GB2138719A - Grinding apparatus - Google Patents

Abstract

A machine for grinding small ferrite discs to a required thickness has a continuously rotating turntable 8 incorporating a number of vacuum chucks 9. Ferrite discs are loaded onto the vacuum chucks 9 in a region 16 and are moved, by rotation of the turntable to a first grinding position 10 where they are ground by a coarse grinding wheel 11 then a fine grinding wheel 12. The workpieces are inverted in the region 17 before passing to a second grinding position 10A where the reverse sides are ground in the same way. Finally the finished workpieces are removed in the region 16. The grinding wheels used in this system need be only of the same order of size as the workpieces to be ground. Since the grinding wheels themselves contribute a significant part of the cost of a grinding machine this constitutes a considerable cost saving compared with conventional machines where much larger grinding wheels are required. <IMAGE>

Description

SPECIFICATION Grinding apparatus This invention relates to a machine for grinding very hard materials. It arose when considering problems involved in the grinding to a specified thickness of small ferrite discs two to three inches in diameter, such discs being needed for various instruments. The invention is however also applicable to the grinding of ceramics, glass, stone, hardened steel and other materials. A special grinding wheel is required for steel.

In the past, ferrite discs such as mentioned above have been ground on a general purpose grinding machine shown schematically in Figure 1. Using a mixture of wax and resin, a number of the discs 1 are mounted on a steel mounting plate 2 which is then held by a magnetic chuck 3 and rotated about an axis 4 at a relatively slow speed.

A large diamond grinding wheel 5, rotating at high speed about an axis 6, moves in a direction indicated by the arrow 7, perpendicular to the axes 4 and 5, until it has completely traversed the plate 2, grinding the discs 1 to the required thickness.

A disadvantage of the aforementioned technique is that a considerable amount of time is involved in: cleaning the steel plates like that shown at 1; heating the ferrite discs; applying the waxlresin mixture; loading the discs on the plates; cooling the plates and cleaning them; cleaning the magnetic chuck; loading the plates; grinding a first cut; stopping the machine and measuring the size; grinding the second cut; stopping the machine and measuring for size again; removing the plates and cleaning them with the discs still affixed; removing the discs and then repeating the operation to grind the opposite sides of the discs. Furthermore, the diamond grinding wheel 5 needs to be of comparable diameter to the plate 2 and is therefore very costly.

This invention provides apparatus for grinding workpieces comprising a grinding position at which is located a rotatable grinding wheel for grinding the workpieces, a turntable or other rotatable holder for moving the workpieces in turn to the grinding position; and a plurality of rotatable vacuum chucks for holding the workpieces as they are moved through the grinding position.

By employing the invention, whilst one workpiece is being ground, other workpieces can be mounted or removed from the grinding machine. This greatly improves the time taken for a given grinding operation. Furthermore, machines constructed in accordance with the invention require only a relatively small and inexpensive grinding wheel of the same order of size as the workpieces to be ground. This is in contrast with conventional grinding wheels such as shown at 5 on Figure 1 which need to be of the same order of size as the plate 2 on which the workpieces are mounted. The small size of the grinding wheel leads to a very significant saving in cost.

Because the small grinding wheels, which can be used when the present invention is employed, are relatively inexpensive it is practicable to have two grinding positions which may be diammetrically opposite each other on the turntable. In this arrangement a first side of the workpieces can be ground at one of the stations, and the workpieces then inserted so that the opposite side can be ground at the second position. The relative cheapness of the grinding wheels also allows two grinding wheels to be located at each grinding position: one being relatively coarse to remove the majority of the material to be ground away, and the other relatively fine to bring the workpiece to exactly the required dimension.

One way in which the invention may be employed will now be described with reference to Figures 2 and 3 of the accompanying drawings in which: Figure 2 is a plan view of a grinding machine constructed in accordance with the invention; and Figure 3 is a schemmatic side elevation (also shown partly in cross section) of the grinding machine of Figure 3.

Referring to both Figures 2 and 3, a turntable 8 rotates on a vertical axis 8A and carries a number of vacuum chucks 9 which rotate on vertical aces 9A. Above the turntable are two grinding positions 10 and 1 OA diammetrically opposite each other.

At each grinding position are two grinding wheels, a coarse wheel 1 1 or 1 A and a fine wheel 12 or 1 2A. These wheels are supported on air bearings 13 (Fig. 3) mounted on a yoke 14 which also supports the turntable but is not shown in Figure 2.

In operation, ferrite discs 15 to be ground to a specified thickness are mounted on the vacuum chucks in a loading and unloading region 16 between the two grinding positions. Rotation of the turntable, which is continuous at a speed of about three to four inches per minute, then brings the discs 15 into contact in turn with the coarse grinding wheel 11 which performs a first cut, and the fine wheel 12 which performs a second cut. In a region 17 the workpieces are inverted before passing to the second grinding position 1 OA where their reverse sides are ground in the same way as at the first position 10. Finally the finished workpieces are removed at the region 16 and replaced by new workpieces to be processed.

Within the turntable 8 is a mechanism for rotating the chucks at around 100 revolutions per minute and applying vacuum to them during the periods that the workpieces are in contact with the grinding wheels. The rotational movement and suction is discontinued in the regions 16 and 17 to allow manipulation of the workpieces at those regions.

By employing a machine like that illustrated it is expected that it will be possible to perform the grinding operations over five times as quickly as was possible using the conventional technique described with reference to Figure 1 and at a considerably reduced cost in capital expenditures because of the relatively small diameters of the grinding wheels.

Claims (8)

1. Apparatus for grinding workpieces comprising a grinding position at which is located a rotatable grinding wheel for grinding workpieces, a turntable or other rotatable holder for moving the workpieces in turn to the grinding position and a plurality of vacuum chucks or other rotatable suction devices for holding the workpieces as they are moved through the grinding position.

2. Apparatus according to claim 1 in which there are two grinding positions at opposite sides of the rotatable holder.

3. Apparatus according to claim 1 or 2 in which, at the or each grinding position, there is a relatively coarse and a relatively fine grinding wheel, these wheels being arranged to operate in turn on each workpiece.

4. Apparatus according to any preceding claim in which the or each grinding wheel contains diamond abrasive.

5. A method of grinding workpieces using apparatus according to claim 2 wherein the workpieces are inverted after passing one grinding station and before reaching the other.

6. A method of grinding ceramic, glass orferrite workpieces using an apparatus in accordance with any one of claims 1 to 4.

7. Apparatus according to claim 1 and substantially as described with reference to Figures 2 and 3 of the accompanying drawings.

8. A method of grinding ferrite workpieces substantially as described with reference to Figures 2 and 3.