The products of the rolling process are classified as follows : -
Puddled Bars, also known as No. 1 or rough bars.
The puddled bar obtained by the processes above described is of a very weak and inferior quality.
In order to improve the quality of the material, the puddled bar is cut up into short lengths and subjected to the processes of piling, reheating, and rolling.
The effect of these processes is - 1st, To drive out the slag; 2d, To give uniformity of structure, weak parts of one bar being brought alongside the strong parts of other bars; 3d, To produce a finished surface.
Some of the harder kinds of iron are, however, worked chiefly by the hammer, the bar being passed through the rolls only at the last when it is to receive its finished section.
Merchant Bar or Common Iron, known also as No. 2, is produced by piling up short lengths of puddled bars, raising them to a welding heat, and passing them through rollers. This amalgamates them into a single bar, and gives the iron a fibrous structure which greatly increases its strength.
This quality of bar is, however, still very inferior, being hard and brittle.
It can be forged only with difficulty, and is useful only for the commonest purposes.
Best Bar is produced by cutting up merchant bars, and repeating the processes of piling, reheating, and rolling.
In some cases the top and bottom of the pile are made with bars that have been twice rolled.
Best bar is far tougher and more easily worked than merchant bar, and is generally used for ordinary good work.
Best Best and Best Best Best iron bars are those which have respectively been submitted to three and four repetitions of the processes of piling, welding, and rolling.
Scrap Bars are made from short pieces that are useful for no other purpose welded and rolled together into a single bar.
When the scraps used are old pieces not thoroughly cleaned, the resulting bar is of an inferior description.
If, however, the scraps used are of new and clean iron, such as the short ends cut off finished rails, an iron of capital quality is produced, which is known as best scrap or best best scrap.