14 



CHILLED IRON. 



upright shaft, opposite opinions arc to bo met with as to 

 whether a chilled cast-iron or hardened steel step is the 

 harder. In this instance other considerations — as compara- 

 tive contexture of the rubbing surfaces in contact, tenacity, 

 lubrication, etc., — come in to affect the result. A tool that 

 cuts chill must seemingly be harder than the chill itself, 

 but in this case tenacity comes in as a factor. For laminat- 

 ing and sometimes punching hot metals, the nature of the 

 hardness of chilled cast-iron enables it to hold the field. 

 Obviously a hardened steel roll for a sheet mill would 

 become worthless as soon as it approached an annealing 

 temperature (ranging from 420° to 600° Fahr.) in work. 



With respect to the strength and fatigue resistance of 

 chilled castings, details were given of some impact tests 

 made in July, 1864, at Pontypool, in the presence of Captain 

 Palliser, upon some of his cliillcd artillery bolts, 12J inches 

 long by 4 inches diameter, made from Pontypool cold-blast 

 pig iron. Those made from No. 1 pig iron (the most gi'aphi- 

 tic and costly) broke more easily than those from No. 2 ; and 

 so on, until those made from No. 4 were tested, when the 

 maximum strength was readied. No. 4 pig iron was in 

 fracture a pale grey, bordering on mottled. The bolts 

 made from it chilled throughout; those made from No. 1 

 pig would not chill more than -| inch deep. The same mould 

 chills were used for all the bolts. 



Several points regarding foundry operations in the pro- 

 duction of chlled castings were raised for discussion. They 

 embraced the depth of chill to bo imparted to chilled rolls 

 and railway wheels, and, in the case of traction wlieolsj 

 the width of chill in the tread ; preparation of the chills 

 (by coating with various car'bonaceous matters, lime, beer 

 grounds, or occasionally some mysterious compost) and 

 moulds ; selection and mixture of pig irons ; methods and 



