600mm Effective Width | Roller Hearth Bright Annealing Furnace for Steel Pipe | Non-Oxidation Annealing & Batch Heat Treatment System for Precision Steel Tubes

1. Product Overview

This roller hearth bright annealing furnace line is specifically designed for batch annealing of precision steel tubes (φ14–38.1mm, wall thickness 1–2.5mm, length 6000mm). Featuring a nitrogen-hydrogen protective atmosphere, it ensures decarburization-free and oxidation-free annealing, delivering a bright, clean surface finish. The production line consists of a feed roller conveyor, preheating zone, heating furnace, slow cooling zone, water cooling zone, and discharge roller conveyor – designed for continuous, high-volume operation, suitable for SAE 1008/1010 steel tube bright annealing.

2. Industry Challenges & Root Cause Analysis

Oxidation and decarburization after annealing:Steel tubes develop scale when exposed to air during high-temperature annealing, degrading surface quality. Root cause: lack of protective atmosphere or unstable atmosphere control.

Difficulty maintaining furnace temperature uniformity:Large temperature variations along length and cross-section in conventional furnaces result in inconsistent hardness within the same batch. Root cause: irrational heating element layout, insufficient temperature zone division, and inadequate thermocouple placement.

Trade-off between cooling efficiency and surface quality:Rapid cooling causes tube deformation, while slow cooling reduces productivity. Root cause: water cooling section length, zoning, and circulation system not optimally designed for tubing.

High energy consumption and heat loss:Inadequate furnace insulation leads to excessive heat dissipation. Root cause: improper refractory selection, poor furnace sealing, and unused waste heat.

Poor production continuity:Speed mismatch between sections causes bottlenecks in tube transfer. Root cause: lack of synchronized drive control and detection/alarm mechanisms.

3. Solution

3.1 Nitrogen-Hydrogen Protective Atmosphere System:Uses nitrogen as carrier gas (90–95%, ~50m³/h) and hydrogen as reducing atmosphere (5–10%, ~5m³/h), ensuring tubes remain in reducing atmosphere throughout heating and cooling – oxidation-free, decarburization-free, bright surface. Soft curtain doors and hoods at both ends effectively prevent atmosphere leakage.

3.2 Precision Temperature Control & Uniform Heating:Heating power 180kW, 4 independent temperature zones with intelligent controllers and SCR power regulators – control accuracy ±1℃, furnace uniformity longitudinal ±6℃ / cross-section ±3℃. Radiant tubes horizontally arranged in upper/lower layers, 42V low-voltage supply for safety.

3.3 Segmented Water Cooling System:Water cooling section total length 7600mm, consisting of transition section + 4 water-cooled jackets, circulating cooling water ~30m³/h (recycled). Tubes enter water at ~800℃, discharge temperature ≤150℃ – efficient cooling without quenching deformation.

3.4 High-Standard Furnace Insulation:Furnace wall composite structure: high-alumina bricks (BB) + insulation board + calcium silicate board + PVC blanket, wall thickness 400mm, shell temperature rise ≤50℃. Roof uses 1260℃ ceramic fiber blanket stacked, fixed with stainless steel fasteners – low heat loss, low operating energy consumption.

3.5 Full-Line Synchronous Drive:Each section driven by variable-frequency geared motors with double-row chain ring drive – each roller independently powered. Transmission abnormalities trigger detection switch alarms. Furnace rollers made of heat-resistant stainless steel with high-temperature bearings and aluminum alloy heat-dissipating bases – reliable at high temperatures.

3.6 Intelligent Control System:PLC + touchscreen centralized control, auto/manual modes. Critical parameters (temperature, speed, alarms) automatically recorded and stored for 6 months, exportable to Excel. Faults trigger audible/visual alarms and are logged. Emergency power failure: automatically closes hydrogen valve, opens nitrogen purge valve, manually closed after 120-minute delay – ensuring safety.

4. Technical Specification 

5. Selection Guide

5.1 Recommended Scenarios

• High-volume bright annealing production of precision steel tubes

• Heat treatment of low-carbon steel tubes such as SAE 1008/1010

• Customers with strict requirements for surface brightness and zero oxidation/decarburization

• Continuous, highly automated heat treatment production lines

5.2 Key Selection Considerations

1. Tube specifications: Verify diameter (φ14–38.1mm), wall thickness (1–2.5mm), length (6000mm) are compatible

2. Capacity: Design capacity 300kg/h – calculate against daily output requirements

3. Protective atmosphere supply: Buyer to provide N₂ + H₂ mixed atmosphere, flow ≥60m³/h

4. Cooling water conditions: Buyer to provide low-calcium industrial circulating water, inlet temp 10–30℃, pressure 0.2–0.3MPa, flow ≥30m³/h

5. Facility space: Total equipment length 36820mm – verify installation area availability

6. FAQ

Q1: What surface quality can be achieved after annealing?

A: Under N₂–H₂ protective atmosphere (90–95% N₂ + 5–10% H₂), annealed tubes are free of scale and decarburized layers, with a bright metallic finish – ready for subsequent processing or direct use.

Q2: Can the equipment handle different tube diameters?

A: Yes. Effective height is 150mm – all tubes within φ14–38.1mm can be processed. Changeover between specifications requires no tooling replacement – simply adjust process parameters.

Q3: Does water cooling cause tube deformation?

A: The water cooling section uses a multi-jacket design with transition section + 4 stages of gradual cooling, discharge temperature ≤150℃. Circulating cooling water with controlled temperature rise effectively prevents deformation from sudden chilling.

Q4: How is safety ensured during power outages?

A: The control system includes emergency safety interlocks. On power failure, the hydrogen valve automatically closes and the nitrogen purge valve opens for furnace purging; the valve is manually closed after a 120-minute delay – preventing hydrogen accumulation risks.

Q5: Can the equipment connect to MES systems?

A: Equipped with PLC and touchscreen – key parameters automatically recorded and stored for 6 months, exportable to Excel. Data acquisition interfaces support MES integration upon request.

7. Why Choose Wuxi Wondery

• Premium international components: PLC & inverters, intelligent temperature controllers, Schneider electrics, Isolite refractories, Japanese CKD solenoid valves – long-term reliability

• Precision temperature control: 4 independent zones, ±1℃ accuracy, ±6℃/±3℃ uniformity – batch consistency guaranteed

• N₂–H₂ protective atmosphere: Prevents oxidation and decarburization – bright, clean surface after annealing

• Full automation: Touchscreen centralized control – automatic data logging and export

• Comprehensive safety interlocks: Emergency hydrogen shut-off, automatic nitrogen purge, audible/visual alarms with fault logging

• Full support: User manual, inspection report, remote diagnostics, and on-site service available