A loading dock door starts to bite its latch. The lock side has dropped half an inch, and the top edge scrapes the frame head every cycle. Nobody suspects the two pieces of steel holding the whole leaf: the hinges. The delay is expensive, because a sagging door points to worn hinge knuckles or pins, and every extra week grinds the whole opening out of square.
Our factory answer is shorter than the catalog: the parts you choose decide how the door ages.
How Hinges Carry an Industrial Door
Follow the load path. The full weight of the door hangs on its hinges through every opening cycle. The hinges pass it into the roller stems, and the industrial door tracks and rollers hand it on to the building. Panel hinges on a sectional door do double duty, carrying the next panel and the roller stem together. A hinge is therefore the axle of the door: knuckle, pin and leaves working as one bearing.
Reading it as a bearing explains most field behavior, because bearings fail from overload, dirt, corrosion and lost lubrication, and hinge knuckles fail the same way. The rest of this page applies that logic: pick the class