Which Low-Temperature Binder Works Best for Magnesia Dry Ramming Mix? Two Popular Options Compared
As an essential material, steel plays a pivotal role in the economic development of countries worldwide. A tundish is a vessel used in steelmaking and is a critical component of the continuous casting process. Its main functions are as follows:
1)Reduce the static pressure of molten steel, maintain a stable liquid level in the tundish, and ensure the smooth flow of molten steel into the mould.
2)Promote the flotation of inclusions in molten steel to purify the liquid steel.
3)Distribute molten steel: for multi-strand continuous casters, the tundish directs molten steel to the respective individual moulds.
4)Reserve molten steel to maintain a consistent casting speed during ladle changes in sequential continuous casting, enabling multi-heat continuous casting.
In summary, the core functions of a tundish include pressure reduction, flow stabilization, inclusion removal, molten steel storage, and distribution.
As one of the working lining materials for tundishes, magnesia dry ramming mix features easy installation, simple drying, excellent slag resistance, and minimal contamination of molten steel. It also significantly reduces workers' labor intensity, requires only simple construction equipment, and facilitates rapid tundish demolition and relining.
01. Test
1.1 Test Purpose
This test aims to compare two types of medium- and low-temperature binders: phenolic resin and glucose. The comparison focuses on cold strength after drying and demoulding, structural integrity, and corrosion resistance.
1.2 Raw Materials
The primary raw material used in the test is 90-grade sintered magnesia with particle size fractions of 5–3 mm, 3–1 mm, ≤1 mm, and 0.074 mm fine powder. The binders mainly include phenolic resin, glucose, and anhydrous sodium silicate.
1.3 Test Methods
Two groups of specimens were prepared separately using phenolic resin and a combination of glucose and anhydrous sodium silicate as binders. The prepared samples were subjected to cold crushing strength tests after firing at 270 °C, 1350 °C, and 1500 °C, as well as rotary slag corrosion resistance tests.
02. Results and Discussion
2.1 Effect of Different Binders on Strength
After heat treatment at 270 °C, magnesia dry ramming mixes bonded with either phenolic resin or glucose both achieved a crushing strength of more than 7 MPa. Both formulations satisfy the required low-temperature demoulding strength. No obvious surface damage was observed after demoulding, ensuring intact specimen surfaces. Relevant test data are listed in Table 1.
2.2 Slag Resistance Performance of Different Binders
During the test, steel slag was added to the slag resistance furnace when the furnace temperature reached approximately 1300 °C, and then the temperature was raised to 1580 °C. After testing, the residual thickness of the phenolic-resin-bonded magnesia dry ramming mix was about 46 mm, while that of the glucose-bonded counterpart was approximately 44 mm.
It can be concluded that the phenolic-resin-bonded magnesia dry ramming mix exhibits better slag resistance than the glucose-bonded grade. The dosage of glucose binder used is higher than that of phenolic resin, resulting in a lower MgO content in the glucose-bonded formulation and consequently slightly inferior slag corrosion resistance.
03. Construction Scheme for Magnesia Dry Ramming Mix
Magnesia dry ramming mix is generally installed by vibration using an integral formwork system, followed by baking, with demoulding performed as the final step.
3.1 Formwork Preparation
Steel formwork fabricated by integral welding is adopted and equipped with vibration motors mounted on the top. During fabrication, the outer surface of the formwork shall be kept as flat and smooth as possible. All welding seams shall be ground smooth with grinding wheels where welding marks are present. Prior to the installation of the magnesia dry ramming mix, thoroughly clean the formwork surface. Afterwards, coat the formwork with a mixture of graphite and waste engine oil to facilitate subsequent demoulding.
3.2 Tundish Preparation
Due to the inherent properties of magnesia dry ramming mix, construction should not be carried out when the tundish temperature is excessively high. Construction is recommended to begin after the tundish has cooled to approximately 50 °C. Before construction, thoroughly remove all debris from the permanent lining and the interior of the tundish. Water spraying inside the tundish is prohibited.
3.3 Construction
First, install the tundish nozzle seating bricks and ensure that all seating bricks are level and lie in the same plane. Plug the inner holes of the seating bricks with woven bags or other suitable fillers to prevent material leakage. Place the dry mix on the tundish bottom and compact it to the designed base lining thickness. After the base lining has been completed, lower the formwork into the tundish. Ensure uniform and symmetrical gaps between the formwork and the permanent lining during placement to avoid uneven working lining thickness. Then secure the formwork in position, evenly fill the space around the perimeter of the formwork with magnesia dry mix, and compact the material using poking rods. Once charging is complete, apply vibration for 3 to 5 minutes.
3.4 Heating and Curing
After vibration forming, heat the interior of the formwork using a tundish baker. The binder in the dry mix carbonizes upon heating, forming a carbon-bonded structure that provides strength. The formwork temperature shall be controlled between 250 °C and 350 °C, with a heating duration of approximately 2 hours. After the formwork has completely cooled, carry out demoulding and inspect the integrity of the formed working lining. Repair any defective areas as required.
04. Conclusion
The service life of magnesia dry ramming mix varies depending on the steel grades being cast. Under normal conditions, no obvious defects occur as long as the MgO content meets the design specifications. Based on laboratory test results and field application feedback, both phenolic-resin-bonded and glucose-bonded magnesia dry ramming mixes can meet on-site operational requirements.
However, glucose binder is prone to thermal decomposition and moisture generation when stored under high ambient temperatures on site, which can deteriorate the bonding performance of the glucose-bonded dry mix. Therefore, prolonged storage at the job site will adversely affect its service performance.