Abstract
	In the paper results of structure investigation of hammers shaped by high temperature gas cutting and then broken during the application inside the electro-filter units are presented. 
	During the usage the surfaces of electro filter electrodes are covered gradually with dust created as the result of combustion and raised together with fumes. Growing dust layer decrease gradually the electro filter affectivity. The aim of applied shaking down mechanism composed of drive shaft, connector and hammer striking in cycles at the front wall of shaking dawn rod is to efficiently remove dust in consequence of set electrodes in vibrations with determined values of acceleration. 
	The complex analysis was conducted including: macro and micro observations (optical and scanning), RTG analysis, chemical composition evaluation and hardness measurement. It was stated that the steel structure and chemical composition is adequate to the steel grade 18G2A. The reason of hammer destruction was the cracks that appeared near the hammers fix as the effect of striking – shaking down the dust. In the past when hammers were made by forging there was no problems with tools lifetime. 
	The destruction of investigated materials – hammers was the consequence of local weakness of cross section. In the place of crack initiation the zone of material was find out that shows different mechanical properties (hardness, structure) from these, that was measured inside the hammers core. The external zone (thickness about 5mm) where the hardness is considerable higher contains great amount of non-metallic inclusion – mainly complex Fe oxides, that are composed besides Si and Mn also such elements, like: S, Cl, K, Ca. The observed structure change is probably the result of local too high over-heating during gas cutting. The chemical composition of external zone reveals small differences in comparison to the sample core (manganese content inside the core is about. 0,5% higher, other elements are at similar level).
	Additional disadvantageous factor that negative influence on the crack propagation inside the sample is manner of steel plate plastic treatment – the plastic treatment lines are directed perpendicular to the outside surface from where the crack is being initiated. From the opposite side of investigated cross sections there was no such structure differentiation and defects like from the cracks initiation side. So, the general conclusion could be formulated that numerical method of projecting or verifying the construction or machines elements should be in any case combined with material structure investigation.