THE MTXIXC AXI) OUARKV IXDLSTKV K^S 57 



Sharp, angular sand free from clay, sandy loam, clayey sand and 

 even fine gravel are all used in the foundries, but the material 

 having by far the most universal use and serving the most purposes, 

 is a fine grained clayey sand or loam, and it will be the only type of 

 molding sand discussed in this paper. ^ 



Although an experienced foundr}nnan can usually gage quite 

 accurately the value of a sand by an ordinary visual examination 

 and the " feel " of a moist sample, yet there are definite qualities 

 which a sand must possess in order to be classed as a brass sand, 

 core sand, sand for rough castings, etc. 



A pure white quartz sand when moistened and packed into a 

 definite form, seems to have no tendency to " stand up " well in a 

 firm mass, but on the slightest touch crumbles and falls apart. In 

 casting, the sand must be of such a character that after firmly 

 tamping it around the pattern, the latter may be drawn out and the 

 walls or projections of the cavity w'ill retain their position until 

 the metal can be poured in, and also exposed portions must resist 

 the abrading action of the stream of metal. This property is termed 

 the " bonding power " and can be measured by various means such 

 as by making briquets of the sand and determining their tensile 

 strength. The chief factors determining the bonding power are (i) 

 the amount of clay present in the sand; (2) the amount of water 

 with which it was tempered; (3) the amount of tamping given it. 

 In special cases various clays or certain organic substances are 

 added to increase the bonding power. In a series of tests made on 

 molding sands of Wisconsin^ the clay percentage ranged from a 

 slight amount up to 3944 per cent with an average in 34 samples 

 of 13.18 per cent. After the sand has been several times subjected 

 to the heat in casting, its clay content becomes dehydrated, loses its 

 plasticity and bonding power and the sand becomes " dead." 



Permeability is the property which all molding sands must 

 possess to a certain extent, of allowing the steam, heated air, or 

 other gases to pass through the pores of the sand and escape during 

 the casting. The permeability of a sand depends upon the amount 

 of pore space or voids and upon the shape and size of such voids, 

 the latter factor being as important as the former. The work of 

 King and Slichter- has demonstrated that the porosity of a sand 

 depends on the size and arrangement of the grains, that a sand 

 composed of well rounded grains will have a smaller amount of 



^ Rics. Wis. Geol. Sur. Bi>l. 15. igo6. p. 205. 



2U. S. Geol. Sur. i^tli .*\n. Rep't, pt. 2. p.209-15, 306. 



