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The Performance Requirements and Testing Methods of Green Sand

High-quality foundry sand should have different and necessary prosperities for good metal castings. According to casting alloy type, casting size, thickness, pouring temperature, metal hydraulic head, sand compaction methods, gating system shape, position, and vents, as well as dry conditions of sand surface and so on, different performance requirements on green sand are proposed.

Among them, the most important, which directly affect casting quality and wet performance of the molding process are water, permeability, strength, compaction rate, deformation, broken index, mobility, clay content, effective clay content, particle composition, Myanmar compounds, sand temperature, gas evolution, effective coal content, loss on ignition, anti-sand, anti-sticky sand and so on.

This article mainly discusses five performance requirements and testing methods.

1. Water
In order to get the required wet strength and toughness, clay sand must contain the right amount of water, too dry or too wet are not suitable for modeling, and it is difficult to cast qualified castings. Therefore, the wet and dry extent of green sand must be kept in a suitable range.

2. Permeability
Compact sand can let the gas escape and this ability is known as permeability. The level of permeability is mainly affected by the sand size, size distribution, grain shape, clay content, the binder type, its added quantity and the binder distribution in the sand and effects of sand compaction. For single wet sand and facing sand, the permeability should not only have a lower limit, but also strictly define the upper limits.

3. Wet strength
Foundry sand must have certain strength to withstand various external forces. The sand strength is expressed by the stress value of standard sample under destruction of external force. The common units of measurement are MPa or kPa. In wet casting, we often examination the test wet compressive strength and also measure the wet shear strength and wet tensile strength. In the production, we often use surface hardness tester to measure hardness, which reflects the quality of sand compaction and the strength of the mold surface.

4. Mobility
In force or under gravity, sand moves relatively between the appearance and the sand, this ability is known as liquidity. Sand with good mobility can form cavity of even compaction, no local loose, clean cut, smooth surface, which helps prevent mechanical sticky sand and get smooth castings. In addition, it can also reduce labor intensity and improve productivity and facilitate the realization of mechanization of moulding and core-making process.

5. Gas evolution and effective coal dust content
In order to check the iron castings’ ability to resist mechanical sticky sand and calculate the effective coal content of sand, gas evolution test is the common method used in China. Gas-forming property (gas evolution) are mostly used to test the gasification of the sample heated in a closed system or the volume of gas produced, or to measure the gas pressure, or weigh the residue quality to determine gas evolution.

High-quality foundry sand plays an important role in metal casting, so we should choose the good green sand and produce better castings.

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