Introduction:The die frame is the "skeleton" of the rolling mill, while the liner plates and sliding plates are the core components that bear pressure and perform sliding movements. Compared to the easily damaged parts such as bearings and rollers, the faults of the die frame and liner plates belong to major structural and systematic failures of the equipment. Once there is an excessive gap, erosion, or jamming, it will directly cause rolling jitter, poor plate shape, failure of the lowering action, and unplanned shutdown of the entire line. Moreover, these issues usually require major overhauls to be resolved. This article analyzes the root causes of liner plate lubrication failure, excessive gap, material mismatch, and frame wear through four typical real-case scenarios, and provides feasible rectification and online repair solutions.
The frame window of a hot rolling 1780 finishing mill unit adopts a structure of copper-based alloy liner plates and wear-resistant sliding plates, which bears all the vertical and horizontal loads of the rolling mill, including roll reduction, rolling impact, and frame positioning. This part operates under a low-speed and heavy-load sliding friction condition. It relies on a centralized dry oil lubrication system for continuous oil replenishment, and is the core component that ensures the flexibility of roll reduction and the stability of the frame.
During the rolling process of thick-section steel billets, the machine group suddenly encountered a pressing-down jamming issue. The pressing-down screw mechanism became sluggish and unresponsive, unable to adjust the roll gap normally. As a result, the production line was forced to stop urgently. Upon disassembly and inspection of the window interface of the frame, it was found that on both the inlet and outlet sides, the sliding plates had suffered extensive high-temperature oxidation, with the surface alloy layer peeling off, local areas showing adhesive damage, and the contact surface between the liner plate and the frame sliding plate completely lost the oil film, presenting a state of dry metal friction and jamming. Severe liner plate brake failure occurred.
1. Fully unclog the lubrication pipeline of the plaque, replace the blocked oil connection joints and aged oil pipes, and test the oil supply pressure and oil output status at each point to ensure uniform and unobstructed oil supply at each lubrication point of the sliding plate.
2. Polish and repair the contact surfaces of the abraded and scratched sliding plates, use the plane grinding process to correct the flatness of the mating surface, eliminate protrusions and burrs, and ensure smooth sliding contact.
3. Before heavy-load rolling, add a manual grease replenishment process to establish a stable oil film in advance and avoid the risk of instantaneous heavy-load dry grinding.
4. Establish a special point inspection ledger for plaque lining plate lubrication, daily check the oil output at each lubrication point, and test the grease condition weekly to eliminate the risks of oil pipeline blockage and lack of oil.
After the rectification, the problems of liner plate erosion, press-down jamming, and machine frame brake failure were completely eliminated. The adjustment accuracy of the press-down system returned to the standard level. The sliding board moved smoothly without any jamming. The stability of the rolling process for thick-section steel billets was significantly improved, completely resolving such major shutdown risks.
The window of the frame of a medium-thick plate rolling mill is designed with a standard clearance of 0.15–0.25mm on one side, and it is subjected to alternating rolling impact loads over a long period of time. The clearance of the sliding plate of the frame is a key parameter for controlling the horizontal oscillation of the rolling mill and the stability of the roll gap. Any deviation from the standard clearance will directly affect the rolling accuracy of the plates and the smooth operation of the equipment.
During the rolling process of the rolling unit, low-frequency vibrations and frame shaking occurred continuously. The rolled plates frequently deviated, the plate surface showed periodic undulations, and the thickness tolerance exceeded the standard. Even after multiple adjustments of the reduction parameters and corrections of the roller accuracy, the problem could not be solved. The actual measurement of the sliding clearance between the frame window and the slide plate showed that the maximum clearance reached 0.65mm, which far exceeded the design standard and was classified as a serious excessive clearance failure.
1. Long-term impact wear causes the gap to continuously expand: The steel plate bites the steel and the impact load from the throw steel occurs frequently. The sliding plate and the liner plate undergo repeated friction and wear over a long period of time, gradually exceeding the specified clearance, resulting in the failure of the horizontal positioning of the frame.
3. Excessive clearance triggers chain vibration: The excessive clearance causes the rolling mill to undergo horizontal movement during the rolling process, resulting in dynamic deviation of the roll gap. Eventually, this is directly reflected as quality defects such as sheet deviation, wavy shape, and uneven thickness, forming a chain problem of "equipment clearance exceeds limit → product quality defects".
1. The gap between the sliding plate is adjusted using the gasket fine-tuning method. Based on the actual measured wear amount, the stainless steel adjustment gasket is added or subtracted precisely, and the gap on one side is strictly calibrated to the standard range of 0.15–0.25mm.
2. For severely worn sliding plates and liner plates, they can be used face-down or replaced entirely. The window fitting accuracy is corrected, and the foundation of the frame shaking is eliminated.
3. A quarterly special inspection system for the gap of the arch is established. During each major repair， the gap of the window and the parallelism of the frame must be measured. When the wear exceeds the limit， timely fine-tuning and compensation are carried out to prevent the accumulation of excessive gap.
4. The rolling process is optimized to reduce the impact speed during the steel biting moment， reduce the alternating impact load on the frame， and delay the wear rate of the sliding plate.
The window alignment accuracy of the sign frame has been fully restored. The problems of frame vibration and horizontal movement have been completely eliminated. The quality defects such as board deviation, wavy shape, and thickness fluctuation have been significantly reduced. The rolling stability has been significantly improved. There is no need to frequently adjust the process parameters. The equipment and product quality have both reached the standards.
A high-speed bar high-line rough rolling unit has a large rolling load and a high frequency of impacts. The original equipment was configured with high lead-copper alloy wear-resistant liners, which ensured stable service life. During the inspection and renovation process, in order to control costs, ordinary cast iron liners were replaced. However, these liners were not suitable for light-load conditions and were highly incompatible with the heavy-load impact conditions of the unit.
After replacing the ordinary cast iron liners, the equipment went into operation for only 20 days before the liners began to show extensive wear, grooves, deformation, and the clearance between the components rapidly exceeded the normal liner's 6-8 month service life. The equipment also emitted abnormal noises, had excessive vibration, decreased pressing adjustment accuracy, and frequently required shutdown for inspection and replacement of the liners. As a result, the operation and maintenance costs increased instead of decreasing.
1. The material's wear resistance does not match the working conditions: Ordinary cast iron liners have high hardness but poor toughness and weak impact resistance, and are only suitable for light-load, non-frequent impact sliding conditions; while the heavy-load, high-frequency impact conditions of the rough rolling unit require high toughness, high wear resistance, and anti-galling copper alloy liners. Mismatching will lead to rapid wear and damage.
2. Insufficient anti-friction and high-temperature resistance: During the rolling process, friction causes temperature rise. Cast iron liners have poor high-temperature resistance and dry grinding resistance. Local high temperatures can cause thermal deformation and surface scratches, accelerating wear failure.
3. Cost reduction selection： Blindly replacing low-cost parts， ignoring the hard requirements of the working conditions (load， impact， temperature) on the material， resulting in the reverse cost reduction problem of "frequent replacement of low-cost parts， with higher overall costs".
1. Restore the original high-maintenance copper alloy lining plates, strictly matching the heavy-load impact conditions of the rough rolling process, and eliminating the problem of material mismatch.
2. Establish a material selection standard for equipment accessories, matching the lining plate and slide plate materials according to the rolling load, impact frequency, and working temperature categories, and prohibiting the random replacement of non-standard accessories.
3. Standardize the acceptance process of spare parts, verifying the material, hardness, and wear resistance parameters of the lining plates and slide plates before they are stored in the warehouse, and prohibiting the use of unqualified parts.
4. For machine positions with extremely high impact, regularly increase lubrication and optimize the rolling buffer parameters to reduce the operating load of the lining plates.
The service life of the liner plates has been restored to the standard cycle, completely solving the problems of short-term rapid wear and frequent replacements. All equipment vibrations and abnormal noises have been eliminated. The adjustment accuracy of the pressing system is stable. Although the single-piece purchase cost has increased, the overall downtime, labor costs, and repeated maintenance costs have been significantly reduced, achieving true quality improvement and cost reduction.
A 10-year-old hot-rolled wide-gauge steel rolling mill has been operating continuously at full capacity for a long time. The base of the bell-shaped window has been subjected to sliding friction, impact loads, and alternating stresses from heat and cold for a long period, resulting in uniform wear. This is a structural failure due to equipment aging. The traditional solution requires downtime for major repairs, disassembly of the frame, and machining and repair, which leads to long downtime and significant loss of production capacity.
The working surface of the base of the plaque window has suffered overall wear, and the clearance throughout the area has exceeded the standard. The rigidity of the frame has decreased, resulting in continuous excessive vibration during the rolling process. The control accuracy of the plate shape is insufficient, and the qualified rate of high-end specification plates is low. Local areas of the window have minor scratches and groove defects. Regular adjustments and replacements of gaskets and liners have been unable to compensate for the wear. The equipment accuracy continues to deteriorate.
2. Oxide scale abrasive wear: Fine iron oxide dust from the site enters the mating surface, forming abrasive wear, which accelerates the loss of the frame base.
3. Frame fatigue deformation: Long-term alternating impact loads cause local micro-deformation of the frame, resulting in uneven mating surface fit and intensified local wear, gradually leading to loss of accuracy.
1. Surface pre-treatment: Polish and clean the worn-out working surface of the plaque window, remove the oxide layer, oil stains, and fatigue layer. Smooth and level the damaged areas, ensuring the repaired surface is clean and regular.
2. High-molecular wear-resistant coating repair: Use industrial wear-resistant repair materials for layer-by-layer application and leveling. Precisely restore the original fitting dimensions of the window. The material has high wear resistance, impact resistance, and self-lubrication properties, suitable for heavy-load sliding conditions of the rolling mill.
3. Precise size calibration: After curing and养护， use a dial indicator and feeler gauge to conduct comprehensive detection of the fitting clearance， and fine-tune the gasket and pad to ensure that the parallelism and clearance of the window meet the standards.
4. Post-repair protection and reinforcement： After the repair is completed， optimize lubrication and dust protection to prevent abrasive particles from invading and slow down the subsequent wear rate.
This online repair does not require disassembling the frame or prolonged downtime, significantly reducing the overhaul period and maintenance costs. After the repair, the accuracy of the arch window is fully restored, the rigidity of the frame is significantly improved, the rolling vibration and plate shape deviation problems are completely resolved, the operational stability of the equipment reaches the new machine standard, the wear resistance of the repair layer is excellent, and it can be used stably for a long time. This provides a low-cost and high-efficiency solution for the precision repair of old rolling machines.
The problems of the die frame, liner plates and slide plates of the rolling mill, which seem to be simple wear and jamming, are actually systematic issues related to lubrication management, gap control, material matching, and major overhaul processes. Compared to easily damaged parts such as bearings and rolls, the frame belongs to the core structure of the equipment. Once its accuracy is lost, simply replacing the easily damaged parts cannot solve the problem completely. Equipment operation and maintenance management needs to shift from "replacement repair" to "precision maintenance", through regular gap calibration, lubrication control, material standardization, and precise repair, to fundamentally prevent major downtime failures of the frame type.
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