Wyniki 1-6 spośród 6 dla zapytania: authorDesc:"Ján TURŇA"

Measurement of roll temperature in stretch reducing mill DOI:10.15199/24.2017.8.24

  Introduction. During rolling of seamless steel tubes in a stretch reducing mill (SRW) the tubular feedstock passes several 3-roll stands with circular/oval rolling gap without any internal tool. The input feedstock of a mod erate length is usually stretched many-folds, depending on the final tube dimensions [1]. In this paper, we focused on the cooling effect of water sprayed onto the roll sur face during stretch reducing of various tube dimensions. In Železiarne Podbrezová tube rolling plant the thin- -walled tube dimensions appear to be critical for maintain ing sufficiently high rolling exit temperature (Tdov > Ar3). To solve this problem we must first measure the actual temperature of the rolls in order to decide whether there is a margin for further lowering of the water flow rate; too little cooling could be detrimental to the life span of the rolls. For this, two different approaches to temperature mea surement can be adopted. In 2016, roll temperature mea surements were carried out periodically using MICRO-EP SILON thermoME-TER LS portable laser pyrometer (Fig. 2) with spectral sensitivity (8 ÷ 14) μm and 200ms sensing period (time constant of the device is 150 ms). However, we were not measuring the working surface temperature direct ly; the measurements were carried out on the oxidized side surface of the rolls. In addition, test measurements of the glossy working surface of the rolls were performed, too, but the glossy nature of the surface with very small emisivity rendered these measurements unreliable. Next to the con tactless measurement method we also carried out contact measurem[...]

The influence of reduction on the surface temperature in the process of drawing tubes DOI:10.15199/24.2019.8.12

  Introduction. Cold drawing technology used for manufacturing of precision seamless steel tubes in Železiarne Podbrezová depends on many factors, two of which are the initial and the final tube dimensions[1-4]. The proper selection of area reductions is therefore a crucial task as the improper reduction sequence may lead to excessive straining, possibly causing cracks or even material failure[1-3]. In plug drawing technology, the inner diameter of the tube takes the exact dimension while the wall thickness is being reduced. Cold drawing using a fixed plug is a versatile technology, sporting high productivity and relatively low demands on drawing tools. As the main tool, the reducing die is being used[1-3]. A cylindrical plug is inserted into the die orifice, being fixed on a mandrel. The proper alignment of the die and the plug is necessary for attaining correct dimensions of the tube after drawing and also for drawing in general, see Fig. 1 [1-3]. The drawing technology. The process of a tube cold drawing is schematically depicted in Fig. 2. The main production steps are as follows [2-4]: - feedstock pre-processing, - cold and hot pointing of tube ends, - chemical treatment of the tube (pickling, phosphating, lubrication), - cold drawing, [...]

Analysis of eccentricity hot rolled tubes DOI:10.15199/24.2016.8.16

  Analiza mimośrodowości rur walcowanych na gorąco The production programme of ironworks Železiarne Podbrezová a.s. deals primarily with the production of seamless steel tubes rolled from billets from company’s foundry. This paper deals with the study of the transverse defects causes of tubes, especially eccentricity that is evaluated at each technological node separately. The problem of tube eccentricity is considered as a p rimary factor of geometrical deviation. The current method of eccentricity evaluation has been examined. Part of the paper comes up also with the continuous evaluation of tube eccentricity in real production runs. This evaluation takes place once a month, with 98% of seamless tubes produced with eccentricity not exceeding 5%. Conclusions in this paper are decisive for taking preventive measures for eccentricity to occur and also for fixing the measurement methodology for eccentric tubes. Program produkcji huty Železiarne Podbrezová a.s. obejmuje głównie wytwarzanie rur stalowych bez szwu walcowanych z wlewków pozyskanych z własnej odlewni [...]

The comparison of cooling efficiency of twoo types of nozzles for roll cooling on selected stands in stretch reducing mill DOI:10.15199/24.2018.9.7

  Introduction. Stretch reducing mill (SRW) is a hot rolling mill for manufacturing of seamless tubes. Here, the final tube dimensions and final mechanical properties of hot rolled tubes are achieved after cooling [1-5]. During rolling of tubes in SRW the tubular feedstock (“the hollow") of a moderate length passes several stands with circular or oval rolling gap without using any internal tool. During stretch reducing the diameter and wall thickness of the hollow are changed, depending on the final dimensions. The stretch reducing mill can be used [1-9]: - To extend the production range of tubes of small dimensions, - To produce the tubes with small and medium diameter, - To reduce the production costs. Condition of the rolls in SRW stands are of vital importance for obtaining the final diameter and surface quality of the tube. Thus it is necessary to focus on the surface temperature of the hollow and optimal surface temperature of the rolls. Therefore, decision has been made to optimize the roll cooling process by means of a new set of nozzles with smaller nominal flow rate [1-10]. Methodology and instruments for temperature measurement. When choosing the appropriate methodology of temperature measurement, two basic methods were at our hand: contact and contactless. The contact method proved to be more suitable for measuring the surface temperature of the roll [9-14]. Contactless measurement would be very difficult to use for several reas[...]

The influence of technological parameters for the manufacture of precision seamless tubes for automotive industry DOI:10.15199/24.2019.8.5

  Introduction. On the basis of the increasing demand of tubes for the automotive industry, which in recent years once with the requested commodities of each company is also Zeleziarne Podbrezová (ZP) market needs for this industry. Due to the very specific and complicated production with the need to observe high standards, whether it is a tolerance of geometric dimensions, or compliance with material properties, it is necessary to ensure, during the production itself, mapping of the entire technological flow. In this paper, we looked at two different technologies of pulling and comparing them in terms of geometric accuracy. The first method consisted of draws on mandrel and the second method being a hollow sinking. In these processes, due to the need to know the parameters affecting the drawing itself, we have measured the temperature of the tube surface just behind the tool working surface. The other parameters analysed were the properties of the material itself, which, both at the input and output, greatly affect the forming process itself. The technically cold drawing process of the tubes is shown in Fig. 1 and consists of several technological nodes. Due to the drawing process, it is necessary to properly set the parameters of these technological nodes, such as heat treatment, which must ensure good formability of the material. It is important to ensure the correct chemical treatment which reduces the coefficient of friction and thus also the actual drawing temperature. Other parameters th[...]

Microstructure aspects and comparison of mechanical properties of cold drawn precision seamless tubes DOI:10.15199/24.2019.8.8

  Introduction. In this paper, we focused on a detailed mapping of the selected cold drawing of tube production technology, which is commonly used in cold-drawn tube factory. Its essential foundation is to emphasize the input material with a view to microstructure and mechanical properties, emphasizing the possibilities of the following forming process. In previous experiments, a methodology for determining intense tensile strength by mechanical properties was proposed. Given the economic and technological savings, it is important to propose adjustments that modify the process while not compromising the microstructural properties of the material, necessary to apply additional limit deformations in the process itself. The whole technological process consists of individual technological nodes (Fig. 1), which must meet the necessary standards resulting from the set technological process. By modifying a specific technological node in this case of the drawing process, it allows for the omission of the entire process, which has an economic benefit and, last but not least, saving time and performance for individual employees. To meet these conditions, it is necessary to observe the conditions of the input material properties (Fig. 2) and this is in our case a rolled tube. This paper describes the first course of selected tube drawing technology in terms of microstructure and mechanical properties. In the first run, the starting material and two consecutive strokes are described without intermediate annealing and subsequent heat treatment [3]. Experimental material. The experimental material was selected on the basis of the ZP production portfolio. Considering the extensive experiments that were conducted to innovate [...]

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