Bambang Suharno

Effect of Casting Design to Microstructure and Mechanical Properties of 3 Mm TWDI Plate

The problem occurs in producing thin wall ductile iron (TWDI) is high cooling rate due to its thickness. Cooling rate must be strictly maintained to prevent carbide formation. There are many ways to control cooling rate. Casting design is one of these, especially gating system design. This parameter is often chosen because of its independence. Major changes in equipment and raw material used in the foundry are not needed when a casting design is chosen to deal with cooling rate. This paper discusses the effect of gating system design on microstructure and mechanical properties of 3 mm TWDI plate. A casting design based on gating system design is made to produce 1, 2, 3, 4, and 5 mm TWDI plates. There are three designs coded as T1, T2, and T3. These three designs were also used in making 1 mm TWDI plates of which the result has been published. The plate with thickness of 3 mm will be used for automotive component like the crankshaft made by Martinez. The moulds used were furan sand. Beside the experiment, casting design simulation with Z-Cast was also conducted to see the behaviour of solidification in 3 mm TWDI plate. Simulation result showed every design has its own solidification behaviour for 3 mm TWDI plate, especially for T2. Experiment result showed that all the designs have microstructure consisting of nodule graphite in ferrite matrix, no trace of carbide and skin effect are formed. Skin effect length is various for all designs. Nodularity exceeded 75% and nodule count exceeded 900 nodules/mm2. Brinell hardness number for all design is beyond standard given by JIG G5502. As for UTS and elongation none of the designs exceed the minimal standard. Experiment results confirmed simulation result. Compared to the previous result nodularity and nodule count decrease and curve trends for every result are not the same.

The Use of Mixture of Piper Betle and Green Tea as a Green Corrosion Inhibitor for API X-52 Steel in Aerated 3.5 % NaCl Solution at Various Rotation Rates

Flow induced corrosion due to the presence of turbulent flow often occurs which causes severe internal thinning and promotes premature leakage. In practice, the common method for controlling such internal high corrosion rate is chemical injection using corrosion inhibitor such as amine based which utilizing adsorption or film forming mechanism. Unfortunately, the protection performance of such inhibitor might be less effective due to turbulent flow induced. The aim of this work is to study the use of mixture of piper betle and green tea as an alternative of green corrosion inhibitor (eco-friendly) to reduce the corrosion rate of API X-52 steel in aerated 3.5 % NaCl solution in turbulent flow condition whether high inhibitor efficiency can be achieved. The method of corrosion rate measurements was conducted using electrochemical polarization equipped with CMS100-Gamry Instruments and DC105 software as well as Rotating Cylinder Electrode (RCE) simulation. The mechanism of inhibition was also investigated using Electrochemical Impedance Spectroscopy (EIS) method with EIS300 software. The results showed that the addition of mixture of 1000 ppm piper betle and 4000 ppm green tea extracts with Reynold number ranging from 0 up to 30000 reduced the corrosion rates significantly with its approximately 90 % inhibitor efficiencies achieved. In addition, EIS spectra showed that in the absence of corrosion inhibitor, the Warburg impedance (diffusion controlled) was significantly attributed to the overall impedance but in the presence of corrosion inhibitor, capacitive impedance (charge transfer controlled) was mainly attributed to the overall impedance.

The Effects of Plates Position in Vertical Casting Producing Thin Wall Ductile Iron

In the general rule of casting design the thickest part of the cast should be placed near to the ingate. This arrangement was meant to guarantee the completion of filling process. An unusual vertical casting design to produce plates with different thicknesses was established based on the idea that the heat from molten metal will always warm up its entire runner. In this design the thinnest plate is placed near to the ingate. The design was made for producing thin wall ductile iron. This research was conducted to see the effects of reverse thickness arrangement in casting design to the microstructure and mechanical properties of the plates. Plates produced by this design were compared to plates produced by the same design with general casting arrangement. Thicknesses of the plates produced in this casting were 1, 2, 3, 4, and 5 mm. The moulds used were made from furan sand. Beside experiment, casting design simulation with Z-Cast was also conducted to ensure the completion of filling process and to see the manner of solidification. Casting simulation showed that arrangement of plates gave different filling and solidification manners. Although there were some differences, the filling was successful for both arrangements of plates. Skin effect was found in both designs. Nodule counts and nodularity were higher in the new design while average nodule diameters were lower. The result gained in tensile and hardness test did not follow the correlations in the characteristic of graphite. Mechanical properties showed that position of plate, ignoring the thickness, influence tensile strength and hardness.

Cooling Rate Analysis of Thin Wall Ductile Iron Using Microstructure Examination and Computer Simulation

Cooling rate plays an important role in thin wall ductile iron solidification, due to their thickness. Casting simulation is use as a tool to estimate the cooling rate. In the other hand, every microstructure has its own cooling rate. This paper explores the similarity of solidification mechanism between simulation and graphite characteristics. Three types of casting design simulated and produced. Solidification mechanism is analyzed based on cooling rate sequence and trend line matching. Temperature gradient and thermocouple function represent simulation while graphite characteristic represent experiment. The result shows that similarity in solidification mechanism is not found between simulation with experiment due to lack of parameters in both sides.

Development of Steel Wire Rope – Reinforced Aluminium Composite for Armour Material Using the Squeeze Casting Process

Steel wire rope – reinforced aluminium composite - has been developed to improve the ballistic properties and mobility of armour material. Critical to obtaining ballistic resistance is that the materials must be sufficiently hard and strong, especially at the surface where a projectile will first make impact. To obtain this resistance, aluminium alloys can be strengthened by adding Cu and Mg. This research studied the ballistic properties of aluminium composites with varied Cu and Mg content. The matrix used in this study was an Al-7Si master alloy with 0.08-1.03 wt. % Mg and 0.05-3.75 wt. % Cu, both independently and in combination. A high carbon steel wire rope was used as strengthening material. The samples were produced through the squeeze casting process with a pressure of 1 MPa at semi-solid melting temperatures of 590-610 °C. The slab was then rolled for 10 % reduction to increase the hardness. Ballistic testing was performed in accordance with ASTM F1233 by using a 9 mm calibre projectile and 900 direction. Micro structural observation was conducted in the as-cast and ballistic samples, performed with optical microscope and scanning electron microscope (SEM). The results showed that squeeze casting may improve interfacial wettability and reduce void. The increase in Mg resulted in the decline of interfacial voids, but Cu addition tended to increase them. The aluminium armour was able to withstand a 9 mm calibre projectile, although some cracks were visible. The wire rope was not effective in stopping the penetration of a 7.62 mm calibre projectile.

Characteristic of skin formation using zircon- and graphite-coated mold in thin wall ductile iron fabrication

One of the problems in thin wall ductile iron (TWDI) fabrication is skin formation during the casting. The presence of this skin will decrease strength and strain of the TWDI. One of the ways to control this skin formation is to change the cooling rate during the process through a mold coating. In testing the effectiveness of skin prevention, the following variables were used for the mold coating i.e. (i) graphite: (ii) zirconium; and (iii) double layer of graphite-zirconium. After the process, the plates were characterized by non-etching, etching, tensile test, and SEM observation. The results showed that the average skin formation using graphite: 65 µm; zirconium: 13.04 µm; and double layer of graphite-zirconium: 33.25 µm. It seems that zirconium has the most effect on the skin prevention due to sulfur binding and magnesium locked, which then prevented rapid cooling resulting in less skin formation. The results also showed the number of nodules obtained in specimen with graphite: 703 nodules/mm2 with av...

Effects of Ceramic Fibre Insulation Thickness on Skin Formation and Nodule Characteristics of Thin Wall Ductile Iron Casting

Skin formation has become one of the problems in the thin wall ductile iron casting because it will reduce the mechanical properties of the materials. One of the solutions to reduce this skin formation is by using heat insulator to control the cooling rate. One of the insulators used for this purpose is ceramic fibre. In this research, the thickness of the ceramic fibre heat insulator used in the mould was varied, i.e. 50 mm on one side and 37.5 mm on the other side (A), no heat insulator (B), and 37.5 mm on both sides (C). After the casting process, the results were characterized in terms of metallography by using scanning electron microscope (SEM) and tensile test for mechanical properties. The results showed that the skin thickness formed in A is 34.21 μm, 23.38 μm in B, and 27.78 μm in C. The nodule count in A is 541.98 nodule/mm2 (84.7%) with an average diameter of 15.14 μm, 590 nodule/mm2 (86.7%) with an average diameter of 13.18 μm in B, and 549.73 nodule/mm2 (87.2%) with an average diameter of 13.95 μm in C. The average ultimate tensile strength for A was 399 MPa, B was 314 MPa, and C was 415 MPa. Microstructural examination under SEM showed that the materials have a ductile fracture with matrix full of ferrite.

Properties of Fe-Mn-C Alloy as Degradable Biomaterials Candidate for Coronary Stent

The development of biomaterial has reached biodegradable stage. Biodegradable means it can be degraded after certain period of time after implantation and cause no harm for the system. Degradable Biomaterial has the potential to be used as Coronary Stent to minimize the risk from thrombosis issue. Thrombosis is a symptom of body defense where will be a clots blood effect around stent area. The formation of clots blood will disturb a blood flow in artery and it will result a restenosis effect.

Corrosion Behavior of Fe-Mn-C Alloy as Degradable Materials Candidate Fabricated via Powder Metallurgy Process

Fe-Mn alloys are prospective degradable materials for coronary stents. Several methods and strategies are investigated to produce excellence properties for this application, such as addition of alloying elements. The study is focused on the corrosion behavior of novel Fe-Mn alloys, i.e. Fe-25Mn-1C and Fe-35Mn-1C fabricated by powder metallurgy process. Addition of carbon is intended to obtain the phase that has ability to easily degradable without compromising its mechanical properties. The results show that austenite phase formed from this process and corrosion rate increased in proportion with the manganese addition from 32.2 mpy (Fe-25Mn-1C) to 43.7 mpy (Fe-35Mn-1C) using polarization methods. The presence of porosity, which cannot be extinguished by sintering, makes the degradation favorable. The results of this study indicate that these alloys have prospective properties to be applied as degradable biomaterials.

Coke and coal as reductants in manganese ore smelting: An experiment

Abstract The effect of coke and bituminous coal on the reduction of medium-grade manganese ore in ferromanganese production was investigated. Charges of 30 kg medium grade manganese ore, 12 kg limestone and varied amounts of coke and coal were smelted in a Submerged Electric Arc Furnace (SAF) at temperatures of 1300°C to 1500°C. The composition of the ferromanganese and the slag were determined by X-Ray Fluorescence. It was found that using coke as a single reductant resulted in a 96% yield of ferromanganese which was higher than by using coal either as a single reductant or in a mixture of coal and coke. It was also found that using coke as a single reductant resulted in the lowest specific energy consumption. Using coal as reductant produced ferromanganese containing high sulfur and phosphorus.