Generally, as a thumb rule, between 0.10 kg to 0.24 kg per ton of liquid steel. However, it depends also on the extent of sequence casts and ladle and tundish configurations. General experience from many steel plants show that RHAN consumption is nearly 50% lower than conventional covering compounds like rice husk ash powder.
In contact with liquid steel, RHAN becomes sintered bonded agglomerates of nearly 100% amorphous silica with high porosity within the balls, and significant amount of voids exist in the matrix between the individual balls. Thus there is no need to add any excess quantity, rather the temperature profile in the tundish is to be monitored for its insulation performance.
By virtue of product design, RHAN is always promoted as a self-leveler and spreader. Therefore it cannot create a heap near the continuously moving parts which are going in and coming out of liquid steel. However, the possibility of such jamming cannot be ruled out. Experience in many steel plants usage has shown that as long as excessive slag ingress in the tundish is restricted, there is no problem of jamming. Still, during initial phases of trials, care should be taken to monitor such sensitive areas.
No. Due to its self-spreading characteristics, RHAN can be added near the turbulent zone (liquid steel entry zone) and it will spread by itself within a few seconds. However, in case a baffle (dams and weirs) is used in the tundish, obviously RHAN needs to be added on both sides of the baffle. Moreover, in case any other additive like synthetic slag, etc are added in the tundish, then for effective results RHAN should be added in 3 or 4 segments of the tundish, viz, stopper area, shroud area, thermal probe area, etc.
Many steel plants are successfully using RHAN without any such problems mainly because these high temperature amorphous silica agglomerates (balls) are fairly inert in nature. Sometimes negligible gripping is noticed with the tundish refractories at the neck level in case the refractory material is reactive to silica. However, in case of substantial slag ingress from the ladle to the tundish, there is a good chance of hard crust formation due to reinforcement effect of solid RHAN in the solidifying slag matrix.
Generally, argon flushing in the tundish to prevent air ingress is fairly soft (less than 0.8 bar pressure), so this does not create any significant turbulence or directional metal flow. But in case of excessive argon bubbling there will be turbulent metal flow away from the ladle shroud. This will tend to push the RHAN away from the shroud area due to its free-flowing nature, thus exposing the tundish metal to “red eye” phenomena.
No. There is no free C available in RHAN except the organic binder. Carbon is generated during calcinations of rice husk which is easily oxidized at high temperature to carbon monoxide (CO) and carbon di-oxide (CO2). These gases mostly fill the internal pores and external voids and must escape to the atmosphere. However, as per customers’ choice, various carbon containing grades of RHAN are available, starting from 24% C down to as low as 1.5% C.
Yes, RHAN does pick up moisture on long storage. Amorphous silica is highly hygroscopic and the organic binder further aggravates this. So, as the storage is extended the moisture level of manufacturing time of ~ 0.2-0.3% gradually increases. With this increasing moisture, the product can lose its green strength and become friable. Such products when used in hydrogen sensitive steel grades may give rise to hydrogen contamination. It is thus recommended that under highly humid atmospheric conditions the product should be used within 3 months for optimal performance
Yes, a proto-type is under development which principally collects the RHAN by gravity from a silo or big bag into a pressure vessel which then pneumatically conveys the product in a moderately dense phase. The rate of flow can be controlled by the diameter of the delivery tube and air pressure.
Generally no, because it is a short time contact. So, the economic solution is to use ambient (atmospheric) air.
Well, some plants are using it successfully to avoid dusty and polluting environment and also to avoid 2 product application. However, ladles are normally tapped with 1 or 2 tons of slag on top and most have a cover lid for effective insulation, so the cost/benefit ratio is sometimes under question for purely insulation purposes.
Yes. In long duration transfer ladles it helps to avoid heat loss and crust formation. It is also a wonderful solution for blast furnace runner/slag runner to maintain a liquid pool between thecasts.
The price of RHAN is higher than powder but lower than granules, so cost-wise it appears to be more expensive than powder. But by virtue of its 50% lower consumption than powder, no shrinkage at high temperatures and perfect insulation properties, it is the most economic solution for liquid steel insulation when considered on the basis of cost/ton of liquid steel. Moreover, for long distance transportation it provides tremendous savings in transport costs as compared to powder or granule due to its higher bulk density at room temperature (see Comparative Table).
It is tailor-made to customer requirements, but the usual packing sizes are 2 kg, 5 kg, 6 kg and 10 kg per packet.
IIts certified storage life is 6 months from date of manufacture, but it is recommended to be used within 3-4 months for best performance. The following conditions are recommended to be maintained during storage: • Covered area • Airy and well ventilated • Stacking above floor level, preferably on platforms • A reasonable gap between one stack and the next for ventilation and inspection access. • No direct moisture contamination
Rescon for nearly four decades, continues its journey towards excellence. Today it is a household name in liquid steel insulation. Naturally available agro waste- Rice husk duly calcined converts the product into amorphous silica with some residual carbon. Combustion with excessive or insufficient oxygen thus controls the residual carbon content to the specified limit of the user.