Exposed parts to cast iron

Liquid cast iron is also used in aluminum smelters to seal/attach the large anodes on their support (the support is called a “hexapode”). Small ovens are used to melt the cast iron at over 900 deg C.

It is necessary to remove the dross containing the impurities which form on the top of the oven. Operators use spoons/shovels to remove the dross. In most cases this is done manually with the operator standing as close as possible to the oven.

The metal spoon requires a “poteying” operation (application of a liquid form material which will partially protect the spoon and decrease the sticking of the cast iron on the spoon). However, poteying does a poor job at protecting the spoon. It does not last for more than 2 to 7 dips in the liquid metal. The cast iron still adheres to the spoon, significantly increasing its weight and requiring more effort for the operators. Cast oven dross skimming is known for causing undesired health and safety consequences for the workers.

The life of spoons is so short in some plants that several spoons are required to completely remove the dross in one single oven production batch.

The challenge was obviously to develop a more resistant spoon addressing at the same time the problem of sticking.

Metal 7 developed its M7-B211 ceramic base coating applied by thermal spraying.

It is applied directly on the same original carbon steel spoon.  

It has eliminated the need of poteying.

It does not contain any moisture.  The spoon does not have to be dried before usage which was the case with the former spoon after the poteying. 

Characteristics of the M7-B211 coating:

-    It withstands very high temperatures and thermal cycling (thermal shocks);

-    Minimum sticking of the cast iron or dross on the spoon. Any sticking (if it does occur) would easily fall off the spoon simply by letting it cool down for few minutes;

-    Effective protection against corrosion and erosion caused by the contact with the liquid cast iron and the dross;

-    Thermal barrier protecting the metal substrate of the spoon;

-    Dielectric properties. 

The M7-B211 coating for skimming spoons of Metal 7 have yielded the following benefits for the aluminum plants:

-    Reduction by 90 % of the consumption of skimming spoons in the anode sealing dept. They withstand close to 100 dips in the cast iron oven compare to 2 to 7 for the original steel spoons.

-    Almost no sticking of cast iron or dross on the spoon surface. This translates into significant improvement in the dross cleaning operation for the workers with a better yearly health and safety record for the department.

-    Reduced overall operation costs for the anode sealing department.