U

Ultimate Tensile Strength (uts):  The maximum tensile stress a metal can stand. See Tensile Strength.

Ultrasonic Cleaning:  Immersion cleaning aided by ultrasonic waves which cause microagitation.

Ultrasonic Testing:  A nondestructive method of testing metal for flaws based on the fact that ultrasonic waves are reflected and refracted at the boundaries of a solid medium.

Unkilled Steel:  A wild steel insufficiently deoxidized so that it evolves gas and blowholes during solidification.

Urea Formaldehyde Resin:  A thermosetting product of condensation from urea or thio-urea and formaldehyde, soluble in water and used as a sand binder in core and mold compounds.