Chromite sand has been selected and used in foundries as a result of its unique combination of properties. The properties listed below generally result in a better surface finish and reduced likelihood of casting defects. Scroll down to learn more on each property
The Thermal Conductivity of chromite sand is higher than the other commercially available foundry moulding sands. This results in a mild chilling of the surface and a thicker solidified skin. This thicker skin improves the casting surface and reduces the likelihood of casting defects. Generally, foundries use Chromite Sand for one of the following reasons:
Chromite is used as it has the ability to resist metal penetration by molten steel and oxides in the metal. This is mainly due to the chilling ability of chromite to make the oxides less fluid when in contact with the mould
The basic to neutral pH of chromite significantly reduces the likelihood of reaction defects. These are most often seen when the acidic nature of the silica sand moulds react with the basic nature of manganese steel castings.Maintaining a consistent pH is also critical as some modern binder systems cannot cope with a pH that is too high or variable.
Chromite sand formulated in prepared sand mixtures for the core room or in green-sand molding applications will be influenced by the screen distribution. The CastTherm family of chromite sand is a naturally occurring, sub-angular chromite aggregate mined in the heart of the Bushveld Complex in South Africa, in partnership with Rand York Minerals. These next-generation chromite sands have become popular for various alloys because of the available screen distributions and the average grain-fineness number.
The past 10 years of casting production have seen a dramatic increase in demand for intricate designs and shapes, to meet the constantly changing customer requirements. The availability of the multiple screen distribution CastTherm Sands has met this need. Table 1 is a representation of these next-generation chromite sands. (Pictures 1, 2, and 3 show CastTherm manufacturing.)
The CastTherm 45 product is the conventional material used by steel foundries for mold and core production where high thermal conductivity, heat resistance, high dimensional stability and, casting surface finish are critical. In addition to these characteristics of CastTherm sand in steel foundry applications, it is important to understand the behavior that sintering characteristics have on chromite sand.
Silica content as it relates to sintering characteristics is not actually SiO2 but a range of low melting point silicates that occur naturally occur in mineral deposits, including enstatite, anorthite, and phlogopite. With this in mind, the determined levels of aluminum and calcium can help define the various types of lower melting-point silicates. As a result of comprehensive research evaluations, it has been determined that the desired level of SiO2 measured in the chemical analysis of chromite sand is 1.0% maximum.
Molding and coremaking capabilities have improved to meet the demand of the intricate designs and shapes of castings required by casting buyers. In green-sand molding operations, the CastTherm sand will mix effectively with bentonite-based prepared sand. As the demand for various alloys grows, additional green-sand additives will be necessary to develop the desired green-sand mixtures. Since foundries require both green-sand molding operations and core room applications, CastTherm sand has been proven to work with most resin systems now available. The screen distributions of the CastTherm sand influences the percentage of resin and catalyst/co-reactant. (See Table 4 for the physical properties of CastTherm sands.)
Chromite Sand is a special sand with very good properties at high temperatures. Provides a high resistance to penetration of the liquid metal, and compared with other sands produce more rapid cooling of the casting. Thermal expansion is much lower than the silica sand thus reducing the problems resulting from the expansion of the sand. Supplied with a size 46-55 AFA and typical content of their major oxides is Cr2O3: 46 %, FeO : 27 % , Al2O3 : 15 % and MgO : 10%.
The chromite sand is compatible with all chemical processes of agglomeration of moulds and cores. Currently used large amounts of chromite sand in the foundry industry for the manufacture of moulds and cores. Chromite Sand is applicable to all types of steels and very appropriate for chrome steel, chrome-nickel and manganese steel. Has the advantage over silica sand that is less reactive with manganese oxide, reducing the problems of ignition and metal-mould reactions .
Foundry grade chromite sand has several uses.In iron and steel foundries, the ideal casting sand is chromite because of its high melting point, resistance to thermal shock and low thermal expansion properties.Moreover, foundry grade chromite sand works well in ladle filler sands (also called filler sand or sliding gate mix or plugging sand) to prevent the molten steel from contacting the mechanism that controls the sliding gate of the ladle.In addition, chromite sand is used in refractory bricks such as chrome-magnesite and chrome-corundum bricks.
At Plomp Mineral Services, we supply LG6 (lower group chromitites of the Bushveld complex) foundry grade chromite sand, originating from the Dwarsrivier Chrome Mine in South Africa. Our chromite sand is famous for its superior quality and has the following general specification:
We supply our chromite sand in bulk, paper bags and big bags and can deliver by truck, container, rail, barge and ship from our stocks.We will send you our Technical Data Sheet (TDS) and Safety Data Sheet (SDS) on request.Minerals such as chromite are exempt from registration under REACH. The international Harmonized System Code or HS Code of chromite sand is 2610.00, the European GN code is 2610.0000.
Ferrochrome is an important alloy in stainless steel making due to its contribution to high strength and corrosion resistance. In this present study, ferrochrome was derived from Indonesian chromite sand with low-grade Cr/Fe ratio. In order to improve the ratio, beneficiation process such as pre-magnetic separation and reduction process at 1000°C for 60 minutes was required. The process followed by another magnetic separation, thus the Cr/Fe ratio was increased from 0.9 to 1.6. The reduction process used coconut shell charcoal as reductant and limestone as an additive. The beneficiated sand chromite was briquette using bentonite as a binder in 2 wt.% before it was smelted in a submerged electric arc furnace to produce ferrochrome. Basicity was controlled by the addition of limestone and it was varied from 0.4-1.6. Furthermore, the composition of ferrochrome was analyzed by using X-Ray Fluorescence. From this experiment, the result showed that chromium recovery and specific energy was decreased with the increasing of slag basicity.
As legend has it Galileo watched a suspended lamp swing back and forth in the cathedral of Pisa and thus began his study of pendulums. The Sand Pendulum takes this scientific principle (a weight mounted so that it can swing freely under the influence of gravity) to create interesting and unique designs on sand.
Separation of quartz sand and chromite sand into different material groups during used sand reclamation (see Sand regeneration). In comparison with quartz sand, chromite sand has a higher temperature resistance and better thermal conductivity. These attributes make this mold material especially suitable for mold areas with high material accumulation and for materials with high casting temperatures, for example in steelcasting. On the one hand, chromite sand guarantees high quality for certain casting products, on the other hand, this kind of sand increases the cost of molding material, if there is no internal circulation system. Chromite sand is considerably more expensive than quartz sand. The mixture of chromite sand and quartz sand which arises inevitably at the shake-out grid usually leads to problems with the quality of the casting, as well as increased costs, when reused. For this reason, these sand varieties must be separated and put back into the mold material cycle separately. As chromite sand is slightly magnetic, modern systems separate chromite sand from quartz sand in a way that results in very pure materials, so that it can flow back into the mold and core production process as a replacement for new sand. In the system shown in Fig. 1 (GUT GmbH, Freudenberg), the flowable and dust-free sand is separated in four steps using a combined technology of two magnetic stages, a density separation and the corresponding sieving technique. In the first separation step (I) quartz sand is separated from the magnetic particles by a high power magnetic drum. The quartz sand can be reused directly in the sand cycle. The so-called magnetic fraction passes through the next three steps of the plant (II-IV), where the chromite sand is refined. During this process, undesired materials, such as exothermic risers, are largely eliminated from the sand. Chromite sand is sometimes used as facing sand, whereby quartz sand is used as filler sand but also as a mold material for core production. Consequently, in addition to quartz sand and binder residues, the accumulating used sand also contains valuable chromite sand which is to be reclaimed during used sand conditioning. The separation is carried out using a magnetic separator as the chromite sand can be weakly magnetized. Permanently magnetic, high intensity separators are used in combination with cleaning and dust-removal devices. The magnetic separator has two consecutive separation steps. In the first step, magnetic metal parts are removed, while in the second step, the chromite sand is separated from the quartz sand with a stronger magnet. If necessary, a third step with a magnet with an even stronger magnetic field can be included in order to reclaim almost 100 % pure quartz sand. Each magnetic roller has a magnetic disk, whereby the magnetic field strength is adapted to suit the material which is to be separated. The use of permanent magnets requires only a low amount of electricity compared with electromagnets. A vibrating trough allows the sand to flow over the whole width of the first conveyor belt. The conveyor belts are made of thin but highly strong material. When the sand on the belt runs over the magnetic roller, the magnetic components stay stuck to the belt. As the sand does not come into contact with the magnetic roller, it does not experience any wear. A positive air pressure between the conveyor belt and the magnetic rollers prevents dust from getting in. 781b155fdc