Difference of foundry chromite sand and olivine sand
Both natural chrome ore sand and olivine sand can be used in the foundry field, but there are great differences between the two. There are several differences between foundry chromite sand and olivine sand.
1. Composition
– Foundry chromite sand: also known as foundry chromium sand, the main component is chromite, its chemical formula is usually expressed as (Fe,Mg)Cr₂O₄, containing chromium trioxide (Cr₂O₃) and other components. Natural chromium ore generally has a Cr₂O₃ content of about 30% – 55%, and only Cr₂O₃ content of more than 46% can be called foundry-grade chromium ore.
– Foundry olivine sand: mainly composed of olivine minerals, the chemical formula is (Mg,Fe)₂[SiO₄], the main components are magnesium oxide (MgO), silicon dioxide (SiO₂) and a small amount of iron oxide (FeO), etc.
2. Physical properties
– Color: Chromite sand is generally black; olivine sand is usually green to yellow-green.
– Density: Foundry grade Chromite sand has a relatively high density, generally 4.0 – 4.8g/cm³; olivine sand has a relatively low density, about 3.2 – 3.6g/cm³.
– Hardness: Chrome ore sand has a relatively high hardness, with a Mohs hardness of about 5.5 – 6.5; olivine sand has a Mohs hardness of between 6.5 – 7.0.
3 Chemical properties
– Refractoriness: Chromite sand has a high refractoriness, which can reach above 1800℃; olivine sand generally has a refractoriness of 1690 – 1710℃.
– Chemical stability: Chromite sand has good chemical stability and does not react chemically with metal oxides; olivine sand is also chemically stable, but may react with certain metal oxides at high temperatures.
4. Thermal conductivity
– Foundry chromite sand has high thermal conductivity, which can make the casting cool quickly during the casting process, which is conducive to grain refinement and improve the mechanical properties of the casting. It is especially suitable for casting processes with high requirements for cooling speed.
– Olivine sand has relatively low thermal conductivity, and the cooling speed of the casting is slow. It has certain advantages for some alloy castings that are not suitable for rapid cooling, and can reduce the thermal stress and crack tendency of the casting.
5. Anti-sand sticking performance
– Chromite sand has good anti-sand sticking performance, which can effectively prevent metal liquid penetration and sand sticking. It is especially suitable for castings such as carbon steel and alloy steel that are prone to sand sticking.
– Olivine sand also has good anti-sand sticking ability, which can play a certain anti-sand sticking effect on a variety of alloy castings, but in some occasions with extremely high requirements for anti-sand sticking, the effect may not be as good as chromium ore sand.
6. Collapsibility
– The collapsibility of chromite sand for foundry is general, and it is relatively difficult to clean the sand core after casting, and some special cleaning processes may be required.
– Olivine sand has good disintegration, and the sand core is easy to clean after casting, which can reduce the cleaning cost and labor intensity.
7. Application
Applicable alloy types
– Chromite sand is mainly used for casting ferrous metals such as carbon steel, alloy steel, stainless steel, etc., and is widely used in the production of large steel castings and thick-walled castings.
– Olivine sand is suitable for casting a variety of alloys, including ferrous metals and non-ferrous metals, such as cast iron, cast steel, aluminum alloy, copper alloy, etc., especially in the production of small and medium-sized castings with high requirements for the surface quality and internal quality of castings.
8. Casting process
– Chromium ore sand is often used in processes such as investment casting and sand casting, especially in key parts that require rapid cooling and prevent sand sticking, such as hot joints of steel castings.
– Olivine sand is used in processes such as investment casting, sand casting, and lost foam casting. Due to its good comprehensive performance, it is suitable for the production of castings with various complex shapes and precision requirements.
9. Cost
– The price of chromite sand is relatively high, mainly because its resources are relatively scarce. The chromium ore sand on the market is mainly imported from South Africa and other countries, and the cost is relatively high.
– Olivine sand is abundant in resources and relatively cheap, which can reduce the casting production cost.
