How to avoid clogging in tundish nozzles

Various methods employed to avoid clogging in Tundish nozzles are:

1.Erosion of Alumina build-up

2.Steel reinforcement of Alumina matrix

3.Flow model studies

4.Argon purging facility in the bore of nozzles

5.Anti-clogging mix employment at bore

Tundish nozzles are manufactured by alumina carbon refractory material. The porosity ranges between 12%-15%. In order to have a purging facility however, the bore porosity must be >18% without compromising strength. 

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The results of tundish nozzles Clogging

Clogging in continuous casting tundish nozzles is build-up of material in flow passage between the tundish and mold, and results in:

Decrease in productivity

If clogging becomes sufficiently severe, the flow control device will no longer be able to compensate, resulting in either a decrease in casting speed or making it necessary to replace the nozzle. These events reduce net casting throughput and thereby reduce productivity.

Increase in cost

Depending on the casting shop, some portions of clogged nozzles (e.g. submerged entry nozzle) can be independently replaced during casting. This is done by use of a sub entry shroud or a tube changing SEN. However other clogged refractory (e.g. tundish nozzle) can only be replaced by changing tundishes. Therefore nozzle clogging results in additional costs in terms of tundish refurbishment or nozzle replacement.

Depletion of quality

Clogged particles can get dislodged from the build-up and result in unacceptable cleanliness-related defects in the product. The restriction of flow passage may also cause biased flow patterns in the mold which thereby cause quality problems such as mold flux ingestion, shell thinning etc.

The process of Continuous Casting has achieved new heights in recent years, as tundishes are no longer treated as simply a transfer vessel but as a metallurgical reactor. Progress in technology has led many producers to move to casting high quality steel of all grades with very long casting duration i.e. >20 hrs. We all know nozzle clogging has been a serious productivity and quality problem in continuous casting of Aluminium killed steel, which limits the slab casters to last a defined (short) time. This led to development of TCD (Tube Changing Device) casters where the SEN can be changed during an ongoing casting process.

In addition, products of steel-refractory interactions such as CA6, commonly found in tundish nozzles, were observed in the lab tests. Alumina-graphite nozzle materials were shown to clog at a faster rate since industrial alumina-graphite has strong thermochemical interactions with steel. No significant steel-refractory interactions were observed in the pure oxide or zirconia-graphite nozzles however.

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FAQ:

What is a tundish nozzle?

Tundish Nozzles are an integral part of Continuous Steel Casting process. These products are instrumental in controlling the flow of Molten Steel from Tundish to Continuous Casting.

What is the function of a nozzle?

The primary function of a nozzle is to control flow rate and convert the spray liquid into droplets (via atomisation) that are of a suitable size for depositing on the intended target.

What is the result of tundish nozzle clogging?

Irregular flow through a tundish nozzle increases the probability of generating a number of quality defects such as re-oxidation of the steel and slag entrapment. Nozzle clogging also affects productivity in that less steel is able to be cast because of the blockage in the nozzle.

What is the HS code for tundish nozzle?

69032090

Why is my tundish nozzle clogging?

The cause of the clogging is related to a combination of operating criteria including ladle slag practice, tundish refractory, deoxidation methodology and temperature.

What causes nozzle clogging?

The reason behind this problem is that some of the old material remains in the extruder due to the lower temperature needs of the new material. As a result, the old filament will not melt completely, and the residue left behind may cause the nozzle to clog in the long run.