A method for the production of a control cover layer onto the thread of a metal screw part by the application of a thermoplastic polyester resin

摘要

1313042 Coated threaded fasteners LONGLOK FASTENERS CORP 5 May 1971 [13 May 1970 19 April 1971] 13388/71 Heading B2E [Also in Division F2] A threaded fastener having self-locking characteristics by virtue of a patch of thermoplastic material blended to a plurality of threads of the fastener is produced by heating the fastener to a temperature in excess of the melting point of the thermoplastic material but below the decomposition temperature thereof, and applying a solid unitary blank of the thermoplastic material to the heated fastener at a preselected location thereon to cause the heated crests of the threads engaged with the blank to divide the blank into discrete segments, which segments melt and flow into valleys of adjacent threads at the preselected location to bond to adjacent flanks of the threads defining the valleys and form a cohesive patch of solid material at the preselected location. The thermoplastic material may be polyester, preferably polyalkylene phthalates. Other suitable polyester resins are listed. The fastener may be a nut or a bolt and may be degreased and/or grit blasted prior to application of the thermoplastic material. The fasteners may be cadmium-plated or preferably of carbon steel and plated with cadmium after the patch is applied. As shown in Fig. 5 a blank 22 of thermoplastic material is deposited on the screw thread of a bolt 20, heated to above the melting point of the thermoplastic material and a pressure shoe 25 contacted with the blank 22 under the pressure of a spring for about one second. The softened blank sags into the valleys of the screw thread and forms pools 28 on the bottoms of the valleys of the screw thread as shown in Fig. 7. Preferably the heated fastener is then quenched in water. The resiliency of the plastics patch may be increased by subsequently soaking the, fastener in an oven after the quenching. In another embodiment a pressure shoe to form the plastics strip to the curved configuration of the screw fastener is in the form of a metal cradle having a longitudinal cavity that conforms to the cross-sectional curvature of the lower half of the horizontal screw fastener (Figs. 8-14 not shown).