The manufacturing of a glass-lined (enamel-lined) reactor is an extremely sophisticated and highly specialized industrial process that combines pressure-vessel fabrication with industrial glass-enamel fusion technology. These reactors are widely used in pharmaceuticals, chemicals, pesticides, dyes, food, and new-material processing due to their excellent corrosion resistance and durability.

The complete production process can be divided into two major stages:

Fabrication of the steel shell (metal substrate)

1. Glass-lining (enamel) preparation and high-temperature firing

2. Below is a comprehensive, step-by-step explanation of the full manufacturing workflow.

Stage 1: Fabrication of the Steel Substrate (Metal Body)

The purpose of this stage is to build a high-strength steel pressure vessel that meets strict mechanical performance standards and can withstand multiple high-temperature firing cycles.

1. Steel Material Selection

Glass-lined reactors require special low-carbon, fully killed steel such as Q245R. The content of carbon, sulfur, and phosphorus must be strictly controlled:

l Low carbon → Improves enamel adhesion and reduces cracking.

l Low sulfur → Prevents “fish-scale” defects (blisters caused by trapped gases).

l Low phosphorus → Ensures stable metallurgical properties during firing.

Using improper steel grades will result in enamel detachment, cracking, or explosive spalling during firing.

2. Cutting and Forming

Different sections of the reactor are formed using high-precision metalworking equipment:

Head (dish end) forming

l Steel plates are cut according to design specifications.

l Hot pressing or cold spinning is used to form hemispherical, dish, or ellipsoidal heads.

Cylindrical body

l Plates are rolled into cylinders using a plate-rolling machine.

l Longitudinal seams are welded to close the cylinder.

3. Welding and Heat Treatment

Welding is a critical operation. Only certified welders can perform the process.

l Welding method: TIG root welding + multi-pass filler welding

l Requirement: Smooth, defect-free welds that endure high-temperature firing

After welding, the vessel undergoes stress-relief annealing:

l The reactor is heated to 600–650°C

l Kept at temperature for several hours

l Slowly cooled in the furnace

This step removes internal stress from welding and forming. Without stress relief, the vessel may deform during enamel firing, causing cracks in the glass layer.

4. Machining and Surface Preparation

After heat treatment, the steel substrate undergoes:

Flange machining

l Ensures flatness, surface roughness, and sealing precision

Surface blasting (sandblasting or shot-blasting)

l Removes rust, scale, oil, and oxide layers

l Creates a clean metal surface with micro-anchoring texture

l Enhances adhesion between enamel and steel

This is one of the most decisive factors in final product quality.

Stage 2: Glass-Lining (Enamel) Coating and High-Temperature Firing

This stage determines the chemical resistance, bonding strength, and lifespan of the reactor.

5. Enamel Slurry Formulation and Ball Milling

Raw materials include:

l Quartz

l Feldspar

l Borax

l Kaolin

l Clay

l Additives and electrolytes

These materials are precisely weighed and placed into a ball mill for long-term grinding until a fine, uniform, milky-white enamel slurry is produced.

The particle size distribution of the slurry directly influences the density, smoothness, and corrosion resistance of the final enamel layer.

6. Enamel Application (Coating Process)

The enamel slurry is applied to the inside surface of the steel vessel using:

l Immersion coating

l Spray coating

l Flow coating

Conditions must be strictly controlled:

l Dust-free environment

l Stable temperature and humidity

l Uniform coating thickness

The final enamel system typically uses:

l 1 layer of ground coat (base enamel)

l 2 layers of cover coat (surface enamel)

Total thickness: 0.8–2.0 mm

Too thin → poor corrosion resistance
Too thick → cracking during firing

7. Drying

Coated vessels are moved into a drying kiln:

l Approx. 100°C

l Slow, uniform moisture removal

This prevents bubbling and micro-cracks during high-temperature firing.

8. High-Temperature Firing (Enamel Fusion)

This is the core stage that fully transforms the enamel into a bonded glass layer.

The vessel is pushed into a giant furnace heated to around 900°C.

During firing:

1. Organic binders burn off

2. Enamel particles melt into a glassy liquid

3. Iron oxide (FeO) forms on the steel surface

4. The molten enamel dissolves FeO

5. A strong chemical-bond transition layer forms between steel and enamel

6. The vessel cools in air, forming a hard, glossy glass surface

This steel-glass chemical bond is what enables the exceptional corrosion resistance of glass-lined reactors.

9. Multiple Coating and Firing Cycles

The steps coating → drying → firing are repeated for each enamel layer.

Standard industrial practice:

l 1 base coat firing

l 2 cover coat firings

After each firing, enamel thickness and quality are inspected before proceeding.

Final Stage: Inspection, Testing, and Assembly

10. Quality Inspection

Quality testing includes:

l Appearance examination

l Smoothness

l Gloss

l Uniform color

l No cracks, bubbles, pinholes, fish-scale defects

Thickness testing

l Using electromagnetic enamel thickness tester

High-voltage spark test

l Enamel is scanned at 20kV/mm

l Any discharge point indicates a defect

Pressure vessel testing

l Hydrostatic pressure test

l Air-tightness test

Only vessels passing all tests can proceed to assembly.

11. Final Assembly and Packaging

Assembly includes:

l Mechanical seal

l Stirring system

l Baffles

l Jacket insulation

l Nozzles and flanges

Critical sealing surfaces are protected, and the finished reactor is packaged for shipping.
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