Global Success Story: Duolin Welcomes Indian Client to Accept Two Automatic Long Bar Heat Treatment Lines

Duolin is proud to announce the successful acceptance of two fully automatic continuous hardening and tempering lines by our valued Indian customer.

This project began in November 2025 during the customer's initial visit to discuss technical specifications for a continuous long bar heat treatment solution. Following order confirmation, Duolin completed the engineering, manufacturing, and assembly of both custom lines in just two months. In January 2026, the client returned for final acceptance testing, expressing high satisfaction with both the surface finish and core hardness results. This partnership is set to create significant new economic growth for our client in 2026.

What is a Long Bar / Thread Bar Heat Treatment Production Line?

The steel bar induction hardening and tempering system is a non-standard, customized production line designed for continuous thermal processing. Its core function relies on electromagnetic induction to rapidly heat steel bars to critical transformation temperatures, followed by controlled quenching and tempering to achieve superior mechanical properties.

Technical Specifications

• Workpiece Diameter: $Phi 6text{ mm}$ to $Phi 150text{ mm}$

• Workpiece Length: $1,000text{ mm}$ to $14,000text{ mm}$

• Applicable Materials: Solid long bars, thread bars, and steel pipes

Core Processing Stages

• Medium-Frequency Induction Heating: An alternating magnetic field induces precise current within the steel bar. Multi-zone heating controls ensure uniform temperature distribution from the surface to the core across all diameters.

• Segmented Quenching (850°C – 920°C): Heated bars pass directly into a 360-degree spray ring system. Segmented flow controls regulate cooling velocity, achieving a targeted case depth between $2text{ mm}$ and $6text{ mm}$.

• Precision Induction Tempering (500°C – 650°C): Quenched bars are immediately tempered to relieve internal stresses, prevent cracking, and deliver an optimal balance of tensile strength and impact toughness.

• Closed-Loop Automation & Monitoring: Powered by an integrated PLC platform, infrared pyrometers, and digital flow sensors monitor temperature and quench parameters in real time, ensuring consistent metallographic quality across every batch.