When it seems one grease is not enough: protecting bearings under combined extreme demands
Bearing overheating eliminated in a high-speed cellulose hammer mill
Some bearing applications do not present one demanding condition. They present several simultaneously. A hygiene products manufacturer in Italy operated a Siemens cellulose hammer mill with a bearing running at 3,000 rpm under a radial load of approximately 5 kN, in an environment continuously contaminated with cellulose dust. Each of those conditions alone narrows the range of suitable lubricants. In combination, they eliminate most greases from consideration. Interflon Grease HS2 was formulated precisely for this type of application: variable, multi-demand conditions where a conventional grease optimised for a single performance window will inevitably underperform. For a full technical overview of Grease HS2 and its performance across variable operating conditions, visit the Grease HS2 solution page.
The application: three demands, one bearing
The mill runs an SKF 2213 ETN9-C3 self-aligning double-row ball bearing, a C3 internal-clearance variant specified for applications with higher thermal expansion and dynamic loads. The bearing has a bore diameter of 65 mm. At 3,000 rpm, this gives a DN value of >195,000 mm·rpm, a level at which grease selection becomes critical and the range of suitable products narrows considerably. The bearing operates under a radial load of approximately 5 kN. The process environment generates a continuous stream of fine cellulose particles that penetrate bearing housings and contaminate the lubricating grease.
These three conditions interact in ways that make lubrication significantly more difficult than any one of them in isolation:
- At 3,000 rpm, the bearing generates sustained shear forces that degrade conventional grease thickener structures over time, compromising film thickness and overall surface protection.
- Especially under a radial load of 5 kN, any deterioration in the protective lubricating film leads directly to metal-to-metal contact and accelerates friction and wear.
- Cellulose is highly absorbent and fibrous, properties that directly interfere with oil film formation on bearing surfaces and break down the structure of the lubricating grease over time. Combined with the shear forces of high-speed operation and the contact stress of high load, this contamination does not simply add to the problem: it multiplies it.
Each factor accelerates the degradation caused by the others, creating conditions for exponentially worsening friction, wear and lubricant breakdown.
This is the operating profile that exposes the limits of greases formulated for steady-state conditions, and that do not take highly impactful contamination into account. A grease optimised for high speed alone may handle the rotational demands but offer insufficient protection when load and contamination reduce its effective film thickness. A grease developed for high loads may handle the load but degrade too quickly under sustained high-speed shear. Most greases require a choice. Grease HS2 does not.
Before the switch
The hammer mill runs on four bearings, all monitored continuously by the Siemens SIMATIC system. The result, before the switch to Grease HS2, was a consistent and worsening pattern: grease hardening, contamination fouling of the lubricating grease, frequent leakage at the seals, and bearing temperatures climbing above the 65°C warning threshold. On multiple occasions, bearing 4 exceeded the 75°C automatic shutdown limit, stopping the production line and requiring operators to disassemble, clean and re-lubricate before restart.
The Siemens SIMATIC bearing temperature monitor shortly before the intervention. Bearing 1 reads 64.4°C, approaching the 65°C warning threshold. The lubrication timer shows the relubrication interval has been exceeded by more than 22 hours. Warning threshold: 65°C. Automatic shutdown threshold: 75°C.
| “When the monitoring system exceeds 60°C, the machine stops automatically and operators must disassemble and clean the bearing.” From the facility maintenance records, hygiene manufacturing facility, Italy |
Why Grease HS2 works where others struggle
Interflon Grease HS2 is not a high-speed grease, or a high-load grease, or a contamination-resistant grease. It is engineered to deliver consistent protection across all three conditions simultaneously: precisely what this application requires.
Three characteristics of Grease HS2 are directly relevant here:
Its film thickness responds to operating speed across a range of -35°C to +120°C. At 3,000 rpm, it maintains a protective lubricating film designed and optimised to reduce internal friction and temperature increase. During start-stop cycles and load transitions, when metal-to-metal contact is most likely, the adaptive lubricating film thickens to ensure surface separation. This is not a trade-off between two performance states. It is consistent protection across both extremes, and everything in between.
Its non-polar thickener system allows very high additive functionality that remains effective across the full lubrication interval, not only immediately after application. In a high-shear environment, this matters: the grease does not deplete its protective capacity within hours of relubrication, nor does it show a gradual decline in protective performance as additives are used up. With Grease HS2, the additive package protects both the oil and the surfaces at a consistently high level.
MicPol® is Interflon’s proprietary friction-reduction technology. Micronised, polarised additives bond directly to the metal surface, forming a protective barrier that remains effective between lubrication events. In this application, that surface-bonded layer also acts as a physical barrier that helps keep cellulose fibres away from the bearing’s running track and C3 clearance, preventing the absorption of base oil by cellulose debris that would otherwise accelerate grease depletion. The technology is PFAS-, microplastics- and nanotechnology-free.
The intervention
The Interflon Technical Adviser cleaned the bearing thoroughly using Interflon Eco Degreaser, removing all residue of the previous hardened lubricant. This step is critical regardless of what replacement product follows: residual degraded grease limits the performance of any new lubricant and reintroduces the contamination that caused the original failure. The bearing housing was then repacked by hand with Grease HS2 applied with a grease gun, and reassembled within a single scheduled maintenance window.
The SKF 2213 ETN9-C3 bearing during preliminary cleaning and relubrication. Interflon Eco Degreaser was used to remove all residue of the previous hardened lubricant before Grease HS2 was applied. Complete removal of degraded grease before relubrication is critical for this case: residual contaminated lubricant reduces the effectiveness of any replacement product regardless of its formulation.
Results
Temperature data were recorded continuously by the facility’s Siemens SIMATIC monitoring system across all four mill bearings. Following relubrication with Grease HS2 on 5 August 2025, bearing temperatures rose briefly during the initial churning phase as the grease distributed across the bearing surfaces, then fell sharply and returned to the stable baseline of 50–55°C last seen before April 2025.
Bearing temperatures across all four mill bearings, February to September 2025. Bearings 1 and 3 ran on the OEM-specified Klüber Isoflex NBU 15 throughout the entire monitoring period. The sharp drop in bearing 4 (purple) on 5 August marks the point of relubrication with Interflon Grease HS2, after which temperatures returned to the stable baseline last seen before April 2025. The gradual temperature increase in bearing 4 from late September is consistent with seasonal variation in ambient conditions and increased production load; the bearing continued to operate without relubrication throughout. The isolated spike in bearing 2 (pink) on 21 August was caused by pre-existing mechanical damage unrelated to lubrication.
| Metric | Before Grease HS2 | After Grease HS2 |
|---|---|---|
| Peak bearing temperature | 70°C → >75°C (shutdown) | 50–60°C (stable) |
| Automatic production stoppages | Repeated | Zero |
| Grease condition | Hardened, contaminated, leaking | Stable, no leakage |
| Bearing replacement required | Yes (bearing 2) | None |
| “We believe Grease HS2 delivers optimal performance for high-speed applications (3,000 rpm) with high inertial loads (approximately 5 kN.).” Maintenance Engineer, hygiene manufacturing facility, Italy, August 2025 |
A separate temperature spike on bearing 2 on 21 August was caused by pre-existing bearing damage unrelated to lubrication. Grease HS2 slowed further deterioration and the bearing was replaced in a planned intervention with no production impact. No emergency stoppages occurred after the switch.
Bearings 1 and 3 continued to run on the OEM-specified Klüber Isoflex NBU 15 throughout the monitoring period. Their temperature profiles remained higher and less stable than bearing 4 following the switch to Grease HS2, providing an unplanned but direct comparison under identical operating conditions in the same machine.
As of the time of writing, bearing 4 continues to operate without relubrication since the original intervention on 5 August 2025.
Following the documented results, the facility formally registered Interflon as a direct supplier and added Grease HS2 to its approved product list for stock, a decision that reflects confidence in consistent, repeatable performance rather than a one-off fix.
Does your application combine multiple lubrication demands?
High speed, high load, process contamination, variable running speeds and operating conditions: the more of these factors are present simultaneously, the more likely it is that a conventional grease is the limiting factor in your bearing performance. An Interflon Technical Adviser can assess your specific application and identify whether a lubrication mismatch is driving your maintenance costs. Documented outcomes before any broader commitment is required.
Author: Janneke van der Pol, MLT1
Based on technical documentation and field data by: Vincenzo Tais, Technical Director, Interflon Italy
Frequently Asked Questions about bearing lubrication in high-speed applications
Hammer mills and defibrators combine rotational speed, significant load, and process contamination in ways that individually narrow the range of suitable lubricants and, in combination, eliminate most greases from consideration. At 3,000 rpm, sustained shear forces degrade conventional thickener structures. Under high load, any reduction in film thickness leads to metal-to-metal contact. Process contamination with cellulose fibres exponentially increases lubrication problems derived from the combination of high speeds and loads. A grease that handles one of these demands well will often fail when the others are present simultaneously.
Most bearing greases are formulated to optimise performance within a defined operating window: a specific combination of speed, load and temperature. Grease HS2 is engineered differently: its film thickness responds to changing operating conditions rather than being fixed, its non-polar thickener system enables additive effectiveness under high shear and high load conditions, and MicPol® technology provides a surface-bonded protective film that reduces friction and remains active between lubrication events. These three characteristics work together to cover the full range of demands simultaneously.
Yes. Grease HS2 is designed for any rolling element bearing application where operating conditions are variable or where multiple demanding conditions are present simultaneously. It is used across drive shaft lubrication, conveyor bearing applications, electric motor bearings, and other high and variable-speed applications, even where water wash, dirt or process contamination may occur and high loads may be present. It is also frequently used to consolidate several application-specific greases into a single product, reducing stock complexity and eliminating misapplication risk.
With correct lubrication, the facility in this case documented a normal operating range of 45–55°C across all four mill bearings during summer months. Temperatures consistently above 60°C indicate a lubrication problem that warrants investigation. In this application, the automatic shutdown threshold is 75°C. Bearing temperature is one of the clearest indicators of lubrication effectiveness in high-speed applications: a stable temperature within the expected range confirms that the grease is maintaining its protective film under operating conditions. In this application, elevated temperature is a warning that cellulose contamination is negatively impacting oil bleed and protective film formation, a situation that worsens progressively once the first temperature increases are observed.
