CHAPTER XXXII 

 THE MAKING AND WORKING OF WROUGHT IRON 



435. Manufacture of Wrought Iron. Wrought iron, 

 oftentimes called bar iron, is made from the rough pig iron. 

 In the process of manufacture, it is first refined in the "pud- 

 dling furnace." Here it is exposed to a very great heat, and is 

 stirred about while a strong current of air plays over it. The 

 intense heat converts the carbon matter remaining in the 

 iron into carbon dioxide. As this escapes, all earthy impuri- 

 ties rise to the surface in the form of slag, and are allowed to 

 run off. Gradually as the iron is purified it becomes pasty or 

 tough, and when this toughening process begins the iron is 

 called a bloom. This takes place even though the heat of the 

 furnace be undiminished. After a while, the iron is with- 

 drawn and while red hot is either beaten (worked) with a 

 forge trip hammer, which drives out the remaining slag, or 

 is subjected to rolling. This latter process compresses its 

 particles and makes it more tenacious. The metal is rolled 

 while hot into bars of inferior quality. These bars are cut 

 into short lengths and piled crossways. They are later re- 

 heated and rehammered or rolled, after which they are known 

 as merchant bars and in this form are used for common 

 girder work, ladders, fire bars, etc. Any desired shape may 

 be given to the bars by means of dies. The operations of 

 cutting, piling, etc., may be repeated several times to give 

 the desired strength and tenacity. 



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