Corrosion Prevention for Porous Bronze Bearings

For bearings with a porous bronze inner structure, the following corrosion prevention methods can be employed:

Bronze Powder Sintering

The porous bronze inner layer is created by sintering a nominal 0.010 inch (0.25 mm) layer of carefully sized, bearing quality bronze powder onto the steel backing. This process securely bonds the bronze to the steel substrate.

Resin Impregnation

The porous bronze inner layer is impregnated with an acetal resin, which fills the porous structure and provides additional corrosion resistance.

Heat Conduction and Dimensional Stability

The bronze inner layer serves as an effective heat conductive path, minimizing undue temperature rise at the bearing surface. This helps maintain dimensional stability of the bearing.

Coating Options

For further corrosion protection, additional coatings can be applied over the porous bronze structure, such as:

• Electroless nickel plating
• PTFE coatings
• Epoxy coatings

The choice of coating depends on the specific operating environment and corrosive conditions the bearing will be exposed to. Our Applications Engineering Department can provide guidance on the most suitable coating system for your application.Regular inspection and maintenance of the corrosion protection system is crucial to ensure long-term performance and prevent premature failure. Our team can assist with developing an appropriate inspection and maintenance plan tailored to your needs.For more information or to discuss your specific requirements, please consult our Applications Engineering Department

Polymer friction coatings on bushings can now meet higher performance requirements for parts by reducing friction, extending wear life, lowering system noise, and improving corrosion resistance, all while reducing system costs.

What is a Polymer Coating?

A polymer coating is a thin layer of polymer added to flat or irregular substrates. Polymer coatings can be functional, protective, or decorative and are also used for modifying surfaces. Although mostly organic, these coatings may also include ceramic or metallic particles to enhance durability, functionality, or aesthetics.

In applications, it’s often necessary to combine bulk and surface properties under different locations, timings, and environmental conditions. Polymer coatings are typically used to modify substrate surface performance and enhance overall functionality, making them a significant branch of tribological materials science.

What are the main components of a polymer coating?

The term “polymer coating” indicates that these coatings are primarily made of polymers. However, coating formulations comprise organic and inorganic components: binders, fillers (or pigments), additives, and solvents.

What other types of surface coatings are there besides polymer?

Coatings come in inorganic and organic forms, with the most common industrial coatings being polymer and metal coatings. Friction coatings are primarily based on polymer technology to minimize friction and possess self-lubricating properties. Such coatings are relatively low-cost and can be applied using conventional spraying techniques. In contrast, metal coatings require more specialized equipment and are more costly, though they offer better durability and temperature resistance but are less suitable for tribological applications due to higher friction.

What is Surface Coating Technology?

Surface coating technology involves applying a thin film or dissimilar material on a substrate to enhance surface characteristics. Surface coatings can specifically provide chemical or anti-corrosion protection, improve hardness and durability, offer self-lubricating properties during relative motion and contact with other objects, or even just for decorative purposes. This technology ensures effective mechanical or chemical bonding between the coating and the underlying surface. Surface coating technology aims to extend the life of moving parts by minimizing friction, reducing energy consumption, improving efficiency; simplifying designs with self-lubricating behaviors without the need for external lubricants like grease or oil; and enhancing durability by reducing the risk of seizure damage to wear components, thus protecting more expensive elements.

What are Thermoplastic Coatings?

Most polymer coatings are thermoplastic polymers. In thermoplastic polymers, the individual large molecules of the polymer are entwined but largely remain independent of each other. Therefore, thermoplastic coatings have high flexibility, good elongation capabilities, and high impact resistance, though they are less scratch-resistant. They offer excellent corrosion resistance.

Steel vs. Bronze Backing

PTFE Coated Bush – Wrapped Composite Sliding Bearing

Materials:

• Steel (Tin-Plated)
• Sintered Bronze
• PTFE (Polytetrafluoroethylene)

Type:

• Bronze/PTFE Maintenance-Free Composite Bearing

Standards:

• DIN 1494 / ISO 3547

Properties:

• Offers excellent sliding and wear behavior suitable for all types of movement.
• Features a high load capacity.
• Includes cylindrical bushings and flange bushings with a dry sliding PTFE layer, eliminating the need for lubrication, though it remains an option.

Product Range:

• We quickly produce all special designs, including cylindrical and flange bushings, thrust washers, and strips as standard fabrications.
• Custom punchings and moldings are available based on customer requirements.

Additional Products:

• Spherical Plain Bearings
• Hardened Steel Bush
• High Strength Bronze Bush Composite

This maintenance-free solution is ideal for applications requiring robust performance without the need for ongoing lubrication, ensuring long-term reliability and efficiency.

Test C (ISO 3547-2: Test C) for Multi-Layer Bearings Tolerance 

To inspect the inner diameter of the bushing, it should be pressed into a reference ring gauge specified in ISO 3547-1:1999. The inner diameter can be measured using a three-point measuring device or assessed with GO and NO GO plug gauges. For practical usage, it is generally recommended to use GO and NO GO gauges. Under these conditions, the GO plug gauge should pass through the bushing’s bore with a manual force not exceeding 250N, while the NO GO plug gauge should not be able to pass through under the same conditions. After the bushing is pressed into the ring gauge, its outer diameter may become permanently deformed, rendering it unusable. To ensure consistent results between the manufacturer and the customer, it should be agreed upon whether the results are to be obtained by measuring or by gauging.

Technical Details

Housing

The housing bore should have a chamfer to facilitate assembly during pressing of the bushing into the housing. Chamfer Fc x 20° ± 5° is essential for easier assembly.

Wall Thickness

The wall thickness of metallic bearings can be minimized to achieve a more compact mechanical design.

Length

Generally, the length of a bearing is calculated by the ratio of the bearing length to the inner diameter $L/D$. For standard applications, a ratio $L/D=0.5–2.0$ is used. For applications involving high load, high speed, and uneven contact, it is recommended to use $L/D=0.8–1.0$.

Metal Bushing Installation

Pressure Assembly Typically, bushings can be installed using pressure assembly. During assembly, the mandrel should be pressed in slowly. Direct striking of the bushing is prohibited to prevent deformation. Before assembly, ensure the housing bore's inner surface is smooth and free from foreign objects.

Cooling Assembly Using liquid nitrogen or dry ice for cooling assembly is more effective compared to mechanical pressure fitting. The standard freezing temperatures range between -40°C to -70°C. The freezing time generally exceeds one hour, but this may vary based on the wall thickness and fit tolerance of the parts.

Calculation of Bearing Shrinkage The shrinkage of the bearing can be calculated using the following formula: $\text{AD}=D\times a\times \Delta T$ Where:

• $\text{AD}$ is the outer diameter shrinkage
• $D$ is the outer diameter of the bearing
• $a$ is the linear expansion coefficient (1/10^5 K)
• $\Delta T$ is the temperature difference