| Abrasive 3 | (english) A substance capable of grinding away another material. |
| Abrasive Wear | (english) The displacement and / or detachment of metallic particles from a surface as a consequence of being exposed to flowing fluids or gases. |
| Abrasive Wheels | (english) Wheels of a hard abrasive, such as Carborundum used for grinding. |
| ABSOLUTE PRESSURE | (english) The indicated value of the weight of the earth's atmosphere. At sea level, this value is approximately 14.65 psi (pounds per square inch). |
| ACCUMULATOR | (english) A vessel, normally cylindrical, which is used to store fluid and gas for future release of the energy in the compressed fluid and gas. Normally contains a diaphragm or piston between the fluid (liquid) and gas chambers. Fluid is normally introduced at one end and the gas at the opposite end. |
| Acid Process 1 | (english) A process of making steel, either Bessemer, open-hearth or electric, in which the furnace is lined with a siliceous refractory and for which low phosphorus pig iron is required as this element is not removed. |
| Acid Process 2 | (english) A steel making method using an acid refractory-lined (usually silica) furnace. Neither sulfur or phosphorus is removed. |
| Acid-Process | (english) A process of making steel, either Bessemer, open-hearth or electric, in which the furnace is lined with a siliceous refractory and for which low phosphorus pig iron is required as this element is not removed. |
| Acme Thread | (english) A screw thread having a 29 degree included angel. Used largely for feed and adjusting screws on machine tools. |
| Activation | (english) The changing of the passive surface of a metal to a chemically active state. Contrast with passivation. |