How does a ball bearing door hinge work?

Question

I've been unable to find a clear explanation of the design principle behind a ball bearing door hinge.

In the image below, the casing for a ball bearing assembly is highlighted.

One description states:

Ball bearings are engineered to throw the knuckle weight against specially hardened steel raceways, which ride on the bearing surfaces. The one-piece cup protects the bearings from moisture and dust.

Can anyone clarify what this means, and the internal layout of the assembly?

I'm also wondering about their durability, given that the mechanism isn't solid metal, but has internal (presumably moving) components under the casing. How thick is the casing, and does it carry all of the vertical load, or is the load shared with the internal components?

Answer 1

The casing is very thin and its purpose it to keep the bearing's balls in place, protect them from dust and grime and to hold in some lubricant. It doesn't share any load. The hinges are very durable as the friction load is much less than with a regular hinge. They are also quieter.

Below are a few diagrams on what might be inside a ball bearing hinge:

Hope this helps.

Answer 2

The casing is just to stop the balls falling out. It doesn't take any of the vertical load. Inside the case there is a series of ball bearings arranged around the hinge pin. The ball bearings take all the load. When the hinge is turned, the balls rotate. The result is that there is no sliding of metal surfaces over each other, so there is very much less friction than with a normal hinge (where the two parts of the hinge just slide over each other). It is the same reduction in friction when you try to drag a bike with its wheels jammed, compared to when the wheels can turn.

They should be much more durable than normal hinges because of the reduced friction (leading to less wear). They can also take much heavier loads without sticking.