The Truth About Fluid Dynamic Bearing (FDB) Fans

[nextpage title=”Introduction”]

The fluid dynamic bearing (FDB) was first used in hard disk drives. It is a modification to the standard sleeve bearing to improve the lubrication of the bearing, and thus increase the life span of the fan while retaining one of the most positive aspects of sleeve bearing fans, which is the low noise level. However, what can be classified as fluid dynamic bearing is somewhat controversial, and designs vary greatly.

According to some manufacturers, in order to be considered a “true” fluid dynamic bearing, the inner of the bearing must have herringbone-shaped inner grooves, as shown in Figures 1 and 2.

Figure 1: Matsushita-patented fluid dynamic bearing design

Figure 2: Matsushita-patented fluid dynamic bearing design

However, this particular design is patented by Matsushita (Panasonic) and, therefore, only fans with bearings manufactured by companies that paid licensing fees to Matsushita will have this design. Because of that, bearings based on this design are more expensive, increasing the price of final products.

Bearing manufacturers that invested money licensing this design spend a good deal of time and money convincing its clients (fan manufacturers) that only bearings using this design can be called “fluid dynamic.” Therefore, there is a tendency for fan manufacturers that use Matsushita’s patented fluid dynamic bearings to think or even say that fans from other manufacturers using different fluid dynamic designs are “fake” or not “true” fluid dynamic bearings. Technically speaking, any kind of design that uses the principle of hydrodynamics can be called “fluid dynamic,” as this name, apparently, is not patented. Performance, however, may be different depending on the design that is used.

So, there is a second group of fan manufacturers that use a different design for their fluid dynamic bearings, as they decided to create their own design instead of licensing Matsushita’s design. From our research, these alternative designs vary greatly (we could identify four different ones within the thirteen fans we disassembled), with some more sophisticated (and likely better) than others.

Here is where the confusion starts. One of these alternative designs (let’s call it “alternative design 1”) is called “fluid dynamic bearing” by the companies that use it, but they are also called “rifle bearing” by several other companies. So, while technically speaking rifle bearing is a type of fluid dynamic bearing, companies that use the Matsushita-base design feel that this particular alternative design should use a different name (“rifle”), to make it clear for the user that the design of the bearing is not the same.

We have to agree that using two different names for the same thing is confusing. Users may think that a fan with an FDB bearing is better than a fan advertised as using a rifle bearing, while in fact this FDB fan may use a rifle bearing, and there may be no difference in the technology used by the two fans.

Some of the companies that use a non-Matsushita design call their bearings hydro dynamic, or HDB, in order to make it clear that they use an alternative design and not Matsushita’s. We think this is a good idea.

The difference of the design used on the bearing helps to explain why some FDB fans are much more expensive than others: fans with Matsushita’s bearing design will be much more expensive than a fan with a less sophisticated and easier to manufacture FDB design.

In the table below, we summarize the fans we disassembled (all of them sold as either “fluid dynamic bearing” or “hydro dynamic bearing”) and what we found out about them. Since we’ve already shown the Matsushita design in Figures 1 and 2, in the next pages we will show the other four designs we identified.

[nextpage title=”Alternative Design 1 (Rifle Bearing)”]

The “alternative design 1” we identified is shown in Figure 3, and is used in fluid dynamic bearing fans from Aerocool, Arctic, BitFenix, and SilenX. On this design, the inside of the bearing is smooth, and there are several grooves alongside the exterior of the bearing, where lubricant flows from one end of the bearing to the other. The number of grooves vary: we saw twelve on the Aerocool Shark 120mm Black Edition and Arctic AFACO-120P0-GBA01, ten on the Arctic AFACO-12PP0-GBA0, and nine on the BitFenix BFF-LPRO-12025R-RP and SilenX EFX-12-15. From all “alternative” fluid dynamic bearing designs, this is the most high-end. The confusion here is that this kind of bearing is also called “rifle bearing” by several companies. Companies that sell fans based on Matsushita’s design think that fans based on this alternative design should all be called “rifle bearing,” so users would be able to compare apples to apples.

Figure 3: Alternative design 1 – rifle bearing (Aerocool Shark 120mm Black Edition)

[nextpage title=”Alternative Design 2″]

This design, found on the Logisys LT80UVBL fan, is the simplest of all designs we saw, and we even question if it could be classified as fluid dynamic – in our opinion, it is a regular sleeve bearing. The only difference between this design and a regular sleeve bearing is the presence of two grooves alongside the exterior of the bearing. Differently from the alternative designs 1 and 3, the external groove is not connected to the ends of the bearing, so we wonder how the grooves would make the lubricant flow. The interior of the bearing is smooth.

Figure 4: Alternative design 2 (Logisys LT80UVBL)

[nextpage title=”Alternative Design 3″]

This design, used by the NZXT FX-140LB, is comprised of a single groove alongside the exterior of the bearing, but differently from what happens with the alternative designs 2 and 4, this groove connects both ends of the bearing, allowing the lubricant to flow. The interior of the bearing is smooth.

Figure 5: Alternative design 3 (NZXT FX-140LB)

[nextpage title=”Alternative Design 4″]

And the fourth alternative design we saw was used by the Thermaltake AF0043 fan, which is sold as hydro dynamic bearing (HDB), not fluid dynamic (FDB). This is a small yet important difference, as the savvy user can assume that HDB fans are not based on Matsushita’s design. It has three grooves alongside the exterior of the bearing, and the exterior of the bearing has a somewhat different shape. Since there is no connection between the grooves and the ends of the bearing, we wonder how these grooves transport lubricant. According to Thermaltake, this bearing is from YS Tech and is called Sintetico. The presentation available is poorly written and it does not explain properly how this bearing works.

Figure 5: Alternative design 4 (Thermaltake AF0043)