Poldihammer
The Poldihammer is a handy device for hardness testing . Technically, it is a dynamic plastic hardness measurement and a modification of the classic Brinell method. In contrast to this, however, it can be used anywhere, even with already assembled components and in any position, as long as the test device can be placed perpendicular to the component and there is room for the hammer to blow. The Poldihammer is named after the Poldihütte (steel works in Kladno near Prague), where it was developed around 1900.
The Poldihammer consists of a housing with a firing pin and a hardened steel ball with a diameter of 10 mm at the head of the housing. A hardness comparison rod is inserted between the ball and the firing pin and locked in place by a compression spring of the firing pin. The ball is only guided laterally so that it touches the component to be tested at the front and the comparison rod inside. By striking with a hand hammer weighing around 1 kg, the ball is pressed simultaneously into the test piece and into the introduced comparison piece made of metal. Both test impressions are measured with a magnifying glass or microscope and the hardness of the test piece is determined from the ratio of the two impression diameters with the help of a comparison table.
The hardness values determined in this way do not exactly match the statically determined hardness values, but are sufficient for most industrial requirements. The "Poldi hardness" differs somewhat from the more exact Brinell hardness of a test laboratory, because the longer pressure load on a press has a different effect than a short hammer blow. In addition, with the Poldihammer, the compressive forces on the comparison rod and the sample are not exactly the same.
Impact hardness testers are a simple, practical substitute for static presses and are primarily used for testing heavy castings and forgings as well as large bars in material stores. In principle, they are also suitable for testing other hard, homogeneous materials.
The Baumann hammer works in a similar way , in which a 5 mm test ball is not pressed into the specimen by a hammer but by the impact of a steel spring.