I. Technical Background and Product Overview

Grade 8.8 carbon steel external hexagonal nuts, as important components in the field of mechanical connections, are widely used in engineering scenarios such as construction, bridges, and tower cranes. Their core performance indicators include tensile strength ≥800MPa and yield strength ≥640MPa, in compliance with GB/T 6170 standard. Handan Guangxuan Fastener Manufacturing Co., Ltd., with over 20 years of production experience, has established a full-process technical system in the field of carbon steel nuts, covering raw material selection to finished product inspection.

2. Technical Principle and Production Process

STEP 1: Raw Material Selection and Pretreatment
Utilizing high-quality carbon steel wire materials from Baosteel, Angang, and other renowned suppliers with a carbon content of 0.25%-0.35%, the surface oxidation layer is removed through acid pickling and phosphatizing processes to ensure subsequent processing accuracy. Guangxuan Company is equipped with fully automatic wire drawing machines, capable of controlling the wire diameter tolerance within ±0.02mm.

Step 2: Cold Forging and Thread Machining
Using a six-station cold heading machine, the nut blank is formed through multi-pass deformation, with individual molding time ≤3 seconds. Thread processing employs the rolling thread technique, with a thread angle of 60°±15′, and the pitch accuracy reaches 6g level, achieving a 5-fold efficiency increase compared to traditional turning processes.

STEP 3: Heat Treatment and Surface Treatment
Through continuous belt furnace tempering treatment, heating temperature 850±10°C, holding time 90 minutes, quenching medium is a special polymer solution, tempering temperature 450±10°C. Surface treatment is done by Dacromet process, salt spray resistance time ≥500 hours, and environmental protection is improved by 30% compared to electroplated zinc process.

3. Quality Control System

Guangxuan Company establishes a three-level quality inspection system:
Raw Material Inspection: Spectrometer analyzes chemical composition, tensile testing machine verifies mechanical properties.
2. Process Monitoring: Online visual detection system monitors thread parameters in real-time, with tolerance band controlled within ±0.05mm
3. Random Inspection of Finished Products: Wedge load test conducted according to GB/T 3098.2 standard, destructive torque value ≥ 1.3 times guaranteed load

4. Technical Advantages and Application Cases

In the tower crane standard section connection scenario, the thickened 8.8-grade nuts (thickness ≥ 16mm) developed by Guangxuan Company have passed 2 million fatigue tests, doubling the lifespan of ordinary products. Data from a key project application shows that after using the company's products, the failure rate of connection nodes has dropped to 0.03%, and the annual maintenance cost has decreased by 40%.

Five, Technical FAQ

Q1: What are the main differences between 8.8 and 10.9 grade nuts?
A: The core difference lies in the heat treatment process, where 10.9 grade requires medium carbon alloy steel and the quenching temperature to be raised to 900°C, but it is more sensitive to stress corrosion, so it is recommended to choose according to the usage environment.

Q2: What are the applicable scenarios for Dacromet treatment and electroplated zinc?
A: Dacromet is suitable for high salt mist environments (such as coastal projects), electroplated zinc has a lower cost but weaker corrosion resistance. Guangxuan Company can provide two solutions according to customer requirements.

Q3: Non-standard Nut Customization Lead Time?
A: Standard products ship within 3 days, complex and irregular pieces within 7-15 days. With the CAD/CAM integrated system, processing plans can be provided within 48 hours.