An excavator ring gear (also known as a slewing bearing or slew ring) is a rotational rolling-element bearing that supports the upper carriage of the excavator with a hydraulically rotating upper deck (revolving 360 degrees). It contains mounting holes, an inner ring or outer ring, spacer, isolation holder, grease hole, and seals.
3 Warning Signs of Ring Gear Problems
1) Play or clearance in the bearing often signifies that the ring gear is worn. A new bearing is assembled with a specific amount of clearance to compensate for slight out-of-flatness in a mounting structure. Wear can increase this clearance dramatically.
2) Grinding, popping, or clicking noises from the ring gear typically mean there could be inadequate lubrication and/or excessive wear in the ring gear, or loose bolts.
3) An increase in torque or binding can mean uneven wear in the ring gear. If the turning torque of the bearing increases substantially or the bearing has tight spots, the load is probably unevenly distributed. With excavators, the operator may sense a resistance to swing and find that the upper boom swings an inch or two past the point where it should stop. In advanced stages of wear, the bearing will pop and crack as the machine digs and swings.
By monitoring the symptoms of bearing wear and doing regular preventive maintenance, you can significantly reduce the chances that a bearing will fail prematurely. This in turn minimizes expense because it keeps equipment working productively, avoiding breakdowns that lead to costly downtime and repairs.
Longer bearing life also means, of course, that bearings can be replaced less often, stretching budgets further. And when the time for replacement comes, consider having your old bearings remanufactured instead of buying new ones. Well-maintained bearings can typically be repaired for less than half the cost of a new replacement, if repaired before they fail.
Maintenance points for Ring Gears
a) Lubrication
A ring gear should be lubricated at regular intervals with heavy-duty, extreme-pressure grease. Apply a liberal shot to the fittings around the bearing's circumference at the interval recommended in the operator's manual. Excavators should be re-lubricated about every 100 hours of operation. While adding grease, the bearings should be rotated to spread the grease throughout. Pump it in until you see the old grease squeeze past the seal; this is called purging. Purged grease carries contaminants out of the ring gear. Rub some between your thumb and forefinger - if you feel grit or metal chips, you may have a bearing problem. Grease tends to dry out over long periods of time, allowing condensation to form within a bearing. You can avoid this by introducing grease at least every six months, even when the equipment is sitting idle. Ring gears have gear teeth that require different lubrication. Since the meshing action of the teeth tends to squeeze out lubricant, gears should be lubricated every eight hours on slow-rotating or intermittently rotating equipment like excavators. Small amounts of grease should be introduced at the point of mesh between the gear and pinion.
b) Seals
The seals on the bearing should be visually inspected periodically to be sure they are intact. Many people overlook the importance of seals, but they aid considerably in preventing bearing raceway contamination.
c) Bolts
A torque check on bolts should be part of any routine maintenance procedure. The frequency of these checks depends on the severity of service. Vibration and shock tend to loosen bolts, but periodic torque checks and tightening will help maintain the proper preload level. Mounting bolts should be torqued to the proper level and checked periodically to ensure proper pre-tension. Improperly pre-tensioned bolts can fail, causing damage to equipment and, even more importantly, injuries to workers. Bolt creep is another factor that should be monitored. Tightened bolts tend to creep or elongate over a period of time, reducing preload. Elevated temperatures can also increase bolt creep, so take this into consideration when developing a torque-check schedule.
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