Patent GB-775555-A (GB)
Title: Improvements in and relating to the manufacture of abrasive discs or the like
IPC: B24D18/00
Filed: 1952-04-25
Abstract: <PICT:0775555/III/1> <PICT:0775555/III/2> <PICT:0775555/III/3> A process for the manufacture of abrasive discs comprises securing a backing disc of the shape of the disc to be formed to a jig or the like by means of suction which keeps it substantially flat, applying an adhesive layer to the backing disc, applying heat to render the adhesive tacky, applying a layer of abrasive grains to the adhesive layer, applying a second abrasive layer and heat treating the disc to cure the adhesive, at least the steps up to and including the application of the layer of abrasive grains being carried out while the backing disc s secured to the jig or the like.  The jig comprises a cup shaped head 10 mounted on a turntable 12; the upper portion of the head is closed by a plate 14 having a number of apertures such as holes 16 or slots communicating with the cup interior 18 which through the stem 20 is connected to a source of vacuum.  The holes 16 may be joined by grooves 22 in the upper plate surface which may have a number of ring grooves or a network of grooves into the bases of which the upper ends of the holes 16 enter.  One or more ring grooves 24 may be arranged right round the periphery of the plate in which rubber or other sealing members 26 may be secured.  The heads 10 may be shaped with a central recess 64 for use in making recessed or dished discs; a cap 66 can be placed over the portion 64 to prevent the central disc boss being covered with adhesive and abrasive.  The cups are of such dimensions for given sizes of disc that the disc edges overlap the cup peripheries and thus prevent adhesive creeping around the disc edges and fouling the discs or the plates.  A projection 32 is preferably provided in the centre of each cup on which the central disc aperture is empaled to position the disc on the plate.  Detachable means such as paper or aluminium caps can be provided for placing over the projection to prevent the disc centres from being fouled by adhesive.  An annular slot or groove 34 may be provided in the top surface of the plate 14 surrounding the projection 32 so that the inner edge of the disc overhangs the slot or groove edge to prevent adhesive creeping round the edge of the disc aperture.  For discs not having a central aperture the projection 32 is omitted and may be detachable for this purpose. The cups 10 are connected by a line 38 with a source of vacuum, e.g. one or more vacuum pumps operated by electric motors. Cooling means for the heads may be provided e.g. external cold air blasts which may be supplied by fans operated by the vacuum pump motors.  Alternatively the cups may be cooled by passing a cooling medium through ducts 40 in the cup walls.  Heads 10 are mounted on a conveyer such as a circular turntable 12 or rotary device; the heads may be arranged in concentric circles or other patterns.  All the heads are connected through rigid or flexible ducts to a vacuum line leading to a vacuum pump.  The turntable is rotated on a shaft 42 in a substantially horizontal plane so as to pass the heads through a number of working stations arranged serially round a frame in which the turntable rotates. At the first station 44 discs 28 supplied by a conveyer 46 are mounted on the heads; the discs are coated with adhesive as by spraying from a jet 50, heated in a tunnel 52 sufficiently to render the adhesive tacky, coated with abrasive grains by a spray 54, coated with a second layer of adhesive by spray 56 and heated in an oven 58 to dry or cure the adhesive.  The discs are finally stripped from the cups at 60 and carried away by conveyer 62.  The discs may be heated in a tunnel between stations 54, 56 to a point at which the grains are caused to adhere to the first adhesive layer so as not to be detached therefrom by the application of the second adhesive layer. The discs may be removed from the cups after the second application of adhesive and dried as in an oven. At the grain spreading station 54 the grain may be sprayed on to the discs or delivered to the discs from a vibrating sieve.  The cups may be vibrated to spread the grains evenly over the discs or the grains may be spread evenly over the discs by subjecting them to electric vibrations.  Any excess grain may be removed by a blower or suction device.  The cups are preferably rotatably mounted on the turntable and may be freely rotatable or mechanically rotated.  The tunnels may be heated by direct convection, by electronic infra red heat or by gas burners. Resin adhesives are preferably used.  The plate 14 may be heated during at least part of the process as by electric elements or by steam ducts in it.  The cups may be of cast metal forged steel or reinforced plastic.  Specification 686,303 [Group XXIII] is referred to.