INTRODUCTION

Although later we shall be much concerned with single indi­vidual Diamonds used as tools, we shall find that so many mass-production processes employ Diamond grits, sometimes freely suspended in an oil or grease but much more frequently bonded into a metal or a resin matrix, that at this stage we shall discuss the production, properties and dispensation of such grit. The consumption of grit in industry is formidably large. Of the six tons or so of mined Diamond employed in industry some four tons is used as grit. Add to this the fact that perhaps some two tons of synthetic grit is now also con­sumed in the world and it will be apparent that Diamond grit is the most important single item of consumption in the whole output of Diamond. Not surprisingly, then, much technical research and development have gone into perfecting the uses of this material. Even at, say, £2 a Carat (and the cost of grading can raise this a good deal) one ton of grit may be worth £10 000 000 so that the grit consumed by industry reaches formidable value each year. The consumption is growing steadily, probably increasing 10% each year and, as we shall show later, this material plays a major part in both heavy and light engineering production lines.

Grit is now very largely mainly incorporated as an abrasive and grinding material bonded into cutting wheels and grinding discs. Therefore, industry has imposed quite severe demands as to the character of the grit required for specific purposes. To begin with, industry reasonably enough expects such expensive grinding material (almost £5000 for 1 lb weight) to have a high degree of purity. Thus much attention is paid to this aspect. Furthermore, the demands of industry are such

that grit particles are required to be specified according to (a) size, (b) shape and (c) strength, as different characteristics are desirable for different applications. The grit is made by crushing rough Diamonds which are unsuited for GEMS, either in ball mills or with crushing mortars. The material is carefully cleaned with strong acids and alkalis to remove impurities and leave the residual Diamond very clean and crisp. Diamond is so chemically resistant that this cleaning treatment has not the slightest effect on the sharpness of the edges of the particles;

The days of amateur grit manufacture and testing and grad­ing by rubbing between the fingers have now gone. Diamond grit is now essentially a closely regulated abrasive material in which the size, shape (i.e. with or without sharp points) and the length of time the material lasts in use are all aspects of technological and economic importance to the user and I therefore to the supplier too.

As far back as 1485 Leonardo da Vinci described the prepa­ration of Diamond grit in his time. The Diamond was wrapped in lead and beaten with a hammer, the flattened sheet so formed being often re-folded and beaten. The Diamond grit was recovered as a scum by melting the lead, subsequently washing the particles in strong acid.

Today a broad distinction is made between the larger particles and the finer, for methods are now available for sorting the larger particles according to shape as well as size, and according to the work the particles have to perform.