Parts exposed to liquid aluminium

Liquid aluminum attacks metal parts. Furthermore, it progressively builds up on the part surface. The deterioration of the metal component and the stickiness require that parts be replaced prematurely requiring frequent shutdowns of the process line reducing productivity of the plant.

The most conventional method used in the industry to protect parts consists in applying manually with a brush a liquefied protective product which will reduce sticking. This method is referred to as “poteying”.

Poteying has significant limitations.   It has a very short life.  In many applications, a new layer of material has to be brushed over the part after very few or short exposition(s) to the liquid aluminium.  It also reduces to some degree the sticking.  Equipment operators still have to shake vigorously or knock several times the part to release the aluminum stuck on its surface.

Furthermore, most “poteying” materials are water base products. Complete drying of the parts is required before exposing them to liquid aluminum in order to prevent explosions. Corrosion of the steel bar with such water based material is also a concern.

The R&D team of Metal 7 focused on the development of a more permanent solution which would eliminate the need for poteying.

The objectives in the development of the solutions are the following:

•    Eliminate the need for poteying;
•    Prevent sticking of the aluminum to the surface;
•    Increase durability of the parts in protecting them against the aggressive liquid aluminum.
•    Reducing the iron contamination of the aluminum caused by the rapid deterioration of the steel parts.

A numbers of years were required to develop and tests different coating options in its laboratories and in aluminum smelters. Metal 7’s offers now solutions all adapted to the specific needs of the liquid aluminum applications. They are protective coatings applied by thermal spraying which cover all surfaces of the parts exposed to the liquid aluminum.

Among those solutions, we find the coating M7-B42 and the M7-B512 having the following characteristics:

•    High resistance to high temperature and thermal shocks
•    Non-stick properties against liquid aluminum and dross;
•    Effective protection against corrosion and erosion caused by the contact with liquid aluminum;
•    Thermal barrier protecting the base metal part;
•    High dielectric properties;

Typical applications:

1-    Skimming blades (blades removing the dross over the aluminum mould);
2-    Mixing, scrapping and cleaning rake or scrappers (rakes used in cast house oven to mix the aluminum with other metals and to clean the oven);
3-    Thermocouples;
4-    Etc. 

1-    Skimmer blades:  Skimming blades are used on the automatic skimming system installed over the carrousel of the sows/ingots mould in the cast house.  They clean the dross forming on the top of the mould during the aluminum casting process.

Benefits of the coated skimmer blades are: 

-    The adhesion of liquid aluminum to the parts is minimal.  Operators in the cast house even reprogrammed the operation of equipment to eliminate the knocking of the blades which was previously required to dislodge the aluminum build-up on the part.  It is no longer necessary;

-    Increase of the blade life by more than tenfold;

-    Continuous and efficient operation of the dross removal;

-    Important reduction or elimination of the poteying requirement.

-    Increased equipment availability = higher productivity;

-    Higher purity of the aluminum with lower contamination by the iron contained in the base material of the blades (longer blade life);

2-    Mixing, scrapping and cleaning rakes: Large rakes or scrappers are used in the cast oven to mix the aluminum alloy (liquid aluminum with other materials). They are also use to scrape the bottom of the oven at the end of the process or to clean the dross on the top. They are usually made of carbon steel.

The benefits of the coated rakes are:

-    Three times the life of the carbon steel rakes;

-    Much lower iron contamination in the aluminum thanks to the longer life of the rakes;

-    Minimal sticking – no additional weight added by the build-up of material; 

-    Much lighter weight rakes than the concrete scrappers available on the market;

3-    Thermocouples: Thermocouples are used at different locations in the cast house of an aluminum plant. They are inserted in a protective tube which is subject to rapid degradation when immersed in liquid aluminum.

The benefits of the coated solutions for thermocouple tubes are basically the longer life (more that ten times the life of uncoated thermocouples) and lower maintenance costs required for replacement of the part.