With no moving parts, journal bearings may appear to be relatively simple. But there's a lot going on with this technology today in the way of technological innovation.
Design News: What is a journal bearing?
Harris : A journal bearing is a plane bearing, which means that it has no rolling elements. Unlike other bearings, they do not involve point or line contact. Because we're using a projected area (the diameter of the shaft times the length of the bearing), we get much more surface area, and the load is distributed more evenly. There are both lubricated and self-lubricating designs. Typically, these bearings are used in high-load, slow-speed applications involving mechanical linkages that are pivoting and may have linear motion.
Q: Are these bearings easier to apply?
A: When engineers buy a rolling element bearing, it is already heat treated, hardened, and polished. With a journal bearing, you have to address the mating surface for each individual application. In order to do this well, we need to understand something about the application. We have to know if the bearing is going to be used in the atmosphere or outdoors. We need to know if it is going to be used in fresh water or seawater. We need to know if there is a potential for galvanic corrosion. The answers to these questions will determine the specific choice of materials bearing design.
Q: More and more engineers are employing this type of bearing in their designs. Why?
A: I think the main reason for using journal bearings is to get a competitive advantage. Maintenance-free designs continue to be the goal of virtually every designer out there, and we have bearing products that can help them achieve this goal. For example, our Duralon®bearings are self-lubricating, with a woven Teflon®liner backed by fiberglass and resin to withstand demanding loads and speeds in a wide range of applications. Also, we're offering more and different types of bearings than in the past.
Q: What are some of the specific new developments in journal bearings?
A: One hot area right now is non-round bores. A typical journal bearing is a cylindrical member with a mating surface. Bearings in a square or hex bore configuration function as torque-transmitting devices. In other words, they are able to transmit torque through an assembly at the same time that they allow linear motion of the shaft. The real advantage is that they simplify the assembly: If an engineer eliminates a shaft and one or two bearings by using a square shaft and bearing, then he or she simplifies the design and maintenance and lowers the cost.
Q: How can engineers successfully apply journal bearings in their designs?
A: Engineers need to keep two books handy when they are designing mechanical linkages: One is engineering mechanics and the other one is metallurgy. The key to good design is to understand where the loads are coming from-not so easy a task when you're dealing with complex mechanisms. Take four-bar linkages, for example, in which the stresses are not necessarily perpendicular to the load. Engineers also need to know what the duty cycle will be, including the oscillation angle and the magnitude of the load and the frequency.
Q: Has your role as bearing supplier changed, and if so, how?
A: We're getting more involved in applications engineering, where we help the customer not only understand the metallurgical aspects of the design, but also get involved with improvements to the design that may reduce cost, simplify the number of parts, and so on.
Q: What new developments can we expect to see down the road?
A: We're continuing our work in composite bearings and new configurations. In fact, we just filed a patent for a new design involving a multiple thread form. The goal is to help improve the performance of our bearing products.
Bernard Harris has spent 33 years at Rexnord in the capacity of research engineer and manager. He is the co-inventor of the Duralon®/ Tuflite®composite bearing, and holds 24 patents (with four pending) on various composite bearing types. In his present position, he has taken a successful research project and developed it into a business. He has numerous articles published in trade magazines and has given a number of technical seminars to engineering audiences. He has chaired and was a speaker for 13 years at the Self-Lubricated Non-Metallic Bearings Seminar at the University of Wisconsin-Milwaukee Continuing Education Program. Harris has a degree in mechanical engineering from the Milwaukee School of Engineering and is a member of the American Society of Mechanical Engineers.