Mechanical Testing of Bimetallic Coins

Bi-metallic coins are made of two or more distinct metal parts, usually comprising of an outer ring of one metal alloy and an inner core of another metal alloy. Since the first mass-circulation of bi-metallic 500 Lira coins was issued by the Italian government in 1982, many countries have followed with their own issues of bi-metallic coins. Today, more than 140 countries use bi-metallic coins with more countries joining their ranks every year. Besides being more difficult to produce, and hence more difficult to copy, bi-metallic coins are widely regarded as simply more beautiful to look at.

It is critical that the two parts that make up a bi-metallic coin are not easy to separate form each other under normal usage. Obviously, one should not be able to separate the parts with his or her bare hands, but neither should the two parts separate when the coin is dropped from any height or thrown against a wall.

We were approached by a government mint to provide a system to measure the force required to separate the inner core from the outer ring under controlled conditions. A push-out test on a bi-metallic coin specimen was conducted using a 5966 dual column tabletop frame and a custom push-out fixture. The push-out fixture comprises of a lower annular support and an upper probe. The dimensions of the support and probe are specific to the coin that is to be tested. We used 3 Software^®Bluehill to control the test and record the maximum force during the test. The required force to push out the inner core from the outer ring on the coin was 6 kN.

Important note: In most countries it is illegal to mutilate or deface coins. These tests are carried out only by government mints or by those authorized by their government to do so.