Effect of Plate Thickness and Casting Position on Skin Effect Formation in Thin Wall Ductile Iron Plate

Abstract

In producing Thin Wall Ductile Iron (TWDI) plate, special notice should be taken on the skin effect formation. Skin effect is a rim of flake interdendritic graphite formed in the surface. In a normal ductile iron casting, skin effect can be removed with machining process. Unfortunately this procedure cannot be applied in TWDI due to the thickness. This paper discusses the effect of casting design to the skin effect formation. Vertical casting design is used in this work. Variations are made in the thicknesses of the plate. The T1 model is equipped with 5 plates with thicknesses of 1, 2, 3, 4, and 5 millimeters; while the T1-Mod is equipped also with 5 plates, but with the same thickness, which is 1 mm. Skin thicknesses, nodule count, and nodularity are measured by NIS Element software. The result showed that skin effect formation is determined by magnesium content and cooling rate. Skin effect thicknesses are determined by cooling rate and the interaction area of molten metal with the mould. The presence of the skin effect in similar thickness and position of plate improved nodule count. In the same thickness, without the presence of the skin effect, the nodule count tends to increase as the positions of the plates increase. In the design ranging from 1 to 5 mm plate thickness, the highest nodule count is 1284 nodule/mm 2 gained by 1 mm plate thickness in 1st position and the lowest one is 512 nodule/mm 2 gained by 5 mm plate thickness in 5th position. As for the design of all 1 mm thickness where skin effect is not formed the highest nodule count is 1689 nodule/mm 2 gained by 1 mm plate thickness in the 5th position and the lowest is 1113 nodule/mm 2 gained by 1 mm plate thickness in the 1st position (near the in gate). The highest nodule count is 90 and the smallest is 85.

Thin Wall Ductile Iron Castings

“…Aufderheiden [13] found that besides magnesium content, the type of sand also contributed to the formation of skin effect. Sulamet-Ariobimo [38] found that besides magnesium content, cooling rate also influences the formation of skin effect. [19] stated that skin effect tends to disturb the tensile properties.…”

Thin-Wall Ductile Iron Castings

“…Aufderheiden [13] found that besides magnesium content, the type of sand also contributed to the formation of skin effect. Sulamet-Ariobimo [38] found that besides magnesium content, cooling rate also influences the formation of skin effect. Goodrich in Dix [19] stated that skin effect tends to disturb the tensile properties.…”

INVESTIGASI MORFOLOGI TWDI (Thin Wall Ductile Iron)AKIBAT PROSES MULTI STAGE SPHEROIDISING

“…Nama lapisan tersebut flake graphite rim anomaly [19] skin effect. Ketebalan lapisan maksimum yang pernah dicapai 20/0,2 mm [20]. Lapisan ini sangat mengganggu sifat tarik, menurunkan kekuatan & keuletan karena grafit serpih berperan sebagai konsentrasi tegangan & menjadi lokasi permulaan retak, lapisan kulit dihilangkan dengan proses permesinan.…”

“…Kombinasi jenis inokulan dengan urutan inokulasi dipilih mendasarkan pada pengalaman pengecoran [16]. Meskipun pasir halus & cetakan dilapisi menyebabkan jarak lebih jauh logam cair, kekerasan & kekuatan sampel menurun [20] [26].…”

“…Sulamet [20] memproduksi TWDI, perhatian khusus harus diambil pada pembentukan efek kulit. efek kulit tepi serpihan grafit inter dendritik terbentuk di permukaan.…”