Scale Formation on HSLA Steel during Continuous Casting Part II: The Effect of Surface Conditions

The present research addresses the effect of surface condition on oxide scale formation at high temperatures such as those experienced during secondary cooling in Continuous Casting. Tests were carried out in clean, as-cast and surfaces covered with casting powder to replicate the oxidation/re-oxidation after the mould. Specimens oxidized at 1000, 1100 and 1200 °C under dry air and water-vapour conditions revealed that the oxide scale formation is strongly influenced by temperature, environmental and surface conditions. The oxide scale thickness increases with temperature alterations in the surface (e.g., as-cast and covered with powder) where oxides and carbonates from the casting powder accelerate oxidation kinetics leading to thick and unstable scales. A high amount of carbon is present on surfaces covered with casting powder where it diffuses through the oxide scale forming CO and CO2 which lead to stress accumulation that makes scales prone to defects such as pores, voids and micro-cracks. Ultimately, if wüstite remains attached to the steel surface or inside oscillation marks, it may disturb heat transfer during secondary cooling which has deep industrial implications for crack formation and overall casting yield. Therefore, accurate insights on scale type and growth mechanisms could lead to accurate control of its formation during casting.

Metal matrix production: Casting of recycled aluminum cans and incorporation of rice husk ash and magnesium

This research experimented with different aluminum can casting compositions from recycled materials. The objective was to analyze the casting yield and the resulting chemical compositions of the process. In the first process, 20 kg of aluminum cans was melted, resulting in a 10.2 kg ingot, which presented a 51% yield. In the second process, 10 kg of 6063 T6 aluminum was used and 10.2 kg of the first casting was added. This mixture produced an ingot of 50% recycled aluminum and 50% 6063 aluminum that weighed 18.23 kg. Similarly, a second ingot was produced, but with the addition of 4 wt% of rice husk ash and 2 wt% of magnesium. From each ingot, the samples were removed for chemical analyses, which consisted of tests of the samples that had the incorporation of rice husk ash in the molten aluminum. These analyses included scanning by electron microscopy, density analysis, Brinell hardness, and Charpy impact force tests. The results of the second ingot analysis showed superior characteristics in Si and Mg levels due to the addition of rice husk ash and magnesium. Also, the second ingot presented increased hardness as well as a reduction fragility and density.

Characterization of Microstructure and Shrinkage Porosity of a Semi-Solid Metal Slurry in Gravity Die Casting

Current aluminum automotive parts such as wheels, engine and transmission components are produced by tilted gravity die casting for control gas porosity. But, there are still problems resulting in inefficient production: shrinkage porosity, microstructure size and uniformity. Shrinkage porosity is one of the major issues which affects mechanical properties such as strength and elongation in tilted pour permanent mold. Recent work using slurry casting technique has shown potential in gravity sand casting. Results show that the casting parts have complete filling at low solid fractions and the casting yield is also higher than conventional gravity sand casting. This paper extends important work for potential industrial applications in gravity die casting: microstructure size, uniformity, solid fraction control for micro shrinkage level.

Casting Design Modification to Improve Casting Yield in Producing Thin Wall Ductile Iron Plate

Cooling rate plays an important role in the formation of thin wall ductile iron microstructure due to their thickness, which is 3 mm below based on Stefanescu. Cooling rate is closely related to casting design and determines the microstructure. This paper discusses the effect of casting design modification to casting yield and microstructures. Modification was made on a patented design used previously to produce thin wall ductile iron plates. The design was minimized and casting simulation was used to analyze castability of the design. After that, the design were casted in several pouring temperatures. Improvement was made to casting design based on the failure during the experiment. Casting process took place after simulation analysis. The casting product was fully casted as shown by the simulation. The casting yield has improved to 28%. When all plates were examined for microstructure, the result showed that all the microstructure of the plates was not graphite in ferrite matrix as occurred in the patented design but it was graphite in pearlite matrix.

Analysis of Shrinkage Characteristics of Aluminium Silicon Alloy

Analysis of shrinkage characteristics of Aluminium-Silicon alloy was studied theoretically and experimentally. The Aluminium alloys considered in the study are A413 (LM6), A360 (LM9) and A380 (LM24). Extensive literature survey has suggested that cavity filling and solidification process are two most critical aspects to produce high quality casting components. A statistical model of parameters and response to understand the influence of parameters on shrinkage and casting yield studies has been presented. Experiments were conducted in foundry in industrial environment to produce commercially treated aluminium alloy castings in sand mould. Alloy was found to be most significant factor influencing shrinkage. The yield of casting was improved using insulating and exothermic sleeves. Solidification time of exothermic riser was 10 % more than insulated riser. Thus, in order to produce radiographic quality casting a theoretical and experimental method is presented so that number of trials in foundry is reduced which leads to increased reliability and productivity. Study also shows that by using sleeves considerable metal is saved, energy saving during melting, improved quality, reduced cost and increased capacity of plant can be achieved.

The Effect of Vertical Step Block Casting to Microstructure and Mechanical Properties in Producing Thin Wall Ductile Iron

Thin wall ductile iron (TWDI) is introduced to fulfill the needs of lighter material in automotive parts that will reduce fuel consumption. Problem occurs during the production of TWDI due to the casting thickness. TWDI casting thickness classified to below 5 mm. Many designs have been made to answer the problem in producing thin wall ductile iron. Soedarsono et al established vertical step block casting design. This design based on Y-block principle that allows direct pouring of liquid metal to the mold without passing any gating system. This design will increase casting yield. The parameter of this research is pouring basin placement to study the effect of plate arrangement to filling and solidification. This research is conducted to see the effect of pouring basin placement to microstructure and mechanical properties of TWDI. The Design is made to produce 5 plates with different thickness that is 1, 2, 3, 4, and 5 mm. All of the plates arranged parallel in line. Pouring basin located in 2 ways. The first type located pouring basin above the plate of 5 mm thickness while the second one located it above the plate with 1 mm thickness. The first type coded as T4 while the second coded as T5. The moulds made from furan sand. The result shows although cold shut occurred in both pouring basin placements due to pouring discontinuity but shrinkage only formed in T5 on its plate with 1 mm thickness. Microstructure of all the plates presented nodule graphite in pearlite matrix. Carbide and skin effects also detected. Average nodularity is above 80% while the nodule count is between 614 to 1269 nodule/mm2. Most of the Brinell hardness number exceeded maximum limit given by JIS G5502 but the UTS is below the minimum limit except for 3 mm plate thickness of T5. All elongation values below the minimum standard. The results confirm that pouring basin location is important in casting design following Y-Block principle.

Effects of Steelmaking Ladle Holding Period on Continuous Casting Yield

The study was undertaken to ascertain the effects of holding time during secondary steel making, casting duration, strand loss per heat, and tonnage of steel returned per heat on continuous casting yield (%). A total of 1910 heats, spanning a period of seven years (41 production months) were used for the study. Monthly tonnage of liquid steel produced and cast and the corresponding yield were computed from the casting reports. Also extracted from the casting reports are the average monthly holding time (mins) during secondary steel making, monthly average heat casting duration (minutes), average strand loss per heat and monthly average tonnage of steel returned per heat. A statistical package for social sciences (SPSS) was used to analyse the data obtained. The yield was found to be negatively correlated to steel holding time during secondary steel making (-0.257 mins), strand loss per heat (-0.753 tons), and tonnage of heat returned per heat (-0.944 tons), but positively correlated to casting duration (0.371 mins). The result showed that increase in holding time during secondary steel making, strand loss per heat and tonnage of steel returned per heat decrease the yield of continuous casting process. The model formulated was able to explain 93.4% of the total variation in the observed yield. Efforts should therefore be made to monitor and reduce these parameters that decrease the yield through proper process control, regular checks of the continuous casting machines, replacement of worn out moulds, and in-house training and retraining of casters for optimum process performance.

Analysis and Optimization on the Gating System of Aluminum Alloy Piston in Casting

Shrinkage porosity defects occurring in ring groove underside the pin hole of aluminum piston are strongly influenced by the time-varying temperature profiles inside the solidifying casting. By adopting the finite element analysis software PROCAST and combining with production practice, the gating system which has open-cycle ring feeding channel in the bottom of the piston was compared with conventional techniques; the influence of opening angle of ring feeding channel and different process parameters on shrinkage distribution was researched. The results show the gating system with open-cycle ring feeding channel can satisfy progressive solidification and effectively eliminate the shrinkage in ring groove underside piston pin hole, and can greatly reduce the riser size and improve casting yield; the opening angle influences shrinkage distribution and can be adjusted to achieve effective feeding; shrinkage size is influenced by pouring temperature and casting speed which have less effect on shrinkage distribution. The system of ring feeding channel is adopted, the opening angle and process parameters are adjusted, all which can effectively eliminate shrinkage in the bottom of the piston, improve casting yield and process rate.