| Block, Jo | (english) Shop name for a Johnnson gage block, a very accurate measuring device. |
| Blocker | (english) Preform die or impression, used when part cannot be made in a single operation. |
| Bloom 2 | (english) A semi-finished hot rolled product, rectangular in cross section, produced on a blooming mill. For iron and steel, the width is not more than twice the thickness, and the cross-sectional area is usually not less than 36 sq. in. Iron and steel blooms are sometimes made by forging. |
| Bloomery | (english) A primitive furnace used for direct reduction of ore to iron. |
| Blooming-Mill | (english) A mill used to reduce ingots to blooms, billets slabs, sheet-bar etc., |
| Blow | (english) The impact or force delivered by one workstroke of the forging equipment. |
| Blow Back | (english) A coating defect consisting of a lower coating film weight on the bottom of the coated sheet caused by high velocity air in the oven. Blow back usually occurs with high solids coatings which have little solvent to evaporate and "set" the film. |
| Blow Down | (english) Process that rids boiler feed water of solids and maintains the proper chemical balance of the feed water. Blow down can also be used to rid drum(s) of excess water. |
| Blowhole | (english) A defect in a casting caused by trapped steam or gas. |
| Blowhole 2 | (english) A cavity which was produced during the solidification of metal by evolved gas, which in failing to escape is held in pockets. |