June 25, 2008

Barrel Polishing

Another long practiced, but crude method of overcoming the need for mechanization is known as barrel polishing. Originally this was only suitable for small, fairly simple and robust shapes, which were placed in a cylindrical container or barrel, together with a mass of pebbles or rounded abrasive shapes and a lubrication liquid. The whole assembly was then slowly rotated for some hours. The rubbing and tumbling of the abrasive shapes against the work pieces smoothed them in a rather unselective manner, but the process often inflicted as much damage as it removed. This process has been much improved, sometimes by substituting vibratory or other more gentle motion, so that quite delicate and fragile parts can be treated. Even so, these processes do not produce the best finish, but they have the merit of requiring little labor.

Metal finishing is the last step in the production process, and it is at this stage that a flawless surface must be produced in spite of any substance damage, dents, scratches, etc. which the article may have acquired during previous processes. It is obvious, but little regarded in practice, that care in the selection of the original material and in the handling during all stages of the manufacturing process can materially reduce the cost of the final smoothing operations.

In conclusion to this section it can not be too strongly emphasized that although these pre-polishing treatments do not themselves produce a lustrous and polished surface, they, and they only lay the foundation for a high quality final finish. The quality of a polished surface lies not in reflected in it. Only if the preliminary smoothing has been conscientiously done can clear, sharp reflected images be obtained. Fuzzy, distorted images can not be corrected by the final 'shining-up' operation and are a sure sign of insufficient pre-polishing.

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