Editorial Technical Reference

Slag Notch

This page explains how Slag Notch is classified within Basic Metal Manufacturing. Technical values and manufacturer relationships are research references; confirm the current specification and supplier evidence for each order.

Technical Definition & Core Assembly

A controlled opening in a furnace hearth designed for the removal of molten slag.

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Product Specifications

Technical details and manufacturing context for Slag Notch

Definition
The slag notch is a critical component of industrial furnace hearths, specifically engineered to provide a controlled exit point for molten slag—the waste byproduct formed during metal smelting or refining processes. Located at the appropriate level in the hearth wall, it allows for the periodic or continuous tapping of slag to maintain optimal furnace operation, prevent overflow, and separate impurities from the molten metal bath. The notch is typically a refractory-lined aperture with a removable plug or gate. During operation, accumulated slag floats on top of the denser molten metal. When the slag level reaches a predetermined height, the plug is removed or the gate is opened, allowing the slag to flow out by gravity through a runner or launder system for disposal or further processing, before the opening is resealed. The slag notch is designed to operate under high temperatures (1400–1600 °C) and pressures (1.0–1.6 MPa), with a nominal diameter typically ranging from 50 to 200 mm. It is constructed with refractory materials such as high-alumina or magnesia-carbon brick, encased in a steel retaining ring. Cooling water flow (10–30 m³/h) and pressure (0.3–0.6 MPa) are required to prevent overheating of the frame. Sealing surface flatness must be ≤0.05 mm to ensure leak-tightness, and the leakage rate is specified as ≤0.1% (Class A). The refractory material grade (A–C per ISO 10081-1) affects service life. The weight ranges from 500 to 2000 kg, and actuation torque for manual or hydraulic operation is 200–800 N·m. These parameters are reference ranges; actual values must be confirmed with the manufacturer for specific applications. Standards such as ISO 6708, ISO 17584, and ISO 10081-1 are referenced for verification. The slag notch is essential for efficient slag removal, preventing furnace damage, and ensuring metal quality.
Working Principle
The slag notch operates on the principle of density separation. Molten slag, being less dense than the molten metal, accumulates on top of the metal bath. The notch is positioned at a height corresponding to the slag layer. When slag reaches the notch level, the plug or gate is opened, allowing slag to flow out by gravity through a runner or launder. The opening is then resealed to maintain furnace integrity. The refractory lining protects the structure from high temperatures and chemical attack, while cooling water prevents overheating of the frame. The sealing surface ensures minimal leakage, and the actuation mechanism allows controlled tapping.
Common Materials
Refractory brick (e.g., high-alumina, magnesia-carbon), Steel casing/retaining ring
Technical Parameters
ParameterTypical rangeNotes & selection driver
Nominal Diameter50–200 mmMatches furnace tapping rateISO 6708
Operating Temperature1400–1600 °CRefractory lining required
Cooling Water Flow Rate10–30 m³/hPrevents overheating of frame
Cooling Water Pressure0.3–0.6 MPaEnsure adequate flow
Sealing Surface Flatness≤0.05 mmCritical for leak-tightnessISO 17584
Refractory Material GradeA–CHigher grade for longer lifeISO 10081-1
Weight500–2000 kgAffects installation and support
Leakage Rate≤0.1 %Class A per ISO 5208 Measured at the stated test pressure
Actuation Torque200–800 N·mFor manual or hydraulic operation

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Components / BOM
  • Refractory Lining Part
    Forms the internal, wear-resistant surface of the notch, containing the molten slag and resisting erosion/corrosion.
    Material: High-alumina or basic refractory brick/monolithic
  • Steel Casing/Retaining Ring Part
    Provides structural support and containment for the refractory lining, and facilitates mounting to the hearth structure.
    Material: Heat-resistant steel (e.g., carbon steel plate)
  • Tapping Plug/Gate
    A removable or operable closure mechanism to open and seal the notch for controlled slag tapping.
    Material: Refractory plug or steel gate with refractory facing
  • Water Cooling System
    Circulates water through the notch frame so the steelwork survives beside flowing slag.

Application & selection

Application Fit & Sizing Matrix

Operational Limits
pressure: 0-0.5 bar (atmospheric to slight positive pressure)
flow rate: Variable, controlled by opening size and slag viscosity
temperature: 1200-1600°C (typical molten slag range)
slag concentration: 100% molten slag (no dilution required)
Media Compatibility
✓ Blast furnace slag (ironmaking) ✓ Electric arc furnace slag (steelmaking) ✓ Copper smelting slag
Unsuitable: Highly corrosive acidic slags (e.g., from certain non-ferrous processes)
Sizing Data Required
  • Required slag removal rate (tons/hour)
  • Furnace hearth diameter and geometry
  • Slag viscosity and solidification temperature

Risk, maintenance & compliance

Reliability & Engineering Risk Analysis

Failure Mode & Root Cause
Thermal fatigue cracking
Cause: Cyclic thermal stress from repeated exposure to high-temperature molten slag during tapping and subsequent cooling, leading to crack initiation and propagation in the refractory lining.
Erosion and wear
Cause: Abrasive flow of molten slag during tapping operations, combined with chemical attack from slag components, degrading the refractory material and altering the notch geometry.
Maintenance Indicators
  • Visible cracks or spalling in the refractory lining around the slag notch opening
  • Irregular or enlarged slag flow pattern during tapping, indicating altered notch geometry
Engineering Tips
  • Implement regular thermal imaging inspections to monitor temperature gradients and detect early signs of refractory degradation before visible damage occurs.
  • Use high-quality, slag-resistant refractory materials specifically designed for thermal cycling, and ensure proper installation with controlled curing and drying procedures.

Indicative industry ranges for design and RFQ preparation. Confirm the exact figures and applicable standard with the manufacturer before specifying.

Compliance & Manufacturing Standards

Applicable Standards
ASTM A36/A36M - Standard Specification for Carbon Structural Steel DIN 17100 - General structural steel grades; quality standards

Quoted from the published standard.

Manufacturing Precision
  • Bore diameter: +/-0.05mm
  • Surface flatness: 0.15mm per 100mm length
Quality Inspection
  • Dimensional verification with coordinate measuring machine (CMM)
  • Ultrasonic testing for internal defects
Technical documentation
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Inspection readiness
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Frequently Asked Questions

What is the primary function of a slag notch?

The slag notch provides a controlled opening in the furnace hearth to remove molten slag, which is a waste byproduct of metal smelting. It helps maintain furnace operation and separate impurities from the metal bath.

What materials are used in slag notch construction?

Slag notches are typically lined with refractory brick such as high-alumina or magnesia-carbon, and have a steel casing or retaining ring for structural support.

What are typical operating parameters for a slag notch?

Typical parameters include operating temperatures of 1400–1600 °C, pressures of 1.0–1.6 MPa, and nominal diameters of 50–200 mm. Cooling water flow is 10–30 m³/h at 0.3–0.6 MPa. These are reference ranges; actual values must be confirmed.

How is the slag notch sealed to prevent leakage?

The sealing surface flatness must be ≤0.05 mm, and the leakage rate is specified as ≤0.1% (Class A). The plug or gate must be properly seated and maintained to ensure leak-tightness.

Data basis: editorial classification, named public sources where available, and source-reviewed manufacturer records. See the editorial policy.

Related equipment

Industrial Ecosystem & Supply Chain Structure

Data Basis

Editorial classification, named public sources where available, and source-reviewed manufacturer records.

Preliminary Technical Classification
This page supports structured research, RFQ preparation, and supplier evaluation. It does not replace buyer-led supplier qualification, standards review, or technical approval.

Compiled and source-reviewed by the CNFX editorial team. Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review · Page last updated 12 October 2026

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