1 Correct matching relationship and clearance determination of four-row cylindrical roller bearings for rolling mills
(1) Determine the correct assembly relationship of four-row cylindrical roller bearings for rolling mills
The correct assembly relationship of four-row cylindrical roller bearings for rolling mills should be that each set of bearings should be assembled with a specific bearing seat, one or several fixed ends of rollers, according to the provisions of four-row cylindrical roller bearings for rolling mills. After the bearing, bearing seat, supporting parts and rolls are assembled, the parallelism between the working side of the bearing seat and the busbar of the roll should be measured and adjusted to ensure that after the roll system is installed in the arch, the centerline of the roll is in the same vertical. in plane.
Since the inner ring of the four-row cylindrical roller bearing used in the rolling mill can be separated, usually a rolling mill usually needs to prepare at least one set of spare rolls. In this way, if the strict specification requirements are not carried out during the use process, the actual production process often occurs not according to the original The phenomenon that the assembly relationship is used for bearing assembly, especially when there is a problem with one set of bearings, when the production task is busy, the manager often asks to disrupt the original pairing relationship. This will seriously affect the correct assembly position of the rolls in the arch, and even affect the shape quality of the rolled products.
After this fixed assembly relationship is broken, the running-fit relationship between the rolling element and the raceway is broken, which will cause serious uneven stress on the rolling element and the raceway. Fatigue pitting; in severe cases, the rolling elements are broken, which damages the inner and outer ring raceways of the bearing, causing the bearing to burn and lock.
Therefore, the assembly relationship of four-row cylindrical roller bearings for rolling mills is not allowed to be damaged casually. At present, individual enterprises have not yet had a deep understanding of this point. Many four-row cylindrical roller bearings for rolling mills are damaged due to this. of.
(2) Determination of bearing clearance
Bearing clearance is an important technical parameter for whether the bearing can work normally. It directly affects the load distribution, friction, temperature rise and service life of the bearing. Due to the poor working conditions of rolling mill bearings, the rolling load, speed, lubrication, temperature rise, fit interference, and rotation accuracy should be considered. The principle is that when the working conditions allow, the smaller the bearing clearance, the better the service life of rolling mill bearings. The rolling mill adopts four-row cylindrical roller bearings for standard rolling mills. In general, the standard clearance of group C3 or C4 is used for the clearance. For four-row cylindrical roller bearings for high-precision rolling mills, the clearance needs to be determined by the technical personnel of the bearing manufacturer and the bearing manufacturer according to the precision requirements of the rolling mill. The machining allowance is reserved for the outer circle of the inner ring of the bearing, and the inner ring of the bearing is assembled to the roll. Later, the outer circle of the inner ring of the bearing is ground to the specified size together with the roller surface to obtain high-precision coaxiality tolerance.
During the use of rolling mill bearings, it can be judged whether the bearing clearance is appropriate according to the damage of the bearing.
①If the bearing burns out, it is not because the inner ring of the bearing slides on the roll diameter, or the bearing is overheated due to the relative friction and poor lubrication of the related parts. It can be considered that the working clearance of the rolling mill bearing is too small.
②The bearing rings and rollers are broken. If it is not due to the raw materials, bearing quality, excessive impact load and poor installation, it can be considered that the working clearance of the rolling mill bearing is too large, so that the bearing load angle is too small (the ideal load bag Angle is 120 ° ~ 150 °), resulting in a large strain pressure per unit area of the material and a large roller load.
In addition, when the rolling mill bearings of different manufacturers are used interchangeably, it is necessary to pay attention to whether the selection standard of the rolling mill bearing clearance is the same (that is, whether the inner circle size and tolerance of the outer bearing components are consistent), the size and tolerance value of the inner ring raceway Whether it is the same and whether the clearance is the same, otherwise the bearings cannot be interchanged. This is another reason why it is emphasized that the bearing must have a fixed assembly relationship.
Reasonable and reliable matching accuracy is also a prerequisite for the normal use of rolling mill bearings. The inner ring of the four-row cylindrical roller bearing in the rolling mill roll system bears the circumferential radial load, so it must be an interference fit with the roll neck; the outer ring supports the concentrated load and needs to be over-fitted with the box hole; the matching bearing only bears the axial direction. Load and axial positioning function, and require easy loading and unloading, so the inner ring of the bearing and the roll neck use clearance fit, the outer ring can not bear radial force, and the box hole is a large clearance fit.
2 Strengthen the purchase, supply and incoming inspection of bearings, and continuously accumulate experience
There are many bearing manufacturers in my country now producing four-row cylindrical roller bearings for rolling mills. Due to the different technical levels of each manufacturer, the quality of the bearings produced is also very different. Therefore, more inspections must be carried out in the process of purchasing bearings. According to the actual use situation, continue to explore and summarize, and find a supplier that suits the requirements of the enterprise. At the same time, strengthen the inspection of the bearing in the factory to ensure the quality of the purchased bearings.
Due to the particularity of four-row cylindrical roller bearings for rolling mills, although JB/T5389.1-2005 “Four-row cylindrical roller bearings for rolling mills” stipulates the corresponding standards, in actual use, there are often many enterprises based on The situation of signing non-standard bearings with the bearing manufacturer due to the special requirements of the equipment.
For standard bearings, it can be accepted in accordance with the requirements of JB/T5389.1-2005 and the corresponding supporting standards.
For non-standard bearings, in addition to the acceptance according to the contract, and the requirements of JB/T5389.1-2005 and the corresponding supporting standards, the following points should also be noted:
①Whether the bearing marks are clear and identifiable, and whether the codes such as the factory name and year are qualified.
②Whether there are bumps, abrasions, turning tool marks, rust, black spots, material defects, etc. on the bearing surface, these traumas will often become stress concentration points, resulting in bearing fatigue damage.
③Whether the bearing is missing parts, such as ferrules, washers, bushings, retaining rings, seat rings, rolling elements, cages, sealing rings, etc., are not allowed to be missing.
④ Check whether the bearing has mismatched parts.
⑤ Check whether there is any mismatch in the specifications of the bearing parts.
3 Strictly and scientifically formulate the production process to avoid bearing overload
It has been mentioned many times that the characteristics of roller bearings are: harsh working environment, large workload, high unit pressure, large heat generation, and short life. It can be said that if the bearings can be used in accordance with the specifications, the normal scrapping standard can be fully met. However, in the actual use process, various overload phenomena often occur. Here, one is the human factor, the other is the accident factor, and the third is the equipment factor. No matter what kind of overload, it will have a relatively large impact on the bearing, and the serious one will cause an accident.
When the bearing operates under overload conditions, abnormal wear and fatigue damage will generally occur, and even equipment accidents such as rolling elements breakage and instantaneous bearing damage occur.
Common rolling mill bearing overload forms are as follows:
①Stable one-way overload: For example, there is a problem with the installation of the components of the rolling mill drive system, and the change of the roll diameter makes the transmission takeover deflection angle of the drive system too large and other reasons to generate additional loads. Such loads are stable and unidirectional. This type of overload generally does not have a large overload value, but this type of overload generally has a long action time and is not easy to be found. It will be found when a problem occurs. For this type of overload, it can be avoided by strengthening equipment overhaul, maintenance and maintenance, and standardizing equipment management in accordance with equipment drawings, technical requirements and overhaul and maintenance procedures. The key is to strengthen the responsibility of operators, maintenance and management personnel.
②Cyclic load overload: The unreasonable arrangement of the rolling process makes the distribution of the processing rate of the rolling passes unreasonable, and the load distribution of the bearing in each rolling pass is uneven, which makes the bearing run under a large load for a long time. There are four aspects here. s reason.
First, the technical level of the process scheduling personnel, or the lack of understanding of the technical parameters and performance parameters of the rolling mill, and the unreasonable rolling process arranged, resulting in overloading of the rolling mill.
Second, in order to unilaterally pursue the output, the process arrangement of high processing rate was deliberately carried out, and the bearing capacity of the rolling mill was not considered much, resulting in overload of the rolling mill.
The third is that the rolling mill operators do not operate according to the process, steal rolling passes during use, or change the reasonable rolling process, causing the rolling mill to be overloaded.
Fourth, the rolling mill with roll bending function, the bending force is too large, and the bending force and the deformation resistance of the rolling piece act together on the bearing of the rolling mill, causing the bearing to be overloaded.
The above four situations all cause the bearing to work under the condition of cyclic load overload for a long time.
③Instantaneous overload: during rolling work. Due to the occurrence of process accidents, the bearing is overloaded instantaneously, such as the roll wrapping after the strip is broken, and the tolerance of the rolled strip section is too large; for the hot rolling mill, the billet temperature is too low, the head is rolled and so on. The rolling mill bearing is subjected to concentrated overload load in a short period of time, causing damage and failure.
In steel rolling machinery and equipment, the most common occurrence of roll bearing is unidirectional overload or cyclic overload overload. These overload effects often cause local fatigue cracks in the rolling elements, resulting in bearing fatigue failure.
How to avoid the overload of four-row cylindrical roller bearings for rolling mills is the key factor to improve their effective service life. Judging from the actual use situation, copper processing enterprises unilaterally pursue production, resulting in the long-term overload operation of four-row cylindrical roller bearings for rolling mills.