Electro-dynamic passive magnetic bearings are now viewed as a feasible option when looking for support for high-speed rotors. Nevertheless, because of the skew-symmetrical visco-elastic properties of such bearings, they are prone to operational instability. In order to avoid this, the paper proposes the addition of external damping into the newly designed vibrating laboratory rotor-shaft system. This may be achieved by means of using simple passive dampers that would be found among the components of the electro-dynamic bearing housings along with magnetic dampers, which satisfy the operational principles of active magnetic bearings. Theoretical investigations are going to be conducted by means of a structural computer model of the rotor-shaft under construction, which will take into consideration its actual dimensions and material properties. The additional damping magnitudes required to stabilize the most sensitive lateral eigenmodes of the object under consideration have been determined by means of the Routh-Hurwitz stability criterion.
Simulation software dedicated for design of casting processes is usually tested and calibrated by comparisons of shrinkage defects distribution predicted by the modelling with that observed in real castings produced in a given foundry. However, a large amount of expertise obtained from different foundries, including especially made experiments, is available from literature, in the form of recommendations for design of the rigging systems. This kind of information can be also used for assessment of the simulation predictions. In the present work two parameters used in the design of feeding systems are considered: feeding ranges in horizontal and vertical plates as well as efficiency (yield) of feeders of various shapes. The simulation tests were conducted using especially designed steel and aluminium castings with risers and a commercial FDM based software. It was found that the simulations cannot predict appearance of shrinkage porosity in horizontal and vertical plates of even cross-sections which would mean, that the feeding ranges are practically unlimited. The yield of all types of feeders obtained from the simulations appeared to be much higher than that reported in the literature. It can be concluded that the feeding flow modelling included in the tested software does not reflect phenomena responsible for the feeding processes in real castings properly. Further tests, with different types of software and more fundamental studies on the feeding process modelling would be desirable.
This work reports on cadmium and lead contaminations in the edible snail Helix pomatia harvested in Poland. One hundred and 24 samples of Helix pomatia meat collected from seven provinces (voivodeships) of Poland were analyzed for their trace metal levels by graphite furnace atomic absorption spectrometry (GFAAS). The research was conducted in 2 stages. The 1st stage analyzed snail meat prior to any further technological treatment (raw meat). In the 2nd stage, the trace element levels were measured in meat subjected to technological treatment (processed meat). The trace element contents in raw meat samples ranged from 0.06 mg kg-1 to 0.22 mg kg-1 for Cd and from 0.06 mg kg-1 to 0.18 mg kg-1 for Pb. The analyses revealed an increase in the cad- mium content from 0.12 mg kg-1 to 0.18 mg kg-1 in thermally treated snail meat and no changes in lead concentration during the two-stage heat treatment. Regulation (EC) 1881/2006 does not specify the Cd and Pb residue limits in meat of terrestrial edible snails. The limits are set for in- vertebrate aquatic organisms meat (i.e. shellfish, mollusc, cephalopod) and range from 0.5 mg/kg to 1.5 mg/kg of tissue fresh weight for Pb and from 0.5 mg kg -1 to 1 mg kg-1 for Cd (EU Commis- sion 2006). The results demonstrate that the land snail Helix pomatia has a tendency to bioaccu- mulate trace elements, and the cooking process is likely to affect (increase) the Cd content in the snail meat.