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Optimized Gating System for Steel Castings

Optimized Gating System for Steel Castings JMEPEG (2018) 27:5152–5163 The Author(s) https://doi.org/10.1007/s11665-018-3497-1 1059-9495/$19.00 R. Dojka, J. Jezierski, and J. Campbell (Submitted November 11, 2017; in revised form April 24, 2018; published online July 5, 2018) Computer modeling using a commercially available software package was used to explore the optimization of filling systems based on the relatively new concepts of avoiding entrainment of air bubbles and oxides by avoiding surface turbulence. The test casting was based on a pattern for a traditional top poured test bar, whose cross section was a tri-lobed clover-like shape. The study illustrates clearly that the detailed design of the filling system has a major influence on the conditions for defect generation during filling. Traditional steel casting systems using the widely popular assembly of preformed refractory tubes were found to behave poorly. Systems were demonstrated which were capable of delivering highly controlled filling behavior. The latest systems to be developed employed (1) a naturally pressurized filling system and (2) the use of filters placed flush on the top of the runner to act as bubble diverters, together with (3) terminal spin traps. These novel filling systems demonstrated excellent performance in simulation, in agreement with practical experience of the capability (of the trident gate in particular) to produce, for the first time in the history of casting, defect-free castings on a routine basis. a crack in the liquid metal, leading to the initiation of cracks Keywords casting and solidification, casting defect, gating sys- and hot tears in the casting. tem, modeling and simulation, steel casting It is surprising how many of our common casting defects are the fault of entrained oxides and bubbles. For instance in the case of gas porosity, pores up to about 5 mm diameter are the result of entrained air bubbles, whereas finer bubbles are usually 1. Introduction bifilms inflated by gases in solution, often hydrogen. All cracks and hot tears appear to be the product of entrained bifilms. Sand Modern foundry engineering is a well-developed and inclusions are a reliable sign of turbulence; the air displaced sophisticated industry utilizing cutting-edge technologies and backwards and forwards through the mold wall oxidizes away tools including 3D printing, robots and automated manufactur- the sand binder. Once the sand is unbonded, it can be pulled ing. Despite this, the most important production technology away from the mold wall, penetrating the surface of the liquid remains the use of greensand molds poured with cast iron or metal via the surface oxide film. The result is that sand inclusions steel (Ref 1-3). This traditional technology is widespread are usually found to be wrapped in their oxide paper bag from because of its low cost and adequate quality. However, the the entrainment event. [Campbell records that he has never quality requirements are continuously growing. It is recently known sand inclusions to result from poor sand quality (Ref 8)]. becoming common for the customer to specify a requirement to In general, providing they do not lead to cracks, the presence pass the stringent dye penetrant test. This inspection technique of bifilms in steels does not contribute to the rejection or illustrates the inadequacies of many current filling system scrapping of the casting because the population of these defects designs (Ref 4-7), since the presence of surface-breaking oxide is usually invisible. However, properties, particularly toughness bifilms, cracks and bubbles is now clearly revealed. and fatigue, are reduced. It seems that bifilms are sufficiently Turbulence during the pouring of metals generates two main small and compacted during turbulence that a high proportion defects: (1) entrained air bubbles and (2) entrained oxide films can pass straight through a ceramic foam filter. For instance a from the surface of the liquid metal. The oxides are always 20 ppi (pores per inch) filter gives a pore diameter of approx- entrained with the dry top surface of the oxide folded over imately 1 mm, allowing a 10-mm diameter bifilm, when raveled against itself. This unbonded double interface (a bifilm) acts as and compacted by turbulence to around 1 mm diameter, can pass through with ease. Thus, the filter is not capable of filtering out bifilms. Fortunately, however, filters are effective in resisting the passage of bubbles. This is really important during the priming J. Campbell: Professor Emeritus. of the filling system, the early seconds of filling when the 100% This article is an invited submission to JMEP selected from air in the system is required to be displaced by 100% metal. The presentations at the Symposium ‘‘Solidification, Casting, Foundry transition is unfortunately often messy and ragged, so that and Liquid Metal Processing,’’ belonging to the Topic ‘‘Joining’’ at the priming bubbles are a major component of the early flow regime, European Congress and Exhibition on Advanced Materials and and need to be kept out of the casting. If they succeed to enter the Processes (EUROMAT 2017), held September 17-22, 2017, in casting they create a long bubble trail, a kind of lengthy bifilm Thessaloniki, Greece, and has been expanded from the original and leak path from the bottom to the top of the casting. The fact presentation. that bubbles are greatly damaging to the casting has been R. Dojka and J. Jezierski, Department of Foundry Engineering, realized only relatively recently (Ref 8). Silesian University of Technology, Gliwice, Poland; and J. Campbell, The current paper presents the results of an approach to test Department of Metallurgy and Materials, University of Birmingham, the behavior of filling systems designed to fill completely (Ref Birmingham, UK. Contact e-mail: jan.jezierski@polsl.pl. 5152—Volume 27(10) October 2018 Journal of Materials Engineering and Performance 8), thereby excluding all air so far as possible, and thereby that the systems are practical and economic, permitting their reduce or prevent the occurrence of surface turbulence and the use for medium and heavy cast steel casting manufacture in entrainment of bubbles and bifilms. Naturally, it is necessary steel foundry plants. Fig. 1 Test mold according to Polish Standard PN-H-04309: 1976 Fig. 2 Initial technology, distribution of metal velocity and fill trackers after 1, 2 and 4 s from the beginning of pouring Journal of Materials Engineering and Performance Volume 27(10) October 2018—5153 The authors have in mind application of good systems in a local Polish foundry manufacturing heavy steel castings with a weight of up to around 30 tonnes, frequently in single units. Much of the molding process is carried out by hand, which provides an opportunity to shape the gating system closely to the theoretically ideal model. For such single heavy castings, failure is unthinkably costly, so that any additional help to ensure success is always welcome (Ref 9- 14). The casting manufacturing design concepts encompass an extensive body of knowledge enshrined in Campbells Ten Rules (Ref 8). However, the two key elements applying to the filling system are (1) the critical velocity for the avoidance of entrainment defects (Ref 6), and (2) the avoidance of entrained air and oxide entering the mold cavity (Ref 15- 17). Therefore, only these most important practical issues were included here for optimization. Other researchers are beginning to adopt these rules and are finding them useful (Ref 18-21). The paper describes the systematic evaluation of a number of gating systems in current use including the extended runner, spin trap, vortex gate, trident gate and others, using computer simulation. Fig. 3 A simple solution for the problem of circular and rectangu- 2. Experimental Method lar runner junctions Two computer packages: NovaFlow&Solid by NovaCast and Magma by Magmasoft, were used. A series of different gating systems were applied to a casting based on a test mold according to Polish Standard PN-H-04309: 1976 Cast steel—testing, casting and sampling, the so-called clover test piece. This sample test shape is commonly used in Poland for the evaluation of the mechanical properties of cast steel (Fig. 1). The steel test piece weighs 20 kg. Instead of the traditional filling of the mold by top pouring, the authors evaluated a series of different bottom gated systems. Bottom gating avoids any fall of the metal inside the mold cavity. It also provides filling against the gravity, allowing the achievement of non-turbulent filling, in sharp contrast to top pouring. It is one of the aspects of filling technology strongly recommended by Campbell and others (Ref 19, 22-25). All Fig. 4 Developed transition of the sprue from (1) circular to rectan- modeling trials have been made using the steel grade GS-52 gular cross section and (2) tapered hyperbolically according to DIN 1681, with the pouring temperature set at Fig. 5 Improper transition of a sprue from a circular to rectangular cross section 5154—Volume 27(10) October 2018 Journal of Materials Engineering and Performance Fig. 6 Extended runner, distribution of velocity and fill tracker 1570 C. The nominal composition of this steel is < 0.30% C; ladle; a technique known as contact pouring. Both of these 0.30-0.60% Si; 0.20-0.50% Mn; < 0.04% P; < 0.04% S. The techniques are known to be essential for the production of low- minimum mechanical properties of the steel are YS = 260 defect castings (Ref 8). MPa, UTS = 520 MPa, E = 18%, impact strength ISO- It is important to bear in mind that practically all V = 22 J. currently available computer packages are unable to model The sprue entrance is considered in every case to be the presence of bubbles in the flow of liquids. This means completely filled by liquid metal. This is rarely met in practice that an important aspect of gating design cannot be unless one of only two conditions is met: (1) The entrance is simulated, so that all current attempts at simulation unfor- filled by an offset step basin with a stopper sealing the sprue tunately remain limited. Nevertheless, the authors believe that entrance. The stopper is raised, permitting the fill of the sprue the present work illustrates that much can be achieved and only when the basin is filled up to the design fill level. (2) The demonstrates important improvements which the application sprue is filled by direct contact with the nozzle of a bottom-pour of recent concepts make possible. Journal of Materials Engineering and Performance Volume 27(10) October 2018—5155 the same cross-sectional area tend to behave differently: the slimmer the runner the more laminar the flow. A slim rectangular runner 30 9 6 mm was therefore selected. As a consequence, the sprue had the additional requirement to change gradually from a circular cross section at its entrance, to a rectangle at its exit, to match perfectly to the entrance to the runner. The sophisticated shape of the sprue described above contrasts with a commonly used junction of a round sprue to a rectangular runner. This junction works badly, with the liquid ricocheting back and forth down the runner, never properly filling the runner, as shown schematically in Fig. 3 (Ref 8). The improved sprue design by the authors for this simulation is shown in Fig. 4. The studies show that improper tapering and transition causes, as shown in Fig. 5, depressurization and non-filling of the sprue. The metal stream clearly free-falls down the early part of the sprue, and so does not have the advantage of some boundary friction. The higher velocity into the mold is seen to cause jetting. However, it should be realized that the real situation is more damaging still as a result of the simulation not modeling bubbles. The plunging stream conditions in the sprue will entrain copious volumes of air, probably in a mix of at least 50/50 air/metal. This massive influx of air will severely damage the casting by both bifilm and bubble entrainment (Ref 7). Fig. 7 Centrifugal slag trap, velocity distribution and fill tracker 2.3 Extended Runner Another traditional filling system uses a simple extension of the runner to capture the first metal through the system because 2.1 State-of-the-Art Pouring Procedure it was assumed to be relatively cold. This was true, but A conventional gating system constructed by using prefab- probably of negligible importance. Close examination of Fig. 6 ricated 15-mm diameter refractory tubes was simulated as a shows no great benefit to metal temperature through the gate. In base against which newer developments could be assessed. In any case, the real problem requiring solution was not lack of this case, the rate of metal flow from the ladle was 5 kg/s. temperature, but excess of defects resulting from its unavoid- Figure 2 presents a distribution of metal velocity and a fill able mixing with air in the initially empty filling channels. In tracker that defines a distribution and life time of metal portion particular, its content of bubbles would add to the problems of a entering the sprue after 1, 2 and 4 s from the beginning of significant bifilm population already generated. pouring. It can be noticed that the velocity of the metal at the Figure 6 presents the distribution of velocity during the entrance to the mold cavity exceeds 3 m/s, greatly exceeding filling. It is clear that while the extension is filling, the velocity the safe gate velocity 0.5 m/s, resulting in a clear jetting effect. through the gate is close to a gentle and safe value in the range The numerous splashes and droplets would result in a poor- 0.5-1.0 m/s. However, at the instant the extension is filled, the quality casting with generous quantities of entrained defects. gate is now subject to the full pressure head of the sprue, and a The impacts between droplets and splashes will create oxide jet is formed; the velocity of metal entering the mold cavity has bifilms (Ref 15) which will degrade the mechanical properties jumped to over 2 m/s. This disturbance to the rising surface of and the appearance of the casting. the melt is seen to continue high into the mold, leading to bifilm formation and laps on the casting surface (the lap constituting a 2.2 Tapering of the Down-Sprue bifilm crack defect) which may lead to macroscopic cracking of the casting. The poor performance of the basic pipework system seen in In addition, the small volume of the extension causes a back Fig. 2 raises the question, What should the perfect gating wave (which would have been expected to be even more system look like? There are a number of options. But some significant if the runner had been deeper, allowing more head clear process steps include the following factors. room for back-flow). Some back-flow from the extension into First, in place of constant diameter preformed refractory the casting is clearly seen in the tracking result, confirming that tubes, the cross-sectional shape of the filling system channels some of the damaged melt will find its way into the casting. The requires to be tailored to the shape of the flowing liquid. authors tried different modifications of this solution, but even Almost all bottom-pour ladles have round-shaped nozzles increasing the extension to the top of the mold did not result in which need to match the shape of the entrance to the gating the elimination of the jetting effect. system. From that point onwards in the filling system, the sprues cross section should gradually narrow, tapering accord- 2.4 Centrifugal Slag Trap ing to the natural hyperbolic curve of a falling stream. The authors in their most recent studies confirmed (Ref 26) that Various versions of a centrifugal slag traps have been liquid metal flowing through runners with larger perimeter but described in the literature for a long time. It may be built in a 5156—Volume 27(10) October 2018 Journal of Materials Engineering and Performance Fig. 8 Vortex gate scheme number of ways, but one thing is constant—the component to The above system was not easily molded, requiring multiple be used as a spin trap is located in front of the mold cavity. The vertical partings or the use of complex cores. An analogous authors performed many simulations using a number of design, a barrel trap, was devised by authors to create a different diameter-to-height ratios, but the effect was always system similar to the centrifugal slag trap, but because of the similar to that presented in Fig. 7. The technique initially looks horizontal axis of the barrel it would be easier to mold. A filter promising, but the trap finally fills, which causes a sudden placed flush with the runner was provided to divert bubbles increase in velocity with a consequential catastrophic jetting (and other less dense components such as slag) into the barrel effect. Impurities originally held in the middle of the trap are where they could be centrifuged into its center. However, the pushed inside the mold cavity. The centrifugal slag trap cannot computer simulation revealed a similar problem to the slag be recommended. trap; when the filling of the barrel was complete, the Journal of Materials Engineering and Performance Volume 27(10) October 2018—5157 centrifugally concentrated impurities appear to flow back to the filter, either clogging the filter or reducing the casting quality. It seems the barrel trap is yet another technique which cannot be recommended. 2.5 Vortex Gate The vortex gate (Fig. 8) enjoyed some early success for larger castings by reducing the high velocity of metal entering the mold cavity. Its huge ability to reduce velocity resulted simply from the ratio of areas of the runner and the vortex cylinder, being the ratio of the horizontal flow area to the vertical flow area. It was not difficult to reduce flow velocity by a factor of 10. At that time, such large velocity reductions were not easily achieved by any other simple technique. The cylinder was equipped with a collar around its base (described elsewhere as a spinner disk) to guide the initial metal around the cylinder, gaining its circular motion, and avoiding its direct impact and splashy vertical climb up the far wall of the cylinder. Another feature of the vortex gate was a ceramic Fig. 9 Vortex gate, velocity distribution and fill tracker Fig. 10 Spin trap scheme 5158—Volume 27(10) October 2018 Journal of Materials Engineering and Performance Fig. 11 Spin trap, velocity distribution and fill tracker foam filter placed on the top in an effort to reduce the rotational component of speed before it entered the mold. As shown in Fig. 8, the velocity of metal entering the mold cavity in this solution is 0.78 m/s, which makes a significant improvement compared to previous systems, but the rotational flow of the first portions of metal entering the mold cavity remains too turbulent. (The limited effectiveness of the foam filter in reducing the rotational speed is confirmed by practical experience. It may have been improved by the use of straight vertical pores of a pressed or extruded filter.) From practical trials, however, it has been found that a major fault with the vortex gate is that it centrifuges bubbles into the center of the vortex cylinder from where they are unable to escape. They build up and coalesce to a single bubble, which grows in size under the filter until it has sufficient buoyancy to force though the filter. The flow up through the casting is highly damaging to the casting; the long bubble trails generate long bifilm cracks and leak paths. (Unfortunately, the deleterious action of bubbles in the flowing metal, a major feature, cannot yet be simulated as mentioned above.) Fig. 12 Simplified spin trap, velocity distribution and fill tracker Journal of Materials Engineering and Performance Volume 27(10) October 2018—5159 Fig. 13 Trident gate scheme come into action, and the velocity through the gate reaches its 2.6 The Tangential (Flush) Filter and Terminal Spin Trap full value of several meters per second. The volume of the trap In this filling system (Fig. 10), the vertical ingate is needs to be sufficiently large to ensure that the trap only fills protected from the ingress of bubbles by a filter which acts as after the gate is filled, and sufficient depth of metal has arrived a bubble diverter. The filter is placed flush with the top of the in the mold cavity to suppress jetting. The height-to-diameter runner so that, instead of the bubbles accumulating under the ratio of a spin trap, and its optimum volume as a function of filter, they are encouraged to flow past and into the runner casting size and geometry, will be subject to further examina- extension. The bubbles are then trapped, together with the cool tion. and damaged priming metal, by the centrifugal action inside the A further feature of this filling system should be noted. spinner. Because the sprue is nicely tapered, so as to fill completely and The spinner at the end of the runner has a further important thereby exclude air, and because air bubbles from the priming role; the gradual filling of the trap causes a steady increase in of the system are encouraged to divert, instead of passing back pressure in the runner. This pressure, effectively starting through the filter, the filter transmits only relatively good from zero, acts to drive the initial slow filling of the gate, quality metal rather than masses of oxides. In practice, ensuring that the velocity through the gate is too low to cause therefore, it is successful to pass large volumes of metal jetting. This is clearly achieved as shown in Fig. 9 and 10. Only without any danger of blockage. This behavior contrasts with when the trap is filled does the full head height of the sprue 5160—Volume 27(10) October 2018 Journal of Materials Engineering and Performance Fig. 14 Trident gate, velocity distribution and fill tracker the use of filter placed after drain pipe sprues, which generate degrade flow and the quality of the casting beyond what Fig. 12 so much oxide that the filter can pass only limited quantities of can show. The use of the preformed tubes for filling systems metal prior to blocking (Ref 27). cannot be recommended at this time. Naturally, the cross section of the ingate should be sufficiently large to reduce the speed of metal entering the 2.7 Trident Gate mold cavity to a value in or below the range 0.5-1.0 m/s. In Fig. 11, the initial velocity of metal entering the mold cavity is The trident gate is the most recent development in the quest 0.3 m/s. for reliable, high-quality, gravity casting techniques (Ref 27). 2.6.1 The Tangential (Flush) Filter and Terminal Spin In common with the previous technique, it has a filter flush Trap Made from Preformed Refractory Tubes. If the with the runner to avoid bubbles so far as possible, and the filling system is constructed from prefabricated refractory provision of a spin trap which not only captures bubbles and tubes, for ease of assembly and molding, instead of being damaged metal, but raises the pressure slowly on the ingate molded directly in sand, Fig. 12 shows the result. The initial filter to avoid jetting into the mold. velocity of metal in the mold cavity is around 0.6 m/s; As an additional feature, it has a bubble trap and second however, jetting effect is evident. Although this filling behavior filter placed vertically, so if any bubbles get through the first might appear marginally acceptable, the constant diameters of filter, the second filter would divert them upwards into the the preformed tubes cannot follow the necessarily changing bubble trap. form of the liquid stream, and do not therefore constrain the The system was devised by Puhakka and Campbell in 2014 flow. As a result, air entrainment and bubble formation will (Ref 27). The schematic diagram of a trident gate is shown in occur (not easily detected in the simulations), which will further Fig. 13. Its rather complex form is not easily molded, and so is Journal of Materials Engineering and Performance Volume 27(10) October 2018—5161 2. M. Holtzer, R. Danko, and S. Zymankowska-Kumon, The State of Art contained within a two-parted sand core, having an outward and Foresight of Worlds Casting Production, Metalurgija, 2014, 53(4), block-like shape, which is planted on the runner and molded p 697–700 into place in the sand mold. This solution has been used with 3. J. Danko and M. Holtzer, The State of Art and Foresight of Worlds great success with aluminum alloys (Ref 28-30). It appears to Casting Production, Metalurgija, 2006, 45(4), p 333–340 be capable of routinely making defect-free Al alloy castings. 4. L. Camek, P. Lichy, I. Kroupova, J. Duda, J. Beno, M. Korbas, F. The technique may also be useful for ferrous alloys but has yet Radkovsky, and S. Bliznyukov, Effect of Cast Steel Production Metallurgy on the Emergence of Casting Defects, Metalurgija, 2016, to be widely tested in practice. 55(4), p 701–704 Figure 13 presents a simulation of metal velocity. During 5. E. Foglio, M. Gelfi, A. Pola, S. Goffelli, and D. Lusuardi, Fatigue the initial phase of mold cavity filling, the velocity is around Characterization and Optimization of the Production Process of 0.35 m/s. The analysis of fill trackers presented in Fig. 14 Heavy Section Ductile Iron Castings, Int. J. Metalcast., 2017, 11(1), p shows that filling is equally good as in the case of spin trap 33–43 6. J. Campbell, Stop Pouring, Start Casting, Int. J. Metalcast., 2012, 6(3), solution. Overall, in addition to the advantages of a spin trap its p 7–18 two-stage filtration plus integral bubble trap appears to be 7. J. Campbell, Melting, Remelting, and Casting for Clean Steel, Steel highly effective in keeping bubbles out of the mold cavity. Res. Int., 2017, 88(1), p 1600093 8. J. Campbell, Complete Casting Handbook, 2nd ed., Butterworth- Heinemann, Oxford, 2015 9. S.G. Acharya, J.A. Vadher, and K.D. Kothari, Evaluation of Critical 3. Conclusions Parameters for Sand Inclusion Defect in FNB Casting, Arch. Foundry Eng., 2017, 17(1), p 5–12 10. S.G. Acharya, J.A. Vadher, and P.V. Kanjariya, Identification and The paper presents a systematic comparison of a number of Quantification of Gases Releasing From Furan No Bake Binder, Arch. gating systems for steel castings, using computer simulation. Foundry Eng., 2016, 16(3), p 5–10 They were based on the filling of a clover-like test sample and 11. P. David, J. Massone, R. Boeri, and J. Sikora, Gating System Design to led to the following conclusions: Cast Thin Wall Ductile Iron Plates, Int. J. Cast Met. Res., 2006, 19(2), p 98–109 • Computer modeling confirmed the effectiveness of gating 12. G.L. Di Muoio and N.S. Tiedje, Achieving Control of Coating Process in your Foundry, Arch. Foundry Eng., 2015, 15(4), p 110–114 systems to control the velocity and surface turbulence of 13. A. Modaresi, A. Safikhani, A. Noohi, N. Hamidnezhad, and S. Maki, the metal entering the mold cavity (but it is acknowledged Gating System Design and Simulation of Gray Iron Casting to that the simulations could not include the presence of air Eliminate Oxide Layers Caused by Turbulence, Int. J. Metalcast., bubbles in the metal flow). 2017, 11(2), p 328–339 Filling systems molded to follow the shape of the falling 14. Z. Ignaszak, Discussion on Usability of the Niyama Criterion for Porosity Predicting in Cast Iron Castings, Arch. Foundry Eng., 2017, stream (particularly the naturally pressured system) are 17(3), p 196–204 successful to reduce the conditions for forming entrain- 15. J. Campbell, The Consolidation of Metals: The Origin of Bifilms, J. ment defects. Mater. Sci., 2016, 51(1), p 96–106 The filling system constructed from preformed refractory 16. J. Campbell, Sixty Years of Casting Research, Metall. Mater. Trans. A, tubes performed poorly. 2015, 46A(11), p 4848–4853 The various vortex systems were all found to perform 17. J. Campbell, Crack Populations in Metals, Aims Mater. Sci., 2016, 3(4), p 1436–1442 poorly for different reasons. 18. F. Hsu, M. Jolly, and J. Campbell, Vortex-Gate Design for Gravity The various systems using (1) naturally pressurized chan- Casting, Int. J. Cast Met. Res., 2006, 19(1), p 38–44 nel designs; (2) filters placed flush on runners to divert 19. F. Hsu, M. Jolly, and J. Campbell, A Multiple-Gate Runner System for bubbles; and (3) sufficiently large spin traps on the ends Gravity Casting, J. Mater. Process. Technol., 2009, 209(17), p 5736– of runners performed excellently. For the first time, it seems that techniques are now available for the production 20. R. Ahmad and M. Hashim, Effect of Vortex Runner Gating System on the Mechanical Strength of al-12si Alloy Castings, Arch. Metall. of defect-free castings. Mater., 2011, 56(4), p 991–997 21. N. Ducic, R. Slavkovic, I. Milicevic, Z. Cojbasic, S. Manasijevic, and R. Radisa, Optimization of the Gating System for Sand Casting Using Genetic Algorithm, Int. J. Metalcast., 2017, 11(2), p 255–265 Open Access 22. H. Zhou, L. Luo, Z. Shi, J. Dong, and W. Ma, Filling Pattern of Step Gating System in Lost Foam Casting Process and Its Application, Adv. This article is distributed under the terms of the Creative Commons Mater. Res.-Switz, 2013, Pts 1–3, 602-604, p 1916–1921 Attribution 4.0 International License (http://creativecommons.org/ 23. D. Yang, S. Li, F. He, W. Sung, J. Kao, and R. Chen, Twin Gating licenses/by/4.0/), which permits unrestricted use, distribution, and System Design for Typical Thin Wall Stainless Steel Castings Based on reproduction in any medium, provided you give appropriate credit Fast Pouring Mechanism, Appl. Mech. Mater., 2014, Pts 1 and 2, 457- 458, p 1657–1660 to the original author(s) and the source, provide a link to the 24. R. Ranjan, N. Kumar, R. Pandey, and M. Tiwari, Agent-Based Design Creative Commons license, and indicate if changes were made. Framework for Riser and Gating System Design for Sound Casting, Int. J. Prod. Res., 2004, 42(22), p 4827–4847 25. K. Renukananda and B. Ravi, Multi-Gate Systems in Casting Process: References Comparative Study of Liquid Metal and Water Flow, Mater. Manuf. 1. M. Soinski, P. Kordas, and K. Skurka, Trends in the Production of Process., 2016, 31(8), p 1091–1101 Castings in the World and in Poland in the XXI, Century, Arch. 26. J. Jezierski, R. Dojka, K. Kubiak, W. Zurek, and T. Ltd, Experimental Foundry Eng., 2016, 16(2), p 5–10 Approach for Optimization of Gating System in Castings, Metal 2016: 5162—Volume 27(10) October 2018 Journal of Materials Engineering and Performance 25th Anniversary International Conference on Metallurgy and Mate- 29. J. Sturm, G. Dieckhues, and S. Sikorski, Systematic Optimization of rials, 2016, p 104–109 Aluminum Sand Casting Gating Systems, Trans. Am. F, 2012, 120(120), p 13–21 27. J. Campbell, Mini Casting Handbook, Aspect Design, Malvern, 2017 30. Y. Jiang, Y. He, Y. He, X. Qian, Y. Huang, L. Xu, W. Tian, and E. Mao, 28. M. Bruna, D. Bolibruchova, and R. Pastircak, Reoxidation Processes Analysis and Optimization on the Gating System of Aluminum Alloy Prediction in Gating System by Numerical Simulation for Aluminium Piston in Casting, Appl. Mech. Mater., 2011, Pts 1 and 2, 80-81, p 32–35 Alloys, Arch. Foundry Eng., 2017, 17(3), p 23–26 Journal of Materials Engineering and Performance Volume 27(10) October 2018—5163 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Materials Engineering and Performance Springer Journals

Optimized Gating System for Steel Castings

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Springer Journals
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Copyright © 2018 by The Author(s)
Subject
Materials Science; Characterization and Evaluation of Materials; Tribology, Corrosion and Coatings; Quality Control, Reliability, Safety and Risk; Engineering Design
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1059-9495
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1544-1024
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10.1007/s11665-018-3497-1
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JMEPEG (2018) 27:5152–5163 The Author(s) https://doi.org/10.1007/s11665-018-3497-1 1059-9495/$19.00 R. Dojka, J. Jezierski, and J. Campbell (Submitted November 11, 2017; in revised form April 24, 2018; published online July 5, 2018) Computer modeling using a commercially available software package was used to explore the optimization of filling systems based on the relatively new concepts of avoiding entrainment of air bubbles and oxides by avoiding surface turbulence. The test casting was based on a pattern for a traditional top poured test bar, whose cross section was a tri-lobed clover-like shape. The study illustrates clearly that the detailed design of the filling system has a major influence on the conditions for defect generation during filling. Traditional steel casting systems using the widely popular assembly of preformed refractory tubes were found to behave poorly. Systems were demonstrated which were capable of delivering highly controlled filling behavior. The latest systems to be developed employed (1) a naturally pressurized filling system and (2) the use of filters placed flush on the top of the runner to act as bubble diverters, together with (3) terminal spin traps. These novel filling systems demonstrated excellent performance in simulation, in agreement with practical experience of the capability (of the trident gate in particular) to produce, for the first time in the history of casting, defect-free castings on a routine basis. a crack in the liquid metal, leading to the initiation of cracks Keywords casting and solidification, casting defect, gating sys- and hot tears in the casting. tem, modeling and simulation, steel casting It is surprising how many of our common casting defects are the fault of entrained oxides and bubbles. For instance in the case of gas porosity, pores up to about 5 mm diameter are the result of entrained air bubbles, whereas finer bubbles are usually 1. Introduction bifilms inflated by gases in solution, often hydrogen. All cracks and hot tears appear to be the product of entrained bifilms. Sand Modern foundry engineering is a well-developed and inclusions are a reliable sign of turbulence; the air displaced sophisticated industry utilizing cutting-edge technologies and backwards and forwards through the mold wall oxidizes away tools including 3D printing, robots and automated manufactur- the sand binder. Once the sand is unbonded, it can be pulled ing. Despite this, the most important production technology away from the mold wall, penetrating the surface of the liquid remains the use of greensand molds poured with cast iron or metal via the surface oxide film. The result is that sand inclusions steel (Ref 1-3). This traditional technology is widespread are usually found to be wrapped in their oxide paper bag from because of its low cost and adequate quality. However, the the entrainment event. [Campbell records that he has never quality requirements are continuously growing. It is recently known sand inclusions to result from poor sand quality (Ref 8)]. becoming common for the customer to specify a requirement to In general, providing they do not lead to cracks, the presence pass the stringent dye penetrant test. This inspection technique of bifilms in steels does not contribute to the rejection or illustrates the inadequacies of many current filling system scrapping of the casting because the population of these defects designs (Ref 4-7), since the presence of surface-breaking oxide is usually invisible. However, properties, particularly toughness bifilms, cracks and bubbles is now clearly revealed. and fatigue, are reduced. It seems that bifilms are sufficiently Turbulence during the pouring of metals generates two main small and compacted during turbulence that a high proportion defects: (1) entrained air bubbles and (2) entrained oxide films can pass straight through a ceramic foam filter. For instance a from the surface of the liquid metal. The oxides are always 20 ppi (pores per inch) filter gives a pore diameter of approx- entrained with the dry top surface of the oxide folded over imately 1 mm, allowing a 10-mm diameter bifilm, when raveled against itself. This unbonded double interface (a bifilm) acts as and compacted by turbulence to around 1 mm diameter, can pass through with ease. Thus, the filter is not capable of filtering out bifilms. Fortunately, however, filters are effective in resisting the passage of bubbles. This is really important during the priming J. Campbell: Professor Emeritus. of the filling system, the early seconds of filling when the 100% This article is an invited submission to JMEP selected from air in the system is required to be displaced by 100% metal. The presentations at the Symposium ‘‘Solidification, Casting, Foundry transition is unfortunately often messy and ragged, so that and Liquid Metal Processing,’’ belonging to the Topic ‘‘Joining’’ at the priming bubbles are a major component of the early flow regime, European Congress and Exhibition on Advanced Materials and and need to be kept out of the casting. If they succeed to enter the Processes (EUROMAT 2017), held September 17-22, 2017, in casting they create a long bubble trail, a kind of lengthy bifilm Thessaloniki, Greece, and has been expanded from the original and leak path from the bottom to the top of the casting. The fact presentation. that bubbles are greatly damaging to the casting has been R. Dojka and J. Jezierski, Department of Foundry Engineering, realized only relatively recently (Ref 8). Silesian University of Technology, Gliwice, Poland; and J. Campbell, The current paper presents the results of an approach to test Department of Metallurgy and Materials, University of Birmingham, the behavior of filling systems designed to fill completely (Ref Birmingham, UK. Contact e-mail: jan.jezierski@polsl.pl. 5152—Volume 27(10) October 2018 Journal of Materials Engineering and Performance 8), thereby excluding all air so far as possible, and thereby that the systems are practical and economic, permitting their reduce or prevent the occurrence of surface turbulence and the use for medium and heavy cast steel casting manufacture in entrainment of bubbles and bifilms. Naturally, it is necessary steel foundry plants. Fig. 1 Test mold according to Polish Standard PN-H-04309: 1976 Fig. 2 Initial technology, distribution of metal velocity and fill trackers after 1, 2 and 4 s from the beginning of pouring Journal of Materials Engineering and Performance Volume 27(10) October 2018—5153 The authors have in mind application of good systems in a local Polish foundry manufacturing heavy steel castings with a weight of up to around 30 tonnes, frequently in single units. Much of the molding process is carried out by hand, which provides an opportunity to shape the gating system closely to the theoretically ideal model. For such single heavy castings, failure is unthinkably costly, so that any additional help to ensure success is always welcome (Ref 9- 14). The casting manufacturing design concepts encompass an extensive body of knowledge enshrined in Campbells Ten Rules (Ref 8). However, the two key elements applying to the filling system are (1) the critical velocity for the avoidance of entrainment defects (Ref 6), and (2) the avoidance of entrained air and oxide entering the mold cavity (Ref 15- 17). Therefore, only these most important practical issues were included here for optimization. Other researchers are beginning to adopt these rules and are finding them useful (Ref 18-21). The paper describes the systematic evaluation of a number of gating systems in current use including the extended runner, spin trap, vortex gate, trident gate and others, using computer simulation. Fig. 3 A simple solution for the problem of circular and rectangu- 2. Experimental Method lar runner junctions Two computer packages: NovaFlow&Solid by NovaCast and Magma by Magmasoft, were used. A series of different gating systems were applied to a casting based on a test mold according to Polish Standard PN-H-04309: 1976 Cast steel—testing, casting and sampling, the so-called clover test piece. This sample test shape is commonly used in Poland for the evaluation of the mechanical properties of cast steel (Fig. 1). The steel test piece weighs 20 kg. Instead of the traditional filling of the mold by top pouring, the authors evaluated a series of different bottom gated systems. Bottom gating avoids any fall of the metal inside the mold cavity. It also provides filling against the gravity, allowing the achievement of non-turbulent filling, in sharp contrast to top pouring. It is one of the aspects of filling technology strongly recommended by Campbell and others (Ref 19, 22-25). All Fig. 4 Developed transition of the sprue from (1) circular to rectan- modeling trials have been made using the steel grade GS-52 gular cross section and (2) tapered hyperbolically according to DIN 1681, with the pouring temperature set at Fig. 5 Improper transition of a sprue from a circular to rectangular cross section 5154—Volume 27(10) October 2018 Journal of Materials Engineering and Performance Fig. 6 Extended runner, distribution of velocity and fill tracker 1570 C. The nominal composition of this steel is < 0.30% C; ladle; a technique known as contact pouring. Both of these 0.30-0.60% Si; 0.20-0.50% Mn; < 0.04% P; < 0.04% S. The techniques are known to be essential for the production of low- minimum mechanical properties of the steel are YS = 260 defect castings (Ref 8). MPa, UTS = 520 MPa, E = 18%, impact strength ISO- It is important to bear in mind that practically all V = 22 J. currently available computer packages are unable to model The sprue entrance is considered in every case to be the presence of bubbles in the flow of liquids. This means completely filled by liquid metal. This is rarely met in practice that an important aspect of gating design cannot be unless one of only two conditions is met: (1) The entrance is simulated, so that all current attempts at simulation unfor- filled by an offset step basin with a stopper sealing the sprue tunately remain limited. Nevertheless, the authors believe that entrance. The stopper is raised, permitting the fill of the sprue the present work illustrates that much can be achieved and only when the basin is filled up to the design fill level. (2) The demonstrates important improvements which the application sprue is filled by direct contact with the nozzle of a bottom-pour of recent concepts make possible. Journal of Materials Engineering and Performance Volume 27(10) October 2018—5155 the same cross-sectional area tend to behave differently: the slimmer the runner the more laminar the flow. A slim rectangular runner 30 9 6 mm was therefore selected. As a consequence, the sprue had the additional requirement to change gradually from a circular cross section at its entrance, to a rectangle at its exit, to match perfectly to the entrance to the runner. The sophisticated shape of the sprue described above contrasts with a commonly used junction of a round sprue to a rectangular runner. This junction works badly, with the liquid ricocheting back and forth down the runner, never properly filling the runner, as shown schematically in Fig. 3 (Ref 8). The improved sprue design by the authors for this simulation is shown in Fig. 4. The studies show that improper tapering and transition causes, as shown in Fig. 5, depressurization and non-filling of the sprue. The metal stream clearly free-falls down the early part of the sprue, and so does not have the advantage of some boundary friction. The higher velocity into the mold is seen to cause jetting. However, it should be realized that the real situation is more damaging still as a result of the simulation not modeling bubbles. The plunging stream conditions in the sprue will entrain copious volumes of air, probably in a mix of at least 50/50 air/metal. This massive influx of air will severely damage the casting by both bifilm and bubble entrainment (Ref 7). Fig. 7 Centrifugal slag trap, velocity distribution and fill tracker 2.3 Extended Runner Another traditional filling system uses a simple extension of the runner to capture the first metal through the system because 2.1 State-of-the-Art Pouring Procedure it was assumed to be relatively cold. This was true, but A conventional gating system constructed by using prefab- probably of negligible importance. Close examination of Fig. 6 ricated 15-mm diameter refractory tubes was simulated as a shows no great benefit to metal temperature through the gate. In base against which newer developments could be assessed. In any case, the real problem requiring solution was not lack of this case, the rate of metal flow from the ladle was 5 kg/s. temperature, but excess of defects resulting from its unavoid- Figure 2 presents a distribution of metal velocity and a fill able mixing with air in the initially empty filling channels. In tracker that defines a distribution and life time of metal portion particular, its content of bubbles would add to the problems of a entering the sprue after 1, 2 and 4 s from the beginning of significant bifilm population already generated. pouring. It can be noticed that the velocity of the metal at the Figure 6 presents the distribution of velocity during the entrance to the mold cavity exceeds 3 m/s, greatly exceeding filling. It is clear that while the extension is filling, the velocity the safe gate velocity 0.5 m/s, resulting in a clear jetting effect. through the gate is close to a gentle and safe value in the range The numerous splashes and droplets would result in a poor- 0.5-1.0 m/s. However, at the instant the extension is filled, the quality casting with generous quantities of entrained defects. gate is now subject to the full pressure head of the sprue, and a The impacts between droplets and splashes will create oxide jet is formed; the velocity of metal entering the mold cavity has bifilms (Ref 15) which will degrade the mechanical properties jumped to over 2 m/s. This disturbance to the rising surface of and the appearance of the casting. the melt is seen to continue high into the mold, leading to bifilm formation and laps on the casting surface (the lap constituting a 2.2 Tapering of the Down-Sprue bifilm crack defect) which may lead to macroscopic cracking of the casting. The poor performance of the basic pipework system seen in In addition, the small volume of the extension causes a back Fig. 2 raises the question, What should the perfect gating wave (which would have been expected to be even more system look like? There are a number of options. But some significant if the runner had been deeper, allowing more head clear process steps include the following factors. room for back-flow). Some back-flow from the extension into First, in place of constant diameter preformed refractory the casting is clearly seen in the tracking result, confirming that tubes, the cross-sectional shape of the filling system channels some of the damaged melt will find its way into the casting. The requires to be tailored to the shape of the flowing liquid. authors tried different modifications of this solution, but even Almost all bottom-pour ladles have round-shaped nozzles increasing the extension to the top of the mold did not result in which need to match the shape of the entrance to the gating the elimination of the jetting effect. system. From that point onwards in the filling system, the sprues cross section should gradually narrow, tapering accord- 2.4 Centrifugal Slag Trap ing to the natural hyperbolic curve of a falling stream. The authors in their most recent studies confirmed (Ref 26) that Various versions of a centrifugal slag traps have been liquid metal flowing through runners with larger perimeter but described in the literature for a long time. It may be built in a 5156—Volume 27(10) October 2018 Journal of Materials Engineering and Performance Fig. 8 Vortex gate scheme number of ways, but one thing is constant—the component to The above system was not easily molded, requiring multiple be used as a spin trap is located in front of the mold cavity. The vertical partings or the use of complex cores. An analogous authors performed many simulations using a number of design, a barrel trap, was devised by authors to create a different diameter-to-height ratios, but the effect was always system similar to the centrifugal slag trap, but because of the similar to that presented in Fig. 7. The technique initially looks horizontal axis of the barrel it would be easier to mold. A filter promising, but the trap finally fills, which causes a sudden placed flush with the runner was provided to divert bubbles increase in velocity with a consequential catastrophic jetting (and other less dense components such as slag) into the barrel effect. Impurities originally held in the middle of the trap are where they could be centrifuged into its center. However, the pushed inside the mold cavity. The centrifugal slag trap cannot computer simulation revealed a similar problem to the slag be recommended. trap; when the filling of the barrel was complete, the Journal of Materials Engineering and Performance Volume 27(10) October 2018—5157 centrifugally concentrated impurities appear to flow back to the filter, either clogging the filter or reducing the casting quality. It seems the barrel trap is yet another technique which cannot be recommended. 2.5 Vortex Gate The vortex gate (Fig. 8) enjoyed some early success for larger castings by reducing the high velocity of metal entering the mold cavity. Its huge ability to reduce velocity resulted simply from the ratio of areas of the runner and the vortex cylinder, being the ratio of the horizontal flow area to the vertical flow area. It was not difficult to reduce flow velocity by a factor of 10. At that time, such large velocity reductions were not easily achieved by any other simple technique. The cylinder was equipped with a collar around its base (described elsewhere as a spinner disk) to guide the initial metal around the cylinder, gaining its circular motion, and avoiding its direct impact and splashy vertical climb up the far wall of the cylinder. Another feature of the vortex gate was a ceramic Fig. 9 Vortex gate, velocity distribution and fill tracker Fig. 10 Spin trap scheme 5158—Volume 27(10) October 2018 Journal of Materials Engineering and Performance Fig. 11 Spin trap, velocity distribution and fill tracker foam filter placed on the top in an effort to reduce the rotational component of speed before it entered the mold. As shown in Fig. 8, the velocity of metal entering the mold cavity in this solution is 0.78 m/s, which makes a significant improvement compared to previous systems, but the rotational flow of the first portions of metal entering the mold cavity remains too turbulent. (The limited effectiveness of the foam filter in reducing the rotational speed is confirmed by practical experience. It may have been improved by the use of straight vertical pores of a pressed or extruded filter.) From practical trials, however, it has been found that a major fault with the vortex gate is that it centrifuges bubbles into the center of the vortex cylinder from where they are unable to escape. They build up and coalesce to a single bubble, which grows in size under the filter until it has sufficient buoyancy to force though the filter. The flow up through the casting is highly damaging to the casting; the long bubble trails generate long bifilm cracks and leak paths. (Unfortunately, the deleterious action of bubbles in the flowing metal, a major feature, cannot yet be simulated as mentioned above.) Fig. 12 Simplified spin trap, velocity distribution and fill tracker Journal of Materials Engineering and Performance Volume 27(10) October 2018—5159 Fig. 13 Trident gate scheme come into action, and the velocity through the gate reaches its 2.6 The Tangential (Flush) Filter and Terminal Spin Trap full value of several meters per second. The volume of the trap In this filling system (Fig. 10), the vertical ingate is needs to be sufficiently large to ensure that the trap only fills protected from the ingress of bubbles by a filter which acts as after the gate is filled, and sufficient depth of metal has arrived a bubble diverter. The filter is placed flush with the top of the in the mold cavity to suppress jetting. The height-to-diameter runner so that, instead of the bubbles accumulating under the ratio of a spin trap, and its optimum volume as a function of filter, they are encouraged to flow past and into the runner casting size and geometry, will be subject to further examina- extension. The bubbles are then trapped, together with the cool tion. and damaged priming metal, by the centrifugal action inside the A further feature of this filling system should be noted. spinner. Because the sprue is nicely tapered, so as to fill completely and The spinner at the end of the runner has a further important thereby exclude air, and because air bubbles from the priming role; the gradual filling of the trap causes a steady increase in of the system are encouraged to divert, instead of passing back pressure in the runner. This pressure, effectively starting through the filter, the filter transmits only relatively good from zero, acts to drive the initial slow filling of the gate, quality metal rather than masses of oxides. In practice, ensuring that the velocity through the gate is too low to cause therefore, it is successful to pass large volumes of metal jetting. This is clearly achieved as shown in Fig. 9 and 10. Only without any danger of blockage. This behavior contrasts with when the trap is filled does the full head height of the sprue 5160—Volume 27(10) October 2018 Journal of Materials Engineering and Performance Fig. 14 Trident gate, velocity distribution and fill tracker the use of filter placed after drain pipe sprues, which generate degrade flow and the quality of the casting beyond what Fig. 12 so much oxide that the filter can pass only limited quantities of can show. The use of the preformed tubes for filling systems metal prior to blocking (Ref 27). cannot be recommended at this time. Naturally, the cross section of the ingate should be sufficiently large to reduce the speed of metal entering the 2.7 Trident Gate mold cavity to a value in or below the range 0.5-1.0 m/s. In Fig. 11, the initial velocity of metal entering the mold cavity is The trident gate is the most recent development in the quest 0.3 m/s. for reliable, high-quality, gravity casting techniques (Ref 27). 2.6.1 The Tangential (Flush) Filter and Terminal Spin In common with the previous technique, it has a filter flush Trap Made from Preformed Refractory Tubes. If the with the runner to avoid bubbles so far as possible, and the filling system is constructed from prefabricated refractory provision of a spin trap which not only captures bubbles and tubes, for ease of assembly and molding, instead of being damaged metal, but raises the pressure slowly on the ingate molded directly in sand, Fig. 12 shows the result. The initial filter to avoid jetting into the mold. velocity of metal in the mold cavity is around 0.6 m/s; As an additional feature, it has a bubble trap and second however, jetting effect is evident. Although this filling behavior filter placed vertically, so if any bubbles get through the first might appear marginally acceptable, the constant diameters of filter, the second filter would divert them upwards into the the preformed tubes cannot follow the necessarily changing bubble trap. form of the liquid stream, and do not therefore constrain the The system was devised by Puhakka and Campbell in 2014 flow. As a result, air entrainment and bubble formation will (Ref 27). The schematic diagram of a trident gate is shown in occur (not easily detected in the simulations), which will further Fig. 13. Its rather complex form is not easily molded, and so is Journal of Materials Engineering and Performance Volume 27(10) October 2018—5161 2. M. Holtzer, R. Danko, and S. Zymankowska-Kumon, The State of Art contained within a two-parted sand core, having an outward and Foresight of Worlds Casting Production, Metalurgija, 2014, 53(4), block-like shape, which is planted on the runner and molded p 697–700 into place in the sand mold. This solution has been used with 3. J. Danko and M. Holtzer, The State of Art and Foresight of Worlds great success with aluminum alloys (Ref 28-30). It appears to Casting Production, Metalurgija, 2006, 45(4), p 333–340 be capable of routinely making defect-free Al alloy castings. 4. L. Camek, P. Lichy, I. Kroupova, J. Duda, J. Beno, M. Korbas, F. The technique may also be useful for ferrous alloys but has yet Radkovsky, and S. Bliznyukov, Effect of Cast Steel Production Metallurgy on the Emergence of Casting Defects, Metalurgija, 2016, to be widely tested in practice. 55(4), p 701–704 Figure 13 presents a simulation of metal velocity. During 5. E. Foglio, M. Gelfi, A. Pola, S. Goffelli, and D. Lusuardi, Fatigue the initial phase of mold cavity filling, the velocity is around Characterization and Optimization of the Production Process of 0.35 m/s. The analysis of fill trackers presented in Fig. 14 Heavy Section Ductile Iron Castings, Int. J. Metalcast., 2017, 11(1), p shows that filling is equally good as in the case of spin trap 33–43 6. J. Campbell, Stop Pouring, Start Casting, Int. J. Metalcast., 2012, 6(3), solution. Overall, in addition to the advantages of a spin trap its p 7–18 two-stage filtration plus integral bubble trap appears to be 7. J. Campbell, Melting, Remelting, and Casting for Clean Steel, Steel highly effective in keeping bubbles out of the mold cavity. Res. Int., 2017, 88(1), p 1600093 8. J. Campbell, Complete Casting Handbook, 2nd ed., Butterworth- Heinemann, Oxford, 2015 9. S.G. Acharya, J.A. Vadher, and K.D. Kothari, Evaluation of Critical 3. Conclusions Parameters for Sand Inclusion Defect in FNB Casting, Arch. Foundry Eng., 2017, 17(1), p 5–12 10. S.G. Acharya, J.A. Vadher, and P.V. Kanjariya, Identification and The paper presents a systematic comparison of a number of Quantification of Gases Releasing From Furan No Bake Binder, Arch. gating systems for steel castings, using computer simulation. Foundry Eng., 2016, 16(3), p 5–10 They were based on the filling of a clover-like test sample and 11. P. David, J. Massone, R. Boeri, and J. Sikora, Gating System Design to led to the following conclusions: Cast Thin Wall Ductile Iron Plates, Int. J. Cast Met. Res., 2006, 19(2), p 98–109 • Computer modeling confirmed the effectiveness of gating 12. G.L. Di Muoio and N.S. Tiedje, Achieving Control of Coating Process in your Foundry, Arch. Foundry Eng., 2015, 15(4), p 110–114 systems to control the velocity and surface turbulence of 13. A. Modaresi, A. Safikhani, A. Noohi, N. Hamidnezhad, and S. Maki, the metal entering the mold cavity (but it is acknowledged Gating System Design and Simulation of Gray Iron Casting to that the simulations could not include the presence of air Eliminate Oxide Layers Caused by Turbulence, Int. J. Metalcast., bubbles in the metal flow). 2017, 11(2), p 328–339 Filling systems molded to follow the shape of the falling 14. Z. Ignaszak, Discussion on Usability of the Niyama Criterion for Porosity Predicting in Cast Iron Castings, Arch. Foundry Eng., 2017, stream (particularly the naturally pressured system) are 17(3), p 196–204 successful to reduce the conditions for forming entrain- 15. J. Campbell, The Consolidation of Metals: The Origin of Bifilms, J. ment defects. Mater. Sci., 2016, 51(1), p 96–106 The filling system constructed from preformed refractory 16. J. Campbell, Sixty Years of Casting Research, Metall. Mater. Trans. A, tubes performed poorly. 2015, 46A(11), p 4848–4853 The various vortex systems were all found to perform 17. J. Campbell, Crack Populations in Metals, Aims Mater. Sci., 2016, 3(4), p 1436–1442 poorly for different reasons. 18. F. Hsu, M. Jolly, and J. Campbell, Vortex-Gate Design for Gravity The various systems using (1) naturally pressurized chan- Casting, Int. J. Cast Met. Res., 2006, 19(1), p 38–44 nel designs; (2) filters placed flush on runners to divert 19. F. Hsu, M. Jolly, and J. Campbell, A Multiple-Gate Runner System for bubbles; and (3) sufficiently large spin traps on the ends Gravity Casting, J. Mater. Process. Technol., 2009, 209(17), p 5736– of runners performed excellently. For the first time, it seems that techniques are now available for the production 20. R. Ahmad and M. Hashim, Effect of Vortex Runner Gating System on the Mechanical Strength of al-12si Alloy Castings, Arch. Metall. of defect-free castings. Mater., 2011, 56(4), p 991–997 21. N. Ducic, R. Slavkovic, I. Milicevic, Z. Cojbasic, S. Manasijevic, and R. Radisa, Optimization of the Gating System for Sand Casting Using Genetic Algorithm, Int. J. Metalcast., 2017, 11(2), p 255–265 Open Access 22. H. Zhou, L. Luo, Z. Shi, J. Dong, and W. Ma, Filling Pattern of Step Gating System in Lost Foam Casting Process and Its Application, Adv. This article is distributed under the terms of the Creative Commons Mater. Res.-Switz, 2013, Pts 1–3, 602-604, p 1916–1921 Attribution 4.0 International License (http://creativecommons.org/ 23. D. Yang, S. Li, F. He, W. Sung, J. Kao, and R. Chen, Twin Gating licenses/by/4.0/), which permits unrestricted use, distribution, and System Design for Typical Thin Wall Stainless Steel Castings Based on reproduction in any medium, provided you give appropriate credit Fast Pouring Mechanism, Appl. Mech. Mater., 2014, Pts 1 and 2, 457- 458, p 1657–1660 to the original author(s) and the source, provide a link to the 24. R. Ranjan, N. Kumar, R. Pandey, and M. Tiwari, Agent-Based Design Creative Commons license, and indicate if changes were made. Framework for Riser and Gating System Design for Sound Casting, Int. J. Prod. Res., 2004, 42(22), p 4827–4847 25. K. Renukananda and B. Ravi, Multi-Gate Systems in Casting Process: References Comparative Study of Liquid Metal and Water Flow, Mater. Manuf. 1. M. Soinski, P. Kordas, and K. Skurka, Trends in the Production of Process., 2016, 31(8), p 1091–1101 Castings in the World and in Poland in the XXI, Century, Arch. 26. J. Jezierski, R. Dojka, K. Kubiak, W. Zurek, and T. Ltd, Experimental Foundry Eng., 2016, 16(2), p 5–10 Approach for Optimization of Gating System in Castings, Metal 2016: 5162—Volume 27(10) October 2018 Journal of Materials Engineering and Performance 25th Anniversary International Conference on Metallurgy and Mate- 29. J. Sturm, G. Dieckhues, and S. Sikorski, Systematic Optimization of rials, 2016, p 104–109 Aluminum Sand Casting Gating Systems, Trans. Am. F, 2012, 120(120), p 13–21 27. J. Campbell, Mini Casting Handbook, Aspect Design, Malvern, 2017 30. Y. Jiang, Y. He, Y. He, X. Qian, Y. Huang, L. Xu, W. Tian, and E. Mao, 28. M. Bruna, D. Bolibruchova, and R. Pastircak, Reoxidation Processes Analysis and Optimization on the Gating System of Aluminum Alloy Prediction in Gating System by Numerical Simulation for Aluminium Piston in Casting, Appl. Mech. Mater., 2011, Pts 1 and 2, 80-81, p 32–35 Alloys, Arch. Foundry Eng., 2017, 17(3), p 23–26 Journal of Materials Engineering and Performance Volume 27(10) October 2018—5163

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