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Coarse Rolling Mill Universal Joint Coupling

Usage Status of Coarse Rolling Mill Universal Joint Coupling

The universal joint coupling is a critical component of the main drive system of the coarse rolling mill. Its function is to transmit the torque output by the main motor to the mill roller, thereby completing the normal production rolling. Since the commissioning of the rolling line in 2006, based on the on-site working conditions, the usage life of the coupling, the complexity of replacement, and the relatively long replacement time, it is generally replaced every two years. This replacement is typically scheduled during longer-term maintenance or overhauls, and the cross assembly components have never been replaced individually in between.

Replacement Scheme and Principle of Cross Assembly

Due to fatigue damage leading to failure and shutdown of the cross assembly bearings on the universal joint coupling below the hot-rolled coarse rolling mill, the cross assembly components must be replaced. According to the conventional replacement method, the entire shaft with the cross assembly components should be replaced. However, due to the complexity of the on-site operation space and the structure of the main drive device of the coarse rolling mill, replacing the entire coupling requires dismantling the upper universal joint coupling first and then dismantling and replacing the lower one. This process takes more than 48 hours, involves high labor intensity, numerous safety hazards, and causes significant disruption to normal production.

Therefore, based on the actual on-site conditions, the connection structure of the universal joint coupling cross assembly, and the connection method with the mill roller, a replacement method utilizing the coarse rolling mill working rolls was devised. This method involves using the working rolls to carry the cross assembly components in and out of the rolling mill, avoiding the need for the overall replacement of the upper and lower universal joint couplings and reducing the operation time.

Replacement Method and Steps

The replacement method and steps are as follows:

Based on the actual on-site conditions, determine the replacement plan, assess the reliability of the operation method, prepare the necessary tools, complete the work permit, and load the new cross assembly components onto the offline working rolls.

Use the roll-changing trailer to extract the upper and lower working rolls, support them under the lifting guide rail with channel steel to prevent the guide rail from tilting due to the increased weight of the cross assembly components, and simultaneously disassemble the connecting bolts of the cross assembly components.

Use the roll-changing trailer to load the upper and lower working rolls, open the clamping device, and disassemble the shaft sleeve clamping pads.

Close the clamping device, insert wedge blocks into the clearance between the cross shaft and the forkhead hole, and weld and fix the cross assembly components with channel steel to prevent relative movement and deviation of the various components of the cross assembly. Remove the connecting bolts.

Weld and reinforce the cross assembly components with the bearing seat of the working rolls using channel steel to prevent the cross assembly components from separating from the flat head of the working rolls during extraction.

Jog the balance hydraulic cylinder of the universal joint coupling, disengage the end teeth connecting the cross assembly components with the coupling body, extract the upper and lower working rolls, and remove the rolling mill roller and cross assembly components as a whole.

Check the position of the cross assembly components on the centerline of the working rolls, adjust the angle, elevation, and other parameters of the newly loaded cross assembly components to be completely consistent with the removed ones, and fix them with wedge blocks and channel steel.

Reassemble following the above steps, install the bolts, and tighten them. Remove the auxiliary channel steel, install the coupling tightening pads, extract the working mill roll, and disassemble the channel steel under the lifting guide rail.

Conduct trial operation and debugging. Repeatedly insert and extract the upper and lower working rolls to check if the roll installation and removal are smooth.

Completion of the operation, clean up the site, and remove the work permit. Close coordination with production operators is essential during the replacement operation to ensure safety.


After consulting with the universal joint coupling manufacturer and other steel rolling mills, no similar replacement method has been found. This method avoids dismantling components such as dust pipes above the coupling, the balance shaft bushing of the coupling, and connecting bolts on the motor side of the coupling. It significantly reduces labor intensity and operation time, ensuring safety and reliability. The method is advanced, and the results are remarkable.

This operation method has achieved substantial economic and social benefits, calculated as follows:

Social Benefits

Following the conventional method of replacing the entire coupling, replacing the lower universal joint coupling cross assembly requires dismantling the upper universal joint coupling, with a total operation time exceeding 48 hours and significant labor intensity and safety hazards. Using this method, the replacement of the lower universal joint coupling cross assembly only takes 12 hours, reducing the operation time by 36 hours, with low labor intensity and high safety reliability.

Work hours are crucial for the scheduling of maintenance personnel. This method can save 720 work hours (20×36), benefiting the arrangement of maintenance personnel in similar projects in the future.

Economic Benefits

The project requires 20 workers, assuming an hourly cost of 30 yuan for technical workers. The cost savings can be calculated as follows:

20×36 (hours)×30 = 21,600 yuan

The hot rolling mill produces 400 tons of rolled steel per hour, allowing for the additional production of steel:

36×400 = 14,400 tons

Calculating the profit per ton of steel as 30 yuan, the additional profit is:

14,400×30 = 432,000 yuan

The total economic benefits generated amount to 216,000 + 432,000 = 648,000 yuan.

This replacement method saves time, is safe and reliable, and involves minimal labor intensity. It is suitable for rolling mill equipment with similar structures for the replacement of universal joint couplings and working rolls.

Contact Us

Contact: Ed Lee

Phone: +86 13613237999

Tel: +86 13613237999

Add: Runhao steel rolling machinery, dalinggongzhuang village, Fengrun District, Tangshan City, Hebei Province