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Mechanical - Rotary Bearings

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Mechanical

Rotary Bearings

Bearings play key role in just about all motion systems. At Motion Solutions, we understand that better than almost any company in this space. After all, we began as a bearing consultancy and bearings were some of the earliest products we distributed. Proper bearing selection and implementation are among our core competencies to this day. For our customer base, that is critical because the choice of bearing can make or break performance of a system.

One of the biggest mistakes OEMs make is to rough out a design without considering bearings from the very beginning. A worn bearing can cause system misalignment that can increase wear on the actuator. That, in turn, makes the motor work harder. The net result may be early motor failure that leads to hours or even days of downtime¾and will repeat, if the bearing issue is not resolved. Equipment builders need to have a plan in place from the start.

The bearing needs to be able to accommodate the load, not just in terms of magnitude but also direction. The type of bearing that can handle a radial load may not be able to handle an axial load, for example, or a combination of the two. Duty cycle is important, as is speed.

Much discussion takes place about motor sizing but proper sizing for bearings is just as important. Undersizing can lead to early failure but oversizing increases both cost and footprint without providing measurable benefit. Finally, the structure needs to include enough space to accommodate the bearing. After all, the best bearing in the world won’t help if it doesn’t fit.

Our engineering team has extensive experience in designing systems and choosing bearings. Take advantage of their expertise to specify the best bearing for your application.

Ball Bearings

ball bearingBall bearings use balls as the rolling element. The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. Ball bearings use seals to contain lubrication and keep out particles to extend the operating lifetime. Precision ball bearings are used in high-performance applications found in a variety of markets, including automation, aerospace, robotics, healthcare, and machine tools.

 

Radial Ball Bearings

Radial ball bearings are workhorse rotary bearings, widely available in a range of sizes, materials, and prices. They can operate at very high speeds and provide good heat dissipation. The addition of cages helps keep balls separate, reducing friction and boosting efficiency. Radial ball bearings have lower load capacity than angular contact bearings as a result of contact angles and fewer balls. This is important to keep in mind¾overloading can cause surface damage such as brinelling, spalling, or fretting, leading to premature failure.

Angular bearingAngular-Contact Ball Bearings

Not every load is purely axial or purely radial. Angular-contact bearings are designed for hybrid radial-axial loads. The outer raceway features a raised shoulder to support the load across the contact angle. The contact angle increases the load capacity of the bearing, enabling it to handle a larger load in the thrust direction.

A single angular contact bearing can only take thrust in one direction. As a result, these bearings are almost always used in pairs, with individual bearings oriented with opposing contact angles such that between the two bearings, the system can support thrust in both directions. The exact details of the configurations vary: Bearings can be arranged back to back, face to face, in tandem, or separately at opposite ends of the shaft. Back-to-back orientation works best for supporting moment loads. Face-to-face orientation tolerates misalignment, making it a good fit for tasks like supporting the end of a ball screw. Tandem bearings are installed facing the same way, which limits them to handling a thrust load in only one direction but at almost twice the magnitude; an additional bearing will be needed to accept thrust in the opposite direction.

The choice of cage material offers additional degrees of freedom. Angular-contact bearings typically use either plastic or phenolic cages. Phenolic cages tend to be somewhat stronger than plastic versions and retain lubricant better for longer lifetime.

Thrust Ball Bearings

Many applications present demanding size and weight specifications. Thin-section bearings deliver smooth motion in a very narrow form factor. Because of their size, they have a lower load capacity. Care should be taken during sizing.

thin bearingThin-Section Bearings

Modern manufacturing puts the emphasis on maximizing operational equipment effectiveness (OEE) and increasing uptime. Condition monitoring is an essential tool for achieving this goal. Condition data provides insight into the health, operation, and performance of equipment, facilities, and even the products being manufactured. This typically encompasses factors like temperature, pressure, humidity, vibration, and current or voltage. An increase in the temperature of a motor might indicate lubricant breakdown, for example. The appearance of a spike in the vibration frequency spectrum of a pump might highlight erosion of the vanes. Increased current draw can indicate worn bearings or gears. With these types of insights, maintenance teams can troubleshoot faults more effectively and also help prevent them in the first place.

Roller Bearings

roller-based bearingRoller-based bearings use rollers instead of balls to provide the separation between moving parts. Rollers are available in a number of shapes, including linear and convex. They provide better load distribution, which enables them to handle higher loads. They are very good for applications requiring high stiffness. The trade-off is that the greater contact area also reduces efficiency.

Tapered Roller Bearings

Tapered roller bearings are shaped like the frustrum of a cone. This shape enables them to more effectively handle mixed loads. On the downside, the increased contact area of the rollers reduces efficiency.

Needle Roller Bearings

Needle roller bearings are cylindrical roller bearings that are very long for their diameters. This high aspect ratio enables them to support large radial loads in very compact form factors. Housings are divided into machined (precision) and pressed (drawn-cup) types. Drawn-cup needle bearings minimize size; for highly space-constrained applications, needle bearings are available with no inside housing.

thrust bearingThrust Bearings

Thrust bearings are designed to support high axial loads. Instead of using two concentric raceways, as is commonly found in bearings, they use a pancake form factor consisting of two flat, toroidal raceways pressed together to enclose rollers oriented radially from the center. This configuration enables a thrust bearing to support a high axial load without damage.

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