Maintenance Tips Extend Mechanical Bearing Durability
Bearings play a crucial role in modern machinery, as their quality directly influences the performance of the entire equipment. This article covers the installation, maintenance, disassembly, and common issues related to bearings, with the hope of being beneficial to everyone’s production processes.
Bearing installation
The installation of bearings directly affects the accuracy, life, and performance. Therefore, the design and assembly departments should fully study the installation of bearings and carry out the work in accordance with the following standards:
(1) Clean the bearings and related parts of the bearings;
(2) Check the size and finishing of related parts;
(3) Install (open the bearing package just before installation);
(4) Check after the bearing is installed;
(5) Supply lubricant.
Generally, grease lubrication does not require cleaning; grease is simply filled directly into the bearings. In contrast, lubricating oil does not need to be cleaned either. However, for bearings used in instruments or high-speed applications, it is important to clean them with clean oil to remove any rust inhibitors that may have been applied. If the rust inhibitors are not removed, the bearings can be susceptible to rust, so they should not be left unattended.
Additionally, bearings that have been sealed with grease should not be used directly without cleaning. The installation method for bearings varies depending on their structure, fit, and other conditions. Typically, since the shaft rotates, the inner ring must have an interference fit. Cylindrical bore bearings are generally pressed in using a press or installed with a hot fit. For tapered holes, the bearings can be installed directly on a tapered shaft or with the assistance of a sleeve.
01. Installation of cylindrical bore bearings
(1) Pressing method
The press-in method is commonly used for installing small bearings. To begin, place a pad on the inner ring and use a press to gently press it until the inner ring makes close contact with the shaft shoulder. It is important to avoid placing a pad on the outer ring during installation, as this could cause indentations and damage to the raceway; this practice must be strictly prohibited. Before operation, applying oil to the mating surface can facilitate smoother installation.
If using a hammer to install the bearing, ensure that you place a pad on the inner ring. This hammering method is only suitable for cases with a small interference fit and should not be used for larger interference fits, or for medium and large bearings.
For non-separable bearings, such as deep groove ball bearings, where both the inner and outer rings require an interference fit, you should use a pad and simultaneously press both rings together using a screw or oil pressure. When dealing with self-aligning ball bearings, the outer ring can easily tilt. Therefore, even if an interference fit is not required, it is advisable to install it with a pad.
In the case of separable bearings, like cylindrical roller bearings and tapered roller bearings, the inner ring should be installed on the shaft, while the outer ring should be installed on the outer housing. When combining the separately installed inner and outer rings, it is crucial to align them closely to ensure that their centers do not deviate. Forcing them together can result in the raceway surface becoming damaged.
(2) Hot-fitting method
Large bearings require significant force to be pressed into place, making the process quite challenging. To ease this, the hot-fitting method is commonly employed, which involves heating the bearing in oil to expand it before installing it on the shaft. This technique allows for a quick operation without applying excessive force to the bearing. The heating temperature of the bearing depends on its size and the necessary interference. Here are some precautions for hot-fitting operations:
(a) The bearing should not be heated to more than 120°C.
(b) To prevent the bearing from directly contacting the bottom of the oil tank, consider placing it on a metal mesh table or suspending it.
(c) Heat the bearing to 20°C to 30°C above the required temperature to ensure that the inner ring does not cool down during installation, which could make it difficult to fit.
(d) After installation, the bearing will cool and contract in width. It is important to secure it with a shaft nut or another suitable method to avoid creating a gap between the inner ring and the bearing shoulder.
02. Installation of tapered bore bearings
When dealing with bearings that have tapered bores, the inner rings are typically installed using an interference fit. The level of interference depends on how far the inner ring is pushed onto the tapered shaft diameter, adapter sleeve, or withdrawal sleeve.
For small and medium-sized bearings, the inner ring can be positioned correctly on the tapered shaft diameter using a bearing installation tool or a locking nut. If an adapter sleeve is used, a sleeve nut that can be secured with either a hook wrench or an impact wrench should be employed. When utilizing a withdrawal sleeve, a bearing installation tool or an end plate can be used to push it into the inner bore of the bearing.
Larger bearings require more force for installation; therefore, hydraulic nuts should be used. Hydraulic nuts are effective in installing tapered bore bearings onto tapered shaft diameters, adapter sleeves, and withdrawal sleeves.
03. Installation of the housing
When installed in the housing, there is typically a looser fit for the inner ring, while the outer ring has an interference fit. The outer ring is usually pressed in using a press, or it can be installed using a shrink-fit method after cooling. However, when dry ice is used as a coolant for the shrink fit installation, moisture from the air can condense on the surface of the bearing. Therefore, it is important to take appropriate anti-rust measures.
04. Check the bearing during operation
After installation, it’s essential to perform an operational check to verify that the installation is correct. For small machinery, you can manually rotate the parts to ensure they move smoothly. Look for any issues such as interference from foreign objects, scars, indentations, or uneven rotation torque that may arise from poor installation or inadequate processing of the mounting seat. Additionally, check for excessive torque caused by insufficient clearance, installation errors, or seal friction.
If everything checks out and there are no abnormalities, you can proceed with a powered operation. Since large machinery cannot be rotated manually, it’s important to turn off the power immediately after starting it without a load. Perform an inertial operation to check for vibrations, sounds, or any contact between rotating parts. Only enter powered operation after confirming that no issues are present.
When disassembling, it’s crucial to follow basic rules and use appropriate tools and methods depending on the type of bearing. If the bearing is tightly fitted to the shaft and loosely fitted in the housing, you can remove the bearing with the shaft from the housing. Then, use a press or other disassembly tools to remove the bearing from the shaft.
Several common bearing disassembly methods:
1. Disassembly of the outer ring
To disassemble the outer ring with an interference fit, first prepare by setting several screws around the circumference of the housing for the outer ring extrusion. Tighten these screws evenly while disassembling the ring. Typically, these screw holes are covered with blind plugs. For split bearings, such as tapered roller bearings, several cuts should be made on the housing shoulder. The bearings can then be disassembled using a press with a gasket or by gently tapping them.
2. Disassembly of the inner ring
The inner ring can be disassembled by using a press to pull it out. It is crucial to ensure that the inner ring can withstand the pulling force. Additionally, regardless of the type of fixture used, it must be securely clamped to the inner ring’s side. To facilitate this, it is important to consider the size of the shaft shoulder or evaluate the metal machining of the upper groove on the shoulder to ensure compatibility with the drawing fixture.
For large bearings, the inner ring is disassembled using oil pressure. Oil pressure is applied through the designated oil hole in the bearing, making it easier to remove the ring. In cases of bearings with significant width, both the oil pressure method and a drawing fixture are employed for disassembly.
Cylindrical roller bearings’ inner rings can be disassembled through induction heating. This method involves quickly heating a specific section to expand the inner ring, allowing for easy removal. Induction heating is also beneficial when multiple inner rings need to be installed simultaneously.
3. Unloading
Unloading is a straightforward and common method of disassembly. This technique involves using the force of hammering to displace matching parts and separate them from one another, achieving the goal of disassembly. The primary tools used for unloading include hand hammers, specifically ordinary fitter’s hand hammers, punches, and pads.
When unloading, different methods and steps should be employed based on the structure of the machine. For example, sliding bearing bushings and rolling bearing jackets are often interference-fitted in their holes, making unloading essential for their removal. During this process, it is important to pad the hammered end face of the bushing. When dealing with small-diameter bushings, using a stepped punch is advisable. The small diameter of the punch should match the inner hole of the bushing, while the larger diameter should be approximately 0.5 mm smaller than the outer diameter of the bushing.
To disassemble large-diameter bushings and rolling bearings, sleeves are often utilized. For the removal of standard small bearing covers, the method of symmetrically driving inclined washers is commonly used to open the bearing covers.
Precautions for bearing use:
Bearings are precision CNC machined components, and regardless of their high-performance capabilities, improper use can prevent them from achieving their intended effects. Here are some important precautions to follow when using bearings:
1. Maintain Cleanliness
It’s essential to keep bearings and their surroundings clean. Even tiny dust particles, which may be invisible to the naked eye, can enter the bearings and lead to increased wear, vibration, and noise. Ensure that both the bearings and their surrounding components are free from dust and dirt, and keep your tools and work environment clean as well.
2. Exercise Caution During Installation
Avoid using excessive force when handling bearings. Do not hammer the bearings directly or transmit pressure through the rolling elements.
3. Utilize Appropriate Installation Tools
Always use specialized tools for installation and avoid makeshift tools like cloths or short fibers to prevent damage.
4. Prevent Rust Formation
When handling bearings, make sure to wash any sweat off your hands and apply high-quality mineral oil before beginning. Pay particular attention to rust prevention during rainy seasons and in summer.
Under specific operating conditions, bearings can last longer than traditional calculations suggest, particularly when subjected to light loads. These special conditions occur when a lubricating film effectively separates the rolling surfaces (tracks and rolling elements), reducing the surface damage that contaminants may cause. In fact, under ideal circumstances, it is possible to achieve what is known as permanent bearing life.
Common problems and countermeasures in the use of bearings:
Strong metal sound
1. For abnormal loads: select the appropriate assembly clearance and preload. 2. To address poor assembly: improve shaft processing accuracy and installation methods. 3. If lubricant is insufficient: add or use an appropriate lubricant.
Regular sound
1. Foreign matter can cause groove rust, indentations, and scars: clean the affected parts and apply clean grease. 2. Groove peeling is due to fatigue wear; replace the bearings.
Irregular, abnormal sound
1. Foreign matter intrusion: clean the affected parts and apply clean grease. 2. Excessive clearance: ensure proper fitting and select the appropriate clearance. 3. Steel ball damage: replace bearings if there is fatigue peeling or foreign matter present.
Abnormal temperature rise
1. Excess Lubricant: Reduce the amount of lubricant used.
2. Insufficient or Unsuitable Lubricant: Increase the lubricant or select a more appropriate type of lubricant.
3. Creep of Mating Surface or Oversized Sealing Device: Adjust the outer or inner diameter of the bearing’s mating surface and change the sealing design.
The rotation vibration of the shaft is large
1. Spalling: Replace the bearing if fatigue spalling occurs. 2. Poor assembly: Improve machining accuracy of the shaft and enhance the installation method. 3. Foreign matter intrusion: Clean the relevant parts and use clean grease.
Lubricant leakage and large discoloration
1. Too much lubricant: reduce the lubricant. 2. Foreign matter intrusion: clean the relevant parts.
If you want to know more or inquiry, please feel free to contact info@anebon.com
Anebon alyways upholds the philosophy of “Be No.1 in high-quality, be rooted on credit and trustworthiness for growth”. Anebon will keep on to serve previous and new prospects from home and overseas whole-heatedly for Ordinary Discount die casting service, CNC Milling, metal turning services and Machining.