*1 Materials are hard but weak under impact. Glasses, stones, ceramics, etc. fall under this category.
An agglomerated abrasive grain is a spherical grain that is aggregated without using binder (bonding agent), from nanoscale (1/1 million-mm size) oxide ultrafine particles (Fig. 1A) and made the diameter of a large bead of micron scale (1/1000-mm size) (Fig. 1B) . Cohesive force among the ultrafine particles is controlled to make the whole grain wear gradually, bearing working points refreshed spontaneously and continuously. This spontaneous cutting edge generation effect is distinctive.
Fig.1 SEM images of agglomerated abrasive grain
The mimetic diagrams in Fig. 2 are of the polishing mechanism at the time an agglomerated abrasive grain is used as lapping film. First, as shown in Fig. 2 (A), the agglomerated abrasive grain is fixed to PET films by an adhesive material (glue). As this agglomerated abrasive grain is of large microscale diameter, it can protrude easily from the adhesive material. At the early stage of polishing, because there are fewer working points, higher pressure can be obtained, resulting in higher polishing efficiency. As polishing advances, abrasive grain gradually wears out spontaneously as shown in Fig. 2 (B), and the form changes. Here, because nanoscale ultrafine particles work on polishing, at each working point contacting the workpiece, the cut becomes fine-sized and refreshes itself at all times; this achieves a high quality polished surface. In addition, because scraps of workpiece and grains are discharged, clogging is avoided and thus stable polishing is achieved. The result is that a sheet of film achieves functions from coarse grain (efficient) to fine grain (high quality) concurrently without becoming clogged. Figure 3 is a photo of the actual agglomerated abrasive grain observed at the time of polishing.
Fig. 2 Scheme of polishing mechanism by agglomerated abrasive grain
Fig. 3 Laser 3D microscope photo observed at the time of polishing by agglomerated abrasive grain
Figure 4 shows the case example of BK7 optical-glass substrate (φ150) polished by a single-side surface polishing machine. The agglomerated abrasive grain film is attached to the surface plate of the polishing machine, where 200 ml/min. of demineralized water is supplied. The optical mirror plane below 30nmRt was achieved from a initial roughness of 2µmRt without exchanging the film.
Fig. 4 Mirror-finish case example of BK7 optical glass
If the cohesive force, the distinctive characteristics of this technology, is controlled properly, we can generate spontaneous wear of grain before causing deep scratches. In so doing, the application of mirror finishing can extends also to elastic materials and is not limited to hard optical glasses.
Figure 5 shows several different grain varieties of which cohesive force is controlled. By weakening cohesive force a little, this approach can be used to descale the water scales on the mirrors. Beside descaling, it can also remove small scratches, renewing the shabby looking mirrors into shining new articles. If weaker the cohesive force, it can be used to clean the tap on which water scale is attached as a metal polisher. If the cohesive force becomes much weaker, then it can be applied to polish off the yellow tints of a deteriorated car headlight as a resin washer.
Based on the unique characteristics shown above, namely the ability to remove surface stains without causing coarse scratches to base materials, we believe that this new technology can be also be applied to surface cleaning field from the precision polishing field.
Fig. 5 Variety and their assumed applications of agglomerated abrasive grain
Mirror water scale cleaning
Mirror water scale cleaning
Car headlight cleaning