Bolt and Nut Galvanizing Drying Tunnel Oven

The Bolt and Nut Galvanizing Drying Tunnel Oven is a continuous industrial heat treatment equipment specially designed for fasteners (such as bolts, nuts, washers, and other components) after processes including electro-galvanizing, hot-dip galvanizing, passivation, and other surface treatments. It is mainly used for continuous dehydration, drying, and hydrogen embrittlement relief treatment (hydrogen de-embrittlement baking) through controlled heating.

Core Applications

Drying After Surface Treatment

After galvanizing, passivation, and rinsing processes, the equipment quickly removes surface moisture from fasteners to prevent moisture retention and secondary corrosion.

Hydrogen De-Embrittlement Baking

High-strength bolts (such as Grade 8.8 and above) are prone to hydrogen embrittlement during acid pickling and electroplating processes. They require prolonged baking at approximately 200°C to promote the release of absorbed hydrogen atoms from the steel structure.

Coating Curing

Used for heat curing of fasteners with special coatings, such as Dacromet (zinc-chromium coating) and Magni coating.

Applicable Standards

The equipment manufacturing and process implementation generally comply with the following standards:

GB/T 3098.1 / ISO 898-1

Mechanical properties of fasteners — Specifies requirements for high-strength fasteners, including heat treatment requirements related to hydrogen embrittlement prevention.

JB/T 10214

Technical requirements for industrial continuous heat treatment mesh belt furnaces.

GB 5226.1

Electrical safety requirements for machinery — Electrical equipment of machines.

GB/T 13345

Specifications related to zinc-water separation and temperature control during metal surface heat treatment processes.

Equipment Features

Continuous Mesh Belt Conveying System

Uses high-temperature-resistant stainless steel mesh belts to achieve automatic loading and unloading of materials, making it suitable for high-volume continuous production lines.

Hot Air Circulation System

Equipped with powerful circulation fans and multiple independent temperature control zones to ensure uniform temperature distribution inside the furnace (usually within ±5°C).

High-Efficiency Energy-Saving Insulation

Adopts high-density aluminum silicate fiber insulation to reduce external surface temperature, minimize heat loss, and improve energy efficiency.

Intelligent Temperature Control

Equipped with PID intelligent temperature controllers or PLC systems with touch screens, allowing precise setting and control of multi-stage heating curves.

FAQ

Q1: What is the typical working temperature of this drying tunnel oven?

A: For ordinary moisture drying, the operating temperature is usually between 100°C and 150°C. For hydrogen de-embrittlement baking of high-strength bolts, the temperature is generally set between 200°C and 230°C.

Q2: Why must high-strength bolts be baked after galvanizing?

A: Acid pickling and electroplating processes may cause hydrogen atoms to penetrate into the steel structure. This can lead to sudden fracture of high-strength bolts under stress levels lower than their nominal tensile strength, a phenomenon known as hydrogen embrittlement. Baking treatment is performed to remove hydrogen atoms and ensure the safety and reliability of the fasteners.

Q3: Can the mesh belt speed be adjusted?

A: Yes. The equipment is usually equipped with a frequency converter for speed regulation. Users can freely adjust the mesh belt running speed according to bolt sizes and required heat treatment time to meet different process requirements.

Q4: What heating energy sources are commonly used for this type of equipment?

A: The most common heating method is electric heating using heating tubes. For factories with suitable conditions, customized heating options such as natural gas, liquefied petroleum gas (LPG), or steam heating can also be provided to reduce operating costs.

Q5: Will excessive accumulation of bolts inside the furnace affect drying performance?

A: Yes. Excessive stacking may cause uneven heating of the lower-layer materials and prevent moisture from evaporating effectively. It is recommended to equip the system with an automatic feeding and spreading device, such as a vibratory feeder, to ensure that bolts are evenly distributed in a single layer or thin layer on the mesh belt.