I. Mesh-Belt Low-Temperature Tempering Furnace (Front-End Host)

Functionality

1. Heating method: Electric heating optional; forced-air circulation design ensures uniform furnace temperature, adjustable between 300–450°C.
2. Structure: Continuous conveyance via a stainless steel heat‑resistant mesh belt, enclosed furnace chamber, and a mild protective atmosphere to prevent back‑fire oxidation and yellowing.
3. Process function:

1. Discharge: After tempering, allow the parts to cool naturally in air until the temperature drops below 80°C, then transfer them to the blackening bath.

II. Continuous Blackening Tank (Oxidation and Bluing Treatment Unit)

Process Principle

Equipment Composition

1. Main blackening tank: carbon steel liner with anti-corrosion steel plate, heated by electric heating or thermal oil, with temperature control set at 135–145°C; the tank is equipped with a stirring and tumbling mechanism to ensure complete immersion of the workpieces in the treatment solution.
2. Pre‑wash tank: Quenched workpieces are first rinsed with clean water to remove dust and contaminants, thereby preventing contamination of the blackening solution.
3. Post‑overflow rinse tank: After blackening, perform multi‑stage rinsing with clean water to remove residual strong alkaline solution from the surface, thereby preventing re‑whitening and white spotting.
4. Chemical formulation: high-temperature alkaline blackening agent, cyanide-free and environmentally friendly formula, producing a uniformly black coating.

Key role

• Appearance: The screw features a uniform black finish, enhancing the overall aesthetic of the hardware product.
• Basic corrosion protection: isolates from air to provide mild rust prevention, laying the groundwork for subsequent oiling.
• It masks the slight oxidation discoloration from heat treatment and ensures consistent color across batches.

III. Hot-air Drying Oven (dewatering and drying after blackening and water washing)

Functionality

1. Heating method: electric hot-air circulation / fuel-fired hot air; temperature adjustable from 100 to 160°C.
2. Structure: High-speed hot-air blowing on both the upper and lower sides, with continuous conveyor belt transport in a tunnel configuration.
3. Design Highlights:

Defects of Not Drying

IV. Automatic Rust-Prevention Oil‑Bath (Final Anti-Corrosion Process)

Two mainstream structures are available.

1. Soaking-type oiling tank The workpiece is fully immersed in a rust-preventive oil bath, with bottom‑mounted vibration to drain excess oil, which then automatically returns to the circulation system.
2. Spraying + Roller-Applying Oil : Suitable for small self-tapping screws, providing a thin, evenly distributed oil film under low pressure, saving oil and preventing oil buildup.

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