FOUNDING; FOUNDRY 



481 



containing from 3 cwts. to 5 cwts. of iron, and a quantity proportional to the estimate 

 given below. The amount of the charges varies of course with the size of the furnace, 

 and the speed required for the operation. The pigs must bo previously broken into 

 pieces weighing at most 14 or 16 Ibs. The vanes of the blowing fan make from 

 625 to 650 turns per minute. The two cupolas represented in fig. 1003, and another 

 alongside in the plan, may easily melt 6 tons of metal in 2f hours ; that is 2 tons 

 per hour. This result is three or four times greater than what was formerly obtained 



1002 



in similar cupolas, when the blast was thrown in from small nozzles with cylinder 

 bellows, moved by a steam-engine of 10 horse-power. 



In the course of a year, a considerable foundry like that represented in the plan, 

 jig. 991, will consume about 300 tons of coke in melting 1,240 tons of cast iron; con- 

 sisting of 940 tons of pigs, of different qualities, and 300 tons of broken castings, gate- 

 pieces, &c. Thus it appears that 48 Ibs. of coke are consumed for melting every 

 2 cwts. of metal. 



Somewhat less coke is consumed when the fusion is pushed more rapidly, to collect 

 a great body of melted metal for casting heavy articles ; and more is consumed when, 

 as in making many small castings, the progress of the founding has to be slackened 

 from time to time ; otherwise, the metal would remain too long in a state of fusion, 

 and probably become too cold to afford sharp impressions of the moulds. 



It sometimes happens that in the same day, with the same furnace, pieces are to be 

 cast containing several proportions of different kinds of iron ; in which case, to prevent 

 an intermixture with the preceding or following charges, a considerable bed of coke 

 is interposed. Though there be thus a little waste of fuel, it is compensated by the 

 improved adaptation of the- castings to their specific objects. The founding generally 

 begins at about 3 o'clock P.M., and goes on till 6 or 8 o'clock. One founder aided by 

 four labourers for charging, &c., can manage two furnaces. 



The following is the work of a well-managed foundry in Derby. 



200 Ibs. of coke are requisite to melt, or bring down (in the language of the founder), 

 1 ton of cast iron, after the cupola has been brought to its proper heat, by the com- 

 bustion in it of 9 baskets of coke, weighing, by my trials, 40 Ibs. each = 360 Ibs. 



The chief talent of the founder consists in discovering the most economical mix- 

 tures and so compounding them as to produce the desired properties in the castings. 

 One piece, for example, may be required to have great strength and tenacity to bear 

 heavy weights or strains ; another must yield readily to the chisel or the file : a 



VOL. II. II 



