SF-1 (DU) and SF-2 (DX) are both composite bushings designed to reduce friction, wear, and maintenance in industrial machinery and other demanding applications. The main difference is their material structure and lubrication behavior.
SF-1 (DU) is a steel-backed, sintered bronze-based composite bearing material with a porous bronze layer impregnated with a solid lubricant and covered by a low-friction PTFE-based sliding layer. It is widely used where low friction, high load capacity, and minimal additional lubrication are required.
SF-2 (DX) is also a layered composite material, but its structure is designed for applications where higher wear resistance, greater load capability, and better tolerance of lubrication conditions are required. DX materials are commonly selected for applications involving higher loads, oscillating motion, or less favorable lubrication conditions.
The best choice depends on load, speed, temperature, lubrication, mating surface condition, shaft hardness, and the expected service life.
What Are SF-1 (DU) and SF-2 (DX) Composite Bushings?
SF-1 (DU) and SF-2 (DX) are sliding bearing materials used to form self-lubricating or low-maintenance bearings and bushings. They normally consist of several functional layers, with each layer serving a different purpose.
A typical composite bushing combines:
The result is a bearing material that combines mechanical strength with controlled friction and wear resistance.
Unlike a conventional bronze bushing that may depend on regular grease or oil, composite bushings can operate with little or no additional lubrication in many applications.
SF-1 (DU) vs. SF-2 (DX): At a Glance
| Property | SF-1 (DU) | SF-2 (DX) |
| Material type | Multi-layer composite | Multi-layer composite |
| Typical construction | Steel backing + sintered bronze + low-friction sliding layer | Steel backing + porous bronze/polymer-based sliding structure |
| Main purpose | Low friction and reduced maintenance | High wear resistance and demanding sliding applications |
| Lubrication | Often maintenance-free or requires very little additional lubrication | Can work with initial lubrication and/or additional lubrication depending on design |
| Friction properties | Very low friction | Low friction with strong wear performance |
| Load capacity | High for a thin-wall composite bearing | High, particularly in demanding applications |
| Wear resistance | Very good under suitable conditions | Very good, especially where lubrication and load conditions vary |
| Typical applications | Automotive, hydraulic, industrial machinery | Industrial machinery, hydraulic systems, automotive and heavy-duty mechanisms |
| Maintenance | Low | Low to moderate depending on operating conditions |
| Best selection factor | Low friction and maintenance-free operation | Load, wear, lubrication and operating conditions |
Exact properties vary by manufacturer and material grade. Engineering selection should therefore be based on the supplier's current material data rather than the product name alone.
Material Composition of SF-1 (DU)
SF-1 (DU) is a well-known family of composite bearing materials used for low-friction applications.
A typical SF-1 (DU) structure contains three functional layers.
Steel Backing
The steel backing provides mechanical support and gives the thin bearing wall its structural strength.
This allows the bushing to have a relatively small wall thickness while maintaining good dimensional stability.
The backing also helps transfer the applied load into the housing.
Sintered Bronze Layer
A porous sintered bronze layer is bonded to the steel backing.
The bronze layer provides mechanical support for the sliding layer and creates a controlled interface between the steel backing and the bearing surface.
Its porous structure can also retain lubricating materials.
PTFE-Based Sliding Layer
The sliding surface normally contains PTFE and other additives selected to control friction and wear.
This layer is responsible for the low-friction behavior of SF-1 (DU).
Depending on the specific formulation, the sliding layer can contain solid lubricant additives that help maintain low friction during operation.
This layered construction is one reason SF-1 (DU) can provide good friction properties without depending entirely on conventional oil or grease lubrication.
Material Composition of SF-2 (DX)
SF-2 (DX) is another class of composite materials used for bearings and bushings.
The material is designed for applications where the bearing must withstand repeated sliding contact while maintaining good wear resistance.
A typical DX-type construction includes:
The exact composition varies between manufacturers and product grades.
This difference matters because two products marketed as DX may not have exactly the same friction coefficient, wear rate, temperature range, or load capacity.
For purchasing and engineering work, always compare the technical data for the actual material grade.
Why Sintered Bronze Is Used in Composite Bushings
Sintered bronze provides a strong and porous intermediate layer between the backing and sliding surface.
The powder metallurgy process creates interconnected pores in the bronze.
These pores can provide space for lubricants and help form a stable transition between the structural backing and the sliding layer.
Sintered bronze is also useful because it offers good dimensional stability and supports the polymer sliding layer under load.
This is different from a traditional solid bronze bushing, where the entire bearing is made from a relatively thick bronze alloy.
A composite design uses each material where it performs best:
Lubrication: SF-1 (DU) vs. SF-2 (DX)
Lubrication is one of the most important differences to consider when comparing composite bushings.
SF-1 (DU) Lubrication
SF-1 (DU) is often selected for applications requiring maintenance free or very low-maintenance operation.
The low-friction sliding layer contains lubricating components that reduce direct metal-to-metal contact.
As a result, many SF-1 applications do not need continuous grease or oil supply.
This can be useful when:
However, "maintenance-free" should not be interpreted as "suitable for every dry-running application."
Load, sliding speed, temperature, shaft roughness, counterface hardness and environment all affect bearing life.
SF-2 (DX) Lubrication
SF-2 (DX) materials can also provide low-friction operation, but the material family is often used in applications where additional lubrication can be provided when required.
This can be useful for applications with:
A lubricated DX bushing can use grease or oil to reduce friction and heat and to help remove wear particles from the sliding interface.
The correct lubrication method depends on the specific DX grade.
What Does "Maintenance-Free" Mean for a Composite Bushing?
A maintenance-free bearing is a bearing designed to operate without routine relubrication under its specified operating conditions.
It does not mean that the bearing can ignore installation or operating limits.
For example, a bushing may require no regular grease supply but still fail prematurely if:
Therefore, maintenance-free operation is a system-level result, not simply a property of the bearing material.
Wear Rates: What Is the Difference?
There is no single wear rate that applies to every SF-1 (DU) or SF-2 (DX) bushing.
Wear depends strongly on the operating conditions.
A useful engineering concept is:
Wear increases as load and sliding distance increase, while suitable lubrication and a properly prepared mating surface can reduce wear.
Important variables include:
Wear Under Dry Running
SF-1 (DU) is commonly used for dry-running applications because its sliding layer is designed to provide low friction without continuous external lubrication.
During dry operation, the transfer film formed on the mating surface can affect friction and wear.
A suitable mating surface helps the bearing form a stable sliding interface.
If the shaft is too rough, the bearing surface may wear faster.
Wear With Additional Lubrication
When a compatible lubricant is available, friction and wear can often be reduced.
This does not automatically mean that a lubricated bushing will last longer than a dry-running bushing.
The lubricant must be compatible with the bearing material and operating environment.
Too much lubricant can also attract contaminants in some industrial applications.
High Load and Load Capacity
High load capacity is a common reason for using composite bearings.
The steel backing and sintered bronze support layer provide mechanical strength, while the sliding layer provides the required friction and wear characteristics.
However, load capacity cannot be evaluated by radial load alone.
Engineers should consider the relationship between:
For sliding bearings, the PV value, which combines pressure and velocity, is often used when evaluating operating limits.
A bushing operating under a high load at very low speed may behave differently from one operating under a lower load at high speed.
Friction Properties of SF-1 and SF-2
Low friction is one of the main advantages of composite bearing materials.
Lower friction can reduce:
SF-1 (DU) is particularly well known for low-friction dry-running applications.
SF-2 (DX) can provide a useful balance between friction, lubrication and wear resistance in applications where the operating conditions may be more demanding.
Actual friction coefficients depend on the material grade and test conditions.
For this reason, catalog friction values should be treated as reference data rather than guaranteed field performance.
The Role of the Mating Surface
The bearing is only one part of a sliding system.
The mating surface can have a major effect on service life.
A suitable shaft or counterface should have:
A rough or damaged shaft can accelerate wear even when the bushing material itself has excellent wear resistance.
This is particularly important for thin-wall composite bearings because the sliding layer may be relatively thin.
Service Life of SF-1 (DU) and SF-2 (DX)
The service life of a composite bushing cannot be predicted accurately from material name alone.
A practical service-life evaluation should consider the complete operating profile.
Factors That Affect Service Life
Load
Higher load generally increases contact pressure and wear.
Sliding Speed
Higher speed can increase heat generation and affect the transfer film.
Temperature
Temperature affects both polymer properties and lubricant behavior.
Lubrication
Suitable lubrication can improve friction and wear performance in applications designed for lubrication.
Shaft Condition
An unsuitable shaft surface can significantly reduce bearing life.
Contamination
Dust, metal particles and abrasive contaminants can increase wear.
Alignment
Misalignment can create localized pressure and uneven wear.
Motion Type
Continuous rotation, oscillation, reciprocating movement and intermittent movement produce different wear patterns.
SF-1 (DU) vs. SF-2 (DX): Which One Should You Choose?
The decision should be based on the application rather than the material name.
Choose SF-1 (DU) When:
Typical applications include automotive mechanisms, hydraulic components, industrial machinery and general sliding mechanisms.
Choose SF-2 (DX) When:
The exact selection should be verified against the manufacturer's load, speed, temperature and lubrication data.
Automotive and Industrial Applications
Composite bearings and bushings are widely used in automotive industrial applications because they can combine low friction, compact dimensions and reduced maintenance.
Typical applications include:
In hydraulic equipment, composite bushings may be used at pivot points and in mechanisms where space is limited and contamination or lubrication access is a concern.
Why Composite Materials Can Reduce Maintenance
Traditional bearings may require regular grease or oil supply.
Composite materials can reduce this requirement by combining structural and lubricating functions into a thin bearing layer.
This can provide several benefits:
For equipment with many bearing points, even a small reduction in lubrication requirements can reduce the total maintenance workload.
SF-1 (DU) vs. SF-2 (DX) Comparison Table
| Selection Factor | SF-1 (DU) | SF-2 (DX) |
| Dry running | Excellent for suitable applications | Depends on specific grade |
| Low friction | Excellent | Very good |
| Wear resistance | Very good | Very good to excellent depending on grade |
| Lubrication requirement | Often none or minimal | Often benefits from lubrication |
| Additional lubrication | Usually not required | May be used where applicable |
| High load | Suitable within rated limits | Suitable within rated limits |
| Maintenance | Very low | Low to moderate |
| Service life | Highly dependent on PV and counterface | Highly dependent on load, lubrication and counterface |
| Best use | Low-friction, maintenance-free designs | Lubricated or demanding sliding applications |
How to Improve Wear Resistance in Composite Bushings
If wear is higher than expected, changing the bushing material is not always the first step.
Check the complete bearing system.
1. Check the Shaft
Verify shaft hardness and surface roughness.
2. Check Alignment
Poor alignment can create edge loading.
3. Check Load
Compare actual operating loads with the manufacturer's limits.
4. Check Sliding Speed
Confirm that the actual speed is suitable for the bearing material.
5. Review Lubrication
If the selected material supports lubrication, verify lubricant type, quantity and supply method.
6. Control Contamination
Abrasive particles can greatly increase wear.
7. Check Installation
Incorrect press-fit, housing dimensions or bearing clearance can cause premature failure.
Are SF-1 and SF-2 Better Than Traditional Bronze Bushings?
Not in every application.
Traditional bronze bushings can be a good choice where:
Composite bushings can be more attractive where:
The correct choice depends on the complete operating environment.
Common Selection Mistakes
Choosing by Load Alone
A bushing with sufficient static load capacity may still fail because of excessive sliding speed or temperature.
Ignoring the Mating Surface
A good bearing material cannot compensate for an unsuitable shaft.
Assuming All DX Materials Are the Same
DX is a material family and product designation used by different suppliers. Always check the actual technical specification.
Adding Grease Without Checking Compatibility
Additional lubrication can help some bearings but may not be appropriate for every composite material.
Using "Maintenance-Free" as a Guarantee
Maintenance-free operation applies only when the bearing is used within its specified conditions.
Frequently Asked Questions
What is the main difference between SF-1 (DU) and SF-2 (DX)?
SF-1 (DU) is generally selected for low-friction, dry-running and low-maintenance applications. SF-2 (DX) is commonly considered where wear resistance, lubrication and demanding operating conditions require a different material balance. The exact difference depends on the manufacturer's material grade.
Is SF-1 (DU) maintenance-free?
SF-1 (DU) can provide maintenance-free operation in suitable applications because its sliding layer contains low-friction and lubricating components. However, load, speed, temperature, shaft condition and contamination must remain within the recommended limits.
Does SF-2 (DX) require lubrication?
Not necessarily. The lubrication requirement depends on the specific DX material and application. Some DX-type composite bushings are designed for dry operation, while others can benefit from oil or grease.
Which has better wear resistance, SF-1 or SF-2?
Neither should be declared universally better. Wear resistance depends on the material grade and operating conditions. SF-2 (DX) is often considered for demanding applications where wear performance and lubrication are important, while SF-1 (DU) performs very well in suitable dry-running applications.
Can SF-1 and SF-2 bushings handle high loads?
Yes. Both material families can be designed for high-load applications. However, the allowable load depends on pressure, speed, temperature, bearing geometry and lubrication.
What is the role of sintered bronze in a composite bearing?
Sintered bronze provides a strong intermediate layer between the backing and sliding surface. Its porous structure can also support lubricant retention and help bond the functional sliding layer to the backing.
What is a solid lubricant?
A solid lubricant is a material that reduces friction without requiring a liquid or grease film. PTFE and graphite are common examples used in different bearing materials.
How does the mating surface affect bearing life?
The mating surface directly affects friction and wear. Correct hardness, surface roughness and finish can help the bearing achieve its expected wear rate and service life.
Can composite bushings replace bronze sleeve bearings?
In many applications, yes. Composite bushings can replace traditional bronze sleeve bearings when their load, speed, temperature and lubrication limits match the application.
Are composite bushings suitable for automotive applications?
Yes. Composite bearings are used in various automotive mechanisms because they can provide low friction, compact dimensions, good wear resistance and reduced maintenance.
Do composite bushings need additional lubrication?
Some are designed for dry operation and need little or no additional lubrication. Other materials can benefit from oil or grease. The correct approach depends on the specific bearing material and operating conditions.
How can I increase the service life of a composite bushing?
Use the correct bearing material, maintain the recommended load and speed, prepare the mating surface correctly, control contamination, maintain proper clearance and use compatible lubrication when required.
Final Takeaway
SF-1 (DU) and SF-2 (DX) composite bushings use layered composite materials to combine mechanical support, low friction and wear control in a compact bearing design.
SF-1 (DU) is a strong option when low friction, dry running, maintenance-free operation and reduced maintenance are important. SF-2 (DX) can be a better fit when the application places greater emphasis on wear resistance, lubrication and demanding operating conditions.
The final selection should not be based on the product name alone. Load capacity, PV value, friction properties, temperature, shaft condition, lubrication, motion and contamination should all be reviewed together.
When these factors are matched correctly, composite bearings and bushings can provide long service life, reduced wear and predictable maintenance requirements across automotive and industrial machinery applications.
