TRANSACTIONS OF THE SECTIONS. 215 



On the Sand-Blast Process for Cutting and Ornamenting Stone, Glass, and 

 other Hard Substances. By W. E. Newton, C.E. 



In this process a stream of sand is introduced into a rapid jet of steam or air so 

 as to acquire a liigli velocitj^, and is then directed upon any hard or brittle sub^ 

 stance so as to cut or wear awa^^ its surface. 



For work, such as cutting or ornamenting- stone, where a considerable quantity 

 of material is to be removed, a steam-jet of from 60 to 120 lbs. pressure has o-ene- 

 rally been used as the propelling- agent. The sand is introduced by a centraf tube 

 of about J-iuch bore, and the steam issues from an annular passage surrounding 

 the sand-tube. The impetus of the steam then drives the sand through a chilled iron 

 tube i-iuch bore and about 6 inches long, imparting Aelocity to it in the passage, 

 and the sand hnally strikes upon the stone, which is held' about 1 inch distant 

 when a deep narrow cut is desired, but may be 10 or 15 inches distant when a 

 broad surface is to be operated on. 



This chilled iron tube is the only part of the apparatus which is worn away by 

 the cutting-action of the sand ; it is so arranged as to be easily replaced, and lasts 

 about ten hours. 



To produce ornaments or inscriptions on stone, either in relief or intaglio, a 

 stencil or template of iron or caoutchouc is held on or cemented to the stone, and 

 the sand-jet is moved with an even and steady motion over the whole surface, so 

 that all the exposed parts may be operated upon and cut to the same depth. 



The skill and time of the artist may be devoted exclusively to making the stencil 

 or template ; this being prepared, the most elaborate and intricate designs can be 

 cut as rapidly as the most simple. A template of cast iron ^^ inch thick will serve 

 to make 100 cuts ^\ inch deep in marble, and will then be worn down to about -jV 

 inch thickness. Malleable iron templates last about four times as long as cast iron. 



The durability of caoutchouc as compared with stone, under these circumstances, 

 is remarkable. A stencil made of a sheet of vulcanized caoutchouc about ^V inch 

 thick, exposed to sand driven by 50 lbs. steam at 2 feet distance, has lasted with 

 scarcely perceptible wear while 50 cuts were made in marble, each cut being about 

 i inch deep, or about 12^ inches in all, or 200 times the thickness of the caoutchouc. 

 With a supply of steam equal to about 1^ horse-power, at a pressure of about 

 100 lbs., the catting effect per minute was about 1^ cubic inch of granite, or 4 cubic 

 inches of marble, or 10 cubic inches of rather soft sandstone. To cut a face or level 

 surface on a rough stone, the sand-jet is made to cut a groove about 1 inch deep 

 along the whole leng-th of the stone ; the overhanging edge is then broken off with 

 the hammer, and the jet is advanced an inch and a new groove is cut, and its 

 overhanging edge is broken off, and so on. 



^ To cut a deep channel, as in quarrying, two jets set at divergent angles are used. 

 These jets make parallel grooves about 3 inches apart, leaving between them a 

 narrow fin or tongue of stone, which is broken off by a tool ; the jets are then 

 advanced and new grooves cut. The sides of the channel are parallel, and it is 

 made -wide enough to permit the whole jet-pipe to enter, so that it may be cut to 

 any desired depth, say 8 or 10 feet. 



When effects of a more delicate nature are desired, as when engraving on glass 

 only small quantities of material are to be removed ; the blast of air from an ordi- 

 nary rotary fan will then be found sufficient as the propelling medium. 



Sand driven by an air-blast of the pressure of 4 inches of water will completely 

 grind or deptdish the surface of glass iu ten seconds. 



If the glass be covered by a stencil of ])aper or lace, or by a desig-n dra-wn in any 

 tough elastic substance, such as half-dried oil, paint, or gum, a picture will be 

 engraved on the surface by the impact of the sand on the exposed parts. 



I'hotographic copies, in bichromated gelatin, from delicate line engravings, have 

 been thus faithfully reproduced on glass. 



In photographic pictures in gelatin, taken from nature, the lights and shadows 

 produce films of gelatin of dillerent degi-ees of thickness. A carefully regulated 

 sand-blast will act upon the glass beneath these hlms more or less powerfully in 

 proportion to the thickness of the films, and the half-tones or gradations of ifo-ht 

 and shade are thus produced on the glass. 



