The research conducted in this paper concerns the influence of the continuous casting process of tin-zinc-lead bronze on the wear of the graphite crystallizer. Observations and testing of the external surface of the cast rods indicate their good quality, without casting defects. No excessive surface degradation was observed on the inner surface of the crystallizers after casting. It was assessed that the surface quality of the crystallizer would be acceptable for further use, despite stuck residue, mainly in the crystallization zone

Brudny, A.

Cwolek, B.

Juszczyk, B.

Kulasa, J.

Malec, W.

English

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785METALURGIJA 61 (2022) 3-4, 785-788A. BRUDNY, J. KULASA, B. CWOLEK, W. MALEC, B. JUSZCZYKINFLUENCE OF THE CONTINUOUS CASTING PROCESS  OF TIN-ZINC-LEAD BRONZE ON THE WEAR OF THE GRAPHITE CRYSTALLIZERReceived – Primljeno: 2021-10-30Accepted – Prihvaćeno: 2022-03-25Preliminary Note – Prethodno priopćenjeThe research conducted in this paper concerns the influence of the continuous casting process of tin-zinc-lead bronze on the wear of the graphite crystallizer. Observations and testing of the external surface of the cast rods in-dicate their good quality, without casting defects. No excessive surface degradation was observed on the inner surface of the crystallizers after casting. It was assessed that the surface quality of the crystallizer would be accept-able for further use, despite stuck residue, mainly in the crystallization zone.Keywords: bronze, continuous casting, graphite crystallizer, surface, structureISSN 0543-5846METABK 61(3-4) 785-788 (2022)UDC – UDK 669.35.6:621.74.04:66.065-678.5:621.9.015:620.18 =111INTRODUCTIONOne of the basic factors responsible for the produc-tion of high-quality rods in the continuous casting pro-cess are correctly selected casting conditions. Changing parameters such as casting speed and cooling water flow, apart from affecting the appropriate surface qual-ity, affects mainly the microstructure, and thus the me-chanical properties of the produced material [1, 2]. An important, but frequently ignored, factor in addition to properly selected casting parameters is the quality and kind of the used crystallizer. During the continuous casting process, especially of alloys containing aggres-sive elements, excessive wear of the graphite material occurs through the process of crystallizer surface degra-dation, consisting mainly of abrasive and erosive wear of mainly the internal part in the crystallization zone and directly behind it. Additionally, the casting process and the quality of the obtained castings are influenced by the crystallizer-cooler system, including the type of crystallizer geometry and its fitting with the cooling head through the efficiency of heat removal in the crys-tallization system. The better the surface quality of the crystallizer, the higher the casting efficiency. Increasing the efficiency of heat flow is possible by using crystal-lizers with high surface quality (low roughness) and properly matched to the crystallization system [3]. In addition to the properly selected crystallizer in terms of material and structure, an effective way to improve the heat removal effect in the crystallization zone is also to change the liquid inlet system to the cooler, which changes the liquid flow from laminar to vortex. The ef-fect of swirling and the intensity of turbulence of the casting liquid in the crystallizer improves the homoge-neity of the microstructure of the produced castings [4]. Crystallizers used in continuous casting of non-ferrous metals are made of graphite due to its self-lubricating properties, which eliminates the need for additional lu-bricants. Despite many advantages, graphite crystalliz-ers are susceptible to oxidation and metal particles tend to stick to their surface. Thus, it is necessary to periodi-cally regenerate crystallizers, but with the required high dimensional accuracy, the use of crystallizers after re-generation becomes impossible. The degradation of graphite consumables in a continuous casting line is mainly related to the chemical effect of liquid metal and high temperature. Crystallizers wear fairly quickly due to the friction between the surface of the crystallizer and the solidifying metal. In addition, crystallizers are also subject to mechanical wear, mainly during assembly in the crystallizer-cooler system, as well as in the initial stage of casting, due to inappropriate feeding of a starter bar into the crystallizer. Therefore, it is necessary to se-lect an appropriate type of graphite material from which the crystallizer is made, strictly depending on the chem-ical composition of the cast alloy and the form of the cast product in order to extend the correct operation and life of a crystallizer. Using crystallizers made of inap-propriately selected graphite materials generates high costs related to their frequent replacement with new ones, and thus the necessity to pause the production process and reassembling the crystallizer-cooler sys-tem. In the foundry of non-ferrous metals and their al-loys, graphite products are also used for heating ele-ments, crystallizers, and crucibles [5, 6]. As part of this work, laboratory scale tests were carried out to deter-mine the influence of the process of tin-zinc-lead bronze continuous casting on the wear of graphite crystallizer. Most often, the crystallizers used for casting non-fer-A. Brudny (anna.brudny@imn.gliwice.pl)J. Kulasa, B. Cwolek, W. Malec, B. Juszczyk, Łukasiewicz Research Network – Institute of Non-Ferrous Metals, Gliwice, Poland786  METALURGIJA 61 (2022) 3-4, 785-788A. BRUDNY et al.: INFLUENCE OF THE CONTINUOUS CASTING PROCESS OF TIN-ZINC-LEAD BRONZE…rous metals and their alloys are made of isostatically pressed graphite.EXPERIMENTAL PROCEDUREGraphite used for crystallizers should have high hardness and mechanical resistance. During the tests of casting rods from the CuZn5Sn5Pb2 grade alloy, a crys-tallizer made of R4550 grade isostatically pressed graphite material was selected for evaluation, the se-lected properties of which are presented in Table 1 [7]. Table 1 R4550 grade graphite material properties [7]Typical properties Units/ ValuesAverage grain size μm 10Bulk density g/cm3 1,83Open porosity Vol, % 10Medium pore entrance diameter μm 1,8Coecient of permeability  (ambient temperature)cm2/s 0,06Rockwell hardness HR 5 / 100 90Resistivity μΩm 13Flexural strength MPa 60Compressive strength MPa 130Dynamic modulus of elasticity MPa 11,5 x 103Thermal expansion (20 – 200 °C) K–1 4,2 x 10–6Thermal conductivity (20 °C) Wm–1K–1 105Ash content ppm 20During the continuous casting trials, one of the pro-cess parameters, the feed forward, was gradually in-creased while maintaining the reverse feed rate and the time of standstill at a constant level. The remaining pa-rameters were adjusted to maintain approximately con-stant temperature of the metal bath and the temperature of the crystallizer (the flow of water cooling the sys-tem). Ø15 mm rods were cast in two strands. The con-tinuously cast material was visually assessed to be good with no surface defects. For further macro and micro-structure studies, samples of the cast rod were taken at the beginning and the end of the casting process.RESULTS AND DISCUSSIONAnalysis of the surface of used crystallizersThe used crystallizer was tested after a 16-hour cast-ing process of the CuZn5Sn5Pb2 alloy on a ConCas-Tech MINI SCC laboratory line for continuous casting. The chemical composition results of this alloy are shown in Table 2. Table 2 Chemical composition of CuZn5Sn5Pb2 rods/ wt.%Cu Zn Sn Pb Ni Fe P SBal. 5,24 4,55 2,68 0,42 0,15 0,020 0,018The study of the surface analysis of the direct contact between metal and graphite was carried out together with a microanalysis of the chemical composition of a two-strand crystallizer made of isostatically pressed R4550 Figure 1 View of the used R4550 grade graphite crystallizerFigure 2  View of the cross-section of strands 1 and 2  of the R4550 grade crystallizerFigure 3 Surface analysis – part 1, strand 1grade material using a Zeiss Evo MA10 scanning elec-tron microscope (SEM) equipped with SE, BSE and En-ergy Dispersive Spectroscopy (EDS) SDD Quantax XFlash® 5010 Bruker detectors. The study of the analy-sis of the surface of the crystallizer walls which have con-tact with liquid metal was one of the elements of assess-ing the wear of the crystallizer exposed to temperature, liquid metal, and the aggressive air atmosphere. The test results for the crystallizer on which the CuZn5Sn5Pb2 alloy rods were cast are shown in Figures 1 ÷ 6.The wear analysis of the tested crystallizer was car-ried out in two areas:• part 1 of the crystallizer - the area where the so-lidified metal leaves the crystallizer,• part 2 of the crystallizer - the area where the met-al starts to solidify.In part 1, due to the occurring greater friction of the metal against the walls of the crystallizer, the presence of numerous metal traces rubbed onto the surface of the graphite material was observed.The surface analysis showed the presence of stuck zinc and lead residue as well as other alloying elements 787A. BRUDNY et al.: INFLUENCE OF THE CONTINUOUS CASTING PROCESS OF TIN-ZINC-LEAD BRONZE…METALURGIJA 61 (2022) 3-4, 785-788of the cast material (copper, tin) on the surface of the crystallizer. These analyses are illustrative as they con-cern only a specific area or point on the tested sample.As a result of the analysis of the internal surface of the crystallizer, the effects of wear can be observed, i.e., wear of the internal part due to metal-graphite friction, and burn-out due to high temperature and the presence of oxygen.Macro and microstructure of continuously cast rods The results of the macrostructure analysis of the cast rods are shown in Figure 7, and the microstructure in Figures 8, 9. No internal casting defects were observed for any of the tested samples. Depending on the place of sampling for testing (the beginning or the end of the casting process), and thus depending on the parameters of the casting process, a different macrostructure of the material of the cast rod was observed, which is obvi-ously related to the change in the casting speed and cooling intensity. The increase in cooling intensity re-sults in a gradual change in the direction of growth of the columnar crystals, and then the appearance of peri-odic changes related to the casting cycle.Cast materials have a multiphase microstructure where the basic structural component is a solid solution of tin and zinc in copper. In the microstructure, there are lead precipitations located in the interdendritic spaces and at the grain boundaries, and the precipitations of the α + δ eutectoid, also present in the interdendritic spaces. The characteristic relief of the surface of the specimens after etching is related to the strong dendritic segrega-tion typical of Cu-Sn alloys.Microstructure tests, carried out for a batch of rods obtained from continuous casting trials, and carried out Figure 6 Surface analysis – part 2, strand 2Figure 4 Surface analysis – part 2, strand 1Figure 5 Surface analysis – part 1, strand 2Figure 7 The macrostructure of continuously cast rodsFigure 8  The microstructure on the rod cross-section - the beginning of the casting processFigure 9  The microstructure on the rod cross-section - the end of the casting process788  METALURGIJA 61 (2022) 3-4, 785-788A. BRUDNY et al.: INFLUENCE OF THE CONTINUOUS CASTING PROCESS OF TIN-ZINC-LEAD BRONZE…by the observation methods of light microscopy and scanning electron microscopy with numerous EDS analyses, were related to an attempt to assess the impact of excessive wear of the crystallizer on the possible oc-currence of impurities and internal defects in the cast material.Surface analysis of the cast rods The surface of the rods was free from casting de-fects, such as misruns, tears. Periodic traces, related to the casting cycle, of light and dark grey colour and dif-ferent intensity were observed (Figures 10, 11). character corresponding with the casting parameters used. The presence of internal defects on a macroscopic scale was not observed. The rod microstructure is typi-cal of cast materials, dendritic, with a solid solution ma-trix based on α copper with strong dendritic microsegre-gation and α + δ eutectoid regions and lead particles present in the interdendritic spaces. No significant amounts of contamination, cracks or microshrinkages were observed.No excessive surface degradation was observed on the inner surface of the crystallizer after casting.It was assessed that the surface quality of the crys-tallizer would be acceptable for further operation, de-spite stuck metallic residue, mainly in the crystalliza-tion zone. In the place of abrasions of the crystallizer as a result of the casting process, the occurrence of stuck metallic residue did not lead to a deterioration of the quality and changes in the dimensions of the cast rods.AcknowledgementsThe research was carried out as part of the project: Techmatstrateg (TECHMATSTRATEG2/408701/2/NCBR/2019) co-funded by the National Centre for Re-search and Development. REFERENCES[1] P. Strzępek, A. Mamala, M. Zasadzińska, P. Noga, M. Sadzikowski, The Influence of the Continuous Casting Conditionson the Properties of High-Strength Two-Phase CuMg Alloys, Materials, 13 (2020) 21, 4805, DOI: 10.3390/ma13214805 [2] M. Zasadzińska, T. Knych, B. Smyrak, P. Strzępek, Inve-stigation of the Dendritic Structure Influence on the Elec-trical and Mechanical Properties Diversification of the Continuously Casted Copper Strand, Materials, 13 (2020) 23, 5553, DOI: 10.3390/ma13235513[3] P. Kwaśniewski, P. Strzępek, G. Kiesiewicz, Sz, Korda-szewski, K. Franczak, M. Sadzikowski, W. Ściężor, A. Brudny, J. Kulasa, B. Juszczyk, R. Wycisk, M. Śliwka External Surface Quality of the Graphite Crystallizer as a Factor Influencing the Temperature of the Continuous Ca-sting Process of ETP Grade Copper, Materials, 14 (2021), 6309, DOI: 10.3390/ma14216309[4] Y. Han, Y. Xiao, A.Y. Zhang, F. Liu, E.L. Yu, Y. Gao, Study on influence of lateral liquid feeding into crystallizer on solidification process of copper billets, International Journal of Heat and Mass Transfer, 125 (2018), 104-115, https://doi.org/10.1016/j.ijheatmasstransfer.2018.04.068.[5] V. E. Bazhenov, A. V. Koltygin, Yu. V. Tselovalnik, A. V. Sannikov, Determination of Interface Heat Transfer Coef-ficient between Aluminum Casting and Graphite Mold, ISSN 1067-8212, Russian Journal of Non-Ferrous Metals, 58 (2017) 2, 114-123.[6] K. Franczak, P. Kwaśniewski, K. Kiesiewicz, M. Za-sadzińska, B. Jurkiewicz, P. Strzępek, Z. Rdzawski, Rese-arch of mechanical and electrical properties of Cu-Sc and Cu-Zr alloys, Archives of Civil and Mechanical Enginee-ring, 20 (2020) 28, DOI: 10.1007/s43452-020-00035-z [7] https://www.sglcarbon.com/pdf/SGL-Datasheet-SIGRA-FINE-R4550-EN.pdfNote:  The translator responsible for English language: Małgorzata Krystowska, Gliwice, Poland.Figure 10  Surface analysis of a continuously cast rod - the beginning of the casting processFigure 11  Surface analysis of a continuously cast rod - the end of the casting processThe EDS microanalysis of the surface of the cast rods indicates the presence of large amounts of carbon on the surface in the form of graphite residue from the crystallizer rubbed onto it, numerous sweating, mainly lead, and less often stuck residue with a high tin content.CONCLUSIONThe conducted trials of continuous casting of CuZn-5Sn5Pb2 alloy rods in laboratory conditions allowed to obtain good quality material.Observations and tests of the external surface of the cast rods indicate their good quality, without casting de-fects. Only cyclical changes in the form of discoloration and traces of carbon from the crystallizer rubbed onto the metal are visible on the surface.The conducted research indicates the presence of lo-cal lead and tin enriched areas, which is a typical phe-nomenon for this type of alloys prone to segregation.The structural tests of the cast rods showed a macro-structure typical for continuously cast materials, its 

Influence of the continuous casting process of TIN-ZINC-LEAD bronze on the wear of the graphite crystallizer

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