From Air Handlers to Humanoid Joints: Heat is Part of the Motion Equation

Why Temperature Matters in Precision Motion It’s hot out there. Across much of the country, air conditioners are working overtime, refrigerators are working harder, and ice makers may be among the most appreciated machines in the building..

Applications Why Temperature Matters in Precision Motion It’s hot out there. Across much of the country, air conditioners are working overtime, refrigerators are working harder, and ice makers may be among the most appreciated machines in the building. Behind many of the systems helping to beat the heat are components most people never think about: Bearings.

Bearings support the motors, fans, blowers, pumps, compressors and other rotating equipment that keep air and fluids moving. But while those machines work to cool buildings and processes, their bearings face a thermal challenge of their own. And that challenge extends far beyond HVAC and refrigeration.

Heat is Part of the Motion Equation Even in rolling-element bearings designed to minimize friction, some friction, and therefore heat generation, is unavoidable. In a rolling bearing, operating temperature is influenced conditions. Load, speed, preload or internal clearance, lubricant type and quantity, seal friction, alignment and heat generated all contribute to the bearing’s thermal operating condition.

That matters because temperature changes the system. As bearing temperature increases, the rings, rolling elements, shaft and housing expand. Because those components do not necessarily expand at the same rate, or experience the same temperature, the bearing’s operating clearance or preload can change.

In a precision application, that change can affect friction, stiffness, running accuracy and ultimately bearing life. Lubrication adds another variable. Grease and oil viscosity decrease as temperature rises.

If lubricant viscosity becomes too low for the operating speed, load and contact conditions, the lubricant film separating the rolling surfaces can become insufficient, increasing the risk of wear and surface damage. But more lubrication isn’t automatically better. In grease-lubricated bearings, excessive grease fill can increase churning and drag, generating additional heat; the very condition the designer is trying to control.

Temperature isn’t simply something happening to the bearing. It can change how the bearing operates. Bearing design is a balancing act.

The Bearings Behind the Cooling On a hot August afternoon, bearing-supported equipment is operating all around us. Air-handling systems use motors and blowers to circulate conditioned air through buildings. Fans move enormous volumes of air through industrial facilities.

Pumps circulate cooling fluids. Refrigeration and compressor systems keep food, beverages and manufacturing processes at controlled temperatures. Even the refrigerator and ice maker in the break room depend on small motors and rotating components doing their jobs reliably.

These applications vary enormously in size and operating conditions, but they share an important requirement: Reliable motion, hour after hour. And increasingly, another rapidly growing technology faces its own version of the same challenge. Speed Changes the Conversation Higher rotational speed can increase frictional heat generation, making bearing geometry, cage design, lubrication and sealing increasingly important.

A contact seal, for example, can provide valuable protection against contamination, but contact between the seal lip and rotating ring also generates friction. In an application where contamination protection is critical, that tradeoff may be entirely appropriate. In a high-speed precision application, however, the designer may need to evaluate whether a shield, non-contact seal or another sealing approach provides a better balance.

The same principle applies to lubricant selection and fill quantity. There is rarely a single characteristic called “the best bearing.” Bearing design is a series of engineering tradeoffs based on what the application actually requires. “Temperature isn’t simply something happening to the bearing.

It can change how the bearing operates.” Now Put All That Inside a Robot Humanoid robots make the thermal problem particularly interesting because multiple heat-generating components can occupy the same compact joint. A joint may combine an electric motor, reducer or transmission, bearings, encoder, braking components and electronics within a tightly constrained envelope. Heat generated ’t remain neatly isolated from the others.

At the same time, the bearing system may be asked to provide high rigidity, low friction and precise rotational accuracy while supporting radial, axial and moment loads. For a robotic joint, engineers therefore aren’t selecting a bearing based on load capacity alone. They may also need to consider: Stiffness.

Preload. Starting and running torque. Speed.

Lubrication. Sealing. Packaging.

Accuracy. Duty cycle. And temperature.

Those variables interact. Increasing preload, for example, can increase system rigidity—but excessive preload can also increase friction and heat generation. Increasing sealing effectiveness may improve contamination resistance—but may also increase torque.

Reducing package size saves valuable space—but concentrates components and can make thermal management more difficult. That’s where bearing selection becomes system engineering. Smaller Doesn’t Mean Simpler This challenge isn’t unique to robotics.

As equipment becomes smaller, faster and more powerful, engineers are continually being asked to achieve more performance in less space. Miniature bearings may operate inside precision encoders. Thin-section bearings can help reduce packaging space.

Crossed roller and four-point contact bearings can support complex loading conditions in compact assemblies. Ball screw support bearings help enable accurate linear motion. The bearing itself may be a relatively small component, but its interaction with the surrounding system can have a significant impact on performance.

That’s why successful bearing selection begins with understanding the application, not simply choosing a part number from a catalog. Managing Heat is Part of the Design Whether it’s an air handler running through the hottest afternoon of the year or a compact joint controlling the movement of a humanoid robot, temperature isn’t an isolated specification. It interacts with speed, load, lubrication, clearance, preload, sealing and the surrounding components.

Understanding those relationships is part of designing reliable motion. So the next time you walk into an air-conditioned building on a 95-degree afternoon, you might want to appreciate the machinery quietly working behind the scenes. Somewhere inside, a lot of very hardworking bearings are having a much hotter day than you are.

Precision in Motion. Wondering which variables matter most in your application? The engineering team can help evaluate how load, speed, temperature, lubrication, and other operating conditions influence bearing selection.

“Keeping things cool is easy to appreciate. The engineering that makes it possible is easier to overlook.” Bearing Visit Bearing at Booth 519 during RoboBusiness, October 20–21 in Santa Clara, California, to discuss precision bearing solutions for humanoid robots, robotic joints, actuators, encoders and other advanced motion systems. Mark your calendars for RoboBusiness where you will find Bearing at Booth 519!

How KMK Bearing Applies This

At KMK Bearing (SINO BEARINGS, KMK brand) these principles guide the bearings we manufacture in Chengdu, China. Our process chain - material selection, heat treatment, precision grinding, superfinishing and cleanroom assembly - is built to the standards described above, whether for a standard catalog part or a custom-engineered solution.

• 20+ years of precision bearing manufacturing
• Materials from chrome steel to 17-4PH stainless steel and full ceramic (ZrO2, Si3N4)
• In-house heat treatment and metrology to P4/P2 (ABEC 7/9) precision
• Custom designs and low-MOQ prototyping from drawings or samples

Discuss your application with kevin@sinoti.com or browse our bearing catalog.

SINO BEARINGS (KMK) - Perfect Quality -- Great Service -- Customized.

Source: Bearing News