The plunger must conform to very high standards. It is a moving part which must be low-wear but at the same time highly conductive.
Close tolerances must be included in the above criteria when plungers are used for small centers. The plungers are manufactured with maximum precision on long-turning lathes and then refined. In most cases, the plunger is coated with gold.
Plungers are manufactured of hardened finegrained steel for use in heavy-duty operating time situations. The emphasis is on tips with extra penetration, for example pointed tips. Aged copper-beryllium (CuBe) is used for plungers, especially when high demands are made of electrical conductivity for longterm constancy. With regard to environmental aspects, these are taken care of by the 100% wet-processing of the beryllium and by the coating on the plungers.
Test probes with CuBe plungers are suitable for measurement tasks in the case of potential difference and for high-current applications.
The brass plunger design with equally good conductivity is suitable for low-wear applications, e.g. charging contacts with very short travel and non-aggressive tip styles.
Alternatively, the plungers are fitted with different improvement coatings which, in addition to the electrical conducting and contact characteristics, are intended to satisfy specific requirements in respect of abrasion resistance and corrosion protection