Simulation of the austenitic manganese steel balls casting and comparison with the experimental results.

Marta, Constantin ; Doroftei, Ioan ; Prisacaru, Gheorghe 等

1. INTRODUCTION

Hadfield steel with very different chemical compositions but observing the ratios [M.sub.n]/C= 10 and Cr/C = 0,8 ... 1,92 has a very wide utilisation in the casting of parts that have to resist to abrasive wearing (in very hard conditions ) and to corrosion (Sporea & Crainic 2005). Some of the work-parts obtained by OAM casting are also the balls for grinding the hard rocks in mills with balls. One analysed the exploitation behaviour of manganese steel balls (Ivan&Mladen 2001) compared to that of the balls made of stainless steel, cast nickel alloy, or chilled iron. In the case of hard or very hard materials grinding one obtained more reduced wear by using the manganese steel balls. The high resistance to wear and tear, the small prices of OAM balls, the world shortage of ferroalloys, all this encouraged the research in the field. The technical aspects, i.e. steel contraction of 2,5-3% provoking large cavity and implicitly the influence of casting defects on the life duration of the ball were improved through simulations having led to the finding of certain solutions of cavity concentration to the core of the ball. (Cristea 2006). The simulation was performed on a 12-ball sand mould, with gate end and central feeding. The results of the research can be applied to the entire range of OAM balls, for diameters between 60-130 mm, and also to other parts (Suratnam 1998). The simulation was done with Magmasoft (MAGMA GIESSEREITECHNOLOGIE 2005).

2. MAGMASOFT SIMULATION PROGRAMME

This simulation programme represents for the caster and for the designer an instrument enabling them to rapidly test a great number of options, it also allows the selection of the optimal combination for improving and optimising of the casting process. The use of the MAGMASOFT software imposes the following main compulsory stages : pre-processing of start initial data of the simulation, calculus of the simulation with the selection of the adequate solver (simulator), post-processing with the presentation of the simulation results. Then one defines the components of the casting system according to classes of materials, i.e.:

--Cast Alloy;

--Sand Mould;

--Feeder;

--Gating and Inlet

[FIGURE 1 OMITTED]

This denomination allows the identification of components in the casting process. It is not the material that is named, but only the function of each component in the casting process. The definition of the components is done considering the geometry of the part subjected to simulation, more precisely the 100-mm diameter sphere, cast from the alloy which will be defined as class of materials, i.e. G1X20CrMn130- make steel, in sand mould defined also as class of materials, based on theoretical studies about casting simulation in moulding mixtures for balls for 100-mm spheres. The casting of balls is made in 12-ball sand moulds, with central feeding and end gate for every 6 balls. For the situations in which the casting system is symmetrical, like in our case, in order to reduce the simulation times, the software allows simulation only on a quarter of the cast mould, according to Fig.1. The simulation is thus performed for a quarter of the inlet, half of the feeder and 3 balls. The software allows the calculation of the interior volume of the mould, which is of 62853 cmc. For the simulation of solidification one established the check points of the mould filling and part solidification, which allows a certain closeness to reality. The results of simulation for the casting ensemble are represented through the porosity criterion, and we remark the shrinkage and the maximum porosity respectively, according to the colour code in the inlet and in the feeder Figure 2.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

The casting temperature is of 1440[degrees]C, the filling time being of 10 s. The balls cast in these moulds under the above conditions should exhibit a pipe cavity as small as possible, placed in the central area of the part. In order to visualise the results of the simulation and the location of the casting defect in the balls, one of the balls was sectioned, the porosity being approximately assessed by means of the colour bar in the right side. All the results of casting are 3-D. The casting defect is in the interior of the cast part and is defined through the porosity criterion, ranging between 20-23%. This variant is interesting because the defect is within the part. It can be stated that the casting fault defined by porosity criteria (Figure 3) is place in the centre of the work part.

3. PRACTICAL TESTS FOR BALLS CASTING OF THE SPHERE WITH 100 MM DIAMETER

For highlighting and establishing the importance of the MAGMASOFT simulation system, castings were performed for the 100-mm balls in similar conditions with that of MAGMASOFT programme. After the casting process the ball was sectioned and it had a hole similar (Figure 4) with that obtained by simulation (Figure 5), in the case of the GX120 CrMnl30 steel. The cavity has the following dimensions : along the vertical diameter--15 mm, and along the horizontal diameter--around 10 mm. The maximum depth of cavity is of about 7 mm. The volume of the cavity determined also through liquid insertion is of 5,5 cm3. The volume of the cavity / shrinkage is estimated based on the fact that the work is done on sectioned parts. Compared to the volume of the part, the volume of the cavity represents 1.051% of the total part volume. With the help of the technology designed we cast 1500 balls. For the verification of results the weight of balls was also measured. The weight variations ranged between 4.370 kg and 4.470 kg, which confirms the validity of the casting technology. Another imposed issue refers to the sphericity of the cast balls. One performed measurements along 3 diameters and the deviations were between +2 and -2 mm

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

4. CONCLUSION

By using the simulation software the traditional casting tests are much reduced. One avoids the refuse cast parts and assures the quality of the finite product since the beginning of manufacture. Within the elaboration of a casting project one can elaborate several versions containing different variants of the casting system, so that the improvement of the casting system be done only through modification of the geometry and parameters of the casting process, the analysis of results, their comparison and the selection of the optimum solution, thus avoiding the doubling of work and saving time and money. The use of the technology realised on the basis of simulation does not trigger the obtaining of the most perfect and the less expensive part. The simulation does not take into account the elaboration technology, the technologies of mould extraction or the modality of application of the appropriate heat treatment, these being parameters of the manufacturing process. Another three very important factors in the case of the OAM casting, i.e. the temperature at the beginning of casting and the casting times, the mould temperature, the materials use are integrated into the pre-processor and have a decisive influence on the results. The simulation method using MAGMASOFT and having as idea the placement of the contraction to the core of the ball is original and along with the obtaining of more reduced holes is a consequence of the appropriate casting technologies used, in order to have a spherical shape, which triggers a uniform wear and tear of the sphere's surface and the increase of the exploitation duration. The results of the simulation are valid only of the austenitic manganese steel with the following chemical composition: C = 1,05 - 1,35, Cr = 1,50 - 2,50, Mn//C ratio = 10.

5. REFERENCES

Cristea, C.; (2006) Theoretical and experimental studies on the casting of steel balls with high contents of manganese for ore-grinding crushers), D. P. Publishing House, ISBN code 973-30-1522-9, Bucharest

Ivan, St., & Ghita, M. (2001) Symposium, Western University, On the duration of exploitation of wear-resistant steel of the T110Mnl30 Type.pag.400-405, ISSN 1453-7394, 9-12 November, 2006,Timisoara

Sporea, I.; Crainic, N. & Mladen, M, (2005) On casting of austenitic manganese steel in wear-resistant parts, Annals of the University of Oradea, Mechanics fascicle, pag.479-486, ISSN 1011-2855, 12-15 May, 2005, Oradea.

Suratman R.; (1998) Alloy Design and Casting Practice of Hadfield's Manganese Steel, Metallurgical Science and Technology, Vol. 1, 1990, pag. 822-840, 12-16 July, 1998, Hawaii

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