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(11) | EP 0 370 713 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Polishing apparatus |
| (57) Polishing apparatus comprises a drum (2) for containing polishing material and workpieces
to be polished. The drum (2) is arranged to rotate about a first axis. To overcome
the disadvantage that, above certain speeds and with rotation about a single axis,
the drum contents become trapped against the interior by centrifugal force, the drum
(2) is arranged to rotate about a second axis which is radially offset from the first
axis. |
[0001] The present invention relates to polishing apparatus comprising a drum for containing polishing material and an article or articles to be polished, which drum is arranged to rotate about a first axis.
[0002] One example of polishing apparatus of the above type is shown in Figure 4 of the accompanying drawings, where a polygonal polishing drum B is mounted for rotation by means of a shaft A which is supported on a stand C. At one end of the polishing drum B is an opening D, closed by a cover E by means of screws.
[0003] A pulley F is secured to the shaft A such that the shaft A is driven in rotation by means of a motor G via a belt H.
[0004] In this known polishing apparatus, the cover E is removed to charge polishing material J and articles such as workpieces K to be polished. Enough space is left for the free movement of the polishing material and workpieces in the polishing drum B. The opening D is then closed with the cover E fixed by means of the screws. Then the motor G is driven so that the polishing drum B is rotated around the axis of the rotating shaft A.
[0005] As the polishing material J and the workpieces K tumble around in the drum B, the workpieces are polished.
[0006] As the speed of rotation is increased, the centrifugal force acting on the polishing material and the workpieces will be increased leading to the result that they will be forced onto the inner peripheral surface of the polishing drum. In such a state, the polishing material and the workpieces will be stationary with respect to each other and no polishing of the workpieces will occur. In this known polishing apparatus, therefore, the speed of rotation of the polishing drum has to be kept relatively low so that there is an upper limit to the relative movement between the polishing material and the workpieces.
[0007] An object of the present invention is to provide a polishing apparatus which is capable of highly efficient polishing with a large amount of relative movement between the polishing material and the workpiece.
[0008] The present invention is characterised in that the drum is arranged to rotate about a second axis which is radially offset from the first axis.
[0009] The first axis will normally extend through the centre of the drum, and the second axis will lie outside of the drum so that the first axis will describe a circle around the second axis although arrangements are possible where this is not the case. The rotation of the drum about the first axis can then be increased beyond that of the prior art apparatus where the centrifugal forces trap the polishing material and workpieces on the inner peripheral surface of the drum, with the rotation of the drum about the second axis counter-acting at least continually this effect.
[0010] In the accompanying drawings:
Figure 1 is a front view showing a polishing apparatus;
Figure 2 is a side view of the apparatus of Figure 1 with the drum and balance weights turned through 90°;
Figure 3 is an explanatory view of the apparatus, and
Figure 4 is a front view of the prior art apparatus.
[0011] Figures 1 and 2 show a polishing apparatus having a rotary shaft 11 which is divided in two portions which are rotatably supported on the right and left ends of a stand 3. Balance weights 12 and 13 of the same shape as each other are fixed to the shaft 11.
[0012] A second shaft 14 is mounted for rotation on the balance weights 12 and 13 at a position radially offset from and parallel to the axis of the shaft 11 and a polishing drum 2 is fixed to the shaft 14. On the inner surface of this polishing drum 2, a coating such as rubber and having an uneven surface is applied throughout. Covers 15 are arranged at two diametrically opposite places and at opposite ends of the polishing drum 2.
[0013] A pulley 15 is fixed to one end of the shaft 11 and is connected by a belt 8 to another pulley 21 drivable by a motor 7 which is mounted on the stand 3. Rotation of the pulley 15 via the belt 8 and pulley 21 rotates the shaft 11.
[0014] Further, a second pulley 16 is mounted for rotation on the shaft 11 and a third pulley 17 is fixed to the shaft 14. The pullies 16 and 17 are connected to each other by a belt 18.
[0015] The motor 7 is drivingly connected to another pulley 22 which is connected by a further belt 23 to the pulley 16 rotatably mounted on the shaft 11.
[0016] A discharge trough 19 is pivotally mounted on the stand 3 and is located adjacent to the cover 5 at the end of the drum 2 adjacent to the balance weight 13. A mesh 20 is fitted to the trough 19. The constitution of other portions of the apparatus is the same as the known polishing apparatus described already with reference to Figure 4.
[0018] Polishing material and the workpieces are loaded into the polishing drum 2 through the opened cover 5 at the end adjacent to the counter weight 12 leaving enough free space in the polishing drum for movement of the polishing material and the workpieces. The cover 5 is then screwed back on. The motor 7 is then driven to rotate the pulley 15 via the belt 8 and the pulley 21. The rotation of the pulley 15 rotates the shaft 11 at a fixed speed. Rotation of the shaft 11 rotates the balance weights 12 and 13 and causes the polishing drum 2 to revolve round the axis 11C of the shaft 11, the axis 14C of the shaft 14 describing a circular orbit ℓl as shown in Figure 3.
[0019] Simultaneously with this revolution, the motor 7 drives the pulley 16 by way of the pulley 22 and the belt 23. The pulley 17 is then driven by the pulley 16 through the belt 18 causing the shaft 14 to rotate and thus the drum 2 to rotate about the axis 14C of the shaft 14.
[0020] Figure 3 shows the different states in the revolution of the polishing drum 2 round the axis 11C of the shaft 11 and also round the axis 14C of the shaft 14. In the rotation of the polishing drum 2, the centrifugal force f due to the rotation of the polishing drum 2 about the axis 11C, the centrifugal force due to the rotation of the drum about the axis 14C, gravity and the uneven surface of the rubber coating on the inner surface of the drum co-operate to thoroughly agitate the polishing material and the workpieces to enhance the polishing efficacy.
[0021] Upon completing a full polishing operation, the motor 7 is stopped and the cover 5 at the end adjacent to the balance weight 13 is opened to unload the polishing material and the workpieces from the polishing drum 2 into the discharge trough 19. The workpieces rest on the mesh 20 and the polishing material passes therethrough to the bottom of the discharge trough 19 for removal.
[0022] The balance weights 12 and 13 balance the rotation of the polishing drum 2 preventing the shaft 11 from breaking due to an unbalanced load being applied to the shaft 11, thereby a high speed operation can safely be achieved.
[0023] The sizes of the pulleys and their arrangement can be chosen such that the upper cover 5 of the drum 2 at the end adjacent to the balance weight 12 remains uppermost as shown in Figure 2, or such that, as the drum is rotated about the axis 11C in a clockwise direction, the drum is rotated about the axis 14C in a clockwise or anticlockwise direction.
1. Polishing apparatus comprising a drum (2) for containing polishing material and
an article or articles to be polished, which drum (2) is arranged to rotate about
a first axis (14C), characterised in that the drum is arranged to rotate about a second
axis (11C) which is radially offset from the first axis (14C).
2. Polishing apparatus as claimed in claim 1, characterised in that it includes balance
weights (12,13) at each end of the drum (2).
3. polishing apparatus as claimed in claim 2, characterised in that the drum (2) is
mounted for rotation on the balance weights (12, 13).