Greenmoulding sand

expertiseBurnt-on sand

Penetration

Explosion Penetration

Sand Inclusions

Micro-cavities

Swelling

Broken Mould

Pinholes

Lustrous Carbon Inclusions

Slag Inclusions

Scarred Surface

Metal Penetration

Erosion

Surface Roughness

Fissure Defects

Scabbing

Surface Blowholes

Blowholes at Angles

Nature of DefectThin sand crusts firmly adhering to the casting. Defect occurs more frequently with thickwalled castings at high casting temperature.

RemediesIncrease amount of lustrous carbon producers and coke producers in the moulding sand. Increase amount of new sand if sintering point of the sand is low and oolitization is high.

Nature of DefectRoughness caused by the moltenmetal penetrating the immediate sand grains of the mould surface, particularly in softly rammed areas.

RemediesUse finer sand. Improve rammingof the moulds. Reduce compactabil-ity of the moulding sand. Increase amount of carbonaceous additive. Increase amount of coke in the moulding sand.

Nature of DefectExtensive penetration, when the mould is filled too quickly.

RemediesReduce amount of free water.Increase milling time of the moulding sand. Increase oolitization rate of the moulding sand.

Nature of DefectIrregularly formed sand inclusionsjust underneath the casting surface, associated with products from the metal slag reaction in other areas.

RemediesKeep the moulding sand sufficiently plastic by good sand preparation and sand cooling. Adjust to optimum compactability. Reduce the tendency of the mould to stick to the patternby the use of parting agents.

Nature of DefectPorous structure found in thearea of the casting which is lastto solidify.

RemediesDefect occurs with alloys havinga wide solidification range. Little influencing by the moulding sand. Reduction of organic material and an increase in the moisture level will improve thermal conductivity of themoulding sand.

Nature of DefectIrregular bulges, in most cases widely spread, sometimes with rough sur-face and/or penetration.

RemediesReduce compactability of the mould-ing sand. Ram moulds better and more evenly. Make sand less sensi-tive to over- and underramming by increasing the amount of bentonite.

Nature of DefectFlash-like metal penetration in the mould, sometimes parts of the mould are included in the casting.

RemediesAdd more bentonite to increase green tensile strength. Raise com-pactability of the moulding sand.

Nature of DefectAccumulation of small subsurfacerounded holes. Defects appear after annealing and light machining.

RemediesNormally the defect is of a metallurgi-cal nature. The mould material may have a certain effect. In case of pin holes the moisture, the organic addi-tions and the amount of nitrogen inthe moulding sand should be reduced.

Nature of DefectFormation of surface irregularities, inclusions and laps due to non-wet-ting characteristic of lustrous carbon, often associated with the use of Cold-Box cores.

RemediesUse dried Cold-Box cores. Reduce amount of lustrous carbon producer in the moulding sand. Use carbonaceous additive with a higher coking residue.

Nature of DefectNon-metallic irregular shapedinclusions, when occurring, tendto be on upper casting surfaces.

RemediesThe defects are caused by slag being present with the molten metal in the pouring ladle. If the formation is due to eroded sand, reduce the amount of inert fines and use a more activelustrous carbon producer. Increase milling time of the moulding sand.

Nature of DefectScarred casting surface around hot spots, particularly with SG cast iron.

RemediesReduce amount of impurities present in the sand that are destroying the oxide skin.

Nature of DefectFirmly adhering agglomerates of sand/metal at hot spots and in softly rammed areas.

RemediesReduce compactability of the sand. Improve ramming of the moulds. Increase amount of carbonaceous ad-ditive and coke in the moulding sand.

Nature of DefectThe sand is washed away, mostly near to the sprue, often accompanied by sand inclusions. Bulges arise on the casting near to the gate.

RemediesAvoid drying out of the moulding sand. Increase amount of bentonite in the sand. Increase milling time of the moulding sand. Increase mould com-paction. Use carbonaceous additive with a high lustrous carbon produc-ing ability.

Nature of DefectRough casting surface finish dueto coarse sand.

RemediesUse finer sand. Increase amountof lustrous carbon producing material in the moulding sand. Increase the amount of fines e.g. coke in the sand.

Nature of DefectNarrow, crack-like cavitiesvertical to the surface. Dendriteformation in the cavities.

RemediesThe defect is of a metallurgical nature due to too much nitrogen contained in the iron. Reduce the amount of ni-trogen in the moulding sand. Use low nitrogen containing carbonaceous additive. Reduce addition of carbona-ceous additive in the moulding sand.

Nature of DefectMushroom type defect with sharp edges parallel to the casting surface.

RemediesIncrease bentonite level. Use carbona-ceous additive with a wide softening range. Increase the amount of car-bonaceous additive in the moulding sand. Reduce amount of new sand.

Nature of DefectCavities with smooth walls,singularly or in groups.

RemediesLow casting temperatures areoften the cause. Benefits maybe obtained by increasing mould permeability. Reduce fines or add coarser new sand. Reduce organic additions to the sand.

Nature of DefectSmooth wall cavities at the angles of the casting.

RemediesThe cause is insufficient feeding and rate of solidification. Influencing by moulding sand is possible. Reduce the moisture content and the organic additions of the sand. Improve the venting of the mould.©

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