A lubricating device refers to a mechanism that supplies lubricating oil to the machine during operation. It is extensively utilized in industrial machinery, such as stamping machinery, and plays a crucial role in ensuring the smooth movement of its parts.
The conventional lubrication method can be classified into liquid lubricating oil (also known as thin oil), semi-solid lubricating grease (commonly referred to as yellow grease), and solid lubrication (using graphite) based on the type of lubricating material used between the friction pairs.
Characteristics of each lubrication method
Liquid lubrication
Liquid lubricating oil typically refers to thin oil lubrication, which is used in combination with an oil machine for circulating lubrication. The applicable parts typically include gear transmissions, rolling bearings, sliding surfaces between metals, and more. However, the properties of the oil used vary depending on the place of use.
For instance, gear oil must consider the factor of gear load in order to prevent damage between gears. If the wrong type of lubricating oil is used, the equipment’s service life will be reduced. As such, it is essential to ensure that critical parameters such as the type and viscosity of lubricating oil are not mistaken.
Figure 1 illustrates the lubrication of bearings and sliding surfaces.
During daily spot inspections, it is essential to check each oil supply device, such as the oil machine, distribution valve, flow detection valve, etc., to ensure that the lubricating oil is flowing correctly since the oil machine device can automatically supply lubricating oil circularly.
For the bearing bush structure of sliding friction (as shown in Figure 2), the connection between the eccentric mechanism of the punch and the connecting rod usually adopts a metal shaft and bearing bush.
However, unlike rolling bearings, metal shafts are subject to different loads, and the availability of adequate lubricating oil is crucial. If there is insufficient lubricating oil, it can result in burns and mechanism bite in a short period.
Therefore, special attention should be paid to the physical photo of the bearing bush, as illustrated in Figure 3.
Semi solid grease
Semi-solid grease usually refers to yellow grease, which has a consistency similar to that of lubricating oil. Due to its semi-solid nature, grease requires a certain level of hardness. The choice and use of hardness depend on the load and temperature of the lubricated part.
There are several ways to supply grease, including automatic pump supply, manual grease gun supply, and sealing grease during assembly. To ensure proper lubrication, daily inspections are necessary for all oil feeding methods.
For automatic pump supply (see Figure 4), an electric pump delivers grease through piping to multiple lubrication points. It is crucial to check for grease leaks at each connection point along the piping.
If grease leakage occurs at the connecting point of the piping (see Figure 5), there is a high likelihood that proper lubrication is not being achieved at all points.
Fig. 5 oil supply pipeline
o prevent potential issues, certain components that can be lubricated using a manual grease gun may be fitted with emergency grease nipples for backup purposes.
As copper alloy is frequently utilized for these types of connecting pipes, using a screw wrench to fasten the nut could cause damage. Therefore, it is recommended to use a specialized wrench for locking instead.
Solid lubrication
Solid lubrication may not be a common term that people come across often. Its primary components are graphite, molybdenum disulfide, and other similar substances.
Most people may have used a knife to sharpen the graphite refill of a pencil when they were young. It is noteworthy that touching the black powder is slippery, and this can be attributed to the powder’s solid lubricating properties.
In essence, the powder found in the graphite refill of a pencil serves as a solid lubricant.
Ability judgment of routine inspection personnel
Solid and semi-solid lubrication methods are used for machine operation. The choice of lubrication method and the type of oil or grease used depend on the skills of the equipment designer and maintenance inspector.
Table 1 shows the capabilities that daily equipment inspectors should possess.
Fig. 6 depicts a network diagram of the skills required for spot inspection personnel.
The red circle generally refers to the ability range of newcomers, while the green circle represents the abilities of senior personnel.
A rating of 1 indicates a complete inability to understand;
A rating of 2 means that you can identify related factors and symptoms of lubrication;
A rating of 3 refers to the abnormal diagnosis method that can explain the stress of the rotating shaft;
A rating of 4 means that you can master the measurement method of shaft vibration, including speed, acceleration, displacement, and other measurements;
Finally, a rating of 5 indicates the cycle number analysis method that can explain the vibration and the degree of damage caused.
Lubrication spot inspection method
The most common issue with stamping machinery is related to the bearings. An abnormal bearing can be identified by heating, vibration, and unusual sounds.
The primary causes of bearing abnormalities are poor lubrication or foreign matter contamination.
Here is a brief list of several methods for inspecting lubrication points on bearings.
Table 1 ability evaluation of routine inspection personnel
| Serial number | Self evaluation | Ability |
| 1 | Understand the types, additives, extreme pressure agents and viscosity of lubricating oil | |
| 2 | Understand the lubrication method of rotating shaft and the purpose of rolling bearing and bearing bush. Characteristics, etc | |
| 3 | Understand the judgment method of lubricant deterioration. Differences between lubricating oil and grease | |
| 4 | It can identify the causes and solutions of shaft heating | |
| 5 | You can master the measurement method of shaft vibration. Including velocity, acceleration, displacement and other measurements | |
| 6 | Understand the types and uses of thermometers and the differences between reversible thermometers and irreversible thermometers | |
| 7 | Master the applicable temperature, types and characteristics of lubricating oil | |
| 8 | Understand the differences between lubricating oil and grease, their supply methods and service environment |
Temperature spot check method
When a bearing has a problem, it often generates heat. If this heating is caused by the early deterioration of lubricating oil or grease, maintenance should be performed beforehand. However, it is best to identify a hot bearing during daily spot inspections before it becomes a serious problem.
At times, the bearing may appear normal during spot inspections, only to become abnormal later. Setting temperature detection is a common method during routine inspections. There are two types of thermometers used for this purpose: reversible thermometers that measure temperature changes, and irreversible thermometers that record the highest temperature reached.
In the event of an abnormal bearing, the temperature can be detected and recorded. Apply an irreversible temperature tape (as shown in Fig. 7) to the bearing to monitor its temperature.
When the temperature rises, the color of the device turns black, indicating the highest temperature.
During daily spot checks, it is easy to confirm if the temperature indicates any abnormality compared to the previous reading.
This device is commonly used on electrical distribution boards.
When the bearing is abnormal, the degree of temperature rise varies according to the number of revolutions or load, but it can rise to the temperature of molten steel.
Figure 8 shows that the steel ball in the bearing with abnormal heating is deformed due to high temperature.
If the steel ball turns purple, it may indicate that the bearing part has been heated to 800 degrees Celsius. Abnormal heating of bearings can result in fire accidents, so special attention should be given to this issue.
Bearings are not only utilized in punch machines but also in other machines or conveyor belts. Emergency stop mechanisms are often installed as sensors to detect abnormalities.
Vibration measurement with vibrometer
To measure the vibration of a bearing, it is recommended to use a professional vibration meter. This device can measure various vibration elements, such as displacement, speed, and acceleration, and can confirm any imbalance or damage to the bending or rotating parts of the bearing shaft.
By using a vibration meter, you can quantitatively measure the vibration and determine the state of the bearing. Therefore, it is widely used as a benchmark monitoring tool.
However, it is important to understand the measurement method of vibration and the significance of vibration values when using vibration timing. Acquiring such skills takes considerable time.
Moreover, the damage state of each part of the bearing, such as the outer wheel, inner wheel, and ball, can be determined by analyzing the measured vibration value by cycle number. Measuring vibration displacement, velocity, and acceleration is called a simple diagnosis, while determining the damage state through cycle number analysis is called a precise diagnosis.
Depending on their importance, simple diagnosis and precise diagnosis are carried out on the production site separately.
Measured with abnormal sound stethoscope
The technique used to measure with an abnormal sound stethoscope involves using a stethoscope or stethoscope rod and directly listening to confirm whether the sound produced from the rotating bearing is the same as that heard during normal usage. This requires spot inspectors to possess a deep understanding of all kinds of abnormal sounds and to reach a high level of skill.
To analyze the lubricating oil and grease used in the bearing, the direct microscope method is used to confirm the bearing metal’s oil analysis. This method involves extracting the lubricating oil or grease from the bearing or directly examining the type, shape, and quantity of the metal powder used in the bearing with instruments like a microscope.
This method permits the physical removal of the damaged piece from the bearing to confirm and understand the initial damage state of the bearing. However, it is similar to the vibration meter.
Mastering the technology and skills demands specialized knowledge and equipment.
Conclusion
In today’s work and production environment, there are many technologies and skills available for detecting abnormal bearings. Choosing the most suitable method from among these is crucial.
Once a method is selected, it is important for inspectors to learn, test, and analyze more in order to effectively utilize the chosen technology or skill.
