chromite sand separation plant by sogemi | foundry-planet.com - b2b portal

chromite sand separation plant by sogemi | foundry-planet.com - b2b portal

The chromite sand use has been increased in the steel foundries in last two decades. The chromite is used as facing sand due to its high conductivity of heat that avoids the sintering of the sand in contact with the molten metal and so permit to reach a good surface of the castings.Starting from a mixture in granular size of silica sand and chromite sand, Sogemi plant is able to separate completely the chromite sand from the silica sand.

After these different steps, by means of two pneumatic conveyors , the silica sand and the Chromite sand are transported in the required storages.Sogemi plant can provide a Chromite sand purity up to 99 %.

Sogemi has realized its first Chromite separation plant in 1994, in one steel foundry Cividale s.p.a that works with alpha-set process, phenolic-alcaline process.In this foundry Sogemi has combined its Chromite separation plant with its thermal reclamation plant: by means of this combined system the chromite separated sand is thermally reclaimed and re-used and utilized at 100% in the process without adding new chromite sand.In our experience hence there two ways to utilize the Chromite separation plant (depending on the type of castings production and chemical binder):

After this first plant, with a capacity of 6 t/h, Sogemi has installed many others Chromite separation plants in Europe, Russia and Brazil as well, in different foundries with different chemical process, like polyurethane, alkaline, sodium silicate etc and with different capacity starting from 6 t/h up to 20 t/h. The last plant in 2013 has been installed in Brazil , in Jundiai SanPaolo Area , in Wier Minerals do Brazil foundry .

foundry chromite sand | sicheng - chromite sand

foundry chromite sand | sicheng - chromite sand

Foundry chromite sand properties enable the material to be used in high duty grey iron and steel foundries as core and mould making sand. Its high thermal conductivity gives it good chilling properties, low thermal expansion gives rise to good dimensional stability. Its basicity being close to neutral allows the use of a wide range of resin bonding systems and inorganic binders, it has a high refractoriness and a broad sieve distribution.

Cr2O3 min. 46.0 % / SiO2 max. 1.0 % / CaO max. 0.3 % excellent sizing (with low fines and no dust) excellent pH values (close to neutral) low acid demand values high refractoriness thermal conductivity

chromite uses | sicheng - chromite sand

chromite uses | sicheng - chromite sand

Foundry chromite sandis a natural process products of chromite through the broken screen classification, chrome ore, its main chemical composition of cr2o3, this kind of sand heated volume stability, high thermal conductivity, when in contact information with the molten metal, not only has good resistance to basic slag, not with ferric oxide and other chemical reactions, and itself has the characteristics of the solid phase sintering, can be a very good prevent the infiltration of molten metal, avoid to touch sand defects, suitable for all kinds of stainless steel, alloy steel and carbon steel gradually shape the original sand core and coating.

1. With excellent chilling characteristics, this characteristic does not reduce the thermal cracking, but can affect the temperature gradient, promote directional solidification without the use of cold iron.

chromite - sciencedirect

chromite - sciencedirect

Chromium (Cr) is a versatile element used in numerous applications in the metallurgical, chemical, foundry sand, and refractory industries. Chromite (FeCr2O4) is the only commercially recoverable source of Cr. South Africa holds approximately three-quarters of the world's viable chromite reserves. Kazakhstan, India, Russia, Turkey, Finland, and Iran follow this country. According to data from the International Chromium Development Association, global chromite use was 29.4metric tons in total (each unit equals 1000kg) in 2014, used 96% in metallurgical, 2% in chemical, 2% in foundry sand, and 0.2% in refractory industries. Because of the industry processes in these sectors, large quantities of Cr are discharged as liquid, solid, and gaseous wastes into the environment and can ultimately have significant adverse biological and ecological effects. Residues from mining and chromite processing are often toxic, not only because of the presence of hexavalent Cr (Cr(VI)) but because of the reagents and other waste materials in overburden and wastes. Governments have undertaken to update some Cr regulations, many of which have resulted in stricter standards. Current efforts are being made to reduce waste or eliminate its hazardous components. This chapter provides information regarding chromite resources in the world: specifically in Turkey, the raw materials used in the Cr industry and waste that is generated, toxicity of the waste to humans and plants, and recovery of useful products from the chromite industry, including recovery processes.

the production process of chromite sand | haixu - chromite sand

the production process of chromite sand | haixu - chromite sand

The feed preparation stage involves the introduction of various physical separation equipment including crushers, screens, and grinding mills. The principal function of this stage is size reduction in preparation for the concentration phase.

The concentration phase introduces hydrocyclone technology and spirals to produce the chrome concentrate from which the final product will be derived. The wastewater from this process will report to tailings dams where an additional filtration stage may be employed.

Our RotoMax logwasher is suitable when processing chromite ore with clay contamination. The scrubbing process of the logwasher facilitates the breaking down and effective removal of these clays from your chromite ore, introducing efficiencies to downstream processes.

industrial foundry sands and binders | lkab minerals

industrial foundry sands and binders | lkab minerals

LKAB Minerals supplies a range of both naturally occurringSodium and activated Calcium Bentoniteraw materials from both USA and Greek origins. Our raw materials are sourced from recognised deposits that ensure supplies of the highest levels of quality and consistency. Our foundry grade materials are categorised by the development of excellent physical properties and high levels of thermal stability. Additionally, all of our available Bentonite raw materials can be supplied pre-blended with carefully selected and pre-graded Coal and Lustrous Carbon producing materials in order to meet the needs of individual customer requirements.

Sourced from our mines and processed in our plant, we offer the foundry market afine milled and dried magnetitefor use as a sand additive. Magnetite will prevent surface defect in the casted metals made in foundries. Depending your production process our magnetite might be a competitive product for your currently used magnetite including synthetic magnetite. To provide our customers with the most appropriate product particle size, we offer different magnetite grades for foundry applications. Besides the existing portfolio of magnetite product, we keep developing new grades to provide new opportunities.

Iron Oxidesare used as core sand additives to suppress the incidence of several sand/binder related defects such as nitrogen carbon pick up, finning/veining, pinholing, and orange peel defect in shell moulding sands. Iron Oxide is available in a range of grades and is customised to individual requirements.

MinSandis a synthetic sand produced from Alumina. Because of its almost perfectly spherical particle shape, MinSand is widely used in the foundry industry as a mould and core sand. In core production, binder savings can be achieved when compared to other sands. This is attained without any loss in the cores strength. At the same time, MinSands excellent flowability during the core making process enables intricate cores to be blown achieving a denser more defined finish. Combining that with its high thermal stability, use of a MinSand core ensures excellent internal casting finishes.

Chromite Sandis a naturally occurring mineral consisting primarily of the oxides of chrome and iron. Its properties enable the material to be used in high duty grey iron and steel foundries as a core and mould making sand. Its high thermal conductivity gives it good chilling properties whilst its low thermal expansion gives rise to good dimensional stability. Its basicity being close to neutral allows the use of a wide range of resin bonding systems and inorganic binders.

Olivineis a naturally occurring mineral sourced from Norway. Olivine Sand is suitable for use in alkaline resin bonded systems and produces a clean surface finish, making it suitable for foundry castings, especially for manganese steel and non-ferrous metals casting.

Zirconium silicate or Zirconis a naturally occurring sand. Zircons low thermal expansion rate, its high thermal conductivity and its non-wettability by molten metal make it an ideal mould and chill sand. Zircon Flour is also used in core and mould coatings to improve surface finish.

Chromite Sand is a naturally occurring spinel consisting primarily of the oxides of chrome and iron. It is a by-product of ferro-chrome production and is mainly used in foundry applications and in glass production.

Fine dried Magnetite, produced from natural iron oxide, is used in foundry as a sand additive to prevent surface defects of the casted metal. Another use for our natural mineral is for heat storage or as an iron source for iron catalysts.

chromite sand foundry sand price | sicheng - chromite sand

chromite sand foundry sand price | sicheng - chromite sand

Foundry Chromite sand is a natural process product of chromite through the broken screen classification, chrome ore, its main chemical composition of cr2o3, this kind of sand heated volume stability, high thermal conductivity, when in contact information with the molten metal, not only has good resistance to basic slag, not with ferric oxide and other chemical reactions, and itself has the characteristics of the solid phase sintering, can be a very good prevent the infiltration of molten metal, avoid to touch sand defects, suitable for all kinds of stainless steel, alloy steel and carbon steel gradually shape the original sand core and coating.

Its properties enable the material to be used in high duty grey iron and steel foundries as core and mould making sand. Its high thermal conductivity gives it good chilling properties, low thermal expansion gives rise to good dimensional stability. Its basicity being close to neutral allows the use of a wide range of resin bonding systems and inorganic binders, it has a high refractoriness and a broad sieve distribution.

south africa foundry chromite sand for foundry industrial manufacturer | sicheng - chromite sand

south africa foundry chromite sand for foundry industrial manufacturer | sicheng - chromite sand

Foundry chromite sandis a natural process products of chromite through the broken screen classification, chrome ore, its main chemical composition of cr2o3, this kind of sand heated volume stability, high thermal conductivity, when in contact information with the molten metal, not only has good resistance to basic slag, not with ferric oxide and other chemical reactions, and itself has the characteristics of the solid phase sintering, can be a very good prevent the infiltration of molten metal, avoid to touch sand defects, suitable for all kinds of stainless steel, alloy steel and carbon steel gradually shape the original sand core and coating.

Its properties enable the material to be used in high duty grey iron and steel foundries as core and mould making sand. Its high thermal conductivity gives it good chilling properties, low thermal expansion gives rise to good dimensional stability. Its basicity being close to neutral allows the use of a wide range of resin bonding systems and inorganic binders, it has a high refractoriness and a broad sieve distribution.

chromite sand - spinel - for the foundry industry | lkab minerals

chromite sand - spinel - for the foundry industry | lkab minerals

Chromite Sand is a naturally occurring spinel consisting primarily of the oxides of chrome and iron. It is a by-product of ferro-chrome production and is mainly used in foundry applications and in glass production.

sand and hardening methods in sand casting process - dongrun casting

sand and hardening methods in sand casting process - dongrun casting

In sand casting, siliceous sand is often used as the foundry sand. Moreover, if the high-temperature performance of siliceous sand can not meet the requirements of use, then these special sands such as zircon sand, chromite sand or corundum sand can be used. The specific function of molding sand binder is to bond loose sand particles into molding sand, so that casting work can be carried out smoothly.

3Heat hardening: when mixing sand, add latent hardener that does not work at room temperature. After the sand mold or core is made, it is heated to allow the latent hardener to function and become an effective hardener.

Poor quality of molding sand will adversely affect the castings obtained by sand casting. For example, it will cause defects such as porosity, sand holes, sticky sand and sand inclusions in the casting. The advantage of chemically hardened sand using resin as a binder is that it is easy to separate the casting and molding sand after pouring, so that the cleaning of the casting can be reduced. At the same time, most of the sand can be recycled.

ZheJiang Dongrun Casting Industry Co,.Ltdwas built in 1995, We have been in the casting industry for more than 25 years. No matter what type of molding you need done, we are the right supplier for your jobs. Unlike other of our competition, we offer four types of castings.

Dongrun Casting have 20000 square meters facility houses and 200 production & test equipment, From quotation and tooling design to casting and finished machining, we can work with you at every stage. We serves wide range of industries-from Fortune 500 corporations to small and midsize OEMs. Our products includes:

the use of chromite sand and pearl sand in the casting process | haixu - chromite sand

the use of chromite sand and pearl sand in the casting process | haixu - chromite sand

Castings are prone to casting defects such as cracks, sticky sand, sand holes, pores and low collapsibility at hot joints and large fillets. The modeling method of mixing sable chromite and pearl sand in a certain ratio and placing them at the hot joints and large round corners of steel castings. Tests have proved that sable chromite and pearl sand can be effectively reduced when mixed in a certain ratio. The sticky sand, sand-packing and crack defects of the steel castings also improve the air permeability and collapsibility of the molding sand, and reduce the cost of castings.

chromite sand casting | haixu - chromite sand

chromite sand casting | haixu - chromite sand

We are chromite sand casting manufacturer, we import chrome ore from south africa ,then crushing and sieving in lianyungang chinaChromite sand casting is a naturally occurring mineral consisting primarily of the oxides of chrome and iron. Its properties enable the material to be used in high duty grey iron and steel foundries as a core and mould making sand. Its high thermal conductivity gives it good chilling properties whilst its low thermal expansion gives rise to good dimensional stability. Its basicity being close to neutral allows the use of a wide range of resin bonding systems and inorganic binders.

Chromite sand casting advantages:Good thermal conductivityGood resistance to thermal shockExcellent resistance to metal penetration or burn-onResists slag attackHigh dimensional stabilityChromite sand physical-chemical index

The chromite sand casting 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 .

chromite separation case study by omega foundry machinery | foundry-planet.com - b2b portal

chromite separation case study by omega foundry machinery | foundry-planet.com - b2b portal

Customer :Noel Village (Integrity Castings)DoncasterUKThe foundry produces castings in over 200 compositions of carbon, alloy & stainless and nickel based alloys. They supply to the petro-chemical, oil & gas industry as well as structural, offshore, tunnelling, mining and steel plant applications.

The AimThe customer had a single rare earth drum magnet that was used to remove as much chromite sand from the reclaimed silica sand as possible (prior to thermal reclamation) and then dispose of. The intention was to invest in new equipment in order to recover as much good quality chromite sand as possible from the moulding sand so that it can be effectively re-used at the mixer.

The Problems FacedChromite sand is para-magnetic, that is it is only slightly magnetic and cannot be effectively removed by standard rare earth magnets without contamination of metal and silica. Even with a series of drum magnet separators, what tends to happen is that there is always a carry-over of silica sand making the quality of the reclaimed chromite poor and only suitable for dumping.The SolutionOmega installed a system that provides up to 99% pure reclaimed chromite sand by using a combination of drum magnet separators and a fluidised density separator.

Principle of OperationFully attrited and cooled sand is held in a "dirty sand silo" and is discharged onto the in-feed electromagnetic feeder for an even & controlled feed over the primary ferrite drum separator. The feeder ensures that the product is thinly spread over the drum to enable maximum effect from the magnet.

The ferrite magnet removes all of the metallic particles from the sand, including chromite gangue, which is rejected allowing the remaining sand mix to then pass to a second electromagnetic feeder (Chromite sand & silica sand blend). The second electromagnetic feeder provides feed to a high intensity magnet which attracts the para-magnetic chromite, fused silica/chromite.

The reject from the rare earth magnet is mainly silica sand, discharging to a surge hopper & pneumatic conveyor which is then transported back to the moulding shop as mechanically reclaimed sand to the silica sand storage hopper for re-use.

Both magnetic drums have an adjustable gate within the casings allowing the sand streams to be finely tuned, the metallics from sand on the ferrite magnet and the chromite from silica on the high intensity magnet. The magnetic quadrant can also be adjusted in respect to its position, for maximum recovery.

The chromite product containing chromite, fused silica/chromite passes to the fluidised density separator. This material is automatically discharged onto a third electromagnetic feeder, in order to ensure the product remains evenly spread. Discharge via a chute is onto the fluidised separator.

Fluidised air is supplied from a high pressure side channel blower, which keeps the volume precise. Air is also filtered prior to fluidisation to prevent the membrane from blocking. The Chromite sand particles being heavier are not lifted by the fluidising air and are driven forwards by the vibratory line of action of the motors. The reject particles being lighter are lifted off the membrane by the fluidising air this prevents the particles being driven forward by the vibratory line of action of the motors onto the membrane. As the deck is inclined the lighter sand will flow backwards over the weir. The line of action and angle of the fluidised separator are adjustable to enable a precise split to occur. As material AFS and sieve analysis can be similar, there will be a small percentage carryover, but not excessive to cause re-use issues. The fluidised separator has three product streams. The first is a waste stream of fused silica and any other waste that has managed to pass over the magnets. The second stream is reclaimed chromite sand. The third stream is any agglomerates that have inclined with the chromite and are rejected as the chromite product passes through an integral mesh panel bonded within the body of the separator. This Chromite product can then be collected in big bags for re-use or collected in a surge hopper and conveyed pneumatically to chromite sand storage.

The plant is controlled from a main control panel with PLC and HMI, fully interlocked and with level probes at appropriate points for level and system control. The plant is designed to be fully automatic and self-supervising with no running adjustments or regulation necessary once commissioned by one of our engineers.

ConclusionAs can be seen from the above XRF results, the seperated chromite sand contains less than 0.5% silica contamination and therefore is perfect for re-use at the mixer. As a general side effect from the casting process, the chromite sand tends to see most of the heat from the molten metal and so is also naturally thermally reclaimed.

The customer now blends the reclaimed chromite with new chromite at a ratio of 50/50 and uses on the pattern face as chill sand as well as in the cores. Chromite dumping has been virtually eliminated and new chromite purchasing has been drastically reduced as well.

chrome sand applications | african pegmatite

chrome sand applications | african pegmatite

These properties allow for the application of chrome sand in heavy duty grey iron and steel foundries as a core and mold making sand, amongst many other applications. Alongside high thermal conductivity, chrome sand has low thermal expansion(1). The following are the uses of foundry chrome sand:

The name green sand is perhaps misleading. It is rather a mixture of which chrome sand is a chief component. Other components include silica sand, zircon sand, olivine, staurolite, graphite, bentonite (clay), water, inert sludge and anthracite. Choosing the type of sand is highly dependent on the temperature at which the metal is poured.

Green sand casting is a simple, scalable and resilient method for the casting of metals. The outcome of the casted product is dependent upon many factors, including the grind size of the sand, the addition of cereal biners, and wetting (see later). Escape of silica is a known issue if silica sands are used, when hot steel is poured into the mould. A higher temperature tolerance across the breadth of the green sand mould may alleviate this - strongly refractory materials such as chrome sand may help.

This is a mixture of raw materials used in the nozzle of a ladle in continuous casting of steel often containing chrome sand. The process of continuous casting involves forwarding the steel ladle from tapping to teaming until a semi-finished product is formed. If the slide gate system (which controls egress from the ladle) doesnt open freely, the process might be delayed and a premature hardening of the moment metal may occur. The slide gate system is responsible for obstructing the flow of molten steel from the teeming ladle to the turn dish.

A granular, refractory material known as filler sand prevents contact between the molten steel and slide gate system, with chrome sand being the most widely used material. Good filler sand must have properties including refractoriness, uniform particle-size distribution, consistent particle-packing density, low thermal expansion, flowability and the ability to form a sintered crust having the appropriate thickness when brought in direct contact with the molten metal.

The refractoriness and the surface melting temperature must tally for ideal filler sand; creating a sintered surface, albeit not one with a large thickness level. A significant amount of pressure is needed to break through a thicker sintered surface which causes a reduction in free opening.

Conversely, rapid sintering of the surface of filler sand limits the permeation of liquid steel into the inner aspect of the nozzle. In 2012, Farshidfar and Kakroudi published a study regarding the use of the foundry chrome sands in the continuous casting process. They concluded that a suitable particle size distribution has a positive influence on flowability and permeability of filler sands. Suitable particle size and distribution are easily attainable with chrome sand.

Chrome sand is used in the production of magnesite chrome refractory bricks which usually contains over 33% of chromium (iii) oxide. Magnesite chrome bricks have specific properties that make them suitable for a variety of applications. Features of these refractory bricks include high refractoriness, high-temperature strength of about 1700 C, strong basic slag erosion resistance, excellent thermal shock resistance, and a certain resistance to acid slag. The applications of magnesite chrome bricks include:

Chrome sand is also used in chrome conundrum refractory brick. This refractory brick has the same properties as that manufactured using magnesite chrome. The applications of chrome conundrum brick include:

Foundry chrome molds the external shape of castings, as well as the internal void spaces. In normal circumstances, sand grains do not stick to each other. As such, binders are added to cause sand grains to adhere to each other. The bonding of sand particles allows a shape to take form when molten metal is poured into a casting mold and cooled off.

A different form of sand with specific physical and chemical features is used in molding certain castings. For instance, a high thermal conductivity which characterizes foundry chrome sands is required for automotive castings including engine blocks and camshafts.

A high thermal conductivity ensures that the castings cool off rapidly; thus, reducing the molten metals potential to penetrate the molds surface. A low thermal expansion which is a crucial feature of foundry chrome sand allows for increased dimensional stability. Additionally, resin bonding systems and inorganic binders are used alongside chrome sand due to its basicity being closer to neutral.

Because of its higher cost relative to other refractory materials, chrome sand is only used in those applications which produce the highest quality alloys, or in the manufacture of reactor cores. Chromite is not easily wetted, meaning a better surface finish is ensured. Unlike silica, chrome sand is basic in nature(2). For castings where a high level of chemical abrasion is likely, such as the production of high manganese Hadfield steel, chrome sand is preferred over silica sand owing to the formers superior chemical resistance at high temperatures.

Unlike conventional sand moulds, chromite moulds can be hard to recover and reuse should there be moderate-to-high amounts of silica present. This is due to a greater likelihood of the chrome becoming contaminated by the silica, and thus its refractoriness is reduced(3). Chrome sand refractories are typically used as a facing sand in silica moulds(4).

Green sand - and other types of - molds, on the small scale, have been produced via 3D printing methods(5) with high degrees of precision and success. Lower quality chromite - such as that reclaimed from other industrial processes - does not have the same levels of thermomechanical robustness as freshly mined and milled chrome sand. It is likely that sintering will occur during the casting process if low quality chrome sand is used, thereby producing an inferior final product(6).

Usually, porcelain tiles are produced with different colors and pigmentations. Colors for fast-fired porcelain tiles are derived from black (Fe1Cr)2O3 pigment which is expensive and synthetic. However, chrome sand offers a cheaper option for pigmenting porcelain tiles and do not allow for the alteration of the microstructure and mechanical properties of the tiles when introduced.

Extracted chromium from chrome sand is used in the production of stainless steel constituting about 18% of the alloy. Hardening of stainless steel is due to the presence of chromium. Furthermore, chromium ensures that this alloy is resistant to corrosive forces at high temperature.

A tundish is an open container with certain holes in to allow molten metal to pass at a predefined rate. Such tundishes need to be lined with an insulatory refractory material so no solidification of metal occurs. Magnesia chrome is a popular choice of refractory for tundish linings for the continuous casting of metals. It is composed of magnesia and chrome sand that have been cured into a porous refractory brick, the added chrome sand is responsible for the enhancement of thermal conductivity relative to pure magnesia alone(7).

As a part of magnesia plaster, chrome sand finds further use in the continuous casting space. This plaster, akin to plaster that may be applied to an interior wall in a house, applied as the top layer of refractory (i.e. in constant contact with molten metal). This layered approach to refractories is highly effective and prolongs the life of the system. The plaster is also used to join refractory bricks. Traditional plaster is mostly porous magnesia, but this has a tendency to be destroyed by the presence of calcium oxide or silica from the slag at high heat. Large amounts of magnesia are replaced with chrome sand in modern plaster mixes. The presence of chromite modulates the basicity gap and prevents penetration of the refractory plaster by the slag(8).

Nichrome is made of about 80% nickel and 20% of chromium. Chromium is the primary reason behind the resistance of this alloy to high temperatures reaching a value of 1250oC. Nichrome alloys are often employed in constructing heating units. Additionally, the ability of nichrome alloys to withstand corrosion and oxidative factors owes a lot to the presence of chromium.

Chrome sand based refractories have a burgeoning important use in the lining of gasifiers. In gasifiers, carbonaceous materials (such as coal, coke and biomass) are converted to synthesis gas. Synthesis gas is used as the primary feedstock for the Fischer-Tropsch process for the synthesis of hydrocarbons. The most common gasifier type is the entrained flow type gasifier.

The major side product from gasification processes is the production of ash. This collects on the reactor walls as slag, which then flows down the wall of the refractory and in some cases can penetrate the porous structure of the refractory, at which unwelcome reactions can occur.

Chrome-alumina is the leading choice for refractory materials for gasifiers(9), with laboratory testing suggesting that chrome sand in large particle size that is densely packed performs the best across a range of gasification scenarios(10). Layered or sectional type arrangements of varying chrome percentage refractories may be used through the gasification equipment, tailored to the localised temperature, minimising the amount of high cost chrome that needs to be used. Alumina-chrome refractories are preferred to alumina and magnesia-chrome refractories in the presence of acidic slag due to their better overall performance(11).

As part of the widest catalogue of high quality refractory materials for the broadest range of applications, chrome sand is available from African Pegmatite; milled, processed and packaged to the precise specifications of any customer.

resins and foundry sands aveks

resins and foundry sands aveks

NO BAKE PROCESS Alp Haset Resins (Phenolic Ester Cured System) Furan and Phenolic Resins (Acid Cured System) GAS CURED PROCESS Sigmacure Cold Box Resins (Amine Cured System) Betaset Cold Box Resins (MF Cured System) Alkafen Resins (CO2 Cured System) HOT BOX RESINS THERMOSHOCK RESINS EXOTHERMIC MATERIALS Insulating Sleeves Exothermic Sleeves Highly Exothermic Sleeves Highly Exothermic Mini Sleeves Feeding Compounds Mouldable Exothermic Compounds MOULD AND CORE COATINGS ADHESIVES COATED SANDS INDUSTRIAL RESINS

The high specific gravity and high thermal conductivity of chromite provide a pronounced chilling effect. Chromite sand has a glossy blackappearance. Chromite is generally used for steel casting to provide chilling. t is difficult to reclaim chromite sand since, if it becomescontaminated with silica, its refractoriness is seriously reduced.

green sand: an introduction to its use in foundries | african pegmatite

green sand: an introduction to its use in foundries | african pegmatite

Green sand is a compound mixture used for casting of metals in foundry applications as a mould. It is green not by colour, but takes the moniker due to the fact that it is not set when the metal is poured into it, rather it is still in the green or uncured state. The name derives from green wood, that is, wood still containing a large quantity of water. Green sand is mostly made up of sand, clay, sludge, anthracite and water. The identity of the sand component is crucial. Green sand casting is a simple, reliable and widely used method of casting metals. Green sand should not be confused with greensand, a type of sandstone with a greenish colour, which is not used in foundry applications.

Green sand is a mixture typically containing a sand (75 to 85% by mass), bentonite or kaolinite clay (5 to 11%, used as a binder), water (2 to 4%), sludge (3 to 5%, acting mostly as filler) and anthracite (<1%, as a carbonaceous additive). The sand itself is one of three main types, depending on the casting material; silica-based, chromite-based or zircon-based. Again, depending on the nature of the casting material, other inorganic compounds may be added(1). As casting deals with high-temperature molten metals/alloys, a high capacity for heat is critical. Green sand is advantageous due to its porous nature, allowing gases produced in the mould to escape.

During the process of casting, the latent heat from the molten metal cures the mould in situ. The molten metal/alloy is poured into the mould directly after it has been compacted into shape. After cooling of the casting, the mould can be removed(2). Spent moulds are typically ground down and re-used, especially if based on one of the more expensive sand types, though it is noteworthy that the US and UK send on average 500kg and 250kg respectively of sand to landfill for every tonne of cast metal(1). Studies have shown that spent foundry sand can be re-used in concrete production(3). Green sand casting is used for a wide variety of casting applications, from small and detailed, to large moulds up to 500 kg in size.

Green sand casting is a simple, scalable and resilient method for the casting of metals. Casting itself is a millenniums-old technique(4). Depending on the choice of sand, the process can be incredibly inexpensive, particularly if silica is the major sand component due to its abundance. Aspects of the casting such as the surface finish of the product can be easily modulated by the grind size of the sand component, which can also be impacted by the addition of cereal binders like dextrin and molasses. Furthermore, the addition of these additives can enhance removability properties. Iron oxide can be added to the green sand in small quantities to prevent metal penetration due to cracking of the mould(5). One notable disadvantage of using silica-type sands as the major green sand component is the potential for the escape of silica particles during the pouring of the metal, which could result in silicosis for foundry workers close by. Green sand moulds, on the small scale, have been produced via 3D printing methods(6) with high degrees of precision and success.

As mentioned, various components of the green sand can be changed, or specific compounds used to deliver a specific outcome, or to provide a green sand that is best suited to a particular metal/alloy, or for better environmental performance in the overall green sand moulding process. Two of the most common changes in green sand moulding are using a chromite-type sand, and by using coal dust (anthracite) in the mix.

Coal dust, or anthracite, is fast becoming a common additive in the green sand moulding process. It is a carbonaceous additive that under foundry conditions combusts and oxidises. Historically, the leading additive in green sand casting, as a carbonaceous material, was highly volatile bituminous coal, often referred to as sea coal. Bituminous coal combusts in the mould upon heating and releases hazardous pollutants such as benzene, xylene and toluene. It is imperative that bituminous coal is replaced with an equally well performing carbonaceous material, but with a less environmentally damaging profile. An experimental study showed that under laboratory conditions, anthracite and lower-grade lignite-type coals(7) emitted significantly less hazardous pollutants than did bituminous coal(8), therefore it can be stated that the incorporation of coal dust into a green sand mould is advantageous from an environmental perspective. It is noted that the casting industry wishes to move away from bituminous coal because of its poor environmental performance (9) and fewer hazardous pollutants mean fewer resources need to be dedicated to scrubbing of the foundrys exhaust overall.

The use of ground anthracite decreases burned-on defects, improves the finish on the surface of the product, and decreases metal penetration. Perhaps its major use, however, is to prevent wetting. Wetting is the process by which the liquid metal/alloy sticks to the sand particles in the green sand mould, leaving them present on the surface of the casted product. Whilst in many cases, mechanical polishing or further machining of the casted product can be performed to remove errant sands, prevention is better than cure. Coal dust provides an effective and inexpensive method of achieving this.

When the mould is heated by the presence of the melted metal/alloy, the coal present decomposes (burns) and gives off carbon dioxide and a variety of volatile organic compounds. The production of such reducing gases inhibits the production of iron oxide (in iron and steel casting applications) which have been hypothesised as an intermediate in the production of burn on - impurity deposits on the surface of the casting(10). In addition, due to the reducing environment, a layer of highly lustrous carbon is deposited on the mould surface, affording a refractory barrier between molten metal and sand, thus improving the surface finish(11) and making the casting easier to remove from the mould.

Chromite (FeCr2O4, iron chromium oxide) is an inorganic material most commonly used as an ore in the production of stainless steel; it is the only ore of chromium. As a refractory material in powdered/granulated form, it is particularly attractive due to its stability at high heat, boasting a melting point of 2150 C. Due to its relatively low abundance (relative to silica), it is a higher-priced sand. As such, chromite is only used in applications requiring the highest quality alloy steels, or for the manufacture of cores. Chromite has low thermal expansion and high thermal conductivity (12).

Valued for its use as a green sand for the production of heavy, sectioned, ferrous-type castings, chromite is not easily wetted and, unlike silica, is basic in nature (13). It is particularly useful in the production of high-manganese content steel (Hadfield steel), as silica does not offer the same levels of chemical resistance(14). It is also commonly used as a mould for aluminium casting.

Chromite moulds can be hard to recover and reuse should there be moderate-to-high amounts of silica present, as this reduces its refractoriness should the chromite become contaminated (15). Despite having more advantageous properties compared to silica, chromite is typically used as a facing sand for silica moulds. That is, where silica sand is used for the bulk of the mould and chromite is used at the interface of green sand and the molten metal (16).

High purity chromite occurs naturally in South Africa (17). It is noted that lower quality chromite - such as that reclaimed from other industrial processes - does not have the same levels of thermomechanical robustness and hence sintering during the casting process can be observed (18).

1 S. Dalquist and T. Gutowski, Life cycle analysis of conventional manufacturing techniques: Sand casting in 2004 ASME International Mechanical Engineering Congress and Exposition, 2004, Anaheim, United States

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