Hardness has been considered to be one of the most important mechanical indicators of material quality. Here, an automated portable hardness tester was used to evaluate dynamic hardness (DH) of vegetable charcoal for industrial application, correlating these results to vegetal material and final temperature of carbonization. Wood specimens from nine vegetal materials were pyrolysed at final temperatures of 300, 450, 600, and 750 °C. A total of 45 wood specimens were used as the sample control. DH of wood and charcoal was determined by an automated portable hardness tester. Wood specimen DH varied from 12.9 to 44 MPa. Wood density (ρ) presented a high positive correlation (r = 0.94) with wood DH. The heavier wood species (ρ = 988.6 kg m–3) is on average 1.93 times denser than the lighter wood (ρ = 512 kg m–3), while the harder wood (DH = 44 MPa) is 3.41 times harder than the softer material (DH = 12.9 MPa). Charcoal specimen DH significantly varies with the final temperature of carbonization: DH was 10.89 MPa for charcoal specimens produced at 300 °C, 3.05 MPa for charcoal produced at 450 °C, 3.44 MPa for charcoal produced at 600 °C, and 4.59 MPa for charcoal produced at 750 °C. Hardness variation between vegetal materials also decreases with the final temperature of carbonization. These findings are important, especially for industries that use the Eucalyptus charcoal as a reducing agent and supporting material in blast furnaces for producing “green steel”. In this industrial segment, a homogeneous product is necessary and the control of the characteristics of the raw material becomes essential.

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A research group on forest products from School of Agriculture – Sao Paulo State University. Brazil developed a portable hardness tester for wood, which is based on a displacement transducer and an embedded electronic processor for dynamic evaluation of hardness. This paper presents the results of calibration tests of the equipment, carried out on seven species of Eucalyptus. A new methodology for dynamic hardness calculation has been introduced, which relays on the reaction force of the indentation, while the measurements of indentation depth are performed under load. A moderate to strong linear correlation to Janka hardness and its variations were found. This new approach avoids the classical problems of Brinell hardness test in terms of “sinking-in” (causing diffuse edges) and elastic recovery of the indentation.