Patent GB-1376971-A (GB)
Title: Apparatus for forming self-locking fasteners
IPC: B29C65/00
Filed: 1972-05-01
Abstract: 1376971 Plastics patch applying apparatus LONG-LOK FASTENERS CORP 1 May 1972 [10 May 1971] 20184/72 Heading B6G Apparatus for forming a patch of plastics material on a threaded fastener to provide the fastener with self-locking characteristics comprises means for heating at least a portion of the fastener to above the flow point of the plastics, means operative to place the fastener in position at a processing station, means operative to advance a section of a strip of plastics to a position adjacent the fastener, means to cut a fragment from the strip and carry the fragment to the fastener, means having a curved working face shaped to the curvature of the fastener and operative to press the fragment into conformity with the surface of the fastener without forcing material of the fragment into the valleys of the threads for a time sufficient to melt the fragment and cause the molten material to flow into the valleys of the threads. Preferably a plurality of fasteners is processed in each cycle of the apparatus. As shown in Fig. 1 a feeding mechanism 10 advances eight rows of the fasteners F through an oven to heat corresponding receiving stations in apparatus 15 where the eight fasteners are released simultaneously to gravitate down eight guides to come to rest against corresponding stops at eight processing stations. The eight fasteners are then clamped in position while eight batch-applying assemblies advance against the immobilized fasteners. Each advancing patch-applying assembly incorporates an adjustable metering mechanism which measures out a pre-determined increment of a plastics strip. With continued advance of the patch-applying assembly, the increment of plastics strip is severed to drop on to the heated fastener. The final stage of the advance of the assembly a pressure head of the assembly shapes the melted plastics to the cross-section curvature of the fastener. The fasteners are then released from the processing station 15 for discharge into a quenching bath 16 provided with a conveyer 18 for delivering the finished product. The absence of a fastener at any one of the eight receiving stations at the start of an operating cycle automatically prevents operation during the cycle of the increment-advancing mechanism of the corresponding plastics-applying assembly. Resiliently yielding operating connections preclude any damage by jamming of the working parts of the apparatus. Various provision including the use of adjustable stops at the eight processing stations makes it possible to change over the apparatus from a run of fasteners of one size to a run of another size. As shown in Fig. 3, each of the eight receiving stations of apparatus 15 has a holder in the form of a receiving fork 22 which receives a fastener F on the corresponding track 12 and as shown in Fig. 9 each of the eight receiving forks 22 discharges the corresponding fastener on to a guide groove 24 of a ramp 25 and the fastener in reclining position comes to rest against a stop bar 26 that extends across the 8 processing stations. While the fastener F pauses at a processing station a corresponding patchapplying assembly 30 advances to the fastener. As shown in Fig. 10 the patch-applying assembly 30 comprises a reciprocating plunger 32 with a water-cooled head 34 slidingly mounted on the leading end of the plunger. A coil or spring 35 acts in compression between a collar 36 on teh plunger in the head 34 to urge the head to a forward limit position shown in Fig. 10 at which a stud 38 carried by the head abuts the forward stop shoulder 40 of a recess 42 in the plunger. As patch-applying assembly 30 advances towards the fastener F, a suitable metering apparatus functions to advance an increment of a plastics strip 46 into position. The metering mechanism includes a normally stationary rack 48 adjacent the path of advance of patch-applying assembly and a pinion 50 on the head 34 of the assembly that engages the rack and rotates in response to the advance of the assembly 34. The pinion 50 co-operates with a pressure roller 52 to advance the plastics strip from a corresponding feed roll (not shown) through a guide slot 54 into the region between the fastener F and the leading end of the plunger 32. The nose of the head 34 is provided with an upper clamp 55 which cooperates with lower clamp 56 under the reclining fastener to immobilize the fastener. The upper clamp 55 comprises a pair of clamp elements which co-operate with the lower clamp 56 to provide a 3-point grip on the fastener. After head 34 makes initial contact with the fastener, the plunger 32 continues to advance with consequent compression of the coil spring 35 and the leading end of the plunger co-operates with the shearing edge 59 of the head 34 to sever the advanced increment of the plastics strip 46. The severed increment of the plastics strip 46 is carried downwardly by the leading end of the plunger on to the screw thread of the fastener F. As the severed plastics strip begins to soften under the heat from the fastener, the leading end of the plunger 32 continues to advance to function as a pressure shoe causing initial contact of the strip with the crest of the threads and at the same time shaping the softened plastics to the cross-sectional curvature of the fastener. After release of the fastener F the plastics strip 46 melts into the valleys of the screw thread to form a plastics pool 62 in the valleys as shown in Fig. 7. After the plastics material is applied to the fasteners, the eight patch-applying assemblies 30 retract upward to permit the springs 35 to return the heads 34 to their normal positions. At the same time the lower clamps 56 at the eight processing stations retract downwardly out of the way and the stop bar 26 retracts upwardly out of the way to free the fasteners for gravitational movement down the ramp 25 to a terminal portion 64 of the ramp (Fig. 3). Immediately thereafter eight pusher fingers 65 on a pusher yoke 66 advance into corresponding slots 68 of the terminal portion of the ramp 25 to push the fasteners into the quenching tank. Means is provided to sense the absence of fasteners on the receiving forks 22 at the receiving stations of the apparatus and eight corresponding solenoids 70 to retract the corresponding racks 48 out of the path of the corresponding pinions 50 to prevent actuation of the pinions. Each rack 48 is on the outer end of the armature 72 of the corresponding solenoid 70 and is normally held in its effective position by coil spring 74 of the armature. The sensing means includes a switch 75 for energizing the solenoids. Each sensing switch 75 is operatively connected to rocker shaft 76 by a torsion spring. United with each sensing switch 75 is a rigid finger 78 and each sensing switch includes a sensing pin 79 which is slidingly mounted into the finger and backs against a leaf spring arm 80. All of the switches 75 are normally closed but each sensing switch opens if its sensing pin 79 contacts the head of the fastener F. In the absence of a fastener at a receiving station at the beginning of an operating cycle, the corresponding sensing switch 75 remains closed to cause energization of the corresponding solonoids 70 throughout the remainder of the operating cycle.