moulds in ladle sand

What is Ladle Sand and How Does it Work?

Ladle sand is a vital component in the industrial production of a wealth of metals. Chrome flour and chrome sand, as refractories, are a crucial part of ladle sand - and is available in high purity for this application and many others from African Pegmatite.

 

A notable increase in the demand for cleaner and better steels along with an increase in the productivity of foundries has dramatically changed the way in which metal and steel are being made via the widespread use of continuous casting.

Continuous casting relies upon ladles to move molten metal from furnace to where they are to be casted, such ladles (often referred to as pots) are large pieces of equipment that are lined with refractory materials so as to avoid solidification of the metal. A key feature of the ladle is the slide gate, which allows the molten metal to be released from the ladle into its next process.

The slide gate can become blocked by solidified metal, which causes a backing up of production and a potential explosion once the gate/tap is freed and opened again. To prevent this, filler sand (also commonly referred to as ladle sand) is used to keep the molten metal away from the slide gate, thereby preventing blockages. The slide gate leads to the nozzle, through which the molten metal leaves.

The use of filler sand has brought some impressive results such as longer holding times and higher steel operating temperatures, providing greater flexibility in the foundry. Naturally, the advent of continuous casting using ladles is reducing the numbers of traditional ladle free plants. With the filler sand contributing towards smooth and highly effective operations, the value and contents of the filler sand itself cannot be underestimated.

foundry-chrome sand

What is Ladle Sand?

Ladle sand (filler sand) is a type of compound sand used by foundrymen to protect the tap/slide gate at the egress point of the ladle, and also at other points throughout the pot. As a refractory material, often containing quartz and other high performing refractories such as chrome sand, filler sand has an excellent tolerance for temperature and a low reactivity with the molten metal.

In addition to high tolerance of heat, ideal filler sand will have low flowability, a narrow and constant particle size distribution, consistent density and low thermal expansion characteristics. When in contact with the molten metal, high quality ladle sand is prized for its ability to rapidly form a sintered layer at the interface, providing a fast and effective protective barrier preventing the molten metal from reaching (and thus blocking) the slide gate and/or tap.

In its primary function, ladle nozzle sand is an effective and optimal material that is used to fill in the gaps and ways out of the ladle in the most effective way. Foundry filler sand is used to fill ladle nozzles prior to tapping molten steel into the ladle.  When the nozzle is opened from the outside, the sand will flow out, the sintered layer will be broken, then it will be followed by the molten metal.

Maximum packing of the sand is important to achieve as this provides the best defence against molten metal permeation into the sand.

What is it made from?

Ladle sands are normally developed to meet the requirements of the steel making facilities all around the world, for general applications, with bespoke blends produced for specialist or high complexity steels. Normally higher quality refined quartz sand, itself a high refractoriness material, with high quality chrome sand and chrome flour are used in the production of sand products.

The custom blending of these elements assists in achieving the perfect standard of foundry filler sand which helps customers purchase products according to their specifications, for the streamlined operation of their foundries, reducing workloads for foundrymen. The blending process is also capable of producing sand products that will be optimised for an increased performance level in the more productive way.

How is it made?

Ladle sand is typically composed of high quality quartz sands with some kind of refractory material included, such as chrome flour or chrome sand. The addition of chrome refractories enhances the performance of the overall sand, much like it does in similar applications such as greensand casting. Ladle sand will be made up in a mixing device and applied to the ladle well in advance of it being filled with molten metal. In the production of filler sand, the infiltration as well as erosion of molten steel should be considered. The fast flow of molten steel is another issue to be addressed - a poorly packed and low density sand may not be best suited to these purposes.

Produced goods from moulds

Early ladle filler sand

The steel ladle refractories are some of the most important and highest consumption areas for refractory in the industry of steel making, having been used in the industry for many years in the continuous casting process. In 1984, at Armco, a refractory research group started to develop and investigate whether the foundry filler sand was effective at making the production process more efficient, before trying it in the field. Many iterations of sand and refractory were probed over time to improve the sand. Research also sought to develop the system to produce for a longer period of time, by improving refractory technology to support the production of stable yet high-quality steel albeit at a lower cost.

What is the purpose of it?

The world is demanding a higher quality of metals and especially steel, which requires extended treatment in the steel ladle and this has made a remarkable impact on the technology in the development of refractories to be used in the ladle. Operational changes including an increase in tapping temperature and holding for longer periods of time, both of which require a more robust refractory such as one that is chrome based. Ladle lining has also represented a vital cost factor in this industry, with steel of higher purity grades has also increased the need for these higher performing ladles and their associated sands. To remedy a blocked nozzle or build up behind a previously stuck slide gate, an oxygen lance must be used. This is a slow and laborious process which can cause damage to the refractory materials lining the pot. Overall, it can be said that the purpose of ladle filler sand is to make the global continuous casting more efficient, by preventing blockages and build ups.

Metal pouring out of crucible into moulds
joints cast from ladle sand moulds

What is the Purpose of it?

The world is demanding a higher quality of steel which requires extended treatment in the steel ladle which has made a remarkable impact on the technology in the refractories of the ladle, for example, to fulfill the needs of highly functional refractories. Operational changes including an increase in tapping temperature, and holding for longer periods of time. Based on these facts, ladle lining has also represented a vital cost factor in this industry not only the refractory cost but majorly for various operational costs too. On the other hand, steel with higher purity grades also increased the need for these.

How is filler sand used in foundries for pouring metal?

A ladle is used in the foundries to receive molten metal or steel and to move it between furnace and where it is to be casted into a mould. The metal is at extremely high temperatures and is liquid. At the opening of the slide gate, the majority of the casting ladle sand will flow out from both the nozzle and the area around the gate, while the ferrostatic pressure in the ladle which is being exerted by the steel will cause the sintered layer to break, thereby releasing the molten metal.

moulds made of green sand
metal products made using coal dust

The Benefits Of Ladle Filler Sand

  1. In the processes of secondary steel refining, this sand filler is being used as a thermal insulating barrier that has the ability to separate the liquid metal and will keep it from creating any direct contact with the system of slide gate of the steel ladle
  2. Casting ladle sand can be used in the filler nozzle, preventing any risk of molten metal build up there
  3. Filler sand can also be used for tapping the holes
  4. Ladle sand can also be used outside the furnace, in the furnace lining outside the furnace in the furnace refining lining, lining parts of ladle slag
  5. Its refractory castable comes with good mechanical behavior and high refractoriness even under high temperature which has the ability to ensure more efficiency
  6. Ladle filler sand containing refractories can be used in a wide range of ladles, able to operate at the highest temperatures in the modern foundry
moulds that use anthracite
coal dust used in the moulding process

How is Chrome Flour and Chrome Sand an Ingredient in Ladle Sand?

Chrome sand and chrome flour is a spinel that occurs naturally and consists of the oxides of iron but primarily chromite. Ladle nozzle sand needs to be made of high-quality materials. Chromate has a high melting point and high thermal conductivity which gives it the ability to better distribute temperature through the sand. It is known for its high refractoriness and broad tolerance to thermal and mechanical shock, in addition to a resistance to chemical attack.

As a premium refractory, chrome sand and chrome flour are known for their ability to withstand high temperatures for lengthy periods of time. Filler sands containing chrome type refractories are known for their appropriate fluidity, high density and a resistance to over sintering. Over sintering may be associated with difficulties in releasing the sand or the molten metal when it is time for casting. Elevated iron oxide levels are to be avoided, as at high temperatures this can form a secondary spinel which has the potential to change the volume of the sintered layer, which can lead to cracking. Cracking itself can lead to the permeation of molten metal into the sand - again making release of the sand and molten metal more difficult.

Casting ladle sand is also used as an effective filler in the ladle wall, protecting the ladle’s outer skin from molten metal, fills the gaps between larger refractory panels and provides more benefits in the steelmaking industries. Chrome flour and chrome sand are often regarded as some of the best refractories for ladle sand owing to their wide ranging performance.

African Pegmatite supplies chrome flour and sand in the following specifications for ladle sand functions, suitable for a variety of filler sand formulations.

SpecificationAFS 45 - 55AFS 60 - 80
Cr2O3 content (%)46 - 46.545 - 47
Cr/Fe ratio1:1.581:1.75
Iron oxide content (%)2525 - 27
Other significant materials present (%)Alumina 15.2, silica 0.5 - 0.8Alumina 14.75, silica 1 - 3
Moisture (%)< 0.2< 0.2

When working with chromium compounds at elevated temperatures, foundrymen will be aware of the risks associated with hexavalent chromium (chromium(vi)), which is highly toxic. The chromium in refractory chrome materials supplied by African Pegmatite contains chromium only in its +3 oxidation state - meaning it is safe to use without any extra safety precautions or mitigation equipment.

Summary

  • Ladle filler sand is a vital component in the large scale production of metals
  • Owing to the high temperatures, ladle sand contains refractory materials, oftentimes including chrome sand and chrome flour
  • Benefits of using chrome flour/chrome sand in ladle sand include the prevention of solidified metal at the slide gate and a lack of build up in the nozzle
  • Without ladle sand, the continuous casting process would not be as efficient
  • Prevention of build up or solidification processes in the ladle by using a suitable filler sand that contains a refractory such as chrome flour will lead to greater cost and labour savings over time

 

African Pegmatite is a leading miner, miller and supplier of the broadest array of refractory materials including high quality chrome flour and chrome sand for the production of vital ladle sand for metals production. Providing years of experience and the most knowledgeable team, African Pegmatite is the go-to partner for any refractory requirement.

chrome_sand
Chromite Flour in a pot