Analysis of Filler Metals Influence on Quality of Hard-Faced Surfaces of Gears Based on Tests in Experimental and Operating Conditions

Hard-facing as a type of the coating depositing is increasingly used today. Physical-chemical-metallurgical characteristics of contact layers in tribo-mechanical systems depend on the operating conditions and the conditions under which the work surfaces were created. That is the reason the influence of the processing procedures and regime, used in the contact surfaces formation, on development of the wear process of contact elements, is being considered ever more. To determine the influence of the hard-facing technology on characteristics of the gears' working surfaces, the experimental investigations were performed on samples hard-faced on the steel for cementation, by varying the filler metals (FM) and the hard-facing regimes. The samples tested were hard-faced by five "hard" and three "soft" filler metals. Experimental investigations included measuring the hard-faced layers' hardness and determination of their microstructure, as well as the wear resistance in the laboratory conditions, on tribometer and on a specially designed device for tests in the real operating conditions of gears. The wear intensity was monitored by the wear trace's width in the laboratory conditions and by the share of the teeth surfaces affected by the destructive pitting in the operating conditions. The results obtained were compared to results of the base metal (BM) tests, which provided the certain conclusions on which filler metal and which welding procedure are the optimal ones for regeneration of the worn teeth surfaces.

Weldability Assessment of Various Steels by Hard-Facing

Two aspects of various steels’ weldability are considered in this article. The theoretical part presents general concepts related to steel’s weldability and the application of the most important methods for its determination. In the experimental section, results of the hard-facing application to several samples are presented, and consist of hardness measurements in the different zones of the welded samples, with the evaluation of those zones’ microstructures. The tested materials included two carbon steels and two alloyed steels, with hard-facing layers deposited by various filler metals. Experimental results were compared to results obtained by calculations; using both, authors were able to conclude which combination of filler metal, welding procedure and, if necessary, heat treatment, would achieve the optimal improvement of weldability in welding/hard-facing of each of the tested base metals.

[Emergencies in arterial hypertension in children]

From March 1982 to March 1992 at the Nephrology Department of Belgrade University Children's Hospital 25 patients (16 females and 9 males, aged from 1.5 to 14 years) were treated for hypertensive emergency. Twenty patients had chronic severe hypertension of whom in 19 it was of renal origin. Five patients had acute hypertension during acute poststreptococcal glomerulonephritis. In 15 patients hypertensive emergency was manifested by neurologic disorders, while in the other patients signs of cardiac failure prevailed. Deterioration of renal function was observed in 9 patients and 2 had sec. haemolytic-uremic syndrome. Three patients died during hypertensive crisis, and the others were successfully treated. The fact that in 50% of patients chronic hypertension could not be revealed until the occurrence of hypertensive emergency, suggests the need of its early detection during systemic check-up.