Analysis of the Causes of Roller Ring Breakage
Steel stacking in finishing mill
When steel is piled up, the heat of the rolled piece is transferred to the roller ring of the adjacent frame, causing the roller ring temperature to rise and the thermal stress to concentrate. However, during the accident handling process, the surface temperature of the roller ring drops rapidly, which makes it easy for the roller ring to break. The main reasons for steel pile up in the unit are as follows:
Improper roll matching.
The Morgan high-speed wire rod finishing unit adopts collective transmission, and the transmission speed ratio of each frame is different. Therefore, when matching the rolls, the finishing mill is required to meet the gear transmission ratio between each frame and also require the outer diameter error of the roller ring of the same frame to be controlled within ±0.05mm. Otherwise, the rolled piece will shake between the two frames, eventually causing steel pile up between the frames.
Poor alignment of the rolling line.
There are various guide grooves such as air seals, water tanks, recovery sections, and pinch rollers in the guides between the frames in the finishing mill and the section from the unit outlet to the laying machine. If the rolled piece is blocked during high-speed operation, it will cause steel pile up.
Failure of the guides of the finishing mill.
Insufficient oil and gas lubrication or cooling of the guide bearings in the finishing mill leads to bearing damage, inflexible rotation of the guide rollers, or jamming and cracking, resulting in steel piles.
Raw material defects.
The raw material billet has defects. During the rolling process of the finishing mill, the local defects in the cross-section of the rolled piece cannot withstand normal pressure deformation and break, resulting in steel piles.
Improper roll gap setting
The roll gap of each rolling mill should be adjusted strictly according to the roll gap range designed in the rolling program table. If the roll gap adjustment of a certain rolling mill is less than the standard or even close to 0mm, friction will occur between the roll rings or between the roll rings and the inlet and outlet guides of the rolling mill, causing a sharp increase in the roll ring stress and surface temperature, resulting in a broken roll accident.
The roller ring is subjected to abnormal impact force
The size of the incoming material of the finishing mill is too large.
The size of the incoming material of the finishing mill is too large.
According to different product specifications, the size of the incoming material of the finishing mill must be strictly controlled within the standard range. If the material size is too large, the impact force on the roller ring of the first rolling mill of the finishing mill will be too large, and the deformation and rolling force will increase, causing the roller to break in the finishing mill.
The guide position is not installed in the center.
The installation of the guide guards of each rolling mill requires that the rolled piece can pass through the guide guard smoothly and cannot cause impact on the roller ring. Otherwise, the rolled piece will cause abnormal impact force on the roller ring every time the steel passes, and eventually a roller breakage accident will occur.
Roller ring cooling effect is not good
In the actual production process, the service life of the tungsten carbide roller ring is closely related to the surface cooling effect. When the roller ring surface is not cooled enough, the surface temperature will rise abnormally, the wear and crack rate will increase, and the service life of the roller ring will be greatly reduced. In severe cases, the roller will be broken. The main reasons for the poor cooling effect are as follows:
Abnormal cooling water pressure.
The cooling water pressure of the roller ring is generally required to be controlled between 0.4-0.6MPa. If the water pressure is too high, the cooling water is easy to splash and cannot take away the heat from the roller ring surface in time, affecting the cooling effect. If the water pressure is too low, the cooling water cannot break through the steam layer formed on the roller ring surface, affecting cooling, or the water flow is relatively insufficient, and the heat from the roller ring surface cannot be taken away in time, affecting cooling.
Abnormal cooling water nozzle or pipeline.
In the actual production process, the cooling of the roller ring fails and the surface temperature rises abnormally due to abnormal cooling water nozzle or pipeline, which eventually leads to a broken roller accident. The main reasons are as follows: ① The cooling water pipeline is damaged and there is leakage. The cooling water is diverted in large quantities before reaching the roller ring, resulting in the failure of the roller ring surface to achieve the expected cooling effect, which eventually leads to an accident. ② The cooling nozzle is blocked. Due to the poor quality of the cooling water, some impurities accumulate at the cooling nozzle, resulting in the inability of the cooling water to spray normally on the roller ring surface, affecting the cooling effect. ③ The cooling nozzle is offset. Due to the low level of installation technology or the displacement of the cooling nozzle during the accident handling process, the cooling water cannot cool the high-temperature area of
The installation and removal temperature of the roller ring does not meet the requirements
During the installation process, the temperature difference between the installation shaft and the taper sleeve and roller ring should be controlled at about 15 degrees. Otherwise, the temperature difference between the installation shaft and the taper sleeve and roller ring is too large, and there is a large difference in thermal expansion. First, the interference force between the roller ring and the taper sleeve is abnormal, and the taper sleeve is easy to fall off automatically; second, the temperature of the roller ring is low. During the pressing process, the internal stress of the roller ring is concentrated. During the production process, the temperature rises, resulting in increased stress and a broken roller accident. Such problems are particularly prominent in the winter production process, so insulation and other measures must be taken to effectively control them.
The working pressure of the roller ring installation is not standard
When the roller ring is installed, its working pressure is lower than the standard requirement, resulting in insufficient interference force between the roller ring and the taper sleeve, causing the taper sleeve to fall off, and eventually leading to roller breakage. On the contrary, if the roller installation pressure is set higher than the standard, the interference force between the roller ring, the taper sleeve and the installation shaft will be abnormally large, causing the roller to break or the roller cannot be removed when it is forced to break.
There are foreign objects on the surface of the roller ring, cone sleeve or mounting shaft
During the installation of the roller ring, impurities such as iron oxide and floating rust on the surface of the roller ring, tapered sleeve or installation shaft were not thoroughly cleaned, resulting in reduced friction between the three, the roller ring slipping or falling off, and ultimately causing a broken roller accident.
The surface of the taper sleeve and the mounting shaft is severely worn
After long-term use, the surface of the tapered sleeve and the mounting shaft will show certain wear. However, when the contact area between the tapered sleeve and the mounting shaft is less than 80%, the expected interference force between the tapered sleeve and the mounting shaft will not be achieved, and it is easy to exit, slip, etc., and eventually cause a broken roller accident.
Related improvement measures
(1) In the daily production process, in accordance with various standard requirements, strengthen online process supervision to reduce the accident rate in the finishing mill.
(2) Regularly check the control of material size to ensure that the material size of the head, middle and tail of each rolling mill is controlled within the standard range.
(3) Use each shutdown to check the cooling water system of each roll to ensure that the cooling effect of the roll ring surface meets the standard requirements.
(4) Monitor the temperature of the roll ring and the installation shaft before installation to ensure that the temperature difference is controlled within a reasonable range. Especially in winter production, the roll ring should be insulated before going online.
(5) Establish a reasonable working pressure for the installation of the finishing roll ring, and regularly maintain and service the roll changing trolley to ensure that the installation pressure of each roll ring is controlled within the standard range.
(6) During the installation of the roll ring, the inner surface of the roll ring, the inner and outer surfaces of the cone sleeve, and the surface of the installation shaft must be thoroughly cleaned to ensure that the surface is clean.
(7) Regularly inspect the cone sleeve and the installation shaft to ensure that the contact surface reaches more than 80%.
By analyzing the causes of roller ring breakage and taking corresponding control measures, good results have been achieved in the actual production process, effectively reducing the incidence of roller breakage accidents, reducing unplanned downtime, and improving production operation rate.
English 