How Is a Mooring Buoy Made?
Other People Are Reading
-
Step 1: Blow Molding the Sphere
-
Most mooring buoys are made from high-density polyethylene (HDPE) through a common manufacturing process known as "blow molding." To begin, small pieces of HDPE are poured into a hopper where they are melted into a homogenous liquid. The liquid HDPE then flows into a long cylinder with a giant drill running along it. This drill rotates slowly, pushing the molten HDPE toward the end of the cylinder.
Once at the end, the HDPE flows into a slightly cooler chamber called the "die head." The die head chamber has a long cylinder running from top to bottom, where a second opening is. This cylinder is known as the "blow pin." An automated gear lifts a gasket at the bottom on the chamber, allowing the liquid HDPE to gently ooze down around the blow pin.
The bottom on the blow pin extends into a sphere-shaped mold, comprised of removable hemispherical molds. Once a set amount of semisolid HDPE is hanging from the blow pin, pressurized air is pumped into the blow pin via an opening at the bottom.
The HDPE is too thick for the air to escape; rather, the pressurized air inflates the HDPE like a balloon. Meanwhile, as the HDPE expands, new molten HDPE is fed into the mold from the die head chamber. Once the HDPE touches the surface of the metal hemispheres, it expands to fit to the entire sphere. The cool metal causes the HDPE to harden, creating a permanent sphere shape.
The gasket then seals shut and the buoy can be removed.
Step 2: Filling the Sphere with Polystyrene Foam
-
The buoy now consists of a hollow HDPE sphere with 1 mm-thick walls and a small opening at the top where the blow pin was. Next, to ensure that buoy stays buoyant even in the event of a leak, two liquids are poured in the opening. Once in contact, these chemicals spontaneously form a hot, rising foam of polystyrene that fills the entire inside of the sphere.
After an hour, when the foam has completely hardened, the manufacturer will drill a 3- to 4-cm wide hole from the blow pin opening to the opposite side. Any jagged edges from the drill are sanded down and paint/decals are applied to the outer shell.
-
Step 3: Fitting the Buoy with Chains
-
A rod with bolt threads along both ends is passed through the central hole. Special disk-shaped seals called "washers" with nuts just above them are screwed firmly to each end of the rod, creating a waterproof seal for the entire hole.
The rod twists into loops on each end, designed for special metal loops with bolts ("shackles") that attach to chains to the mushroom anchor below and the ships above.
-
