Surface tension

Fluids have the ambition to reduce theit surface and to take the energetic most favourable form of a ball-shaped drop (e.g. a waterdrop). This phenomenos is called surface tension. The surface tension is measured in the SI unit N/m. The surface tension is also called interfacial tension which is effective between the interfaces of two materials in any phase.

Interface active substances like oil or grease minimize the surface tension. The quality of a rubber to plastic or rubber to metal bonded part is essentially determined by the use of carrier surfaces free from oil and grease.

The surface tension and, at the same time, the freedom of grease of the surface of a metal or plastic part can be determined by the so-called ink-test-method.