Patent GB-1198945-A (GB)
Title: Improvements in and relating to the Polishing of Glass
Inventor: TWIST DOUGLAS
IPC: B24B7/24
Filed: 1968-02-27
Abstract: 1,198,945. Polishing glass. TRIPLEX SAFETY GLASS CO. Ltd. 25 Feb., 1969 [27 Feb., 1968], No. 9287/68. Heading B3D. [Also in Division B1] A method of polishing a surface of a piece of glass comprises rubbing abrasive over the surface using a power-driven polishing head, and supplying additional abrasive to the surface in response to signals arising from sensing means responsive to the resistance encountered by the polishing head and indicating a rise in resistance. In apparatus for carrying out the method, the abrasive is supplied in suspension from a dispenser 10, Fig. 1, consisting of a container 11 having at its bottom a valve 16 which controls the supply to a pipe 69 and is operated by a rod 17 connected to a solenoid 18. A disc 24 on the rod agitates the liquid in a housing 22 to prevent settling out of the abrasive. Settling out of the abrasive in the container 11 is prevented by vanes 31 on a stirrer 30 which extends from a sleeve 29 having an arm 32 connected to a rod 36 reciprocated by a crank to effect oscillation of the stirrer. The glass 44 to be polished is mounted on a table 45, Fig. 3, which reciprocates horizontally and oscillates about a vertical axis. A polishing head 46 is carried by a shaft 47 which is driven by a belt 48a from an hydraulic motor 48 and is vertically movable by a pneumatic device 49 to press the head against the glass. The dispenser 54 is located adjacent the head and the head assembly is mounted on a carriage 51 which has wheels 52 engaging rails 53 for reciprocation transversely to the direction of reciprocation of the table 45. The polishing head may comprise a metal disc 55, Fig. 4, carrying a pad 56 having V-grooves 57 on its lower face. The disc is secured to a plate 58 joined to a housing 60 on the shaft 47 by spring-loaded bolts 62. The housing and plate are held a small distance apart by a ball 59, the arrangement permitting slight tilting of the head to accommodate uneven glass. During polishing, the load on the hydraulic motor is detected by a sensor, which may consist of a bellows arranged to actuate micro-switches, and, upon an increase in resistance to polishing, actuates the solenoid 18, Fig. 1, to permit discharge of abrasive to the head. The pressure in the circuit may be measured at equal intervals of time and the valve opened for a time dependent on the pressure, or the valve may be opened for a predetermined time every time the pressure reaches a set value, or the pressure may be monitored continuously and the valve arranged to supply abrasive continuously or substantially so according to the pressure. In another arrangement, the hydraulic motor is replaced by a constant voltage motor and the current supplied to the motor indicates the resistance to polishing. In another embodiment, the dispenser consists of a pump which continuously circulates the abrasive in a tank and a valve is located in a pipe in the circuit to discharge the abrasive. In a further embodiment, a rotating polishing head is moved over a stationary sheet of glass by operators who move the head to-and-fro. Additional sensing means may be provided which are responsive if the resitance exceeds a predetermined amount to actuate the device 49 to raise the polishing head from the glass.