Installation

Installation of bearing/gear assemblies should be done in a clean, dry, well-lit area. Housing mounting surfaces and pilots should be unpainted and wiped clean of chips, dirt, and lint, because even soft materials make high spots when entrapped. Any weld spatter, nicks, and burrs should be removed.

The bearing can be lifted or hoisted into position using eye bolts in mounting holes (or nonmetallic slings) which can prevent damage to bearing surfaces and gear teeth.

Inherent to the hardening process of most turntable bearings is a small gap at one point in the raceway; loading holes are drilled through this gap. These gaps (and load hole plugs, in races with through holes) should be positioned at minimum load points if possible. Load hole plugs in races with tapped holes or weld rings must be so positioned. With the rotating race, this is done by placing the loading hole 90° off the maximum load zone from moment loading. With the stationary race, this position depends upon the location of the lightest load relative to the lower structure of the machine.

For good internal load distribution and smooth, low-torque operation, the bearing should be as round as possible when the bolts are tightened. If one race is doweled or piloted, it should be mounted first when possible.

On unpiloted gear bearings the gear/pinion backlash should be checked and adjusted. The minimum backlash point of the gear is often identified by yellow paint in the tooth space. When installing:

• Leave all mounting bolts loose until both mating parts are attached to the bearing.
• While applying a moderate centered thrust load to the bearing, measure the torque to rotate the bearing. Then tighten all bolts to the level prescribed by the bolt manufacturer. This is very important; improperly tightened bolts can fail due to fatigue and can harm equipment and workers.
• Again measure the torque required to rotate the bearing. If greater than the first measurement, the bearing is being distorted. Determineand correct the cause.

After these steps, gears on fixed centers can be checked for backlash, and pinions on adjustable centers set for proper backlash.

When all backlash checks are completed, the gear should be coated with grease suitable for the operating conditions, and rotated to ensure coverage of all contacting surfaces with the pinions.

Complete installation of all rotating components of significant weight, and check bearing for freedom of rotation. Again, excessive torque or variations are indicative of an unsatisfactory installation condition.

Beyond backhoes: Small designs

Significant changes are taking place in the use of slewing ring bearings. The traditional perception of slewing ring bearings as large-diameter, heavysection, low-precision bearings with bolt holes and gears for construction equipment applications is no longer valid; these bearings are increasingly used in smaller, precise applications.

Improved manufacturing methods and design concepts are behind this trend. Smaller, off-the-shelf slewing ring bearings (preloaded to eliminate clearance and improve stiffness) have become standard in the machine tool industry; runout and diameter tolerances for these bearings can be specified in ten-thousandths of an inch, vs. thousandths.

The design is useful in even small designs because it’s simple to bolt a rotating structure to a stationary base.