Sealed (2RS) vs Open Bearings in Dusty or Wet Environments: When a Seal Protects and When It Costs Life

Does the environment itself rule out an open bearing?

Start with the environment, not the seal. An open bearing has no built-in barrier, so it depends on external or continuous lubrication and offers no protection from dust or moisture^5,9.

In a dirty, dusty or wet machine, contaminant reaches the raceway regardless of how good the grease is, because nothing stands between the two⁵.

That is why open bearings are recommended only where continuous external lubrication is supplied and the environment is free of contaminants — a gearbox or engine sump being the usual case⁹.

A sealed (2RS) bearing is the recommended choice where the environment is dirty, dusty, wet or exposed to moisture, or where a maintenance-free solution is wanted^5,9,11.

Its rubber lip contacts the inner ring and forms a tight barrier against dust, dirt and water splashes, and it holds grease inside for the life of the bearing⁵. If your machine sits in washdown, road spray, fibre or process dust, treat the open option as ruled out before you compare anything else.

2RS or ZZ: water protection against temperature

Once the environment rules out open, the choice between a rubber contact seal (2RS) and a metal shield (ZZ) turns on two variables: water and temperature. Rubber seals give the tighter barrier against water and dust, but the seal material sets a ceiling — standard NBR seals degrade above 100-120°C¹¹.

A higher-temperature material such as Viton or fluoroelastomer is needed above that range at added cost⁶. Metal shields tolerate more heat but do not seal against liquid¹¹.

One supplier's selection table puts the split at these conditions: where moisture or liquid contaminants are present and temperature stays below 100°C, 2RS is recommended for more complete sealing.

Where the environment is dusty, temperature may exceed 120°C and no high waterproofing is required, ZZ is recommended because metal covers resist heat better and still block large-particle dust¹¹. Note that the practical ceiling belongs to the seal material, not to "a sealed bearing" as a class.

A claim that sealed motor bearings survive below 150°C reflects a different seal material and application, not a single universal limit². If your duty sits between those two conditions — warm and wet — the sources give no rule.

Ask the supplier which seal compound is quoted and at what temperature it is rated.

When the seal's own friction costs more life than it saves

A contact seal is not free. Seal friction from the lip can account for 30-70% of total bearing friction torque at low to moderate speeds, on top of the rolling and lubricant-churning components that both ZZ and 2RS share¹⁴.

That friction becomes a life problem through a specific cycle: the heat it generates accelerates grease oxidation, oxidised grease thickens, higher viscosity raises friction further, and the bearing runs hotter still¹⁴. One reported case shows the cycle in practice.

A textile loom drive motor ran 2RS bearings near the bearing's limiting speed, and the seal friction was generating enough heat to drive grease oxidation. Switching to ZZ dropped bearing temperature by 12°C and doubled grease service life¹⁴.

The motor enclosure was already sealed against fibre ingress, so the seal was adding heat without adding protection¹⁴. That is the condition to look for in your own machine: if the housing, oil seal or enclosure already excludes the contaminant.

And the bearing runs near its speed limit, the seal is the problem rather than the protection. The sources do not give a general rule for when seal friction outweighs ingress protection, so weigh the two against your own duty.

Does the duty fit inside a lubed-for-life sealed bearing?

Contact seals cut the speed a bearing can run. Two publishers report a reduction of roughly 30-40% versus an open or shielded bearing of the same size^6,22.

One gives a worked size: a 6202 rated 20,000 rpm open is limited to about 12,000 rpm in 2RS form under grease lubrication⁶. If your shaft speed is already close to the open-bearing rating, the sealed version may not be rated for the duty at all.

Expected life is the second check. One source argues that close-fitting seals run hot while loose-fitting seals fail to exclude air and moisture.

It concludes that lubed-for-life bearings are precluded where expected life in a typical plant environment exceeds three years². That is a strong position from a single source, not an industry threshold.

But it points at a real trade-off: a sealed bearing is generally not re-greased, so its factory grease fill has to last the whole service interval^5,9.

Before you commit, confirm the sealed variant's speed rating for your size and lubrication, and check whether your target service interval is one the grease fill can actually reach.

Lubricated for life, or re-greased?

The cover choice and the lubrication plan have to agree. Sealed bearings are generally lubricated for life and are not re-greased during service; they come pre-lubricated and the seals keep the grease in^5,9.

Open bearings are the opposite — they rely on external or continuous lubrication and need regular lubrication and cleaning, which is only practical where the environment is clean and the lubrication point is accessible^5,9.

Grease is the common fill for both ZZ and 2RS bearings, while open bearings more often run on oil, since the open design lets oil circulate in and out freely⁷. That difference matters to your maintenance plan: if you specify 2RS, you are committing to a sealed grease charge for the interval.

And if you specify open, you are committing to a lubrication route that must actually be reachable and kept up. Where the environment is clean and dry with continuous external lubrication, an open bearing is suitable and a seal is not required^9,11.

Where low friction matters more than maximum sealing — a clean, dry, high-speed duty — a shielded bearing is preferred over a sealed one⁹.

Will the cover suffix force a housing or shaft change?

For a given bearing size, the cover suffix does not change the installation dimensions. Using the 608 as the worked example, bore, outer diameter and width are identical across open, Z, ZZ, RS and 2RS variants; the suffix changes only the protection capability and operating characteristics¹⁶.

That means you can settle the seal decision late, after the environment, temperature and speed checks, without reopening the housing or shaft design.

It also means a change from open to 2RS on an existing machine is a like-for-like swap on fit, so the decision can be revisited if the first choice proves wrong in service.

What to confirm before the RFQ goes out

The sources settle the selection logic but not the numbers behind it. Confirm these points with the supplier rather than assuming them from the seal type.

• ✓Ask for the seal compound and its rated temperature range, not just "2RS" — standard NBR and fluoroelastomer have different ceilings.
• ✓Ask for the sealed variant's speed rating at your size and lubrication, since contact seals cut maximum speed by roughly 30-40%.
• ✓Ask whether the seal material is compatible with the specified grease or oil; no source in this set gives a compatibility table.
• ✓Ask for a formal ingress rating if you need one — no source states an IP rating or tested dust/water standard for bearing seals.
• ✓Ask for price and lead time for the sealed and open variants; no source provides either.
• ✓Where the environment is harsh and dusty, ask whether a non-contact labyrinth seal can be layered ahead of the contact seal as a first barrier.
• ✓Confirm the service interval the factory grease fill is expected to cover, since sealed bearings are generally not re-greased.

Where the sources disagree

Two points in this decision are not settled by the evidence, and both affect whether a sealed bearing is viable for your duty.

Before you request a quote

• The evidence leaves this open — put it to the supplier: no source states a formal IP rating or tested dust/water ingress standard for bearing seals.
• The evidence leaves this open — put it to the supplier: no source gives seal-material friction or seal-life curves as a function of temperature.
• The evidence leaves this open — put it to the supplier: no source provides a definitive DN or rpm limit for sealed versus open bearings at a specific size and lubrication.
• The evidence leaves this open — put it to the supplier: no source gives a seal-material/lubricant chemical compatibility table.
• The evidence leaves this open — put it to the supplier: no source quantifies contamination level (particle size, concentration) or moisture level.
• The evidence leaves this open — put it to the supplier: no source gives relubrication interval figures for open bearings in contaminated environments.
• Request a written quote with price basis, MOQ, tooling, payment terms and production lead time.
• The evidence leaves this open — put it to the supplier: no source provides lead times or stock availability data for sealed versus open bearings.