POSSIBILITIES OF FOUNDRY DUST UTILIZATION IN FOUNDRY PROCESS

Transcription

1 Acta Metallurgica Slovaca, Vol. 16, 2010, No. 1, p POSSIBILITIES OF FOUNDRY DUST UTILIZATION IN FOUNDRY PROCESS P. Gengeľ, A. Pribulová, P. Futáš Department of Ferrous Metallurgy and Foundry, Faculty of Metallurgy, Technical University of Kosice, Slovakia Received Accepted Corresponding author: Peter Gengeľ, Telephone number: , Department of Ferrous Metallurgy and Foundry, Faculty of Metallurgy, Technical University of Kosice, Slovakia, Abstract Dusts arise in almost every step of foundry processes. A huge amount of dust is generated by mould sand and core sand preparation. Composition of these dusts depends on used binder. The major compound in these dusts is SiO 2 and when an organic binder is used it is carbon as well. Melting processes are connected with formation of flue dust. Its composition depends on charge composition. Next melting furnaces are mainly used in foundry: cupola furnaces, electric arc furnaces and electric induction furnaces. Cupola furnaces are the biggest producer of flue dust from mentioned furnaces. Flue dust from cupola furnace is very fine-grained dust with a high content of SiO 2 and Fe. Also pouring, feetling, casts cleaning and grinding produce a high amounts of dust. Seven kinds of dust from different parts of cast iron foundry were analysed. On the base of achieved results from chemical analyses, granulometric analyses and microscopic analyses three kinds of dusts were chosen for next purposes preparation of sand mixtures and testing their technological properties. On the base of technological properties results the non-magnetic part of dust from casts cleaning was used. By experiment, that had to determined scubs inclination on casts according to Patterson and Bönisch test. Keywords: casting, recycling, granular materials 1 Introduction The cast iron foundries are classed among heavy environment polluters. In the recent years the enhanced attention is focused mainly to the emission. These polluting matters pollutants includes particulate matters, SO 2, CO, NO x, volatile organic compounds, lead and zinc. Cast iron casts are produced in foundries in various sizes, shapes and weights. On cast iron production appropriate charge is needed, it is especially scrap iron, pig iron, and foundry returns from melting, alloying, and also moulding. The main steps in foundry industry consists from raw materials handling and preparation, melting and molten metal treating, sand mixture and core mixture preparation, molten metal casting, casts cooling and shaking out from moulds, finishing operations of the raw casts [1]. In every of these steps a huge amount of dust is generated.

2 Acta Metallurgica Slovaca, Vol. 16, 2010, No. 1, p The dusts are particles generated from solid matters and dispersed to the air by their motion, charging, cleaning and handling [2]. Flue dusts are also little particles, which are generated when the metal is melting in the furnace. On the present time the dust and flue dust from foundry is highly actual and serious problem. It is generated in almost every step of foundry process and among foundry wastes takes the second place, regarding to quantity. The first place belongs to used sand mixture [4, 5]. 2 Material and experimental methods The main aim of these experiments has been to determine foundry dusts addition possibilities into the sand mixture and their influence on foundry defects scubs on the cast. Testing of foundry dust properties Overall seven kinds of the foundry dusts were analyzed from various foundry parts. Every dust was subjected to chemical and granulometric analyse. On the base of analyses, three kinds of foundry dusts were chosen, namely: 1. non-magnetic part of dust from casts cleaning (A), 2. flue-dust from cupola furnace (B), 3. dust from sand mixture preparation (bentonite sand mixture) and from sand moulding (C). Sand mixture (with dust addition) technological properties testing The new sand mixtures were prepared from 92 % of new SiO 2 (opening material) sand and 8 % of bentonite with 69 ml distilled water addition (amount of water was estimated by calculation). The mixture was mixed for the duration of seven minutes in the sand mill (Fig. 1 A), next sand mixtures were prepared from opening material (new sand, dust), bentonite and distilled water. Proportion of dust in opening material was 2, 5, 7 and 15 % (dust moisture was not taken in to the consideration). From these mixtures testing cylinders (145 g) (Fig. 1 D,E) were prepared, on which a compression strength, shearing strength and permeability (Fig. 1 H,I,F) were measured. Fig.1 Sand mixture technological properties determination; A sand mill, B device for testing element preparation, C core box, D, E testing cylinder, F permeability measure apparatus, G - sand strength apparatus, H compression strength measuring, I shearing strength measuring

3 Acta Metallurgica Slovaca, Vol. 16, 2010, No. 1, p Moulding and casting On the base of previously achieved results was decided that in further experiments the nonmagnetic part of dust from casts blasting (A) will be used. Following experiment had determined the presence of scubs at various dust additions into the sand mixture. The scubs are cast surface defects, which are generated by breaking and unsticking of mould surface layer [3, 6, 7]. Test to scubs inclination according to Patterson and Bönisch was elected. Experiment consisted from pattern on scubs determination moulding (Fig. 2). Three moulds were prepared (Fig. 3), whereby at the first moulding the regular bentonite sand mixture was used, at the second moulding with 10 % of dust content and at the third moulding dust content was 20 %. Fig.1 Pattern Fig.2 Mould Fig.3Casting 3 Results and discussion On the base of above mentioned experiments the next results were achieved. The chemical analyses of tested dusts are given in Tab. 1. Tab. 2 shows the granulometric analyses of tested dusts. Table 1 Chemical analyses of tested dusts Foundry FeO Fe Fe [%] metal SiO 2 CaO MgO MnO ZnO PbO dust [%] [%] [%] [%] [%] [%] [%] [%] C [%] A B C Table 2 Granulometric analyses of tested dusts Grains size [mm] New sand [g] Dust A [g] Dust B [g] Dust C [g] < > Dust from casts blasting Non-magnetic part of dust was used for sand mixture preparation. Following Tab. 3 shows technological properties of sand mixture with gradually dust addition.

4 Acta Metallurgica Slovaca, Vol. 16, 2010, No. 1, p Table 3 Sand mixture properties with addition of dust from casts blasting Dust addition [%] Compression strength [kpa] Shearing strength [kpa] Permeability [n.j.p.] Flue dust from cupola furnace Tab. 4 shows achieved technological properties results with addition of flue dust from cupola furnace. Measurements at 15 % dust addition were not carried by the reason of very low mixture cohesion. This dust gives one of the worst results and as an addition into the sand mixture is inappropriate. Table 4 Sand mixture properties with addition of flue dust from cupola furnace Dust addition [%] Compression strength [kpa] Shearing strength [kpa] Permeability [n.j.p.] Dust from moulding The dust was captured by moulding, so it is highly suitable as an addition into the sand mixture. Tab. 5 shows technological properties results of individual tested sand mixtures. Table 5 Sand mixture properties with addition of dust from moulding Dust addition [%] Compression strength [kpa] Shearing strength [kpa] Permeability [n.j.p.] Tab. 6 shows the weights of used bentonite sand mixture, the weights of the dusts and also casting temperature. The bentonite mixture moisture was 3.54 %. Table 6 Bentonite mixture amount, dust addition and pouring temperature Bentonite sand mixture [kg] Dust [kg] Casting temperature [ C] (0 %) (10 %) (20 %) 1453 After casts cooling, shaking out from mould and cleaning (Fig. 4), it is possible to observe that obvious scub was on the sample number two, whereby sample one and three were without these defects.

5 Acta Metallurgica Slovaca, Vol. 16, 2010, No. 1, p Fig.4 Poured and cleaned tested samples 4 Conclusions Foundry industry generates a huge amount of waste. The foundry dust is a very serious problem because it is created in every step of foundry process and its quantity is on the second place among foundry wastes [4]. Foundry dusts in individual steps of foundry plants differ by their chemical composition, appearance and granulometry. These properties mostly indicated their next utilization possibilities. From seven kinds of foundry dusts three were chosen: Non-magnetic part of dust from casts cleaning (A), flue-dust from cupola furnace (B), dust from sand mixture preparation (bentonite sand mixture) and from sand moulding (C). They were gradually added into the sand mixtures and their technological properties were tested: compression strenght, shearing strenght and permeability. On the base of achieved results it is possible to point out: Flue dust from cupola furnace is not available for sand mixture preparation. Dust from moulding contents high amount of SiO 2 and C, its disadvantage could be high amount of fine fraction, which reflects on permeability. If this kind of dust was added to the sand mixture it would improves its compression strength but on the other hand it could aggravate permeability. Non-magnetic part of dust from casts blasting has the very similar granulometry to the new SiO 2 sand. No bad influnece on compression strength was proved when this kind of dust was added and permeabilty sank only mininum. For the scubs inclination test according to Patterson and Bönisch the non-magnetic part of dust from casts cleaning (A) was chosen. From the results of the Patterson and Bönisch test the inclination to scubs occurrence was not proved by using of dust from casts cleaning in the sand mixture. Scub occurrence at the second sample could be caused by different compression level of sand mixture at the moulding [6]. Acknowledgement The autors gratefully acknowledge for the financial support to the Slovak Research and Development Agency (contract number APVV ). References [1] G. Geshwandtner, S. Fairchild: Emission factors for iron foundries criteria and toxic pollutants, EPA Contract No. 68-D9-0168, Work Assignment No. 5, Air and Energy Engineering Research Triangle Park, North Carolina 27711, August 1990

6 Acta Metallurgica Slovaca, Vol. 16, 2010, No. 1, p [2] J. Kret: Ferrous metallurgy waste recycling, Ostrava, VŠB TU Ostrava, 2003, ISBN (in Czech) [3] Z. Gedeonová: Theory of foundry operations, Vysoká škola technická v Košiciach, Hutnícka fakulta, Bratislava, 1990, ISBN (in Slovak) [4] V. Bednářová: Foundry waste recycling and regeneration of sand mixtures, Ostrava, 2004, ISBN (in Czech) [5] BAT, Integrated Pollution Prevention and Control, Reference Document on Best Available Techniques in the Smitheries and Foundries Industry, July 2004 [6] F. Havlíček: Thermo-physics of casts and mould, ČSVTS-VSŽ Košice, 1975 (in Czech) [7] J. Přibyl: Defects generated at casting and solidification of casts, ČSVTS-VTI-VSŽ Košice, 1974 (in Czech)