Chocolate masses are one of the basic raw materials for the production of confectionery. Knowledge of their rheological and flow behaviour at different temperatures is absolutely necessary for the selection of a suitable technological process in their production and subsequent processing. In this article, the rheological properties (the effect of the shear strain rate on the shear stress or viscosity) of five different chocolate masses were determined—extra dark chocolate (EDC), dark chocolate (DC), milk chocolate (MC), white chocolate (WC), and ruby chocolate (RC). These chocolate masses showed thixotropic and plastic behaviour in the selected range of shear rates from 1 to 500 s⁻¹ and at the specified temperatures of 36, 38, 40, 42, and 44 °C. The degree of thixotropic behaviour was evaluated by the size of the hysteresis area, and flow curves were constructed using the Bingham, Herschel–Bulkley and Casson models with respect to the plastic behaviour of the chocolate masses. According to the values of the coefficients of determination R² and the sum of the squared estimate of errors (SSE), the models were chosen appropriately. The most suitable models are the Herschel–Bulkley and Casson models, which also model the shear thinning property of the liquids (pseudoplastic with a yield stress value). Using the coefficients of the rheological models and modified equations for the flow velocity of technical and biological fluids in standard piping, the 2D and 3D velocity profiles of the chocolate masses were further successfully modelled. The obtained values of coefficients and models can be used in conventional technical practice in the design of technological equipment structures and in current trends in the food industry, such as 3D food printing.

Acta Universitatis Agriculturae et Silviculturae Mendelianae Brunensis, the scientific journal of the Mendel University in Brno, Czech Republic

Awareness of engine oil condition is a valuable indicator for assessing the state of degradation of the lubricant. The article deals with monitoring of chemical elements, especially metals and additives, during lifetime of commercially distributed automobile engine oil Castrol Magnatec 10W–40. Engine oil was regarded as a Newtonian fluid. The passenger car Renault Scenic I with petrol engine (four pistons, volume 1,600 cm³) was used to the observed. Lifetime of automobile engine oil has been stated by car and lubricants producers in interval 15,000 km. The samples of automobile engine oil have been taken in suitable intervals – 1,500 km. Only first sample of used engine oil was taken with raid 20 km. The seasons of monitoring were spring and summer. The spectrometer Spectroil Q100 has been used to monitoring of chemical elements in automobile engine oil. Increase contents of metals and decrease contents of additives were observed. The results were modelled using mathematical models with given the values of coefficient correlation R. Linear function as a mathematical model with the lowest number of degrees of freedom was used. Created mathematical models can be used to predict of conditions of engine oil in the same or similar petrol engine aggregates.

The effect of the passage of agricultural machinery on the soil is influenced by, for example, the inflation pressure in tyres. This article describes the effect of different tyre inflation pressures (200 and 100 kPa) on selected physical soil properties in the field experiment. The undisturbed...

The paper deals with the actual topic of mechanical properties of 3D prints made from the polymer material rPET-G and its changes. Using this material in additive technology has great potential in the automotive industry. The research evaluates five different post-processing modifications of 3D prints from rPET-G (recycled polyethylene terephthalate-glycol) material produced by the Fused Filament Fabrication technology. The post-processing included the chemical smoothing of the samples using dichloromethane vapors and heat treatment in an annealing furnace. An epoxy resin, a synthetic coating, and a water-based coating were also applied. The standard was represented by samples without post-processing modifications, both in the form of recycled material and in the form of virgin PET-G. The texture of the samples was evaluated according to EN ISO 4287. Furthermore, the moisture absorption of the samples was evaluated using the gravimetric method according to EN ISO 62. The mechanical testing of the samples was carried out using a tensile test (EN ISO 527-2), a three-point bending test (EN ISO 178), impact strength (EN ISO 179-2), and a cupping test (EN ISO 1520). Degradation of the coatings took place using cyclic tests, which used a combination of exposure in a salt fog environment and in a climate chamber. The results of the experiments indicate that heat treatment appears to be a universal post-processing technology, as this method statistically improves not only the mechanical properties but also significantly reduces moisture absorption.

This study evaluates the effects of three mechanical pre-treatment methods on S235JRG2 steel sheets: blasting with a synthetic corundum (F40), blasting with steel shot (S170), and grinding with synthetic corundum (P40). Untreated samples served as a reference. The analysis of mechanical pre-treatments focused on surface integrity, including measurements of surface roughness parameters Ra and Rz (ISO 21920-2) and subsurface microhardness (ISO 6507-1). Zinc coatings were assessed through mechanical testing (cupping test, ISO 1520) and corrosion testing in a neutral salt spray environment (ISO 9227), with results evaluated using digital image analysis. Experimental findings indicate that electroplated zinc deposition rates are influenced by surface roughness, while subsurface microhardness has no significant effect. In contrast, for hot-dip galvanizing, both parameters impact the process. The mechanical properties of electroplated zinc coatings are further affected by steel surface integrity, whereas hot-dip zinc coatings are primarily governed by intermetallic phase formation, making the influence of steel surface integrity statistically negligible. Corrosion testing revealed that blasting with a synthetic corundum is particularly unsuitable, as it leads to numerous inhomogeneities in both coating types, accelerating corrosion degradation.