T-Blog, Your Bearing Wikipedia

Bearing torque is the moment required to overcome internal friction to start or maintain rotation of one ring while the other is stationary. Torque or friction generally increases when: Bearing size is increased because a larger ball and retainer must be moved. Load is increased because of greater deformation and resistance to rolling motion. Speed is increased because of increased lubricant drag. Lubrication type is a critical torque factor. Oil-lubricated bearings generally have lower low-speed torque than grease-lubricated bearings. However, grease-lubricated ones may have lower torque at high speeds, particularly if a channeling grease is used. High-viscosity oils have a higher torque than low-viscosity ones. Bearing design also influences torque. Lightweight metal and molded plastic retainers have the least torque for low and moderate speeds. Phenolic and sintered nylon retainers have lower torque at high speed. Very low contact-angle or radial-play values show high torque because inherent geometrical errors in the bearing raceway and balls cause erratic variation in stress and, hence, friction level. Very-high contact angles have higher torque levels because of the sliding motion in the ball-to-race contact area. Torque-test levels vary from manufacturer to manufacturer, and even lot-to-lot for one manufacturer. There are three types of bearing…

In some applications, allowable load seriously influences selection. Major variables affecting load capacity are ball size and number and internal geometry of the bearing. Static: Primary consideration is given to static ratings. A bearing may be deformed permanently by high loads on nonrotating bearings or severe instantaneous loads on rotating bearings. Radial static capacity for instrument bearings is defined as the load causing a permanent, plastic deformation of 0.001 in. of the ball diameter at the ball-raceway contact. This deformation degrades the smoothness and noise level of the bearing. However, in less critical applications, higher loads can be accommodated. Static thrust-load rating is based on two considerations: 1. Load at which the ball-raceway stress approximates that calculated for the heaviest-loaded ball under the limiting static radial load. 2. Load causing the contact area between the ball and raceway to climb over the edge of the raceway shoulder. Thrust ratings vary with contact angle. Lower ratings will result from either low or high angles. Dynamic: Dynamic load ratings are not directly applicable to life prediction of instrument bearings because little life-test data is available. However, metal-fatigue failure is seldom encountered in instrument applications. Recommended use of dynamic load ratings for instrument bearings is limited to…

Even with the most-sophisticated motion controller, designers can still find it difficult to attain precise linear motion unless the mechanical components are appropriately designed for the application. Here are six mechanical and structural factors that affect control-engineering performance. Armed with even with the most-sophisticated motion controller, engineers can still find it difficult to attain precise linear motion unless the mechanical components are appropriately designed for the application. Granted, different markets have varying definitions of precision, from nanoscale levels in the semiconductor industry to the relatively generous 0.01-in. standards seen in packaging or newspaper printing. So the industry and application usually determine the needed level of precision. It’s also important to know the operating environment, because some environments make it more challenging to hit the required target. Let’s start by considering how to define precision. Precision is a combination of accuracy and repeatability. Accuracy, the discrepancy between a movement’s target position and the actual position, reflects motion targets being approached from different directions (multidirectional). So positioning accuracy is the maximum deviation between the actual and target positionsduring each motion. Repeatability relates to how precisely a linear-motion system positions itself when repeatedly approaching a position from the same direction, taking into account…

The goal is smooth, jerk-free motion, long-life, durability, and low cost to improve the quality or parts made by 3D printers. Are bearings or bushings best for 3D printers? And how can they be improved so that 3D printers can more quickly and reliably turn out parts of higher quality? Although increasing the quality and speed of 3D printers involves all the components used in them, a good place to start are the bearings and bushings that make up the linear-motion subsystems critical to 3D printers. Bushings and Bearings and Linear Motion In most 3D printers, the build platform (including the extruder) slides over smooth rods as it moves back and forth. The polished rods support the components and guide the extruder along a precise linear path. Bearings or bushings are used on the straight steel rods to reduce friction and smooth out the motion so that it is jerk-free. Bushings, also known as sleeve or plain bearings, are cylinders generally made of bronze, steel, or polymers. These materials reduce friction and the power needed to create linear or rotational motion, as well as to lower noise and wear. Bronze bushings are sometimes impregnated with oil so they are lube-free, or…

Whether you use cam follower bearings for cam followers, or for track, guide, or support rollers, their performance depends largely on the type you select. Important factors include loads, speeds, misalignment, installation, and lubrication. Cam follower bearings are used mainly in three types of applications: following the surface of a cam, supporting linear motion components, or laterally locating components during linear movement. Of these, cam follower applications range from simple two-dimensional cams to complex three-dimensional indexing cams with multiple followers. Linear motion support applications include platform support rollers and die transfer rollers. Supporting a linear motion component with cam follower bearings reduces sliding friction and track wear. By reducing wear, it also helps maintain precise machine motion. Plus, cam follower bearings guide linear motion components in lateral as well as vertical directions. Basic types Cam follower types include standard stud, heavy stud, and yoke, Figure 1. Both stud types are mounted cantilever-style on a support housing. The heavy stud version is used for heavy loads, shock loading, or applications requiring minimal deflection. Except for the stud diameter and end plate design, standard and heavy stud versions are essentially the same. The yoke version mounts on a pin with a straddle or yoke…

Linear guides are precision mechanical assemblies that operate as part of a system. As such, they can only perform to the degree that they are properly integrated into the overall machine. Merely specifying the appropriate guide is not enough. Building a system that operates as intended requires a clear understanding of how to specify, design, install, and test the linear guide. Here, we discuss several of the most common errors made by designers building linear guides into their systems, and ways to avoid them. Not fabricating mounting surfaces to tolerance. Linear guides are precision-ground at the factory to operate with minimal friction. In an ideal world, the friction of each individual linear guide block would be the same whether it is mounted or not mounted. In reality, any misalignment or out of flatness of the mounting surfaces directly adds preload into the linear guide system. Mounting tolerances encompass both the flatness of the mounting surface to which the rails get mounted and the parallelism of the linear guides to one another. If the friction in a guide increases when the assembly is installed, or is more extreme at one end of travel than the other, the mounting tolerances or rail…

The rolling elements in antifriction bearings are critical components that can affect the overall performance of an entire machine. Engineers must consider their many attributes to get the best bearing performance, including: • Diameter and diameter tolerance. • Axial profile • Radial clearance • Surface finish In many cases, catalog data alone does not provide enough information for engineers to confidently specify a bearing and predict performance — particularly in critical applications. Fortunately, some major bearing manufacturers offer application-analysis services that delve deeper into design and operating details. Such analysis considers all bearing inputs and recommends designs or products that deliver the required performance. As an example, let’s look at some gearbox bearings. These bearings support a helical gear in a simple planetary set, using two rows of loose needle rollers housed in the bore of the gear. Shaft OD is approximately 0.500 in. and gear bore is about 0.750 in. The unit runs at a maximum speed of 2,300 rpm. Among the areas analyzed:• Loads on the bearing and individual needle rollers.• Contact pressure on the most highly stressed rollers.• Subsurface stress in the raceway, and how it compares to the strength of the raceway material. A free-body diagram…

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Custom linear bearings can help solve unique problems. Understanding what situations demand a custom linear bearing is key. Each application is a little bit different. For every load that can be perfectly supported by a stock bearing, there are others that require a customized solution. A project may involve specialized environments, extreme performance demands, tight scheduling, and more. Let’s focus on some of the techniques engineers can use to achieve the system characteristics they want. Most of the conversations that we have with people about customization occur when they’re developing a new product and building their first unit. They may have empirically discovered some undesirable characteristic in their system such as excess vibration or a structural element that leans enough to act as an overhung load. Modeling is important, but you can’t really guess what’s going to happen with a high degree of accuracy until you build the system. Designing for Vacuum Clean-room and vacuum applications have very strict requirements for particulate control. Any time components are in motion, you run the risk of generating particles. Grease can minimize friction, and thus particulation, but many formulations outgas, which can compromise the vacuum. Clean-room greases are designed to address both of…

“Bearings are as good as their lubrication”. The lubrication is the most important factor for bearing life. Several actual statistics show that incorrect lubrication causes more than 50% of premature bearing failures.A correct lubrication must cover: 1. The correct lubricant. Oil or grease? Viscosity? Temperature range? Anticorrosive properties? EP properties? Consistency of the grease? Etc. 2. The correct lubrication system. Oil: Oil bath? Oil splash system? Circulating Oil? Oil mist? Air-oil? Etc. Grease: Greased for life? Manual relubrication? Automatic centralized system? Automatic lubricators? Etc. 3. Place for the correct application. Oil or grease must be applied in the correct place so that the flow of the lubricant goes correctly to/through the bearings in the most efficient way. Example: The W33 groove with holes in the outer ring of spherical roller bearings. 4. The correct quantity of lubricant. Excess of lubricant may be as bad as to little lubricant. Excess of lubricant will increase the friction and this will increase the operating temperature which will destroy the lubricant. Lack of lubricant will logically not create the required lubricating film and metal to metal contact will take place in between the rolling elements and the raceways of the rings of the bearings….