Why is dry vibrating material recommended for continuous casting tundish working linings?

Dry vibrating material for tundishes is a monolithic refractory material formed by vibration without the addition of water or liquid binders. Vibration forms the material into a dense and uniform mass. Upon heating, it develops strength through the application of thermosetting binders or ceramic sintering agents. Dry vibrating material consists of refractory aggregate, powder, sintering agent, and admixtures. Its characteristics are: It flows easily under vibration, and the powder fills the tiny pores between the packed particles even under very low vibration forces, resulting in a dense structure with a high packing density. During use, heating forms a working surface with a certain strength, while the non-working surface remains partially unsintered, retaining its original dense packing structure. This structure helps reduce stress caused by expansion and contraction, hinders the propagation and extension of cracks, prevents the intrusion of molten metal, and facilitates unpacking and cleaning. This material is applied on-site using vibration, making it simple and time-efficient. The working layer can be sintered directly and quickly before being put into service.

Characteristics of dry material in tundish

Dry vibrating material in tundish has the dual advantages of insulation board and coating, and the advantages are as follows:

• It has strong resistance to erosion by molten steel and slag, greatly improving the service life of the working layer, allowing long-term casting and reducing the consumption of refractory materials per ton of steel.
• Dry vibrating material is gradually sintered from the working layer to the permanent layer by relying on the temperature gradient during use, forming a dense structure on the hot surface of the working layer, and there will be no through cracks that cause slag to penetrate into the permanent layer. Since the density of the unsintered layer is low, it is beneficial to the insulation of the tundish.
• Slight shrinkage occurs during sintering, making it easy to turn over and remove the tundish.
• It is easy to construct and can be constructed without water. It can be quickly baked or used directly without baking, increasing the utilization rate of the tundish and extending the service life of the tundish, thereby reducing the number of spare tundishes.
• Since dry vibrating material does not contain water, it can reduce the chance of secondary oxidation of molten steel in the tundish, reduce hydrogen absorption of molten steel, reduce pollution to molten steel, and improve the quality of steel billets.
• Compared with spray paint and coating materials, the use of dry vibrating materials can reduce the energy consumption of baking, reduce labor intensity, and improve labor productivity. Generally speaking, the coating needs to be baked at 800~1000℃ for 2~6 hours, while the dry vibrating materials only need to be baked at 200~300℃ for 45~90 minutes to solidify the binder. The construction equipment is simple and the construction is convenient.
• The service life of dry vibrating materials is long, generally up to 20 hours or more, and up to 60~70 hours in some cases, which greatly improves the labor productivity of the steelmaking process. Dry vibrating materials have obvious advantages in use. They are superior to other working linings in terms of baking time, continuous casting times, and continuous casting time.

Dry vibrating materials for tundishes include magnesium and magnesium-calcium. Since dry materials are non-aqueous, the selection of binders is particularly important. The binder selection must be water-free and non-reactive with magnesia at room temperature. After heating to 200-300 tons, the dry material must possess sufficient strength for demolding. At temperatures around 1550°C, the dry material can be sintered into a solid, integrated unit, ensuring high-temperature performance.

There are two types of binders for tundish dry vibrating materials: organic binders (such as phenolic resin and glucose) and inorganic binders (such as sodium tripolyphosphate and sodium hexametaphosphate, solid water glass, and boric acid).

Tundish Dry Material Application

1. Preparation:

① First, clean the mold and brush all around it with a layer of graphite powder mixed with oil or water. Allow the mold to air dry. Install a functioning vibration motor in the desired position on the mold. After installation, carefully check that it is secure to prevent any fasteners from loosening during use.

② Wait until the tundish temperature drops below 50°C before applying the material. The permanent layer must be cleaned to remove any residual paint or dust. Do not spray water into the tundish.

③ Prepare the required paint.

2. Application Method:

① First, install the tundish nozzle support bricks, ensuring that their top surfaces are aligned. Then, evenly pour the dry material onto the bottom of the tundish and tamp it tightly around the nozzle support bricks. Firm the base material layer by layer by tamping or using a vibrating plate. The material should be applied slightly higher than the top surface of the nozzle block to ensure adequate contact between the formwork and the base material.

② After the base is constructed, place the formwork into the tundish. Ensure the gap between the formwork and the permanent layer is the same thickness on both sides.

③ Pour dry material evenly along the sidewalls, dragging a vibrator around the formwork as you pour to fully degas the dry material and minimize material segregation during formwork vibration.

④ Continue applying layer by layer until the dry material fills the entire gap and is higher than the permanent layer.

⑤ Start the vibration motor inside the mold for 5-10 seconds, then use an auxiliary manual vibration motor to vibrate the mold in one circle around the tundish.

⑥ Add dry material to fill any gaps left by the vibration, and thoroughly compact or tamp the dry material on top.

⑦ Ignite the burner inside the mold to heat the mold, maintaining a temperature between 200°C and 300°C for 1-2 hours.

⑧ After the mold has cooled, remove it with a crane. Be careful not to damage the working lining during removal.

⑨ Before use, bake directly over high heat for approximately 1 hour. It can be used when the temperature reaches above 1000°C.