The Function of The Main Sheave Shaft Bearings
The main sheave shaft bearings go by a variety of names in our industry. Often times we can tell from which region an inquiry is coming from based solely on what you call them. Some examples of what we've heard them called are carrier bearings, torque tube bearings, main bearings, spider bearings, or main sheave shaft bearings among many others.
Broadly speaking, the main bearing set is in place to carry and function as the support of the overall load of the elevator system on the main sheave shaft. It must do so while also eliminating friction which reduces the efficiency of the motor and gear set. It also allows for the precise alignment of the bronze gear and worm gear. It must do all these things for forces applied both radially and axially.
Main Bearings are designed in a variety of different ways for both live and static main shaft applications. Some types are assembled directly on the shaft and housed within the spider assembly and others are external and housed within the pillow block/pedestal bearing.
1. Tapered Roller Bearings Housed Within the Spider’s Hub
2. Tapered Roller Bearings Housed in the Pillow Block/Pedestal Bearing
3. Poured Babbitt Bearing with Marine Grooving in the Pillow Block/Pedestal Bearing
Generally speaking, the low RPM of the drive sheave assembly and the robust construction of the vast majority of geared traction machines means this set of components often far exceed their designed service life and yet are often overlooked when diagnosing issues in the gear set.
What Your Gears May Be Telling You About Your Main Sheave Shaft Bearings
When in good operation, the sheave shaft bearings offer the following advantages:
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Supports applied loads.
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Allows for rotational motion.
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Self-aligns to compensate for force of applied loads
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And…maintains proper clearances, backlash, and contact angle between the bronze gear and worm gear.
It’s not uncommon for a customer to contact us with an overheated worm assembly after just having the worm overhauled. Or a customer may encounter what they believe to be pitting (more often than not it’s “scalling”) on the bronze gear which is a sign of overheating due to friction or particulate in the oil bath. The most unfortunate lessons are learned by technicians who install and run a brand new set of gears on a machine equipped with old worn-out bearings. They quickly find that the gears are precisely machined to tolerances that require the bearings to operate at their rated clearances. The result can sometimes be a total loss for the new gear set.
Gear “Pitting”
In all of these cases, while the gear set itself may be what’s drawing the technician's attention, the problem may actually be the main bearing set. Commonly, once these main sheave shaft bearings wear over time, they begin to allow the bronze gear to sag ever deeper into the worm. It may even be that the worm shaft bearings have also worn in conjunction with the main bearing set which masks any overarching issues.
Key Takeaways:
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Consider making bearing replacements part of long-term preventative maintenance strategies to minimize wear on more costly replacement components such as gear sets.
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When your gear set is exhibiting signs of deterioration, make sure a bearing replacement is done holistically for the entire machine. Address just one sub-assembly may not deliver the results you anticipated due to the interrelation between components.
Here at Titan Machine, we offer high-quality custom machining and repair services available for the elevator industry. We also provide a wide selection of new hoistway and elevator equipment to get your elevator safely fixed back into running order for operations. For more information about sheave shaft bearings or our other types of parts, contact Titan Machine today!
