What Are Dry Bearings? How Do They Work?

Dry bearings are commonly used in aerospace equipment, construction machinery, agricultural equipment, food-processing machinery, and many other industrial applications. Although dry bearings are frequently mentioned, not everyone clearly understands whet thhey are, how they work, how they are constructed, how they differ from self-lubricating bearings and conventionally lubricated bearings, or what their materials, types, advantages, and limitations are. So, in this article, I will explain dry bearings to help you understand.

After understanding dry bearings, you may also want to know where to buy them. BKZ Industry works with long-term partner factories to supply dry bearings according to different application requirements. We can offer a wide range of dry bearing types, materials, and sizes at cost-effective prices. Contact BKZ Industry to discuss your dry bearing requirements.

Now, let us take a closer look at what dry bearings are.

Part 1. What Are Dry Bearings?

Dry bearings, also known as dry-running bearings or lubrication-free bearings, are bearings designed to operate without an external supply of oil or grease.

These bearings are mainly plain bearings with low-friction sliding layers made of or containing PTFE, graphite, polymers, or other solid lubricants. Some rolling bearings that use solid lubricants, such as graphite or molybdenum disulfide, instead of an external supply of oil or grease can also be classified as dry bearings.

How Do Dry Bearings Work?

Dry plain bearings use low-friction, self-lubricating sliding layers containing solid lubricants to reduce friction between the supported component and the bearing surface, allowing the component to rotate, oscillate, or slide normally.

Dry rolling bearings have solid lubricants applied to or incorporated into the bearing in advance. During operation, the solid lubricant provides lubrication between the rolling elements, raceways, and other contact surfaces. At the same time, the rolling motion helps reduce sliding friction between the bearing components and supports the rotating shaft.

Dry Bearings vs Self-Lubricating Bearings vs Lubricated Bearings

With a general understanding of dry bearings, you may ask how dry bearings differ from self-lubricating bearings and lubricated bearings. Without understanding their differences, you may not fully understand the advantages of dry bearings or select the correct bearing option. Therefore, I will use a table to explain the differences between dry bearings, self-lubricating bearings, and lubricated bearings.

In simple terms, dry bearings generally belong to the category of self-lubricating bearings. However, not all self-lubricating bearings are dry bearings. For example, oil-impregnated bearings release stored oil from their porous material during operation, so they are self-lubricating but not strictly dry-running bearings. And conventionally lubricated bearings depend on an external supply of oil or grease for proper operation.

Advantages of Dry Bearings

Now that you understand the definition of dry bearings and have a clear picture of how they work, you may wonder what advantages dry bearings offer and why they are used in so many devices. Here are the key advantages of dry bearings:

Reduced maintenance costs and time: Because dry bearings do not require an external supply of oil or grease during normal operation, they eliminate regular relubrication and can reduce maintenance labor, downtime, and lubricant costs.

Suitable for large equipment and hard-to-access applications: Because dry bearings do not require regular relubrication, they are suitable for large equipment and applications where the bearings are difficult, dangerous, or costly to access and maintain.

Longer service life in suitable applications: Dry bearings can provide a longer service life in applications where conventionally lubricated bearings may fail because of insufficient, contaminated, or improper lubrication.

Lower overall system cost: Because dry bearings do not require an external lubrication system, they may eliminate components such as grease fittings, lubrication pipes, pumps, and reservoirs. This can simplify the design and reduce material costs.

Lower noise and vibration in suitable applications: Many dry bearings are plain bearings that operate through sliding contact rather than rolling contact. Dry bearings made from polymers or composite materials can absorb vibration and operate with less noise in suitable applications.

Limitation of Dry Bearings

Although dry bearings have many advantages, they also have some limitations.

Limited speed and load combinations: Because dry bearings operate without an oil or grease film, friction can generate heat at the sliding surfaces. Therefore, many dry plain bearings may not be suitable for applications that combine high speeds with heavy loads.

Possible stick-slip at low speeds: Some dry plain bearings may experience stick-slip during very slow, intermittent, reciprocating, or frequently starting and stopping movements. Stick-slip occurs when the difference between static and dynamic friction causes alternating sticking and sliding, which may result in uneven motion, noise, or vibration.

Applications of Dry Bearings

With these advantages and limitations, dry bearings are suitable for specific applications, such as:

Aerospace industry: Aircraft landing gear linkages, flight control surface hinges, flap actuators, aircraft door mechanisms, and passenger seat adjustment mechanisms.

Construction machinery: Excavator boom joints, loader linkages, bulldozer blade pivots, crane boom joints, and hydraulic cylinder rod ends.

Agricultural machinery: Tractor three-point linkages, combine harvester joints, baler pivot points, seed drill mechanisms, and irrigation equipment.

Food processing industry: Food conveyors, filling machines, packaging machines, industrial mixers, and bakery equipment.

Marine and offshore industry: Rudder linkages, deck cranes, hatch cover mechanisms, marine winches, and steering systems.

Industrial manufacturing: Assembly lines, robotic arm joints, material-handling equipment, printing machines, and textile machinery.

Part 2. Dry Bearing Materials

Now that you understand what dry bearings are, you also need to consider their materials when selecting a suitable dry bearing. The material affects the bearing’s load capacity, operating speed, temperature resistance, wear resistance, corrosion resistance, and service life.

Dry bearings are generally made from a load-carrying body material combined with a low-friction sliding material or solid lubricant.

Bearing Shell or Body Materials

Steel backing: Commonly used in metal-polymer composite bearings. It provides high mechanical strength and dimensional stability.

Bronze and copper alloys: These include cast bronze, sintered bronze, high-strength brass, and aluminum bronze. They are commonly used for heavy-load and graphite-plugged bearings.

Cast iron: Used in some heavy-duty solid-lubricated bearings because of its strength, rigidity, and wear resistance.

Engineering polymers: Materials such as PA, POM, PEEK, PPS, and other polymer compounds can form the entire bearing body.

Fiber-reinforced composites: Fabric, resin, and reinforcing fibers may be combined to provide strength and a low-friction sliding surface.

Lubrication Layer or Solid Lubricant Materials

PTFE: Provides a very low coefficient of friction and is widely used in metal-polymer composite bearings and fabric-lined bearings.

Graphite: Commonly embedded as plugs in bronze or metal bearing bodies. It is suitable for many low-speed, heavy-load, and high-temperature applications.

Molybdenum disulfide, or MoS₂: Used as a solid lubricant in some metal, polymer, coating, and high-temperature bearing materials.

Polymer-based solid lubricants: Microscopic solid lubricant particles can be distributed throughout an engineering polymer.

Resin-bonded dry lubricants: Graphite, MoS₂, or other solid lubricants may be held together by a resin binder to form a dry-lubricating layer or filling material.

With so many materials available, you can select the most suitable one based on your specific requirements. If you are unsure which material to choose, you can contact BKZ Industry. Its team can help you select a suitable bearing material based on your application and operating conditions.

Part 3. Dry Bearing Types

Dry bearings can be classified in different ways according to their structure, material composition, and lubrication mechanism.

Based on Bearing Structure

Based on their operating structure, dry bearings can be divided into dry plain bearings and dry-lubricated rolling bearings.

1. Dry Plain Bearings

Dry plain bearings operate through sliding contact between the bearing surface and the shaft. They are the most common type of dry bearing and are generally designed to operate without an external supply of oil or grease.

2. Dry-Lubricated Rolling Bearings

Dry-lubricated rolling bearings use balls or rollers between the inner and outer rings. Unlike conventional rolling bearings, which normally rely on oil or grease, these specially designed bearings use dry lubricants such as graphite or molybdenum disulfide.

Based on Material Composition

Based on their material composition, dry bearings can be divided into the following types:

• Steel-Backed Metal-Polymer Bearings
• Bronze-Backed Metal-Polymer Bearings
• Metal Bearings with Embedded Solid Lubricants
• Solid Polymer Bearings
• Fiber-Reinforced Composite Bearings

Part 4. Where to Buy Dry Bearing?

Now that you understand dry bearings, including their materials and types, you may want to know where to buy suitable dry bearings for your application.

BKZ Industry works with long-term cooperative factories to supply different types of dry bearings based on customers’ requirements. Through its established supplier network, BKZ Industry can offer a wide range of dry bearings in different structures, materials, sizes, and designs.

You can send BKZ Industry your bearing model, dimensions, drawing, required quantity, and application conditions. The team will help you confirm the suitable dry bearing and provide a quotation based on your requirements.

Final Words

Dry bearings are designed to operate without an external supply of oil or grease. They are available in different structures and materials, including metal-polymer bearings, solid-lubricant metal bearings, polymer bearings, composite bearings, and specially designed dry-lubricated rolling bearings.

When selecting a dry bearing, you should consider its load, speed, temperature, PV value, shaft material, operating environment, and required service life. If you need to purchase dry bearings, you can contact BKZ Industry for suitable product options and quotation support.