Patent GB-1490744-A (GB)
Title: Tyre grinding machines
IPC: B24B5/36
Filed: 1974-02-09
Abstract: 1490744 Grinding tyres DUNLOP Ltd 3 Feb 1975 [9 Feb 1974] 6032/74 Heading B3D A method of improving the uniformity of a pneumatic tyre or tyre and rim assembly comprises locating the tyre or assembly on rotatable mounting means, rotating the tyre with the tread in engagement with a first rotating grinding wheel, and moving the rotatable mounting means to bring the tread of the tyre while being rotated into engagement with a second rotating grinding wheel, the dirction of rotation of the second grinding wheel or the direction of rotation of the tyre when in contact therewith or both of said directions of rotation being reversed relative to the corresponding direction or directions of rotation when the tyre is in contact with the first grinding wheel. In apparatus for carrying out the method, a frame 2 having four arms 7 ... 10 extending from a turret 11 is rotatably mounted on a base 1, each arm having a chuck 12. The turret is indexable in 90 degree steps to present the chucks sequentially to a loading stage 3, a first grinding stage 4, a second grinding stage 5 and an unloading stage 6. At the grinding stages 4 and 5, platforms 18, 19 extend from the base 1 and each supports a driving mechanism 20 and a grinding apparatus 21 for engaging diametrically opposite sides of the tyre. The turret 11 of the frame 2 is mounted on a shaft 34 which is rotatably supported in the base 1 and carries a four-lobed cam 33 and a chain wheel 38. The cam is engaged by a roller 45 on a member 42 movable about a pivot by a pneumatic device 31. The chain wheel is driven by a chain 50 entrained about a sprocket 51 secured to a lever 36 having a ratchet mechanism and pivotable by a device 35 to index the frame 2, the device 35 is actuated to cause rotation of the lever 36 and sprocket 51 and hence rotation of the wheel 38 and cam 33 through about 15 degrees so that the follower 55 is displaced from the apex 55 of a lobe and actuation of device 51 'then urges the follower down the slope of the lobe to impart rotation to the cam, the ratchet mechanism permitting the movement. The follower rolls down the slope and, because of momentum, climbs the steps of the next lobe until the cam and frame have moved about 75 degrees. Actuation of device 35 causes the sprocket to rotate the cam further up to about 88 degrees when a limit switch is actuated. Final positioning of the 90 degrees indexing is effected by a device 62 moving a roller 63 into a V-shaped block secured beneath an arm of the frame. The frame is locked in position by operation of a device 260, Fig. 6, on the base pressing a pad 262 against a block 250 on the arm, the block being backed by a flange 255 on a block 253 secured to the base. Each grinding stage is substantially identical and consists of a driving mechanism 20 and a grinding apparatus 21. The mechanism 20 comprises a drum 72 for engaging the tread of the tyre, the drum being mounted on a shaft which is carried by a support 70 and driven by reduction gearing and a belt drive from a motor 71. The support is movable about a pivot 74 on the platform 19 by a pneumatic device 91. The grinding apparatus has a grinding wheel which is coupled to a motor and is carried by a support 20b movable about a pivot 74b on the platform 19 by a pneumatic device 91b. The devices 91, 91b are operable to move the drum and grinding wheel from an inoperative position, shown on the right of Fig. 3, to an operative position, shown on the left of Fig. 3, wherein the drum and grinding wheel engage diametrical opposite sides of the tyre to rotate and grind the tyre to a depth determined by an adjustable stop 160. The grinding wheel is surrounded by a cowling having rollers positioned on each side for engaging the tyre and pivoting the cowling so that it does not engage the tyre. The grinding wheels are of tungsten carbide chips and have slightly concave faces. The end of each arm 7 ... 10 has a chuck for receiving a tyre and rim assembly, each chuck having an outer housing 183, Fig. 6, which supports a chuck body 185 in bearings 188, 189, the body having a ring 192 for supporting the tyre assembly. A centring shaft 194 is disposed within the body and is urged downwardly by springs engaging an end cap 208 to cause a tapered portion 202 of the shaft to press resilient fingers 221 on a collet 220 against a central hole 13 of the tyre and rim assembly. At each loading or unloading station, a pressure plate 272, Fig. 1, can be raised by a pneumatic device 270 to engage the end cap and raise the shaft 194 against the pressure of the springs so that the tapered portion 202 is disengaged from the fingers which retract so that a tyre and rim assembly can be loaded or unloaded as the case may be. In operation, at the first grinding station 4, Fig. 2, the tyre and rim assembly and the grinding wheel are rotated clockwise for the first grinding operation. At the second grinding stage 5, the tyre and rim assembly and the grinding wheel are rotated anticlockwise. The reversal of the directions of rotation is stated as preventing feathering of the tread of the tyre. The wheel at the first stage may be coarser than that at the second and be arranged to remove more material. If only a single grinding is required, the machine may be arranged to index in 180 degree steps.