Refractory materials - Composition and Operating Principle of the Automatic Charge-Mixing System for Blast-Furnace Slagging

The automatic gunning mud batching system is a complex industrial system that integrates mechanical transmission, precision weighing, fluid control, thermal engineering (heating and heat preservation), and automated control.

Its core objective is to uniformly mix various solid aggregates and powders with a liquid binder—such as tar, resin, or water—according to a precise formulation, under specified temperature and time conditions, in order to produce gunning mud with stable performance.

The following is a detailed description of the system’s architecture and operating principles:

I. Main System Components (System Composition)

The system typically consists of the following six subsystems:

1.  Raw Material Storage and Preprocessing Subsystem

Aggregate bin / Powder storage silos: used for storing solid raw materials such as corundum, silicon carbide, coke powder, and clay.

Characteristics: The silo body is typically designed with a large taper ( ≥60° ) To prevent bridging, the inner wall is lined with wear-resistant plates (such as ceramic or ultra-high-molecular-weight polyethylene).

Auxiliary: Equipped with a level gauge (high / Low-level alarm, arch-breaking device (pneumatic vibrator or fluidized bed).

Liquid storage tank area: used for storing tar, resin, or water.

Key point: the heating and insulation system is the core. Tar and resins are solid or semi-solid at ambient temperature, so storage tanks must be equipped with electric heating rods or steam coils and wrapped with an insulation layer to ensure that the materials remain flowable (typically maintained at 80 degrees Celsius -120 degrees Celsius , depending on the specific binder).

2.  Feeding and Metering Subsystem (Core Precision Unit)

Solid feeder:

Large aggregate: Use a variable-frequency vibrating feeder or a belt conveyor.

Fine powders: Use a variable-frequency screw feeder (to prevent dust generation and bridging).

Weighing hopper / Scale:

Independent bucket scales or multi-bin shared scales are typically used.

Configure a high-precision weighing sensor ( Load Cells ), featuring shockproof and dustproof capabilities.

For trace additives ( <1kg ), often equipped with a dedicated weightless balance or a micro-screw.

Liquid metering unit:

By means of an insulated metering tank (equipped with a weighing sensor) or a high-precision flowmeter (oval gear) / composed of a mass flow meter.

Screw pumps or gear pumps are typically used as transfer pumps, and the pump casing and piping are fully heated throughout the entire system.

3.  Mixing and Agitation Subsystem (Core Reaction Unit)

Mixed host: The most commonly used is the high-power counter-current mixer ( Intensive Counter-Current Mixer ).

Structure: It consists of a high-speed rotating mixing rotor (which generates shear force) and a low-speed rotating mixing disc (which generates centrifugal force to induce counter-current flow of the material).

Material: The liner and impeller are made of high-chromium cast iron, tungsten carbide spray coating, or ceramic to resist severe abrasion.

Spray system: Equipped with built-in high-pressure nozzles that atomize the heated liquid binder and spray it into the material stream.

Drive unit: high-power motor +  Reducer +  The variable-frequency drive allows speed adjustment to accommodate different mixing stages.

4.  Finished Product Discharge and Packaging Subsystem

Discharge door: a large pneumatic door at the bottom of the mixer, requiring excellent sealing and rapid opening and closing.

Conveying equipment: belt conveyors, screw conveyors, or bucket elevators, which transport the finished product to the packaging machine or the finished-product storage bin.

Packaging / Loading: either an automatic ton-bag packaging machine or a bulk truck loading port.

5.  Dust Removal and Environmental Protection Subsystem

Dust collection points: cover the feed inlet, weighing port, mixer feed inlet, discharge outlet, and packaging machine.

Dust collector: Central pulse-jet baghouse dust collector.

Special requirements: The filter bags must be antistatic (as carbon-containing dust is explosive) and equipped with an explosion-proof pressure-relief design.

Fans and ductwork: Maintain a slight negative pressure in the system to prevent dust from escaping.

6.  Electrical Control and Information Subsystem

Hardware: Programmable Logic Controller (Programmable Logic Controller), touch screen ( HMI ), weighing instruments, and temperature control modules.

Software: formulation management system, production data logging, fault diagnosis, and remote communication interface (integration with the factory) MES/ERP ).

II. Operating Principle (Working Principle)

The entire workflow is a closed-loop automated control process, typically divided into the following stages:

Phase 1: Formula Invocation and Self-Check

The operator is in HMI Select the target formula (e.g., “1 Anhydrous gunning mix for blast furnaces ” ).

The system automatically monitors the material levels in each raw-material bin, liquid temperature, air-supply pressure, and dust-collector status. If any parameter fails to meet the specified threshold—for example, if the tar temperature falls below the setpoint—the system will trigger an alarm and prevent startup.

Phase 2: Precise weighing of solid raw materials (rough addition +  Precision addition)

Coarse feeding: Programmable Logic Controller Control the vibratory feeder or screw conveyor to feed material into the weighing hopper at high speed.

Fine feeding: When the weight reaches the target value of 90%-95% When a height difference is predicted, the feeder switches to low-speed operation.

Stop and Stabilization: Once the target weight is reached, the feeder stops. The system then waits for the readings to stabilize (through filtering) and confirms that the error is within the allowable range (e.g., ±0.2% ).

Discharge: The bottom gate of the weighing hopper is opened, and the material falls into the mixer. This process is typically carried out according to “ Primary coarse aggregate ->  Post-powder ->  Final trace additives ” Proceed in sequence, or in grouped parallel sessions.

Phase 3: Dry Mixing (Pre-Mixing)

The mixer is started, and the mixing bowl and rotor rotate at the set speed.

Under the combined action of centrifugal force and shear force, solid materials undergo countercurrent motion (with the material being thrown upward and the rotor cutting downward), thereby achieving preliminary dry mixing (typically 30 seconds -1 minutes), ensuring uniform distribution of aggregates and powders of different particle sizes.

Phase 4: Wet Mixing (Binder Injection and Dispersion)

Rising temperature / Insulation confirmation: The system confirms that the liquid binder temperature meets the specified requirement.

Atomized Spraying: The delivery pump is started, and the liquid binder is atomized through the internal spray nozzles of the mixer and injected into the vigorously agitated material stream.

Principle: High-speed airflow or mechanical centrifugal force is used to atomize high-viscosity liquids into fine droplets, preventing agglomeration and ensuring that the surface of each aggregate particle is uniformly coated with the binder.

Powerful shearing: The high-speed rotation of the mixing rotor generates tremendous shear forces, which can prevent the formation of “ Powdered lump ” Disperse to make it solid. -  The liquid two phases are fully integrated.

Current monitoring: The control system continuously monitors the main motor current in real time. As the material viscosity increases, the current will rise. When the current reaches the set threshold or the set duration (e.g., 3-5 minutes), indicating that mixing is complete.

Phase 5: Discharge and Cleaning

The bottom gate of the mixer is opened, and the finished ramming mass is discharged into the conveyor equipment below.

If there is a production requirement for the next batch with a different formulation, the system can automatically initiate a cleaning sequence—either by introducing cleaning agents or by using a wall-scraping mechanism to remove residual material—to prevent cross-contamination.

Phase 6: Data Archiving

The system automatically records all data for this batch, including the actual weighing value, mixing time, maximum current, liquid temperature, operation time, and operator.

Generate a quality traceability code and upload the data to the server.

III. Summary

The operating principle of the automatic gunning mud batching system is essentially “ Precise control of the physical state ”：

Quantitative control: Precise solid–liquid ratio achieved through high-precision sensors.

Control of the state: The heating system ensures the flow state of the binder.

Quality control: Microscopic uniform dispersion is achieved through shear and turbulence generated by vigorous counterflow mixing.

This system will move away from the traditional reliance on the experience of master craftsmen. “ Watch the fire, watch the smoke, and rely on touch. ” Transforming the production process of taphole clay into a digital, standardized, and traceable industrial manufacturing workflow is a critical infrastructure for ensuring the long service life and safe operation of modern blast furnaces.