Anatomy of the Silent Fan

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II. Modified Sleeve Bearings

Many manufacturers have developed variants of sleeve bearings that try to combine the positive aspects of sleeve bearing fans along with merits of ball bearing fans. The better known of these different bearing types include Hydro Wave by Panaflo (now part of NMB), Hypro by Adda, Sintec by EBM/Papst, and most recently, Fluid Dynamic by Sony. The Hydro Wave and Sintec bearing types go back a number of years; the FD bearing is relatively new for fans, although it has been used in hard drives since around 2001.

While precise details differ, and engineers from different camps would probably debate relative merits with some conviction, the broad goals of these modified sleeve bearing technologies is to...

  • reduce friction across the shaft / bearing surface,
  • eliminate the relatively quicker loss of lubricant in the bearing,
  • allow great freedom in working position (i.e., not just vertical), and
  • improve high temperature performance and longevity

Details of how these bearing types work are contained in company-sourced documents, which, as you would expect, contain strong partisan opinions. Nevertheless, they are well worth studying if you want to learn more about fan bearing design and the impact they have on fan acoustics.

  • Panaflo Hydro Wave Bearing by Panaflo (Panasonic) (quoted from the Anglia (UK) web site) The Hydro Wave bearing is found on fans from a number of different brands, but mostly on Panasonic fans. The brand is now part of NMB, but HW fans are still listed in the NMB-MAT DC axial fan section of Panasonic's industrial products site. The HW fans have model numbers that start with the letters FBA.

    "HWB addresses the traditional weakness of sleeve bearings… axial friction. By utilizing a unique system, the thrust plate “floats” on a circulating film of oil, which greatly reduces the axial friction and the bearing’s deterioration. The HWB pattern on the bearing virtually eliminates thrust plate contact which is depicted above. As the shaft rotates it acts as a pump constantly circulating the oil in the radial, as well as the axial direction. The sealed system and reservoirs of oil maintain the proper lubrication to minimize mechanical contact and prolong the fan’s life expectancy. The radial direction analysis shown above is essentially the same as a traditional sleeve bearing. Panasonic’s unique HWB reduces the axial contact."

  • Adda, another major DC fan maker for the PC industry, confusingly refers to a proprietary bearing called Hypro: HY - "Hydro-dynamic wave" and PRO - "Oil protection system" about which they claim similar strengths.
    1. By means of reducing the surface friction area between the shaft and the bearing, the bearing temperature will be reduced naturally when HYPRO fan operates.
    2. The unique bearing construction can store and maintain more oil volume with an oil-cycling protection.
    3. The bearing is made of a new alloy material harder than bronze.
  • Sintec Bearing by EBM/Papst (quoted directly from the EBM/Papst web site) This bearing type is found only on certain EBM/Papst models.

Fig. 1: Lubricant circuit in Sintec bearing

"In fact, the single most important factor affecting the reliability of a fan is the composition and reliability of the lubrication system and not the fatigue life of the bearing itself... Papst has conducted comparative life tests which show that fans with particular sleeve bearing systems can now achieve similar reliability to those with ball bearings. i.e. an L10 lifetime of 80,000 hours of operation at an ambient temperature of 40°C.

"Behind this improvement in sleeve bearings lies significant developments in sintering technology, in particular the unique Sintec process used by Papst. This process uses a special metal powder that is pressed into the required shape at very high pressure and then sintered at high temperature. The material created in this way is porous, with the pore volume taking up about 15 to 30% of the bearing. The pores are then filled with lubricant using a vacuum soaking process and a re-circulating reservoir is created to ensure continuing operation over long periods.

Fig 2: The compact Sintec bearing guarantees excellent alignment and a large oil reservoir.

"This unique design of Sintec bearing ensures that lubrication is maintained even when the fan is at rest, so that the bearing is never dry, even during the crucial startup phase. At rest the capillary effect forms a film of lubricant between the shaft and bearing so that lubricant never drains away from the bearing. Then when the fan starts to rotate, a slight pressure difference causes a hydrodynamic pressure wave to be set up in the bearing gap as a result of the rotary movement of the shaft causing the lubricant to circulate around the bearing. This hydrodynamic state produces a lubricating bulge at the narrowest part of the bearing gap, exactly where friction should be greatest, ensuring that the shaft and bearing no longer touch and lubricant is always supplied to exactly where it is needed.

"To ensure re-circulation, the oil pressure that is greatest at the narrowest place of the bearing gap forces the lubricant into the pores of the sintered bearing. To compensate for this, oil flows out from the sintered metal in areas of lower pressure and circulates to the areas of high pressure where it is needed. This re-circulating circuit creates a stable state as in Fig 1.

"To allow the Sintec bearing to take up the radial load of the fans, two bearing positions with sufficient axial spacing are required. The ideal solution is to use double sintered bearings with two separate bearing positions in a single sintered part. The main advantages are improved alignment and a considerably larger oil reservoir due to the larger bearing volume.

"The design also features an additional axial bearing disc which ensures that a stable position is reached in both axial directions. By taking up the axial lateral forces in either direction, fans can be mounted with the shaft in a non-horizontal plane. Under this condition a film of lubricant is formed between the rounded end of the shaft and the disc and a state is achieved similar to that normally seen in a radial bearing."

Fluid Dynamic Bearing (PDF document, linked directly from Jaro Thermal) There appears to be a handful of brands offering fans that employ the FDB bearing, and they generally identify Sony as the maker or inventor of the bearing itself. No information about FDB could be found on any of Sony's English-language sites. The fan brands we found that use FDB bearings are Jaro Thermal, Arctic Cooling, and Scythe. It's clear that Scythe does not manufacture its own fans. Whether Arctic Cooling also employs OEMs is not clear. However, it is clear that Jaro does manufacture its own fans; it's possible that Jaro may be the actual manufacturer of all the FDB fans mentioned above.

The text below is quoted from the web site Green Supply Line:

"The FDB fan's unique design eliminates surface contact between the shaft and bearing, which translates into lower noise, higher reliability, and a longer operating life. The fan also uses a patented "vacuum impregnating oil" that eliminates air bubbles and oil leakage, which means no oil leakage due to changes in air pressure.

"The FDB bearings are manufactured with an extremely thin, herringbone-shaped groove on the interior wall to ensure a constant oil layer. This provides an exceptionally low noise level as low as 19.7 dB for a 92 x 92 x 25 mm fan, said the company. Life expectancy is guaranteed for 80,000 hours at 25 degrees C. Click the link for a look at the FDB bearing's structure.

"The life of this model is achieved by a V-shaped groove that generates the dynamic fluid pressure on the inner surface of a sintered metal sleeve allowing dynamic pressure to build up in the center of the shaft, said Dennis Eisen, vice president of sales for Jaro Thermal. In addition, the less vibration caused by the bearing results in the lower noise, he said.

"The FDB fans may replace conventional dual ball-bearing systems, offering a higher maximum operating temperature up to 90°C compared with 70°C for fans with dual-ball bearing systems. The operating temperature range is -10°C to 90°C. The FDB fans are RoHS compliant."

The following table was extracted from Jaro's brochure, which suggests that the FDB is the most advanced and best performing of all fan bearings.

Jaro's FDB-promotional comparison.
Note: 1B1S = "1 ball, 1 sleeve" bearing; 2BB = two ball bearing

This is the end of our look at fan bearings for now, but the list of fan bearing types does not stop here. There are different types of ball bearing fans, such as dual and single ball bearing fans, mixed sleeve / ball bearing fans, ceramic ball bearing fans, magnetic levitation bearing fans, and so on. Our experience has taught us to be wary of so-called revolutionary designs, and most ball bearing fan variants don't sound as good as the best sleeve and modified sleeve bearing fans. When we run across quiet fans using other types of bearings, we'll tell you about those bearings and update this article.

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