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M. Bieroński, O. Krasa, M. Koza, D. Ksiąźek and R. Kuś

Abstract

In this paper an attempt to determine the relationship between the electrical resistivity and the tensile strength and hardness of cast iron of carbon equivalent in the range from 3.93% to 4.48%. Tests were performed on the gray cast iron for 12 different melts with different chemical composition. From one melt poured 6 samples. Based on the study of mechanical and electro-resistive determined variation characteristics of tensile strength, hardness and resistivity as a function of the carbon equivalent. Then, regression equations were developed as power functions describing the relationship between the resistivity of castings and their tensile strength and hardness. It was found a high level of regression equations to measuring points, particularly with regard to the relationship Rm=f(ρ). The obtained preliminary results indicate the possibility of application of the method of the resistance to rapid diagnostic casts on the production line, when we are dealing with repeatable production, in this case non variable geometry of the product for which it has been determinated before a regression equation.

Open access

D. Książek, M. Koza, M. Bieroński, O. Krasa and R. Kuś

Abstract

The publication presents the results of examination of selected carburizers used for cast iron production with respect to their electric resistance. Both the synthetic graphite carburizers and petroleum coke (petcoke) carburizers of various chemical composition were compared. The relationships between electrical resistance of tested carburizers and their quality were found. The graphite carburizers exhibited much better conductivity than the petcoke ones. Resistance characteristics were different for the different types of carburizers. The measurements were performed according to the authors’ own method based on recording the electric current flow through the compressed samples. The samples of the specified diameter were put under pressure of the gradually increased value (10, 20, 50, 60, and finally 70 bar), each time the corresponding value of electric resistance being measured with a gauge of high accuracy, equal to 0.1μΩ. The higher pressure values resulted in the lower values of resistance. The relation between both the thermal conductance and the electrical conductance (or the resistance) is well known and mentioned in the professional literature. The results were analysed and presented both in tabular and, additionally, in graphic form.

Open access

Maria Wieloch, Piotr Koza, Krzysztof Kuzdak, Piotr Ziemniak and Krzysztof Kołomecki

The aim of the study

was to evaluate the safety of one-day thyroid surgery based on the assessment of the incidence of early postoperative complications.

Material and methods. The study comprised 726 patients who underwent total thyroidectomy during the period between January, 2012 and February, 2013. The study considered the three most common thyroidectomy complications.

Results. In the group of 726 patients, recurrent laryngeal nerve paralysis was observed in 22 cases, accounting for 3.07% of all patients. Postoperative bleeding was observed in 12 cases (1.65%). In 8 cases, bleeding occurred during the first 8 hours after surgery, while in the remaining four cases- 9, 12, 18, and 26 hours after surgery. The study group was divided into three subgroups, in which the concentrations of calcium and parathyroid hormone, 6 hours and 20 hours after surgery, were determined. In the first group (223 patients), only the parathyroid hormone level was determined. The decreased PTH level was associated with the appearance of tetany symptoms in 15% of cases. Amongst patients in whom the parathyroid hormone level was normal, tetany symptoms were observed in 0.5% of cases. In the second group (256 patients), only the serum calcium level was determined. Amongst patients with normal serum calcium levels, 1% of cases presented with tetany symptoms. In patients where the serum calcium level was reduced, tetany symptoms appeared in 35% of cases. In the third group (247 patients), both serum calcium and parathyroid hormone levels were determined. In the group of patients with normal, both serum calcium and parathyroid hormone levels, tetany symptoms were not observed. Amongst patients with normal serum calcium levels and decreased PTH levels on the day of surgery, tetany symptoms were observed in 25% of cases, while during the first postoperative day-37% of cases.

Conclusion. One-day thyroid surgery, due to the appearance of complications cannot be regarded as a completely safe procedure.