portion progressively to build up a deposit of resin on said selected area, the radial thickness of said deposit being greatest substantially midway between longitudinal edges of said deposit and diminishing in thickness towards those edges, fusing adhered particles to a substantially continuous body of resin, and cooling said body of resin to harden it to a solid body resistant to displacement and effective to give a locking action when a complementary threaded member is assembled with said threaded portion. 
     
     
       2. The method of providing a threaded portion of an article with a self-locking element as defined in claim 1 including the step of applying a thin, firmly adherent heat-softenable resin primer coat to said selected area of said threaded portion before heating said threaded portion and applying said stream of resin particles. 
     
     
       3. The method of providing a threaded portion of an article with a self-locking element as defined in claim 1 in which said stream of fine particles is a gaseous jet in which the fine particles are entrained. 
     
     
       4. The method of making a locking-type threaded fastener element including an adhered body of normally hard, tough, resilient thermoplastic resin comprising the steps of heating a threaded metallic fastener element to a temperature above the softening point of said resin, thereafter directing a stream of fine particles of said thermoplastic resin to a selected area of the threaded surface of said fastener element while said threaded portion is at a temperature above the softening point of said resin, catching resin particles from said stream by softening them and causing them to adhere to said fastener element by heat from the surface of said fastener element progressively to build up a deposit of resin on said selected areas, the radial thickness of said deposit being greatest substantially midway between longitudinal edges of said deposit and diminishing in thickness towards those edges, fusing adhered particles to a substantially continuous body of resin by sensible heat supplied from said fastener element, and cooling said body of resin to harden it to a solid body resistant to displacement and effective to give a locking action when said fastener element is assembled with a complementary threaded member. 
     
     
       5. The method of making a locking-type threaded fastener element as defined in claim 4 in which said fastener element is a bolt and is disposed with its axis substantially vertical for application of said thermoplastic resin and in which said stream of resin particles is directed laterally against the selected area of the threaded surface. 
     
     
       6. The method of making a locking-type threaded metallic fastener element as defined in claim 5 in which said fastener element is moved through said laterally directed stream of resin particles. 
     
     
       7. The method of making a locking-type threaded metallic fastener as defined in claim 6 in which said laterally directed stream of resin particles is a gaseous jet in which the resin particles are entrained. 
     
     
       8. The method of making a locking-type threaded metallic fastener element as defined in claim 4 including the step of applying a thin firmly adherent heat softenable resin primer coat to said selected area of said fastener element before heating said threaded portion and applying said stream of resin particles to said element. 
     
     
       9. The method of making a locking-type threaded metallic fastener element as defined in claim 6 including the step of applying a thin firmly adherent heat-softenable resin primer coat to said selected area of said fastener element before heating said threaded portion and applying said stream of resin particles to said element.