At Qingdao SunKai Marine Supplies Co., Ltd., the production workshop for dock rubber fenders is a hive of activity. The warm air is filled with the distinctive scent of natural and synthetic rubber, signaling the start of a meticulous manufacturing process that ensures the highest safety standards for global ports. Here, every step—from raw material preparation to final inspection before vulcanization—is crucial to guarantee that the fenders can withstand the enormous instantaneous forces when ships berth.
“Poor raw material pretreatment can make even the most advanced processes ineffective,” explains Old Chen, head of the raw material area. Workers carefully cut natural rubber blocks into uniform pieces and immerse them in a cleaning tank to remove surface oils and impurities.
Once cleaned, the rubber is blended with styrene-butadiene rubber, carbon black, anti-aging agents, and other auxiliary materials in precisely controlled proportions. “For container terminal fenders, we increase carbon black by 8% to improve wear resistance. For LNG terminals, flame retardants are added to meet safety requirements,” Old Chen adds.
The mixed materials are then processed in a high-pressure internal mixer at 140℃ for 30 minutes, transforming the raw ingredients into a homogeneous, elastic compound rubber. This compound is pressed into sheets of varying thicknesses on a calender, cooled, and then subjected to strict quality inspections to ensure adequate tensile strength before proceeding to the next stage.
At the carcass forming station, a manual + mechanical workflow ensures every fender meets stringent standards. Workers fix custom steel frameworks on rotating workbenches and use semi-automatic winding machines to wrap the rubber sheets alternately with high-strength nylon cord fabric.
During winding, workers carefully monitor density and bonding, using hydraulic compactors every five layers to prevent air bubbles or loosening. Special attention is given to stress concentration points such as fender shoulders, which are reinforced with additional cord layers and marine-grade adhesive.
For large fenders with curved surfaces, SunKai has developed adjustable molds to ensure precise fitting of rubber sheets and prevent arc deviation. “After improving our molds, the fender qualification rate increased from 92% to 99.5% during simulated impact tests,” says the technical supervisor.
Before vulcanization, every fender undergoes full physical examination:
Ultrasonic scanning detects hidden defects like interlayer separation or embedded impurities.
Laser range finders measure critical dimensions (diameter, length) with ±2mm accuracy.
Air tightness testing ensures sealed interfaces hold 0.2MPa without leakage.
“Last month, ultrasonic testing revealed a 1mm impurity in a batch. We immediately reworked the entire batch. Safety is non-negotiable,” says the head of quality inspection.
Fender carcasses that pass layer-by-layer inspection enter the vulcanization tank, completing their final curing transformation. This step gives SunKai’s dock fenders their strength, durability, and impact resistance, making them ideal for ports worldwide.
Today, SunKai produces a range of arch-type, drum-type, and square-type dock fenders, supplying both domestic ports and export markets in Southeast Asia, Europe, and beyond. With decades of experience and solid forming technology, SunKai fenders have become the core equipment for port safety and ship protection.
High-Quality Materials: Natural and synthetic rubber blended with precision.
Advanced Production Equipment: Internal mixers, calenders, winding machines, and vulcanization tanks.
Rigorous Testing: Ultrasonic, laser measurement, and air tightness inspection.
Global Reach: Serving domestic ports and international customers as a trusted China marine equipment supplier.
By combining technical innovation, meticulous quality control, and professional expertise, SunKai Marine Supplies ensures that every fender delivers maximum safety, reliability, and longevity.
