Analysis of the reasons for the breakage of tungsten carbide roller ring in finishing rolling mill and related improvements

1. Analysis of reasons for roller breakage

1.1 During the stacking of steel in the precision rolling unit, the heat of the rolled piece is transferred to the adjacent roller rings, causing the temperature of the roller rings to rise and the thermal stress to be concentrated. However, during the accident handling process, the surface temperature of the roller rings rapidly decreases, making it easy for the phenomenon of roller breakage to occur.

The main reasons for stacking steel inside the unit are as follows:

(1) Improper roller matching. The Morgan high-speed wire rod precision rolling unit adopts collective transmission, and the transmission speed ratio of each frame is different. Therefore, it is required that the precision rolling machine not only meets the gear transmission ratio between each frame, but also requires the outer diameter error of the roll ring of the same frame to be controlled within ± 0.05mm when matching rollers. Otherwise, the rolled piece will shake between the two frames, ultimately causing steel stacking between the frames.

(2) Poor alignment of the rolling line. There are various guide grooves such as air seals, water tanks, recovery sections, and pinch rolls in the guide rails between each frame in the precision rolling unit, as well as the section from the unit outlet to the wire drawing machine. If the rolled piece is obstructed during high-speed operation, it can lead to the phenomenon of steel stacking.

(3) The guide rail of the precision rolling unit is faulty. Insufficient oil and gas lubrication or cooling of the guide bearings in the precision rolling unit can lead to bearing damage, inflexible rotation of the guide rollers, jamming, and cracking, resulting in the phenomenon of steel stacking. (4) Raw material defects. There are defects in the raw material billet. During the rolling process of the precision rolling unit, local defects in the cross-section of the rolled piece cannot withstand normal pressure deformation, resulting in fracture and the formation of steel stacking phenomenon.

1.2 Unreasonable Roll Gap Setting: The roll gaps of each rolling mill should be strictly adjusted according to the roll gap range designed in the rolling program table. If the roll gap adjustment of a certain roll 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 guide of the rolling mill, resulting in a sharp increase in roll ring stress and surface temperature, leading to a roll breakage accident.

1.3 Abnormal impact force on the roller ring

(1) The incoming material size of the finishing mill is too large. According to different product specifications, the incoming material size of the finishing mill must be strictly controlled within the standard range. If the material shape size is too large, the impact force borne by the first rolling mill roll ring of the finishing mill is too large, resulting in deformation and increased rolling force, causing the finishing mill unit to experience roller breakage.

(2) The installation of the guide is incorrect. The installation of guide rails for each rolling mill requires that the rolled parts can smoothly pass through the guide rails without causing any impact on the roll rings. Otherwise, during each pass of steel, the rolled piece will cause abnormal impact force on the roller ring, ultimately leading to the occurrence of roller breakage accidents. The poor cooling effect of the

1.4 roller ring is closely related to the usage cycle of Tungsten Carbide Roller rings and the surface cooling effect in the actual production process. When the surface cooling of the roller ring is insufficient, the surface temperature abnormally increases, and the wear and crack rate will intensify, greatly reducing the service life of the roller ring. In severe cases, roller crushing accidents may occur.

The main reasons for poor cooling effect are as follows:

(1) Abnormal cooling water pressure. The water pressure for roller ring cooling is generally required to be controlled between 0.4 and 0.6 MPa. If the water pressure is too high, the cooling water is prone to splashing and cannot take away the surface heat of the roller ring in a timely manner, which affects the cooling effect. If the water pressure is too low, the cooling water cannot break through the vapor layer formed on the surface of the roller ring, affecting cooling or the water flow rate is relatively insufficient, which cannot take away the surface heat of the roller ring in a timely manner, affecting cooling.

(2) Abnormal cooling water nozzle or pipeline. In the actual production process, abnormalities in the cooling water nozzle or pipeline often lead to roller ring cooling failure, abnormal surface temperature rise, and ultimately result in roller crushing accidents.

The main reasons are as follows:

① The cooling water pipeline is damaged and there is a phenomenon of leakage. The cooling water is heavily diverted before reaching the roller ring, causing the surface of the roller ring to fail to achieve the expected cooling effect, ultimately leading to accidents The cooling nozzle is blocked. Due to the poor quality of the cooling water, some impurities accumulate at the cooling nozzle, causing the cooling water to be unable to spray onto the surface of the roller ring normally, affecting the cooling effect Cooling nozzle offset. Due to low installation technology or displacement of the cooling nozzle during accident handling, the cooling water cannot cool the high-temperature area of the roller ring, resulting in an increase in roller ring temperature and ultimately leading to accidents.

1.5 The installation and disassembly temperature of the roller ring does not meet the requirements. During the installation process, the temperature difference between the installation shaft, cone sleeve, and roller ring should be controlled at around 15 degrees. Otherwise, the temperature difference between the installation shaft, cone sleeve, and roller ring is too large, resulting in significant differences in thermal expansion. Firstly, it leads to abnormal interference force between the roller ring and cone sleeve, and the cone sleeve is prone to automatic detachment; The second reason is that the temperature of the roller ring is relatively low. During the pressing process, the internal stress of the roller ring is concentrated, which is accompanied by an increase in temperature during the production process, leading to increased stress and the formation of roller crushing accidents. This type of problem is particularly prominent in the winter production process, so effective measures such as insulation must be taken to control it.

1.6 The working pressure of roller ring installation is not standard. When the roller ring is installed, its working pressure is lower than the standard requirements, resulting in insufficient interference force between the roller ring and the cone sleeve, causing the cone sleeve to fall off, ultimately leading to roller breakage accidents. On the contrary, if the pressure setting for roller installation is greater than the standard, it will cause abnormal excessive interference force between the roller ring, cone sleeve, and installation shaft, resulting in the inability to remove the forced roller during roller crushing or dismantling.

1.7 There are debris on the surface of the roller ring, cone sleeve, or installation shaft. During the installation process of the roller ring, the oxide scale, floating rust, and other impurities on the surface of the roller ring, cone sleeve, or installation shaft were not thoroughly cleaned, resulting in a decrease in friction between the three, causing the roller ring to slip or fall off, ultimately leading to a roller crushing accident.

1.8 The surface of the cone sleeve and installation shaft is severely worn. After long-term use, the surface of the cone sleeve and installation shaft may experience certain wear. However, when the contact surface between the cone sleeve and the installation shaft is less than 80%, the expected interference force between the cone sleeve and the installation shaft cannot be achieved, making it easy to exit, slip, and other phenomena, ultimately leading to roller breakage accidents.

2. Related improvement measures

(1) In the daily production process, strengthen online process supervision in accordance with various standard requirements, and reduce the incidence of accidents in the precision rolling unit.

(2) Regularly inspect the control of material shape dimensions to ensure that the head, middle, and tail material shape dimensions of each rolling mill are controlled within the standard range.

(3) Check the cooling water system of each roll during each shutdown to ensure that the surface cooling effect of the roll ring meets the standard requirements.

(4) Before installation, monitor the temperature of the roller ring and installation shaft to ensure that the temperature difference is controlled within a reasonable range. Especially in winter production, insulation treatment is carried out on the roller ring before going online.

(5) Develop a reasonable working pressure for the installation of the precision rolling roller ring, and regularly maintain and upkeep the roller changing trolley to ensure that the installation pressure of each roller ring is controlled within the standard range.

(6) During the installation process of the roller ring, the inner surface of the roller 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 installation shaft to ensure that the contact surface reaches over 80%.

3. Conclusion: 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 efficiency.

Company product profile:
Luoyang Golden Egret Geotools Co.,Ltd. founded in2012,is wholly-owned by iisted company XiamenTungsten Co.,Ltd (XTC).As a backbone cemented carbideenterprise of XTC with registered capital of 1.05billionRMB and first investment of ibillion RMB,GEOTOOLSspecializes in producing and selling high quality tungstenpowder,Tungsten Carbide Powder, carbide anvils,carbideroll rings,carbidesubstrates for PDC bit,mining drill bitsand hard facing materials.
Based on decades of production experience of WC based hard-facing materials, world-class technologies and modernautomatic production lines, GEOTOOLS dedicates into development and production of high quality hard facing materialwith high hardness, best wear resistance, best corrosion resistance and application solutions.
XTC brand Thermal Spray Powder mainly includes Wc- based & Cr3C2-based. The WC coating has high hardnessdurable wear resistance, abrasion resistance, corrosion resistance and high bonding strength, mainly used in oil &gas valves, mining tools, injection screws and printing machinery parts, The Cr3c2 coating has higher thermalstability and anti-oxidation, which can be used in a high temperature and corrosive environment, e.g. inner- wall ogas pipeline and pump.
With high degree of sphericity & excellent alloy organization, cemented carbide pellet is mainly used in weldingas an additive material of PTA Powder and tubular weldina rod to improve the wear resistance of the work pieces.
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