Frequently Asked Questions

What are the application scenarios for external-tooth slewing bearings?

In the modern industrial sector, external‑gear slewing bearings, as critical mechanical components, are widely employed in a variety of equipment requiring rotational motion and load support, thanks to their high load‑carrying capacity, precise rotational performance, and exceptional durability. Their distinctive design enables stable operation even under extreme operating conditions, making them an indispensable core component across numerous industries. This article examines the application scenarios of external‑gear slewing bearings from the perspectives of multiple industries, offering readers a deeper understanding of their significance and versatility.

What are the effects of slewing bearing seal design on service life?

As an indispensable key component in mechanical equipment, slewing bearings are widely used in cranes, excavators, turntables, and other machinery. The quality of their sealing design directly affects both the bearing’s service life and the overall reliability of the equipment. A well‑designed seal not only effectively prevents the ingress of contaminants but also ensures the stability and longevity of the lubricant, thereby extending the bearing’s operational lifespan. This paper examines, from multiple perspectives, how the sealing design of slewing bearings influences their service life.

5 Common Mistakes to Avoid When Installing Thin-Wall Crossed-Roller Bearings

Thin‑walled cross roller bearings, owing to their high rigidity, exceptional precision, and compact design, are widely used in industrial robots, precision rotary tables, medical equipment, and other applications. However, many engineers overlook critical details during installation, leading to premature bearing failure, reduced accuracy, or even equipment damage. Drawing on Jiu Liang Bearings’ extensive field‑service experience, this article identifies the five most common—and most detrimental—installation mistakes and offers practical guidance to help you avoid these pitfalls from the outset.

Error 1: Neglecting to clean the mounting surface and ensure its flatness.
Contaminants or surface irregularities on the mounting surface are the most insidious threats to thin‑walled cross roller bearings. Even the slightest burrs, metal filings, or residual oil can cause localized stress concentrations in the raceways during preload, leading to uneven rolling‑element sliding resistance and resulting in abnormal noise or binding.

Correct approach
Thoroughly clean the mating surfaces using non-woven fabric or a dedicated cleaning agent, taking care to avoid leaving any fiber residues.
Use a straightedge or dial indicator to check the flatness of the mounting surface; for thin‑walled bearings, a flatness tolerance of ≤0.005 mm is recommended.
If minor high spots are detected, locally smooth them with an oilstone or fine sandpaper, then wipe the surface with a cleaning agent.
Mistake 2: Installing the bearing by directly striking the outer or inner ring.

Many operators are accustomed to striking the bearing end face directly with a hammer or steel bar, believing this approach saves time and effort. However, for thin‑walled cross‑roller bearings—whose wall thickness is only 30% to 50% of that of standard bearings—such impacts can easily cause raceway deformation, indentation on the raceways, and even result in roller misalignment and seizure.

Correct approach
Use a dedicated press‑fit tool or a hydraulic press to ensure that the force is applied evenly to the mating ring.
If hammering is necessary, a copper or soft-metal bar should be used as a cushion, and the impact points must be symmetrically distributed around the circumference.
For fits with a large interference fit, first heat the bearing in an oil bath or induction heater to 80–100°C (do not exceed 120°C), and then use the principle of thermal expansion to install it easily.
Error 3: Improper preload control—too tight or too loose.
Thin‑walled cross roller bearings typically require a certain amount of preload to eliminate clearance and enhance stiffness. However, excessive preload leads to a sharp increase in friction between the rollers and raceways, causing bearing temperatures to rise rapidly and resulting in premature wear‑out failure; insufficient preload, on the other hand, can cause vibration and inadequate positioning accuracy. This is one of the parameters most prone to confusion in field applications.

Correct approach
Strictly adhere to the bearing manufacturer’s recommended preload torque or axial displacement values. At the time of shipment, Jiuliang Bearings marks the recommended preload torque range on the certificate of conformity.
Prioritize using a torque wrench or a dynamometer for pre-tightening to avoid tightening by feel.
After preloading, manually rotate the bearing to check whether the friction is uniform and free of binding. If you notice a significant increase in resistance at a particular location, inspect the mounting surface and raceway for foreign particles.
Mistake Four: Incorrect selection or improper dosage of lubricant.

Thin-walled cross-roller bearings typically feature a sealed design; once the grease is improperly applied, it becomes extremely difficult to replace later. Common mistakes include using heavy‑duty grease with excessive extreme-pressure additives—which can actually increase rolling resistance—or overfilling to more than 50% of the bearing’s internal volume, leading to overheating due to excessive churning.

Correct approach
Select a grease that matches the bearing’s operating temperature and speed; lithium‑based or complex lithium‑based greases are generally recommended, with a viscosity grade of NLGI 2 or 3.
The initial filling quantity should be controlled at 30% to 40% of the bearing’s internal space, just enough to completely fill the clearance on both sides of the rollers.
For high-speed applications, please consult the Jiuliang Bearing Technical Team; a specialized low-friction grease can effectively reduce temperature rise.
Mistake Five: Neglecting Break-In and Post-Installation Inspection
Many operators put the equipment into full‑load operation immediately after installation, believing that “new bearings do not require a running‑in period.” In reality, the rollers and raceways of thin‑walled cross‑roller bearings need a low‑load break‑in phase to achieve stable contact. Skipping this step can cause even minor manufacturing tolerances or assembly stresses to rapidly worsen under high loads.

Correct approach
After installation, run the equipment at 30% to 50% of its design speed under no-load conditions for 10 to 15 minutes, monitoring both noise levels and temperature throughout.
Gradually increase the load to 70% of the rated value, run the equipment for an additional 20 minutes, and record the temperature-rise curve.
If the temperature rise exceeds 20°C above ambient or if abnormal noise is detected, immediately stop the machine and investigate the cause. Jiu Liang Bearings recommends measuring the rotational torque once after the initial break-in period to establish a baseline for future maintenance comparisons.
The installation quality of thin‑walled cross‑roller bearings directly determines the equipment’s final precision and service life. The five common mistakes listed above are based on JiuLiang Bearings’ years of experience serving thousands of customers; simply exercising a bit more care during installation can help you avoid costly rework and downtime later on. If you encounter any specific issues during installation, please contact JiuLiang Bearings’ Technical Department for personalized guidance.

Crossed Roller Bearing Clearance Adjustment Method: A Step-by-Step Guide to Calibration

Crossed roller bearings are relied upon in applications such as industrial robots, CNC rotary tables, and precision measuring instruments to provide high‑rigidity, high‑precision support; their clearance condition directly affects the equipment’s positioning accuracy and service life. Many technicians have observed during commissioning that, even when the bearing is properly selected, improper clearance adjustment can still lead to vibration, noise, or even seizing. This article focuses on the practical implementation of cross‑roller bearing clearance adjustment, systematically covering everything from theoretical principles and preparatory steps to detailed calibration procedures. Drawing on Jiu Liang Bearings’ extensive field experience in precision motion‑control systems, it helps you master a systematic calibration methodology. Whether you are new to this technology or seeking to optimize your existing processes, this guide offers actionable technical guidance.

I. Understanding the Core Concept of Crossover Roller Bearing Clearance
1.1 What is clearance?
Bearing clearance refers to the maximum radial or axial displacement that can occur between the inner and outer rings when the bearing is either unmounted or mounted. For crossed‑roller bearings, clearance is typically categorized into radial clearance and axial clearance. Because the rolling elements are arranged in a cross pattern, the gap between the inner and outer rings directly determines the bearing’s preload condition. Excessive clearance can lead to reduced rotational accuracy and increased runout, while insufficient clearance may result in excessive heat generation, accelerated wear of the rolling elements, or premature failure.

1.2 Bearing Clearance Grades and Selection Principles
According to national standards and industry practice, the clearance of crossed roller bearings is typically classified into C2 (small clearance), CN (normal clearance), C3 (large clearance), and so on. When selecting a bearing, it is essential to consider factors such as load, rotational speed, temperature variations, and fit tolerances. For example, C2 clearance is often chosen for light‑load, high‑precision applications, while C3 clearance is preferred in heavy‑load conditions with significant temperature fluctuations. Jiu Liang Bearings clearly specifies the factory‑set clearance range for each model in its product catalog; users should verify prior to installation that the selected clearance matches the actual operating conditions.

II. Preparatory Work and Measuring Instruments for Adjusting Bearing Clearance

2.1 List of Key Measurement Tools
High-precision dial indicator or micrometer dial indicator (resolution 0.001 mm)
Magnetic dial indicator stand and bracket
Torque wrench (used to control preload when tightening bolts)
Bearing-specific press plate or installation tooling
Cleaning cloth, rust-preventive oil (unless otherwise specified, use the same type of grease originally supplied with the bearing)
2.2 Pre-Adjustment Environment and Inspection Requirements
Ensure that the work surface is level and free of oil or grease, and that operators wear clean gloves. After removing the bearing from its packaging, first visually inspect it for dents or rust, then manually rotate the inner and outer rings to check for any abnormal binding. For precision products such as Jiuliang bearings, a long‑lasting anti‑rust coating is applied at the factory; no additional cleaning is required before measurement. If the ambient environment contains significant dust, it is recommended to perform operations in a cleanroom or under a localized dust‑proof enclosure.

III. Step-by-Step Guide to Adjusting the Clearance of Crossed Roller Bearings—Detailed Instructions in Stages
The following describes the most common scenario of negative clearance (preload) adjustment, which is suitable for precision rotary tables requiring high rigidity.

Step 1: Perform the initial bearing installation and apply axial preload.
Secure the bearing’s outer ring to the housing, but do not fully tighten the inner ring at this stage. Use a dedicated press plate to apply the specified preload evenly (refer to the Jiu Li Bearing Installation Specifications for the appropriate preload torque corresponding to the bearing model). If no specific values are available, initially apply a force approximately 10% greater than the theoretical value, then gradually reduce it until it falls within the target range.

Step 2: Install the dial indicator and establish the zero reference.
Secure the magnetic dial indicator stand near the end face of the bearing’s outer ring, and position the indicator probe so that it presses perpendicularly against either the inner ring’s end face or the outer ring’s side (depending on whether you are measuring axial clearance or radial clearance). Rotate the bearing through more than one full revolution, and record the amplitude of the dial indicator’s pointer fluctuations. If the fluctuation is less than 0.01 mm, the bearing exhibits a certain degree of preload. If the variation is significant, proceed to the next step of fine adjustment.

Step 3: Adjust step by step using the locking bolts.
Tighten the inner-ring lock bolts in a diagonal sequence, in 2–3 stages; after each tightening, remeasure the end‑face runout. The target is to keep the dial indicator reading within the range of 0.002–0.005 mm (the exact tolerance depends on the bearing’s inner diameter—larger diameters may allow a slightly wider range). During tightening, rotate the bearing by hand while tightening to check for smooth operation. If significant resistance accompanied by unusual noise is detected, it indicates excessive preload; immediately loosen the bolts, reduce the shim thickness, or replace the adjustment ring.

Step 4: Final Locking and Re‑measurement
Once the dial indicator readings meet the specified tolerances and the rotational feel is smooth and uniform, use a torque wrench to tighten all bolts to the final specified torque. Rotate the bearing again and measure runout at the same location to verify that the tightening process has not altered the clearance. Finally, apply grease evenly around the bearing and perform a low-speed run of at least 10 continuous revolutions to confirm that there are no abnormal temperature rises.

IV. Post-Adjustment Verification and Common Troubleshooting

4.1 Verification Method
Radial clearance verification: A fixed load is applied radially to the bearing outer ring, and the displacement is measured.
Axial clearance verification: measured using an axial loading fixture in conjunction with a dial indicator.
Rotational accuracy verification: A standard disk is mounted on the inner ring of the bearing, and radial and axial runout are measured using a lever dial indicator mounted on the base.
4.2 Common Issues and Solutions
Rotational jitter after adjustment: Possible causes include excessive preload or contamination entering the rolling elements. Countermeasures: Disassemble and clean, then readjust the shim thickness.
The clearance fails to remain stable after adjustment: Possible causes include loose bolts or deformation of the bearing housing. Countermeasures: Check the flatness of the mating surfaces and apply thread-locking adhesive.
Vibration intensifies at high speeds: Possible causes include uneven clearance or misalignment during outer ring installation. Countermeasures: Re‑align the mounting surface and ensure that the bearing housing’s perpendicularity is better than 0.02 mm.
V. Common Questions Regarding Clearance Adjustment of Crossed Roller Bearings
Q1: Must clearance adjustment be completed before equipment assembly?
The optimal time for adjustment is when the bearing has been mounted in its housing but before the drive components have been connected. If the assembly is already complete, fine adjustments can still be made using specialized tooling; however, such adjustments are subject to limited precision and carry higher risks. It is therefore recommended to incorporate an adjustment step during the installation phase.

Q2: Are Koryo bearings pre‑adjusted at the factory, or do they still require on‑site adjustment?
Jiuliang bearings are manufactured with a standard clearance that meets the requirements of most general‑purpose applications. However, for high‑precision equipment—such as CNC rotary tables—final fine adjustments are still necessary on site, taking into account the actual interference fit and operating temperature conditions. Users may refer to Jiuliang’s clearance correction coefficient table to apply appropriate compensation.

Q3: Is it dangerous if the adjusted clearance value becomes negative (i.e., an interference fit)?
A negative value indicates that the bearing is already under preload. An appropriate amount of negative clearance can enhance system stiffness, but it must be kept within the limits specified by the bearing design—typically no more than one-third of the raceway depth allowance. Exceeding this range can lead to increased sliding friction between the rolling elements and, in severe cases, cause scuffing or burn damage.

Conclusion

Clearance adjustment of crossed roller bearings is a technically demanding task that requires both experience and meticulous attention to detail, as it directly impacts the equipment’s final rotational accuracy and service life. By applying the principles outlined in this article—along with proper tool preparation, step-by-step adjustment procedures, and verification protocols—you should now possess the fundamental skills needed to perform calibration independently. In practice, it is advisable to consult the technical documentation provided by the bearing supplier (such as Jiuliang Bearings), since recommended preload values vary across different series and sizes. Once you have mastered the correct adjustment methodology, you can further adapt your approach to suit specific on-site conditions, ensuring that crossed roller bearings deliver their full performance potential.